Head tracking system with inertial management unit for tracking helmet orientation
A head tracking system HTS configured to determine a head position and/or a head orientation of a user includes one or more optical sensors producing optical measurements; and one or more inertial sensors producing inertial measurements; a processor configured, when the optical sensors fail to provide optical measurements to determine the head location and the head orientation of a user, to operate in a coasting mode using the inertial measurements from the one or more inertial sensors to determine the head location and the head orientation of a user.
1 . A head tracking system (HTS) comprising:
an optical sensor configured to produce an optical measurement;
an inertial sensor configured to produce an inertial measurement; and
a processor configured to operate in a coasting mode, when the optical sensor fails to provide the optical measurement for determining a head location of a user and/or a head orientation of a user, the coasting mode using the inertial measurement from the inertial sensor to determine the head location of the user and the head orientation of the user, the processor configured to
determine a figure of merit (FOM) for a coasting error based on a combination of an error in an estimated bias of the inertial sensor, an error due to random drift and noise of the inertial sensor, and an error due to gain and alignment errors of the inertial sensor,
compare the FOM with a threshold to determine whether the inertial measurement provides a valid or invalid head location and/or head orientation, and
determine a subsequent operation from a plurality of possible subsequent operations of the HTS based on whether the head location of the user and/or the head orientation of the user is valid or invalid.
2 . The head tracking system according to claim 1 , wherein when the coasting error is less than the threshold the head location of the user and/or head orientation of the user is valid.
3 . The head tracking system according to claim 1 , wherein when the coasting error is greater than or equal to the threshold, the head location of the user and/or head orientation of the user is invalid.
4 . The head tracking system according to claim 1 , wherein the HTS further includes an action control module to determine which subsequent operations are available.
5 . The head tracking system according to claim 4 , wherein the available subsequent operation comprises a normal operation when the head location of the user and/or head orientation of the user is valid.
6 . The head tracking system according to claim 4 , wherein the available subsequent operation comprises a limited operation when the head location of the user and/or head orientation of the user is invalid, and the operation does not need the head location of the user or the head orientation of the user.
7 . The head tracking system according to claim 4 , wherein the available subsequent operation comprises declaring tracking invalid when the head location of the user and/or head orientation of the user is invalid, and the operation does need the head location of the user or the head orientation of the user.
8 . The head tracking system according to claim 1 , wherein the processor is configured to:
determine the head position of the user and/or the head orientation of the user from one or both of the optical sensor and the inertial sensor;
determine the head position of the user and/or the head orientation of the user from the inertial sensor if the optical measurement is invalid;
determine the head position of the user and/or the head orientation of the user from the optical sensor if the inertial measurement is invalid.
9 . The head tracking system according to claim 1 , further configured to determine a rate of changes of FOM to identify trends and potential risks.
10 . The head tracking system according to claim 1 , wherein the inertial sensor is one of three or more gyroscopes located on a head worn assembly associated with the HTS.
11 . The head tracking system according to claim 1 , wherein the optical sensor is a camera in a vicinity of the HTS being configured to receive optical measurements from one or more light elements located on a head worn assembly associated with the HTS.
12 . The head tracking system according to claim 1 , further comprising an interface to receive aircraft orientation, aircraft position and associated latencies of the aircraft orientation and aircraft position data which is used in calculating the FOM.
13 . The head tracking system according to claim 1 , incorporated into a head worn display assembly such as a helmet.
14 . A head worn display assembly configured to present real and virtual images to a user based on a head position and a head orientation provided by the HTS of claim 1 .
15 . The head worn assembly of claim 14 , further including an optical display to display the real and virtual images to a user wearing the head worn assembly, wherein the presentation of at least the virtual images is based on the FOM of the inertial measurement.
16 . The head worn assembly of claim 14 , wherein the optical display comprises at least one of a visor-projection display system, and a waveguide-based display, arranged to present virtual images such that they appear overlain through a visor of the head worn display.
17 . A method to determine a head location and a head orientation of a user to which real and virtual images are to be presented using a head tracking system (HTS) configured to produce optical measurements and to produce inertial measurements, the method comprising:
using, when optical measurements are unavailable, the inertial measurements to determine the head location and position;
determining a figure of merit (FOM) for coasting errors based on a combination of an error in an estimated bias of an inertial sensor that produces one or more of the inertial measurements, an error due to random drift and noise of the inertial sensor, and an error due to gain and alignment errors of the inertial sensor;
comparing the FOM with a threshold to determine whether the one or more inertial measurements provide a valid or invalid head location and/or head orientation; and
determining a subsequent operation from a plurality of possible subsequent operations of the HTS based on whether the head location and/or head orientation is valid or invalid.
18 . The method of claim 17 , wherein determining the head location and/or head orientation is valid when the FOM is less than the threshold, and wherein determining the head location and/or head orientation is invalid when the FOM is greater than or equal to the threshold.
19 . The method according claim 18 , further comprising determining which subsequent operations are available via an action control module, further comprising one or more of:
determining the possible subsequent operation to be a normal operation when the head location and/or head orientation is valid, or the operation does not need the position or location of the user;
determining the possible subsequent operation to be a limited operation when the head location and/or head orientation is invalid, and the operation does not need the position or location of the user; and
determining the possible subsequent operation to be declaring tracking invalid when the head location and/or head orientation is invalid, and the operation does need the position or location of the user.
20 . The method according to claim 17 , further comprising determining a rate of changes of FOM to identify trends and potential risks.
21 . The method according to claim 17 , further comprising notifying a vehicle control system when the FOM is invalid to enable the vehicle control system to reset head tracking.