# US 12,768,671 B2 · Dynamic IMU calibration and sensor fusion

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- Number: US 12,768,671 B2
- Document ID: US12768671B2
- Status: Granted
- Kind: B2
- Application number: 18/238,880
- Filed: 2023-08-28
- Published: 2024-02-29
- Granted: 2026-10-20
- Earliest claimed: 2022-08-26
- Assignees: Rajant Health Incorporated
- Applicants: Rajant Health Inc.
- Inventors: Muthukumaran Chandrasekaran; Jack Mountney; Robert Joseph Schena
- Web page: https://patentgrep.com/patent/US12768671B2

## CPC

- G01C 25/005: {initial alignment, calibration or starting-up of inertial devices}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)

## Abstract

Disclosed herein are systems and methods for computer-assisted sensor calibration where the computer receives raw accelerometer data, raw gyroscope data, and raw magnetometer data and performs spatial calibration. The calibration data is used to calculate orientation data, and then then calibrated data and calibration data are used to provide corrected linear acceleration data that may be used by sensors to provide more accurate readings, for example, with regard to physiological data. In certain embodiments, in certain embodiments, the sensor calibration further employs a 9-axis IMU (“Inertial Measurement Unit”) comprising an accelerometer, gyroscope and magnetometer to provide calibration data.

## Claims

### Claim 1

A computer-implemented method for dynamic sensor calibration, the method comprising:
receiving initial IMU data from an inertial measurement unit (IMU) of a wearable health monitoring device having one or more physiological sensors outputting physiological sensor data, the initial IMU data comprising raw accelerometer data, raw gyroscope data, and raw magnetometer data;
performing sensor calibration using the initial IMU data to calculate a plurality of initial IMU calibration parameters;
using the plurality of initial IMU calibration parameters, by a sensor fusion module, to calculate an initial estimated orientation of the wearable health monitoring device;
using the initial estimated orientation, by a gravity removal module, to calculate initial linear acceleration data indicative of the past linear acceleration of the wearable health monitoring device;
using the past linear acceleration of the wearable health monitoring device to remove motion artifacts from the physiological sensor data output by the wearable health monitoring device;
storing the initial IMU calibration parameters and the past linear acceleration of the wearable health monitoring device;
receiving updated IMU data from the IMU of the wearable health monitoring device;
using the updated IMU data to calculate updated IMU calibration parameters; and
using the updated IMU calibration parameters to back-calibrate linear acceleration data indicative of the past linear acceleration of the wearable health monitoring device.

### Claim 2 (depends on 1)

The method of claim 1, wherein there are up to thirty-six IMU calibration parameters.

### Claim 3 (depends on 1)

The method of claim 1, further comprising:
comparing a plurality of previously calculated calibration parameters from the inertial measurement unit to the plurality of calibration parameters; and
updating the plurality of calibration parameters at an external calibration updater located at a wearable device prior to their transmittal to the sensor fusion module.

### Claim 4 (depends on 1)

The method of claim 1, wherein the sensor fusion module is used to determine acceleration due to gravity that is projected onto x, y, and z axes.

### Claim 5 (depends on 1)

The method of claim 1, wherein historical calibration data is used to update bias and sensitivity parameters.

### Claim 6 (depends on 1)

The method of claim 1, further comprising transmitting the corrected linear acceleration data to a Bluetooth Module for delivery to a second computer.

### Claim 7

A non-transitory computer storage medium that stores a program thereon that causes a computer to execute a process comprising:
receiving initial IMU data from an inertial measurement unit (IMU) of a wearable health monitoring device having one or more physiological sensors outputting physiological sensor data, the initial IMU data comprising raw accelerometer data, raw gyroscope data, and raw magnetometer data;
performing sensor calibration using the initial IMU data to calculate a plurality of initial IMU calibration parameters;
using the plurality of initial IMU calibration parameters, by a sensor fusion module, to calculate an initial estimated orientation of the wearable health monitoring device;
using the initial estimated orientation, by a gravity removal module, to calculate initial linear acceleration data indicative of the past linear acceleration of the wearable health monitoring device;
using the past linear acceleration of the wearable health monitoring device to remove motion artifacts from the physiological sensor data output by the wearable health monitoring device;
storing the initial IMU calibration parameters and the past linear acceleration of the wearable health monitoring device;
receiving updated IMU data from the IMU of the wearable health monitoring device;
using the updated IMU data to calculate updated IMU calibration parameters; and
using the updated IMU calibration parameters to back-calibrate linear acceleration data indicative of the past linear acceleration of the wearable health monitoring device.

### Claim 8 (depends on 7)

The non-transitory computer medium of claim 7, wherein there are up to thirty-six IMU calibration parameters.

### Claim 9 (depends on 7)

The non-transitory computer medium of claim 7, wherein the program further causes the computer to execute a process comprising:
comparing a plurality of previously calculated calibration parameters from the inertial measurement unit to the plurality of calibration parameters; and
updating the plurality of calibration parameters at an external calibration updater located at a wearable device prior to their transmittal to the sensor fusion module.

### Claim 10 (depends on 7)

The non-transitory computer medium of claim 7, wherein the sensor fusion module is used to determine acceleration due to gravity that is projected onto x, y, and z axes.

### Claim 11 (depends on 7)

The non-transitory computer medium of claim 7, wherein historical calibration data is used to update bias and sensitivity parameters.

### Claim 12 (depends on 7)

The non-transitory computer medium of claim 7, wherein the corrected linear acceleration data is transmitted to a Bluetooth Module for delivery to a second computer.