WO2021171030A1

WO2021171030A1 - A camera assembly

Info

Publication number: WO2021171030A1
Application number: PCT/GB2021/050492
Authority: WO
Inventors: Dominic George Webber; David Charles Richards
Original assignee: Cambridge Mechatronics Limited
Priority date: 2020-02-26
Filing date: 2021-02-26
Publication date: 2021-09-02
Also published as: CN115151862A; GB2592579A; GB2607837A; GB202213133D0; GB202002731D0

Abstract

A camera assembly (100) comprising: a housing (10); a window (12) on a first side of the housing (10); an image sensor (40) extending along the first side (10a) of the housing (10) or along a second side (10b) of the housing (10) opposite the first side, an optical path (2, 4, 6) being defined between the window (12) and the image sensor (40); and a first reflector (20) and a second reflector (30) sequentially positioned along the optical path (2, 4, 6) for forming an image onto the image sensor (40), the first and second reflectors (20, 30) are each configured to deflect the optical path (2, 4, 6); wherein the second reflector (30) is configured to focus the image onto the image sensor (40).

Description

A CAMERA ASSEMBLY

Field

The present invention generally relates to a camera assembly.

Background

With improvements in optics and computational photography, modem smartphone cameras strike a good balance between imaging quality and convenience. More than ever users are relying on their smartphones for their everyday imaging needs. However, there is constant consumer demand for superior handset photography to undertake more demanding imaging tasks.

One way to improve image quality in a smartphone is to place multiple cameras in order to augment imaging quality. Such an arrangement may emulate the image quality and feature set offered by conventional digital single lens reflex (DSLR) cameras. However, these arrangements occupy significant space at the expense of other key components, such as handset batteries.

Summary

Image quality is largely dependent on the size of image sensor employed. More specifically, the larger the imaging area through increased pixel number and/or size, the more optical information can be captured. In addition, a large format image sensor may perform much better in low light use cases and therefore require less image correction. However, due to the design constraints of smartphone devices, there is limited space to accommodate optics and focal lengths for telephoto capabilities. Thus, the imaging area of image sensors provided in smartphones is often in the order of tens of mm². These image sensors are significantly smaller than those used in DSLR cameras, where imaging areas are at least an order of magnitude larger.

The present invention describes a camera assembly comprising a pair of sequentially arranged reflectors to provide a lengthened optical path. In other words, the camera assembly may resemble a periscope, where at least one of the reflectors is configured to reflect and focus an image as projected onto an image sensor. Advantageously, such an arrangement may allow a larger image sensor to be placed in a smartphone.

According to a first aspect of the present invention, there is provided a camera assembly comprising: a housing; a window on a first side of the housing; an image sensor extending along the first side of the housing or along a second side of the housing opposite the first side, an optical path being defined between the window and the image sensor; a first reflector and a second reflector sequentially positioned along the optical path for forming an image onto the image sensor, the first and second reflectors are each configured to deflect the optical path; wherein the second reflector is configured to enlarge the image that is being formed onto the image sensor, in absence of any optical element provided between the second reflector and the image sensor in the optical path.

Broadly speaking, the camera assembly may resemble a periscope where the relative positions of the image sensor and the window preclude a direct line-of-sight. When provided in a smartphone device, the housing may be significantly greater in length and width in comparison to its depth. As such, the optical path may extend along the length or the width of the housing . Advantageously, such arrangement may significantly increase the focal length, without also increasing the thickness of the smartphone as in conventional camera assemblies.

The window, or aperture, may position on a ceiling of the housing. The window may allow incident light to enter the housing before it is sequentially reflected by the first reflector and the second reflector to form an image on the image sensor. The image sensor may be supported on a support structure provided on a base of the housing or the ceiling of the housing. The placement of the image sensor may be chosen to accommodate other components in the smartphone.

