Temperature drift compensation for liquid lenses

1. Lens, comprising:

a container ( 100 ) defining a volume (V) which is filled with a transparent liquid ( 2 ), wherein the container ( 100 ) comprises a transparent and elastically deformable membrane ( 20 ) and a rigid member ( 30 ), wherein the membrane ( 20 ) and the rigid member ( 30 ) delimit said volume (V), and

a lens shaping element ( 200 ) that contacts the membrane ( 20 ) and defines an area ( 21 ) of said membrane ( 20 ), which area ( 21 ) has an adjustable curvature for adjusting the focal length of the lens ( 1 ),

the lens ( 1 ) is configured to compensate a thermal expansion of the liquid ( 2 ) and/or a change of the refractive index of the liquid ( 2 ) due to an increased temperature of the liquid ( 2 ) in order to reduce an unwanted thermally induced change of the focal length of the lens ( 1 ),

the container ( 100 ) further comprises a ring member ( 50 ) for compensating said thermal expansion of the liquid ( 2 ), wherein said ring member ( 50 ) is connected to the rigid member ( 30 ) and extends circumferentially along an extension plane and comprises a dimension in a direction (z) perpendicular to said extension plane characterized in that the rigid member ( 30 ) comprises a linear thermal expansion coefficient that is smaller than the linear thermal expansion coefficient of the ring member ( 50 ), and the ring member ( 50 ) is arranged in a circumferential groove ( 31 ) of the rigid member ( 30 ).

2. Lens according to claim 1 , characterized in that the linear thermal expansion coefficient of the ring member ( 50 ) is one of: equal to, smaller, or larger than the linear thermal expansion coefficient of said liquid ( 2 ).

3. Lens according to claim 1 , characterized in that the ring member ( 50 ) is in thermal contact with said liquid ( 2 ) and is configured to expand when the temperature of the liquid ( 2 ) increases such that said volume (V) increases, wherein said increase in volume (V) corresponds to an increase of the volume (VL) of the liquid ( 2 ) that occurs when the temperature of the liquid ( 2 ) increases such that the curvature of said area ( 21 ) of the lens ( 1 ) remains constant when the temperature of the liquid ( 2 ) increases.

4. Lens according to claim 1 , characterized in that said volume (V) comprises a first section (V 1 ) having a first diameter (D 1 ), and wherein said volume (V) comprises an adjacent second section (V 2 ) having a second diameter (D 2 ) that is larger than the first diameter (D 1 ) of the first section (V 1 ), and wherein said sections (V 1 , V 2 ) comprise a different height in a direction perpendicular to said diameters (D 1 , D 2 ).

5. Lens according to claim 1 , characterized in that the ring member ( 50 ) protrudes out of said groove ( 31 ) in said direction (D) normal to said extension plane, or wherein said ring member ( 50 ) is completely arranged in said groove ( 31 ).

6. Lens according to claim 1 , characterized in that the thermal expansion of the ring member ( 50 ) in said direction (z) is suppressed by a fixture means ( 60 ) such that the ring member ( 50 ) predominantly thermally expands in a radial direction (R) running perpendicular to said direction (z).

7. Lens according to claim 1 , characterized in that the lens ( 1 ) comprises a bimetal actuator ( 71 , 72 ) which is configured to expand the ring member ( 50 ) or container ( 100 ) in said direction (z) for compensating a thermal expansion of the liquid in said volume.

8. Lens according to claim 1 , characterized in that the container ( 100 ) further comprises a chamber ( 80 ) for compensating said thermal expansion of the liquid ( 2 ), which chamber ( 80 ) defines a further volume (V 3 ) separated from said volume (V), which further volume (V 3 ) is filled with a further liquid ( 2 ′), wherein particularly said further volume (V 3 ) comprises a dimension in said direction (z) that is larger than the dimension of the liquid ( 2 ) or volume (V) in the same direction (z), wherein particularly said further volume (V 3 ) extends into a circumferential groove ( 32 ) of the rigid member ( 30 ), and is further delimited by said ring member ( 50 ) and a further ring member ( 81 ), wherein said ring member ( 50 ) protrudes from an inner edge ( 32 a ) of the groove ( 32 ) in said direction (z) and is encompassed by the further ring member ( 81 ) that protrudes from an outer edge ( 32 b ) of the groove ( 32 ) in said direction (z).

