IMAGING OPTICAL SYSTEM

Abstract

The invention relates to an imaging optical system (1) comprising a folding component (2) and a tunable optical component (3) that are arranged on an optical path of the optical system (1), wherein the tunable optical component (3) comprises a first optical surface (7), a second optical surface (8) and a deformable internal space (9) between the first optical surface (7) and the second optical surface (8), which internal space (9) is filled with a transparent liquid (11), wherein an optical property of the tunable optical component (3) is adjustable by altering a shape of the internal space (9). The imaging optical system (1) further comprises a moveably mounted cage element (13) that at least partly encloses the folding component (2) and is mechanically coupled to the tunable optical component (3) such that a displacement of the cage element (13) causes a change of the optical property of the tunable optical component (3) and an actuator (14, 15, 16) that is arranged between the folding component (2) and the cage element (13) and the actuator (14, 15, 16) is configured to exert a displacement force to the cage element (13).

Claims

1. Imaging optical system comprising a folding component and a tunable optical component that are arranged on an optical path of the optical system; wherein the tunable optical component comprises a first optical surface, a second optical surface and a deformable internal space between the first optical surface and the second optical surface, which internal space is filled with a transparent liquid, wherein an optical property of the tunable optical component is adjustable by altering a shape of the internal space; the imaging optical system further comprising a moveably mounted cage element that at least partly encloses the folding component and is mechanically coupled to the tunable optical component such that a displacement of the cage element causes a change of the optical property of the tunable optical component; an actuator that is arranged between the folding component and the cage element and the actuator is configured to exert a displacement force to the cage element.

2. Imaging optical system according to claim 1, wherein either the tunable optical component is a tunable prism, the first optical surface is rigid and the second optical surface is rigid, and the optical property is adjustable by changing an angle between the first optical surface and the second optical surface, or wherein the tunable optical component is a tunable lens, the first optical surface and/or the second optical surface is deformable, and the optical property is adjustable by changing an angle between the first optical surface and the second optical surface and/or by changing a shape of the deformable first optical surface and/or the second optical surface.

3. Imaging optical system according to claim 2, wherein the imaging optical system comprises at least one image sensor that is arranged in the optical path of the imaging optical system, wherein the folding component is arranged between the tunable optical component and the image sensor along the optical path.

4. Imaging optical system according to claim 2, comprising at least one image sensor that is arranged in the optical path of the optical system and wherein the tunable optical component is arranged between the folding component and the image sensor with respect to the optical path.

5. Imaging optical system according to claim 1, wherein the cage element is moveably mounted with respect to the folding component by a bearing means, wherein the bearing means is configured such that the cage element is rotatable about at least one rotation axis that is perpendicular to an optical axis, which extends between the folding component and the tunable optical component, such that an optical image stabilization is effected by means of the imaging optical system, and/or wherein the bearing means is configured such that the cage element is displaceable along the optical axis that extends between the folding component and the tunable optical component, such that focusing is effected by means of the imaging optical system,

6. Imaging optical system according to claim 5, wherein the bearing means is an elastic spring element that is essentially flat and in at least one state extends perpendicular to the optical axis between the cage element and the tunable optical component, preferably wherein the bearing means comprises a mechanical abutment that delimits a displacement of the cage element (13).

7. Imaging optical system according to claim 1, wherein the actuator comprises at least one coil and at least one magnet, wherein the coil is fixedly arranged with respect to the folding component and the magnet is fixedly attached to the cage element, wherein preferably the magnet is arranged at a distance between 3 mm and 15 mm, highly preferably a distance between 5 mm and 10 mm, to the rotation axis of the cage element.

8. Imaging optical system according to claim 7, wherein a magnetic shield element is arranged on a side of the magnets (21, 22, 26) facing away from the coil (23, 24, 27) respectively.

9. Imaging optical system according to claim 7, wherein the actuator is a first actuator and the displacement force is a first displacement force, and wherein the coil and the magnet of the first actuator are arranged such that the first displacement force causes a rotation of the cage element about a first rotation axis (19) that is perpendicular to the optical axis such that an optical imaging stabilisation is effected by means of the imaging optical system, and/or wherein at least the first displacement force is directed parallel to the optical axis and causes a displacement of the cage element along the optical axis such that a change of the focal plane of the tunable optical component is effected.

