Head-mounted display and method for assembling the same

Abstract

A method for assembling a head-mounted display is disclosed, the method comprising: providing a subassembly in a mount, the subassembly comprising an optical train having an output from which to present a virtual image to a user in a first eye and an input for receiving light carrying a virtual image from an image source, the method comprising: first positioning an image source at the input to the optical train; generating a test virtual image in the image source; monitoring at least one quality of the test virtual image output from the optical train at the output; adjusting the position and orientation of the image source, further monitoring at least one quality of the test virtual image, and repeating the adjustment and further monitoring until at least one quality is above an acceptable threshold, thereby identifying the working position of the image source with respect to the input to the optical train, and fixing the image source in the subassembly at the working position.

Description

Technical Field

[0001] The present invention relates to a method of assembling a head-mounted display, a related head-mounted display subassembly, and a related head-mounted display.

Background Art

[0002] Head-mounted displays that use a reflective surface and an image source often require extensive calibration before use.

Summary of the Invention

[0003] According to a first aspect of the present invention, a method of assembling a head-mounted display is provided, the method comprising: providing a subassembly at a mount, the subassembly comprising an optical train having an output for presenting a virtual image to a user therefrom at a first eye and an input for receiving light carrying the virtual image from an image source; first, positioning the image source at the input to the optical train; generating a test virtual image at the image source; monitoring at least one quality of the test virtual image output from the optical train at the output; adjusting the position and orientation of the image source and further monitoring at least one quality of the test virtual image; repeating the adjustment and further monitoring until at least one quality is above an acceptable threshold, thereby identifying an operating position of the image source relative to the input to the optical train; fixing the image source at the subassembly at the operating position; and comprising.

[0004] Monitoring at least one quality of the virtual image at the output may comprise providing an image sensor at the optical train output, collecting optical data, and processing the optical data.

[0005] Processing optical data may involve evaluating the module transfer function (MTF) or contrast transfer function (CTF) of the virtual image in the output.

[0006] Positioning the image source may involve mounting the image source in an adjustable jig, further comprising configuring the adjustable jig to facilitate translation along the x, y, and z axes, and rotation around each of the x, y, and z axes. The adjustable jig may be configured for positional accuracy to a tolerance of plus or minus 1 micron. The mount and adjustable jig may be fixed to a common substrate.

[0007] The method further comprises providing an image source coupled to an end casing having an open side, providing a docking portion in a subassembly for accommodating the open side of the end casing over a range of positions, the docking portion being close to an optical train input, first positioning the end casing at the docking portion, and thereby first positioning the image source at the optical train input, wherein identifying the operational position of the image source with respect to the input to the optical train comprises identifying the alignment position between the end casing and the docking portion, the alignment position defining the operational interstice between the end casing and the docking portion.

[0008] Furthermore, fixing the image source in the subassembly at the operating position may involve applying an adhesive substance to the operating gap.

[0009] The method provides an end casing or docking portion having at least one conduit through which an adhesive can be applied to the operating gap, and the step of fixing an image source in a subassembly comprises applying an adhesive in the conduit to at least partially close the operating gap and to join the end casing to the docking portion. Furthermore, the method may include curing the adhesive.

[0010] The method may include providing a docking portion having a substantially cylindrical outer surface and providing an end casing having a substantially cylindrical inner surface wider than the outer surface of the docking portion, wherein the initial positioning of the image source in the optical train involves sliding the inner surface of the end casing on the outer surface of the docking portion.

[0011] This method may include providing a conduit as at least one opening in the open casing, the conduit interconnecting the inner surface of the end casing with the surrounding environment.

[0012] The method may include providing an intermediate housing for a series of relay lenses in a subassembly, the intermediate housing having a stepped inner surface that defines at least one ledge for reliably positioning at least one of the series of relay lenses.

[0013] Furthermore, this method may include forming an intermediate housing by a machining process and forming a cavity in a subassembly to receive the intermediate housing.

