Patent Description:
In order to enable successful use of devices with variable optical power or variable deflection, high accuracy of the variable parameter is required. This may be achieved by accurate calibration of the optical device. Accurate calibration is hard to achieve due to dependencies on temperature, hysteresis and long-term drift phenomena, i.e. creep. Another way to control the variable parameter is to develop a model of the optical device that could predict changes of the variable parameter caused by temperature, hysteresis and creep. However, still with this method, the model cannot predict exact values of the variable parameter for each optical device but only average values.

Pertinent prior art is disclosed in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>.

Accordingly, there is a need for improving control of such optical devices to achieve accurate control and to obtain technically feasible solutions.

It is an object of the invention to improve improving control of variable lenses and adjustable light deflectors. Particularly, it is an object to improve measurement of variations in optical power and/or beam deflection of variable lenses and light deflectors.

In a first aspect of the invention there is provided a controllable optical assembly according to claim <NUM>, with a variable optical power and/or a variable beam deflection, the optical assembly comprises.

With the actuators arranged to generate a controllable bending and/or tilt of at least the first cover member it is understood that the actuators may alternatively or additionally be arranged to generate a controllable bending and/or tilt of the first and/or the second cover member. One or more sensors may be arranged to provide the measurement signal so that the measurement signal is indicative of the bending or tilt of the first and/or the second cover member.

According to an alternative embodiment not falling within the scope of the claimed invention, the controllable optical assembly comprises either the first or the second sensor and would therefore be arranged to provide only one measurement signal from which the control signal is obtainable so that the measurement signal is indicative of the bending and/or tilt of at least the first cover member.

Advantageously, by measuring the bending of the cover member and thereby the change of optical power, or the tilt of the cover member and thereby the beam deflection, the measured change can be used in a feedback control system to accurately adjust the actuator to achieve a desired tilt or optical power.

Compared with other solutions using image sensor readings and processing to control the optical power, the direct measurement of e.g. lens bending, provides direct measurements of the optical power and thereby enables faster adjustments, e.g. in a feedback control loop. For example, it is known to use phase detectors in cameras for obtaining image sharpness measurements and using the measurements for adjusting image sharpness. However, phase detectors do not provide information about optical power.

The controllable optical assembly may further comprise a support structure arranged to support the first cover member and/or the second cover member. The use of two different sensors wherein one of the sensors is an optical sensor and wherein another of the sensors is a deformation sensor combines the advantages of each of the sensors, e.g. so that the high accuracy of the optical sensor is combined with the direct stress sensing capabilities of the deformation sensors or other advantages such as low cost or simplified design of one of the sensors.

In an example, the deformation sensor, e.g. a piezo sensor, is used to control bending of the cover member based on sensor readings from the deformation sensor. For example, sensor readings from a piezo actuator which also serves as a piezo sensor may be used in an open loop algorithm which determines the voltage to be applied to the piezo actuator. An example of this open loop control is described in published <CIT>.

To increase accuracy the open loop control may be combined with a closed loop control where the sensor reading from the optical sensor is compared with a reference for the bending of the membrane.

The first and second sensors may be arranged to obtain measurement signals indicative of the bending and/or tilt of the first cover member, e.g. by connecting the deformation sensor with the first cover member to detect deformations of the first cover member and by arranging the optical sensor to optically detect changes in bending and/or tilt of the first cover member.

Examples of the deformation sensor includes the piezo electric sensor element such as the piezo electric element of one or more of the actuators. Other examples of the deformation sensor include strain gauge sensors in configurations as described herein. Examples of the optical sensor include any of the optical sensor configurations described herein where the light beam is reflected by at least the first cover member or transmitted through at least the first cover member.

The first and second sensor signals may each be indicative of bending or tilt. It is also possible that one of first and second sensors signals are indicative of bending while the other is indicative of tilt.

The control system can be configured to generate the control signal dependent on the first and second measurement signals to achieve a desired bending and/or tilt of the first and/or the second cover member. For example, the first and second measurement signals may be combined to improve measurement accuracy. In another example, the first measurement signal provides measurement of bending while the second measurement signal provides measurement of tilt. It is also possible that the first measurement signal may be used for initial adjustment of bending or tilt, while the second measurement signal may be used for continued adjustment of bending or tilt e.g. according to a set-point reference.

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

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

According to an embodiment, the controllable optical assembly comprises one or more elastic elements connecting the displacement actuators with the first cover member and/or the second cover member, wherein at least a portion of each of the one or more elastic elements is arranged to deform elastically in response to the actuator displacement.

Advantageously, the elastic elements may reduce undesired deformation in the cover member, which could be generated by stiff connections.

According to an embodiment, the one or more sensors are arranged to measure the deformation of a portion of the respective one or more elastic elements.

The measurement of the deformation generated in the elastic structure may advantageously be used for determining the tilt or bending of the cover member.

According to an embodiment, the support structure comprises a rigid frame.

The support structure, which alternatively could be less rigid, may be arranged to at least partially surround the non-fluid body and so that the support structure is separated from the non-fluid body to allow the non-fluid body to expand without contacting the support structure at least along a part of the support structure which surrounds or partially surrounds the non-fluid body.

The rigid support structure may be used for placement of a compensation sensor arranged so that it is not, or substantially not, exposed to deformation in response to bending of the first or the second cover member, wherein the at least one compensation sensor is of the same type as the one or more deformation sensors. The compensation sensor can be used for compensating temperature dependencies. Advantageously, when the support structure is separated from the non-fluid body, the support structure is not exposed to deformations in response to actuations and can therefore hold the compensation sensor.

According to an 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.