9. Lens according to claim 1 , characterized in that the rigid member ( 30 ) comprises a base ( 300 ) extending along said extension plane and a protrusion ( 301 ) protruding from the base ( 300 ) in said direction (z) normal to said extension plane, wherein said ring member ( 50 ) encompasses said protrusion ( 301 ), and wherein particularly the ring member ( 50 ) and said protrusion ( 301 ) define a circumferential gap ( 35 ) being filled with said liquid ( 2 ), which gap ( 35 ) forms part of said volume (V) of the container ( 100 ).

10. Lens according to claim 9 , characterized in that said protrusion ( 301 ) comprises a face side ( 301 a ) facing said membrane ( 20 ), wherein said face side ( 301 a ) comprises a recess ( 301 b ).

11. Lens according to claim 1 , characterized in that the rigid member ( 30 ) forms a transparent optical element facing the membrane ( 20 ), particularly a corrective optical element, particularly a lens.

12. Lens according to claim 1 , characterized in that the membrane ( 20 ) is connected to the ring member ( 50 ), particularly to a face side ( 50 a ) of the ring member ( 50 ) facing away from the rigid member ( 30 ).

13. Lens according to claim 1 , characterized in that rigid member ( 30 ) comprises a through hole ( 303 ) for passing light through the rigid member ( 30 ), wherein the membrane ( 20 ) is connected to the rigid member ( 30 ), and wherein a transparent optical element ( 90 ) is connected to the ring member ( 50 ) and faces the membrane ( 20 ).

14. Lens according to claim 1 , characterized in that for compensating said thermal expansion of the liquid ( 2 ), the lens ( 1 ) comprises a first and a second spring means ( 5 , 6 ) being in thermal contact with the liquid ( 2 ), wherein each spring means is preloaded against the membrane ( 20 ) such that the latter is in a force equilibrium position, wherein said two spring means ( 5 , 6 ) have a different change of Young's modulus over a certain temperature range so that said force equilibrium position of the membrane ( 20 ) depends on the temperature of the liquid ( 2 ) in a way that said thermal expansion and/or refractive index change of the liquid ( 2 ) is compensated such as to maintain the focal length of the lens constant.

15. Lens according to claim 1 , characterized in that the container ( 100 ) comprises a bottom ( 111 ) comprising an expansion element ( 110 ), which expansion element ( 110 ) is connected to the rigid element ( 30 ) and faces the membrane ( 20 ), wherein the expansion element ( 110 ) is configured to expand with increasing temperature such that said bottom ( 111 ) of the container ( 100 ) bends outwards for compensating the thermal expansion of the liquid ( 2 ).

16. Lens according to claim 1 , characterized in that the container ( 100 ) comprises a contraction element ( 112 ) comprising a negative thermal expansion coefficient, wherein the contraction element ( 112 ) participates in delimiting said volume (V) of the container ( 100 ) such that the contraction element ( 112 ) contracts with increasing temperature leading to an increased volume of the container (V) for compensating said thermal expansion of the liquid ( 2 ).

17. Lens according to claim 1 , characterized in that the lens comprises a pump ( 120 ) being configured to pump discrete amounts of liquid ( 2 ) into or out of the volume (V) so as to compensate a thermal expansion of the liquid ( 2 ) and a change of the refractive index of the liquid ( 2 ) due to an increasing temperature of the liquid ( 2 ) at the same time.

18. Lens according to claim 1 , characterized in that said volume (V) is separated into a lens volume (V′) and a reservoir volume (V″) being in flow connection with said lens volume (V′), wherein the reservoir volume (V″) is configured to expand when the temperature of the liquid ( 2 ) increases such that said reservoir volume (V″) increases, wherein said increase in reservoir volume (V″) corresponds to an increase of the volume (VL) of the liquid ( 2 ) that occurs when the temperature of the liquid ( 2 ) increases such that the curvature of said area ( 21 ) of the membrane ( 20 ) remains constant when the temperature of the liquid ( 2 ) increases.

19. Lens according to claim 18 , characterized in that the actuator ( 40 ) is designed to push liquid ( 2 ) out of the reservoir volume (V″) into the lens volume (V′) for adjusting the curvature of said area ( 21 ) of the membrane ( 20 ).

20. Lens according to claim 1 , characterized in that the lens ( 1 ) further comprises an actuator ( 40 ) configured to adjust the curvature of said area ( 21 ) of the membrane ( 20 ) in order to adjust the focal length of the lens ( 1 ) by exerting a force onto the membrane ( 20 ).