[0014] The method may be for a subassembly comprising a frame having at least one mount for a casing and a reflector; a relay optical system mounted on the casing and defining an input to an optical train; and a reflector mounted on at least one mount for the reflector and configured to receive light from the relay optical system and provide an output from the optical train.

[0015] The frame can be formed by additive manufacturing techniques.

[0016] The method may be for a head-mounted display further comprising a further optical train and a further image source associated with the user's other eye, wherein the method comprises performing the method of any one of the prior claims with respect to the further optical train and further image source for the other eye.

[0017] A head-mounted display subassembly is provided, comprising: an optical relay assembly configured to receive light carrying a virtual image from an image source; a frame having a casing for optical components; a casing comprising a cavity housing the optical relay assembly; a casing reflector configured to receive light from the optical relay assembly; a docking portion configured to house a predetermined form of image source attached to the end casing over a range of alignment; a back reflector mounted on the frame and configured to receive light from the casing reflector; and a combiner mounted on the frame and configured to receive light from the back reflector.

[0018] The optical relay assembly may comprise a set of lenses arranged in sequence.

[0019] The optical relay assembly may comprise an intermediate housing having an inner and outer surface, the intermediate housing holding a pair of lenses on its inner surface and connecting to a cavity on its outer surface. Furthermore, the inner surface may have a stepped profile for holding one or more of the set of lenses.

[0020] According to a third aspect of the present invention, there is provided a head-mounted display comprising a sub-assembly according to the second aspect, a mount for an image source, an image source attached to the mount, and an end casing having an open side for connection to the sub-assembly, wherein the end casing is coupled to the sub-assembly at a docking portion.

[0021] The docking portion may be joined to the end casing in an adhesive-filled gap.

[0022] Here, embodiments of the present invention are described by way of example only with reference to the drawings.

Brief Description of the Drawings

[0023] [Figure 1a] FIG. 1a shows a view of a head-mounted display device, defining cross-sections X-X and Y-Y through the right-eye casing and the left-eye casing of the display device, respectively. [Figure 1b] FIG. 1a shows a view of a head-mounted display device, defining cross-sections X-X and Y-Y through the right-eye casing and the left-eye casing of the display device, respectively. [Figure 2a] FIG. 2a shows a view of the head-mounted display device shown in FIGS. 1a and 1b, accompanied by a view through cross-section X-X through the right-eye casing, and area S is defined around the cross-section. [Figure 2b] FIG. 2b shows an enlarged view of area S. [Figure 3] FIG. 3 shows cross-section Y-Y through the left-eye casing. [Figure 4a-4c] FIGS. 4a-4c show the top (or XY plane), front (ZY plane), and side (ZX plane) of a user wearing the head-mounted display device. [Figure 5] FIG. 5 shows a mount and jig for assembling the head-mounted display device. [Figure 6] FIG. 6 shows a flowchart of a method for assembling the head-mounted display. [Modes for carrying out the invention]

[0024] An example of a head-mounted display 100 is shown with reference to the drawings, particularly Figures 1a, 1b, 2a, 2b, and 3.

[0025] (For clarity, not all components in all diagrams are labeled. Furthermore, the diagrams use a naming convention in which components on the right side of the device have the suffix "a" and equivalent components on the left side have the suffix "b". Therefore, references to "b" components should be clear to the reader, even if only equivalent "a" components are shown or labeled in the diagrams.)

[0026] The head-mounted display 100 is configured to be worn within the user's field of vision.

[0027] The head-mounted display 100 includes a sub-assembly 200.

[0028] The subassembly 200 includes a frame 210.

[0029] The frame 210 comprises a first portion 213a positioned for the user's right eye and a second portion 213b positioned for the user's left eye.

[0030] The first part 213a comprises a first casing 208a for housing a first set of optical components, a mount 203a for a back reflector 204a, and a mount 205a for a front combiner 206a. The back reflector may alternatively be called a Brow reflector or Brow mirror. The back mount may alternatively be called a Brow mount.

