Patent Description:
Head-mounted displays are used in various fields, including engineering, medical, military, and video gaming. In some instances, head-mounted displays may present information or images to a user as part of a virtual reality or augmented reality environment. As an example, while playing a video game, a user may wear a head-mounted display to immerse the user within a virtual environment.

Conventional head-mounted displays provide inadequate or no adjustment to accommodate differing head sizes, face shapes, and eye spacings. As a result, some users may find it difficult to enjoyably wear head-mounted displays. For instance, if the lens tubes are horizontally misaligned with the user's eyes, a scene presented on the head-mounted display may only be partially visible to the user. If the display panels are too close or too far from the use's eyes, the user's field of view (FOV) may not be optimized. Conventional head-mounted displays may therefore be unable to accommodate different users. Head-mounted displays that are adjustable tend to be difficult and/or inconvenient to adjust by virtue of crude adjustment mechanisms, and they do not provide an optimized level of comfort, leaving the user frustrated.

<CIT> discloses a device configured to adjust interpupillary distance in a head mounted display. The device includes a gear.

<CIT> discloses an interpupillary distance adjusting mechanism for use in a binocular telescope.

<CIT> discloses a head mounted display comprising an interpupillary distance adjusting mechanism. The mechanism comprises a gear.

The same, or like, reference numbers in different figures indicate similar or identical items.

As mentioned above, head-mounted displays (HMDs) have a wide range of applications and, in some instances, may need to accommodate for varying head sizes, face shapes, and eye spacings among different users. Conventional HMDs, however, offer little to no adjustment to adapt to different users. For instance, in conventional HMDs, the distance between the lens tubes may be fixed, or, if adjustable, the adjustment mechanism may be difficult or inconvenient to operate, especially while wearing the HMD. In conventional HMDs, the distance between the user's face and the display panels (or lenses) may also be fixed, or, if adjustable, the adjustment mechanism may be difficult or clunky to operate, especially while wearing the HMD.

Described herein are, among other things, techniques and systems, including a HMD, for adjusting the spacing between a pair of lens tubes of the HMD to accommodate users of varying interpupillary distances (IPDs). For example, a HMD may comprise a rod coupled to a midframe of the HMD, a pair of lens tubes coupled to the rod (e.g., via a pair of movable frames that are coupled to the pair of lens tubes), each lens tube/movable frame being movable bidirectionally along the rod (e.g., in a first direction toward a left side of the HMD or in a second direction toward a right side of the HMD). The HMD may also include an actuator accessible from outside of a housing of the HMD, as well as a movable elongate member coupled to the actuator and to the midframe. A first biasing member coupled to the movable elongate member and to the midframe is configured to resist movement of the movable elongate member in a direction of travel of the elongate member. A rotatable gear coupled to the midframe and disposed between the pair of lens tubes/movable frames is engaged with the movable elongate member, and a pair of second biasing members coupled to the rod are configured to physically bias the pair of lens tubes/movable frames towards the rotatable gear (e.g., by physically biasing the pair of movable frames against a pair of spiral projections extending from a face of the rotatable gear).

Also described herein are, among other things, techniques and systems, including a HMD, for adjusting the spacing between the user's face and the lenses of the HMD to adjust the field of view (FOV) and/or the eye relief to accommodate different users. For example, a HMD may comprise a pair of lens assemblies coupled to a first portion of the HMD. An actuator disposed on a first side of the HMD may be accessible from outside of a housing of the HMD, and a pair of gear assemblies disposed on opposite sides of the HMD may be connected by a connecting rod and coupled to a second portion of the HMD that is movable relative to the first portion of the HMD. One of the gear assemblies of the pair of gear assemblies is disposed on the first side and coupled to the actuator such that actuation of the actuator causes the pair of gear assemblies to move the second portion of the HMD relative to the first portion of the HMD.

Also described herein are, among other things, an electronic device (e.g., a HMD) having a housing made of a spectrum-transmissive material configured to allow electromagnetic radiation of a specific spectrum to pass therethrough. An outer surface of the housing may be coated with a spectrum-opaque material that is configured to block the electromagnetic radiation of the specific spectrum, and one or more locations on the outer surface are devoid of the spectrum-opaque material to provide one or more spectrum-transmissive windows on the housing. One or more spectrum-specific components (e.g., sensors, beacons, etc.) can be disposed inside the housing behind the one or more spectrum-transmissive windows.

A process for manufacturing an electronic device (e.g., a HMD) having at least one window that allows electromagnetic radiation in a specific spectrum to pass through the at least one window may include forming a housing for the electronic device out of a first material that is configured to allow the electromagnetic radiation in the specific spectrum to pass therethrough, painting an outer surface of the housing with a second material that is configured to block the electromagnetic radiation in the specific spectrum, and removing the second material from at least one location on the outer surface to create the at least one window. In some embodiments, the specific spectrum is the IR spectrum.

The present disclosure provides an overall understanding of the principles of the structure, function, manufacture, and use of the systems and methods disclosed herein. One or more examples of the present disclosure are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that the systems and methods specifically described herein and illustrated in the accompanying drawings are non-limiting embodiments. The features illustrated or described in connection with one embodiment may be combined with the features of other embodiments, including as between systems and methods. Such modifications and variations are intended to be included within the scope of the appended claims.

<FIG> illustrates a front perspective view of an example head-mounted display (HMD) <NUM> (sometimes referred to herein as a "wearable display," a "VR headset," an "AR headset," or a "headset") with a visor <NUM> shown exploded from the HMD <NUM> to reveal a modular accessory compartment <NUM>. The HMD <NUM> may include a front portion (or main unit) that is positioned in front or over the eyes of the user to render images output by an application (e.g., a video game). In some instances, the application may execute on a computing device (e.g., a personal computer (PC), game console, etc.) associated with and/or communicatively coupled to the HMD <NUM>. In some instances, the HMD <NUM> may not rely on an external computing device and may execute an application and render corresponding images using on-board components (e.g., logic, hardware, memory, processors (e.g., central processing units (CPUs), graphics processing units (GPUs), etc.), batteries, and so forth). The HMD <NUM> may be configured to output a series of images (frames) viewed by the user through optics within the HMD <NUM>, making the user perceive the images as if immersed in a virtual reality (VR) or augmented reality (AR) environment.

