Patent Description:
Head-mounted displays such as virtual reality glasses use lenses to display images for a user. A display may create images for each of a user's eyes. A lens may be placed between each of the user's eyes and a portion of the display so that the user may view virtual reality content.

If care is not taken, a head-mounted display may be vulnerable to damage. An optical system in the head-mounted display may include a lens directly adjacent to a display, which runs the risk of unwanted collisions between the lens and the display in the event that the head-mounted display is dropped or hit by an external object. Such collisions can damage the lens and the display in the head-mounted device.

It would therefore be desirable to be able to provide improved head-mounted displays. <CIT> discloses a head-mounted display device which includes a mechanism to move lenses across the optical path.

The invention is defined by the independent claim. A selection of optional features of the invention is set out in the dependent claims.

Head-mounted displays may be used for virtual reality and augmented reality systems. For example, a pair of virtual reality glasses that is worn on the head of a user may be used to provide a user with virtual reality content.

An illustrative system in which a head-mounted display such as a pair of virtual reality glasses is used in providing a user with virtual reality content is shown in <FIG>. As shown in <FIG>, virtual reality glasses (head-mounted display) <NUM> may include a display system such as display system <NUM> that creates images and may have an optical system such as lens system <NUM> through which a user (see, e.g., user's eyes <NUM>) may view the images produced by display system <NUM> by looking in direction <NUM>.

Display system <NUM> may be based on a liquid crystal display (e.g., liquid-crystal-on-silicon), an organic light-emitting diode display, an emissive display having an array of crystalline semiconductor light-emitting diode dies, and/or displays based on other display technologies. Separate left and right displays may be included in system <NUM> for the user's left and right eyes or a single display may span both eyes.

Visual content (e.g., image data for still and/or moving images) may be provided to display system (display) <NUM> using control circuitry <NUM> that is mounted in glasses (head-mounted display) <NUM> and/or control circuitry that is mounted outside of glasses <NUM> (e.g., in an associated portable electronic device, laptop computer, or other computing equipment). Control circuitry <NUM> may include storage such as hard-disk storage, volatile and non-volatile memory, electrically programmable storage for forming a solid-state drive, and other memory. Control circuitry <NUM> may also include one or more microprocessors, microcontrollers, digital signal processors, graphics processors, baseband processors, application-specific integrated circuits, and other processing circuitry. Control circuitry <NUM> may use display system <NUM> to display visual content such as virtual reality content (e.g., computer-generated content associated with a virtual world), pre-recorded video for a movie or other media, or other images. Illustrative configurations in which control circuitry <NUM> provides a user with virtual reality content using display system <NUM> may sometimes be described herein as an example. In general, however, any suitable content may be presented to a user by control circuitry <NUM> using display system <NUM> and lens system <NUM> of glasses <NUM>.

Communications circuits in circuitry <NUM> such as communications circuitry <NUM> may be used to transmit and receive data (e.g., wirelessly and/or over wired paths). Communications circuitry <NUM> may include wireless communication circuitry such as one or more antennas and associated radio-frequency transceiver circuitry. Transceiver circuitry in communications circuitry <NUM> may include wireless local area network transceiver circuitry (e.g., WiFi® circuitry), Bluetooth® circuitry, cellular telephone transceiver circuitry, ultra-wideband communications transceiver circuitry, millimeter wave transceiver circuitry, near-field communications circuitry, satellite navigation system circuitry such as Global Positioning System (GPS) receiver circuitry (e.g., for receiving GPS signals at <NUM> or for handling other satellite positioning data), and/or wireless circuitry that transmits and/or receives signals using light (e.g., with light-emitting diodes, lasers, or other light sources and corresponding light detectors such as photodetectors). Antennas in communications circuitry <NUM> may include monopole antennas, dipole antennas, patch antennas, inverted-F antennas, loop antennas, slot antennas, other antennas, and/or antennas that include antenna resonating elements of more than one type (e.g., hybrid slot-inverted-F antennas, etc.).

