Patent Description:
In a camera, the purpose of OIS is to compensate for camera shake, that is vibration of the camera, typically caused by user hand movement, that degrades the quality of the image captured by the image sensor. Mechanical OIS typically involves detecting the vibration by a vibration sensor such as a gyroscope sensor, and controlling, on the basis of the detected vibration, an actuator arrangement that adjusts the camera apparatus to compensate for the vibration. Several techniques for adjusting the camera apparatus are known. OIS by processing of a captured image is possible in principle but requires significant processing power. Accordingly, there has been developed mechanical OIS in which the optical system of the camera is adjusted mechanically.

A number of actuator arrangements employing mechanical OIS techniques are known and applied successfully in relatively large camera apparatuses, such as digital still cameras, but are difficult to miniaturise. Cameras have become very common in a wide range of portable electronic equipment, for example mobile telephones and tablet computers, and in many such applications miniaturisation of the camera is important. The very tight packaging of components in miniature camera apparatuses presents great difficulties in adding OIS actuators within the desired package.

In one type of mechanical OIS, the camera unit comprising an image sensor and a lens system for focussing an image on the image sensor is tilted relative to the support structure of the camera assembly around two notional axes that are perpendicular to each other and to the light-sensitive region of the image sensor. Such a type of OIS will be referred to herein as "OIS-tilt". <CIT> and <CIT> each disclose camera assemblies of this type in which a plurality of shape memory alloy (SMA) actuator wires are arranged to drive tilting of the camera unit. In such a camera, sufficient clearance needs to be provided to allow for tilting of the entire camera unit.

In another type of mechanical OIS, a lens assembly is moved orthogonal to the optical axis of the at least one lens. Such a type of OIS will be referred to herein as "OIS-lens shift". OIS-lens shift has the potential to reduce the size of the overall package for the camera as compared to OIS-tilt because only the lens assembly is moved and the lateral movement thereof requires less clearance than tilting the entire camera. <CIT> and <CIT> each disclose camera assemblies of this type in which a plurality of SMA actuator wires are arranged to drive movement of the lens arrangement. <CIT> and <CIT> use different suspension systems for the lens assembly, utilising beams and ball bearings, respectively.

Background information can be found in: <CIT>, which describes a surveillance video camera that has a CCD sensor panel that may be moved perpendicular to the optical axis; <CIT>, which describes an image sensor device; <CIT>, which describes an actuator having SMA connected in a push-pull arrangement; <CIT>, which describes a drive unit and imaging device; <NPL>), which describes an SMA actuator that uses resistance feedback control; and <CIT>, which describes an image stabilisation device.

The first aspect of the present invention is concerned with an alternative camera assembly that can provide OIS using SMA actuator wires.

According to a first aspect of the present invention, there is provided a camera assembly as claimed in claim <NUM>.

The first aspect of the present invention therefore provides relative movement between the image sensor and a lens assembly provided in a camera in which the camera assembly may be incorporated. That relative movement provides OIS in a similar manner to OIS-lens shift. As the movement is driven by plural SMA actuator wires, this achieves similar advantages to those described in <CIT> and <CIT>. For example, the use of SMA actuator wires facilitates miniaturisation compared to other types of actuator, and the dimension along the optical axis may be reduced compared to OIS-tilt arrangements.

However, the first aspect of the present invention differs from OIS-lens shift in that the image sensor, rather than the lens assembly, is moved laterally. This provides a number of advantages as follows.

Movement of the image sensor is typically more convenient, as the image sensor is a smaller component than the lens assembly. This facilitates miniaturisation of the camera.

Also, provision of OIS by movement of the image sensor can improve the performance of the OIS compared to OIS-lens shift. While the major component of shake-induced image blur is in the plane perpendicular to the optical axis, rotational blur can also be caused by rotation around the optical axis. A counter-rotation of the lens assembly has no effect on this rotation induced blur, as the lens assembly is typically rotationally symmetric around the optical axis. However, the first aspect of the present invention allows rotational image stabilisation also to be provided. That is, the image sensor may be supported on the support structure in a manner further allowing rotation of the image sensor about an axis orthogonal to the light-sensitive region, and the plural shape memory alloy actuator wires may be provided in an arrangement capable, on selective driving, of rotating the image sensor about that axis.

The present invention therefore provides relative movement between the image sensor and a lens assembly provided in a camera in which the camera assembly may be incorporated. That relative movement provides OIS in a similar manner to OIS-lens shift.