The HMD <NUM> may include a visor <NUM> that is swappable, or interchangeable, with other types of visors. The visor <NUM> may be of a customized shape, a customized material, and/or the visor <NUM> may include customized artwork (e.g., colorings, stickers, markings, holes, surface features, etc.). A user can interchange the visor <NUM> with a different visor to change the look or appearance of the HMD <NUM> on the front of the HMD <NUM>. A different user that uses the HMD <NUM> may have his/her own customized visor <NUM> such that, and this user may remove an existing visor <NUM> and replace the existing visor <NUM> with his/her own, customized visor. The visor <NUM> may be removably attached to a front of the HMD <NUM> in any suitable manner, such as by a magnetic coupling mechanism(s) (e.g., magnets on the front of the HMD <NUM> that couple to corresponding magnets on the visor <NUM>), a hook-and-loop fastener (e.g., Velcro®), pins, screws, hooks, a snap/press fit mechanism, adhesive, or any suitable type of fastener.

The visor <NUM>, when attached to the HMD <NUM>, may cover a compartment <NUM> (sometimes referred to herein as a "modular accessor compartment <NUM>"). The compartment <NUM> may be any suitable shape. <FIG> depicts a rectangular compartment <NUM> that is recessed a distance into the front of the HMD <NUM>. The compartment <NUM> may include a port <NUM>, such as a universal serial bus (USB) port <NUM>, that is electrically connected to components of a printed circuit board (PCB) within the housing of the HMD <NUM>. The port <NUM> may allow a user to connect modular accessories to the HMD <NUM> to provide further customization to users of the HMD <NUM>. For example, a light(s) (e.g., light emitting diodes (LEDs)) may be connected to the port <NUM> so that power can be supplied to the lights to turn on the lights. These lights could be disposed in the compartment <NUM> behind visor <NUM>, which may be made of optically transparent material (e.g., clear or tinted plastic) to provide a customized lighting effect to the HMD <NUM>. The visor <NUM> may be any suitable color, and when the visor <NUM> covers lights within the compartment <NUM> that are connected via the port <NUM>, the visor <NUM> may illuminate to provide a customized visual appearance. In some embodiments, a display (e.g., a liquid crystal display (LCD)) can be connected to the port <NUM> and disposed within the compartment <NUM> to render images on the display while the HMD <NUM> is worn by a user. In other scenarios, an auxiliary camera(s) can be connected to the port <NUM> and disposed in the compartment <NUM>. In some embodiments, auxiliary and/or backup compute resources (e.g., processing, storage, power, etc.) can be connected via the port <NUM> to enhance the processing power, the storage capacity, and/or the battery life of the HMD <NUM>.

<FIG> illustrates a front perspective view of a front portion of the HMD <NUM> of <FIG>, according to an embodiment of the present disclosure. As shown in <FIG>, the HMD <NUM> may include one or more front-facing cameras <NUM>(<NUM>) and/or <NUM>(<NUM>). <FIG> depicts an embodiment with two front-facing cameras <NUM> including a first camera <NUM>(<NUM>) and a second camera <NUM>(<NUM>), but any suitable number of front-facing cameras <NUM> can be utilized. The front-facing cameras <NUM> can be used for any suitable purpose, such as optical tracking, pass-through imaging (e.g., projecting images of a real-world environment on the HMD <NUM>, such as by projecting real-world imagery atop a VR scene), obstacle detection (e.g., detecting objects in the real-world environment and possibly warning the user of a potential collision with such objects), recording video of the environment during gameplay, etc. The front-facing camera(s) <NUM> can be located at any suitable location on the HMD <NUM>, such as on the front of the HMD <NUM> towards the bottom of the HMD <NUM> (e.g., in the bottom half of the HMD <NUM>), as shown in <FIG>.

<FIG> illustrates a rear perspective view of the example HMD <NUM> of <FIG> in a configuration where a head strap <NUM> of the HMD <NUM> is attached to a main unit <NUM> of the HMD <NUM>, according to an embodiment of the present disclosure. <FIG> illustrates the example HMD <NUM> shown in <FIG>, except in a configuration where the head strap <NUM> has been removed from the main unit <NUM> of the HMD <NUM>. The head strap <NUM> may be removed, such as to swap, or interchange, the head strap <NUM> with a different head strap <NUM>. Extended periods of use of the HMD <NUM> may result in the material of certain portions of the head strap <NUM> absorbing bodily odors, and, as a result, a user may wish to remove the head strap <NUM> at times, such as to "air out" the head strap <NUM>, to clean the head strap <NUM>, to replace the head strap <NUM> with a new head strap. In some cases, a user may wish to interchange, or swap, the head strap <NUM> with a different type of head strap (e.g., one with different features, such as different headphones, different adjustment mechanisms, etc.). This provides further customization of the HMD <NUM> for different users.

As shown in <FIG>, the head strap <NUM> may be removed by removing an actuator <NUM> (e.g., a rotatable knob) located on a side of the HMD <NUM> to access one or more screws <NUM>(<NUM>), or similar fasteners. The removal of the actuator <NUM> may be accomplished in any suitable manner, such as by forcibly pulling outward on the actuator <NUM> to remove the actuator <NUM> from a mounting pin <NUM>(<NUM>). The mounting pin <NUM>(<NUM>) may be inserted through a main aperture in a portion of the head strap <NUM>, while the one or more screws <NUM>(<NUM>) may be screwed into one or more corresponding apertures <NUM>(<NUM>) in the portion of the head strap <NUM> to secure the head strap <NUM> to the main unit <NUM>. A user can unscrew the screw(s) <NUM>(<NUM>), and then slide the portion of the head strap <NUM> off of the mounting pin <NUM>(<NUM>) to remove one side of the head strap <NUM> from a corresponding side of the main unit <NUM>. On the opposite side of the main unit <NUM>, there may be one or more screws (e.g., similar to the screws <NUM>(<NUM>)) that are screwed into one or more corresponding apertures <NUM>(<NUM>) in another portion of the head strap <NUM> in order to secure the head strap <NUM> to the main unit <NUM> on the opposite side of the main unit <NUM>. A user can unscrew those screws on the opposite side of the main unit <NUM> to remove the other side of the head strap <NUM>, and, thus, the entire head strap <NUM>, from the main unit <NUM>. <FIG> also shows a belt loop <NUM> at a top of the main unit <NUM> of the HMD <NUM> that is configured to receive a top member of the head strap <NUM> by looping the top member of the head strap <NUM> through the belt loop <NUM> and securing the top member of the head strap <NUM> to itself. The securing mechanism of the top member of the head strap <NUM> may be any suitable mechanism, such a hook-and-loop fastener (e.g., Velcro®), snaps, etc. In this manner, the head strap <NUM> is removable, and may be reattached at will by the user.

