Head-mounted display systems with power saving functionality

1. A head-mounted display system configured to project light to an eye of a user to display augmented reality image content in a vision field of said user, said head-mounted display system comprising:

a frame configured to be supported on a head of the user;

a head-mounted display disposed on the frame, said display configured to project light into said user's eye to display augmented reality image content to the user's vision field, at least a portion of said display being transparent and disposed at a location in front of the user's eye when the user wears said frame such that said transparent portion transmits light from a portion of the environment in front of the user and said head-mounted display to the user's eye to provide a view of said portion of the environment in front of the user and said head-mounted display;

one or more sensors comprising an inward-facing imaging system configured to sense one or more facial features; and

processing electronics in communication with the display and the one or more sensors, the processing electronics configured to:

determine whether the frame is not supported on the head of the user; and

cause the head-mounted display system to reduce the power of the one or more components of the head-mounted display system in response to at least in part on a determination that the frame is not supported on the head of the user,

wherein the processing electronics is configured to determine whether the frame is not supported on the head of the user by:

receiving from the inward-facing imaging system a first image;

receiving from the inward-facing imaging system a second image after the first image; and

analyzing the first image and the second image to identify one or more periocular features, wherein the frame has been removed from the head of the user if the one or more periocular features are identified in the first image and not identified in the second image.

2. The display system of claim 1 , wherein the one or more sensors further comprise one or more motion sensors configured to measure change in position of the frame, and wherein the processing electronics is further configured to:

receive from the one or more motion sensors data relating to movement of the frame;

determine whether the frame has been stationary for a period of time greater than or equal to a threshold period of time based at least in part on the received data; and

cause the head-mounted display system to reduce power of one or more components of the head-mounted display system in response to at least in part on a determination that the frame has been stationary for the period of time greater than or equal to the threshold period of time.

3. The display system of claim 2 , wherein the one or more motion sensors comprise one or more inertial measurement units (IMUs).

4. The display system of claim 2 , wherein the processing electronics is configured to determine whether the frame has been stationary for the period of time greater than or equal to the threshold period of time by:

receiving measurements from the one or more motion sensors; and

analyzing the received measurements to determine whether the frame has not moved for the period of time greater than or equal to the threshold period of time, wherein the frame has been stationary for the period of time greater than or equal to the threshold period of time if the frame has not changed position for at least the threshold period of time.

5. The display system of claim 2 , further comprising one or more clocks on a chip to monitor the period of time.

6. The display system of claim 1 , wherein the one or more sensors further comprise an outward facing imaging system.

7. The display system of claim 6 , wherein the processing electronics is further configured to:

determine whether the frame has been stationary for a period of time greater than or equal to a threshold period of time by:

receiving images in sequence from the inward-facing imaging system and/or the outward-facing imaging system; and

analyzing the received images to determine whether the frame has not moved for the period of time greater than or equal to the threshold period of time, wherein the frame has been stationary for the period of time greater than or equal to the threshold period of time if the images have not changed for at least the threshold period of time; and

cause the head-mounted display system to reduce power of one or more components of the head-mounted display system in response to at least in part on a determination that the frame has been stationary for the period of time greater than or equal to the threshold period of time.

8. The display system of claim 1 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by dimming or turning off a light source of the display.

9. The display system of claim 1 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by reducing a refresh rate associated with the display.

10. The display system of any of claim 1 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by reducing the power of the one or more sensors.

11. A head-mounted display system configured to project light to an eye of a user to display augmented reality image content in a vision field of said user, said head-mounted display system comprising:

a frame configured to be supported on a head of the user;

a head-mounted display disposed on the frame, said display configured to project light into said user's eye to display augmented reality image content to the user's vision field, at least a portion of said display being transparent and disposed at a location in front of the user's eye when the user wears said frame such that said transparent portion transmits light from a portion of the environment in front of the user and said head-mounted display to the user's eye to provide a view of said portion of the environment in front of the user and said head-mounted display;

one or more strain gauges configured to sense pressure exerted by a portion of the user's head on a temple, band, or nose pad of the frame; and

processing electronics in communication with the display and the one or more strain gauges, the processing electronics configured to:

determine whether the frame is not supported on the head of the user; and

cause the head-mounted display system to reduce the power of the one or more components of the head-mounted display system in response to at least in part on a determination that the frame is not supported on the head of the user.

12. The display system of claim 11 , wherein the processing electronics is configured to determine whether the frame is not supported on the head of the user by:

receiving sensed pressures from the one or more strain gauges; and

analyzing the sensed pressures to indicate whether the frame is not in physical contact with the user's head, wherein the frame is not supported on the head of the user if the sensed pressures indicate non-contact with the user's head.

13. The display system of claim 11 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by dimming or turning off a light source of the display.

14. The display system of claim 11 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by reducing a refresh rate associated with the display.

15. A head-mounted display system configured to project light to an eye of a user to display augmented reality image content in a vision field of said user, said head-mounted display system comprising:

a frame configured to be supported on a head of the user;

a head-mounted display disposed on the frame, said display configured to project light into said user's eye to display augmented reality image content to the user's vision field, at least a portion of said display being transparent and disposed at a location in front of the user's eye when the user wears said frame such that said transparent portion transmits light from a portion of the environment in front of the user and said head-mounted display to the user's eye to provide a view of said portion of the environment in front of the user and said head-mounted display;

one or more pressure sensors configured to sense pressure exerted by a portion of the user's head on the frame; and

processing electronics in communication with the display and the one or more pressure sensors, the processing electronics configured to:

determine whether the frame is not supported on the head of the user; and

cause the head-mounted display system to reduce the power of the one or more components of the head-mounted display system in response to at least in part on a determination that the frame is not supported on the head of the user,

wherein the processing electronics is configured to determine whether the frame has been removed from the head of the user by:

receiving from the one or more pressure sensors a first sensed pressure;

receiving from the one or more pressure sensors a second sensed pressure after the first sensed pressure; and

analyzing the first sensed pressure and the second sensed pressure to indicate whether the frame is in physical contact with the user's head, wherein the frame has been removed from the head of the user if the first sensed pressure indicates contact with the user's head and the second sensed pressure does not indicate contact with the user's head.

16. The display system of claim 15 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by dimming or turning off a light source of the display.

17. The display system of claim 15 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by reducing a refresh rate associated with the display.

18. The display system of any of claim 15 , wherein the processing electronics is configured to cause the display system to reduce the power of the one or more components by reducing the power of the one or more pressure sensors.