Multi-axis tilt estimation and fall remediation
Among other things, a vestibular prosthesis includes a wearable motion sensing system, the motion sensing system generating a motion signal indicative of a motion thereof, wherein the motion includes rotation about two distinct axes; a signal processor in communication with the motion sensing system, the signal processor being configured to generate an estimate of a tilt of the motion sensing system; and an actuator responsive to the estimate of the tilt made by the signal processor.
1. A method comprising:
representing a state of a subject wearing a prosthesis as a set of parameters comprising:
biases associated with at least one gyro and at least one accelerometer of the prosthesis,
at least one angular rate associated with the subject, and
a quaternion representing rotation of the subject with respect to a coordinate system,
wherein each of the biases and the at least one angular rate is modeled as first order Markov processes; and
generating, using a Kalman filter, an estimate of a tilt of the subject based on selected values of the parameters and outputs from the at least one gyro and the at least one accelerometer.
2. The method of claim 1 , wherein a range of the tilt includes 90 degrees.
3. The method of claim 2 , wherein the range of the tilt also includes 0 degrees and 180 degrees.
4. The method of claim 1 , further comprising:
generating at least a second estimate of the tilt from Euler angles relating signals from the gyro and the at least one accelerometer, wherein the Euler angles include at least one redundant Euler angle.
5. The method of claim 4 , further comprising combining the multiple estimates of the tilt.
6. The method of claim 1 , further comprising:
delivering, using an actuator, a signal selected from the group consisting of: a tactile signal delivered by vibrating elements, an acoustic signal delivered by a headset, a visual signal delivered by selectively illuminated light sources, and a deployment signal for deploying an airbag, wherein the delivered signal is selected based on the estimate of the tilt.
7. The method of claim 1 , wherein the set of parameters also includes scale factors associated with the at least one gyro and the at least one accelerometer.
8. The method of claim 1 , wherein the angular rate is a derivative of an Euler angle associated with a body frame of the subject.
9. The method of claim 1 , wherein the z axis of a body frame of the subject is parallel to the spine of the subject.
10. The method of claim 9 , wherein the z axis of the body frame is oriented such that movement in a positive z-direction corresponds to movement from the subject's head to the subject's feet.
11. The method of claim 1 , wherein the quaternion is based on measurements from the at least one gyro and the at least one accelerometer.
12. The method of claim 1 , wherein the tilt represents a deviation of an axis of a first frame of reference aligned to a portion of the subject wearing the prosthesis with respect to an axis of a second frame of reference aligned with the direction of gravity.