GB2627229A

GB2627229A - Apparatus and method

Info

Publication number: GB2627229A
Application number: GB2302178.5A
Authority: GB
Inventors: Heijne Nicolas; Benjamin Simpson Brown Andrew
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2023-02-15
Filing date: 2023-02-15
Publication date: 2024-08-21
Also published as: GB202302178D0; WO2024170910A1

Abstract

An apparatus 100 having a support structure 12, a waveguide 34 comprising an entrance pupil 23, and a module 22 having a lens arrangement 26 to direct light from a display 24 into the entrance pupil. The module is rotated relative to the support structure about a first axis by an actuator arrangement 18 wherein the first axis is through the entrance pupil and perpendicular to an optical axis (O) of the lens arrangement. The actuator may rotate the module about a second axis 36 which is perpendicular to the first and optical axes. The rotation of the module may be guided by a bearing arrangement having first and second surfaces 12a, 22a which are biased by a biasing arrangement. The actuator arrangement may reduce the friction between the bearing surfaces and comprise at least first and second shape memory alloy (SMA) elements (1, 2; Fig. 3) for rotation in separate directions. The elements may cross each other. The display may comprise LEDs. The actuator arrangement may move the module to pre‐defined angular positions defined by the bearing arrangement having projections or indentations, a rack and pinion, and flexible elements or connector. Alternative reality (AR) glasses may comprise the apparatus.

Description

APPARATUS and METHOD

Field

The present application relates to an apparatus for expanding the field of view of a device.

Background

The field of view (FOV) of augmented reality (AR) glasses using display is typically defined by the resolution of the display and the optical design of the waveguide/combiner. It would be desirable to increase the FOV of the AR glasses.

Summary

According to an aspect of the present invention, there is provided an apparatus comprising: a support structure; - a waveguide comprising an entrance pupil; - a module comprising: a display; and a lens arrangement configured to direct light output by the display into the entrance pupil of the waveguide; the apparatus further comprising - an actuator arrangement configured to rotate the module relative to the support structure about a first axis which is perpendicular to an optical axis of the lens arrangement.

The first axis may be through the entrance pupil.

The apparatus enables steering of the light input into the waveguide. Accordingly, the angle at which light is directed into the waveguide is changed, which in turn affects the angle at which light is output to the user. By pivoting around the entrance pupil of the waveguide it is possible to change the beam angle to extend the FOV. The display remains perpendicular to the optical axis of the lens arrangement. The display and the lens arrangement are actuated together (by actuating the module).

In some embodiments, the actuator arrangement is configured to rotate the module relative to the support structure about a second axis which is through the entrance pupil and which is perpendicular to both the optical axis of the lens arrangement and the first axis.

In some embodiments the apparatus comprises a bearing arrangement which is configured to guide the rotation of the module relative to the support structure. The bearing arrangement may comprise a plain bearing formed between a first bearing surface on the support structure and a second bearing surface on the module. In other embodiments, no bearing arrangement is present. For example, in embodiments in which SMA is used to drive movement of the module, the module could be suspended by the SMA wires.

In some embodiments the apparatus comprises a biasing arrangement configured to bias the first and second bearing surfaces together. The biasing arrangement may comprise a resilient element (e.g. a spring) and/or a magnet.

In some embodiments the apparatus is configured to hold the module stationary relative to the support structure when the actuator arrangement is unpowered. Accordingly, power is not required to hold the module in a given position and so the overall power consumption of the device on which the apparatus is disposed is reduced.

In some embodiments the actuator arrangement is configured to reduce a normal force between the first and second bearing surfaces during movement of the module relative to the support structure, thereby reducing a frictional force between the first and second bearing surfaces. In this way, higher friction is employed to hold the module still in a given position whereas relatively lower friction is present during movement.

In some embodiments the actuator arrangement comprises one or more shape memory alloy, SMA, elements which are configured to cause the rotation of the module relative to the support structure. Advantageously, the use of SMA allows precise control of the position of the module and provides sufficient force to deform an interconnect (such as a flexible printed circuit, FPC) between the display and the support structure.