If desired, control circuitry <NUM> may determine the location of glasses <NUM> using communications circuitry <NUM>. For example, control circuitry <NUM> may determine the location of glasses <NUM> by processing wireless signals (e.g., ultra-wideband signals, Bluetooth® signals, WiFi® signals, millimeter wave signals, or other suitable signals) using signal strength measurement schemes, time based measurement schemes such as time of flight measurement techniques, time difference of arrival measurement techniques, angle of arrival measurement techniques, triangulation methods, time-of-flight methods, using a crowdsourced location database, and/or other suitable measurement techniques. If desired, control circuitry <NUM> may determine the location of glasses <NUM> using Global Positioning System receiver circuitry in circuitry <NUM> and/or using sensors <NUM> such as proximity sensors (e.g., infrared proximity sensors or other proximity sensors), depth sensors (e.g., structured light depth sensors that emit beams of light in a grid, a random dot array, or other pattern, and that have image sensors that generate depth maps based on the resulting spots of light produced on target objects), sensors that gather three-dimensional depth information using a pair of stereoscopic image sensors, lidar (light detection and ranging) sensors, radar sensors, using image data from a camera, using motion sensor data, and/or using other circuitry in glasses <NUM>.

Input-output devices <NUM> may be coupled to control circuitry <NUM>. Input-output devices <NUM> may be used to gather user input from a user, may be used to make measurements on the environment surrounding glasses <NUM>, may be used to provide output to a user, and/or may be used to supply output to external electronic equipment. Input-output devices <NUM> may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light-emitting diodes for providing a user with visual output, and/or other input-output circuitry.

Input-output devices <NUM> may include sensors <NUM>. Sensors <NUM> may include force sensors, temperature sensors, magnetic sensors, proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, and/or other sensors. For example, sensors <NUM> may include a color ambient light sensor or other ambient light sensor <NUM> for gathering ambient light measurements (e.g., ambient light levels such as ambient light luminance measurements and/or ambient light color measurements such as color temperature measurements and/or color coordinate measurements). Ambient light sensors <NUM> may include inward facing ambient light sensors (e.g., facing eyes <NUM>) and/or outward facing ambient light sensors (e.g., facing the environment in front of the user).

Sensors <NUM> may include one or more cameras <NUM> (e.g., digital image sensors) including cameras for capturing images of the user's surroundings, cameras for performing gaze detection operations by viewing eyes <NUM>, and/or other cameras. Cameras <NUM> may include inward facing cameras (e.g., facing eyes <NUM>) and/or outward facing cameras (e.g., facing the environment in front of the user).

Sensors <NUM> may include one or more motion sensors <NUM>. Motion sensors <NUM> may include one or more accelerometers, compasses, gyroscopes, barometers, pressure sensors, magnetic sensors, inertial measurement units that contain some or all of these sensors, and/or other sensors for measuring orientation, position, and/or movement of glasses <NUM>. Motion sensors <NUM> may produce sensor data that indicates whether glasses <NUM> are in freefall and/or whether glasses <NUM> are being removed from or placed on a user's head. For example, an upward motion arc or lifting from a surface may indicate glasses <NUM> are being placed on or have been placed on a user's head, whereas a downward motion arc or setting down onto a surface may indicate that glasses <NUM> are being removed or have been removed from a user's head.

<FIG> is a cross-sectional side view of glasses <NUM> showing how lens system <NUM> and display system <NUM> may be supported by head-mounted support structures such as housing <NUM> for glasses <NUM>. Housing <NUM> may have the shape of a frame for a pair of glasses (e.g., glasses <NUM> may resemble eyeglasses), may have the shape of a helmet (e.g., glasses <NUM> may form a helmet-mounted display), may have the shape of a pair of goggles, or may have any other suitable housing shape that allows housing <NUM> to be worn on the head of a user. Configurations in which housing <NUM> supports lens system <NUM> and display system <NUM> in front of a user's eyes (e.g., eyes <NUM>) as the user is viewing system <NUM> and display system <NUM> in direction <NUM> may sometimes be described herein as an example. If desired, housing <NUM> may have other suitable configurations.

Housing <NUM> may be formed from plastic, metal, fiber-composite materials such as carbon-fiber materials, wood and other natural materials, fabric, glass, silicone, other materials, and/or combinations of two or more of these materials.