10. Imaging optical system according to claim 9, further comprising a second actuator with at least one coil and at least one magnet, wherein the coil is fixedly arranged with respect to the folding component and the magnet is fixedly attached to the cage element, wherein the coil and the magnet of the second actuator are arranged such that the second displacement force causes a rotation of the case element about a second rotation axis that is perpendicular to the first rotation axis and perpendicular to the optical axis.

11. Imaging optical system according to claim 9, wherein the first actuator comprises a first pair of coils that are arranged in a common first plane and are configured such that in the event of a current flow two opposing magnetic field forces interact with the at least one magnet of the first actuator that is arranged on the cage element and generate the first displacement force that causes the rotation of the cage element about the first rotation axis, and wherein the second actuator comprises a second pair of coils that are arranged in a common second plane that is parallel to the first plane and are configured such that in the event of a current flow two opposing magnetic field forces interact with the at least one magnet of the second actuator that is arranged on the cage element and generate the second displacement force that causes the rotation of the cage element about the second rotation axis, wherein an optical image stabilization is effected by means of the first actuator and/or the second actuator.

12. Imaging optical system according to claim 1, with at least one position sensor, particularly a hall sensor, arranged such as to detect a displacement of the cage element with respect to a fixedly arranged component of the optical system, in particular a coil and/or the folding component.

13. Imaging optical system according to claim 12, wherein a controller is connected to both the position sensor and the actuator by means of a signal-path and is configured to control a relative displacement of the cage element with respect to the folding component of the optical system as a function of a position signal of the position sensor.

14. Imaging optical system according to claim 3, with at least one static lens that is arranged between the folding component and the image sensor along the optical path, and the at least one static lens is movably mounted within a housing wherein a linear actuator is configured to displace the at least one static lens along the optical axis to alter the focus plane and/or the zoom of the imaging optical system.

15. Imaging optical system according to claim 14, wherein the static lens is mounted by means of a bearing comprising a rolling element, a magnet and a magnetic rail being cooperatively configured to bias the static lens against the housing via the rolling element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In the following, examples of the present invention and its preferred embodiments are described with reference to the accompanying drawings.

[0050] FIG. 1 shows an imaging optical system according to a first embodiment of the invention;

[0051] FIG. 2 shows an imaging optical system according to a second embodiment of the invention.

[0052] For better understanding, the reference numerals as used in FIGS. 1 and 2 are listed below. [0053] 1 Imaging optical system [0054] 2 Folding component [0055] 3 Tunable lens [0056] 4 Static lens [0057] 5 Image sensor [0058] 6 Optical axis [0059] 7 First optical surface [0060] 8 Second optical surface [0061] 9 Internal space [0062] 10 Container wall [0063] 11 Optical liquid [0064] 12 Flat glass [0065] 15 First Actuator [0066] 16 Second Actuator [0067] 17 Spring element [0068] 18 Housing [0069] 19 First rotation axis [0070] 20 Second rotation axis [0071] 21 Magnet [0072] 22 Magnet [0073] 23 Coil [0074] 24 Coil [0075] 25 Carrier [0076] 26 Magnet [0077] 27 Coil [0078] 28 Position sensor [0079] 29 Position sensor [0080] 30 Position sensor [0081] 31 Magnetic shield [0082] 32 Magnetic shield [0083] 33 Magnetic shield [0084] 34 Housing [0085] 35 Linear actuator [0086] 36 Coils [0087] 37 Moveable Housing [0088] 38 Magnet [0089] 39 Rolling element [0090] 40 Magnet [0091] 41 Magnet rail [0092] 42 First plane [0093] 43 Second plane

DETAILED DESCRIPTION OF THE INVENTION

[0094] FIG. 1 shows a first embodiment of an imaging optical system 1 in top view.

[0095] The imaging optical system 1 shown in FIG. 1 can be designed for use in a mobile phone (not shown) and to optically detect an object according to the functionality of a camera. In order to improve the image quality, it is possible to compensate for the negative influence of an unsteady guidance of the cell phone by performing a so-called optical image stabilization. In addition, an autofocus function and a zoom function are provided.