[0031] The first casing 208a comprises a mount 201a for a casing reflector 202a and a cavity 212a for receiving an optical relay assembly. The first casing 208a has a generally elongated shape, thereby defining the casing axis. The optical relay assembly may have its optical relay axis defined by an aligned constituent set of optical lenses. The casing is configured such that the casing axis is generally aligned with, or at least parallel to, the optical relay axis in its original position.

[0032] The second part 213b comprises a second casing 208b for a second set of optical components, a second mount 203b for a second back reflector 204b, and a second mount 205b for a second front combiner 206b.

[0033] The second casing 208b includes a mount 201b for the casing reflector 202b and a cavity 212b for receiving the optical relay assembly 400b.

[0034] The second casing 208b comprises a mount 201b, a casing reflector 202b, and a cavity 212b for receiving the optical relay assembly 400b. The second casing 208b has a generally elongated shape, thereby defining the second casing axis.

[0035] The second casing axis and the first casing axis are substantially coplanar but inclined at approximately 130–100 degrees relative to each other. The plane defined by these axes, namely the XY plane, then defines the Z axis perpendicular to it. The Z axis relates to the top and bottom of the device when mounted in a horizontal position.

[0036] For each of these parts, the back reflectors 204a, 204b and the back mounts 203a, 203b define a plane relative to the back reflector and a corresponding back reflector axis (see axis (iv) in Figure 4) perpendicular to this plane.

[0037] For each respective part, the front combiners 206a, 206b and the front mounts 205a, 205b define a plane relative to the combiner and a corresponding combiner axis perpendicular to this plane.

[0038] The back reflector mount and combiner mount are positioned such that the back reflector and combiner can be supported in substantially parallel planes. Therefore, the back reflector axis and the combiner axis are substantially parallel.

[0039] The frame 210 further comprises a bridge member extending between the first casing and the second casing, defining a frame transverse axis. The frame transverse axis is substantially coplanar with the first and second casing axes in the XY plane.

[0040] The bridge member comprises a separate back beam 212 and a front beam 214, each extending between casings 208a and 208b. The back beam 212 extends between the rear surfaces of casings 208a and 208b. The front beam 214 extends between the front surfaces of casings 208a and 208b.

[0041] The back beam 212 is positioned to be higher than the front beam 214.

[0042] The back beam 212 extends back reflector mounts 203a and 203b from the back beam. The front beam 214 extends front mounts 205a and 205b from the front beam.

[0043] The bridge member further includes a bridging column 216 that extends from the center of the HWD100 along the transverse axis of the frame between the front beam 212 and the back beam 214.

[0044] Therefore, the frame 210 defines openings on each side of the device between the casing, the front beam, the back beam, and the bridging columns.

[0045] In this example, the bridge member further comprises attachment points 218 formed by holes suitable for connection to a helmet or helmet bracket (for example, by spacing, number, or threading).

[0046] The frame 210 can be formed, for example, as a single continuous structure (monocoque) by an additive manufacturing process.

[0047] The frame 210 is positioned to be symmetrical with respect to the user's midline when fitted. However, in other cases, the frame may be asymmetrical.

[0048] In addition to the frame 210, the subassembly 200 includes first and second combiners 206a, 206b, first and second back reflectors 204a, 204b, first and second casing reflectors 202a, 202b, and optical relay assemblies 400a, 400b.

[0049] The first and second back reflectors 204a and 204b are attached to their respective back mounts 203a and 203b and extend downward from the frame 210, specifically from the back beam 212.

[0050] The first and second combiners 206a and 206b are mounted to their respective mounts 205a and 205b and extend downward from the frame 210, specifically from the front beam 214. The first and second combiners 206a and 206b extend lower than the back reflectors 204a and 204b so that they can be seen without obstruction by the user.

[0051] Further reference to Figures 2a and 2b shows the internal features of subassembly 200.

[0052] The first and second casing reflectors 202a and 202b are mounted in casing mounts 201a and 201b within their respective casings 208a and 208b.

