# US 2016/0258779 A1 · Inertial Motion Capture Calibration > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0258779 A1 - Document ID: US20160258779A1 - Status: Published application - Kind: A1 - Application number: 14/639,776 - Filed: 2015-03-05 - Published: 2016-09-08 - Earliest claimed: 2015-03-05 - Assignees: Xsens Holding B.V. - Applicants: Xsens Holding B.V. - Inventors: Jeroen D. Hol; Giovanni Bellusci - Web page: https://patentgrep.com/patent/US20160258779A1 ## CPC - G01C 25/005: {initial alignment, calibration or starting-up of inertial devices} - A61B 5/1121: {Determining geometric values, e.g. centre of rotation or angular range of movement} - G01P 21/00: Testing or calibrating of apparatus or devices covered by the preceding groups - A61B 2560/0223: of calibration, e.g. protocols for calibrating sensors - 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) - 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 and method for accurately estimating orientations between inertial sensing units and the body segments of a multi-segment subject to which they are affixed, and for accurately estimating position vectors from sensing units to joint centers of the corresponding body segments. By using the disclosed system and method magnetometers are not required and SDI (strap down integration) increments may be used as input to estimate the position and orientation of the sensors. ## Claims ### Claim 1 A method of inertial motion capture calibration with respect to a subject having N segments connected by joints, wherein N>1 and each segment has affixed at least one sensing unit, each sensing unit containing at least a 3D gyroscope and a 3D accelerometer, the method comprising: defining unknown 3D orientations between sensing units and the corresponding segments the sensing units are attached to; collecting 3D accelerometer and 3D gyroscope data from the sensing units; predicting 3D position and 3D orientation trajectories of the sensing units by integration of the 3D accelerometer and 3D gyroscope data; deriving 3D joint center positions from the predicted position and orientation of the sensing units; generating 3D joint position constraints by equating pairs of 3D joint center positions derived from sensing units on adjoining segments; updating the sensing unit trajectories by applying the 3D joint position constraints; generating a set of at least 3N independent segment orientation constraints, each constraint being a scalar function operating on a 3D orientation of a segment at one or more time instants; and estimating the unknown 3D orientations by applying the segment orientation constraints. ### Claim 2 (depends on 1) The method in accordance with claim 1, wherein the subject is a human body or part of a human body. ### Claim 3 (depends on 1) The method in accordance with claim 1, wherein the subject comprises at least one of an object and a mechanical structure. ### Claim 4 (depends on 1) The method in accordance with claim 1, wherein the joints include at least one of hinge joints and ball-and-socket joints. ### Claim 5 (depends on 1) The method in accordance with claim 1, wherein the 3D accelerometer and 3D gyroscope data comprise orientation and velocity increment signals obtained from pre-processing with SDI (strap down integration). ### Claim 6 (depends on 1) The method in accordance with claim 1, wherein any of the sensing units further include a 3D magnetometer. ### Claim 7 (depends on 1) The method in accordance with claim 1, wherein deriving 3D joint center positions from the predicted position and orientation of the sensing units comprises translating predicted sensing unit positions by known 3D position vectors rotated using the predicted sensing unit orientations. ### Claim 8 (depends on 1) The method in accordance with claim 1, wherein the 3D orientation of segments in the segment orientation constraints are relative to any of an external reference frame, a sensor frame, or another segment frame. ### Claim 9 (depends on 1) The method in accordance with claim 1, wherein estimating the unknown 3D orientations further includes using additional known constraints. ### Claim 10 A method of inertial motion capture calibration with respect to a subject having multiple segments connected by joints, wherein each segment has affixed at least one sensing unit, each sensing unit containing at least a 3D gyroscope and a 3D accelerometer, the method comprising: defining unknown 3D position vectors from the sensing units to corresponding joint centers; collecting 3D accelerometer and 3D gyroscope data from the sensing units; predicting position and orientation trajectories of the sensing units by integration of the 3D accelerometer and 3D gyroscope data; generating 3D joint position constraints by equating 3D joint center positions derived from the predicted position and orientation of two sensing units attached to adjoining segments and the unknown 3D position vectors; and estimating the unknown 3D position vectors and the sensing unit trajectories by applying the 3D joint position