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. An augmented reality display system comprising:
a display configured to project virtual images to eyes of a wearer;
a frame configured to mount the display in front of the eyes of the wearer;
an electromagnetic (EM) field emitter configured to generate a magnetic field;
an EM sensor configured to sense the magnetic field, wherein one of the EM field emitter or the EM sensor is mechanically coupled to the frame and the other of the EM field emitter or the EM sensor is mechanically coupled to a component of the augmented reality display system that is independently movable relative to the frame;
an audio speaker;
a hardware 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; and
a noise canceling circuit configured to cancel magnetic interference in the sensed magnetic field generated by the audio speaker.
2. The augmented reality display system of claim 1 , wherein the noise canceling circuit is configured to:
receive a first signal from the EM sensor;
receive a second signal from the audio speaker;
combine the first signal and the second signal to provide a noise-canceled signal.
3. The augmented reality display system of claim 2 , wherein to combine the first signal and the second signal, the noise canceling circuit is configured to: (a) invert the second signal and add the inverted second signal to the first signal or (b) subtract the second signal from the first signal.
4. The augmented reality display system of claim 2 , wherein the audio speaker comprises a time-varying voltage source and an amplifier, and the second signal is from the time-varying voltage source.
5. The augmented reality display system of claim 2 , wherein the received signals from the EM sensor comprise the noise-canceled signal.
6. The augmented reality display system of claim 1 , wherein the EM sensor comprises the noise canceling circuit.
7. The augmented reality display system of claim 1 , wherein the audio speaker is mechanically coupled to the frame.
8. The augmented reality display system of claim 1 , wherein the display comprises a light field display.
9. The augmented reality display system of claim 1 , wherein:
the component comprises a user-input totem or a belt pack,
the EM sensor is mechanically coupled to the frame, and
the EM field emitter is mechanically coupled to the user-input totem or the belt pack.