However, the present invention differs from OIS-lens shift in that the image sensor, rather than the lens assembly, is moved laterally to the light-sensitive region of the image sensor. This provides a number of advantages as follows.

Also, provision of OIS by movement of the image sensor can improve the performance of the OIS compared to OIS-lens shift. While the major component of shake-induced image blur is in the plane perpendicular to the optical axis, blur can also be caused by rotation around the optical axis. A counter-rotation of the lens assembly has no effect on this rotation induced blur, as the lens or lenses of the lens assembly are typically rotationally symmetric around the optical axis. However, the present invention allows rotational image stabilisation also to be provided. That is, the image sensor may be supported on the support structure in a manner further allowing rotation of the image sensor about an axis orthogonal to the light-sensitive region, and the plural shape memory alloy actuator wires may be provided in an arrangement capable, on selective driving, of rotating the image sensor about that axis.

For suspending the carrier on the support structure and allowing movement of the image sensor relative to the support structure in any direction laterally to the light-sensitive region of the image sensor, the present invention uses at least one plain bearing comprising a bearing surface on each of the carrier and the support structure, which bearing surfaces bear on each other. A plain bearing is a bearing comprising two bearing surfaces which bear on each other, permitting relative sliding motion. Of course, a plain bearing is a simple type of bearing which is known for use in other applications. Inevitably, the friction within the bearing adversely affects the performance, particularly in a miniature arrangement.

However, surprisingly, a plain bearing can in fact be used to provide good performance in which the friction is sufficiently low to allow lateral movement. Particular advantage is achieved in the case that the actuator arrangement comprises plural SMA actuator wires, as SMA provides a high actuation force compared to other forms of actuator, which assists in overcoming the friction in a plain bearing.

Furthermore, this type of suspension of at least one plain bearing in the second aspect of the present invention provides particular advantages, as follows.

Firstly, a plain bearings may be formed with inherently small size along the height of the bearing, that is along the optical axis, especially compared to a suspension system employing balls. This allows the size of the suspension to be reduced along the optical axis compared to the use of ball bearings, for example as disclosed in <CIT>.

Secondly, the image sensor generates a large amount of heat. Thus, it is desirable that the image sensor is attached to other components that act as a heat sink to allow that heat to be dissipated. This reduces the temperature rise of the image sensor and the thermal degradation that results from the image sensor self-heating.

One approach for dissipating generated heat would be to attach a heat sink to the image sensor and moving both the image sensor and the heat sink. However this is not desirable, particular in a miniature camera, because it requires both the heat sink and the image sensor to be moved, thus increasing the size and/or the power consumption of the camera assembly.

The at least one plain bearing not only suspends the image sensor and allows its movement, but also facilitates heat transfer from the image sensor to the support structure. This is because the bearing surface on each of the carrier and the support structure bear on each other and thus provide a continuous region of thermally conductive material without an air gap. This provides a path having good thermal conductivity for dissipating heat from the image sensor, as well as providing the requisite suspension.

The bearing surfaces may each be planar. This improves the thermal conductivity of the planar bearing by providing a relatively large area of contact.

A fluid may be disposed between the bearing surfaces, for example a grease. This may improve the thermal conductivity of the planar bearing, especially if the fluid is chosen to have a high thermal conductivity.

The present invention provide particular advantage when applied to a camera assembly for miniature camera, for example where the light-sensitive region of the image sensor has a diagonal length of at most <NUM>.

To allow better understanding, an embodiment of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:.

A camera apparatus <NUM> that incorporates an OIS-sensor shift camera assembly <NUM> in accordance with the present invention is shown in <FIG>, which is a cross-sectional view taken along the optical axis O. The camera apparatus <NUM> is to be incorporated in a portable electronic device such as a mobile telephone, or tablet computer. Thus, miniaturisation is an important design criterion.

The camera assembly <NUM> is shown in detail in <FIG>, <FIG> being a side view of the camera assembly <NUM>, <FIG> being a perspective view of a moving plate <NUM> of a carrier <NUM> of the camera assembly <NUM>; and <FIG> being a plan view of the camera assembly <NUM>. For clarity, <FIG> and <FIG> omit the flexures <NUM> described below. The camera assembly <NUM> may be manufactured first and then assembled with the other components of the camera apparatus <NUM>.