<FIG> illustrates a rear perspective view of the main unit <NUM> of an example HMD <NUM> of <FIG> with a face gasket <NUM> decoupled from the main unit <NUM>, according to an embodiment of the present disclosure. The face gasket <NUM> may be removably attached to the main unit <NUM> of the HMD <NUM> in any suitable manner, such as by a magnetic coupling mechanism, a hook-and-loop fastener(s) (e.g., Velcro®), pins, screws, hooks, a snap/press fit mechanism, adhesive, or any suitable type of fastener. <FIG> depicts an embodiment where a magnetic coupling mechanism(s) is used to removably couple the face gasket <NUM> to the main unit <NUM>. For example, a plurality of first magnetic elements <NUM>(<NUM>)-(<NUM>) (e.g., metal screws) disposed on a rear of the main unit <NUM> may couple with a plurality of second magnetic elements <NUM>(<NUM>)-(<NUM>) (<NUM>(<NUM>) and <NUM>(<NUM>) not shown in <FIG>) disposed on a front of the face gasket <NUM>. In this manner, the face gasket <NUM> can be easily and conveniently secured in, or removed from, the rear of the main unit <NUM>. The face gasket <NUM> may be padded on a rear of the face gasket <NUM> to provide a comfortable fit when the HMD <NUM> is worn. As mentioned, extended periods of use of the HMD <NUM> may result in the material of particular components, such as the face gasket <NUM>, absorbing bodily odors. As a result, a user may wish to remove the face gasket <NUM> at times, such as to "air out" the face gasket <NUM>, to clean the face gasket <NUM>, to replace the face gasket <NUM> with a new face gasket, or the like. In some embodiments, a user may wish to interchange, or swap, the face gasket <NUM> with a different type of face gasket (e.g., one with different features, profiles, contours, etc.). This allows for even further customization of the HMD <NUM> for different users.

<FIG> illustrates a partial front and bottom view of the example HMD <NUM> of <FIG> with a front portion of the HMD housing removed to reveal components of an interpupillary distance (IPD) adjustment mechanism, the IPD adjustment mechanism being adjusted to a first end of an adjustment range in <FIG>, and to a second end of the adjustment range in <FIG>, according to an embodiment of the present disclosure. The IPD adjustment mechanism of the HMD <NUM> allows for adjusting the horizontal spacing between a pair of lens tubes of the HMD <NUM>. <FIG> and <FIG> depict example lens tubes <NUM>(<NUM>) and <NUM>(<NUM>) (sometimes referred to herein as "lens assemblies") that may be brought closer together or moved farther apart using the IPD adjustment mechanism to decrease or increase, respectively. the horizontal spacing therebetween. Notably, the IPD adjustment mechanism described herein, among other things, is convenient to operate while wearing the HMD <NUM>, is operable using a single hand or finger, and includes a double-biasing assembly to provide smooth, controlled operation of the IPD adjustment mechanism over an adjustment range. This allows for fine tuning the distance between the lens tubes <NUM>(<NUM>) and <NUM>(<NUM>) to correspond to the IPD of the user.

As shown in <FIG> and <FIG>, the IPD adjustment mechanism may comprise an actuator <NUM>. The actuator <NUM> may be located on a bottom of the HMD <NUM> towards (or within) a right half or a left half of the HMD <NUM>. Although the actuator <NUM> can be implemented in any suitable way (e.g., a rotatable knob, a lever, a depressible button that toggles between adjustment positions, etc.), the actuator <NUM> shown in <FIG> and <FIG> comprises a knob that is slidable (or otherwise movable) within a channel <NUM> defined in the housing of the HMD <NUM>. The actuator <NUM> is configured to be actuated by a user of the HMD <NUM> to adjust the spacing between the lens tubes <NUM>(<NUM>) and <NUM>(<NUM>) (as depicted in <FIG> and <FIG>). Accordingly, the actuator <NUM> is accessible from outside of the housing of the HMD <NUM>. In the example of <FIG> and <FIG>, moving the actuator <NUM> to a first end of the channel <NUM> (e.g., as shown in <FIG>) maximizes the horizontal distance (or spacing) between the pair of lens tubes <NUM> of the HMD <NUM>. Moving the actuator <NUM> to a second end of the channel <NUM> (e.g., as shown in <FIG>) that is opposite the first end of the channel <NUM> minimizes the horizontal distance (or spacing) between the pair of lens tubes <NUM> of the HMD <NUM>. In this manner, users with smaller IPDs can adjust the knob towards the second end of the channel <NUM> (as shown in <FIG>), while users with larger IPDs can adjust the knob towards the first end of the channel <NUM> (as shown in <FIG>). Markings may be provided on the outer surface of the HMD housing along the channel <NUM> to indicate to a user that the horizontal spacing between the lens tubes <NUM> is adjustable. Because the actuator <NUM> and channel <NUM> are located on either a right half or a left half of the HMD <NUM>, on the bottom of the HMD <NUM>, a user can easily and conveniently slide the actuator <NUM> within the channel <NUM> using his/her right or left thumb (e.g., a single hand) to adjust the spacing between the lens tubes <NUM>. The location of the actuator <NUM> and channel <NUM>, along with its ease of operation, allow the user to adjust the lens tube <NUM> spacing with a single hand, and to do so while wearing the HMD <NUM> so that the user does not have to take off the HMD <NUM> or hold it with two hands while adjusting the lens tube <NUM> spacing. This allows for attaining the optimal lens tube <NUM> spacing quicker because the user can wear the HMD <NUM> while adjusting the lens tube <NUM> spacing to determine, in real-time, which position of the actuator <NUM> is optimal for them.

The IPD adjustment mechanism may include components internal to the housing of the HMD <NUM> that allow for smooth and effortless operation of IPD adjustment mechanism. For example, an end of the actuator <NUM> that is internal to the HMD housing may be coupled to a movable elongate member <NUM> at a first end of the elongate member <NUM>. The elongate member <NUM> may be horizontally oriented and adjacent to the bottom of the HMD <NUM>, as shown in <FIG> and <FIG>. However, it is to be appreciated that other orientations of the elongate member <NUM> are possible. A channel or slot may be defined in the elongate member <NUM> adjacent to an end of the elongate member <NUM> that is coupled to the actuator <NUM>, and an anchor <NUM> mounted to a midframe of the HMD <NUM> may extend through the channel/slot of the elongate member <NUM> to allow the elongate member <NUM> to translate bidirectionally (e.g., in a first or second horizontal direction, when the HMD <NUM> is upright oriented) over the adjustment range of the IPD adjustment mechanism. In this manner, the elongate member <NUM> is coupled to the midframe of the HMD <NUM> while being movable bidirectionally.

