Sensor-based control of optical devices with variable optical power or variable beam deflection

Abstract

The present invention relates to a controllable optical assembly, such as a controllable lens or a controllable beam deflector. The optical assembly comprises first and second cover members, one of which is a transparent cover member and the other of which is a transparent or reflective cover member. A transparent, deformable non-fluid is sandwiched between the first and second cover members, whereby the first and second cover members and the non-fluid form a lens or optical deflector. An actuator is arranged to generate a controllable bending and / or tilting of at least the first cover member in response to a control signal. One or more sensors are provided for generating a measurement signal indicative of the bending or tilting of the first and / or second cover members. The control signal is determined based on the measurement signal.

Description

[Technical Field]

[0001] The present invention relates to an optical device having variable optical power or variable beam deflection, and to a method for controlling such an optical device. [Background technology]

[0002] The successful use of devices with variable optical power or variable deflection requires high precision of the variable parameters. This is achieved by accurate calibration of the optical device. Accurate calibration is difficult to achieve due to temperature dependence, hysteresis, and long-term drift phenomena (e.g., creep). Another method for controlling the variable parameters is to develop a model of the optical device that can predict the change in the variable parameters due to temperature, hysteresis, and creep. However, even with this method, the model cannot predict the exact value of the variable parameters for each optical device, but only the average value.

[0003] Therefore, there is a need for improved control of such optical devices to achieve precise control and to provide a technically viable solution. Summary of the Invention

[0004] The object of the present invention is to improve the control of variable lenses and adjustable optical deflectors, and in particular to improve the measurement of optical power fluctuations and / or beam deflection fluctuations in variable lenses and optical deflectors.

[0005] In a first aspect of the present invention, there is provided a controllable optical assembly having variable optical power and / or variable beam deflection, said optical assembly comprising: a first cover member and a second cover member, one of which is a transparent cover member and the other of which is a transparent or reflective cover member; a transparent, deformable, non-fluid material sandwiched between first and second cover members, whereby the first and second cover members and the non-fluid material form a lens or optical deflector having an optical axis that intersects the non-fluid material and the first and / or second transparent cover members; one or more actuators arranged to generate a controllable bending and / or tilting of at least the first cover member in response to a control signal, the control signal being derivable from the first and second measurement signals; first and second sensors arranged to provide first and second measurement signals, whereby the measurement signals are indicative of bending and / or tilting of at least the first cover member, the first sensor being an optical sensor and the second sensor being a deformation sensor; Equipped with.

[0006] It is understood that by actuator arranged to generate a controllable bending and / or tilt of at least the first cover member, the actuator may alternatively or additionally be arranged to generate a controllable bending and / or tilt of the first and / or second cover members. One or more sensors may be arranged to provide a measurement signal, such that the measurement signal is indicative of the bending and / or tilt of the first and / or second cover members.

[0007] According to an alternative embodiment, the controllable light assembly comprises either the first or the second sensor, and the light assembly is therefore arranged to provide only one measurement signal from which a control signal is derived, such that the measurement signal is indicative of bending and / or tilting of at least the first cover member.

[0008] Advantageously, by measuring the bending of the cover member and the resulting change in optical power, or the tilt of the cover member and the resulting beam deflection, the measured changes can be used in a feedback control system to precisely adjust the actuator to obtain the desired tilt or optical power.

[0009] Compared to other solutions that use image sensor reading and processing to control optical power, for example, direct measurement of lens curvature provides a direct measurement of optical power, which allows for faster adjustments, for example in a feedback control loop. For example, it is known to use a phase detector in a camera to obtain a measurement of image sharpness and use that measurement to adjust the image sharpness. However, the phase detector does not provide information about the optical power.

[0010] The controllable light assembly may further comprise a support structure arranged to support the first cover member and / or the second cover member.

[0011] Using two different sensors, one optical and the other deformation, combines the advantages of each sensor, for example, combining the high accuracy of an optical sensor with the direct stress sensing capability of a deformation sensor and other advantages such as low cost and simple design of one of the sensors.

[0012] In one embodiment, a deformation sensor, such as a piezoelectric sensor, is used to control bending of the cover member based on sensor readings from the deformation sensor. For example, sensor readings from a piezoelectric actuator that also functions as a piezoelectric sensor can be used in an open-loop algorithm to determine the voltage to apply to the piezoelectric actuator. An example of this open-loop control is described in International Application No. 2019 / 170793, the contents of which are incorporated herein by reference. For increased accuracy, open-loop control may be combined with closed-loop control, in which sensor readings from an optical sensor are compared to a membrane bending criterion.

[0013] The first and second sensors may be arranged, for example, to obtain a measurement signal indicative of the bending and / or tilt of the first cover member by connecting a deformation sensor to the first cover member to detect deformation of the first cover member and by arranging an optical sensor to optically detect changes in bending and / or tilt of the first cover member.

[0014] Examples of deformation sensors include piezoelectric sensor elements, such as the piezoelectric elements of one or more actuators. Other examples of deformation sensors include strain gauge sensors of the configurations described herein. Examples of optical sensors include any of the optical sensor configurations described herein in which a light beam is reflected by or transmitted through at least the first cover member.

[0015] The first and second sensor signals may each indicate bending or tilt, or one of the first and second sensor signals may indicate bending and the other may indicate tilt.

[0016] The control system can be configured to generate control signals in response to the first and second measurement signals to obtain a desired bending and / or tilt of the first and / or second cover members. For example, the first and second measurement signals may be combined to improve measurement accuracy. In another embodiment, the first measurement signal provides a measurement of bending and the second measurement signal provides a measurement of tilt. Also, the first measurement signal may be used for initial adjustment of bending or tilt and the second measurement signal may be used for ongoing adjustment of bending or tilt, for example, based on a set point reference.

[0017] According to one embodiment, the second cover member is a prism and the first cover member is a reflective cover member arranged opposite the hypotenuse of the prism to reflect at least a portion of the intensity of the incident light, and one or more actuators may therefore be arranged to generate a controllable tilt of the reflective cover member.

[0018] According to one embodiment, the one or more actuators are displacement actuators capable of generating a linear or substantially linear displacement.

[0019] According to one embodiment, the controllable light assembly comprises one or more elastic elements connecting the displacement actuator with the first cover member and / or the second cover member, at least a portion of each of the one or more elastic elements being arranged to elastically deform in response to displacement of the actuator.

[0020] Advantageously, the elastic element can reduce undesired deformation of the cover member that may occur with a rigid connection.