[0053] The reflector and mount tend to terminate at the innermost part of the casing.

[0054] Each casing reflector 202a, 202b and associated mount defines an associated casing reflector axis, both planar and perpendicular thereto. Referring particularly to Figures 3 and 4, the casing reflector axis (iii) is inclined with respect to the casing axis (ii) in two planes: 20–30 degrees in the XY plane and 10–20 degrees in the ZX plane.

[0055] Each back reflector 204a, 204b and mount defines a back reflector plane and a corresponding back reflector axis (vi). Each back reflector axis is inclined with respect to the relay optical axis in two planes: 40–50 degrees in the XY plane and 130–150 degrees in the ZX plane.

[0056] Each combiner 206a, 206b and mount defines the combiner plane and the corresponding combiner axis (v). Each combiner is tilted at 40-50 degrees in the XY plane and 130-150 degrees in the ZX plane.

[0057] The optical relay assemblies 400a and 400b are mounted in their respective casing cavities 212a and 212b.

[0058] Each optical relay assembly comprises intermediate housings 402a, 402b and a series of relay lenses 408a, 408b.

[0059] The intermediate housing 402a has a stepped cylindrical inner surface 404a defining at least one ledge 405a. Each ledge 405a is configured to receive a relay lens, thereby precisely positioning the lens relative to the intermediate housing 402a.

[0060] The outer surface of the intermediate housing 402a is shaped to correspond to the inner surface of the casing cavity 212a. In this example, the intermediate housing has a stepped cylindrical outer surface.

[0061] Therefore, the intermediate housing 402a has the form of a stepped tube and can thus be manufactured with high precision (for example, by machining, more specifically by a turning process).

[0062] The outermost end of the intermediate housing 402a is configured to extend beyond the casing 208a, thereby being exposed and capable of being coupled to the end casing 300a.

[0063] Furthermore, referring to Figures 2a, 2b, and 3, the head-mounted display device 100 also comprises a first end casing 300a and a second end casing 300b. Each end casing 300a, 300b is attached to the outside of the respective subassembly 200.

[0064] Each end casing 300a, 300b has the configuration of an open casing and thus defines open sides 302a, 302b. The open sides 302a, 302b are configured to connect to the outermost parts 406a, 406b (or docking parts) of the subassembly 200.

[0065] In this embodiment, the open sides 302a and 302b define substantially cylindrical inner surfaces 310a and 310b that are wider than the outer surface of the subassembly 200. Therefore, the end casings 300a and 300b and the subassembly 200 do not fully fit together, leaving interstitial gaps 105a and 105b between them. This allows for a range of alignment and position that can be held before the end casings 300a and 300b and the subassembly 200 are fixed together.

[0066] The open sides 302a and 302b also include conduits 306a and 306b that extend between the surrounding environment and the inner surfaces of the casings 300a and 300b. Such conduits 306a and 306b allow the adhesive to enter.

[0067] Furthermore, each end casing 300a, 300b includes mounts 304a, 304b to which image sources 360a, 360b are attached. The mounts define a plane to which the image sources 360a, 360b are to be attached, and thus define a corresponding image mount axis (i) that is inclined with respect to the end casing axis.

[0068] Image sources 360a and 360b are arrays of pixels for directly generating light that carries a virtual image. In this example, image sources 360a and 360b are LED arrays, more specifically MLED arrays. Feeds for driving the image sources are connected to the image sources.

[0069] Figure 4 shows a head-mounted display 100 positioned correctly by the user. The user defines the cross-sectional, frontal, and midline views.

[0070] When the HWD100 is fitted by the user, the XY plane of the HWD100 is parallel to the user's cross-section. Furthermore, the casing axis is located approximately at the user's eyebrow level, and the lateral inclinations of the HWD100 extend outward toward each temple.

[0071] Additionally, there is a back reflector at approximately the user's eyebrow level.

[0072] Furthermore, it can be seen that the central portion of each reflector is roughly located on the same ZX plane, parallel to the user's midline.