The image sensor and may extend across a plane, wherein at least a part of the optical path extends parallel to the plane. Thus, the first reflector may first deflect the optical path into a direction parallel to an imaging area of the image sensor, wherein the second reflector may deflect the optical path towards the image sensor for projecting the image thereon.

For the avoidance of doubt, the term ‘focus’ in this application may be expressed in a way that light rays originating from a point on an object are brought to converge at a point on the image sensor. Whilst this is conceptually accurate, in all practical systems the light rays can only converge to cover some finite area, meaning that the point is inevitably blurred by the imaging system. However, it is possible to define an acceptable level of blur, which is usually a function of the minimum detectable feature size of the image sensor, below which the image is regarded to be in adequate focus. For imaging systems applicable for this present invention, the acceptable level of blur is a disc of the order of 1 or 2pm. It is also worth noting that typical imaging systems attempt to bring a plane of points from the object space into sharp focus on a plane of the imaging space, although that is not an inherent requirement.

For the avoidance of doubt, the term ‘enlarge’ in this application may be expressed in a way that light rays originating from a point on an object are brought to converge over a larger area on the image sensor than that achievable by a non-focusing optical element. In other words, the second reflector provides positive magnification on the image.

The second reflector may be fixedly positioned on the base or the ceiling of the housing. Optionally, the second reflector is configured to have a positive focal length for effecting the focussing of image onto the image sensor. Thus, upon reflection, the image as projected on the image sensor may be magnified, or enlarged. Advantageously, such magnified image may be projected onto all or most of the imaging area of the large format image sensor, thus allowing a high-quality image to be captured, as well as performing more demanding imaging tasks.

Optionally, the second reflector comprises a gradient-index (GRIN) prism having a gradient of refractive index across the prism. Optionally, the GRIN prism is formed by one of neutron irradiation, chemical vapour deposition, partial polymerisation and ion exchange. The use of GRIN prism may advantageously lead to a compact and robust second reflector, whilst being able to be produced in a cost-efficient manner.

Alternatively, or in addition, the second reflector comprises a convex mirror or a prism having a curvaceous form. Advantageously, the simplicity of a convex mirror may allow the second reflector to be manufactured more readily.

Optionally, the first reflector and/or the second reflector comprises a reflective coating at a reflective surface. The reflective surface may be any surface on the first reflector and/or the second reflector.

Optionally, the first reflector and the second reflector are each configured to deflect the optical path to a direction perpendicular to respective incident light along the optical path. This arrangement may advantageously result in a more compact camera arrangement, e.g. a camera arrangement that is thinner than its optical length. Alternatively, the first reflector and the second reflector may deflect the optical path by any angle other than 90° depending on the space available within the housing.

Optionally, one or both of the length and the width of the image sensor are greater than a depth of the housing defined by the said opposite sides of the housing. In other words, the image sensor has a dimension larger than the depth of the housing thus preclude it being mounted onto a surface other than on of the opposite sides of the housing.

Optionally, the first reflector comprises a mirror and/or a prism. The mirror and/or prism may only be responsible for reflecting incident light towards the second reflector, and does not carry out any focusing of incident light, e.g. the mirror and/or prism forming the first reflector may not have a positive or a negative focal length.

Optionally, the camera apparatus further comprises one or more optical elements provided along the optical path, the one or more optical elements and the second reflector and/or the first reflector are configured to collectively focus the image onto the image sensor, e.g. the one or more optical elements is configured to, along with the second reflector, focus the image onto the image sensor. Preferably, some or all of the optical elements may be positioned in between the first reflector and the second reflector along the optical path. In some embodiments, the one or more optical elements may be positioned at any location along the optical path. In other words, the optical element and the second reflector may collectively carry out image focusing. For example, the optical element may form a first focusing stage for focusing an incident light onto the second reflector. The second reflector may form a second focusing stage to focus the focused light to form an image on the image sensor.