Such actuators may be surface mounted actuators arranged to generate surface strain on the cover member.

For example, the one or more actuators comprises one or more piezo electric elements connected to the surface of the first cover member.

The one or more piezo electric elements may comprise a ring shaped piezo electric element connected to the surface of the first cover member, wherein the ring shaped piezo electric element is configured with an aperture to enable transmission of the light.

According to an embodiment the one or more sensors comprise a piezo electric sensor element. Advantageously, piezo electric sensor elements may be used to achieve a high bandwidth of the measurement signal.

For example, the piezo electric sensor element may be one of the piezo electric elements used as an actuator. Accordingly, the piezo actuator may serve both as an actuator and as a sensor. <CIT> describes how the piezo actuator can be used to determine a transfer function dc(V) for the piezo actuator based on measured transition times tt between two voltages applied to the piezo actuator. Thus, measures which depend on the piezo actuator, such as the capacitance of the piezo actuator, can be used to determine a transfer function of the piezo actuator so that it can be controlled e.g. in an open loop configuration.

According to an 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 the second cover member. In this case the sensors may be arranged to measure the sensor deformation.

The optical assembly may comprises at least one compensation sensor arranged so that it is not, or substantially not, exposed to deformation in response to bending of the first or the second cover member, wherein the at least one compensation sensor is of the same type as the one or more deformation sensors. The at least one compensation sensor may be connected to the support structure.

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

According to an embodiment, the deformation sensors are arranged symmetrically relative to an optical axis of the lens. For example, two or more deformation sensors may be arranged with the same radial distance to the optical axis and with the same circular arc-length between the sensors.

According to an embodiment, the control signal(s) is/are determined dependent on the measured deformations of the plurality of deformation sensors. For example, the control signals may be determined dependent on e.g. averages or differences from multiple sensors, or individual control signals may be determined for individually controllable actuators.

According to an embodiment, the sensor comprises a light source arranged to transmit a light beam so that the light beam is affected by the bending or tilt of the first and/or the second cover member, and where the sensor comprises a light detector (<NUM>) arranged to measure a change of the light beam relating to the bending and/or tilt.

According to an embodiment, the light source is arranged so that the light beam is reflected by the first or the second cover member arranged to be bent or tilted.

According to an embodiment, the light detector comprises at least two individual light detectors, each of the individual light detectors are capable of generating an output signal which is correlated with the power of the light impinging the individual light detector.

For example, two light individual light detectors may be used for sensing tilt in only one dimension. Three individual light detectors may be used for sensing tilt in two dimensions, although four individual light detectors may be preferred.

According to an embodiment, an output aperture of the light source and input apertures of the individual light detectors are arranged so that they face the first or the second cover member.

According to an embodiment, the light source is arranged at a center of a circle which circumscribes the individual light detectors.

According to an embodiment, the light source is arranged so that the light beam, such as the center of the intensity profile of the light beam, hits the first and/or the second cover member a distance away from the optical axis.

According to an embodiment, a plane of incidence spanned by the light beam and the surface normal at a location where the light beam hits the first and/or the second cover member does not comprise the optical axis.

According to an embodiment, the light source is arranged so that the light beam is transmitted through the first or the second cover members and wherein the light detector is arranged to measure the transmitted light beam. The light detector may be arranged so that its input aperture faces the optical axis.

A second aspect of the invention relates to an electronic device such as a camera module comprising the optical assembly according to the first aspect and a control system arranged to generate the control signal dependent on the first and second measurement signals to achieve a desired bending or tilt of the first and/or the second cover member. The electronic device may be a camera module, a light beam scanner, or other electronic device. For example, the light beam scanner may use the controllable beam deflection device, possibly the controllable lens, for various beam scanning purposes such as image projection, bar code scanning and 3D scanning.

A third aspect of the invention relates to method for controlling an optical assembly according to the first aspect, the method comprises.

In general, the various aspects and embodiments of the invention may be combined and coupled in any way 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 hereinafter.

<FIG> shows an optical assembly <NUM> comprising a controllable lens <NUM> having a variable optical power. The upper illustration is a top view, and the two lower illustrations are side views showing the lens in two different actuation states. The lens comprises a first cover member <NUM> and a second cover member <NUM>. In an embodiment, the first and second cover members are a transparent. Alternatively, one of the first and second cover members is reflective, e.g. provided with a reflective metal layer to provide full or partial reflection so that the incident light beams are reflected back to the opposite transparent cover member.

For example, the second cover member may comprise a reflective surface arranged to reflect incident rays transmitted through the transparent first cover member back to the first cover member cover member. For convenience, examples and embodiments herein refer to transparent cover members <NUM>, <NUM>.

The lens <NUM> further comprises a transparent, deformable, non-fluid body <NUM> sandwiched between the first and second cover members, so that the first and second cover members and non-fluid body constitute the lens having an optical axis <NUM> intersecting the first and second cover members and the non-fluid body. The non-fluid body <NUM> abuts the inwardly facing surfaces of the first and second cover members <NUM>, <NUM>.

The optical axis <NUM> may be defined as the axis which passes through centers of the first and second cover members <NUM>, <NUM> and the non-fluid body <NUM> and which is normal to a plane of one of the cover members. The optical axis is further defined according to conventional optical definitions.

One or more actuators <NUM> are arranged to generate a controllable bending, tilt or displacement or a combination thereof. The thereby controllable change of the overall outer shape of the lens is controlled dependent on an electrical or optical control signal, such as a control signal generated by a control system <NUM>.