A first end of a first biasing member <NUM> may be coupled to a first end of the elongate member <NUM>, and a second end of the first biasing member <NUM> may be coupled to the midframe of the HMD <NUM>. Here the first end of the elongate member <NUM> (coupled to the first biasing member <NUM>) is farthest from the actuator <NUM> while a second end of the elongate member <NUM> is closest to the actuator <NUM>. The second end of the first biasing member <NUM> may be attached to the midframe of the HMD <NUM> at a point that is closer to the actuator <NUM> than the first end of the elongate member <NUM> is to the actuator <NUM>. In this manner, the first biasing member <NUM> is configured to physically bias the elongate member <NUM> in a horizontal direction by applying a biasing force to the elongate member <NUM> that resists the movement of the elongate member <NUM> in a direction of travel of the elongate member <NUM>. In the example of <FIG> and <FIG>, when the actuator <NUM> is moved from the left end of the channel <NUM> to the right end of the channel <NUM> (from the perspective of <FIG> and <FIG>), the elongate member <NUM> is translated in a rightward direction of travel, and the first biasing member <NUM> resists the rightward movement of the elongate member <NUM> due to a biasing force applied to the elongate member <NUM> in the leftward direction (from the perspective of <FIG> and <FIG>). In some embodiments, the first biasing member <NUM> is a spring whose biasing force on the elongate member <NUM> increases as the elongate member <NUM> is moved farther and farther in the rightward horizontal direction (from the perspective of <FIG> and <FIG>). This biasing force from the first biasing member <NUM> causes the sliding movement of the actuator <NUM> within the channel <NUM> to be smooth, rather than a jerky movement, when the user slides the actuator <NUM> within the channel <NUM>. Additionally, or alternatively, one or more friction members may aid in resisting the movement of the actuator <NUM> within the channel <NUM> to make the movement smoother and more controlled to fine tune the IPD adjustment with greater ease.

The elongate member <NUM> may include a plurality of teeth that span at least a portion of the elongate member <NUM> on a top side of the elongate member <NUM>. The teeth of the elongate member <NUM> engage with teeth of a rotatable gear <NUM> (sometimes referred to herein as a "spiral gear") mounted to an axle on the midframe of the HMD <NUM>. The gear <NUM> may be disposed at or near a middle of the HMD <NUM> and between a pair of movable frames <NUM>(<NUM>) and <NUM>(<NUM>), which are coupled to the pair of lens tubes <NUM>. The gear <NUM> may include a face having a pair of spiral projections <NUM>(<NUM>) and <NUM>(<NUM>) extending from the face of the gear <NUM>. A rod <NUM> (sometimes referred to herein as a "sliding rod") may be coupled to the midframe of the HMD <NUM>. The sliding rod <NUM> may be horizontally oriented (when the HMD <NUM> is upright oriented) and may substantially span a width of the HMD <NUM>. As mentioned, each lens tube <NUM> of the pair of lens tubes <NUM> may be coupled to a corresponding movable frame <NUM> within the HMD housing, and each movable frame <NUM> may include a wing member <NUM> projecting from a back side of the moveable frame <NUM> that is coupled to the sliding rod <NUM> (e.g., by the sliding rod <NUM> passing through an aperture in the wing member <NUM>). In this manner, the pair of lens tubes <NUM> may be coupled to the rod <NUM> via the movable frames <NUM>. As shown in <FIG>, each wing member <NUM> may also include a projection <NUM> that extends horizontally from the wing member <NUM> towards the gear <NUM>. The projection <NUM> that extends from the wing member <NUM> engages one of the spiral projections <NUM> extending from the face of the gear <NUM>. For example, a first projection <NUM>(<NUM>) may extend from the wing member <NUM>(<NUM>) and may engage the spiral projection <NUM>(<NUM>), while a second projection <NUM>(<NUM>) may extend from the wing member <NUM>(<NUM>) and may engage the spiral projection <NUM>(<NUM>).

A pair of second biasing members <NUM>(<NUM>) and <NUM>(<NUM>) may be coupled to the sliding rod <NUM>. For example, the second biasing members <NUM> may comprise springs that are placed over the sliding rod <NUM> and positioned between a stop <NUM> on the sliding rod <NUM> and the wing member <NUM> of each movable frame <NUM>. <FIG> and <FIG> show a first stop <NUM>(<NUM>), and a second biasing member <NUM>(<NUM>) between the first stop <NUM>(<NUM>) and the wing member <NUM>(<NUM>), as well as a second stop <NUM>(<NUM>), and a second biasing member <NUM>(<NUM>) between the second stop <NUM>(<NUM>) and the wing member <NUM>(<NUM>). Each of the second biasing members <NUM> may be fixed in position relative to the sliding rod <NUM> at one end of the second biasing member <NUM> (e.g., at the stop <NUM> on the sliding rod <NUM>), and the second biasing members <NUM> may apply a biasing force to the corresponding wing member <NUM> that is coupled to the sliding rod <NUM>, the biasing force being applied in a direction toward the gear <NUM> such that the projection <NUM> that extends horizontally from the wing member <NUM> is physically biased against the corresponding spiral projection <NUM> extending from the face of the gear <NUM>. Because the movable frames <NUM> are movable bidirectionally along the rod <NUM> between left and right sides of the HMD <NUM>, the movable frames <NUM>, and, hence, the lens tubes <NUM> coupled to the movable frames <NUM>, are moved in response to actuation of the actuator <NUM>.

As shown in <FIG> and <FIG>, a user can slide the actuator <NUM> of the IPD adjustment mechanism within the channel <NUM>, which causes the elongate member <NUM> to translate in a first direction (e.g., a rightward direction from the perspective of <FIG> and <FIG>). The teeth of the elongate member <NUM> that engage with teeth of the gear <NUM> cause the gear <NUM> to rotate. In a first rotational direction of the gear <NUM>, the spiral projections <NUM> extending from the face of the gear <NUM> may apply a force to the projections <NUM> extending from the wing members <NUM> of the movable frames <NUM> to move the movable frames <NUM> (and, hence, the lens tubes <NUM>) farther apart to increase the spacing between the lens tubes <NUM> (as shown in <FIG>). In a second rotational direction of the gear <NUM>, the pair of second biasing members <NUM> apply a biasing force to the wing members <NUM> of the movable frames <NUM> to move the movable frames <NUM> (and, hence, the lens tubes <NUM>) closer together to decrease the spacing between the lens tubes <NUM> (as shown in <FIG>). This is, in part, due to the spiral projections <NUM> on the gear <NUM> spiraling inward from respective points at a periphery of the gear <NUM> to respective points closer to a center of the gear <NUM> than the respective points at the periphery.