The optical elements may comprise one or more lenses supported by one or more lens carriages. One or more lenses in a lens carriage may be movable along their optical axis between the first reflector and the second reflector, so as to effect zoom and auto focus (AF). Alternatively, or in addition, one or more lenses in a lens carriage may be movable in a direction orthogonal to their optical axis so as to effect optical image stabilisation (OIS).

Alternatively, the first reflector and the second reflector are configured to collectively focus the image onto the image sensor, e.g. the first reflector, along with the second reflector, are configured to focus the image onto the image sensor. Optionally, the first reflector comprises one or more of a gradient- index (GRIN) prism, a convex mirror and a prism having a curvaceous form, e.g. the first reflector may configure to have a positive focal length. For example, the first reflector may comprise a GRIN prism for reflecting and focusing incident light onto the second reflector. In such embodiments, AF and/or OIS may be achieved by moving the first reflector and/or the second reflector, for example in a direction along and/or orthogonal to their optical axes. That is, the reflection and focussing may be achieved by using two GRIN prisms. Advantageously, such arrangement minimises the number of optical components required and thus, for example, minimises the weight in the smartphone device. Optionally, the camera assembly further comprises an adjustable shutter positioned in the optical path between the first and second reflectors, wherein elements of the adjustable shutter are moveable for controlling the amount of light passing through, and thereby varying the depth of field in the camera assembly. For example, the adjustable shutter may be an adjustable iris comprising at least one moveable leaf for controlling the amount of light passing therethrough. The adjustable shutter may preferably be positioned in between the first reflector and the optical element, and/or it may be positioned in between the optical element and the second reflector.

Optionally, the camera assembly further comprises a Shape Memory Alloy (SMA) actuator, the SMA actuator comprises one or more SMA components (e.g. lengths of SMA wire) each configured to, on contraction, effect the said movement. For example, the SMA actuator may be used for effecting movement in the lens carriage, and/or be used for manipulating at least one movable leaf of the adjustable shutter. In some embodiments, a single SMA actuator may be used for moving the lens carriage as well as operating the adjustable shutter. In other embodiments, discrete SMA actuators may each be used for effecting movement of the lens carriage and the adjustable shutter.

As an example, the SMA actuator may comprise eight lengths of SMA wires for controlling the movement of the lens carriage with up to six degrees of freedom to provide zoom, AF and OIS capabilities. Such an arrangement is disclosed in WO2011/104518A1.

Preferably, AF and OIS functionalities may be provided by discrete actuators in stacked arrangement each responsible for a particular function. For example, the actuator arrangement may be similar to W02016/009200A1 which discloses the use of a voice coil motor (VCM) for moving the lens carriage along an optical axis to perform AF, in addition to an SMA actuator having four lengths of SMA wires configured to shift the lens carriage orthogonally to the optical axis so as to provide OIS.

The SMA wires may be formed from any suitable shape memory alloy material, typically a nickel- titanium alloy (e.g. Nitinol), but they may also contain tertiary components such as copper. The SMA wires may have any cross-sectional profile and diameter suitable for the application. For example, the SMA wires may have a cross section diameter of 25 pm capable of generating a maximum force of between 120mN to 200mN whilst maintaining the strain in the SMA wire within safe limits (e.g. a 2- 3% reduction in length from an original length). Increasing the diameter of each SMA wire from 25 pm to 35pm approximately doubles the cross-sectional area of the SMA wire and thus approximately doubles the force provided by each SMA wire.

Preferably, the SMA actuator is configured to be driven by a pulse width modulation (PWM) drive signal. Advantageously, the use of PWM drive signal may lead to more actuate positioning of the lens carriage(s), as well as power distribution amongst the SMA wires.

The image sensor may be of any format and size. Preferably, the camera assembly forms a part of a smartphone and the image sensor has an image sensing surface of at least 116mm², or at least 225mm², or at least 286mm², or at least 329mm², or at least 370mm², or at least 548mm². For example, the image sensor may be a large-format image sensor commonly referred to as an 1” format image sensor, or a four-thirds image sensor, or any other large-format sensor.