Input-output devices <NUM> and control circuitry <NUM> may be mounted in housing <NUM> with lens system <NUM> and display system <NUM> and/or portions of input-output devices <NUM> and control circuitry <NUM> may be coupled to glasses <NUM> using a cable, wireless connection, or other signal paths.

Display system <NUM> may include a source of images such as pixel array <NUM>. Pixel array <NUM> may include a two-dimensional array of pixels P that emit image light. Pixels P may be liquid-crystal-on-silicon pixels (e.g., with a frontlight), organic light-emitting diode pixels, light-emitting diode pixels formed from semiconductor dies, liquid crystal display pixels with a backlight, etc.). Display system <NUM> may include additional layers such as additional layers <NUM>. Additional layers <NUM> may include one or more polarizers (e.g., one or more linear polarizers, to provide polarized image light), one or more wave plates (e.g., a quarter wave plate to provide circularly polarized image light), one or more optical films, and/or other layers.

Lens system <NUM> may include one or more lenses. Lenses in lens system <NUM> may include one or more plano-convex lenes (e.g., a first plano-convex lens having a convex surface <NUM> facing display system <NUM> and a second plano-convex lens having a concave surface <NUM> facing eyes <NUM>). This is, however, merely illustrative. Other lens arrangements may be used in lens system <NUM>, if desired. Lens system <NUM> may include one lens, two lenses, three lenses, or more than three lenses.

Optical structures such as partially reflective coatings, wave plates, reflective polarizers, linear polarizers, antireflection coatings, and/or other optical components may be incorporated into glasses <NUM> (e.g., system <NUM>, etc.). These optical structures may allow light rays from display system <NUM> to pass through and/or reflect from surfaces in lens system <NUM> to provide lens system <NUM> with a desired lens power.

As shown in <FIG>, glasses <NUM> may include one or more actuators such as actuators <NUM>. Actuators <NUM> may be linear or rotational and may include electric actuators, mechanical actuators, electromechanical actuators, pneumatic actuators, hydraulic actuators, and/or other suitable actuators. Actuators <NUM> may be used to adjust the distance D between lens system <NUM> and display system <NUM>. Control circuitry <NUM> may, if desired, use actuators <NUM> to adjust distance D to accommodate the user's eye prescription (e.g., to accommodate different diopter ranges). For example, control circuitry <NUM> may adjust distance D to one value according to the prescription of a first user and may adjust distance D to another value according to the prescription of a second user. To achieve the desired distance D, actuator <NUM> may be configured to move lens system <NUM> along the Z-axis while display system <NUM> remains fixed, may be configured to move display system <NUM> along the Z-axis while lens system <NUM> remains fixed, and/or may be configured to move both lens system <NUM> and display system <NUM> along the Z-axis.

If desired, control circuitry <NUM> also uses actuators <NUM> to move lens system <NUM> and/or display system <NUM> along the Y-axis to accommodate different interpupillary distances associated with different viewers. Control circuitry <NUM> may measure the interpupillary distance of each viewer by capturing images of the viewer's eyes with camera <NUM> or other sensors and processing the resulting eye position data to extract information on the locations of the viewers pupils. Control circuitry <NUM> may match the distance between the centers of left and right lens systems <NUM> to the measured interpupillary distance.

If desired, actuators <NUM> may be configured to move display system <NUM> and/or lens system <NUM> in other ways. In general, actuators <NUM> may be configured to move display system <NUM> and/or lens system <NUM> in any suitable fashion (e.g., linearly along the X, Y, and/or Z axes, and/or rotationally about the X, Y, and/or Z axes).

Display system <NUM> and optical system <NUM> of glasses <NUM> may be configured to display images for a user's eyes <NUM> using a lightweight and compact arrangement. In some arrangements, display system <NUM> may be relatively close to lens system <NUM>. For example, when glasses <NUM> are in use, the distance D between display system <NUM> and lens system <NUM> may be between. <NUM> and <NUM>, between. <NUM>, between. <NUM> and <NUM>, less than <NUM>, greater than <NUM>, or other suitable distance.