The one or more SMA wires may be connected between the module and the support structure. For example, the one or more wires could be crimped to each of the module and the support. Alternatively, two portions of a given wire may be connected (e.g. crimped) to one of the support structure and module and a further portion may be hooked over an element of the other of the module and the support structure.

In some embodiments the actuator arrangement comprises a first SMA element and a second SMA element, wherein the first SMA element is configured to rotate the module in a first direction about the first axis and the second SMA element is configured to rotate the module in a second direction about the first axis. In some embodiments the first and second elements cross over eachother when viewed along the first axis.

In some embodiments the actuator arrangement comprises four SMA elements. The actuator arrangement may comprise a total of four SMA elements.

In some embodiments the actuator arrangement comprises eight SMA elements. The actuator arrangement may comprise a total of eight SMA elements.

In some embodiments the actuator arrangement comprises eight SMA actuator elements inclined with respect to a notional primary axis with two SMA elements on each of four sides around the primary axis, the SMA elements being connected between the movable element and the support structure so that on contraction two groups of four SMA elements provide a force on the movable element with a component in opposite directions along the primary axis.

In some embodiments a frictional force between the first and second bearing surfaces when the one or more SMA elements are uncontracted is greater than a weight of the module.

In some embodiments the display is a microLED display or an OLED display. Alternatively, the display may comprise an LCoS (liquid crystal on silicon) display or any other display.

In some embodiments the actuator arrangement is configured to move the module between a series of pre-defined angular positions with respect to the support structure. In some embodiments the bearing arrangement is configured to define the angular positions.

In some embodiments the bearing arrangement comprises a series of projections and/or detents to define the angular positions.

In some embodiments the apparatus further comprises a rack and pinion wherein the module comprises the pinion and the actuator arrangement is configured to move the rack.

In some embodiments the apparatus further comprises a flexible connector for carrying electrical signals between the support structure and the display. Such a connector may comprise a flexible printed circuit (FPC) for example.

In some embodiments the bearing arrangement comprises a plurality of flexure elements supporting the module on the support structure in a manner allowing the module to rotate about the first axis on deflection of the flexure elements.

In some embodiments the one or more SMA elements comprises at least four SMA elements; and the apparatus further comprises a biasing element arranged to resist translation of the module in a plane perpendicular to the optical axis of the lens arrangement.

According to another aspect of the present invention, there is provided a wearable device comprising the apparatus of any preceding claim. In some embodiments the device is a pair of augmented-reality glasses.

According to another aspect of the present invention, there is provided an actuator arrangement suitable for use in an apparatus according to any one of claims 1 to 23.

Brief description of the drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic view of an apparatus according to the present disclosure; Figure 2 is a schematic view of an SMA wire arrangement; Figure 3 is a schematic view of an apparatus according to the present disclosure; Figure 4 is a schematic view of an apparatus according to the present disclosure; Figure 5 is a schematic view of an apparatus according to the present disclosure; Figure 6 is a schematic view of an apparatus according to the present disclosure; Figure 7A is a schematic view of an apparatus according to the present disclosure; Figure 7B is a schematic view of an apparatus according to the present disclosure; Figure 8 is a schematic view of a flexure arrangement; Figures 9A and 9B are schematic views of an arrangement for defining angular positions of the module; and Figure 10 is a schematic view of an actuator arrangement.

Detailed description

With reference to Figure 1, an apparatus 100 is described. The apparatus may be part of a wearable device, for example a pair of augmented reality (AR) glasses.

The apparatus 100 comprises a module 22 and a support structure 12. The module 22 is configured to move relative to the support structure 12 and the apparatus 100 comprises an actuator arrangement 18 to drive the movement. The apparatus may comprise a bearing arrangement (not shown) to support the movement of the module with respect to the support structure 12.

The module 22 comprises a display 24 and a lens arrangement 26. The module 22 may comprise a housing which supports the display 24 and the lens arrangement 26. The display 24 may be any device which outputs light for formation into an image. The display 24 may comprise a microLED, OLED or LCoS display, for example. The lens arrangement 26 comprises one or more lenses.