[0073] During operation, the virtual image is encoded as a drive signal and supplied to the image sources 360a and 360b.

[0074] The image sources 360a and 360b then illuminate the pixels in their array, generating light that carries a virtual image. This light is transmitted inward towards the relay optics 400a and 400b.

[0075] Light is received in relay optics 400a and 400b and transmitted inward through a series of lenses 408a and 408b toward casing reflectors 202a and 202b.

[0076] Light is received by casing reflectors 202a and 202b and reflected at least partially toward back reflectors 204a and 204b. Due to the relative inclination between the casing reflector axis (iii) and the casing axis (ii), the light is directed backward and downward.

[0077] Light is received by back reflectors 204a and 204b and reflected at least partially toward combiners 206a and 206b. Due to the relative inclination between the casing reflector axis (iii), the casing axis (ii), and the back reflector axis (vi), the light is directed forward and downward.

[0078] In combiner 206, the relative inclination between the casing reflector axis (iii), the casing axis (ii), the back reflector axis (vi), and the combiner axis (v) directs the light backward and substantially horizontally. Combiners 206a and 206b are at the user's eye level. Therefore, the light is reflected at least partially toward the user's eyes.

[0079] The relay optical system 400, casing reflector 202, back reflector 204, and combiner 206 represent a sub-assembly optical train.

[0080] Referring to Figure 5, the apparatus 500 for aligning the respective image sources 360a and 360b contained in the end casings 300a and 300b is shown in the HMD device subassembly 200.

[0081] The device 500 includes a mount 503 for holding the subassembly 200.

[0082] The apparatus 500 further comprises jigs 505a and 505b for each of the end casings 300a and 300b to be positioned in the subassembly. Each jig 505a, 505b holds the end casings 300a, 300b in close proximity to the mounted subassembly 200 and is configured to allow translation and rotation of the end casing 300a or 300b relative to the subassembly 200. Each jig can be finely adjusted in the position and orientation of its respective end casing. Each jig can translate its respective end casing relative to the mounted subassembly 200 on three axes and rotate it about the three axes.

[0083] The apparatus 500 further comprises a substrate 501 to which the mount 503 and jigs 505a and 505b are fixed.

[0084] The device 500 further comprises a monitoring device which includes a pair of image sensors 507a and 507b, a processor 504, and a display 506.

[0085] Each imaging device is positioned at the respective output of the subassembly 200 and generates image data 502a, 502b which are transmitted to the processor 504 via a wired or wireless connection. The processor 504 receives the image data and generates monitoring data 509. The processor 504 is linked to a display 506 so that the monitoring data 509 can be visually represented to the user.

[0086] A method 600 for assembling the head-mounted display 100 should be described with reference to Figure 6.

[0087] Method 600 comprises providing a subassembly 200. Step 602 comprises mounting the subassembly 200 on the mount 503.

[0088] Step 604 comprises performing the initial positioning of the image source 360 ​​within the subassembly 200, specifically within the input region of the subassembly 200.

[0089] Step 606 comprises generating a test image in the image source 360. This is done by sending an appropriate image signal to the image source 360, thereby causing the image source 360 ​​to generate light that carries the test image. The light generated by the image source will then propagate through the optical train of the subassembly 200 and will tend to reach the output from the optical train.

[0090] Step 608 comprises monitoring the quality of the test image at the output from the optical train. Monitoring can be performed by a user directly observing a virtual image at the output and subjectively evaluating its quality. Alternatively, monitoring can be performed by placing image sensors 507a, 507b at the output and relaying the collected optical data 502a, 502b to a processor 506, which may process the optical data to generate monitoring data 509 that can be output as a human-readable image on a display 506.

[0091] More specifically, the optical data 502a and 502b may be processed in processor 506 to determine the module transfer function (MTF) for the test image. Alternatively, the optical data 502a and 502b may be processed to determine the contrast transfer function (CTF).

[0092] If the image quality exceeds an acceptable threshold, as evaluated in step 608, the image source and subassembly will be considered operationally aligned.