[0021] According to one embodiment, the one or more sensors are arranged to measure deformation of a portion of each of the one or more elastic elements.

[0022] Measurement of the deformation occurring in the elastic structure is advantageously used to determine the tilt or bending of the cover member.

[0023] According to one embodiment, the support structure comprises a rigid frame.

[0024] The support structure may alternatively be less rigid but may be positioned to at least partially surround the non-fluid body, thereby spacing the support structure from the non-fluid body and allowing the non-fluid body to expand along at least a portion of the support structure that surrounds or partially surrounds the non-fluid body without contacting the support structure.

[0025] The rigid support structure may be used to position compensation sensors arranged so as not to be exposed to, or substantially not to be exposed to, deformation in response to bending of the first or second cover member, and at least one compensation sensor may be of the same type as the one or more deformation sensors. The compensation sensor may be used to compensate for temperature dependence. Advantageously, when the support structure is separated from the non-fluid body, the support structure is not exposed to deformation in response to actuation and may therefore support the compensation sensor.

[0026] According to one embodiment, the first cover member is fixed to the support structure and the one or more actuators are connected to a surface of the first cover member.

[0027] Such an actuator may be a surface mounted actuator arranged to induce a surface strain in the cover member.

[0028] For example, the one or more actuators may comprise one or more piezoelectric elements connected to a surface of the first cover member.

[0029] The one or more piezoelectric elements may comprise a ring-shaped piezoelectric element connected to a surface of the first cover member, the ring-shaped piezoelectric element configured with an opening to allow light to pass therethrough.

[0030] According to one embodiment, the one or more sensors comprise a piezoelectric sensor element, which can advantageously be used to obtain a high bandwidth of the measurement signal.

[0031] For example, the piezoelectric sensor element may be one of the piezoelectric elements used as an actuator. Thus, the piezoelectric actuator may function as both an actuator and a sensor. International Application Publication No. 2019 / 170793, incorporated herein by reference, describes how a piezoelectric actuator can be used to determine a transfer function dc(V) of the piezoelectric actuator based on a transition time tt measured between two voltages applied to the piezoelectric actuator. Thus, measurements dependent on the piezoelectric actuator, such as the capacitance of the piezoelectric actuator, can be used to determine the transfer function of the piezoelectric actuator, which can be controlled, for example, in an open-loop configuration.

[0032] According to one embodiment, the one or more sensors are deformation sensors connected to a surface of the one or more actuators. For example, the one or more actuators, such as linear displacement sensors, may be sandwiched between the one or more deformation sensors and the first or second cover member. In this case, the sensors may be arranged to measure the deformation of the sensors.

[0033] The optical assembly may include at least one compensation sensor positioned so as to be unexposed to, or substantially unexposed to, deformation in response to bending of the first or second cover member, the at least one compensation sensor being of the same type as the one or more deformation sensors.

[0034] At least one compensation sensor may be connected to the support structure.

[0035] The at least one compensation sensor and the one or more deformation sensors may be arranged such that a temperature dependency of the one or more deformation sensors is compensated for by a corresponding temperature dependency of the at least one compensation sensor.

[0036] According to one embodiment, the deformation sensors are arranged symmetrically with respect to the optical axis of the lens, for example, two or more deformation sensors may be arranged at the same radial distance from the optical axis and with the same arc length between the sensors.

[0037] According to one embodiment, the control signal is determined in response to the deformations measured by the multiple deformation sensors, for example the control signal may be determined in response to, for example, an average or difference from the multiple sensors, or individual control signals may be determined for the individually controlled actuators.

[0038] According to one embodiment, the sensor comprises a light source arranged to propagate a light beam such that the light beam is affected by bending or tilting of the first and / or second cover members, and the sensor comprises a light detector arranged to measure changes in the light beam related to the bending and / or tilting.

[0039] According to one embodiment, the light source is arranged such that a light beam is reflected by the first or second cover member which is arranged to be bent or tilted.

[0040] According to one embodiment, the photodetector comprises at least two individual photodetectors, each capable of generating an output signal correlated to the power of light incident on the individual photodetector.

[0041] For example, two separate photodetectors may be used to provide tilt sensing in only one dimension, or three separate photodetectors may be used to provide tilt sensing in two dimensions, although four separate photodetectors are preferred.

[0042] According to one embodiment, the output openings of the light sources and the input openings of the respective photodetectors are arranged to face the first and second cover members.

[0043] According to one embodiment, the light source is placed at the center of a circle surrounding the individual photodetectors.

[0044] According to one embodiment, the light source is positioned such that the light beam, such as the centre of the intensity profile of the light beam, strikes the first and / or second cover member a predetermined distance from the optical axis.

[0045] According to one embodiment, at the location where the light beam strikes the first and / or second cover member, the plane of incidence formed by the light beam and the surface normal does not include the optical axis.

[0046] According to one embodiment, the light source is arranged to transmit a light beam through the first or second cover member, and the light detector is arranged to measure the transmitted light beam, and the light detector may be arranged with its input aperture facing the optical axis.

[0047] A second aspect of the present invention relates to an electronic device, such as a camera module, comprising an optical assembly according to the first aspect and a control system arranged to generate control signals in response to the first and second measurement signals to obtain a desired bending or tilt of the first and / or second cover members. The electronic device may be a camera module, an optical beam scanner, or other electronic device. For example, the optical beam scanner may use a controllable beam deflection device, possibly a controllable lens, for various beam scanning purposes, such as image projection, barcode scanning, 3D scanning, etc.

[0048] A third aspect of the present invention relates to a method of controlling an optical assembly according to the first aspect, said method comprising the steps of: obtaining first and second measurement signals from the one or more sensors, whereby the measurement signals are indicative of bending and / or tilting of the first and / or second cover members; determining a control signal based on the measurement signal; controlling the bending and / or tilting of the first and / or second cover members in response to the control signal; It has.

[0049] The various aspects and embodiments of the invention generally may be combined or combined in any manner possible within the scope of the invention. These and other aspects, features and / or advantages of the invention will be apparent from and elucidated with reference to the embodiments described herein.