The apparatus 100 further comprises a waveguide 34 which has an entrance pupil 23. The module 22, which may otherwise be referred to as a light engine, is configured to direct light output by the display into the entrance pupil 23 of the waveguide 34 via an input coupler 28 (e.g. a grating). The input coupler may be integral with (e.g. within) the waveguide. Light then exits the waveguide 34 via an output coupler 30 (e.g. a grating) and reaches the eye of a user (denoted by reference numeral 32).

The module 22 is configured to rotate relative to the support structure 12. Specifically, the module 22 is configured to rotate about a first axis through the entrance pupil 23 of the waveguide 34 which is perpendicular to an optical axis (0) of the lens arrangement. In Figure 1, the first axis comes out of the page, through the point at which the light from the display enters the waveguide (i.e. the entrance pupil 23). In this way, the module 22 follows the arc (denoted A) shown in Figure 1. By rotating the module in this way, the angle at which light enters the waveguide is altered. This has the effect that the angle at which light exits the waveguide is altered. Accordingly, the field of view (FOV) of the display can be increased.

The module 22 may be configured to rotate about a second axis which is perpendicular to the first axis and to the optical axis (0) of the lens arrangement and also runs through the entrance pupil 23. This second axis is denoted by the dashed line labelled 36 in Figure 1. In rotating the module about the second axis 36, the module would rotate along an arc into and out of the page.

The actuator arrangement may comprise any suitable actuator for driving the rotation of the module.

For example, the actuator arrangement may comprise one or more voice coil motors (VCM), one or more shape memory alloy elements or any other suitable actuator.

With respect to Figure 2, an actuator arrangement 18 for use in the apparatus 100 shown in Figure 1 is described. The actuator arrangement 18 comprises eight SMA wires. Two of the SMA wires 1-8 are arranged on each of four sides around a notional primary axis P. The two of the SMA actuator wires 1-8 on each side, for example SMA wires 1 and 2, are inclined in opposite senses with respect to each other, as viewed perpendicular from the primary axis P, and cross each other. The four sides on which the SMA wires 1-8 are arranged extend in a loop around the primary axis P. In this example, the sides are perpendicular and so form a square as viewed along the primary axis P, but alternatively the sides could take a different quadrilateral shape. In this example, the SMA actuator wires 1-8 are parallel to the outer faces of the movable element 11 which conveniently packages the module 2 but is not essential.

Within each group, the SMA wires on opposite sides (for example on one hand SMA actuator wires 1-2 and on the other hand SMA actuator wires 3-4) when differentially actuated drive tilting about a lateral axis perpendicular to the primary axis P. Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes. Accordingly, such an actuator arrangement may be used to drive the rotation of the module 2 about the first and second axes as described above. This arrangement is described in application W02011/104518 which is incorporated herein by reference in its entirety. An advantage of using such a suspended wire system is that the centre of rotation of the module is not fixed by a bearing system but can be controlled by utilsing the correct combination of translations and rotations driven by the SMA wires.

A modified wire arrangement is shown in Figure 3. As compared to figure 2, the SMA wires are shifted along the optical axis, closer to the entrance pupil 3. This has the effect that the wire centre is closer to the entrance pupil 3 and hence the stroke of the SMA wires is increased. The stiffness of the electrical interconnect between the display and the support structure should also be considered to ensure that this does not constrain motion of the module.

Further wire arrangements which could be employed to drive the rotation (tilting) of the module are described in W02010029316A2, W02010089529A1 and W02020074899A1, each of which are incorporated herein in their entirety.

It may be advantageous to create a fixed pivot for the module. This can be achieved either using bearings or a flexure arrangement. If using bearings, a plain bearing arrangement could be a circular bearing surface if a single rotational degree of freedom (DOE) is required or spherical if two rotational DOFs are required.

With reference to Figure 4, a bearing arrangement for supporting rotation of the module 2 is described.