[0093] If the image quality falls below an acceptable threshold, as evaluated in step 608, the method returns to step 604, and the position is adjusted before repeating steps 606 and 608. This loop continues until motion alignment is established.

[0094] Once motion alignment is performed, the image source 360 ​​is fixed to the subassembly 200 without moving any further relative to each other.

[0095] In some examples, the image source 360 ​​is mounted within an end casing 300 having open sides that fit over a docking section 406 exposed at the leading edge / outer end of the subassembly 200. This fit allows for a range of relative position and orientation in which the end casing 300 and the subassembly 200 overlap. This range of position and orientation allows for adjustment / repositioning of the image source 360 ​​within the subassembly 200. This fit tends to define a gap 105 between the end casing 300 and the docking section 406. During motion alignment, this gap defines the motion gap.

[0096] The end casing 300 is further provided with conduits 306 through which adhesive (such as low-shrinkage optical cement) can be applied to the working gap 105 in order to join the parts together. A curing step may be provided after the application of the adhesive to facilitate the joining.

[0097] Such a method has been found to enable positional accuracy between the end cap containing the image device and the subassembly 200 to tolerances of plus or minus 1 micron and plus or minus 0.5 microns.

[0098] As shown in Figure 3, the conduit 306 is a hole that penetrates the wall of the end casing 300, and connects the inner surface of the end casing to the surrounding environment.

[0099] Method 600 can be performed on one image source 360a, 360b independently of the other image source 360b, 360a. Therefore, both image sources can be applied to the subassembly 200 substantially simultaneously or at different times.

[0100] In describing the present invention, features are defined in physical space by referring to both of a pair of mutually orthogonal axes (X, Y, and Z), and by referring to the relative positions of front versus back, inside versus outside, and top versus bottom. Front versus back roughly corresponds to the X-axis, inside versus outside roughly corresponds to the Y-axis, and top versus bottom roughly corresponds to the Z-axis. These terms are used to facilitate the description of complex physical features and are not intended to be limiting, for example, insofar as the “top” component must always be positioned at a higher elevation than the “bottom” component.

[0101] Specific components such as LED arrays and low-shrinkage optical cement are mentioned. However, suitable alternatives will be obvious to those skilled in the art.

[0102] Reflectors may be substantially reflective or partially reflective. They may be configured to be partially translucent. Reflectors may be provided in the form of mirrors or mirror surfaces.

[0103] The combiner may be partially transparent to bring about an augmented reality head-mounted display (for example, a display that blends virtual images with a real-world ambient view).

Claims

1. A method for assembling a head-mounted display, wherein the method is: A subassembly is provided in the mount, and the subassembly comprises an optical train having an output for presenting a virtual image from thereto to the user in the first eye, and an input for receiving light carrying the virtual image from an image source. First, position the image source at the input to the optical train, The process involves generating a test virtual image in the aforementioned image source, Monitoring the quality of at least one of the test virtual images output from the optical train in the output, Adjust the position and orientation of the image source, and further monitor the quality of at least one of the test virtual images. The adjustment and further monitoring are repeated until at least one quality exceeds an acceptable threshold, thereby identifying the operational position of the image source with respect to the input to the optical train. The image source is fixed in the subassembly at the aforementioned operating position, A method that includes [a certain feature].

2. Monitoring the quality of at least one of the virtual images in the output means The optical train output is provided with an image sensor, Collecting optical data and Processing the aforementioned optical data, The method according to claim 1, comprising:

3. The method according to claim 2, wherein processing the optical data comprises evaluating the module transfer function (MTF) or contrast transfer function (CTF) of the virtual image in the output.

4. The method according to any one of claims 1 to 3, wherein positioning the image source comprises mounting the image source in an adjustable jig.

5. The method according to claim 4, wherein the adjustable jig is configured to facilitate translation along the x, y, and z axes and rotation about each of the x, y, and z axes.

6. The method according to claim 4 or 5, wherein the adjustable jig is configured for positional accuracy to a tolerance of plus or minus 1 micron.