[0050] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 1 shows an optical system with a controllable lens having variable optical power. [Figure 2] FIG. 2 shows a controllable lens that is provided with at least one compensation sensor in addition to the deformation measurement sensor. [Figure 3A] FIG. 3A shows an embodiment of a controllable lens in which actuators are arranged to produce a controllable bending and / or tilt. [Figure 3B] FIG. 3B shows an embodiment of a controllable lens in which actuators are arranged to produce a controllable bending and / or tilt. [Figure 4A] FIG. 4A shows an example of an elastic element connecting the displacement actuator and the cover member. [Figure 4B] FIG. 4B shows an example of an elastic element connecting the displacement actuator and the cover member. [Figure 4C] FIG. 4C shows an example of an elastic element connecting the displacement actuator and the cover member. [Figure 5A] FIG. 5A shows an optical assembly with a controllable beam deflector. [Figure 5B] FIG. 5B shows an optical sensor used when the first cover member is arranged to be bent by a displacement actuator. [Figure 6A] FIG. 6A shows the details of the optical sensor. [Figure 6B] FIG. 6B shows the details of the optical sensor. [Figure 7] Figure 7 shows the linear performance of the optical sensor. [Figure 8] Figure 8 shows the linear performance of the optical sensor. [Figure 9] FIG. 9 shows an alternative optical sensor configured to determine the optical power of a controllable lens. [Figure 10A] FIG. 10A shows the output signal from the optical sensor of FIG. [Figure 10B] FIG. 10B shows the output signal from the optical sensor of FIG. [Figure 11A] FIG. 11A shows another configuration of an optical sensor configured to determine the optical power of a controllable lens. [Figure 11B] FIG. 11B shows a curve showing the relationship between the ratio of the diameter of the light beam spot on the detector of the optical sensor in the x-axis and the y-axis. [Figure 12] FIG. 12 shows an electronic device such as a camera module with an optical assembly. DETAILED DESCRIPTION OF THE INVENTION

[0052] FIG. 1 shows an optical assembly 199 including a controllable lens 100 with variable optical power. The top figure is a top view, and the bottom two figures are side views showing the lens in two different operating states. The lens includes a first cover member 111 and a second cover member 112. In one embodiment, the first and second cover members are transparent. Alternatively, one of the first and second cover members is reflective, e.g., provided with a reflective metal layer that provides total or partial reflection so that an incident light beam is reflected to the opposite transparent cover member.

[0053] For example, the second cover member may include a reflective surface arranged to reflect incident light transmitted through the transparent first cover member back to the first cover member. For convenience, examples and embodiments herein will refer to transparent cover members 111, 112.

[0054] The lens 100 further comprises a transparent, deformable non-fluid 105 sandwiched between first and second cover members, the first and second cover members and the non-fluid forming a lens having an optical axis 150 intersecting the first and second cover members and the non-fluid. The non-fluid 105 contacts the inner surfaces of the first and second cover members 111, 112.

[0055] An optical axis 150 may be defined as a line normal to the surface of one of the cover members, passing through the center of the first and second cover members 111, 112 and the non-fluid body 105. The optical axis is further defined according to conventional optical definitions.

[0056] One or more actuators 120 are arranged to produce a controllable bending, tilting or displacement, or a combination thereof, which causes a controllable change in the overall shape of the lens in response to electrical or optical control signals, such as those generated by control system 190.

[0057] At least one of the first and second cover members 111, 112 is configured to bend due to a force or torque applied by the actuator 120. It is generally understood that the force comprises a force distributed over an area, for example due to a stress caused by a strain generated by a piezoelectric element attached to the surface.

[0058] The lens comprises a support structure 130 arranged to support the first and / or second cover members 111, 112. In this example, the first cover member 111 is supported by (e.g., fixed to) the support structure 130, and the second support member 112 is not in contact with the support structure 130.

[0059] One or more sensors 140 are positioned to measure deformation correlated to bending, tilt, displacement, or a combination thereof. For example, in FIG. 1 , different control of the right and left actuators 120 can cause the first cover member 111 to bend asymmetrically, effectively creating a tilting effect. In the example of FIG. 1 , the sensors 140 can be strain gauges or other types of sensors capable of measuring deformation or strain. In this embodiment, the strain gauges are mounted atop surface-mounted piezoelectric elements to measure deformation of the piezoelectric elements correlated to at least bending of the first cover member 111.

[0060] A control system 190 is provided to generate control signals in response to the measured deformation or in response to measurements generally indicative of the bending or tilt, such as in response to a measured change in tilt or optical power, to obtain a desired bending and tilt, or a combination thereof, of the first and / or second cover members. For example, the control system 190 may include a feedback control system configured to minimize the difference between the measured tilt or bending and the desired tilt or bending. The control system 190 may be integrated with the lens, or it may be a separate control system configured to receive deformation signals from a deformation sensor and send control signals to the actuator 120.

[0061] The transparent, deformable, non-fluidic lens body 105 is preferably made from an elastic material. Because the lens body is non-fluidic, a fluid-tight seal is not required to seal the lens body to prevent leakage from the lens body. As shown, the lens 100 includes a gap 182 between the support structure 130 and the non-fluidic body 105. Therefore, movement of the non-fluidic body 105 is unrestrained along a direction radial to the optical axis 150, i.e., perpendicular to the optical axis. In a preferred embodiment, the lens body is fabricated from a soft polymer, which may include a number of different materials, such as silicone, polymer gel, polymer networks of cross-linked or partially cross-linked polymers, and miscible oils or oil combinations. The modulus of elasticity of the non-fluidic lens body may be greater than 300 Pa, thereby avoiding deformation due to gravity during normal operation. The refractive index of the non-fluidic lens body may be greater than 1.3. The non-fluid body 105 may have a refractive index that is equal to, substantially equal to, or close to, the refractive index of the first and second cover members 111, 112 to reduce reflections at the boundaries of the non-fluid body 105.

[0062] The cover members 111, 112 are generally plate-like in shape and may have a preformed shape, such as a sphere, a flat surface, or a combination thereof. The cover members 111, 112 may be fabricated from a number of different materials, such as acrylic, polyolefin, polyester, silicone, polyurethane, or glass. At least one of the first and second cover members 111, 112, which is configured to be deformed by the actuator, has a stiffness suitable for being bent by actuation of the actuator 121. Generally, the material of the first and / or second cover members 111, 112 may be formed from a material having a Young's modulus in the range of 5 MPa to 100 GPa to provide the necessary stiffness. For example, borosilicate glass has a Young's modulus of 63 GPa, and fused silica glass has a Young's modulus of 72 GPa.

