Actuation for a focus adjusting head mounted display
A head mounted display (HMD) includes an electronic display configured to display a virtual scene to a user, an optics block, an eye tracking system, and a varifocal actuation that mechanically changes a distance between the optics block and the electronic display. The varifocal actuation block is configured to change a focal length of the HMD based on the eye position of the user and includes a motor, a power screw coupled to the actuating motor configured to turn responsive to actuation of the motor, and a nut sled on the power screw that is coupled to the electronic display. The nut sled is configured to move back and forth along a length of the power screw responsive to the power screw being turned by the motor that results in movement of the electronic display relative to the optics block.
1. A varifocal actuation block comprising:
a motor;
a power screw coupled to the motor and configured to turn in response to actuation of the motor;
a nut sled on the power screw coupled to an electronic display screen of a head mounted display (HMD), the nut sled configured to move back and forth along a length of the power screw in response to the power screw being turned by the motor resulting in movement of an electronic display screen relative to an optics block of the HMD, wherein movement of the electronic display screen relative to the optics block changes a focal length of the optics block; and
an encoder configured to:
receive an input corresponding to a focal length for a frame of a virtual scene being presented on the electronic display screen;
determine a position for the electronic display screen relative to the optics block to achieve the focal length; and
provide the motor with an instruction causing the electronic display screen to move relative to the optics block to achieve the focal length for the frame of the virtual scene.
2. The HMD of claim 1 , wherein the varifocal actuation block further comprises:
one or more guide pins guiding movement of the electronic display screen relative to the optics block along the optical axis of the optics block.
3. The HMD of claim 2 , wherein the power screw operates as a primary guide for movement of the electronic display screen relative to the optics block and the one or more guide pins operate as a secondary guide used to prevent rotation of the electronic display screen about the optical axis.
4. The varifocal actuation block of claim 1 , further comprising:
a bracket holding the motor and the power screw mounted to a housing of the HMD, wherein the nut sled on the power screw coupled to the electronic display screen moves the electronic display screen relative to the optics block to change the focal length for a user viewing content displayed on the electronic display screen at an exit pupil of the HMD.
5. A head mounted display (HMD) comprising:
at least one processor;
an electronic display screen configured to display a virtual scene to a user wearing the HMD;
a optics block comprising one or more lenses configured to focus light from the electronic display screen to an exit pupil of the HMD;
an eye tracking system configured to determine an eye position of the user, the eye tracking system comprising:
an infrared camera; and
a hot mirror configured to reflect infrared light from an eye of the user wearing the HMD to the infrared camera;
a varifocal actuation block configured to change a focal length of the optics block based on the eye position of the user, the varifocal actuation block comprising:
an actuating motor;
a power screw coupled to the actuating motor and configured to turn in response to actuation of the actuating motor; and
a nut sled on the power screw and coupled to the electronic display screen, the nut sled configured to move back and forth along a length of the power screw in response to the power screw being turned by the actuating motor resulting in movement of the electronic display screen relative to the optics block; and
an encoder in communication with the eye tracking system and the varifocal actuation block, the encoder configured to:
receive the eye position determined by the eye tracking system;
determine the focal length of the optics block that provides focus for the eye position; and
provide an instruction to the varifocal actuation block to move the electronic display screen to a position providing focus for the eye position determined by the eye tracking system.
6. The HMD of claim 5 , wherein the varifocal actuation block moves the electronic display screen relative to the optics block along an optical axis of the optics block.
7. The HMD of claim 5 , wherein the varifocal actuation block further comprises:
one or more guide pins guiding movement of the electronic display screen relative to the optics block along the optical axis of the optics block.
8. The HMD of claim 7 , wherein the one or more guide pins are attached to the electronic display screen, a male end of each guide pin coupling with a female end of the guide pin fixed to the optics block.
9. The HMD of claim 7 , wherein the one or more guide pins are attached to the optics block, a male end of each guide pin coupling with a female end of the guide pin fixed to the electronic display screen.
10. The HMD of claim 7 , wherein the power screw operates as a primary guide for movement of the electronic display screen relative to the optics block and the one or more guide pins operate as a secondary guide used to prevent rotation of the electronic display screen about the optical axis.
11. The HMD of claim 5 , wherein the varifocal actuation block further comprises:
a bracket holding the motor and the power screw mounted to a housing of the HMD, wherein the nut sled on the power screw coupled to the electronic display screen moves the electronic display screen relative to the optics block to change the focal length for a user viewing content displayed on the electronic display screen at an exit pupil of the HMD.
12. The HMD of claim 5 , wherein the hot mirror is positioned to reflect the infrared light from the eye of the user wearing the HMD to the infrared camera, wherein the hot mirror is transparent to visible light allowing the light from electronic display to pass through to the user unimpeded while reflecting the IR light to infrared camera.
13. A head mounted display (HMD) comprising:
at least one processor;
an electronic display screen configured to display a virtual scene to a user wearing the HMD;
a optics block comprising one or more lenses configured to focus light from the electronic display screen to an exit pupil of the HMD;
a varifocal actuation block configured to change a focal length of the optics block based on the eye position of the user, the varifocal actuation block comprising:
an actuating motor;
a drive mechanism coupled to the actuating motor; and
a sled on the drive mechanism coupled to the electronic display screen, the sled configured to move back and forth along a length of the drive mechanism in response to actuation by the actuating motor resulting in movement of the electronic display screen relative to the optics block; and
an encoder in communication with the varifocal actuation block, the encoder configured to determine a focal length of the optics block for the virtual scene and provide an instruction to the varifocal actuation block to move the electronic display screen to a position providing focus for the determined focal length.
14. The HMD of claim 13 , wherein the drive mechanism is a power screw, a ball screw, or geared spindle drive.
15. The HMD of claim 13 , wherein varifocal actuation block further comprises:
one or more guide pins guiding movement of the electronic display screen relative to the optics block along the optical axis of the optics block via the one or more guide pins.
16. The HMD of claim 15 , wherein the one or more guide pins are attached to the electronic display screen, a male end of each guide pin coupling with a female end of the guide pin fixed to the optics block.
17. The HMD of claim 15 , wherein the one or more guide pins are attached to the optics block, a male end of each guide pin coupling with a female end of the guide pin fixed to the electronic display screen.
18. The HMD of claim 15 , wherein the power screw operates as a primary guide for movement of the electronic display screen relative to the optics block and the one or more guide pins operate as a secondary guide used to prevent rotation of the electronic display screen about the optical axis.
19. The HMD of claim 13 , wherein the varifocal actuation block further comprises:
a bracket holding the motor and the power screw mounted to a housing of the HMD, wherein the nut sled on the power screw coupled to the electronic display screen moves the electronic display screen relative to the optics block to change the focal length for a user viewing content displayed on the electronic display screen at an exit pupil of the HMD.