The apparatus 100 comprises a plain bearing arrangement. The support structure 12 comprises a first bearing surface 12a. The module 22 comprises a second bearing surface 22a. The plain bearing is formed by the first and second bearing surfaces which are both curved. The bearing surfaces follow an arc, the centre of which is at the entrance pupil 3. The bearing surfaces could instead by made to have the shape of a portion of a sphere (e.g. they could have a hemispherical shape) to facilitate rotation of the module about two perpendicular axes. SMA wires 1 and 2 are shown in Figure 4. A further pair of wires (arranged in the same way) are disposed on the opposite side of the module.

With reference to Figure 5, the bearing arrangement may be disposed underneath the module 22 (i.e. on a side of the module opposite to the entrance pupil 3). The apparatus 100 may comprise a biasing arrangement for biasing the two bearing surfaces 12a and 22a together. In the embodiment shown in Figure 4, the biasing arrangement comprises a first spring 40 and a second spring 42. The springs 40 and 42 bias the module 22 down onto the support structure 12. On contraction, the SMA wires 1 and 2 act to reduce a normal force between the first and second bearing surfaces 12a and 22a. Accordingly, frictional surfaces between the first and second bearing surfaces 12a and 22a are reduced during movement. The resultant force of the wires (which reduces the normal force) should not be high enough to pull the module off of the bearings. Instead of or in addition to the springs, a magnet could be used to provide a biasing force. For any given biasing arrangement, the bearing arrangement could be disposed on one side of the module and the biasing arrangement could be disposed on the opposite side of the module.

The first and second bearing surfaces 12a and 22a and/or the springs 40 and 42 may be configured such that when no power is supplied to the SMA wires, frictional forces between the bearing surfaces are sufficient to hold the module still with respect to the support structure 12.

Figure 6 shows a different bearing arrangement in which the bearing surfaces are arranged differently as compared to the embodiment of Figure 5.

A further biasing arrangement and a further bearing arrangement is shown in figures 7a and 7b. In both Figure 7A and 7B, the biasing arrangement comprises a spring 40 which imparts an upwards force on the module 22, onto the second bearing surface 22a. The SMA wires 1 and 2 oppose this force, reducing friction between the bearing surfaces. Figures 7A and 7B show different wire arrangements which could be used to move module 22.

As mentioned above, a flexure arrangement could be used to support movement of the module 22. An example of a flexure arrangement 44 is shown in Figure 8. The module 22 (not shown) would be connected to an outer portion of the flexure 44. The flexure may also provide a restoring force to centre the module once power to the SMA wire(s) is withdrawn. Pivot portions 50 and 52 allow rotation of the module about a first axis. Pivot portions 54 and 56 allow rotation of the module about a second axis perpendicular to the first axis.

With reference to Figures 9A and 9B, the bearing surfaces may comprise detent positions to define a series of angular positions of the module 22 with respect to the support structure 12. The first bearing surface 12a may comprise a series of detents and the second bearing surface 22a may comprise a set of corresponding teeth for engaging with the detents. Advantageously, these pre-defined positions aid in accurately positioning the module 22. Figure 9A shows the module 22 in a first angular position and figure 9B shows the module 22 in a second angular position, different to the first.

An alternative is to use the base of the module 22 as a rack with an associated pinion gear. Figure 10 shows such an arrangement. The module 22 comprises a series of teeth and the apparatus 100 comprises a pinion gear 46 which is moved relative to the support structure 12 (not shown) by SMA wires 1 and 2. Movement of the pinion drives rotation of the module.

Some of the above-described actuator assemblies comprise at least one SMA element. The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together.

In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and/or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and/or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling or deposition and/or other forming process(es). The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field.

It will be appreciated that there may be many other variations of the above-described examples. Instead of rotating the module, an intermediate component (such as a mirror or prism) could be rotated instead in order to alter the angle of the light entering the waveguide. Also, it will be appreciated that there are various different configurations of bearings and wire arrangements which could be used depending on the optimum configuration for the space allowed. Further, an overcentre mechanism could be used, for example a spring connected to a pivot on the support structure which imparts a force on the module in a direction on displacement in that direction of the module (e.g. by one or more SMA wires) from a central position.

Eye-tracking may be used to determine the target position of the module. The module may be rotated based on detected eye movements.