[0063] The bending of the first and / or second cover members 111, 112 is due, at least in part, to a radially varying reaction force from the lens body 105, which affects the deflection of the cover members 111, 112 and therefore affects optical power rather than simply compressing the lens body in an orthogonal direction without changing the deflection. A detailed description of the effect of the lens body 105 on the curvature of the cover members is provided in WO 2019 / 002524 A1, which is incorporated herein by reference.

[0064] In the example of FIG. 1 , the one or more actuators 120 include one or more piezoelectric elements attached to the surface of the first cover member 111. For example, a single actuator 120 of a piezoelectric element in the form of a sheet or annular ring as shown is attached to the surface of the first cover member 111 to provide bending of the first cover member. One or more sensors 140 may be disposed on the annular piezoelectric element. Instead of an annular piezoelectric element, multiple piezoelectric elements may be distributed along a circle around the optical axis 150. One or more sensors may be disposed between the distributed piezoelectric elements or between the other actuators 120.

[0065] Thus, one or more deformation sensors may be connected to a surface of one or more actuators, for example, such that the one or more actuators are sandwiched between the one or more deformation sensors and the first cover member. Alternatively or additionally, one or more deformation sensors may be connected to a surface of the first or second cover member 111, 112.

[0066] Other configurations of the actuator 120 are also possible. For example, a linear displacement actuator may be disposed between the first and second cover members 111, 112 and connected to the inner surfaces of the cover members 111, 112 via a resilient element, such as a bendable element, arranged to accumulate a relative displacement, e.g., in a radial direction, between the actuator 120 and connection points on the cover members 111, 112. In this case, one or more sensors 140 may be attached to one or more of the inner and outer surfaces of the cover members.

[0067] The one or more piezoelectric actuators 120 are arranged such that the lens 100 has an inner portion 181 that defines a lens area surrounded by the one or more piezoelectric actuators 120, thereby allowing light to pass unobstructed through the lens area. The non-fluid 105 is arranged to cover at least the lens area, but may also extend beyond the extension of the lens area towards the periphery of the first or second cover member 111, 112.

[0068] The actuator 120 may be configured to independently cause a controllable bending of the first or second cover members 111, 112. Thus, actuation of the actuator may cause the first and / or second cover members to bend into a concave or convex shape, which may impart optical power to light passing through the lens.

[0069] Alternatively, one or more actuators 120 may be arranged to displace and / or tilt one of the cover members 111 relative to the other 112. For example, actuators 120 may be arranged between cover members 111, 112 to change the relative angle between the two cover members, e.g., to change the direction of imaging light passing through lens 100, as described above.

[0070] In another embodiment, one of the cover members 111, 112 is provided with a reflective surface, allowing the beam deflection of the reflected beam to be adjusted by controlling the tilt of the cover member.

[0071] The actuator may advantageously be arranged to bend one of the cover members 111 in combination with tilting to generate optical power and beam deflection. The combination of tilting and bending may be used with transparent or reflective cover members. The beam deflection may be used to achieve optical image stabilization (OIS) in cameras such as smart phone compact cameras.

[0072] The support structure 130 may be configured as a rigid frame that does not deform or does not substantially deform when the cover members 111, 112 connected to the support structure are deformed or exposed to stresses from the actuators. The support structure may be arranged to at least partially surround the non-fluid body, thereby providing continuous support for the connected cover members 111, 112. Furthermore, the controllable lens 100 may be arranged with a gap 182, such as an air gap 182, between the periphery of the non-fluid body 105 and the support structure, i.e., a gap extending radially relative to the optical axis 150 and radially separating the periphery of the non-fluid body 105 from the support structure 130. This gap allows the non-fluid body to expand radially unrestrained in response to actuation of the actuators.

[0073] The output signal from the sensor 140 may depend on other physical effects besides deformation, such as temperature, hysteresis, creep, etc. At least the temperature dependence of the sensor 140 may be compensated for, or at least partially compensated for, when two identical sensors are placed close to each other.

[0074] 2 shows that the controllable lens is configured with at least one compensation sensor 240 in addition to the deformation measurement sensor 140. The compensation sensor 240 is arranged so that it is not, or is not substantially, exposed to deformations responsive to bending of the first or second cover member. Since the compensation sensor and the deformation sensor are of the same type, they have substantially the same dependence on other physical influences such as temperature.

[0075] By connecting a pair of sensors, including one compensation sensor 240 and one measurement sensor 140, in a Wheatstone bridge circuit, where the compensation sensor and the measurement sensor are resistive strain sensors, the output signal from the Wheatstone bridge is compensated for physical effects that affect both the compensation sensor 240 and the measurement sensor 140. This ensures that changes in temperature, etc., do not cause corresponding changes in the output signal from the Wheatstone bridge. That is, temperature changes affect both sensors 140, 240 in the same way. Because the temperature changes of the two sensors are identical, their resistance ratios do not change, and the effects of temperature changes are minimized or substantially eliminated. In this way, the temperature dependence of the first and second deformation sensors 140 can be compensated for by the corresponding temperature dependence of the respective first and second compensation sensors 240.

[0076] The compensation sensor may be connected to the support structure such that it is not, or is only slightly, exposed to deformation when the first or second cover member is deformed.

[0077] 2, four deformation sensors 140 and associated compensation sensors 240 are arranged rotationally symmetrically about the optical axis 150 of the lens 100. For example, multiple deformation sensors can be used to minimize aberrations that may occur in response to bending.

[0078] Advantageously, a control signal or signals for an individual actuator 120, such as first and second control signals for the first and second actuators 120, may be determined based on sensor signals from multiple deformation sensors. For example, a single control signal may be determined as a function of an average or difference of multiple sensor signals from multiple sensors 140, or multiple control signals for corresponding multiple actuators 120 may be determined based on multiple sensor signals.

[0079] The sensor signals from the multiple deformation sensors 120 may indicate that the bending deformation of the first cover member is deviated at different angular positions around the optical axis 150. The measured deviations can then be used to control the multiple actuators 120 so that each measured bending deformation approaches the same bending standard or the deviation is minimized.

[0080] 3A-3B show a main schematic diagram of an embodiment of a controllable lens 100, in which an actuator 120 is arranged to generate controllable bending and / or tilting of the first and / or second cover members 111, 112 in response to measurement signals from one or more sensors 140, according to similar principles as described for the other embodiments.

[0081] The actuators 120 are displacement actuators 303 capable of generating a displacement in response to a control signal. Each of the actuators 120 may have a displacement element 301 arranged to displace in a direction parallel or substantially parallel to the optical axis 150.