The camera assembly <NUM> comprises a support structure <NUM> on which is supported an image sensor <NUM> having a light-sensitive region <NUM>. The optical axis O is orthogonal to the light-sensitive region <NUM>. The image sensor <NUM> captures an image and may be of any suitable type, for example a CCD (charge-coupled device) or a CMOS (complimentary metal-oxide-semiconductor) device. As is conventional, the image sensor <NUM> has a rectangular light-sensitive region <NUM>. Without limitation to the invention, in this example the camera apparatus <NUM> is a miniature camera in which the light-sensitive region <NUM> of the image sensor <NUM> has a diagonal length of at most <NUM>.

The image sensor <NUM> is mounted on a carrier <NUM> which comprises a moving plate <NUM>. The moving plate <NUM> may formed from sheet material, which may be a metal for example steel such as stainless steel. The moving plate <NUM> is shown in isolation in <FIG> and includes flexures <NUM> that are described in more detail below.

Although the carrier <NUM> comprises a single moving plate <NUM> in this example, optionally the carrier <NUM> may comprise other layers which may be attached to or laminated with the moving plate <NUM>.

The support structure <NUM> comprises a support plate <NUM> which may formed from sheet material, which may be a metal for example steel such as stainless steel.

Although the support structure <NUM> comprises a single support plate <NUM> in this example, optionally the support structure <NUM> may comprise other layers which may be attached to or laminated with the support plate <NUM>.

The support structure <NUM> further comprises a rim portion <NUM> fixed to the front side of the support plate <NUM> and extending around the support plate <NUM>. The rim portion <NUM> has a central aperture <NUM>.

The support structure <NUM> further comprises an IC (integrated circuit) chip <NUM> and a gyroscope sensor <NUM> fixed on the rear side of the support plate <NUM>. A control circuit described further below is implemented in the IC chip <NUM>.

The moving plate <NUM>, together with the image sensor <NUM>, is suspended on the support structure <NUM> in a manner allowing movement of the image sensor <NUM> in any direction laterally to the light-sensitive region <NUM> of the image sensor <NUM> (i.e. laterally of the optical axis O and parallel to the plane in which the light-sensitive region <NUM> extends) and further allowing rotation of the image sensor about the optical axis O. In the illustrated example, the moving plate <NUM> is suspended on the support structure <NUM> by a suspension system in the form of a plain bearing <NUM> provided between the support plate <NUM> and the moving plate <NUM> as will now be described.

In this example, the plain bearing <NUM> comprises a first bearing surface <NUM> on the carrier <NUM>, in particular being the lower surface of the moving plate <NUM>, and a second bearing surface <NUM> on the support structure <NUM>, in particular being the upper surface of the support plate <NUM>. In this example, bearing surfaces <NUM> and <NUM> are each planar. The bearing surfaces <NUM> and <NUM> bear on each other and thereby suspend the carrier <NUM> on the support structure <NUM>. Since the bearing surfaces <NUM> and <NUM> may slide relative to each other, they allow movement of the image sensor <NUM> in any direction laterally to the light-sensitive region <NUM> of the image sensor <NUM> and further allow rotation of the image sensor about the optical axis O.

The plain bearing <NUM> not only suspends the image sensor <NUM>, but also facilitates heat transfer from the image sensor <NUM> to the support structure <NUM>. This is because the bearing surface surfaces <NUM> and <NUM> provide a continuous region of thermally conductive material without an air gap. This provides a path having good thermal conductivity for dissipating heat from the image sensor <NUM>, as well as providing the requisite suspension. This allows the support structure <NUM> to act as a heat sink for the image sensor <NUM>.

Heat transfer from the image sensor <NUM> is further facilitated by forming the moving plate <NUM> and support plate <NUM> from materials having a high thermal conductivity, for example metal.

<FIG> illustrate some alternative constructions for the plain bearing <NUM> in which bearing members providing at least one of the bearing surfaces <NUM> and <NUM> are employed, instead of the bearing surfaces <NUM> and <NUM> being surfaces of the moving plate <NUM> and the support plate <NUM>.

In the alternative of <FIG>, the bearing <NUM> includes a bearing member <NUM> fixed to the moving plate <NUM>. Thus, the first bearing surface <NUM> is the lower surface of the bearing member <NUM> and the second bearing surface <NUM> is the upper surface of the support plate <NUM>.