[0096] The imaging optical system 1 comprises a folding element 2, a tunable optical component 3, which is designed as a tunable lens, a plurality of rigid lenses 4 and an image sensor 5, all of which lie in a common optical path of the imaging optical system 1. According to this embodiment, the optical path of the imaging system runs orthogonally through the image plane and is deflected by 90° by means of the folding element 2 such that a part of the optical path runs along the optical axis 6. In other words, optical axis 6 corresponds to a part of the optical path, which runs between the image sensor 5 and the folding element 2. It is an advantage of the embodiment as shown in FIG. 1 that the major amount of the components of the imaging optical system are arranged along the optical axis 6. Advantageously, the imaging optical system 1 can be incorporated in mobile phones having a flat design, wherein the optical axis 6 extends in the main extension plane of the mobile phone.

[0097] The tunable optical component 3 comprises two optical surfaces 7, 8 that each are designed as deformable membranes, wherein optical surface 7 is a first optical surface that faces the folding component 2 and wherein the optical surface 8 is a second optical surface that faces away from the folding component 2. Between the optical surfaces 7 and 8 there is an internal space 9, which is delimited by a container wall 10 in lateral direction with respect to the optical axis 6. The container wall 10 may be considered as a third optical surface of the tunable optical component 3.

[0098] The internal space 9 is filled with a transparent optical liquid 11. By changing a relative position between the both optical surfaces 7 and 8 it is possible, to change at least one optical property of the tunable lens. This allows the course of the optical path to be changed as required, for example in order to compensate for undesired vibration of the cell phone and thereby provide the above-mentioned optical image stabilization.

[0099] Additionally, it is possible to change the focal plane of the tunable optical component 3 and thereby effect a change of the focal plane in order to improve the image quality. As shown in FIG. 1, this is done by moving the tunable optical component against a flat glass 12, which deforms the second optical surface 8 and increases the pressure in the transparent liquid 11. This in turn causes a change of curvature of the first surface 7 facing the folding component 2. The variability of the curvature geometry of the second surface is indicated by dashed lines in FIG. 1.

[0100] To effect an adjustment of the tunable optical component 2, the imaging optical system 1 shown in FIG. 1 has a design that includes a cage element 13 that is movably mounted with respect to the folding element 2 and can be dislocated by means of a plurality of actuators 14, 15, 16 in order to perform the functions described above. As can be seen in FIG. 1, cage element 13 surrounds the folding component 2 on three sides. Along the optical path, the cage element has two openings, one of which is open in the image plane and the other in the direction of the tunable optical component 3. The optical path thus impinges the folding component 2 through one opening, is folded by 90° and leaves the cage element 13, through another opening along the optical axis 6.

[0101] According to the embodiment shown in FIG. 1, a flat spring element 17 is arranged between the cage element 13 and a housing component 18 of the imaging optical system 1. The spring element 17 is a bearing element and serves to movably guide the cage element 13 in order to achieve a deformation of the internal space 9. Here, two ends of the cage element 13 are mechanically coupled to the tunable optical component 3 circumferentially in the region of the container wall 10. Such a mechanical coupling allows movements and forces of the cage element 13 to be transferred to the tunable optical component 3.

[0102] According to its function as a bearing element, the spring 17 serves to define the degrees of freedom of the cage element, whereby in the present case a displacement of the cage element 13 along the optical axis 6, a tilt about a first rotation axis 19 and a tilt about a second rotation axis 20 is possible. As mentioned above, this is made possible in the example shown by means of three actuators 14, 15, 16, as explained in detail in the following.

[0103] Actuators 14 are 15 identical and can both be considered a first actuator in terms of the invention. Actuator 14 and 15 each comprise a magnet 21, 22 and a coil 23, 24 wherein the magnets 21, 22 are arranged on the cage element 13 and are thus moveable with respect to the folding element 2. The coils 23, 24 are held by a carrier 25, which is fixedly arranged with respect to the folding component 2.

