Motion analysis system

• US 20020040601A1
• Filed: 07/26/2001
• Published: 04/11/2002
• Est. Priority Date: 10/14/1997
• Status: Active Grant

• Current Assignee: Garmin Limited
• Original Assignee: James K. Rooney, Kenneth R. Fyfe, Kipling W. Fyfe
• Inventors: Rooney, James K., Fyfe, Kipling W., Fyfe, Kenneth R.
• Granted Patent: US 6,513,381 B2
• Time in Patent Office: Days
• US Class Current: 73/490
• 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 method of determining gait kinematics for a subject in each of a plurality of strides comprised during each stride defining a fresh datum plane, determining angles between a pair of accelerometers and said datum plane, said pair of accelerometers being adapted to measure acceleration in two directions, the two directions being separated by a known angle of greater than 0°

, and being adapted to measure acceleration in a plane of motion substantially perpendicular to said datum plane, measuring acceleration in said plane of motion in said two directions, converting said accelerations to provide determination of a gait kinematic result for each said stride.

2. The method as defined in claim 1 wherein the two directions are substantially mutually perpendicular.

3. The method as defined in claim 1 wherein the gait kinematic result is selected from the group consisting of acceleration in a selected direction, velocity in a selected direction or distance in a selected direction.

4. The method as defined in claim 3 wherein the selected direction is parallel to the datum plane and in said plane of motion.

5. The method as defined in claim 3 wherein the selected direction is perpendicular to said datum plane and in said plane of motion.

6. The method as defined in claim 3 further comprising integrating the acceleration in a selected direction to determine velocity in a selected direction.

7. The method as defined in claim 3 further comprising integrating velocity in a selected direction to define distance traveled in a selected direction.

8. The method as defined in claim 1 wherein the fresh datum plane is preferably defined when the pair of accelerometers are at a selected position relative to the datum plane.

9. The method as defined in claim 8 wherein the pair of accelerometers are in the selected position as indicated by foot impact with a surface just prior to a stance phase of the gait.

10. The method as defined in claim 9 wherein the fresh datum plane is defined at foot impact plus 0.1 seconds

11. The method of claim 1 wherein the gait kinematic result is horizontal acceleration and the method further comprising integrating said horizontal acceleration to define stride velocity.

12. The method of claim 1 wherein the gait kinematic result is velocity in a selected direction and the method further comprises integrating said velocity in a selected direction to define distance in said selected direction.

13. The method as defined in claim 1 further comprising adjusting for drift error correction.

14. The method as defined in claim 1 further comprising determining the subject'"'"'s mass and using the mass to determine impact force.

15. The method as defined in claim 1 further comprising measuring acceleration in a lateral direction out of the plane of motion and converting said accelerations measured by the pair of accelerometers and the lateral accelerometer to provide acceleration in a selected direction.

16. The method as defined in claim 15 wherein the lateral direction is substantially perpendicular to each of the pair of accelerometers.

18. The device of claim 17 wherein the two directions are substantially mutually perpendicular.

19. The device of claim 17 wherein the gait kinematic result is selected from the group consisting of acceleration in a selected direction, velocity in a selected direction or distance in a selected direction.

20. The device of claim 19 wherein the selected direction is parallel to the datum plane and in said plane of motion.

21. The device of claim 17 further comprising a means for adjusting for drift error correction.

22. The device of claim 17 wherein the means for determining angular orientation of said accelerometers to said datum plane comprises of a pair of spaced substantially parallel accelerometers mounted in fixed relation to said datum plane defining surface and means for calculating angular orientation based on differences in accelerations measured by said pair of spaced substantially parallel accelerometers.

23. The device of claim 17 wherein the pair of accelerometers is adapted to measure the acceleration in a plane of motion, and the device further comprising a lateral accelerometer mounted in a fixed and known relationship to the pair of mutually perpendicular accelerometers and adapted to measure acceleration in a third direction selected to be out of the plane of motion.

24. The device of claim 23 wherein the lateral accelerometer is substantially perpendicular to the pair of accelerometers.

26. The method of claim 25 wherein the pair of accelerometers are substantially mutually perpendicular.

27. The method of claim 25 wherein the gait kinematic result is selected from the group consisting of acceleration in a selected direction, velocity in a selected direction or distance in a selected direction.

28. The method of claim 25 wherein the adjusting step is made prior to the step of converting to provide the gait kinematic result.

29. The method of claim 25 wherein the adjusting step is conducted after the step of converting to provide the gait kinematic result.

30. The method of claim 25 wherein the step of adjusting includes employing known limitations in the gait kinematic result.

31. The method of claim 30 wherein any velocity in a selected direction results are adjusted to remove any negative velocity results therefrom.

32. The method of claim 25 further comprising an integration step to derive further gait kinematic results from the gait kinematic result and adjusting for drift error correction in the integration steps.