In the alternative of <FIG>, the bearing <NUM> includes a bearing member <NUM> fixed to the support plate <NUM>. Thus, the first bearing surface <NUM> is the lower surface of the moving plate <NUM> and the second bearing surface <NUM> is the upper surface of the bearing member <NUM>.

In the alternative of <FIG>, the bearing <NUM> includes a bearing member <NUM> fixed to the moving plate <NUM> and a bearing member <NUM> fixed to the support plate <NUM>. Thus, the first bearing surface <NUM> is the lower surface of the bearing member <NUM> and the second bearing surface <NUM> is the upper surface of the bearing member <NUM>.

Where one or more bearing member is used, they may be fixed to the moving plate <NUM> or the support plate <NUM> by adhesive.

Where one or more bearing member <NUM> to <NUM> is used, the or each bearing member <NUM> to <NUM> separates the moving plate <NUM> and the support plate <NUM>, and the thickness of the or each bearing member <NUM> to <NUM> is chosen accordingly.

An advantage of using one or more bearing members <NUM> to <NUM> is that the material of the bearing member may be chosen to improve the bearing performance, for example having a reduced wear and/or reduced coefficient of friction.

In the illustrated example, a single plain bearing <NUM> is provided between the support plate <NUM> and the carrier <NUM>. In this example, the plain bearing <NUM> has a rectangular area of contact <NUM> between the bearing surfaces <NUM> and <NUM> as shown in <FIG> together with the carrier <NUM>. However, in general, the area of contact may be varied and/or plural plain bearings <NUM> may be provided.

<FIG> illustrate the areas of contact <NUM> in some alternative, non-limitative alternative arrangements for the plain bearing <NUM>.

In the case of providing a single plain bearing <NUM>, the area of contact <NUM> of the plain bearing <NUM> may have shapes other than rectangular. By way of example the area of contact <NUM> may have a circular shape as shown in <FIG>, which may be easier to manufacture and/or assist in providing a balanced bearing contact.

The alternative of providing plural plain bearings <NUM> may assist in manufacture and/or assist in providing a balanced bearing contact. Typically at least three plain bearings may be used to provide a stable contact. <FIG> illustrates an example comprising four plain bearings <NUM> with circular areas of contact <NUM> located in the corners of the carrier <NUM>.

Advantageously, plural plain bearings <NUM> each formed by one or more bearing members <NUM> to <NUM> (as in any of the examples of <FIG> described above) may be provided with channels between the bearing members <NUM> to <NUM>. Such channels may collect wear particles. <FIG> illustrates an example of this type comprising six plain bearings <NUM> with rectangular areas of contact <NUM> in a regular rectangular array with channels <NUM> provided therebetween.

The total area of contact of the bearing surfaces <NUM> and <NUM> of the plain bearing <NUM> (being the total area of all the plain bearings <NUM> if more than one is provided) is chosen to control the friction and the thermal conductivity. In general, there is a balance between reducing friction by minimising the total area and increasing thermal conductivity by maximising the total area.

Surprisingly, the use of one or more plain bearings <NUM> can in fact provide good performance as a bearing with friction that is sufficiently low to allow movement perpendicular to the optical axis O, having regard to the force applied by the SMA actuator wires <NUM>. As the plain bearing <NUM> maintain a relatively high total area of contact over the bearing surfaces <NUM> and <NUM>, the impact of wear occurring over time is reduced, compared to a bearing having a point or line contact.

With regard to thermal conductivity, the total area of contact of the bearing surfaces <NUM> and <NUM> of the plain bearing <NUM> is chosen to be sufficiently large with respect to the size of the image sensor <NUM> so that the thermal conductivity removes the heat generated thereby. Typically, the total area of contact may be at least <NUM> times, preferably at least <NUM> times, the area of the light-sensitive region <NUM> of the image sensor <NUM>. The total area of contact may even be larger than the light-sensitive region <NUM> of the image sensor <NUM> or larger than the overall dimensions of the image sensor <NUM>. To achieve this, the carrier <NUM> may be arranged to have larger overall dimensions than the image sensor <NUM>.

The material properties of the bearing surfaces <NUM> and <NUM> are chosen to provide a low friction and low wear plain bearing.

With regard to reducing friction, the bearing surfaces <NUM> and <NUM> may be designed to have a coefficient of friction of <NUM> or less.

