System for capturing movements of an articulated structure

Patent metadata

Field	Value
Publication number	US-9958470-B2
Application number	US-201314382998-A
Country	US
Kind code	B2
Filing date	Mar 7, 2013
Priority date	Mar 8, 2012
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A system for capturing the movements of a body having substantially rigid segments articulated together includes attitude units fastened onto the segments of the body, the units each including at least one accelerometer and one magnetometer, and a reduced number of gyroscopes. The system also includes a pseudo-static state detection module and a module for calculating pseudo-static angles. When all segments are detected in a pseudo-static state, the state vector is provided by the module for calculating pseudo-static angles. When a segment is detected in a dynamic state, the state vector is provided at the output of a Kalman filter.

First claim

The invention claimed is:

1. A system for capturing movements of a structure including at least N substantially rigid segments articulately connected with said structure, said system including:
a set of N accelerometers with at least one measurement axis, each of said N accelerometers being substantially rigidly connected to one of said N segments,
a set of P second sensors capable of returning one direction of a fixed reference frame, each substantially rigidly connected to a segment,
a set of Q third sensors capable of returning a measurement representative of an angular velocity, each substantially rigidly connected to a segment,
a module for communicating the outputs of the N accelerometers, P second sensors and Q third sensors with a computer processing module;
said processing module including a state observer,
said system further including:
a pseudo-static state detection module for detecting a pseudo-static state of each of the segments of said structure,
a pseudo-static orientation calculation module for calculating a pseudo-static orientation of the segments in a pseudo-static state,
a state observer module configured for replacing outputs of a prediction function of the state observer with outputs of the pseudo-static orientation calculation module for the segments for which a detection condition at the output of the pseudo-static state detection module condition is true

wherein the number Q is less than the number N and the number P.

2. The system for capturing movements as claimed in claim 1 , wherein R is equal to a number of branches of the structure whereof the movement is captured, the number Q being less than or equal to R+1.

3. The system for capturing movements as claimed in claim 1 , wherein the second sensors are magnetometers.

4. The system for capturing movements as claimed in claim 3 , wherein the third sensors are gyroscopes.

5. The system for capturing movements as claimed in claim 4 , wherein the observer is a Kalman filter.

6. The system for capturing movements as claimed in claim 5 , wherein the modules thereof are configured by state evolution models of the form:

{

Measurement
=

function
⁡

(
x
)

x
.

=

evolution
⁡

(
x
)

⁢

where:
x designates a state vector of the body;
function designates a characteristic measurement function of the accelerometers, magnetometers and gyroscopes;
Measurement=[Measurement Accelerometer, Measurement Magnetometer, Measurement Gyroscope] designates a measurement vector provided by the accelerometers, magnetometers and gyroscopes;
{dot over (x)} designates the first derivative of x with respect to time; and
evolution designates an evolution function of the body state.

7. The system for capturing movements as claimed in claim 6 , wherein the state vector x is of the form x=[θ, {dot over (θ)}, {umlaut over (θ)}, Acc x , Acc y , Acc z ] where θ, {dot over (θ)} and {umlaut over (θ)} respectively designate an orientation angle of the segments, its first derivative and its second derivative with respect to time, and where Acc x Acc y and Acc z designate components of a frame acceleration Acc of the whole of the body in a terrestrial reference frame (X, Y, Z).

8. The system for capturing movements as claimed in claim 6 , wherein the state evolution model of the Kalman filter uses said pseudo-static angles for the segments detected in a pseudo-static state and the state evolution model of the Kalman filter for the segments detected in a dynamic state.

9. The system for capturing movements as claimed in claim 8 , wherein the state evolution model of the Kalman filter uses an assumption of constancy of accelerations of the articulation angles.

10. The system for capturing movements as claimed in claim 6 , wherein the state vector is estimated from pseudo-static angles at the output of the pseudo-static orientation calculation module, if all the segments are detected in a pseudo-static state and is estimated by the Kalman filter, if at least one segment is detected in a dynamic state.

11. The system for capturing movements as claimed in claim 6 , wherein a criterion of pseudo-staticity is fulfilled by a segment when at least one of the values provided by at least one of the elements of the group including an attitude unit or a gyroscope which is rigidly connected thereto provides at least one measurement chosen from the norm of an acceleration vector and an angle between said acceleration vector and a magnetic field vector which is less than a predetermined threshold value.

12. The system for capturing movements as claimed in claim 6 , wherein the state evolution model of the Kalman filter predicts the angle θ, its first derivative {dot over (θ)} and its second derivative {umlaut over (θ)} via the function defined by:

x
.

=

[

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

Assignees

• Movea
• Commissariat Energie Atomique

Inventors

• Grenet Pierre

Classifications

• G01P15/00 Primary

  Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration · CPC title

• G06F3/011 Primary

  Arrangements for interaction with the human body, e.g. for user immersion in virtual reality (blind teaching G09B21/00) · CPC title

• A61B5/1116

  Determining posture transitions · CPC title

• A63B71/06

  Indicating or scoring devices for games or players {, or for other sports activities} · CPC title