Notably, when the movable frames <NUM> (and, hence, the lens tubes <NUM>) are moved farther apart, the pair of second biasing members <NUM> resist the movement of the movable frames <NUM> in the respective directions of travel of each movable frame <NUM>. This causes the sliding movement of the actuator <NUM> within the channel <NUM> to be smooth and controlled movement, rather than a jerky movement, when the user slides the actuator <NUM> within the channel <NUM>. Thus, the first biasing member <NUM> and the pair of second biasing members <NUM> work together to allow for smooth and controlled sliding movement of the actuator <NUM> within the channel <NUM> so that the user can fine-tune the IPD adjustment with ease, even while wearing the HMD <NUM>. Additionally, or alternatively, one or more friction members may also aid in resisting the movement of the actuator <NUM> within the channel <NUM> to make the movement smoother and easier to fine tune the IPD adjustment. Due to the opposing biasing members and/or friction members, the actuator <NUM> is movable within the channel <NUM> to any position within the channel <NUM>, as desired by the user, and when the user removes his/her finger from the actuator <NUM>, the actuator <NUM> remains stationary at its current position within the channel <NUM>.

As depicted in <FIG> and <FIG>, actuation of the actuator <NUM> causes a corresponding adjustment of the spacing between the lens tubes <NUM> of the HMD <NUM>. For example, moving the actuator <NUM> to a first end of the channel <NUM>, as shown in <FIG> maximizes a horizontal distance (spacing) between the lens tube <NUM>(<NUM>) and the lens tube <NUM>(<NUM>). The lens tubes <NUM> may be substantially aligned horizontally. In As shown in <FIG>, moving the actuator <NUM> to a second end of the channel <NUM> minimizes the horizontal distance (spacing) between the lens tube <NUM>(<NUM>) and the lens tube <NUM>(<NUM>). Intermediate spacings can be achieved by moving the actuator <NUM> to an intermediate position within the channel <NUM>. In this sense, the actuator <NUM> can be moved in a smooth, continuous movement along the channel <NUM>, as opposed to discrete "clicks" between multiple adjustment positions, and the user feels a bidirectional resistance in either direction the actuator <NUM> is moved due to the double biasing assembly described herein.

<FIG> illustrates a partial front perspective view of the example HMD <NUM> of <FIG> with a portion of the HMD housing removed to reveal components of a field of view (FOV) adjustment mechanism, the FOV adjustment mechanism being adjusted to a first end of an adjustment range in <FIG>, according to an embodiment of the present disclosure. <FIG> shows the FOV adjustment mechanism being adjusted to a second end of the adjustment range. The FOV adjustment mechanism depicted in <FIG> and <FIG> allows for adjusting the spacing between the user's face and the lenses or the lens tubes <NUM> (or display panels) of the HMD <NUM>. This field of view (FOV) adjustment mechanism (sometimes referred to herein as an "eye-relief adjustment mechanism"), among other things, is convenient to operate while wearing the HMD, is operable using a single hand, and smoothly adjusts (e.g., increases or decreases) the distance between the lenses of the HMD <NUM> and the user's face over an adjustment range. The FOV adjustment mechanism may comprise an actuator <NUM> disposed on a first side (of two sides; namely, right and left sides) of the HMD <NUM>. In general, the actuator <NUM> is configured to be actuated by a user of the HMD <NUM>, and, accordingly, the actuator <NUM> is accessible from outside of the HMD housing.

Although the actuator <NUM> is shown as a rotatable actuator (e.g., a rotatable knob) in <FIG> and <FIG>, the actuator <NUM> may include any suitable adjustable element such as, without limitation, a dial, a lever, a wheel, and/or a slider (or slidable knob). The actuator <NUM> may be located where the head strap <NUM> adjoins the main unit <NUM> of the HMD <NUM>. The actuator <NUM> may be actuated (e.g., rotated) over an adjustment range such that the actuator can be actuated (e.g., rotated) in a first direction to a first end of the adjustment range to minimize the distance (or spacing) between the lenses and the user's face, and actuated (e.g., rotated) in a second direction that is opposite the first direction to a second end of the adjustment range to maximize the distance (or spacing) between the lenses and the user's face. In this manner, the FOV and/or the eye relief can be optimized for different users. Markings may be provided on the outer surface of the HMD housing around, or on, the actuator <NUM> to indicate to a user that the spacing between the lenses and the user's face is adjustable. Because the actuator <NUM> is located on one side (e.g., the right side or the left side) of the HMD <NUM>, a user can easily and conveniently actuate the actuator <NUM> using his/her right or left hand (e.g., a single hand) to adjust the spacing between the lenses and the user's face. The location of the actuator <NUM>, along with its ease of operation, allow the user to adjust the FOV and/or the eye relief with a single hand, and to do so while wearing the HMD <NUM> so that the user does not have to take off the HMD <NUM> or hold it with two hands while adjusting the FOV and/or eye relief. This allows for attaining the optimal FOV and/or eye relief quicker because the user can wear the HMD <NUM> while adjusting the FOV and/or eye relief to determine, in real-time, which position of the actuator <NUM> is optimal for them.

The FOV adjustment mechanism includes components internal to the housing of the HMD <NUM> that allow for uniform, smooth, controlled, and/or effortless operation of FOV adjustment mechanism. The actuator <NUM> (e.g., a rotatable knob), in addition to being rotatable, may be depressible between a first position and a second position by pushing on the actuator <NUM>, much like a depressible button. A biasing member may bias the actuator <NUM> in an outward direction relative to the HMD <NUM> such that, when a user is not pressing on the actuator <NUM>, the actuator <NUM> is physically biased in a first position where the actuator <NUM> is extended (i.e., not depressed). When the actuator <NUM> is extended, a projection (or tooth) is engaged with a detent, of a plurality of detents internal to the actuator <NUM>, which locks the actuator <NUM> in the sense that the actuator <NUM> is prevented from being rotated in either direction (clockwise or counterclockwise) over the adjustment range. A user can move the actuator <NUM> to a second position where the actuator <NUM> is depressed, which unlocks the actuator <NUM> by disengaging the projection from a detent internal to eh actuator <NUM>. In this second position, while depressing the actuator <NUM>, the user can rotate the actuator <NUM> to adjust the spacing between the lenses and the user's face, as needed. Upon letting go of the actuator <NUM>, or relieving the pressure upon the actuator <NUM>, the biasing member internal to the actuator <NUM> physically biases the actuator <NUM> in the extended, first position to engage the projection with a detent, which locks the actuator <NUM> in position (rotationally). This locking mechanism prevents unwanted adjustment of the spacing between the lenses and the user's face, such as during gameplay when the user wants the FOV and/or eye relief to remain fixed at a desired position.