The bearing surfaces <NUM> and <NUM> may each be made from the same material as the element on which it is formed, for example the support plate <NUM>, moving plate <NUM> or bearing member <NUM> to <NUM>. That material may be selected to provide suitable properties.

Where a bearing member <NUM> to <NUM> is provided its material may be selected to provide suitable properties. By way of non-limitative example, the bearing member <NUM> to <NUM>, where used, may be made from a polymer, for example nylon, polytetrafluoroethylene (PTFE) (e.g. Teflon), an acetal (e.g. Delrin) or an Ultra High Molecular Weight Polyethylene (UHMWPE).

Alternatively, the bearing surfaces <NUM> and <NUM> may be coated with material selected to provide suitable properties. Where a coatings is used, the coating may have lower friction and/or lower wear than the material of the element which is coated, for example the support plate <NUM>, moving plate <NUM> or bearing member <NUM> to <NUM>. By way of non-limitative example, the coating, where used, may be made from a polymer, for example nylon, polytetrafluoroethylene (PTFE) (e.g. Teflon), an acetal (e.g. Delrin) or an Ultra High Molecular Weight Polyethylene (UHMWPE).

A fluid <NUM> may be disposed between the bearing surfaces <NUM> and <NUM>, as shown in the illustrated examples. The material properties of the fluid <NUM> if provided are selected to provide lubrication between the bearing surfaces <NUM> and <NUM> so that the coefficient of friction between the bearing surfaces <NUM> and <NUM> is reduced and/or to have a thermal conductivity that improve the thermal contact between the bearing surfaces <NUM> and <NUM>. For example, the fluid <NUM> may be a grease.

However, the fluid <NUM> is optional. As an alternative to providing the fluid <NUM>, the bearing surfaces <NUM> and <NUM> may be in direct contact. Depending on the material properties of the bearing surfaces <NUM> and <NUM> and/or coatings thereon, this may provide a coefficient of friction and a thermal contact that is sufficient.

In addition, the camera assembly <NUM> comprises two flexures <NUM> connected between the support structure <NUM> and the carrier <NUM> to act as a biasing arrangement that biases the bearing surfaces <NUM> and <NUM> together, as well as providing an electrical connection to the image sensor <NUM>. In this example, the flexures <NUM> are formed integrally with the moving plate <NUM> at one end <NUM> thereof and are mounted to the support plate <NUM> of the support structure <NUM> at the other end <NUM> thereof. Alternatively, the flexures <NUM> could be formed integrally with a plate of the support structure <NUM> and mounted to the carrier, or else could be separate elements mounted to each of the support structure <NUM> and the carrier <NUM>. In any of these examples, the mounting of the flexures <NUM> may be achieved by soldering which provides both mechanical and electrical connection.

The flexures <NUM> are arranged as follows to provide their mechanical function. Each flexure <NUM> is an elongate beam connected between the support structure <NUM> and carrier <NUM>. The flexures <NUM>, due to their intrinsic resilience, bias the support structure <NUM> and the carrier <NUM> together, the biasing force being applied parallel to the optical axis O. This maintains the contact between the bearing surfaces <NUM> and <NUM> of the plain bearing <NUM>. At the same time, the flexures <NUM> may be laterally deflected to permit lateral movement and rotation of the image sensor <NUM> relative to the support structure <NUM> to permit the OIS function.

The flexures <NUM>, again due to their intrinsic resilience, also provide a lateral biasing force that biases the image sensor <NUM> towards a central position aligned with the optical axis O of the lens assembly <NUM> from any direction around that central position. As a result, in the absence of driving of the SMA actuator wires <NUM>, the image sensor <NUM> will tend towards the central position. This ensures that the camera apparatus <NUM> remains functional to capture images, even in the absence of driving of the SMA actuator wires <NUM>.

The flexures <NUM> are designed as follows to provide a suitable retaining force along the optical axis O for the plain bearing <NUM>, and also to permit lateral movement with a lateral biasing force. The magnitude of the lateral biasing force is kept low enough as not to hinder OIS, whilst being high enough to centre the image sensor <NUM> in the absence of driving. Each flexure <NUM> has a cross-section with an average width orthogonal to the optical axis O is that is greater than its average thickness parallel to the optical axis O. Each flexure <NUM> extends in an L-shape around the optical axis O, it in general being desirable that the angular extent is at least <NUM>° as measured between the ends of the flexure <NUM>.