[0082] One or more actuators 120, 303 are arranged to generate a force on the first or second cover member 111, 112 along a path 351 that surrounds the optical axis 150, such as a circle on the surface of the first or second cover member 111, 112 shown in FIG. 3B.

[0083] Actuator 120 may be a linear displacement actuator arranged to apply displacement at several points, here eight points, along path 351, such as a linear piezoelectric or electromagnetic motor, a piezoelectric actuated cantilever actuator, a shape memory alloy, a linear screw drive, or a linear voice coil actuator.

[0084] The actuator is fixed to the support structure 130 such that the displacement element 301 is displaced relative to the support structure 130. In this example, the first cover member 111 is not directly connected to the support structure 130, but is indirectly connected via the actuator 303 and the elastic element 315. A non-actuated cover member, such as the second cover member 112 shown in Figures 3A-3B, may be supported by a further support structure 302, such as the support structure 130. Alternatively, the second cover member 112 may be actuated by another actuator similar to either the displacement actuator 303 or the surface-mounted actuator 120 described in connection with Figures 1-2.

[0085] The channel 351 may, as shown, surround the transparent, deformable non-fluid body 105 such that the non-fluid body 105 is surrounded by the channel 351. However, the channel 351 may also be located inside the extension of the non-fluid body 105. The actuator 120 may also be arranged to act on or be located close to an edge of the first or second cover member 111, 112.

[0086] The actuators 120, 303 are arranged along a path 351 and are positioned to generate a displacement normal or substantially normal to the surface of the cover members 111, 112. "Substantially normal" in this context means a deviation from perpendicularity of, for example, 10-15 degrees. An angular change in the angle between the direction of linear displacement and the surface of the cover members is generated in response to bending of the cover members.

[0087] Operation of the actuators 120, 303 changes the curvature of the first and / or second cover members depending on the force, torque, or displacement applied by the actuators. Thus, by controlling the actuators, the bending of the lens 100, and therefore the optical power, can be controlled. If the actuators are positioned relative to the first cover member, depending on the thickness or stiffness of the cover members and the further support structure 302, the second cover member may also bend, or vice versa.

[0088] By controlling the actuators 120, 303 to generate different forces on the first and / or second cover members 111, 112 for different actuators along path 351, the cover members 111, 112 can be forced to tilt and bend. The tilt of the cover members causes a change in the direction of the optical axis, as shown as exaggerated optical axis 350, thereby causing a change in the direction of transmitted or reflected light. By controlling the tilt of the cover members 111, 112, the change in the direction of the transmitted light can be used to compensate for camera rotation (e.g., due to camera shake), i.e., optical image stabilization (OIS).

[0089] It should be noted that the actuators 120, 303 can be arranged to act on either the first or second cover members 111, 112. It is also possible for the actuators 120, 303 to be arranged to act on both the first and second cover members 111, 112, such that the action of the actuators 120, 303 forces both cover members to bend, and in some cases the actuators on either side can be independently controllable, i.e. the displacement / force applied to one of the cover members can be controlled independently from the displacement / force applied to the other cover member.

[0090] The tilt of one of the cover members 111, 112 of the lens may be applied independently of the bending of another cover member 111, 112 of the lens 100. For example, a displacement actuator 303 may be provided for bending the cover members, while any type of actuator 120 may be provided for bending the first cover member 111.

[0091] In the main schematic diagram of Figure 3A, the displacement of the actuator is amplified via a hinged beam 305 disposed via a hinge connection 306. A sensor 140 may be disposed on the beam to measure the deformation of the beam. The deformation of the beam correlates with bending and tilt, and therefore the sensor signal from the sensor attached to the beam 305 can be used to control the actuators 120, 303 to obtain the desired bending and / or tilt of the first or second cover members 111, 112.

[0092] As an alternative to the displacement actuator 303, a surface mounted actuator 120 such as a piezoelectric element may be attached to the beam 305 to provide linear displacement, for example via a resilient connection 307.

[0093] For practical purposes, a different design than the primary solution shown in FIG. 3A will likely be used, but it will use a displacement actuator 303 based on a similar principle. According to this principle, one or more elastic elements 315, such as hinged beams 305, are arranged to connect the displacement actuator 303 to the first and / or second cover members 111, 112. The elastic elements 315 may have various configurations, but are generally arranged to elastically deform in response to a force applied by the displacement actuator 303. A deformation sensor 140 attached to one or more elastic elements 315 measures the deformation of the elastic elements 315, or the deformation of at least a portion of the elastic elements 315. Due to the relationship between the deformation of the elastic elements and the bending and tilt of the first or second cover members 111, 112, the measured deformation can be used to determine a control signal for controlling the actuator 140.

[0094] The elastic element 315 is elastically deformed in response to the relative displacement between the first or second cover member 111 or 112 and the displacement actuator 303 .

[0095] FIG. 3A shows that in addition to the hinged beam 305 , the elastic connection between the displacement actuator 303 and the first cover member 111 comprises a further elastic element 307 .

[0096] The further elastic element 307 may be arranged to deform at least radially in response to bending or tilting of the first or second cover member 111, 112, such that changes in radial extension of the first or second cover member 111, 112 due to bending or tilting are accumulated by radial deformation. By radial displacement it is understood that at least one component of the relative radial displacement has a component in a direction perpendicular to the optical axis in the radial direction.

[0097] For example, the further elastic element 307 may be made of an elastic adhesive obtained, for example, by performing a bonding process. Preferably, the further elastic element 307 has low stiffness against radial deformation and high stiffness in the displacement direction of the displacement actuator 303 in order to transmit the displacement of the actuator to the cover members 111, 112.

[0098] 4A-4C show an example of an elastic element 315 connecting the displacement actuator 303 and the first cover member 111. In this example, the actuator is also arranged to provide bending of the second cover member 112 via a further elastic element 315a. In these figures, the actuator 303 is not shown, only the contact points of the displacement element 301 and a representation of the actuators 120, 303 are shown.

[0099] The elastic element 315 is comprised of multiple deformable portions in the form of multiple spring elements 401, such as cantilevered metal beams. In response to bending of the first cover member 111, the spring elements 401 bend. The bending of the spring elements 401 provides low stiffness in response to radial deformation toward the optical axis 150, easing the requirement for the elastic elements 315 to provide high stiffness in the direction of displacement of the displacement actuator 303 to efficiently transfer the actuator displacement to the first cover member. Due to the low radial stiffness, bending of the first cover member is not constrained by the elastic elements 315. Each of the spring elements 401 is separated from adjacent spring elements, allowing each spring element 401 to deform independently or substantially independently from adjacent spring elements 401.