This type of compact arrangement may raise the risk of impact between display system <NUM> and lens system <NUM>. Glasses <NUM> may be dropped, or an external object may strike glasses <NUM>. If care is not taken, these types of incidents may cause collisions between lens system <NUM> and display system <NUM>, which can cause damage to one or both system.

To protect display system <NUM> and lens system <NUM>, control circuitry <NUM> may operate glasses <NUM> in first and second modes such as an active use mode and a protected mode. When glasses <NUM> are in active use mode, glasses <NUM> may operate normally and control circuitry <NUM> may set distance D to any suitable distance (e.g., may set distance D to a minimum distance, a maximum distance, or any other suitable distance). Control circuitry <NUM> may, for example, set distance D to a distance that accommodates the user's eye prescription.

When glasses <NUM> are in protected mode, control circuitry <NUM> may take certain actions to protect display system <NUM> and lens system <NUM>. This may include using actuators <NUM> to move display system <NUM> and/or lens system <NUM> along the Z-axis to increase distance D, using actuators <NUM> to move display system <NUM> and/or lens system <NUM> along the Y-axis to increase the lateral distance between display system <NUM> and/or lens system <NUM>, using actuators <NUM> to rotate display system <NUM> away from lens system <NUM> or vice versa, inserting a protective layer between display system <NUM> and lens system <NUM> such as a layer of air, fluid, and/or a layer of material that helps prevent collisions between display system <NUM> and lens system <NUM>.

If desired, control circuitry <NUM> may take other actions to place glasses <NUM> in protected mode. For example, control circuitry <NUM> may provide a protective layer on one or more outer surfaces of glasses <NUM> to protect glasses <NUM> from undesired impact. This may include expanding an outer structure (e.g., expanding a face seal or other air-filled structure), deploying a protective layer across the front of glasses <NUM>, and/or taking other suitable actions. Arrangements in which operating glasses <NUM> in protected mode includes taking steps to prevent collisions between display system <NUM> and lens system <NUM> are sometimes described herein as an illustrative example.

Control circuitry <NUM> may determine when to operate glasses <NUM> in active use mode and when to operate glasses <NUM> in protected mode based on sensor data from sensors <NUM>, based on on/off status information, based on location information, and/or based on other information. For example, control circuitry <NUM> may use sensors <NUM>, on/off status information, and/or location information to determine when device <NUM> is accidentally dropped, to determine when device <NUM> is not in use, to determine when an incoming external object is likely to strike glasses <NUM>, and/or to identify other scenarios in which it may be desirable to place glasses <NUM> in protected mode.

As examples, control circuitry <NUM> may place glasses <NUM> in protected mode when data from motion sensor <NUM> indicates that glasses <NUM> are in freefall, when data from motion sensor <NUM> and/or an inward-facing camera <NUM> indicates that glasses <NUM> have been removed from a user's head, when data from an outward-facing camera <NUM> indicates that an external object is nearing contact with glasses <NUM>, when glasses <NUM> have been turned off or are otherwise not in use, when location information indicates that glasses <NUM> are outside, and/or when other information indicates that glasses <NUM> should be placed in protected mode.

Control circuitry <NUM> may place glasses <NUM> in active use mode when data from motion sensor <NUM> indicates that glasses <NUM> are being lifted off of a surface, when data from motion sensor <NUM> and/or an inward-facing camera <NUM> indicates that glasses <NUM> have been placed on a user's head, when data from an outward-facing camera <NUM> indicates that an external object is no longer nearing contact with glasses <NUM>, when glasses <NUM> have been turned on or are otherwise in use, when location information indicates that glasses <NUM> are inside, and/or when other information indicates that glasses <NUM> should be placed in active use mode. These examples are merely illustrative. In general, control circuitry <NUM> may place glasses <NUM> in active use mode or protected mode in response to any suitable information.

Control circuitry <NUM> may control the left and right systems of glasses <NUM> separately (e.g., such that determining whether to operate the left or right system in active use mode or protected mode is done on a per-eye basis) or control circuitry may control the left and right systems of glasses <NUM> together (e.g., such that the left and right systems are always operated in the same mode).