At least one of the first and second cover members <NUM>, <NUM> are configured to be bent by forces or torques provided by the actuators <NUM>. It is understood that the forces in general comprises forces distributed over an area, e.g. due to stresses generated by strains generated by surface mounted piezo elements.

The lens comprises a support structure <NUM> arranged to support the first cover member and/or the second cover member <NUM>,<NUM>. In this example, the first cover member <NUM> is supported by the support structure <NUM>, e.g. fixed to the support structure, while the second support member <NUM> is not in contact with the support structure <NUM>.

One or more sensors <NUM> are arranged to measure a deformation which correlates with the bending, tilt or displacement, or a combination of these. For example, in <FIG>, if the right and left side actuators <NUM> are controlled differently, the bending of the first cover member <NUM> can be shaped asymmetrically to effectively cause a tilting effect. In the <FIG> example, the sensors <NUM> may be strain gauges or other sensor types capable for measuring deformation, i.e. strain. In this example, the sensor, a strain gauge, is mounted on top of the surface mounted piezo element so that it measures the deformation of the piezo element which is at least correlated with the bending of the first cover member <NUM>.

A control system <NUM> is provided to generate the control signal dependent on the measured deformation - or dependent on measure tilt or a measured change of optical power, in general dependent on a measurement which is indicative of the bending or tilt - so as to achieve a desired bending and tilt, or a combination, of the first and/or the second cover member. For example, the control system <NUM> may comprise a feed-back control system arranged to minimize the difference between the measured tilt or bending and the desired tilt or bending. The control system <NUM> may be integrated with the lens, or the control system may be a separate control system arranged to receive the deformation signals from the deformation sensors and arranged to transmit the control signal to the actuators <NUM>.

The transparent deformable, non-fluid lens body <NUM> is preferably made from an elastic material. Since the lens body is non-fluid, no fluid-tight enclosure is needed to encapsulate the lens body to prevent a leakage therefrom. As illustrated, the lens <NUM> comprises a gap <NUM> between the support structure <NUM> and the non-fluid body <NUM>. The motion of the non-fluid body <NUM> is therefore unrestrained radially relative to the optical axis <NUM>, i.e. along directions perpendicular to the optical axis. In a preferred embodiment, the lens body is made from a soft polymer, which may include a number of different materials, such as silicone, polymer gels, a polymer network of cross-linked or partly cross-linked polymers, and a miscible oil or combination of oils. The elastic modulus of the non-fluid lens body may be larger than <NUM> Pa, thereby avoiding deformation due to gravitational forces in normal operation. The refractive index of the non-fluid lens body may be larger than <NUM>. The non-fluid body <NUM> may have a refractive index which is equal, substantially equal or close to the refractive index of the first and second cover members <NUM>, <NUM> in order to reduce reflections at the boundaries of the non-fluid body <NUM>.

The cover members <NUM>, <NUM> are generally slab-shaped and may have curved such as a pre-shaped, e.g. spherical, shape or plane surfaces or a combination thereof. The cover members <NUM>, <NUM> may be made from a large number of different materials, such as acrylics, polyolefins, polyesters, silicones, polyurethanes, glass and others. At least one of the first and second cover members <NUM>, <NUM> which is arranged to be deformed by the actuators, has a stiffness which is suitable to enable bending by actuation of the actuators <NUM>. In general, the material of the first and/or the second cover member <NUM>, <NUM> may be formed in a material having a Young's modulus in the range between <NUM> MPa and <NUM> GPa to provide the necessary stiffness. For example, Young's modulus for borosilicate glass is <NUM> GPa, and <NUM> GPa for fused silica glass.

The bending of the first and/or second cover members <NUM>, <NUM> is at least partly due to radially varying reaction forces from the lens body <NUM> which affects the Sag of the cover members <NUM>, <NUM> and thus the optical power instead of just vertically compressing the lens body with no change in Sag. A full explanation of the effect of the lens body <NUM> on the curvature of the cover members is described in <CIT>.

In the <FIG> example, the one or more actuators <NUM> comprise one or more piezoelectric elements mounted on the surface of the first cover member <NUM>. For example, a single actuator <NUM> in the form of a sheet and annular ring shaped piezo element as shown is attached on a surface of the first cover member <NUM> in order to provide bending of the first cover member. One or more sensors <NUM> may be arranged on the ring shaped piezo element. Instead of a ring shaped element, a plurality of piezo elements may be distributed along a circle around the optical axis <NUM>. One or more sensors may be arranged between the distributed piezo elements or between other actuators <NUM>.

Accordingly, one or more deformation sensors may be connected to a surface of the one or more actuators, e.g. so 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 the second cover member <NUM>, <NUM>.

Actuators <NUM> configured in other ways are also feasible. For example, linear displacement actuators may be located between the first and second cover members <NUM>, <NUM> and connected with the inwardly pointing surfaces of the cover members <NUM>, <NUM>, e.g. via elastic elements such as bendable elements arranged to accumulated e.g. radial relative displacements between the actuator <NUM> and the connection point on cover member <NUM>, <NUM>. In this case, the one or more sensors <NUM> may be mounted on one or more of the inwardly and outwardly pointing surfaces.

The one or more piezoelectric actuators <NUM> are arranged so that the lens <NUM> comprises an inner portion <NUM> which constitutes the lens area, surrounded by the one or more piezoelectric actuators <NUM>, so that light can pass unobstructed through the lens area. The non-fluid body <NUM> is arranged so that it covers at least the lens area, but may also extend beyond the extension of the lens area towards the perimeter of the first or second cover member <NUM>, <NUM>.