Features of one aspect of the present invention may be combined with compatible features in other aspects of the present invention.

Brief Description of the Drawings

Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figures 1A and IB are respectively side and plan sectional views of a camera assembly according to a first embodiment of the present invention;

Figure 2 is a perspective view of an SMA actuator arrangement of the camera assembly of Figure 1;

Figure 3 is a side view of a camera assembly according to a second embodiment of the present invention; and

Figure 4 is a side view of a camera assembly according to a third embodiment of the present invention

Detailed Description

Figures la and lb are respectively side and plan sectional views of a camera assembly 100 according to a first embodiment of the present invention. The camera assembly 100 is configured to be used in a smartphone device and comprises a housing 10 containing one or more lens elements 62 in between a pair of reflectors 20, 30 along an optical path 2, 4, 6. The optical path 2, 4, 6 is defined between a window 12 on a first side 10a of the housing 10 and an image sensor 40 extending along a second side 10b of the housing 10 opposite the first side. More specifically, the first reflector 20 and second reflector 30 are configured to deflect, or fold, the optical path 2, 4 in order to direct the incident light, though the one or more lens elements 62, to form an image onto the image sensor 40. Thus, the camera assembly 100 may be referred to as a folded optical arrangement, or a periscopic camera.

Folded optics arrangements are particularly useful in devices where the thickness of the device (the Z- direction in Figures la and lb) is constrained. That is, as smartphone devices are becoming thinner with the demand for large format image sensors 40 ever rising, it becomes a challenge to mount a large- format image sensor in the thickness/Z -direction of the smartphone device.

The image senor 40 in the illustrated example is a large-format charged-coupled device (CCD) having an active area of 116mm² (e.g. 13.2mm x 8.8mm for a typical 1-inch format image sensor). In other embodiments, image sensors of various sizes, as well as types (e.g. complementary metal-oxide- semiconductor (CMOS)) may be used depending on the footprint that is available in the smartphone device. The extensive size of the large-format image sensor 40 precludes it from being fitted onto any surface of the housing 10 other than the first and the second sides 10a, 10b . That is, the length and width of the image sensor 40 are greater than the depth Z of the housing 10. Thus, in this example, the planar image sensor 40 is supported along the base of the housing 10b.

As shown in Figures 1A and IB, the optical axis 4 of the lens elements 62 is arranged parallel to the imaging area of the image sensor 40. More specifically, the optical axis 4 of the lens element 62 extends along the length Y of the housing 10 between the first reflector 20 and the second reflector 30. In other words, incident light entering the housing 10 in the Z-direction is being “folded” to pass along the Y- axis by the first reflector, before being “folded” again to pass along in the Z-direction towards the image sensor 40.

The first reflector 20 comprises a prism for effecting total internal reflection at a reflective surface. Alternatively, the first reflector 20 may be a mirror. In the illustrated example, the first reflector 20 is fixedly mounted in relation to the housing 10. In some other embodiments, the mirror may be moveable in the X- and Z-directions and/or tiltable about the X-axis and/or the Z-axis to provide for optical image stabilisation (“OIS”).

The lens element 62 is configured to focus incident light onto the second reflector 30. The degree of focusing offered by the lens element 62 may only be sufficient for projecting an image onto a part of the image sensor, i.e. the image does not project onto all of the imaging area available on the large format-image sensor 40. Thus, the second reflector 30 is configured to carry out further focussing of the light 6 passing through the lens element 62 to form an image on all, or substantially all, of the imaging area on the image sensor 40. Hence, the second reflector 30 not only reflects the incident light 4, it also carries out focussing so as to form an enlarged, or magnified, image on the image sensor 40.