In the assembled state of the camera assembly <NUM>, the flexures <NUM> are deflected from their relaxed state to provide a pre-loading force that biases the support structure <NUM> and the carrier <NUM> together.

The flexures <NUM> are made of a suitable material that provides the desired mechanical properties and is electrically conductive. Typically, the material is a metal having a relatively high yield, for example steel such as stainless steel.

In addition, the flexures <NUM> support electrical tracks connected to at least the image sensor <NUM>. In this manner, the flexures <NUM> provide an electrical function, as well as a mechanical function. This avoids the need for a separate electrical connection to be made to the image sensor <NUM>, which could otherwise hinder the movement of the image sensor <NUM> during OIS.

Although in this example the moving plate <NUM> is suspended on the support structure <NUM> by a suspension system in the form of the plain bearing <NUM>, in accordance with the first aspect of the present invention any other type of suspension system may be provided. For example, a suspension system employing plural beams extending parallel to the optical axis O, for example as disclosed in <CIT> for suspending a lens assembly, or a suspension system employing ball bearings, for example as disclosed in <CIT> for suspending a lens assembly.

Movement of the image sensor <NUM> relative to the support structure <NUM> is driven by an actuator arrangement that is arranged as follows, and seen most easily in <FIG>. The actuator arrangement is formed by a total of four SMA actuator wires <NUM> connected between the support structure <NUM> and the carrier <NUM>. For attaching the SMA actuator wires <NUM>, the carrier <NUM> comprises crimp portions <NUM> fixed to the moving plate <NUM> and the support structure <NUM> comprises crimp portions <NUM> fixed to the rim portion <NUM>. The crimp portions <NUM> and <NUM> crimp the four SMA actuator wires <NUM> so as to connect them to the support structure <NUM> and the carrier <NUM>. The crimp portions <NUM> fixed to the moving plate <NUM> are formed integrally from a sheet of metal so as to electrically connect the SMA actuator wires <NUM> together at the carrier <NUM>.

Although in this example the crimp portions <NUM> and <NUM> are separate elements fixed to the moving plate <NUM> and the rim portion <NUM>, as an alternative the crimp portions <NUM> could be formed integrally with the moving plate <NUM> and/or the crimp portions <NUM> could be formed integrally with the support plate <NUM>.

The SMA actuator wires <NUM> are arranged as follows so that they are capable, on selective driving, of moving the image sensor <NUM> relative to the support structure <NUM> in any direction laterally to the light-sensitive region <NUM> of the image sensor <NUM> and also of rotating the image sensor <NUM> about the optical axis O.

Each of the SMA actuator wires <NUM> is held in tension, thereby applying a force between the support structure <NUM> and the carrier <NUM>.

The SMA actuator wires <NUM> may be perpendicular to the optical axis O so that the force applied to the carrier <NUM> is lateral to the light-sensitive region <NUM> of the image sensor <NUM>. Alternatively, the SMA actuator wires <NUM> may be inclined at a small angle to the light-sensitive region <NUM> of the image sensor <NUM> so that the force applied to the carrier <NUM> includes a component lateral to the light-sensitive region <NUM> of the image sensor <NUM> and a component along the optical axis O that acts as a biasing force that biases the bearing surfaces <NUM> and <NUM> of the plain bearing <NUM> together.

The overall arrangement of the SMA actuator wires <NUM> will now be described, being similar to that described in <CIT>, except that they are connected to the carrier <NUM> for moving the image sensor <NUM>, not to the lens assembly <NUM>.

SMA material has the property that on heating it undergoes a solid-state phase change which causes the SMA material to contract. At low temperatures the SMA material enters the Martensite phase. At high temperatures the SMA enters the Austenite phase which induces a deformation causing the SMA material to contract. The phase change occurs over a range of temperature due to the statistical spread of transition temperature in the SMA crystal structure. Thus heating of the SMA actuator wires <NUM> causes them to decrease in length.

The SMA actuator wires <NUM> may be made of any suitable SMA material, for example Nitinol or another Titanium-alloy SMA material. Advantageously, the material composition and pre-treatment of the SMA actuator wires <NUM> is chosen to provide phase change over a range of temperature that is above the expected ambient temperature during normal operation and as wide as possible to maximise the degree of positional control.