In some arrangements, glasses <NUM> may be operated in an active use mode where display system <NUM> is already sufficiently spaced apart from lens system <NUM> (e.g., due to a given user's particular eye prescription). In these scenarios, it may not be necessary for control circuitry <NUM> to take any action to place glasses <NUM> in protected mode.

<FIG> show how control circuitry <NUM> may place glasses <NUM> in active use mode or protected mode by changing the distance D between lens system <NUM> and display system <NUM>. In the active use mode shown in <FIG>, lens system <NUM> is spaced apart from display system <NUM> by distance D1. In the protected mode of <FIG>, lens system <NUM> is spaced apart from display system <NUM> by distance D2, which is greater than D1. D1 may be any suitable distance (e.g., a distance based on the user's eye prescription or other suitable distance). D1 may, for example, be between. <NUM> and <NUM>, between. <NUM>, between. <NUM> and <NUM>, less than <NUM>, greater than <NUM>, or other suitable distance. D2 may be between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, greater than <NUM>, or less than <NUM>. D2 may be a maximum distance possible between lens system <NUM> and display system <NUM> or may be other suitable distance.

Control circuitry <NUM> may shift from the active mode configuration of <FIG> to the protected mode configuration of <FIG> using actuator <NUM>. Actuator <NUM> may be configured to move lens system <NUM> along the Z-axis (e.g., along an optical axis associated with lens system <NUM>) while display system <NUM> remains fixed, may be configured to move display system <NUM> along the Z-axis while lens system <NUM> remains fixed, and/or may be configured to move both lens system <NUM> and display system <NUM> along the Z-axis. The actuator that is used to switch between active and protected mode may be the same actuator that controls distance D of <FIG> for accommodating different diopter ranges (e.g., one actuator <NUM>, sometimes referred to as a focus motor, may be used for eye prescription accommodation and switching between active and protected mode), or the actuator that is used to switch between active and protected mode may be a different actuator from the actuator that controls distance D for accommodating different diopter ranges.

<FIG> show an example in which lens system <NUM> includes multiple lenses and only one lens is adjusted to switch between active use mode and protected mode. As shown in <FIG>, lens system <NUM> include first lens <NUM> and second lens <NUM>. Second lens <NUM> (sometimes referred to as interposer lens <NUM>) may be interposed between display system <NUM> and first lens <NUM>. Control circuitry <NUM> may place glasses <NUM> in active use mode or protected mode by changing the position of interposer lens <NUM>.

In the active use mode shown in <FIG>, first lens <NUM> is spaced apart from interposer lens <NUM> by distance D3, and interposer lens <NUM> is spaced apart from display system <NUM> by distance D4. In the protected mode of <FIG>, first lens <NUM> is spaced apart from interposer lens <NUM> by distance D5, and interposer lens <NUM> is spaced apart from display system <NUM> by distance D6.

Control circuitry <NUM> may shift from the active mode configuration of <FIG> to the protected mode configuration of <FIG> using actuator <NUM>. Actuator <NUM> may be configured to move interposer lens <NUM> along the Z-axis while display system <NUM> and first lens <NUM> remain fixed, may be configured to move both lenses <NUM> and <NUM> along the Z-axis while display system <NUM> remains fixed, and/or may be configured to move display system <NUM> along the Z-axis while both lenses <NUM> and <NUM> remain fixed.

In arrangements where only interposer lens <NUM> is moved and display system <NUM> and first lens <NUM> are fixed, distance D6 is greater than distance D4, and distance D5 is less than distance D3. In arrangements where both lenses <NUM> and <NUM> are moved and display system <NUM> is fixed, distance D6 is greater than distance D4, and distance D5 is less than, greater than, or equal to distance D3. In arrangements where both lenses <NUM> and <NUM> are fixed and display system <NUM> is moved, distance D6 is greater than distance D4, and distance D5 is equal to distance D3.