In the illustrated embodiment, the second reflector 30 comprises a prism formed from a material that provides a graded refractive index (GRIN). For example, the GRIN prism 30 may have a flat surface to effect total internal reflection whilst producing a gradient of the material’s refractive index along the GRIN prism. Such a GRIN prism may be formed using several techniques, for example neutron irradiation, chemical vapour deposition and partial polymerisation. In particular, neutron irradiation may be carried out on a body of Boron-rich glass, wherein the concentration of boron ion in the glass may be changed through neutron bombardment.

In some other embodiments, the second reflector 30 may be a convex mirror having a positive focal length. That is, the surface of the convex mirror may cause incident light to diverge and thus projects an image onto substantially all of image area of the large format image sensor 40.

When used in a smartphone device, it is desirable to be able to drive the movement of the lens element 62 in each of the X, Y and Z directions as shown in Figures 1A and IB. Movement in the X- and Z- directions can provide for optical image stabilisation (“OIS”), whilst movement in the Y -direction can provide for auto-focus (“AF”). In certain arrangements the lens element 62 may include multiple lenses which are movable relative to each other, with such relative movement providing for zoom.

Figure 2 shows a perspective view of an SMA actuator arrangement in the camera assembly 100 of Figures 1A and IB. The lens element 62 is supported by a lens carriage 60 which provides a structural interface for the wires to attach to without impinging on the optical region of the assembly 100. The lens carriage 60 has two elongate plates 60a, 60b extending down either side of the lens element 62 parallel to the optical axis of the lens element. Together the plates 60a, 60b define a cuboid to which the SMA wires 51 can be connected to each comer (or close to each comer).

The SMA wires are coupled in a symmetric arrangement at side of the lens carriage 60 and are crossed. Each SMA wire 51 is connected between a static crimp which is attached to the housing 10 and a moving crimp which is attached to the lens carriage 60. It can be seen that, by actuating selected ones of the SMA wires 51, the lens carriage 60 can be driven with multiple degrees of freedom. In the most general case, positional control can be provided to move the lens carriage 60 with all the following degrees of freedom: lateral movement in any direction (including in both directions along each of the axes indicated) and tilting or rotation about any axis. Appropriate control of the SMA wires 51 may allow movement in a more restricted manner if desired (e.g. translational movement along each of the axes indicated and rotation about one or more of the axes indicated). The degrees of freedom in the positional control result from the configuration of the SMA wires. The two groups of four SMA wires 51 on either side of the lens carriage 60, if actuated as a group, can each provide a force in opposing directions along the X-axis. Due to the symmetric arrangement, actuation of a corresponding pair of adjacent SMA wires 51 in each group will provide a force along the Y- or Z- axis, whilst actuation of the opposing SMA wires 51 will provide a force in the opposite direction along the same axis. Similarly, it can be seen that differential actuation of wires 51 will cause rotation of the lens carriage 60.

In the camera assembly 100 as shown in Figures 1A and IB, there is provided an adjustable shutter 50 positioned between the first reflector 20 and the lens element 62. The adjustable shutter, upon actuation, is configured to control the amount of light passing therethrough. As such, the /number of the camera assembly 100 is adjustable for varying the depth of view. For example, the /-number may be adjustable in the range between /1.0 to /2.8. The adjustable shutter 50 as shown in this example comprises a leaf shutter actuated by an SMA actuator, however the adjustable shutter may employ any suitable adjustable shutter, and may be controllable by any actuating means, e.g. a voice coil motor (VCM).

Figure 3 is a side view of an alternative camera assembly 200 according to a second embodiment of the present invention. The camera assembly 200 is structurally and functionally similar to the first embodiment 100 as shown in Figures 1A and IB. However, the image sensor 40 as shown in Figure 3 is supported on the ceiling 10a of the housing 10, e.g. on the same side 10a of the housing 10 as the window 12. Thus, the optical path 2, 4, 6 has reversed its direction in the housing 10.