The actuator <NUM> may cause rotation of a pair of gear assemblies on each side of the HMD <NUM> that are connected by a connecting rod <NUM>. The pair of gear assemblies allow for adjusting the lenses closer to, or farther from the user's face. Specifically, the main unit <NUM> of the HMD <NUM> may include a first portion that is coupled to the lens tubes <NUM>, and a second portion that is movable relative to the first portion. For example, the second portion of the HMD <NUM> may be the portion of the main unit <NUM> that is closer to (e.g., in contact with) the user's face while the user is wearing the HMD <NUM>. Referring briefly to <FIG>, this second portion <NUM> is the portion of the main unit <NUM> that the actuator <NUM> is disposed on. The first portion <NUM> of the HMD <NUM> may be the portion of the main unit <NUM> that is farther from (e.g., not in contact with) the user's face while the user is wearing the HMD <NUM>. For example, the first portion <NUM> of the HMD <NUM> may include, without limitation, the lens tubes <NUM>, the display panels, a PCB with electrical components mounted thereon, etc. These first and second portions of the HMD <NUM> are movable bidirectionally, and relative to each other by rotational actuation of the actuator <NUM>.

A first gear assembly disposed on the same side of the HMD <NUM> as the actuator <NUM> may be coupled to the actuator <NUM> and to both the first portion <NUM> of the HMD <NUM> and the second portion <NUM> of the HMD <NUM> that are movable bidirectionally, and relative to each other. The first gear assembly may include a first rotatable gear <NUM>(<NUM>) having teeth that engage teeth of an elongate member <NUM>(<NUM>). The elongate member's <NUM>(<NUM>) teeth may be disposed on a top side of the elongate member <NUM>(<NUM>). The elongate member <NUM>(<NUM>) may be oriented such that the elongate member <NUM>(<NUM>) extends in a direction from a back of the HMD <NUM> to a front of the HMD <NUM>. The elongate member <NUM>(<NUM>) may be coupled to, or engaged with, the actuator <NUM>, and the elongate member <NUM>(<NUM>) may also be coupled to the second portion <NUM> of the HMD <NUM> that is closer to the user's face than the first portion <NUM> of the HMD <NUM>. Because the elongate member <NUM>(<NUM>) is coupled to the second portion <NUM> of the HMD <NUM>, when the actuator <NUM> is rotated, the elongate member <NUM>(<NUM>) translates forward or backward to cause second portion <NUM> of the HMD <NUM> (the portion closer to the user's face) to translate forward or backward relative to the first portion <NUM> of the HMD <NUM> (the portion farther from the user's face that includes the lenses, the displays, and the PCB.

The elongate member <NUM>(<NUM>) may also include teeth that engage teeth of the first gear <NUM>(<NUM>), the first gear <NUM>(<NUM>) being mounted to an axle on the midframe of the HMD <NUM>. The first gear <NUM>(<NUM>) of the first gear assembly engages with a second rotatable gear <NUM>(<NUM>) of the first gear assembly, and the second gear <NUM>(<NUM>) is coupled to the rod <NUM> (sometimes referred to herein as a "connecting rod"). The connecting rod <NUM> may be coupled to the midframe of the HMD, and the connecting rod <NUM> may be horizontally oriented and may substantially span a width of the HMD <NUM>. The connecting rod <NUM> also connects the first gear assembly to a second gear assembly, which is disposed on a second side of the HMD <NUM> opposite the first side of the HMD <NUM> where the first gear assembly is disposed. Rotation of the second gear <NUM>(<NUM>) of the first gear assembly causes a corresponding rotation of the connecting rod <NUM>.

The second gear assembly may include a third rotatable gear that is coupled to the connecting rod <NUM>, much like the second gear <NUM>(<NUM>) of the first gear assembly is connected to the connecting rod <NUM> at the opposite end of the rod <NUM>. Rotation of the connecting rod <NUM> causes a corresponding rotation of this third gear of the second gear assembly. This third gear of the second gear assembly engages with a fourth rotatable gear of the second gear assembly, the fourth gear of the second gear assembly much like the first gear <NUM>(<NUM>) of the first gear assembly. Accordingly, the fourth gear of the second gear assembly may similarly be mounted to an axle on the midframe of the HMD <NUM>. Teeth of the fourth gear engage with teeth of a second elongate member <NUM>(<NUM>) of the second gear assembly. This second elongate member <NUM>(<NUM>) may also have teeth on a top side of the elongate member <NUM>(<NUM>), and the elongate member <NUM>(<NUM>) of the second gear assembly may similarly be attached to the second portion <NUM> of the HMD <NUM> (the portion closer to the user's face) that is movable relative to the first portion <NUM> of the HMD <NUM> (the portion farther from the user's face that includes the lenses, the displays, and the PCB), except that the second elongate member <NUM>(<NUM>) is coupled to the second portion <NUM> of the HMD <NUM> on the opposite side of the second portion <NUM>, as compared to the side where the first elongate member <NUM>(<NUM>) is coupled to the second portion <NUM> of the HMD <NUM>.

Accordingly, as the actuator <NUM> is rotated, both elongate members <NUM>(<NUM>) and <NUM>(<NUM>) of the respective gear assemblies translate forward or backward, depending on the direction of rotation of the actuator <NUM>, to cause the first and second portions of the HMD <NUM> to translate in opposite directions relative to each other, thereby adjusting the FOV and/or eye relief. For example, the first portion <NUM> of the HMD <NUM> (the portion farther from the user's face that includes the lenses, the displays, and the PCB) may move relative to the second portion <NUM> of the HMD <NUM> (the portion closer to the user's face) in a first direction away from the second portion <NUM>, or in a second direction toward the second portion <NUM>. Controlling the movement of these HMD portions using elongate members <NUM>(<NUM>) and <NUM>(<NUM>) on opposing sides of the HMD <NUM> that are connected by a connecting rod <NUM> allows for uniform translation of the first and second portions of the HMD <NUM> relative to each other without any wobbling (or racking) of these portions as they translate bidirectionally forward and backward. This smooth, uniform adjustment provided by the FOV (or eye-relief) adjustment mechanism allows for convenient operation by a user, using a single hand, while wearing the HMD <NUM>.

<FIG> illustrates a front perspective view of the example HMD <NUM> of <FIG>, <FIG> depicting example locations of inconspicuous spectrum-transmissive windows <NUM>(<NUM>)-(N) (collectively <NUM>, N being any suitable integer) in the housing of the HMD <NUM>, according to an embodiment of the present disclosure. In some embodiments, a plurality of corresponding spectrum-specific sensors are mounted inside the HMD housing behind the spectrum-transmissive windows <NUM> as shown by the dashed lines behind each window <NUM>. The sensors within the HMD housing are sensitive to light in a specific spectrum. In some embodiments, the spectrum-transmissive windows <NUM> are infrared (IR)-transmissive windows, and the spectrum-specific sensors positioned behind the windows <NUM> are IR sensors (i.e., sensors configured to detect light in the IR spectrum). Although the examples herein predominantly pertain to IR-transmissive windows and IR sensors, it is to be appreciated that any mention herein of "IR-transmissive" may be replaced with "spectrum-transmissive" for spectrums other than the IR spectrum, and "IR sensors" may be replaced with "spectrum-specific sensors" to describe sensors configured to detect electromagnetic radiation in spectrums other than the IR spectrum. Furthermore, instead of sensors, a plurality of corresponding spectrum-specific beacons may be mounted inside the HMD housing behind the spectrum-transmissive windows <NUM>, the beacons configured to emit light (electromagnetic radiation) in a specific spectrum.