The actuators <NUM> may be configured to solely generate a controllable bending of the first or the second cover member <NUM>,<NUM>. Thus, by the actuation, the first and/or second cover member can be bend into a concave or convex shape and thereby provide an optical power to light transmitted through the lens.

Alternatively, the one or more actuators <NUM> may be arranged to displace and/or tilt one of cover members <NUM> relative to the other <NUM>. For example, the actuators <NUM> may be arranged as explained above, between the cover members <NUM>, <NUM>, so that the relative angle between the two cover members can be changed, e.g. in order to change the direction of imaged light transmitted through the lens <NUM>.

In another example, one of the cover members <NUM>, <NUM> comprises a reflective surface to provide adjustable beam deflection of the reflected beam by controlling the tilt of the cover member.

The actuators may advantageously be arranged to provide bending of one of the cover members <NUM> in combination with tilt in order to generate optical power and beam deflection. The combined tilt and bending may be used with a transparent or reflective cover member. The beam deflection may be used to achieve optical image stabilization (OIS) in a camera such as a compact camera in a smart phone.

The support structure <NUM> may be configured as a rigid frame which is not deformed or substantially not deformed when the cover member <NUM>, <NUM> connected to the support structure is deformed or exposed to stresses from the actuators. The support structure may be arranged so that it at least partially surrounds the non-fluid body and thereby provides a continuous support for the connected cover member <NUM>, <NUM>. Furthermore, the controllable lens <NUM> may be arranged with a gap <NUM> such as an air gap <NUM> between the perimeter of the non-fluid body <NUM> and the support structure, i.e. a gap extending radially relative to the optical axis <NUM> and separating the perimeter of non-fluid body <NUM> in a radial direction from the support structure <NUM>. Due to the gap, the non-fluid body is able to expand unconstrained in the radial direction in response to actuator actions.

The output signal from the sensor <NUM> may depend on other physical effects than deformation. Such other effects comprises temperature, hysteresis and creep. At least temperature dependency of the sensor <NUM> may be compensated, or at least partially compensated, if two identical sensors are arranged close to each other.

<FIG> shows that the controllable lens is configured with at least one compensation sensor <NUM> in additional to deformation measurement sensors <NUM>. The compensation sensors <NUM> are arranged so that they are not, or substantially not, exposed to deformation in response to bending of the first or the second cover member. Since the compensation sensor and the deformation sensors are of the same type, they have substantially the same dependencies to the other physical effects such as temperature.

By connecting a set of sensors comprising one compensation sensor <NUM> and one measurement sensor <NUM>, when they are resistive strain sensors, in a Wheatstone bridge circuit, the output signal from the Wheatstone bridge will be compensated with respect to the physical effects affecting both the compensation sensor <NUM> and the measurement sensor <NUM>. Thus, a change in e.g. temperature will not generate a corresponding change in the output signal from the Wheatstone bridge. That is, any change in temperature will affect both sensors <NUM>, <NUM> in the same way. Because the temperature changes are identical in the two sensors, the ratio of their resistance does not change, and the effects of the temperature change are minimized or substantially eliminated. In this way, a temperature dependency of first and second deformation sensors <NUM> can be compensated by a corresponding temperature dependency of respective first and second compensation sensors <NUM>.

The compensation sensors may be connected to the support structure so that they are not, or only to a small degree, exposed to deformations when the first or the second cover member are deformed.

As shown in <FIG>, the four deformation sensors <NUM> and the associated compensations sensors <NUM> are arranged rotation symmetric relative to the optical axis <NUM> of the lens <NUM>. For example, a plurality of deformation sensors may be used to minimize aberrations which may be generated in response to bending.

Advantageously, the control signal or a plurality of control signals for individual actuators <NUM>, such as first and second control signals for first and second actuators <NUM>, may be determined based on sensor signals from a plurality of deformation sensors. For example, a single control signal may be determined dependent on averages or differences of a plurality sensor signals from multiple sensors <NUM>, or a plurality of control signals for a corresponding plurality of actuators <NUM> may be determined based on a plurality of sensor signals.

Sensor signals from a plurality of deformation sensors <NUM> may show that the bending deformations of the first cover member deviates for different angular positions around the optical axis <NUM>. In that case, the measured deviations may be used for controlling a plurality of actuators <NUM> so that each measured bending deformation approaches the same bending reference, or so that the deviations are minimized.

<FIG> shows a principal sketch of an embodiment of the controllable lens <NUM> wherein the actuators <NUM> are arranged to generate a controllable bending and/or tilt of the first and/or the second cover member <NUM>, <NUM> dependent on the measurement signal from the one or more sensors <NUM> according to similar principles as described for other embodiments.

The actuators <NUM> are displacement actuators <NUM> capable of generating a displacement in response to the control signal. Each of the actuators <NUM> may have a displacement element <NUM> arranged to displace in a direction parallel or substantially parallel with the optical axis <NUM>.

The one or more actuators <NUM>, <NUM> are arranged to generate forces on the first or the second cover member <NUM>, <NUM> along a path <NUM> encircling the optical axis <NUM>, such as a circle on the surface of the first or the second cover member <NUM>, <NUM> (<FIG>).

The actuators <NUM> may be linear displacement actuators, such as linear piezoelectric or electromagnetic motors, piezoelectrically actuated cantilever actuators, shape memory alloys, linear screw drives, or linear voice-coil actuators, arranged to apply a displacement at several points, here eight points, along the path <NUM>.