21. Lens according to claim 20 , characterized in that the actuator is configured to act on the membrane ( 20 ) in order to adjust the curvature of said area ( 21 ) via at least one spring element ( 206 ) comprising a lever.

22. Lens according to claim 20 , characterized in that said actuator ( 40 ) is pretensioned against the membrane ( 20 ) by means of a spring member ( 401 , 402 ) for compensating said change of the refractive index of the liquid ( 2 ) and/or the thermal expansion of the liquid ( 2 ) with temperature.

23. Lens according to claim 20 , characterized in that for compensating said change of the refractive index of the liquid ( 2 ) and/or the thermal expansion of the liquid ( 2 ) said actuator ( 40 ) comprises a coil ( 41 ) and a temperature-dependent resistor ( 45 ) being thermally coupled to the liquid ( 2 ), wherein the resistor ( 45 ) is configured such that when the temperature of the liquid ( 2 ) increases an electrical current that flows through the coil ( 41 )

decreases such that the force of the actuator ( 40 ) onto the membrane ( 20 ) decreases, too, or

increases such that the force of the actuator ( 40 ) onto the membrane increases, too.

24. The lens according to claim 1 , characterized in that the lens ( 1 ) is configured to compensate a thermal expansion or contraction of the liquid ( 2 ) and/or a change of the refractive index of the liquid ( 2 ) due to a change in temperature of the liquid ( 2 ) in order to reduce an unwanted thermally induced change of the focal length of the lens ( 1 ).

25. The lens according to claim 24 , characterized in that said change in temperature of the liquid ( 2 ) results from an external temperature change and/or at least one internal heat source of the lens ( 1 ).

26. The lens according to claim 24 , characterized in that said change in temperature results in a non-uniform distribution of the temperature of the liquid ( 2 ).

27. The lens according to claim 24 , characterized in that said change in temperature is time-dependent.

28. Lens according to claim 1 , characterized in that the lens ( 1 ) comprises an actuator ( 40 ) configured to adjust the curvature of said area ( 21 ) of the membrane ( 20 ) in order to adjust the focal length of the lens ( 1 ).

29. The lens according to claim 28 , characterized in that the lens ( 1 ) comprises a control unit ( 46 ) that is configured to provide a control signal for controlling said actuator ( 40 ) so as to adjust the curvature of said area ( 21 ) of the lens, wherein said control signal is generated such that it compensates for said change in temperature.

30. The lens according to claim 29 , characterized in that the lens ( 1 ) comprises at least one sensor, wherein the control unit ( 46 ) is configured to generate said control signal using values from the at least one sensor, wherein said at least one sensor is particularly one of: a temperature sensor ( 700 ) configured to measure a temperature inside the lens ( 1 ) or close to the lens ( 1 ), a displacement sensor ( 702 ) configured to measure a displacement of the actuator ( 40 ) or the membrane ( 20 ), a motion sensor ( 703 ) configured to detect a relative motion or acceleration of the lens ( 1 ) with respect to an environment of the lens ( 1 ), a sensor ( 704 ) configured to measure the power of said actuator ( 40 ).

31. The lens according to claim 29 , characterized in that the control unit ( 46 ) is configured to execute a control algorithm (ii, iii) that generates said control signal using said values and/or calibration data as well as a functional model in order to compensate for said change in temperature.

32. The lens according to claim 31 , characterized in that the control algorithm compromises at least two sub control algorithms (ii, iii), particularly relating to different aspects of compensating a thermal drift in the focal length of the lens ( 1 ), which sub control algorithms are executed in parallel or in series by the control unit ( 46 ).

33. The lens according to claim 32 , characterized in that the control algorithm comprises a first and a second sub control algorithm (ii, iii), wherein the control unit ( 46 ) is configured to execute these two sub control algorithms (ii, iii) in series, wherein the first sub control algorithm (ii) accounts for time-dependent changes in temperature of the liquid ( 2 ), particularly a temperature gradient, while the second sub control algorithm (iii) accounts for an overall change in the temperature of the liquid ( 2 ) assuming a uniform heat distribution inside the liquid ( 2 ) of the lens ( 1 ).

34. The lens according to claim 33 , characterized in that, the first sub control algorithm (ii) uses a functional model describing said time-dependent changes in the temperature of the liquid ( 2 ), wherein said first sub control algorithm (ii) is configured to dynamically adjust the focal length of the lens ( 1 ), which adjusted focal length forms an input for said second sub control algorithm (iii).