Accordingly, the HMD <NUM> may comprise a housing made of a spectrum-transmissive (IR-transmissive) material, wherein an outer surface of the housing is coated with an IR-opaque material, and wherein one or more locations on the outer surface are devoid of the IR-opaque material, the location(s) corresponding to the windows <NUM>. One or more spectrum-specific sensors (and/or beacons) may be disposed behind the housing at the one or more locations corresponding to the windows <NUM>. In some embodiments, the outer surface of the HMD housing is also coated with a spectrum-transmissive coating that covers the spectrum-opaque material and the one or more locations on the outer surface that are devoid of the spectrum-opaque material. Any suitable IR-transmissive and IR-opaque materials known to a person having ordinary skill in the art can be used herein to create IR-transmissive windows <NUM> that allow electromagnetic radiation (light) in the IR spectrum to pass therethrough. For example, IR-opaque materials may include acrylics or paints that are configured to block electromagnetic radiation in the IR spectrum. An IR-transmissive polycarbonate plastic can be used for the based material of the HMD housing.

The thickness of the housing at the location(s) of the window(s) <NUM> may be thinner than a thickness of the remainder of the HMD housing. In this manner, if sensors are mounted to an inner surface of the HMD housing directly behind the windows <NUM>, the sensors can be brought closer to the outer surface of the HMD housing to minimize the size of the window <NUM>. That said, the size of each spectrum-transmissive window <NUM> may be configurable based on the tolerances for placement of the corresponding sensor behind the spectrum-transmissive window <NUM>. In some embodiments, a spectrum-specific sensor is mounted inside the HMD housing using adhesive behind a corresponding spectrum-transmissive window <NUM>. The spectrum-transmissive window <NUM> may be configured to filter out (or block) electromagnetic radiation in at least one spectrum (e.g., the visible spectrum), while allowing electromagnetic radiation in a specific spectrum (e.g., light in the IR spectrum) to pass through the window <NUM>.

As shown in <FIG>, a plurality of spectrum-transmissive windows <NUM> may be provided on the housing of the HMD <NUM>. At least some of the plurality of spectrum-transmissive windows <NUM> may be located on a front of the HMD <NUM> along a top, along a bottom, and/or along one or more sides of the front of the HMD <NUM>. At least some of the windows <NUM> may be located on a top of the HMD <NUM>, a bottom of the HMD <NUM>, and/or on one or more sides of the HMD <NUM>, as shown in <FIG>. Covering the HMD <NUM> in this manner provides for optimal tracking using an optical tracking system, which may include one or more beacons that emit electromagnetic radiation in the specific spectrum. For example, one or more beacons positioned in an environment of the HMD <NUM> may sweep beams (e.g., fan beams) of IR light across a play space, and the IR sensors disposed inside the HMD housing behind the IR-transmissive windows <NUM> may detect the beam sweeps, and possibly synchronization pulses emitted by the optical tracking system.

The processes described herein are illustrated as a collection of blocks in a logical flow graph, which represent a sequence of operations. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order and/or in parallel to implement the processes.

To process for manufacturing a HMD housing that includes a plurality of spectrum-transmissive windows <NUM> may include, at <NUM>, forming a HMD housing made of a spectrum-transmissive material (e.g., an IR-transmissive polycarbonate plastic). As shown by sub-block <NUM>, forming the housing may include injection molding the HMD housing using an injection molding technique.

At <NUM>, material may be removed from the inner surface of the HMD housing at the locations where spectrum-transmissive windows <NUM> are to be made. This removal of material decreases the thickness of the HMD housing only at the locations where the spectrum-specific sensors (and/or beacons) are to be positioned (e.g., mounted), thereby allowing the sensors/beacons to be brought closer to the outer surface of the HMD housing when positioned next to (e.g., mounted on) the inner surface of the HMD housing, behind the spectrum-transmissive windows <NUM>. Positioning the sensors closer to the outer surface in this manner allows for achieving a field of view (FOV) for the sensors with particular angular range while minimizing the size of the spectrum-transmissive windows <NUM>. In some embodiments, removing material from the inner surface creates recessions in the HMD housing where the sensors/beacons are to be positioned (e.g., mounted). Removing material from the inner surface of the HMD housing also allows for keeping the outer surface flat and smooth (as opposed to creating recessions in the outer surface of the HMD housing).

At <NUM>, the outer surface of the HMD housing can be painted with a spectrum-opaque material (e.g., coating the outer surface of the housing with an IR-opaque film). This may include painting substantially the entirety of the outer surface of the HMD housing to cover the outer surface with the spectrum-opaque material.

At <NUM>, the spectrum-opaque material can be selectively removed from the outer surface at locations behind which the sensors/beacons are to be mounted. This creates spectrum-transmissive windows <NUM> in the HMD housing. As shown by sub-block <NUM>, the selective material removal may include removing the spectrum-opaque material using a laser etching technique. In some embodiments, a circular portion of spectrum-opaque material is removed to create a circular spectrum-transmissive window <NUM> (sometimes referred to herein as an "aperture") in the HMD housing. In some embodiments, a photolithography process can be used at block <NUM> to remove the spectrum-opaque material from the outer surface at the locations of the sensors/beacons. In some embodiments, removing spectrum-opaque material at block <NUM> can include placing stickers on the outer surface of the HMD housing at locations where the spectrum-transmissive windows <NUM> are to be made prior to block <NUM>, then painting the outer surface of the HMD housing with the spectrum-opaque material at block <NUM>, and removing the stickers at block <NUM> to selectively remove the spectrum-opaque material at the sticker locations to create spectrum-transmissive windows <NUM> where the stickers were located. In some embodiments, a fixture having a pattern of pins can be moved to a position where the pins are brought into contact with the outer surface of the HMD housing prior to block <NUM>, and, while the pins are contacting the outer surface, painting the outer surface of the HMD housing with the spectrum-opaque material at block <NUM>, and, removing the pins from the HMD housing at block <NUM> to selectively "remove" the spectrum-opaque material at the locations where the pins were located to create spectrum-transmissive windows <NUM> at those locations. Yet another way of creating spectrum-transmissive windows <NUM> may be to apply an oleophobic coating on the HMD housing in a particular pattern prior to block <NUM>, then paint the outer surface of the HMD housing with the spectrum-opaque material at block <NUM>, at which point the spectrum-opaque material adheres to portions of the outer surface that are free from the oleophobic coating, and does not adhere to portions of the outer surface that are coated with the oleophobic coating.

