Electromagnetic tracking with augmented reality systems
Head-mounted augmented reality (AR) devices can track pose of a wearer's head to provide a three-dimensional virtual representation of objects in the wearer's environment. An electromagnetic (EM) tracking system can track head or body pose. A handheld user input device can include an EM emitter that generates an EM field, and the head-mounted AR device can include an EM sensor that senses the EM field. EM information from the sensor can be analyzed to determine location and/or orientation of the sensor and thereby the wearer's pose. The EM emitter and sensor may utilize time division multiplexing (TDM) or dynamic frequency tuning to operate at multiple frequencies. Voltage gain control may be implemented in the transmitter, rather than the sensor, allowing smaller and lighter weight sensor designs. The EM sensor can implement noise cancellation to reduce the level of EM interference generated by nearby audio speakers.
1. A head-mounted display system comprising:
a display positionable in front of eyes of a wearer;
an electromagnetic (EM) field emitter configured to generate a magnetic field having a frequency wherein the EM field emitter is configured to change a capacitance of a capacitor or to select among a plurality of capacitors in a capacitor bank to dynamically tune the frequency;
an EM sensor configured to sense the magnetic field at the frequency; and
a processor programmed to:
receive signals from the EM sensor indicative of a sensed magnetic field; and
analyze the received signals to determine a position or an orientation of the EM sensor.
2. The head-mounted display system of claim 1 , wherein the EM field emitter comprises:
a first transmitter coil configured to generate a first magnetic field having a first frequency,
a second transmitter coil configured to generate a second magnetic field having a second frequency, and
a third transmitter coil configured to generate a third magnetic field having a third frequency.
3. The head-mounted display system of claim 2 , wherein the EM field emitter comprises a first time division multiplexed (TDM) circuit configured to switch power among the first transmitter coil, the second transmitter coil, and the third transmitter coil.
4. The head-mounted display system of claim 2 , wherein the first transmitter coil, the second transmitter coil, and the third transmitter coil are disposed along with mutually orthogonal axes.
5. The head-mounted display system of claim 2 , wherein the EM field emitter is configured to dynamically tune the first frequency, the second frequency, or the third frequency.
6. The head-mounted display system of claim 3 , wherein the TDM circuit comprises a single amplifier circuit that is TDM switched to each of a plurality of radio frequency (RF) transmitter coils.
7. The head-mounted display system of claim 1 , wherein the EM field emitter is configured to dynamically tune the frequency.
8. The head-mounted display system of claim 1 , wherein the EM field emitter is positioned in a handheld controller.
9. The head-mounted display system of claim 8 , wherein the EM sensor is positioned in the head-mounted display or in a beltpack.
10. The head-mounted display system of claim 1 , wherein the EM field emitter is positioned in the head-mounted display or in a beltpack.
11. The head-mounted display system of claim 10 , wherein the EM sensor is positioned in a first handheld controller.
12. The head-mounted display system of claim 10 , further comprising:
a second EM sensor configured to sense the magnetic field at a second frequency, wherein the EM field emitter is configured to generate the magnetic field at the second frequency.
13. The head-mounted display system of claim 12 , wherein the second frequency is generated by selection of a second capacitor in the capacitor bank.
14. The head-mounted display system of claim 12 , wherein the second EM sensor is positioned in a second handheld controller.
15. The head-mounted display system of claim 14 , further comprising:
a third EM sensor configured to sense the magnetic field at a third frequency, wherein the EM field emitter is configured to generate the magnetic field at the third frequency.
16. The head-mounted display system of claim 15 , wherein the third EM sensor is positioned in a third handheld controller.
17. The head-mounted display system of claim 16 , wherein the EM field emitter is configured to dynamically switch between the first frequency, the second frequency, and the third frequency.
18. The head-mounted display system of claim 16 , wherein the first handheld controller is operated by a first user, the second handheld controller is operated by a second user, and the third handheld controller is operated by a third user.
19. The head-mounted display system of claim 1 , wherein the processor is further programmed to:
receive images of an environment in front of the wearer from one or more cameras.
20. The head-mounted display system of claim 19 , wherein the processor is further programmed to:
analyze the received images to determine whether the EM sensor is outside of a field of view (FOV) of the one or more cameras; and
determine the position or the orientation of the EM sensor based on the sensed magnetic field and whether the EM sensor is determined to be outside of the FOV of the one or more cameras.