<FIG> shows an unclaimed example in which control circuitry <NUM> shifts between active use mode and protected mode by rotating display system <NUM> relative to lens system <NUM>. As shown in <FIG>, control circuitry <NUM> use actuator <NUM> to shift glasses <NUM> from active use mode to protected mode by rotating display system <NUM> about rotational axis <NUM>. This moves display system <NUM> in direction <NUM> from an active use position (where normal axis n is parallel to the Z-axis) to a protected position (indicated with dashed lines), with increased distance between display system <NUM> and apex <NUM> of lens system <NUM>. To place glasses <NUM> in active use mode, control circuitry <NUM> may rotate display system <NUM> back in direction <NUM> about axis <NUM>. If desired, display system <NUM> may rotate about a different axis. Axis <NUM> of <FIG> is merely illustrative. Arrangements where actuator <NUM> rotates lens system <NUM> instead of or in addition to rotating display system <NUM> may also be used.

<FIG> shows an unclaimed example in which control circuitry <NUM> shifts between active use mode and protected mode by moving lens system <NUM> laterally relative to display system <NUM>. As shown in <FIG>, control circuitry <NUM> use actuator <NUM> to shift glasses <NUM> from active use mode to protected mode by shifting lens system <NUM> in direction <NUM> (e.g., parallel to the X- axis) to a protected position (indicated with dashed lines).

The actuator that is used to switch between active and protected mode of <FIG> may be the same actuator that adjusts the lateral position of lens system <NUM> for accommodating different interpupillary distances of different users (e.g., one actuator <NUM>, sometimes referred to as an interpupillary distance motor, may be used for interpupillary distance accommodation and switching between active and protected mode), or the actuator that is used to switch between active and protected mode may be a different actuator from the actuator that accommodates different interpupillary distances.

In the example of <FIG>, control circuitry <NUM> uses fluids to control a distance between display system <NUM> and lens system <NUM> to switch between active use mode and protected mode. As shown in <FIG>, glasses <NUM> may include display system <NUM> and lens system <NUM> mounted in housing <NUM>. Display system <NUM> may be mounted to a support frame such as support frame <NUM> that is coupled to a flexible seal <NUM>. Chamber <NUM> may be located between display system <NUM> and lens system <NUM>.

As shown in <FIG>, glasses <NUM> have has a fluid reservoir such as reservoir <NUM>. The fluid of reservoir <NUM> may pass through one or more openings in housing <NUM> such as opening <NUM>. Opening <NUM> may be uncovered or may, if desired, be covered with a permeable layer such as permeable layer <NUM>. Permeable layer <NUM> may be an adjustable vent that can be opened and closed (e.g., opened and closed in response to control signals from control circuitry <NUM>), or permeable layer <NUM> may be a porous membrane with numerous openings.

Fluid may pass through openings such as opening <NUM> as indicated by arrow <NUM> in response to control signals from control circuitry <NUM>. The fluid may be a gas (e.g., air, nitrogen, etc.) or may be a liquid such as a charged liquid or may be a ferrofluid (e.g., a ferromagnetic material formed from suspended ferromagnetic particles in a liquid carrier). Electrodes for controlling fluid flow may be mounted in any suitable location. When a signal is applied to the electrodes, fluid from layer <NUM> (e.g., electrically charged liquid in reservoir <NUM>) may be drawn into chamber <NUM>. Lateral barrier structures such as housing <NUM> may confine the liquid laterally and may cause the liquid to locally push outwards on display system <NUM> and/or lens system <NUM>, causing distance D to increase so that glasses <NUM> are in protected mode. To shift into active mode, control circuitry <NUM> may draw the fluid out of chamber <NUM> in direction <NUM> and back into reservoir <NUM>, causing distance D to decrease.

If desired, the fluid that fills chamber <NUM> may be air (e.g., from a fan in glasses <NUM>) that is pushed through opening <NUM> into chamber <NUM>. In this type of scenario, electrodes may not be necessary to control the flow of air through opening <NUM> into and out of chamber <NUM>.