Claims

Claims 1. An apparatus comprising: a support structure; a waveguide comprising an entrance pupil; a module comprising: a display; and a lens arrangement configured to direct light output by the display into the entrance pupil of the waveguide; the apparatus further comprising: an actuator arrangement configured to rotate the module relative to the support structure about a first axis which is through the entrance pupil and perpendicular to an optical axis of the lens arrangement.
2. An apparatus according to claim 1, wherein the actuator is configured to rotate the module relative to the support structure about a second axis which is through the entrance pupil and which is perpendicular to both the optical axis of the lens arrangement and the first axis.
3. An apparatus according to any preceding claim comprising a bearing arrangement which is configured to guide the rotation of the module relative to the support structure.
4. An apparatus according to claim 3, wherein the bearing arrangement comprises a plain bearing formed between a first bearing surface on the support structure and a second bearing surface on the module.
S. An apparatus according to claim 4, comprising a biasing arrangement configured to bias the first and second bearing surfaces together.
6. An apparatus according to claim 4 or claim 5, wherein the biasing arrangement comprises a resilient element and/or a magnet.
7. An apparatus according to claim 5 or claim 6 configured to hold the module stationary relative to the support structure when the actuator arrangement is unpowered.
8. An apparatus according to claim 7, wherein the actuator arrangement is configured to reduce a normal force between the first and second bearing surfaces during movement of the module relative to the support structure, thereby reducing a frictional force between the first and second bearing surfaces.
9. An apparatus according to any preceding claim, wherein the actuator arrangement comprises one or more shape memory alloy, SMA, elements which are configured to cause the rotation of the module relative to the support structure.
10. An apparatus according to claim 9, wherein the actuator arrangement comprises a first SMA element and a second SMA element, wherein the first SMA element is configured to rotate the module in a first direction about the first axis and the second SMA element is configured to rotate the module in a second direction about the first axis.
11. An apparatus according to claim 10, wherein the first and second elements cross over eachother when viewed along the first axis.
12. An apparatus according to any of claims 9 to 11, wherein the actuator arrangement comprises four SMA elements.
13. An apparatus according to any of claims 9 to 12, wherein the actuator arrangement comprises eight SMA elements.
14. An apparatus according to claim 13, wherein the actuator arrangement comprises eight SMA actuator elements inclined with respect to a notional primary axis with two SMA elements on each of four sides around the primary axis, the SMA elements being connected between the movable element and the support structure so that on contraction two groups of four SMA elements provide a force on the movable element with a component in opposite directions along the primary axis.
15. An apparatus according to any of claims 9 to 14 when dependent on claim 8 or a claim dependent thereon, wherein a frictional force between the first and second bearing surfaces when the one or more SMA elements are uncontracted is greater than a weight of the module.
16. An apparatus according to any preceding claim, wherein the display is a microLED display or an OLED display.
17. An apparatus according to any preceding claim, wherein the actuator arrangement is configured to move the module between a series of pre-defined angular positions with respect to the support structure.
18. An apparatus according to claim 17, wherein the bearing arrangement is configured to define the angular positions.
19. An apparatus according to claim 18, wherein the bearing arrangement comprises a series of projections and/or detents to define the angular positions.
20. An apparatus according to claim 19, further comprising a rack and pinion wherein the module comprises the pinion and the actuator arrangement is configured to move the rack.
21. An apparatus according to any preceding claim further comprising a flexible connector for carrying electrical signals between the support structure and the display.
22. An apparatus according to any of claims 3 to 21, wherein the bearing arrangement comprises a plurality of flexure elements supporting the module on the support structure in a manner allowing the module to rotate about the first axis on deflection of the flexure elements.
23. An apparatus according to any of claims 9 to 13, or any claim dependent thereon, wherein the one or more SMA elements comprises at least four SMA elements; and the apparatus further comprises a biasing element arranged to resist translation of the module in a plane perpendicular to the optical axis of the lens arrangement.
24. A wearable device comprising the apparatus of any preceding claim.
25. A wearable device according to claim 24, wherein the device is a pair of augmented-reality glasses.
26. An actuator arrangement suitable for use in an apparatus according to any one of claims 1 to 23.