The actuators are fixed to the support structure <NUM> so that the displacement elements <NUM> displaces relative to the support structure <NUM>. In this example, the first cover member <NUM> is not directly connected with the support structure <NUM>, but indirectly via actuators <NUM> and the elastic element <NUM>. The unactuated cover member, such as the second cover member <NUM> as illustrated in <FIG> may be supported by a further support structure <NUM> such as the support structure <NUM>. Alternatively, the second cover member <NUM> may be actuated by other actuators which are similar to either the displacement actuators <NUM> or the surface mounted actuators <NUM> described in connection with <FIG>.

The path <NUM> may encircle the transparent, deformable, non-fluid body <NUM> so that the non-fluid body <NUM> is surrounded by the path <NUM> as illustrated. However, the path <NUM> also be located within the extension of the non-fluid body <NUM>. The actuators <NUM> could also be located so that they act on the edge of the first or second cover member <NUM>, <NUM>, or located proximate to the edge.

The actuators <NUM>, <NUM> are arranged along the path <NUM> and are arranged to generate the displacement in a direction normal or substantially normal to the surface of the cover member <NUM>, <NUM>. Substantially normal, in this context, may imply deviations relative to the normal by up to e.g. <NUM>-<NUM> degrees. Angular variations of the angle between the direction of linear displacement and the surface of the cover member are generated dependent on the bending of the cover member.

The action of the actuators <NUM>, <NUM> changes the curvature of the first and/or the second cover member dependent on the force, torque or displacement provided by the actuators. Thus, by controlling the actuators, the bending and thereby the optical power of the lens <NUM> can be controlled. If the actuators are arranged in connection with the first cover member, the second cover member may also bend, or vice versa dependent on the thickness or stiffness of the cover member and dependent on the further support structure <NUM>.

By controlling the actuators <NUM>, <NUM> to generate different forces on the first and/or second cover member <NUM>, <NUM> for different actuators along the path <NUM>, the cover member <NUM>, <NUM> may be forced to tilt and bend. The tilt of the cover member causes a change of direction of the optical axis, shown as the exaggerated optical axis <NUM>, and thereby a change of direction of the transmitted or reflected light. By controlling the tilt of the cover member <NUM>, <NUM>, the change of direction of the transmitted light can be used to compensate camera rotations (e.g. due to hand shaking), i.e. to obtain optical image stabilization (OIS).

It is noted that the actuators <NUM>, <NUM> could be arranged to act on either the first or the second cover member <NUM>, <NUM>. It is also possible that the actuators <NUM>, <NUM> are arranged to act on both the first and the second cover member <NUM>, <NUM> so that both cover members are forced to bend by the action of the actuators <NUM>, <NUM>, possibly so that actuators on either side are independently controllable, i.e. so that the displacement/force applied on one of the cover members is controllable independent of the displacement/force applied on the other.

The tilt of one of the cover members <NUM>, <NUM> of a lens may be applied independently of the bending of another cover member <NUM>, <NUM> of the lens <NUM>. For example, actuators <NUM> of any type may be provided for bending the first cover member <NUM>, while displacement actuators <NUM> are provided for bending of the cover member.

In the principal sketch in <FIG>, the actuator displacement is amplified via a hinged beam <NUM> arranged via a hinge connection <NUM>. Sensors <NUM> may be arranged on the beam and thereby measures the beam deformation. The beam deformation correlates with the bending and the tilt and, therefore, the sensor signal from the sensors mounted on the beams <NUM> can be used for controlling the actuators <NUM>, <NUM> to achieve a desired bending and/or tilt of the first or the second cover member <NUM>, <NUM>.

As an alternative to displacement actuators <NUM>, surface mounted actuators <NUM> such as piezo elements could be attached to the beams <NUM> and thereby provide a linear displacement, e.g. via elastic connections <NUM>.

For practical purposes, other designs than the principal solution in <FIG> would likely be used, but based on similar principles and use of displacement actuators <NUM>. According to the principle, one or more elastic elements <NUM> such as the hinged beam <NUM> are arranged so that they connect the displacement actuators <NUM> with the first and/or the second cover member <NUM>,<NUM>. The elastic elements <NUM> may have various configurations, but in general are arranged to deform elastically in response to the force applied by the displacement actuator <NUM>. Deformation sensors <NUM> attached to one or more of the elastic elements <NUM> measures the deformation of the elastic elements <NUM>, or the deformation of at least a part of the elastic elements <NUM>. Due to the relationship between the deformation of the elastic elements and the bending and tilt of the first or the second cover member <NUM>, <NUM>, the measured deformations can be used for determining the control signal for controlling the actuators <NUM>.

The elastic elements <NUM> deforms elastically in response to relative displacement between the first or second cover member <NUM>,<NUM> and the displacement actuator <NUM>.

<FIG> shows that the elastic connection between the displacement actuator <NUM> and the first cover member <NUM> in addition to the hinged beam <NUM> comprises a further elastic element <NUM>.

The further elastic element <NUM> may arranged to deform in at least a radial direction in response to bending or tilt of the first or second cover member <NUM>, <NUM>, so that a change of the radial extension of the first or second cover member <NUM>, <NUM> due to the bending or tilt is accumulated by the radial deformation. By the radial displacement is understood that at least a component of the relative radial displacement has a direction perpendicular to the optical axis in the radial direction.

For example, the further elastic element <NUM> may be made from an elastic adhesive e.g. achieved by performing a gluing process. Preferably, the further elastic element <NUM> has a low stiffness in response to deformations in the radial direction and a high stiffness in the direction of displacement of the displacement actuator <NUM>, in order to transfer the actuator displacement to the cover member <NUM>, <NUM>.