[0100] The elastic element 315 comprises a support member 402. The displacement actuator 303 is arranged to act on a surface of the support member 402, as primarily shown.

[0101] In this example, the support member 402 is formed as an annular structure with a hole that defines the opening for the lens 100 .

[0102] In this example, the first and second cover members 111, 112 are independently actuated via an upper resilient element 315 and a lower second resilient element 130a, respectively.

[0103] One or more sensors 140 may be attached to the spring element 401 to measure the deformation, which is at least partly due to bending of the first cover member 111, such that the measurement signal from the sensor 140 is directly related to the bending.

[0104] FIG. 5A shows an optical assembly 599 equipped with a controllable beam deflection device 500. In this embodiment, the second cover member 112 is a prism 501, and the first cover member 111 is a reflective cover member, such as a mirror, positioned opposite the hypotenuse of the prism 501. Incident light 502, i.e., light from the object space to be imaged onto the image sensor, passes through the prism 501 via one of its short sides and enters the first cover member through the non-fluid medium, which reflects the incident light 502 and redirects it in a different direction, e.g., perpendicular or substantially perpendicular to the incident direction. In this way, the reflective first cover member 111 causes the optical axis to be folded. Part of the incident light 502 may be transmitted through the first cover member, for example, due to the partial reflector formed by the first cover member 111.

[0105] A displacement actuator 303, such as that described in relation to Figure 3A, may be arranged to generate a controllable tilt of the reflective cover member 111. As described in relation to Figure 3A, a sensor 140 disposed on the elastic element 315 provides a measurement signal indicative of the actuator's displacement amplitude and, therefore, the tilt angle of the reflective cover member 111. The two actuators shown in Figure 5A may operate in opposite displacement directions to facilitate tilting of the reflective cover member 111. Alternatively, the reflective cover member 111 may be hinged on one side.

[0106] Alternatively, the sensor 140 may be arranged to directly measure the displacement of the actuator 303. Such a sensor may be based on optical distance measurement or resistive distance measurement or may be integrated with the sensor. The displacement actuator 300 may be configured without the hinged beam 305. For example, the displacement actuator 303 may be connected directly to the reflective cover member 111, possibly via a further elastic element 307, if the hinged beam 305 is not used to provide displacement amplification.

[0107] The controllable lens 100 and the controllable beam deflection device 500 are examples of controllable optical assemblies according to various embodiments.

[0108] Similar to FIG. 3A, the first cover member 111 is not directly connected to the support structure 130 but is indirectly connected via the actuator 303 and the elastic element 315 .

[0109] 5A shows an optical sensor 550 as an alternative to sensor 140. Optical sensor 550 comprises a light source 551 configured to output a beam of light, such as a collimated beam 553, and a photodetector 552. Photodetector 552, such as a position-sensitive detector or a quadrant detector, generates an output that depends on the one- or two-dimensional position of beam 553 on detector 552. Thus, optical sensor 550 can measure at least the tilt of first cover member 111.

[0110] 5B shows the optical sensor 550 used in an example where the first cover member 111 is arranged to be bent by a displacement actuator 330 directly connected to the first cover member 111, although a surface-mounted actuator 120 may be used as well. The divergence of the beam is affected by the bending of the first cover member 111, and thus the size of the beam spot on the detector is directly related to the bending of the first cover member. Thus, the detector 552 may generate an output that is dependent on the size of the beam spot. Clearly, the detector 552 may be of a type whose output depends on both the position and size of the beam spot on the detector.

[0111] Thus, in this embodiment, the alternative optical sensor 550 is configured to transmit a light beam 553 through the non-fluid body 105 and through at least one of the first and second cover members 111, 112, whereby the direction and / or divergence of the light beam is affected by at least one cover member 111, 112 arranged to be tilted and / or bent by the actuator 120, 303.

[0112] The control system 190 may be part of the deflection device 500 or the optical sensor 550 and may be arranged to control the actuator 120 based on the measured tilt, such as in a feedback control system in which the difference between the measured tilt and the desired tilt angle is minimized.

[0113] The first cover member 111 may alternatively be configured as a transparent cover member 511 to refract and transmit the incident light 502 through the cover member. The transparent cover member may advantageously be positioned opposite one of the two orthogonal faces of the prism, with a non-fluid 105 sandwiched between the cover member 511 and the prism. The transparent cover member 511 may be used to control the propagation direction of the light beam 502 by controlling the tilt of the cover member 511. Thus, the prism may be composed of a reflective cover member 111 and a refractive, i.e., transparent, cover member 511, as shown in the simplified diagram of FIG. 5C. The actuator 120 for tilting the cover members 111, 511 is omitted from the drawing for clarity.

[0114] Figure 6A shows the light sensor 550 of Figure 5A in more detail. The light sensor 550 comprises a light source 551 arranged to propagate a light beam 553, such as a diverging light beam, towards the back surface 601 of the first cover member 111, i.e. the reflector or transparent cover member 511. The beam 553 is reflected by the back surface 601 and therefore the propagation direction of the reflected beam 553 is affected by the tilt of the cover members 111, 511.

[0115] The back surface 601 refers to the surface facing away from the prism 501. The back surface 601 may be coated to provide reflective properties. Thus, the back surface of the cover member 111, 511 may be used as an alternative to, or in addition to, the front side of the cover member 111, 511, whose front side faces the prism 501, as shown in FIG. 5A. The use of the back surface 601 is advantageous for obtaining independent sensor signals from the detector 552, or from different detectors on different cover members 111, 511, in configurations where the deflection device 500 has both reflective and transparent cover members 111, 511.

[0116] The light detector 552 is positioned to measure a change in the light beam 553 caused by tilting the cover members 111, 511. The change in the light beam 553 may involve a change in the position where the light beam 553 strikes the light detector 552 and / or a change in the size of the spot of the light beam 553 on the light detector 552.

[0117] The photodetector 552 may be comprised of at least four individual photodetectors 602, each capable of generating an output signal that correlates to the power of light incident on the individual photodetector. The signal outputs from the individual photodetectors 602 may be processed to determine a change in tilt of the cover member 111, 511, for example, by comparing the individual outputs. The measured tilt may be used to control the actuator system 120, 303, such as a feedback control system in the control system 190, that minimizes the difference between the measured tilt and the desired tilt angle.

