# US 12,004,852 B2 · Sensor calibration considering subject-dependent variables and/or body positions

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- Number: US 12,004,852 B2
- Document ID: US12004852B2
- Status: Granted
- Kind: B2
- Application number: 15/718,560
- Filed: 2017-09-28
- Published: 2019-03-28
- Granted: 2024-06-11
- Earliest claimed: 2017-09-28
- Assignees: Vital Connect, Inc.
- Applicants: Vital Connect, Inc.
- Inventors: Nandakumar Selvaraj; Thang Tran; Arshan Aga
- Web page: https://patentgrep.com/patent/US12004852B2

## CPC

- A61B 5/11: Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb {(A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721)}
- A61B 5/02416: {using photoplethysmograph signals, e.g. generated by infrared radiation (A61B5/14552 takes precedence)}
- A61B 5/1116: {Determining posture transitions}
- A61B 5/1121: {Determining geometric values, e.g. centre of rotation or angular range of movement}
- A61B 5/6833: {Adhesive patches}
- G01P 21/00: Testing or calibrating of apparatus or devices covered by the preceding groups
- A61B 5/002: {Monitoring the patient using a local or closed circuit, e.g. in a room or building (A61B5/0017 takes precedence)}
- A61B 5/024: Measuring pulse rate or heart rate
- A61B 5/6823: {Trunk, e.g., chest, back, abdomen, hip}
- A61B 2560/0223: of calibration, e.g. protocols for calibrating sensors
- A61B 2562/0219: Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
- A61B 2562/028: Microscale sensors, e.g. electromechanical sensors [MEMS]
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

A system, device and method of calibrating a sensor determine a sensor vector associated with a subject; process the sensor vector; determine a sensor elevation angle as a prediction of the subject's body elevation from a result of processing the sensor vector; and perform calibration using the sensor vector, sensor elevation angle, and a gravity vector.

## Claims

### Claim 1

A method of calibrating a sensor associated with a subject, comprising:
producing, by the sensor, a sensor vector {right arrow over (V)} associated with a body acceleration of the subject relative to a gravity vector;
calibrating 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 the 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
determining a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)}sη.

### Claim 2 (depends on 1)

The method of claim 1, wherein:
the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};
the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′)}u.

### Claim 3 (depends on 1)

The method of claim 1, wherein
the angle δ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)}s to the magnitude of {right arrow over (XY)}.

### Claim 4 (depends on 1)

The method of claim 1, wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

### Claim 5

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.

### Claim 6 (depends on 5)

The system of claim 5, wherein:
the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};
the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′u)}.

### Claim 7 (depends on 5)

The system of claim 5, wherein
the angle ζ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)}s to the magnitude of {right arrow over (XY)}.

### Claim 8 (depends on 5)

The system of claim 5, wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

### Claim 9

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.

### Claim 10 (depends on 9)

The sensor device of claim 9, wherein:
the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};
the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′u)}.

### Claim 11 (depends on 9)

The sensor device of claim 9, wherein
the angle δ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and
the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)}s to the magnitude of {right arrow over (XY)}.

### Claim 12 (depends on 9)

The sensor device of claim 9, wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

### Claim 13 (depends on 9)

The sensor device of claim 9, wherein the structure comprises a patch form factor.

### Claim 14 (depends on 13)

The sensor device of claim 13, wherein the structure comprises an adhesive configured to be removably attached to the subject.

### Claim 15 (depends on 9)

The sensor device of claim 9, wherein the structure comprises an adhesive configured to be removably attached to the subject.

### Claim 16 (depends on 9)

The sensor device of claim 9, further comprising a wireless transmitter configured to store or transmit the determined second elevation angle η.