<FIG> show an example of an elastic element <NUM> connecting the displacement actuators <NUM> with the first cover member <NUM>. In this example, actuators are also arranged to provide bending of the second cover member <NUM>, via a further elastic element 315a. In these figures, the actuators <NUM> are not shown, only the contact points of the displacement elements <NUM> and an indication of the actuators <NUM>, <NUM>.

The elastic element <NUM> is configured with a plurality of deformable portions in the form of a plurality of spring elements <NUM> such as cantilevered metal beams. In response to the bending of the first cover member <NUM>, the spring elements <NUM> bend. The bending of the spring elements <NUM> facilitates requirements of the elastic element <NUM> to provide a low stiffness in response to deformations in the radial direction towards the optical axis <NUM>, and high stiffness in the direction of the displacement of the displacement actuators <NUM> to efficiently transfer the actuator displacement to the first cover member. The low radial stiffness ensures that bending of the first cover member is not restrained by the elastic element <NUM>. Each of the spring elements <NUM> are separated from neighbor spring elements to enable each of the spring elements <NUM> to deform independent or substantially independent from neighbor spring elements <NUM>.

The elastic element <NUM> comprises a support member <NUM>. As principally illustrated, the displacement actuators <NUM> are arranged to act on the surface of the support member <NUM>.

In this example, the support member <NUM> is formed as a ring-shaped structure with a hole constituting an aperture for the lens <NUM>.

In this example, the first and second cover members <NUM>, <NUM> are each actuated independently via the upper elastic element <NUM> and the lower second elastic element 130a.

One or more sensors <NUM> may be attached to the spring elements <NUM> to measure the deformation. The deformation is due, at least partly, to the bending of the first cover member <NUM> whereby the measurement signal from the sensors <NUM> is directly related to the bending.

<FIG> shows an optical assembly <NUM> comprising a controllable beam deflection device <NUM>. In this embodiment, the second cover member <NUM> is a prism <NUM> and the first cover member <NUM> is a reflective cover member such as a mirror arranged opposite to the hypotenuse of the prism <NUM>. The incident light <NUM>, i.e. the light from object space to be imaged onto the image sensor, is transmitted through the prism <NUM> via one of its short sides and through the non-fluid body to the first cover member in order to reflect the incident light <NUM> and redirect the incident light to a different direction, such as a direction which is perpendicular or substantially perpendicular to the direction of incidence. Thus, the reflective first cover member <NUM> causes a folding of the optical axis. A portion of the incident light <NUM> may be transmitted through the first cover member, e.g. due to a partial reflector comprised by the first cover member <NUM>.

Displacement actuators <NUM> as described in connection with <FIG> may be arranged to generate a controllable tilt of the reflective cover member <NUM>. As described in connection with <FIG>, sensors <NUM> arranged on the flexible elements <NUM> provides a measurement signal which is indicative of the displacement amplitude of the actuator and thereby the tilt angle of the reflective cover member <NUM>. The two actuators shown in <FIG> may operate with opposite displacement directions to facilitate tilt of the reflective cover member <NUM>. Alternatively, the reflective cover member <NUM> may be hinged at one side.

As an alternative, sensors <NUM> may be arranged to provide a direct measurement of the displacement of the actuators <NUM>. Such sensors may be based on optical or resistive distance measurements and integrated with the sensors. The displacement actuators <NUM> may be configured without the hinged beam <NUM>. For example, the displacement actuator <NUM> may be connected directly to the reflective cover member <NUM>, possibly via the further elastic element <NUM>, when a hinged beam <NUM> is not used to provide displacement amplification.

The controllable lens <NUM> and the controllable beam deflection device <NUM> are examples of a controllable optical assembly according to various embodiments.

Similarly to <FIG>, the first cover member <NUM> is not directly connected with the support structure <NUM>, but indirectly via actuators <NUM> and the elastic element <NUM>.

<FIG> illustrates an optical sensor <NUM> as an alternative to the sensor <NUM>. The optical sensor <NUM> comprises a light source <NUM> configured to output a light beam such as a collimated beam <NUM> and an optical detector <NUM>. The optical detector <NUM>, such as a position sensitive detector or a quadrant detector, generates an output which is dependent on the beam's <NUM>1D or 2D position on the detector <NUM>. Accordingly, the optical sensor <NUM> is able to measure at least the tilt of the first cover member <NUM>.

<FIG> illustrates the optical sensor <NUM> used in an example where the first cover member <NUM> is arranged to be bent by displacement actuators <NUM> directly connected to the first cover member <NUM>, although surface mounted actuators <NUM> may be used as well. The divergence of the beam is affected by the bending of the first cover member <NUM> and, thereby, the size of the beam spot on the detector is directly related to the bending of the first cover member. The detector <NUM> is therefore capable of generating an output that depends on the size of the beam spot. Clearly, the detector <NUM> may be a type which output is dependent on both the position and size of the beam spot on the detector.

Accordingly in this embodiment, the alternative optical sensor <NUM> is configured to transmit a light beam <NUM> through the non-fluid body <NUM>, through at least one of the first and second cover members <NUM>, <NUM> and so that the direction and/or divergence of the light beam is affected by the at least one cover member <NUM>, <NUM> arranged to tilted and/or bent by the actuators <NUM>, <NUM>.

The control system <NUM> may be part of the deflection device <NUM> or the optical sensor <NUM> and arranged to control the actuators <NUM> based on the measured tilt such as in a feed-back control system where the difference between the measured tilt and the desired tilt angle are minimized.