At <NUM>, after removing the spectrum-opaque material at selective locations, the outer surface of the HMD housing may be painted with a spectrum-transmissive coating (e.g., a hard, clear coat material (or film) that is IR-transmissive) to create a HMD housing with a smooth outer surface and spectrum-transmissive windows <NUM> that are barely visible to the naked eye, even in broad daylight. In low-light environments, the spectrum-transmissive windows <NUM> are at least inconspicuous, if not invisible to the naked eye, and the outer surface of the HMD housing has a smooth appearance.

The disclosed process for manufacturing a HMD housing that includes a plurality of spectrum-transmissive windows <NUM> is more cost effective than manufacturing a similar HMD housing using a so-called "double shot" injection molding process, which involves fabricating a majority of the HMD housing from IR-opaque plastic, and fabricating small portions of the HMD housing from IR-transmissive plastic to create windows over IR sensors mounted inside the HMD housing. By contrast, the disclosed manufacturing process for creating spectrum-transmissive (e.g., IR-transmissive) windows <NUM> on a HMD housing involves using a generally spectrum-transmissive material as the base material for the HMD housing, and then coating the majority of the HMD housing with an spectrum-opaque material, which is more cost effective way, as compared to the double-shot process, to manufacture a HMD housing that includes a plurality of spectrum-transmissive windows <NUM>. Since the HMD housing is made from a spectrum-transmissive material, some light of the specific spectrum (e.g., IR light, if the specific spectrum is the IR spectrum) may pass through a spectrum-transmissive window <NUM> to the underlying sensor while some light of the specific spectrum may be internally reflected within the HMD housing itself. As a result, there is a possibility that some light of the specific spectrum received through one spectrum-transmissive window <NUM>(<NUM>) may reach a nearby sensor (e.g., a sensor behind window <NUM>(<NUM>)) due to these internal reflections. To mitigate the impact of internally reflected light of the specific spectrum on a nearby spectrum-specific sensor, the spectrum-transmissive material used as the base material for the HMD housing may be modified with an additive material that makes the HMD housing slightly more absorptive of the light of the specific spectrum (e.g., slightly more IR absorptive), which mitigates the extent of internal reflections.

Another way of manufacturing a HMD housing that includes a plurality of spectrum-transmissive windows involves using a so-called "in-mold label. " For example, a spectrum-transmissive ink (e.g., IR-transmissive ink) can be printed on a plastic sheet in a particular pattern corresponding to the positioning of the spectrum-transmissive windows on the to-be-formed HMD housing, the sheet with the spectrum-transmissive ink printed thereon can be thermoformed into a desired shape for the HMD housing, and then a spectrum-opaque material can be over-molded onto the thermoformed sheet to create a HMD housing with spectrum-transmissive windows. Yet another way of manufacturing a HMD housing that includes a plurality of spectrum-transmissive windows involves a so-called "laser direct structuring" technique. For example, a HMD housing may be injection molded, and a laser beam may be used to create a recessed pattern in the HMD housing, and a metallization process may plate a metal onto the recessed pattern in the HMD housing to create spectrum-transmissive windows in the HMD housing.

As mentioned, the thickness of the HMD housing at the locations of the spectrum-transmissive windows <NUM> may be made as thin as possible (e.g., by using a subtractive manufacturing process that removes material from the inner surface of the HMD housing at those locations) while a remainder of the HMD housing can maintain a greater thickness to provide rigidity to the HMD housing. Having locally-thinned portions of the HMD housing where the spectrum-specific sensors/beacons are located means that the sensors can be positioned closer to the outer surface of the HMD housing, which reduces the amount of refraction and the amount of optical artifacts as light of the specific spectrum passes through the spectrum-transmissive windows <NUM>. Because the sensors/beacons disposed behind the windows <NUM> can be used in an optical tracking system that tracks the pose of the HMD <NUM> as it moves within a volume, the reduction of refraction and optical artifacts means that a more accurate spectrum-specific (e.g., IR) beam sweep window is achieved. Furthermore, the size of the spectrum-transmissive windows may restrict the angular range over which each spectrum-specific sensor receives light of the specific spectrum, and/or the angular range over which a spectrum-specific beacon can emit light of the specific spectrum. In some embodiments, the spectrum-transmissive windows <NUM> are sized such that the sensors receive, and/or the beacons emit, light of the specific spectrum over an angular range of about <NUM> degrees. A goal may be to make the size of each spectrum-transmissive window <NUM> as small as possible (e.g., for aesthetic purposes), without overly restricting the angular range over which the sensor receives, and/or the beacon emits, the light of the specific spectrum. In some embodiments, the diameter of an individual spectrum-transmissive window may be within a range of <NUM> millimeters to <NUM> millimeters, or within a range of <NUM> millimeters to <NUM> millimeters.

It is to be appreciated that optical tracking of the HMD <NUM> is merely one example use of the spectrum-specific sensors/beacons and the spectrum-transmissive windows <NUM> described herein. For example, a spectrum-specific camera (e.g., an IR camera) may be mounted internally within the HMD housing and underlying a spectrum-transmissive window to remain inconspicuous when the HMD <NUM> is fully assembled. Such cameras may be tracking cameras, or any other type of sensor that is configured to detect electromagnetic radiation of a specific spectrum.

Claim 1:
A head-mounted display, HMD, (<NUM>) comprising:
a rod (<NUM>) coupled to a midframe of the HMD;
a pair of lens tubes (<NUM>) coupled to the rod, each lens tube being movable bidirectionally along the rod;
an actuator (<NUM>) accessible from outside of a housing of the HMD;
a movable elongate member (<NUM>) coupled to the actuator and to the midframe;
a first biasing member (<NUM>) coupled to the movable elongate member and to the midframe, the first biasing member configured to apply a biasing force to the movable elongate member to resist movement of the movable elongate member in a direction of travel of the movable elongate member as the movable elongate member moves;
a rotatable gear (<NUM>) coupled to the midframe and disposed between the pair of lens tubes, the rotatable gear being engaged with the movable elongate member; and
a pair of second biasing members (<NUM>) coupled to the rod, the pair of second biasing members configured to physically bias the pair of lens tubes toward the rotatable gear.