Sensor calibration considering subject-dependent variables and/or body positions

A system to calibrate a sensor associated with a subject, comprising:

• a processor;
• and
• a memory device coupled to the processor, wherein the memory device includes an application that, when executed by the processor, causes the processor to:
• determine a sensor vector {right arrow over (V)} associated with body acceleration of the subject relative to a gravity vector;
• calibrate the sensor vector {right arrow over (V)}, including:
• processing the sensor vector {right arrow over (V)} with the subject at a first elevation angle relative to a reference to produce a first calibrated sensor vector {right arrow over (V)}s, wherein the processing of the sensor vector includes:
• determining an angle α and applying rotational matrix R1 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R1 is an XY rotation for α° around a Z axis,
• determining an angle β and applying rotational matrix R3 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R3 is a YZ rotation for β° around an X axis,
• obtaining user input on an orientation of the sensor with reference to a midline of the body and determining an ideal upright sensor vector {right arrow over (V)}u,
• determining rotational matrix Rs by the product of the rotational matrix R3 and the rotational matrix R1, wherein the rotational matrix Rs, is an intermediate rotational matrix,
• applying the rotational matrix Rs rotation to the ideal upright sensor vector {right arrow over (V)}u, to obtain a rotated ideal upright sensor vector {right arrow over (V′u)}, and
• determining an angle ζ using {right arrow over (V′u)} and applying rotational matrix R2 to the sensor vector {right arrow over (V)} to obtain the first calibrated sensor vector {right arrow over (V)}S, wherein the rotational matrix R2 includes an XY rotation for ζ° around the Z axis;
• determining a second elevation angle η associated with elevation of the subject relative to the reference, wherein the determining of the second elevation angle η includes:
• determining an angle δ and rotational matrix Ry, wherein the rotational matrix Ry is an XZ rotation for δ° around a Y axis,
• applying the rotational matrix Ry rotation to the sensor vector {right arrow over (V)} to obtain {right arrow over (XY)}, wherein {right arrow over (XY)} is the rotated vector on an XY plane,
• determining an angle γ using reference to {right arrow over (XY)} and an ideal gravity vector on supine {right arrow over (G)}S, and
• obtaining the sensor elevation angle η as a function of γ;
• determining rotational matrix Rx, by rotating an YZ plane of the sensor vector {right arrow over (V)} for η° around the X axis;
• calculating a second calibrated sensor vector {right arrow over (V)}Sη as a function of Rx, and the first calibrated sensor vector {right arrow over (V)}S;
• and
• determine a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)}sη.

A sensor device, comprising:

• one or more sensors;
• a structure configured to support the one or more sensors for attachment to the subject;
• a processor;
• and
• a memory device coupled to the processor, wherein the memory device includes an application that, when executed by the processor, causes the processor to:
• determine a sensor vector {right arrow over (V)} associated with body acceleration of the subject relative to a gravity vector;
• calibrate the sensor vector {right arrow over (V)}, including:
• calibrating the sensor vector {right arrow over (V)} with the subject at a first elevation angle relative to a reference to produce a first calibrated sensor vector {right arrow over (V)}s, wherein the processing of the sensor vector includes:
• determining an angle α and applying rotational matrix R1 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R1 is an XY rotation for α° around a Z axis,
• determining an angle β and applying rotational matrix R3 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R3 is a YZ rotation for β° around an X axis,
• obtaining user input on an orientation of the sensor with reference to a midline of the body and determining an ideal upright sensor vector {right arrow over (V)}u,
• determining rotational matrix Rs by the product of the rotational matrix R3 and the rotational matrix R1, wherein the rotational matrix Rs, is an intermediate rotational matrix,
• applying the rotational matrix Rs rotation to the ideal upright sensor vector {right arrow over (V)}u to obtain a rotated ideal upright sensor vector {right arrow over (V′u)}, and
• determining an angle ζ using {right arrow over (V′u)} and applying rotational matrix R2 to the sensor vector {right arrow over (V)} to obtain the first calibrated sensor vector {right arrow over (V)}S, wherein the rotational matrix R2 includes an XY rotation for ζ° around the Z axis;
• determining a second elevation angle η associated with elevation of the subject relative to the reference, wherein the determining of the second elevation angle η includes:
• determining an angle δ and rotational matrix Ry, wherein the rotational matrix Ry is an XZ rotation for δ° around a Y axis,
• applying the rotational matrix Ry rotation to the sensor vector {right arrow over (V)} to obtain {right arrow over (XY)}, wherein {right arrow over (XY)} is the rotated vector on an XY plane,
• determining an angle γ using reference to {right arrow over (XY)} and an ideal gravity vector on supine {right arrow over (G)}s, and
• obtaining the sensor elevation angle η as a function of γ;
• determining rotational matrix Rx by rotating an YZ plane of the sensor vector {right arrow over (V)} for η° around the X axis;
• calculating a second calibrated sensor vector {right arrow over (V)}Sη as a function of Rx and the first calibrated sensor vector {right arrow over (V)}S;
• and
• determine a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)}sη.