[0118] 6B shows an alternative embodiment of a light sensor 550 in which the light source 551 is positioned at the center of each individual light detector 602, i.e., all of the light detectors 602 are positioned to surround the light source 551. In this configuration, the planes of the light source 551 and light detectors 602 may be parallel or substantially parallel to the back surface 601 of the reflective or transparent cover member 111, 511.

[0119] 7 illustrates the linear performance of the optical sensor 550 of FIG. 6A. As shown in the top diagram, the y-axis position output from the detector 552 is slightly dependent on the y-axis tilt angle of the cover member 111 for variations in the x-axis tilt. Similarly, the bottom diagram illustrates that the x-axis position output from the detector 552 is slightly dependent on the x-axis tilt angle for variations in the y-axis tilt. Thus, the output signal from the detector 552 is slightly nonlinear when the tilt angle is a combination of two rotational axes (i.e., when the controllable beam deflection device 500 is configured to provide tilt about two orthogonal x- and y-axes).

[0120] Figure 8 shows the linearity performance of the optical sensor 550 in the configuration of Figure 6B. Thus, this configuration of the optical sensor provides improved linearity in the output signal from the detector 552, thus eliminating the need for calibration of the detector signal output.

[0121] FIG. 9 shows an alternative configuration of an optical sensor 550 configured to determine the optical power of the controllable lens 100 .

[0122] The light source 551 is arranged so that a light beam 553, for example the center of the intensity profile of the light beam 553, strikes the first and / or second cover members 111, 112 at a predetermined distance h from the optical axis 150. In this case, the light beam 553 is preferably a parallel light beam. The surface of the first and / or second cover members 111, 112 that reflects the light beam 553 faces the image sensor 901 of the camera. The distance between the controllable lens 100, such as the reflective surface, and the image sensor 901 is Z. The light detector 552 is arranged to detect at least a portion of the reflection of the light beam 553. The light source 551 and the detector 552 are arranged on opposite sides of the image sensor 901, but are not necessarily collinear with the center of the image sensor 901.

[0123] Although this is not a requirement, if the detector 552 is positioned the same or substantially the same distance Z from the lens 100, the displacement Δ between the position where the reflected beam 553 strikes the detector 552 and the position where the beam 553 reflected from the planar cover members 111, 112 strikes the detector 552 can be expressed as:

[0124] Δ=hZ / 2R

[0125] where h is the distance along the y axis from the optical axis 150 to the point where the light beam 553 strikes the first or second cover member 111, 112, Z is the distance along the z axis between the image sensor 901 and the first or second cover member 111, 112, and R is the curvature (measured as a radius) of the surface of the first or second cover member 111, 112 facing the image sensor 901. The optical power P of the lens, assuming a plano-convex lens, is given by:

[0126]

number

[0127] where nlens and nair are the refractive indices of the lens and the surrounding air. Therefore, the optical power changed by the actuator can be determined from the measured displacement Δ.

[0128] The light source 551 and the detector 552 may be arranged such that the plane of incidence of the light beam 553 includes the optical axis 150, i.e., the light source 551 and the detector 552 are aligned with the image sensor 901. In another embodiment, the light source 551 and the detector 552 are arranged such that the plane of incidence of the light beam 553 does not include the optical axis 150, i.e., the light source 551 and the detector 552 are not aligned with the image sensor 901.

[0129] 10A shows the output signal from detector 552 as a function of optical power, determined from the displacement value Δ, for a distance between detector 552 and optical axis 150 measured along the y-axis of 5 mm (solid curve) and a corresponding distance of 7 mm (dashed curve). In this example, light source 551 and detector 552 are aligned with image sensor 901. As shown, better sensitivity is achieved when detector 552 is positioned further away from image sensor 901, but at the expense of a larger form factor (in the y-axis direction).

[0130] FIG. 10B shows the output signal from detector 552 in a configuration similar to FIG. 10A , where the distance between detector 552 and optical axis 150 is 7 mm. However, in this example, light source 551 and detector 552 are not aligned with image sensor 901, i.e., the plane of incidence does not include optical axis 150. Due to the non-aligned configuration, reflected light beam 553 is displaced on detector 552 in both the x-axis and y-axis directions. The solid lines indicate x-axis displacement as in FIG. 10A , and the dashed lines indicate y-axis displacement. The sensitivity to reflections causing x-axis and y-axis displacement may be used to determine astigmatism, i.e., the different radii of opposing surfaces of first or second cover members 111, 112 in orthogonal directions, by comparing the x-axis and y-axis displacements and using the formula Δ=hZ / 2R with the associated values ​​of h for the two orthogonal directions.

[0131] FIG. 11A shows another configuration of an optical sensor 550 configured to determine the optical power of the controllable lens 100 .

[0132] The lens 100 is positioned between the light source 551 and the detector 552, i.e., such that the light source 551 is arranged to propagate a light beam 553 toward one of the outer surfaces of the first and second cover members 111, 112, and the detector 552 is arranged to receive the light beam 553 that has transmitted through the other outer surface of the first and second cover members 111, 112. Thus, the light beam 553 transmits through the first and second cover members 111, 112 at a high angle of incidence.

[0133] The photodetector 552 may be positioned so that its input aperture faces the optical axis 150 , ie, so that the normal to the detector surface is perpendicular or substantially perpendicular to the optical axis 150 .

[0134] The angle of incidence between the light beam 553 and the surfaces of the first and second cover members 111, 112 may be an angle less than 60 degrees, such as less than 40 degrees or less than 30 degrees.

[0135] The light source 551 and the detector 552 may be arranged so that the plane of incidence of the light beam 553 includes the optical axis 150, or may be arranged so that the plane of incidence does not include the optical axis 150.

[0136] If astigmatism is introduced by the lens 100, for example due to bending errors in the cover members 111, 112 due to actuator inaccuracies, the spot of the light beam 553 will be non-circular (assuming a rotationally symmetric intensity profile of the incident light beam 553), and the output from the individual photodetectors 602 of the detector 552 will generate a signal corresponding to the astigmatism.

[0137] Furthermore, since astigmatism is proportional to the lens power P, the four photodetectors 602 of the detector 552 can be used to determine the lens power P by measuring the deformation of the spot, i.e., the elliptical shape of the spot.

[0138] FIG. 11B shows the relationship between the ratio of the x-axis diameter to the y-axis diameter of the light beam spot on the detector 553 and the lens power P.