33. The method of claim 25 wherein the gait kinematic result is acceleration in said selected direction and the method further comprises integrating the acceleration in a selected direction to define velocity in said selected direction.

34. The method of claim 33 further comprising determining a mean acceleration in said selected direction and removing the mean acceleration from the acceleration in said selected direction prior to integrating to determine velocity in said selected direction.

35. The method of claim 34 conducted for each of a plurality of strides.

36. The method of claim 34 wherein the mean acceleration in a selected direction is obtained from a previously determined gait kinematic result.

37. The method of claim 25 wherein the gait kinematic result is velocity in a selected direction and the method further comprises integrating said velocity in a selected direction to define distance traveled in a selected direction.

38. The method of claim 37 further comprising determining a mean velocity in said selected direction and removing the mean velocity from the velocity in said selected direction prior to integrating to determine distance traveled in a selected direction.

39. The method of claim 25 wherein the gait kinematic result is horizontal acceleration and the method further comprising integrating said horizontal acceleration to define stride velocity.

40. The method of claim 39 further comprising determining a mean horizontal acceleration and removing the mean horizontal acceleration from the horizontal acceleration prior to integrating to determine stride velocity.

41. The method of claim 25 wherein the gait kinematic result is velocity in a selected direction and the method further comprises integrating said velocity in a selected direction to define distance in said selected direction.

42. The method of claim 41 further comprising determining a mean velocity in a selected direction and removing the mean velocity in a selected direction from the velocity in a selected direction prior to integrating to determine distance in a selected direction.

17. A device for measuring gait kinematics comprising means for mounting a pair of accelerometers in a fixed relationship to a datum plane defining surface, said pair of accelerometers being adapted to measure acceleration in two directions, the two directions being separated by a known angle of greater than 0°

, means defining a datum plane for each stride for which said gait kinematics is measured as a plane occupied by said datum plane defining surface when said datum plane defining surface is in a stationary position in a stance phase of said stride, means for determining angular orientation of said accelerometers to said datum plane, means for determining a gait kinematic result based on measurements of acceleration by said pair of accelerometers and said determined angular orientation of said accelerometers to said datum plane.

25. A method of determining gait kinematics comprised during each stride defining a datum plane, determining angles between a pair of accelerometers and said datum plane, said pair of accelerometers being adapted to measure acceleration in two directions, the two directions being separated by a known angle of greater than 0°

and being adapted to measure acceleration in a plane of motion substantially perpendicular to said datum plane, measuring acceleration in said plane of motion in said two directions, converting said accelerations to provide determination of a gait kinematic result for each said stride and adjusting for drift error correction in said gait kinematic result.

43. A device for measuring gait kinematics comprising means for mounting a pair of accelerometers in a fixed relationship to a datum plane defining surface and said pair of accelerometers being adapted to measure acceleration in two directions, the two directions being separated by a known angle of greater than 0°

, means defining a datum plane measured as a plane occupied by said datun plane defining surface when said datum plane defining surface is in a stationary position in a stance phase of said stride, means for determining angular orientation of said accelerometers to said datum plane, means for determining a gait kinematic result based on measurements of acceleration by said pair of accelerometers and said determined angular orientation of said accelerometers to said datum plane and means for adjusting for drift error correction.

44. The device of claim 43 wherein the two directions are substantially mutually perpendicular.

45. The device of claim 43 wherein the gait kinematic result is selected from the group consisting of acceleration in a selected direction, velocity in a selected direction or distance in a selected direction.

46. The device of claim 43 wherein the selected direction is parallel to the datum plane and in said plane of motion.

47. The device of claim 43 wherein the means for adjusting for drift error correction is a system for determining the mean signal of any particular gait signal and applying the mean signal to the particular signal prior to integration to determine further gait kinematic results.

48. The device of claim 43 wherein the means for adjusting for drift error correction is a system for using known physical limits of the derived signal to account for drift.

50. The device of claim 49 wherein the axis of the foot is substantially parallel to the subject'"'"'s sagittal plane and with the datum plane defining surface.

51. The device of claim 49 wherein the axis of rotation is that about which is defined pronation.

49. A device for measuring gait kinematics of a stride in a subject having a foot, the device comprising means for mounting a pair of accelerometers in a fixed relationship to a datum plane defining surface, said pair of accelerometers being adapted to measure acceleration in two substantially parallel directions about an axis of rotation defined by movement of the foot, means defining a datum plane measured as a plane occupied by said datum plane defining surface when said datum plane defining surface is in a stationary position in a stance phase of said stride, and means for calculating angular orientation based on differences in accelerations measured by said pair of accelerometers.

52. A method of determining pronation characteristics of a foot during a stride comprising during each stride defining a datum plane, determining angular acceleration about an axis about which a foot pronates, converting the angular acceleration relative to the datum plane to determine an angle of pronation for the foot.