Figure 4 is a side view of another camera assembly 300 according to a third embodiment of the present invention. The camera assembly 300 is structurally and functionally similar to the first embodiment 100 as shown in Figures 1A and IB. However, in this embodiment, an auxiliary GRIN prism 22 is used in lieu of the first reflector 20 and the lens element 60. More specifically, the auxiliary GRIN prism 22 is configured to reflect and to focus incident light onto the GRIN prism 30. Thus, the two GRIN prisms 22, 30 collectively focus incident light for projecting an image onto the image sensor 40.

The auxiliary GRIN prism 22 is moveable along, or about, one or more axes to provide OIS and AF functionalities. The movement of the auxiliary GRIN prism 22 is caused by an SMA actuator similar to that shown in Figure 2. In other embodiments, the auxiliary GRIN prism 22 is fixedly mounted on the housing 10.

It will be appreciated that there may be many other variations of the above-described embodiments. For example, the camera assembly need not comprise a housing 10 as described herein.

Claims

1. A camera assembly comprising: a housing; a window on a first side of the housing; an image sensor extending along the first side of the housing or along a second side of the housing opposite the first side, an optical path being defined between the window and the image sensor; a first reflector and a second reflector sequentially positioned along the optical path for forming an image onto the image sensor, the first and second reflectors are each configured to deflect the optical path; wherein the second reflector is configured to enlarge the image that is being formed onto the image sensor, in absence of any optical element provided between the second reflector and the image sensor in the optical path.

2. A camera apparatus according to claim 1, wherein the first reflector and the second reflector are configured to collectively focus the image onto the image sensor.

3. A camera apparatus according to claim 1 or claim 2, wherein one or both of the first reflector and the second reflector are configured to have a positive focal length.

4. A camera apparatus according to any one of the preceding claims, wherein one or both of the first reflector and the second reflector comprise a gradient-index (GRIN) prism having a gradient of refractive index across the prism.

5. A camera apparatus according to claim 4, wherein the GRIN prism is formed by one of neutron irradiation, chemical vapour deposition, partial polymerisation and ion exchange.

6. A camera apparatus according to any one of the preceding claims, wherein one or both of the first reflector and the second reflector comprise a convex mirror or a prism having a curvaceous form.

7. A camera apparatus according to any one of the preceding claims, wherein the first reflector and/or the second reflector comprises a reflective coating at a reflective surface.

8. A camera assembly according to any one of the preceding claims, wherein the first reflector is moveable relative to the housing for effecting one or more of zoom, autofocus (AF) and optical image stabilisation (OIS).

9. A camera apparatus according to claim 1, wherein the first reflector comprises a mirror and/or a prism.

10. A camera apparatus according to any one of the preceding claims, further comprising one or more optical elements provided along the optical path, the one or more optical elements and the second reflector and/or the first reflector are configured to collectively focus the image onto the image sensor.

11. A camera assembly according to claim 10, wherein at least one of the optical elements is moveable relative to the housing for effecting one or more of zoom, autofocus (AF) and optical image stabilisation (OIS).

12. A camera assembly according to any one of the preceding claims, further comprising an adjustable shutter positioned in the optical path between the first and second reflectors, wherein elements of the adjustable shutter are moveable for controlling the amount of light passing through and thereby varying the depth of field of the camera assembly.

13. A camera assembly according to any one of the claims 8, 11 or 12, further comprises a Shape Memory Alloy (SMA) actuator, the SMA actuator comprising one or more SMA components each configured to, on contraction, effect the said movement.

14. A camera assembly according to any one of the preceding claims, wherein the first reflector and the second reflector are each configured to deflect the optical path to a direction substantially perpendicular to respective incident light along the optical path.

15. A camera assembly according to any one of the preceding claims, wherein one or more of length and the width of the image sensor being greater than a depth of the housing defined by the said opposite sides of the housing.

16. A camera assembly according to any one of the preceding claims, wherein the camera assembly forms a part of a smartphone, and wherein the image sensor has an image sensing surface of at least 116mm², or at least 225mm², or at least 286mm².