On heating of one of the SMA actuator wires <NUM>, the stress therein increases and it contracts, causing movement of the image sensor <NUM>. A range of movement occurs as the temperature of the SMA increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA actuator wires <NUM> so that the stress therein decreases, it expands under the force from opposing ones of the SMA actuator wires <NUM>. This causes the image sensor <NUM> to move in the opposite direction.

The carrier <NUM> and the image sensor <NUM> are positioned axially within the aperture <NUM> of the rim portion <NUM> of the support structure <NUM>. The four SMA actuator wires <NUM> are arranged on four sides of the image sensor <NUM>. The SMA actuator wires <NUM> are of the same length and have a rotationally symmetrical arrangement.

As viewed axially, a first pair of the SMA actuator wires <NUM> extend parallel to a first axis (vertical in <FIG>) that is lateral to the light-sensitive region <NUM> of the image sensor <NUM>. However, the first pair of the SMA actuator wires <NUM> are oppositely connected to the support structure <NUM> and the carrier <NUM> so that they apply forces in opposite directions along the first axis (vertically up and down in <FIG>). The forces applied by the SMA actuator wires <NUM> of the first pair balance in the event that the tension in each SMA actuator wire <NUM> is equal. This means that the first pair of the SMA actuator wires <NUM> apply a first torque to the image sensor <NUM> (anti-clockwise in <FIG>).

As viewed axially, a second pair of SMA actuator wires <NUM> extend parallel to a second axis (horizontal in <FIG>) that is lateral to the light-sensitive region <NUM> of the image sensor <NUM>. However, the second pair of SMA actuator wires <NUM> are oppositely connected to the support structure <NUM> and the carrier <NUM> so that they apply forces in opposite directions along the second axis (horizontally left and right in <FIG>). The forces applied by the SMA actuator wires <NUM> of the second pair balance in the event that the tension in each SMA actuator wire <NUM> is equal. This means that the second pair of the SMA actuator wires <NUM> apply a second torque (clockwise in <FIG>) to the image sensor <NUM> that is arranged to be in an opposite sense to the first torque. Thus, the first and second torques balance in the event that tension in each SMA actuator wire <NUM> is the same.

As a result, the SMA actuator wires <NUM> may be selectively driven to move the image sensor <NUM> in any direction laterally and to rotate the image sensor <NUM> about the optical axis O.

The magnitude of the range of movement and rotation depends on the geometry and the range of contraction of the SMA actuator wires <NUM> within their normal operating parameters.

This particular arrangement of the SMA actuator wires <NUM> is advantageous because it can drive the desired lateral movement and rotation with a minimum number of SMA actuator wires. However, other arrangements of SMA actuator wires <NUM> could be applied. To provide three degrees of motion (two degrees of lateral motion and one degree of rotational motion), then a minimum of four SMA actuator wires <NUM> are provided. Other arrangements could apply a different number of SMA actuator wires <NUM>. Less SMA actuator wires <NUM> could be provided for lateral motion, but not rotation. Arrangements with more than four SMA actuator wires <NUM> are also possible, and may have advantages in allowing additional parameters to be controlled in addition to motion, for example the degree of stress in the SMA actuator wires <NUM>.

The lateral position and orientation of the image sensor <NUM> relative to the support structure <NUM> is controlled by selectively varying the temperature of the SMA actuator wires <NUM>. This driving of the SMA actuator wires <NUM> is achieved by passing selective drive signals through the SMA actuator wires <NUM> to provide resistive heating. Heating is provided directly by the current of the drive signals. Cooling is provided by reducing or ceasing the current of the drive signals to allow the SMA wire <NUM> to cool by conduction, convection and radiation to its surroundings.

The camera apparatus <NUM> comprises a lens assembly <NUM> that is assembled with the camera assembly <NUM> by being mounted to the support structure <NUM>, in particular to the rim portion <NUM>.

The lens assembly <NUM> comprises a lens carriage <NUM> in the form of a cylindrical body that is mounted to the rim portion <NUM> of the support structure <NUM>. The lens carriage supports at least one lens <NUM> arranged along the optical axis O. In general any number of one or more lenses <NUM> may be provided. Without limitation to the invention, in this example the camera apparatus <NUM> is a miniature camera in which the at least one lens <NUM> (i.e. each lens <NUM> if plural lenses are provided) typically have a diameter of at most <NUM>. The at least one lens <NUM> of the lens assembly <NUM> is arranged to focus an image onto the image sensor <NUM>.