[0139] 11A shows that the light source 551a and the detector 552a may be arranged such that the light beam (dashed lines) passes through other optical components 920, such as a fixed lens, before passing through the controllable lens 100 and / or such that the light beam passes through other optical components 920 after passing through the controllable lens 100. Thus, the controllable lens and other optical components may be arranged along the optical axis between the light source 551 and the detector 552. This may be advantageous in compact optical systems without space to place the light source 551 and / or the detector 552 on opposite sides of the controllable lens 100.

[0140] FIG. 12 illustrates a camera module 900 that includes a controllable lens 100 and an image sensor 901 positioned to receive light transmitted through the lens 100. Optionally, the camera module 900 may include a beam deflection device 500 positioned to receive and redirect incident light 502 to be imaged, and may also include additional optical components, such as fixed optical lenses that may be disposed within a lens stack that may include the controllable lens 100. Thus, the camera module 900 includes an optical assembly 199, 599 embodied by the controllable lens 100 and / or the beam deflection device 500. The optical assembly 199, 599 may be combined into a single optical assembly that includes both the variable lens 100 and the deflection device 500. The camera module 900 may be used in electronic devices such as smartphones. Other electronic devices, such as beam scanners, may use optical assemblies without image sensors for purposes other than imaging.

Claims

1. A controllable optical assembly (199, 599) having variable optical power and / or variable beam deflection, said optical assembly comprising: a first cover member (111) and a second cover member (112), one of the first and second cover members being a transparent cover member and the other of the first and second cover members being a transparent or reflective cover member; a transparent, deformable, non-fluid body (105) sandwiched between the first and second cover members, whereby the first and second cover members and the non-fluid body form a lens or optical deflector having an optical axis (150) intersecting the non-fluid body and the first and / or second transparent cover members; one or more actuators (120) arranged to generate a controllable bending and / or tilting of at least the first cover member in response to a control signal, the control signal being derivable from the first and second measurement signals; first and second sensors (140) arranged to provide said first and second measurement signals, whereby said measurement signals are indicative of bending and / or tilting of at least said first cover member, said first sensor being an optical sensor and said second sensor being a deformation sensor; the optical sensor comprises a light source arranged to propagate a light beam such that the light beam is affected by bending or tilting of the first and / or second cover members, the optical sensor comprising a photodetector (552) arranged to measure changes in the light beam related to the bending and / or tilting; the deformation sensor includes a piezoelectric sensor element connected to the first cover member; A controllable optical assembly, wherein the deformation sensor is connected to a surface of the one or more actuators.

2. 2. The controllable light assembly of claim 1, wherein the second cover member (112) is a prism (501), and the first cover member is a reflective cover member positioned opposite a hypotenuse of the prism to reflect at least a portion of the intensity of incident light (502).

3. 3. A controllable light assembly as described in any one of claims 1 or 2, comprising one or more elastic elements (315) connecting a displacement actuator (303) with the first cover member (111) and / or the second cover member (112), at least a portion of each of the one or more elastic elements being arranged to elastically deform in response to displacement of the actuator.

4. As the second sensor, one or more other deformation sensors different from the deformation sensor are provided, 4. A controllable light assembly according to claim 3, wherein the one or more other deformation sensors (140) are arranged to measure deformation of a portion of each of the one or more elastic elements (315).

5. A controllable light assembly according to any one of claims 1 to 4, wherein a support structure at least partially surrounds the non-fluid body, the support structure being spaced apart from the non-fluid body, and the non-fluid body being allowed to expand along at least a portion of the support structure that surrounds or partially surrounds the non-fluid body without contacting the support structure.

6. A controllable light assembly according to any preceding claim, wherein the one or more actuators comprise one or more piezoelectric elements connected to a surface of the first cover member.

7. 7. The controllable light assembly of claim 6, wherein the one or more piezoelectric elements comprise a ring-shaped piezoelectric element connected to the surface of the first cover member, the ring-shaped piezoelectric element configured with an opening to allow light to pass therethrough.

8. 8. A controllable light assembly according to claim 6 or 7, wherein the piezoelectric sensor elements are the one or more piezoelectric elements configured as the one or more actuators (120).

9. 2. The controllable light assembly of claim 1, wherein the one or more actuators (120) are sandwiched between the one or more deformation sensors (140) and the first or second cover member (111, 112).

10. 10. A controllable light assembly as described in claim 1 or 9, wherein the light assembly (199, 599) comprises at least one compensation sensor (240) arranged so as not to be exposed to deformations corresponding to bending of the first or second cover member, the at least one compensation sensor being of the same type as the deformation sensors connected to the surface of the one or more actuators.

11. 11. The controllable light assembly of claim 10, wherein the at least one compensation sensor (240) is connected to a support structure (130) configured to support the first cover member and / or the second cover member.

12. 2. The controllable light assembly of claim 1, wherein the light source (551) is arranged such that the light beam (553) is reflected by the first or second cover member (111, 112) which is arranged to be bent or tilted.

13. 13. The controllable optical assembly of claim 1 or 12, wherein the optical detector (552) comprises at least two individual optical detectors (602), each of the individual optical detectors capable of generating an output signal correlated to the power of light incident on the individual optical detector.

14. 14. A controllable light assembly as described in claim 13, wherein the output openings of the light sources (551) and the input openings of the individual light detectors (602) are arranged to face the first and second cover members (111, 112).

15. 15. A controllable light assembly according to claim 13 or 14, wherein the light source (551) is arranged at the centre of a circle surrounding the individual light detectors (602).

16. 13. A controllable light assembly as described in claim 1 or 12, wherein the light source (551) is positioned so that the light beam (553) strikes the first and / or second cover members (111, 112) at a predetermined distance (h) from the optical axis (150).

17. 13. A controllable light assembly as described in claim 1 or 12, wherein the light source (551) is arranged so that the light beam (553) passes through the first or second cover member (111, 112), and the light detector (552) is arranged to measure the transmitted light beam.

18. An electronic device (900) comprising the optical assembly (199, 599) of any one of claims 1 to 17 and a control system (190) arranged to generate the control signals in response to the first and second measurement signals to obtain a desired bending or tilting of the first and / or second cover members.

19. 2. A method of controlling an optical assembly (199, 599) according to claim 1, said method comprising: obtaining first and second measurement signals from the one or more sensors, whereby the measurement signals are indicative of the bending and / or tilt of the first and / or second cover members; determining a control signal based on the measurement signal; controlling the bending and / or tilting of the first and / or second cover members in response to the control signal; 2. A method for controlling an optical assembly, comprising:

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