If desired, control circuitry <NUM> may deploy a protective layer when glasses <NUM> are operated in protected mode. This type of arrangement is illustrated in <FIG>. As shown in <FIG>, protective layer <NUM> may be interposed between display system <NUM> and lens system <NUM>. Protective layer <NUM> may be fixed in the position shown in <FIG>, or protective layer <NUM> may be moved to a different location when glasses <NUM> are in active use mode. Protective layer <NUM> may be layer of polymer, carbon fiber, metal, shape memory material, electroactive polymer, piezoelectric materials, other suitable materials, or a combination of these materials. Protective layer <NUM> may be actively controlled (e.g., control circuitry <NUM> may apply control signals to electrodes or other circuitry coupled to protective layer <NUM> to deploy protective layer <NUM>), or protective layer <NUM> may be passive (e.g., protective layer <NUM> may automatically be deployed due to gravity when glasses <NUM> are in freefall, protective layer <NUM> may be a polymer that becomes stiff under strain, or other passive arrangements may be used). If desired, protective layers in glasses <NUM> such as protective layer <NUM> may be deployed in other locations when glasses <NUM> are in protected mode (e.g., on either side of display system <NUM>, on either side of lens system <NUM>, on one or more outer surfaces of glasses <NUM>, etc.). The example of <FIG> is merely illustrative.

<FIG> is a flow chart of illustrative steps involved in operating glasses such as glasses <NUM> of the type shown in <FIG>.

At step <NUM>, control circuitry <NUM> may gather sensor data from sensors <NUM> (e.g., ambient light information from ambient light sensor(s) <NUM>, camera data from camera(s) <NUM>, motion data from motion sensor(s) <NUM>, and/or data from other sensors <NUM>), location data from communications circuitry (e.g., location data gathered using Global Positioning System Receiver Circuitry, radio-frequency transceiver circuitry, sensors <NUM>, or other location tracking circuitry), on/off status information (e.g., whether glasses <NUM> are powered on or off), and/or other information.

At step <NUM>, control circuitry <NUM> may process the data gathered in step <NUM> to determine the current state of glasses <NUM>. Determining the current state of glasses <NUM> may include determining whether glasses <NUM> are in use, not in use, vulnerable to an impending collision, or not vulnerable to an impending collision. Step <NUM> may include, for example, determining whether glasses <NUM> are in free fall or lifted off of a surface using data from motion sensor <NUM>, whether glasses <NUM> have been removed from or placed on a user's head using data from motion sensor <NUM> and/or inward-facing camera <NUM>, whether an external object is nearing contact with or moving away from glasses <NUM> using outward-facing camera <NUM>, whether glasses <NUM> have been turned on or off, whether device <NUM> is inside or outside, and/or determining other information about the status of glasses <NUM> based on the information gathered in step <NUM>.

If it is determined in step <NUM> that glasses <NUM> are in use and/or that no impending collision is likely, processing may proceed to step <NUM>.

At step <NUM>, control circuitry <NUM> may maintain or place glasses <NUM> in active use mode. If glasses <NUM> are already in active use mode, no action may be necessary. If glasses <NUM> are in protected mode, control circuitry <NUM> may shift glasses <NUM> from protected mode to active use mode by reducing the distance between display system <NUM> and lens <NUM> (e.g., using one or more of the arrangements shown in <FIG>, <FIG>, and <FIG>), by retracting or otherwise modifying a protective layer (e.g., protective layer <NUM> of FIG. <NUM>), and/or by taking other actions to place glasses <NUM> in a normal use mode. In active use mode, control circuitry <NUM> may use actuator <NUM> to adjust the distance between display system <NUM> and lens <NUM> based on the user's eye prescription, if desired.

If it is determined in step <NUM> that glasses <NUM> are not in use and/or that an impending collision is likely, processing may proceed to step <NUM>.

Claim 1:
A head-mounted display configured to display images viewable by a user and configured to be powered on and off, comprising:
a display system (<NUM>) including an array of pixels configured to produce the images;
a lens system (<NUM>) through which the images are viewable, wherein the lens system (<NUM>) and the display system (<NUM>) are separated by a distance along an optical axis;
an actuator (<NUM>); and characterised by
control circuitry (<NUM>) that uses the actuator (<NUM>) to increase the distance when the head-mounted display is powered off and decrease the distance when the head-mounted display is powered on.