35. The lens according to claim 1 , characterized in that the lens ( 1 ) comprises a memory ( 701 ) for storing said values measured by said at least one sensor.

36. The lens according to claim 1 , characterized in that the lens ( 1 ) comprises calibration data obtained by calibrating the lens ( 1 ) and stored in a calibration data memory.

37. The lens according to claim 28 , characterized in that the actuator ( 40 ) comprises at least a first coil ( 41 ) for adjusting the curvature of said area ( 21 ) of the membrane ( 20 ) of the lens ( 1 ), and a second coil ( 43 ) wound around said at least one first coil ( 41 ) of the actuator ( 40 ).

38. The lens according to claim 37 , characterized in that the second coil ( 43 ) comprises a plurality of windings, wherein one half ( 43 a ) of the windings is wound in a winding direction while the other half ( 43 b ) of the windings is wound in the opposite winding direction so that the second coil ( 43 ) does not exert any force on the membrane ( 20 ), wherein the lens ( 1 ) is configured to adjust a an electrical current flowing through the second coil ( 43 ) such that a total consumed power of the at least one first coil ( 41 ) and the second coil ( 43 ) remains constant and a local heat source distribution generated by the actuator ( 40 ) does not change.

39. The lens according to claim 37 , characterized in that the lens ( 1 ) is configured to adjust a ratio between the electrical currents in said at least one first coil ( 41 ) and in said second coil ( 43 ) such that the total power is constant and a local heat source distribution generated by the actuator ( 40 ) does not change.

40. The lens according to claim 28 , characterized in that the actuator ( 40 ) of the lens ( 1 ) is configured to adjust the curvature of said area ( 21 ) of the membrane ( 20 ) of the lens ( 1 ) during a duty cycle, wherein the lens ( 1 ) is configured to drive the actuator ( 40 ) at a different power outside the respective duty cycle, wherein said power is chosen such that the average total power of the actuator ( 40 ) remains constant.

41. The lens according to claim 28 , characterized in that the lens ( 1 ) is configured to compensate for a temperature gradient inside the liquid ( 2 ) using at least one of: a spatial separation of the actuator ( 40 ) from the container ( 100 ) of the liquid ( 2 ), a thermal insulation, arranging the membrane ( 20 ) inside or on a lens shaping element ( 200 ) or inside or on a holding apparatus that is configured to induce a counteracting temperature gradient, a heater ( 705 ) comprised by the lens ( 1 ), which heater ( 705 ) is configured to keep the lens temperature constant, an active or a passive cooling means.

42. The lens according to claim 41 , characterized in that the lens ( 1 ) is configured to measure the deflection of the membrane ( 20 ) to determine said strain softening of the membrane ( 20 ), wherein said control unit ( 46 ) is configured to compensate the temperature dependent strain softening.

43. The lens according to claim 28 , characterized in that the actuator ( 40 ) is configured to generate an actuator force for adjusting the curvature of said area ( 21 ) of the membrane ( 20 ) of the lens ( 1 ), wherein a change in said actuator force results in a membrane strain softening caused by viscoelasticity of the membrane ( 20 ) depending on temperature.

44. Lens, comprising:

a container ( 100 ) defining a volume (V) which is filled with a transparent liquid ( 2 ), wherein the container ( 100 ) comprises a transparent and elastically deformable membrane ( 20 ) and a rigid member ( 30 ), wherein the membrane ( 20 ) and the rigid member ( 30 ) delimit said volume (V), and

a lens shaping element ( 200 ) that contacts the membrane ( 20 ) and defines an area ( 21 ) of said membrane ( 20 ), which area ( 21 ) has an adjustable curvature for adjusting the focal length of the lens ( 1 ),

the lens ( 1 ) is configured to compensate a thermal expansion of the liquid ( 2 ) and/or a change of the refractive index of the liquid ( 2 ) due to an increased temperature of the liquid ( 2 ) in order to reduce an unwanted thermally induced change of the focal length of the lens ( 1 ),

the container ( 100 ) further comprises a ring member ( 50 ) for compensating said thermal expansion of the liquid ( 2 ), wherein said ring member ( 50 ) is connected to the rigid member ( 30 ) and extends circumferentially along an extension plane and comprises a dimension in a direction (z) perpendicular to said extension plane

characterized in that the rigid member ( 30 ) comprises a linear thermal expansion coefficient that is smaller than the linear thermal expansion coefficient of the ring member ( 50 ), and the thermal expansion of the ring member ( 50 ) in said direction (z) is suppressed by a fixture means ( 60 ) such that the ring member ( 50 ) predominantly thermally expands in a radial direction (R) running perpendicular to said direction (z).