7. The method according to any one of claims 3 to 6, wherein the mount and the adjustable jig are fixed to a common substrate.

8. The image source is provided, coupled to an end casing having an open side, The subassembly is provided with a docking portion for accommodating the open side of the end casing over a range of positions, and the docking portion is located close to the optical train input. The method comprises first positioning the end casing at the docking portion, thereby first positioning the image source at the optical train input, Herein, identifying the operating position of the image source with respect to the input to the optical train includes identifying the alignment position of the end casing and the docking portion. The alignment position defines the operational gap between the end casing and the docking portion. The method according to any one of claims 1 to 7.

9. The method according to claim 8, wherein fixing the image source in the subassembly at the operating position comprises applying an adhesive substance to the operating gap.

10. The end casing or docking portion is provided with at least one conduit through which adhesive can be applied to the operating gap, The step of fixing the image source in the subassembly comprises at least partially closing the operating gap and applying adhesive in the conduit to join the end casing to the docking portion, The method according to claim 9.

11. The method according to claim 10, further comprising curing the adhesive.

12. The docking portion is provided having a substantially cylindrical outer surface, The end casing is provided having a substantially cylindrical inner surface that is wider than the outer surface of the docking portion, Initially positioning the image source in the optical train involves sliding the inner surface of the end casing on the outer surface of the docking portion. The method according to any one of claims 8 to 11.

13. The open casing is provided with at least one conduit as at least one hole, and the at least one conduit interconnects the inner surface of the end casing with the surrounding environment. A method according to claim 10 or 11, or a method according to claim 12 as dependent on claim 10.

14. The subassembly is further provided with an intermediate housing for a series of relay lenses, the intermediate housing having a stepped inner surface defining at least one ledge for securely positioning at least one of the series of relay lenses. The method according to any one of claims 1 to 13.

15. The intermediate housing is formed by a machining process, The subassembly comprises forming a cavity for receiving the intermediate housing, The method according to claim 14.

16. The aforementioned subassembly is A frame having at least one mount for the casing and reflector, A relay optical system attached to the casing and defining the input to the optical train, A reflector mounted on at least one of the mounts for the reflector, configured to receive light from the relay optical system and to provide the output from the optical train, The method according to any one of claims 1 to 15.

17. The method according to claim 15, wherein the frame is formed by an additive manufacturing technique.

18. The method according to any one of claims 1 to 17, wherein the head-mounted display further comprises a further optical train and a further image source associated with the user's other eye, wherein the method comprises performing the method according to any one of claims 1 to 17 with respect to the further optical train and the further image source for the other eye.

19. A head-mounted display subassembly, An optical relay assembly configured to receive light carrying a virtual image from an image source, A frame comprising a casing for an optical component, and the casing, A cavity housing the optical relay assembly, A casing reflector configured to receive light from the optical relay assembly, A docking portion configured to accommodate a predetermined form of image source attached to the end casing over the alignment range, A back reflector, which is attached to the frame and configured to receive light from the casing reflector, A combiner, which is attached to the frame and configured to receive light from the back reflector, A casing equipped with, A head-mounted display subassembly equipped with the following features.

20. The head-mounted display according to claim 19, wherein the optical relay assembly comprises a set of lenses arranged in a continuous manner.

21. The head-mounted display according to claim 20, wherein the optical relay assembly comprises an intermediate housing having an inner surface and an outer surface, the intermediate housing holding the pair of lenses on the inner surface and connected to the cavity on the outer surface.

22. The head-mounted display according to claim 21, wherein the inner surface has a stepped profile for holding one or more of the series of lenses.

23. A subassembly according to any one of claims 19 to 22, An end casing comprising a mount for an image source, an image source attached to the mount, and an open side for connecting to the subassembly, Here, the end casing is coupled to the subassembly at the docking portion. Head-mounted display.

24. The head-mounted display according to claim 23, wherein the docking portion is joined to the end casing in a gap filled with adhesive.

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