The first cover member <NUM> may alternatively be configured as a transparent cover member <NUM> in order to transmit the incident light <NUM> through the cover member via refraction. The transparent cover member may advantageously be located opposite to one of the two perpendicular faces of the prism, with the non-fluid body <NUM> sandwiched between the cover member <NUM> and the prism. The transparent cover member <NUM>, can be used to control the propagation direction of the light beam <NUM> by controlling the tilt of the cover member <NUM>. Accordingly, the prism may be configured with the reflective cover member <NUM> and the refractive, i.e. transparent, cover member <NUM>, as shown in the simplified illustration in Fig. 5C. Actuators <NUM> for tilting the cover members <NUM>, <NUM> are not included for convenience.

<FIG> shows the optical sensor <NUM> of <FIG> in more detail. The optical sensor <NUM> comprises the light source <NUM> arranged to transmit a light beam <NUM>, such as a divergent light beam, towards the back side <NUM> of the first cover member <NUM>, i.e. the reflector, or the transparent cover member <NUM>. The beam <NUM> is reflected by the back side <NUM> and, therefore, the propagation direction of the reflected beam <NUM> is affected by the tilt of the cover member <NUM>, <NUM>.

By the back side <NUM> is meant the side which faces away from the prism <NUM>. The back side <NUM> may be coated to provide reflection properties. Thus, the back side of the cover member <NUM>, <NUM> may be used as an alternative to, or in addition to, front side of the cover member <NUM>, <NUM> as shown in <FIG>, where the front side faces the prism <NUM>. Use of the back side <NUM> may be advantageous for obtaining independent sensor signals from the detector <NUM>, or different detectors for different cover members <NUM>, <NUM>, in a configuration where the deflection device <NUM> is provided with both the reflective and transparent cover members <NUM>, <NUM>.

The light detector <NUM> is arranged to measure a change of the light beam <NUM> caused by the tilt of the cover member <NUM>, <NUM>. The change of the light beam <NUM> may involve a change of the position where the light beam <NUM> hits the light detector <NUM> and/or a change of the size of the spot of the light beam <NUM> on the light detector <NUM>.

The light detector <NUM> may be configured with at least four individual light detectors <NUM>, where each of the individual light detectors <NUM> are capable of generating an output signal which is correlated with the power of the light impinging the individual light detector. By processing signal outputs from the individual light detectors <NUM>, such as by comparing the individual outputs, changes in the tilt of the cover member <NUM>, <NUM> can be determined. The measured tilt can be used in the control of the actuator systems <NUM>, <NUM> such as in a feed-back control system of the control system <NUM> where the difference between the measured tilt and the desired tilt angle are minimized.

<FIG> shows an alternative embodiment of the optical sensor <NUM> where the light source <NUM> is arranged at a center of the individual light detectors <NUM>, i.e. so that all light detectors <NUM> surrounds the light source <NUM>. In this configuration the plane of the light source <NUM> and light detectors <NUM> may be parallel or substantially parallel with the back side <NUM> of the reflective or transparent cover member <NUM>, <NUM>.

<FIG> shows linearity performance of the optical sensor <NUM> of <FIG>. As shown in the upper figure, the y-position output from the detector <NUM> depends slightly on y-axis tilt angles of the cover member <NUM>, for variations of the x-axis tilt. Similarly, the lower figure shows that the x-position output from the detector <NUM> depends slightly on x-axis tilt angles, for variations of the y-axis tilt. Thus, the output signal from the detector <NUM> is slightly non-linear when the tilt angle is a combination of two rotation axes (in cases where the controllable beam deflection device <NUM> is configured to provide tilt around two perpendicular x and y axes).

<FIG> shows the linearity performance of the optical sensor <NUM> of the <FIG> configuration. Thus, this configuration of the optical sensor shows improved linearity of the output signal from the detector <NUM> and therefore may eliminate the need for calibration of the detector signal output.

<FIG> shows an alternative configuration of the optical sensor <NUM> configured to determine the optical power of the controllable lens <NUM>.

The light source <NUM> is arranged so that the light beam <NUM>, such as the center of the intensity profile of the light beam <NUM>, hits the first and/or the second cover member <NUM>,<NUM> a distance h away from the optical axis <NUM>. In this case the light beam <NUM> is preferable a collimated light beam. The surface of the first and/or the second cover member <NUM>,<NUM> which reflects the light beam <NUM> faces the image sensor <NUM> of the camera. The distance between the controllable lens <NUM>, such as said reflecting surface, and the image sensor <NUM> is Z. The light detector <NUM> is arranged to detect, at least a portion of, the reflection of the light beam <NUM>. The light source <NUM> and the detector <NUM> are located on opposite sides of the image sensor <NUM>, but not necessarily collinear with the center of the image sensor <NUM>.

When the detector <NUM> is located at the same, or substantially the same distance Z from the lens <NUM>, although this is not a requirement, the displacements Δ between the location where the reflected beam <NUM> hits the detector <NUM> and the location where the beam <NUM> reflected from a plane cover member <NUM>, <NUM> hits the detector <NUM> is: <MAT> where h is the distance along the y axis from the optical axis <NUM> to the point where the light beam <NUM> hits the first or second cover member <NUM>,<NUM>, Z is the distance along the z axis between the image sensor <NUM> and first or second cover member <NUM>,<NUM>, R is the curvature (measured as the radius) of the surface of the first or second cover member <NUM>,<NUM> facing the image sensor <NUM>. The optical power P of the lens, assuming a plane-convex lens is given by: <MAT> with nlens and nair being the refractive index of the lens and the surrounding air. Accordingly, the optical power as varied by the actuators can be determined from the measured displacement values Δ.