In this example, at least one lens <NUM> is supported on the lens carriage <NUM> in a manner in which at least one lens <NUM> is movable along the optical axis O relative to the lens carriage <NUM>, for example to provide focussing or zoom, although that is not essential. In particular, the at least one lens <NUM> is fixed to a lens holder <NUM> which is movable along the optical axis O relative to the lens carriage <NUM>. Where there are plural lenses <NUM>, any or all of the lenses <NUM> may be fixed to the lens holder <NUM> and/or one or more of the lenses <NUM> may be fixed to the lens carriage <NUM> and so not movable along the optical axis O relative to the lens carriage <NUM>.

An axial actuator arrangement <NUM> provided between the lens carriage <NUM> and the lens holder <NUM> is arranged to drive movement of the lens holder <NUM> and lenses <NUM> along the optical axis O relative to the lens carriage <NUM>. The axial actuator arrangement <NUM> may be any suitable type, for example being a voice coil motor (VCM) or an arrangement of SMA actuator wires, such as is described in <CIT>.

In addition, the camera apparatus <NUM> comprises a can <NUM> fixed to the support structure <NUM> and protruding forwardly therefrom to encase and protect the other components of the camera apparatus <NUM>.

As discussed above, in operation the SMA actuator wires <NUM> are selectively driven to move the image sensor <NUM> in any direction laterally and to rotate the image sensor <NUM> about the optical axis O. This is used to provide OIS, compensating for image movement of the camera apparatus <NUM>, caused by for example hand shake.

Relative movement of the image sensor <NUM> relative to the support structure <NUM> and hence also relative to the lens assembly <NUM> may be used to stabilise the image against tilting of the camera apparatus <NUM>, i.e. rotation about axes extending laterally to the light-sensitive region <NUM> of the image sensor <NUM>. This occurs in a similar manner to a camera apparatus providing OIS-lens shift of the type disclosed in <CIT> and <CIT> which also involves relative lateral movement of the image sensor <NUM> and lens assembly <NUM>. In addition, rotation of the images sensor <NUM> may be used to stabilise the image against rotation of the camera apparatus <NUM> around the optical axis O. This type of stabilisation is not achieved by a camera apparatus providing OIS-lens shift of the type disclosed in <CIT> and <CIT>.

The SMA actuator wires <NUM> are driven by the control circuit implemented in the IC chip <NUM>. In particular, the control circuit generates drive signals for each of the SMA actuator wires <NUM> and supplies the drive signals to the SMA actuator wires <NUM>.

The control circuit <NUM> receives the output signals of the gyroscope sensor <NUM> which acts as a vibration sensor. The gyroscope sensor <NUM> detects the vibrations that the camera apparatus <NUM> is experiencing and its output signals represent those vibrations, specifically as the angular velocity of the camera lens element <NUM> in three dimensions. The gyroscope sensor <NUM> is typically a pair of miniature gyroscopes, for detecting vibration around three axes, being two axes laterally of the light-sensitive region <NUM> of the image sensor <NUM> and also the optical axis O. More generally, larger numbers of gyroscopes or other types of vibration sensor could be used.

Claim 1:
A camera assembly (<NUM>) comprising:
a support structure (<NUM>);
an image sensor (<NUM>) mounted on a carrier (<NUM>) and having a light-sensitive region (<NUM>), at least one plain bearing (<NUM>) comprising a bearing surface (<NUM>, <NUM>) on each of the carrier and the support structure, which bearing surfaces bear on each other so as to suspend the carrier (<NUM>) on the support structure (<NUM>) and allow movement of the image sensor (<NUM>) relative to the support structure (<NUM>) in any direction laterally to the light-sensitive region (<NUM>) of the image sensor (<NUM>), and in a manner allowing rotation of the image sensor (<NUM>) about an axis orthogonal to the light-sensitive region (<NUM>);
plural shape memory alloy actuator wires (<NUM>) in an arrangement capable, on selective driving thereof, of moving the image sensor (<NUM>) relative to the support structure (<NUM>) in any direction laterally to the light-sensitive region (<NUM>) of the image sensor (<NUM>) and of rotating the image sensor (<NUM>) about said axis; and
a biasing arrangement that biases the bearing surfaces (<NUM>, <NUM>) together, the biasing arrangement comprises at least one flexure (<NUM>), the flexure (<NUM>) supporting electrical tracks connected to the image sensor.