Motion analysis system

• US 6,513,381 B2
• Filed: 07/26/2001
• Issued: 02/04/2003
• Est. Priority Date: 10/14/1997
• Status: Expired due to Term

• Current Assignee: Garmin Limited
• Original Assignee: Dynastream Innovations Incorporated (Garmin Limited)
• Inventors: Fyfe, Kipling W., Fyfe, Kenneth R., Rooney, James K.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/916,744
• Publication Number:
  US 20020040601A1
• Time in Patent Office: 558 Days
• Field of Search: 734/90, 734/92, 734/89, 738/654, 735/10, 702/141, 702/160, 702/166
• US Class Current: 73/510
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/112 Gait analysis
• CPC Class Codes: A61F 2002/7615 Measuring means for implanting artificial joints A61F2/4657
• CPC Class Codes: A61F 2002/764 for measuring acceleration
• CPC Class Codes: A63B 2220/40 Acceleration
• CPC Class Codes: A63B 69/0028 for running, jogging or speed-walking movable endless bands A63B22/02
• CPC Class Codes: G01C 22/006 Pedometers
• CPC Class Codes: G01P 1/127 for acceleration values
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A device comprised of at least a pair of accelerometers and a tilt sensor mounted in fixed relation to a datum plane defining surface (sole of a shoe) may be used for extracting kinematic variables including linear and rotational acceleration, velocity and position. These variables may be resolved into a selected direction thereby permitting both relative and absolute kinematic quantities to be determined. The acceleration is determined using a small cluster of two mutually perpendicular accelerometers mounted on a shoe. Angular orientation of the foot may be determined by double integration of the foot'"'"'s angular acceleration (which requires a third accelerometer substantially parallel to one of the two orthogonal accelerometers). The two orthogonal accelerations are then resolved into a net horizontal acceleration or other selected direction which may be integrated to find the foot velocity in the selected direction. The average of the foot velocity corresponds to the subject'"'"'s gait speed.

Claims

1. A motion analysis system including

A. a plurality of accelerometers for making acceleration measurements;

B. a processor for

i. determining angular acceleration values based on the measurements made by the accelerometers,

ii. compensating for drift errors in the measurements made by the accelerometers to produce corrected angular acceleration values,

iii. calculating angle of rotation values from the corrected angular acceleration values,

iv. calculating velocity in a selected direction based on the calculated angle of rotation values and the measurements made by the accelerometers.

2. The motion analysis system of claim 1 wherein

a. the plurality of accelerometers include two parallel and co-planar accelerometers that are spaced a known distance apart; and

b. the processor determines the angle of rotation values based on the measurements made by the parallel accelerometers.

3. The motion analysis system of claim 1 wherein the processor compensates for drift by

a. defining for a given stride of a gait a datum plane at full foot fall, and

b. determining the angle of rotation values relative to the datum plane.

4. The motion analysis system of claim 3 wherein the processor determines full foot fall at a point in the stride that corresponds to a minimum angle of rotation.

5. The motion analysis system of claim 3 wherein the processor determines full footfall at a point in the stride that corresponds to a predetermined time after heel strike.

6. The motion analysis system of claim 1 wherein the processor

a. calculates angular velocity by integrating the angular acceleration values;

and

b. compensates for drift error by removing a mean angular acceleration value for a given stride before integrating.

7. The motion analysis system of claim 6 wherein the processor further

c. calculates an angle of rotation by a second integration, and

d. compensates for drift error by subtracting a mean angular velocity value for a given stride before performing the second integration.

8. The motion analysis system of claim 1 wherein the processor compensates for drift errors by shifting the calculated velocity by a value that sets a minimum calculated value to zero.

9. The motion analysis system of claim 3 wherein the processor further compensates for drift error by removing a zero offset value from a calculated net horizontal acceleration value to produce a corrected horizontal acceleration value.

10. The motion analysis system of claim 9 wherein the processor calculates horizontal velocity based on the corrected horizontal acceleration value.