[0104] Magnets 21, 22 and coils 23, 24 of the actuators 14 and 15 are arranged such that the generation of a current in the coils 23, 24 causes a magnetic field with a magnetic force, which acts on the respective opposing magnets 21, 22 and thus causes a displacement of the cage element 13. In the embodiment shown here, the possible directions of the forces that can be exerted on the cage element 13 by means of the actuators 14 and 15 are illustrated with arrows. By generating an electric current in the coils 23, 24, a tilting of the cage element about the first rotation axis 19 can be caused by means of oppositely directed forces of the actuators 14 and 15. However, it is equally possible to have the forces act in the same direction, causing a linear displacement of the cage element 13 along the optical axis 6.

[0105] The actuator 16 can be seen as a second actuator in terms of the invention and also comprises a magnet 26 and a coil 27. Magnet 26 and coil 27 are arranged along the optical axis 6. As described with respect to the actuators 14 and 15, magnet 26 is located on the cage element 13, while coil 27 is held by carrier 25 together with coils 23, 24. In accordance with the explanations regarding actuators 14 and 15, it is also possible to generate an electric current in coil 27 in order to exert a displacement force on the magnet 26. In contrast to the actuators 14 and 15, the forces exerted on the cage element 13 in this case act in or out of the image plane, as also illustrated by the arrows. These forces can cause the cage element 13 to tilt about the second axis of rotation 20.

[0106] Each of the actuators 14, 15, 16 comprises a Hall-sensor 28, 29, 30, which allows to determine a position of the cage element 13. The Hall-sensors 28, 29, 30 are connected to a controller (not shown) by means of a signal path. The controller is also connected to the coils 23, 24, 27 and define a control loop, in order to control the position of the cage element 13.

[0107] Magnetic shields 31, 32, and 33 are disposed on cage element 13 and respectively serve to magnetically cover the magnets 21, 22, and 26 from other magnetic fields and vice versa.

[0108] As mentioned above, the imaging optical system 1 according to FIG. 1 comprises a set of rigid lenses 4, that are arranged between folding component 2 and image sensor 5 along the optical path. The set of rigid lenses 4 is held by a housing 37, which is moveably arranged in another housing 34 by means of rolling elements 39. A linear actuator 35 is configured to displace the set of static lenses 4 along the optical axis 6 to alter the focus plane and/or the zoom of the imaging optical system 1. For this purpose, the actuator 35 comprises a plurality of coils 36 that are distributed in the housing 34 parallel to the optical axis 6. A magnetic force may be generated by the coils 36 in order to displace the housing 37 with respect to housing 34 and therefore alter the position of the set of lenses 4 along the optical axis 6.

[0109] To ensure that the bearing arrangement shown here is as free of play as possible, the embodiment according to FIG. 1 also provides for the rolling elements 39 between the housings 34 and 37 to be preloaded by means of a magnet 40 and a magnetic rail 41. Here, magnet 40 is arranged on housing 37, while magnetic rail 41 is arranged on housing 34 and extends parallel to the optical axis 6. The attractive force between the magnet 40 and the magnetic rail 41 causes the housings 34 and 37 to be permanently pressed against the rolling element 39, thus reducing bearing play.

[0110] It should be noted that the linear actuator 35 and the magnetic rail 41 can be arranged in different parts of the housing 34 with respect of its circumference in order to make optimum use of the available design space.

[0111] FIG. 2 shows another embodiment of an imaging optical system 1, which basically has the same structural components as already described with respect to FIG. 1. However, there is a difference in the arrangement and mode of action of the actuators. Contrary to FIG. 1, there are no actuators that are arranged lateral to the optical axis 6. Instead, all actuators 14, 16 are arranged on the optical axis 6.

[0112] The first actuator 14 comprises a first pair of coils that are arranged in a common first plane and are configured such that in the event of a current flow two opposing magnetic field forces interact with the at least one magnet that is arranged on the cage element and generates a force that causes the rotation of the cage element about the first rotation axis 19. The second actuator 16 comprises a second pair of coils that are arranged in a common second plane that is parallel to the first plane and are configured such that in the event of a current flow two opposing magnetic field forces interact with the magnet that is arranged on the cage element and generates a displacement force that causes the rotation of the cage element about the second rotation axis 20. This allows to achieve an optical image stabilization. The focus functionality is achievable by a movement of the set of static lenses 4 along the optical axis 6, as already described with regard to FIG. 1.