Orientation determination for devices generating electromagnetic interference
A mechanism is provided to determine orientation of a device that includes sources of electromagnetic interference. Data generated by one or more gyroscopes in the device, in conjunction with data generated by one or more accelerometers, can be used to generate an estimate of the change of orientation of the device from the time of a last accurate magnetometer reading. In one embodiment, in order to conserve system power, the gyroscope is kept powered down or in a stand-by state until receiving a control signal to power up. The control signal is provided in advance of the source of electromagnetic interference being powered up, thereby providing an accurate starting point from which magnetometer orientation estimates may be calculated during such interference.
1. A system comprising:
a component capable of generating electromagnetic interference;
a first set of directionally-sensitive sensors, wherein
the first set of directionally-sensitive sensors comprises three orthogonally-oriented sensors configured to respond to a magnetic field, and
the first set of directionally-sensitive sensors are mounted within range of the electromagnetic interference wherein generation of the electromagnetic interference causes the first set of directionally-sensitive sensors to generate erroneous data related to the magnetic field;
a second set of directionally-sensitive sensors, wherein
the second set of directionally-sensitive sensors comprises three orthogonally-oriented sensors configured to respond to a constant acceleration, and
the second set of directionally-sensitive sensors are mounted in a fixed orientation to the first set of directionally-sensitive sensors;
a set of gyroscope sensors, wherein
the set of gyroscope sensors comprises three sensors oriented on orthogonally-oriented axes each configured to respond to rotation about a corresponding axis, and
the set of gyroscope sensors are mounted in a fixed orientation to the first and second sets of directionally-sensitive sensors;
a processor, coupled to the first and second set of directionally sensitive sensors and the set of gyroscope sensors, and configured to
determine a first orientation of the system with respect to a global frame of reference using first signals received from the first and second sets of directionally-sensitive sensors at a first time, and
determine a second orientation of the system with respect to the global frame of reference at a second time, using second signals received from the first and second sets of directionally-sensitive sensors, and correlating an observed angular rate of change of the system from first gyroscope signals from the set of gyroscope sensors during a period between the first time and the second time to the rotational change reflected by the first and second signals received from the directionally-sensitive sensors;
determine a third orientation of the system with respect to the global frame of reference using the second orientation, and one or more of third signals received from the first and second sets of directionally-sensitive sensors at a third time and an observed angular rate of change of the system using second gyroscope signals from the set of gyroscope sensors during a period between the second time and the third time, wherein said determining the second and third orientation is performed in response to receiving a control signal.
2. The system of claim 1 , wherein the control signal precedes generation of an electromagnetic interference by the component of the system and the third orientation of the system is determined using the second gyroscope signals.
3. The system of claim 2 further comprising:
a user input device configured to receive a user input and to generate the control signal in response to the user input.
4. The system of claim 3 further comprising:
an electric motor configured to respond to the user input, wherein
the response of the motor generates the electromagnetic interference, and
the component comprises the motor.
5. The system of claim 2 wherein the set of gyroscope sensors is configured to activate in response to receiving the control signal.
6. The system of claim 2 , wherein
the processor is further configured to determine a fourth orientation of the system with respect to the global frame of reference at a fourth time using the third orientation and an observed angular rate of change of the system using third gyroscope signals from the set of gyroscope sensors during a period between the third time and the fourth time.
7. The system of claim 1 wherein the electromagnetic interference generated by the component of the system is initiated between the second time and the third time in response to the control signal.
8. The system of claim 7 further comprising:
an electric motor configured to respond to the user input, wherein the response of the motor generates the electromagnetic interference.
9. A digital still camera comprising the system of claim 8 , wherein
the electric motor is configured to focus an optical lens, and
the control signal is generated by a user input device configured to receive a user input.
10. The digital still camera of claim 9 further comprising:
an image stabilization gyroscope comprising the set of gyroscope sensors.
11. The digital still camera of claim 9 further comprising:
a memory, coupled to the processor and the first set of directionally-sensitive sensors, and configured to periodically store signals received from the first set of directionally-sensitive sensors in a set of buffer registers; and
the processor further configured to access the stored signals at the third time to provide the third signals.
12. The system of claim 2 further comprising:
the second set of directionally-sensitive sensors are configured to generate the control signal in response to a motion of the system.
13. The system of claim 2 wherein the set of gyroscope sensors is configured for constant operation.
14. A method implemented by a digital still camera, the method comprising:
determining a first orientation of the digital still camera with respect to a global frame of reference at a first time using first data generated by a first set of directionally-sensitive sensors and a second set of directionally-sensitive sensors, wherein
the first set of directionally-sensitive sensors comprises three orthogonally-oriented sensors configured to respond to a constant magnetic field,
the first set of directionally-sensitive sensors are mounted on or near a lens comprising a motor capable of generating electromagnetic interference sufficient to cause the first set of directionally-sensitive sensors to generate erroneous data related to the constant magnetic field, and
the second set of directionally-sensitive sensors comprises three orthogonally-oriented sensors configured to respond to a constant acceleration and are mounted in a fixed orientation to the first set of directionally-sensitive sensors;
determining a second orientation of the digital still camera with respect to the global frame of reference at a second time using the first orientation and second data generated by the first and second sets of directionally-sensitive sensors at the second time;
correlating a first observed angular rate of change of the digital still camera generated by a set of gyroscope sensors during a period between the first time and the second time to the rotational change reflected by the first and second orientation, wherein
the set of gyroscope sensors comprises three sensors on orthogonally-oriented axes configured to respond to rotation about a corresponding axis,
the set of gyroscope sensors are mounted in a fixed orientation to the first and second sets of directionally-sensitive sensors and
said correlating is performed in response to a control signal; and
determining a third orientation of the digital still camera with respect to the global frame of reference at a third time using the second orientation, and one or more of data generated by the first and second sets of directionally sensitive sensors at the third time and a second observed angular rate of change of the digital still camera generated by the set of gyroscope sensors during a period between the second time and the third time.
15. The method of claim 14 further comprising:
generating the control signal prior to generating electromagnetic interference by the lens motor of the digital still camera.
16. The method of claim 15 wherein said generating the control signal is performed in response to a user input.
17. The method of claim 16 wherein the response to user input comprises activating a shutter button of the digital still camera.
18. The method of claim 15 further comprising:
determining a fourth orientation of the digital still camera with respect to the global frame of reference at a fourth time using the third orientation and a third observed angular rate of change of the digital still camera using a third set of data from the set of gyroscope sensors during a period between the third time and the fourth time.
19. The method of claim 14 further comprising:
activating a lens focus motor in response to said generating the control signal, wherein said activating the lens focus motor generates electromagnetic interference and said activating is initiated between the second time and the third time.
20. The method of claim 14 further comprising:
activating the set of gyroscope sensors in response to one of the control signal or a signal generated by the first or second set of directionally-sensitive sensors.