# US 2018/0031374 A1 · Method and system for personal dead-reckoning drift compensation using gait characteristics

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- Number: US 2018/0031374 A1
- Document ID: US20180031374A1
- Status: Published application
- Kind: A1
- Application number: 15/224,502
- Filed: 2016-07-29
- Published: 2018-02-01
- Earliest claimed: 2016-07-29
- Assignees: Bionic Power Inc.
- Applicants: Bionic Power Inc.
- Inventors: Daniel Loren Hepler; Clive Edward Mullins
- Web page: https://patentgrep.com/patent/US20180031374A1

## CPC

- G01C 21/188: {for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems}
- A61B 5/112: {Gait analysis}
- A61B 5/6802: {Sensor mounted on worn items}
- A61B 5/7207: {of noise induced by motion artifacts}
- G01C 21/1654: {with electromagnetic compass}
- G01C 21/20: Instruments for performing navigational calculations (G01C21/24, G01C21/26 take precedence)
- G01C 22/006: {Pedometers}
- 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)

## Abstract

Raw dead reckoning data is obtained from an inertial measurement unit (IMU) worn by a user. Drift in the raw data is compensated for by detecting a gait of the user and phase of that gait, and constraining the position of the IMU to lie within corresponding bounds as the IMU moves. The bounds depend on the bodily geometry of the user and the detected gait phase. The raw orientation data of the IMU may be also corrected for drift in a similar way. Gait and gait phase may be detected by sensors in an energy harvester worn around the knee, for example. Drift in the IMU measurements can be compensated for without depending on a GPS signal or on the earth's magnetic field.

## Claims

### Claim 1

A method for compensating for drift in dead reckoning calculations for a user undergoing locomotion comprising:
attaching an inertial measurement unit (IMU) to the user;
defining a first point at which the IMU is located;
detecting a phase of a gait of the user using one or more sensors;
defining bounds for displacement of the IMU during said phase of the gait;
obtaining raw positional data from the IMU for a second point, to which the IMU is displaced by the locomotion of the user;
determining whether said raw positional data lies within or outside of said bounds;
if the raw positional data lies within the bounds, outputting the raw positional data as dead reckoned data for the second point; and
if the raw positional data lies outside the bounds, compensating the raw positional data to result in compensated positional data that is within the bounds and outputting the compensated positional data as the dead reckoned data for the second point.

### Claim 2 (depends on 1)

The method of claim 1, wherein the user is a human.

### Claim 3 (depends on 1)

The method of claim 1, further comprising:
defining a first orientation for the IMU at the first point;
defining further bounds for orientation of the IMU during said phase of the gait;
obtaining raw orientational data from the IMU for the second point;
determining whether said raw orientational data lies within or outside of said further bounds;
if the raw orientational data lies within the further bounds, outputting the raw orientational data as dead reckoned data for the second point; and
if the raw orientational data lies outside the further bounds, compensating the raw orientational data to result in compensated orientational data that is within the further bounds and outputting the compensated orientational data as the dead reckoned data for the second point.

### Claim 4 (depends on 1)

The method of claim 1, wherein the IMU is attached to a lower leg.

### Claim 5 (depends on 4)

The method of claim 4, wherein the phase of the gait starts with a heel strike of the lower leg.

### Claim 6 (depends on 1)

The method of claim 1, wherein the phase of the gait starts with a heel strike.

### Claim 7 (depends on 6)

The method of claim 6, wherein the phase of the gait ends with either:
a lift of said heel; or
a lift of a foot having said heel.

### Claim 8 (depends on 1)

The method of claim 1, wherein the compensated positional data is on a surface of the bounds at a point that is a shortest distance from the raw positional data to the bounds.

### Claim 9 (depends on 1)

The method of claim 1, wherein the bounds move as the user progresses through the gait.

### Claim 10 (depends on 1)

The method of claim 1, wherein said sensors include one or both of a knee angle sensor and a knee angular velocity sensor.

### Claim 11 (depends on 1)

The method of claim 1, further comprising attaching a further IMU to the user and performing one or both of:
further defining the bounds to lie within a predetermined distance from the further IMU; and
defining additional bounds for the further IMU such that the additional bounds lie within a predetermined distance from the bounds.

### Claim 12 (depends on 1)

The method of claim 1, wherein detecting the phase of the gait of the user comprises selecting a gait model from a library of gait models.

### Claim 13 (depends on 1)

The method of claim 1, wherein defining the bounds is based on:
one or more dimensions of the user; and
one or more ranges of motion of one or more body parts of the user.

### Claim 14 (depends on 1)

The method of claim 1, wherein said outputting is to one or both of a data store and a monitoring computer.

### Claim 15 (depends on 1)

The method of claim 1, further comprising converting the dead reckoned data for the second point to dead reckoned data for the user.

### Claim 16

A system for compensating for drift in dead reckoning calculations for a user undergoing locomotion comprising:
an inertial measurement unit (IMU) attached to the user;
one or more sensors attached to the user;
one or more processors; and
modules of program code;
wherein the modules of program code are configured, when executed by the processors to:
define a first point at which the IMU is located;
detect a phase of a gait of the user using the one or more sensors;
define bounds for displacement of the IMU during said phase of the gait;
obtain raw positional data from the IMU for a second point, to which the IMU is displaced by the locomotion of the user;
determine whether said raw positional data lies within or outside of said bounds;
if the raw positional data lies within the bounds, output the raw positional data as dead reckoned data for the second point; and
if the raw positional data lies outside the bounds, compensate the raw positional data to result in compensated positional data that is within the bounds and output the compensated positional data as the dead reckoned data for the second point.

### Claim 17 (depends on 16)

The system of claim 16, wherein said sensors include one or both of a knee angle sensor and a knee angular velocity sensor.

### Claim 18 (depends on 16)

The system of claim 16, wherein said modules of program code are further configured to:
define a first orientation for the IMU at the first point;
define further bounds for orientation of the IMU during said phase of the gait;
obtain raw orientational data from the IMU for the second point;
determine whether said raw orientational data lies within or outside of said further bounds;
if the raw orientational data lies within the further bounds, output the raw orientational data as dead reckoned data for the second point; and
if the raw orientational data lies outside the further bounds, compensate the raw orientational data to result in compensated orientational data that is within the further bounds and output the compensated orientational data as the dead reckoned data for the second point.

### Claim 19 (depends on 16)

The system of claim 16 wherein said IMU, sensors, modules of program code and processors are embodied within an energy harvester.

### Claim 20

A computer readable medium comprising computer readable instructions, which, when executed by a processor, cause a system for compensating for drift in dead reckoning calculations for a user undergoing locomotion to:
define a first point at which an inertial measurement unit (IMU) attached to a user is located;
detect a phase of a gait of the user using one or more sensors that are attached to the user;
define bounds for displacement of the IMU during said phase of the gait;
obtain raw positional data from the IMU for a second point, to which the IMU is displaced by the locomotion of the user;
determine whether said raw positional data lies within or outside of said bounds;
if the raw positional data lies within the bounds, output the raw positional data as dead reckoned data for the second point; and
if the raw positional data lies outside the bounds, compensate the raw positional data to result in compensated positional data that is within the bounds and output the compensated positional data as the dead reckoned data for the second point.