constraints. ### Claim 11 (depends on 10) The method in accordance with claim 10, wherein estimating the unknown 3D position vectors and the sensing unit trajectories further includes using additional known constraints on the 3D position vectors. ### Claim 12 A system of inertial motion capture calibration with respect to a subject having N segments connected by joints, wherein N>1, the system comprising: at least one sensing unit affixed to each segment, each sensing unit containing at least a 3D gyroscope and a 3D accelerometer; and a controller configured to: define unknown 3D orientations between sensing units and the corresponding segments the sensing units are attached to; collect 3D accelerometer and 3D gyroscope data from the sensing units; predict 3D position and 3D orientation trajectories of the sensing units by integration of the 3D accelerometer and 3D gyroscope data; derive 3D joint center positions from the predicted position and orientation of the sensing units; generate 3D joint position constraints by equating pairs of 3D joint center positions derived from sensing units on adjoining segments; update the sensing unit trajectories by applying the 3D joint position constraints; generate a set of at least 3N independent segment orientation constraints, each constraint being a scalar function operating on a 3D orientation of a segment at one or more time instants; and estimate the unknown 3D orientations by applying the segment orientation constraints. ### Claim 13 (depends on 12) The system in accordance with claim 12, wherein the subject is part of a human body. ### Claim 14 (depends on 12) The system in accordance with claim 12, wherein the subject comprises at least one of an object and a mechanical structure. ### Claim 15 (depends on 12) The system in accordance with claim 12, wherein the joints include at least one of hinge joints and ball-and-socket joints ### Claim 16 (depends on 12) The system in accordance with claim 12, wherein the 3D accelerometer and 3D gyroscope data comprise orientation and velocity increment signals obtained from pre-processing with SDI (strap down integration). ### Claim 17 (depends on 12) The system in accordance with claim 12, wherein any of the sensing units further include a 3D magnetometer. ### Claim 18 (depends on 12) The system in accordance with claim 12, wherein the segment orientation constraints are formulated using a segment orientation relative to any of an external reference frame, a sensor frame, or another segment frame. ### Claim 19 A non-transitory computer-readable medium having stored thereon computer-executable instructions for performing inertial motion capture calibration with respect to a subject having N segments connected by joints, wherein N>1, with at least one sensing unit affixed to each segment, each sensing unit containing at least a 3D gyroscope and a 3D accelerometer, the computer-executable instructions comprising: defining unknown 3D orientations between sensing units and the corresponding segments to which the sensing units are attached; collecting 3D accelerometer and 3D gyroscope data from the sensing units; predicting 3D position and 3D orientation trajectories of the sensing units by integration of the 3D accelerometer and 3D gyroscope data; deriving 3D joint center positions from the predicted position and orientation of the sensing units; generating 3D joint position constraints by equating pairs of 3D joint center positions derived from sensing units on adjoining segments; updating the sensing unit trajectories by applying the 3D joint position constraints; generating a set of at least 3N independent segment orientation constraints, each constraint being a scalar function operating on a 3D orientation of a segment at one or more time instants; and estimating the unknown 3D orientations by applying the segment orientation constraints. ### Claim 20 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein the subject includes part of a human body. ### Claim 21 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein the subject comprises at least one of an object and a mechanical structure. ### Claim 22 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein the joints include at least one of hinge joints and ball-and-socket joints. ### Claim 23 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein the 3D accelerometer and 3D gyroscope data comprises orientation and velocity increment signals obtained from pre-processing with SDI (strap down integration). ### Claim 24 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein any of the sensing units further includes a 3D magnetometer. ### Claim 25 (depends on 19) The non-transitory computer-readable medium in accordance with claim 19, wherein the instructions for generating a set of at least 3N independent segment orientation constraints comprise instructions for generating the set of at least 3N independent segment orientation constraints using a segment orientation relative to any of an external reference frame, a sensor frame, or another segment frame.