The light source <NUM> and the detector <NUM> may be located so that the plane of incidence of the light beam <NUM> comprises the optical axis <NUM>, i.e. so that the light source <NUM> and the detector <NUM> are aligned with the image sensor <NUM>. In another embodiment, light source <NUM> and the detector <NUM> are located so that plane of incidence spanned of the light beam <NUM> does not comprise the optical axis <NUM>, i.e. so that the light source <NUM> and the detector <NUM> are not aligned with the image sensor <NUM>.

<FIG> shows the output signal from the detector <NUM> as a function of the optical power determined from the displacement values Δ for a distance of <NUM> between the detector <NUM> and the optical axis <NUM> measured along the y axis (solid curve) and for a corresponding distance of <NUM> (dashed line). In this example, the light source <NUM> and the detector <NUM> are aligned with the image sensor <NUM>. As shown, better sensitivity is achieved when the detector <NUM> is located farther away from the image sensor <NUM>, but at the cost of a bigger form factor (in the y direction).

<FIG> shows the output signal from the detector <NUM> in a similar configuration as in <FIG> with a distance of <NUM> between the detector <NUM> and the optical axis <NUM>. However, in this example, the light source <NUM> and the detector <NUM> are not aligned with the image sensor <NUM>, i.e. the plane of incidence does not comprise the optical axis <NUM>. Due to the non-aligned configuration, the reflected light beam <NUM> displaces both in x and y directions on the detector <NUM>. The solid line shows x displacements as in <FIG>, and the dashed line shows y displacements. The sensitivity to reflections causing displacements in x and y directions may be used to determine astigmatism, i.e. different radii in of the facing surface of the first or second cover member <NUM>,<NUM> in orthogonal directions by comparing the x and y displacements and using the equation <MAT> with the relevant values of h for the two orthogonal directions.

<FIG> shows another configuration of the optical sensor <NUM> configured to determine the optical power of the controllable lens <NUM>.

The lens <NUM> is located between the light source <NUM> and the detector <NUM>, i.e. so that the light source <NUM> is arranged to transmit the light beam <NUM> towards the outward facing surface of one of the first and second cover member <NUM>, <NUM> and so that the detector <NUM> is arranged to receive the light beam <NUM> transmitted through the outward facing surface of the other of the first and second cover member <NUM>, <NUM>. Accordingly, the light beam <NUM> is transmitted through the first and the second cover members <NUM>, <NUM>, at a high incident angle.

The light detector <NUM> may be arranged so that its input aperture faces the optical axis <NUM>, i.e. so that the normal to the detector surface is perpendicular or substantially perpendicular to the optical axis <NUM>.

The incident angle between the light beam <NUM> and the surface of the first and second cover member <NUM>, <NUM> may be below <NUM> degrees, such as below <NUM> degrees or below <NUM> degrees.

The light source <NUM> and the detector <NUM> may be arranged so that the plane of incidence of the light beam <NUM> comprises the optical axis <NUM>, or so that plane of incidence does not comprise the optical axis <NUM>.

In case of astigmatism created by the lens <NUM>, e.g. due to errors in the bending of the cover member <NUM>, <NUM> such as due to actuator inaccuracies, the spot of the light beam <NUM> will be non-circular (assuming a rotation symmetric intensity profile of the incident light beam <NUM>) and the output from the individual light detectors <NUM> of the detector <NUM> will generate signals corresponding to the astigmatism.

Further, since astigmatism is proportional to the lens power P, the lens power P can be determined by measuring the deformation of the spot, i.e. the elliptic shape of the spot, by use of the four detectors <NUM> of the detector <NUM>.

<FIG> shows the relationship between the ratio of x and y diameters of the light beam spot on the detector <NUM> and the lens power P.

<FIG> shows that the light source 551a and the detector 552a may be arranged so that the light beam (dashed line) is transmitted through other optical components <NUM> such as fixed lenses before being transmitted through the controllable lens <NUM>, and/or so that the light beam is transmitted through other optical components <NUM> after transmission through the controllable lens <NUM>. Accordingly, the controllable lens and other optical components may be placed between the light source <NUM> and the detector <NUM> along the optical axis. This may be advantageous in a compact optical system not providing space for placement of the light source <NUM> and/or the detector <NUM> on the opposite sides of the controllable lens <NUM>.

Claim 1:
A controllable optical assembly (<NUM>, <NUM>) with a variable optical power and/or a variable beam deflection, the optical assembly comprises
- a first cover member (<NUM>) and a second cover member (<NUM>), wherein one of the first and second cover members is a transparent cover member, and the other of the first and second cover members is a transparent or reflective cover member,
- a transparent, deformable, non-fluid body (<NUM>) sandwiched between the first and second cover members, so that the first and second cover members and non-fluid body constitute a lens or a light deflector with an optical axis (<NUM>) intersecting the non-fluid body and the first and/or the second transparent cover members,
- one or more actuators (<NUM>) arranged to generate a controllable bending and/or tilt of at least the first cover member dependent on a control signal, where the control signal is obtainable from first and second measurement signals,
- first and second sensors (<NUM>) arranged to provide the first and second measurement signals so that the measurement signals are indicative of the bending and/or tilt of at least the first cover member, and wherein the first sensor is an optical sensor (<NUM>) and the second sensor is a deformation sensor,
- wherein the optical sensor comprises a light source (<NUM>) arranged to transmit a light beam (<NUM>) so that the light beam is affected by the bending or tilt of the first and/or the second cover member, and where the sensor comprises a light detector (<NUM>) arranged to measure a change of the light beam relating to the bending and/or tilt, and
- wherein the deformation sensor comprises a piezo electric sensor element connected to the first cover member, and/or
- wherein the deformation sensor is connected to a surface of the one or more actuators.