45. Lens, comprising:

a container ( 100 ) defining a volume (V) which is filled with a transparent liquid ( 2 ), wherein the container ( 100 ) comprises a transparent and elastically deformable membrane ( 20 ) and a rigid member ( 30 ), wherein the membrane ( 20 ) and the rigid member ( 30 ) delimit said volume (V), and

a lens shaping element ( 200 ) that contacts the membrane ( 20 ) and defines an area ( 21 ) of said membrane ( 20 ), which area ( 21 ) has an adjustable curvature for adjusting the focal length of the lens ( 1 ),

the lens ( 1 ) is configured to compensate a thermal expansion of the liquid ( 2 ) and/or a change of the refractive index of the liquid ( 2 ) due to an increased temperature of the liquid ( 2 ) in order to reduce an unwanted thermally induced change of the focal length of the lens ( 1 ),

the container ( 100 ) further comprises a ring member ( 50 ) for compensating said thermal expansion of the liquid ( 2 ), wherein said ring member ( 50 ) is connected to the rigid member ( 30 ) and extends circumferentially along an extension plane and comprises a dimension in a direction (z) perpendicular to said extension plane

characterized in that the rigid member ( 30 ) comprises a linear thermal expansion coefficient that is smaller than the linear thermal expansion coefficient of the ring member ( 50 ) and the container ( 100 ) further comprises a chamber ( 80 ) for compensating said thermal expansion of the liquid ( 2 ), which chamber ( 80 ) defines a further volume (V 3 ) separated from said volume (V), which further volume (V 3 ) is filled with a further liquid ( 2 ′), wherein particularly said further volume (V 3 ) comprises a dimension in said direction (z) that is larger than the dimension of the liquid ( 2 ) or volume (V) in the same direction (z), wherein particularly said further volume (V 3 ) extends into a circumferential groove ( 32 ) of the rigid member ( 30 ), and is further delimited by said ring member ( 50 ) and a further ring member ( 81 ), wherein said ring member ( 50 ) protrudes from an inner edge ( 32 a ) of the groove ( 32 ) in said direction (z) and is encompassed by the further ring member ( 81 ) that protrudes from an outer edge ( 32 b ) of the groove ( 32 ) in said direction (z).

46. Lens, comprising:

a container ( 100 ) defining a volume (V) which is filled with a transparent liquid ( 2 ), wherein the container ( 100 ) comprises a transparent and elastically deformable membrane ( 20 ) and a rigid member ( 30 ), wherein the membrane ( 20 ) and the rigid member ( 30 ) delimit said volume (V), and

a lens shaping element ( 200 ) that contacts the membrane ( 20 ) and defines an area ( 21 ) of said membrane ( 20 ), which area ( 21 ) has an adjustable curvature for adjusting the focal length of the lens ( 1 ),

the lens ( 1 ) is configured to compensate a thermal expansion of the liquid ( 2 ) and/or a change of the refractive index of the liquid ( 2 ) due to an increased temperature of the liquid ( 2 ) in order to reduce an unwanted thermally induced change of the focal length of the lens ( 1 ),

the container ( 100 ) further comprises a ring member ( 50 ) for compensating said thermal expansion of the liquid ( 2 ), wherein said ring member ( 50 ) is connected to the rigid member ( 30 ) and extends circumferentially along an extension plane and comprises a dimension in a direction (z) perpendicular to said extension plane characterized in that the rigid member ( 30 ) comprises a linear thermal expansion coefficient that is smaller than the linear thermal expansion coefficient of the ring member ( 50 ),

the rigid member ( 30 ) comprises a base ( 300 ) extending along said extension plane and a protrusion ( 301 ) protruding from the base ( 300 ) in said direction (z) normal to said extension plane, wherein said ring member ( 50 ) encompasses said protrusion ( 301 ), and wherein particularly the ring member ( 50 ) and said protrusion ( 301 ) define a circumferential gap ( 35 ) being filled with said liquid ( 2 ), which gap ( 35 ) forms part of said volume (V) of the container ( 100 ), and said protrusion ( 301 ) comprises a face side ( 301 a ) facing said membrane ( 20 ), wherein said face side ( 301 a ) comprises a recess ( 301 b ).