GAIT MONITOR

• US 20110313705A1
• Filed: 12/23/2009
• Published: 12/22/2011
• Est. Priority Date: 12/23/2008
• Status: Active Grant

• Current Assignee: Oxford Brookes University
• Original Assignee: Oxford Brookes University
• Inventors: Esser, Patrick, Howells, Ken, Dawes, Helen, Collet, Johnny
• Granted Patent: US 8,868,369 B2
• Time in Patent Office: Days
• US Class Current: 702/104
• 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: A61B 5/1122 of movement trajectories

Abstract

Vertical centre of mass movement measuring apparatus comprising an inertial sensing device, for producing outputs relating to rotation and acceleration in its local frame of reference and configured for fastening to the back of an animal, preferably a person, a memory and a processor, wherein the processor is programmed to provide a quaternion corresponding to the rotation of the inertial sensing device and a first acceleration, both based on an output of the rotation sensing device, and the processor is programmed to combine the quaternion and the first acceleration and based on the result of the combination to provide, when the device is fastened close enough to the centre of mass of a moving object such as a person, an estimate of vertical displacement, or a derivative of vertical displacement, of the centre of mass in a global reference frame.

Claims

1-32. -32. (canceled)

33. A vertical center of mass movement measuring apparatus comprising:

an inertial sensing device having a local frame of reference and arranged to undergo rotation and acceleration in the local frame of reference, for producing outputs relating to said rotation and acceleration in the local frame of reference, and configured for fastening to the back of an animal having a center of mass;

a memory; and

a processor, wherein the processor is programmed to provide a quaternion corresponding to the rotation of the inertial sensing device and a first acceleration, both based on an output of the rotation sensing device, and the processor is programmed to combine the quaternion and the first acceleration to produce a result, and based on the result to provide an estimate of at least one of a vertical displacement and a derivative of vertical displacement, of the center of mass in a global reference frame.

34. The vertical center of mass movement measuring apparatus according to claim 33 wherein the apparatus is configured to filter the result from the combination of the first acceleration and quaternion.

35. The vertical center of mass movement measuring apparatus according to claim 34 wherein the apparatus is configured to filter data out above a frequency chosen based on maximum stride frequency.

36. The vertical center of mass movement measuring apparatus according to claim 34 comprising a Butterworth filter which filter is configured to be used for the filtering.

37. The vertical center of mass movement measuring apparatus according to claim 33 wherein the apparatus is configured to apply a mathematical function to the result, to remove at least one of noise and errors that contribute to drift.

38. The vertical center of mass movement measuring apparatus according to claim 37 wherein the apparatus is configured to estimate a direct current component of at least one of noise and errors in the result from the combining of the first acceleration and quaternion and configured to select the mathematical function based on the estimate in order to remove it.

39. The vertical center of mass movement measuring apparatus according to claim 37 wherein the mathematical function is a Hanning window.

40. The vertical center of mass movement measuring apparatus according to claim 37 wherein the apparatus is configured to filter the result from the combination of the first acceleration and quaternion and the apparatus is configured to apply the mathematical function after applying the filter.

41. The vertical center of mass movement measuring apparatus according to claim 33 wherein the global reference frame is the reference frame of the earth'"'"'s surface with the vertical direction being the direction of the acceleration of gravity.

42. The vertical center of mass movement measuring apparatus according to claim 33 wherein the inertial sensing device comprises:

at least one of an inertial mass unit and multiple accelerometers measuring linear accelerations in a local frame, and at least one gyroscope measuring rotational movement; and

a device which is arranged to fuse their data outputs using Kalman filtering.

43. The vertical center of mass movement measuring apparatus according to claim 33 wherein the processor is programmed to provide an acceleration in the vertical direction, with the vertical direction being the direction of the acceleration of gravity.

44. The vertical center of mass movement measuring apparatus according to claim 43 wherein the processor is programmed to subtract acceleration of gravity from the calculated acceleration to measure the acceleration of the inertial sensing device in the vertical direction of the global reference frame.

45. The vertical center of mass movement measuring apparatus according to claim 43 wherein the apparatus is configured to measure speed of the inertial sensing device in the vertical direction of the global frame by integrating the acceleration in the vertical direction.

46. The vertical center of mass movement measuring apparatus according to claim 45 wherein the apparatus is configured to filter and de-drift the acceleration in the vertical direction before integration.

47. The vertical center of mass movement measuring apparatus according to claim 43 wherein the processor is programmed to integrate the obtained acceleration in the vertical direction twice to measure changes in the vertical position in the global reference frame.

48. The vertical center of mass movement measuring apparatus according to claim 45 wherein the processor is programmed to integrate data using Simpson'"'"'s rule.

49. The vertical center of mass movement measuring apparatus according to claim 33 wherein the first acceleration is in the form of a vector in three spatial dimensions and the quaternion is in the form of a four by three matrix and is multiplied by the first acceleration vector to provide an acceleration vector in the global reference frame from which at least one of the measure of vertical displacement, and a derivative of vertical displacement, is calculated.

50. The vertical center of mass movement measuring apparatus according to claim 49 wherein the quaternion matrix is of the form

51. The vertical center of mass movement measuring apparatus according to claim 33 wherein the processor is programmed to calculate a quaternion when the inertial sensor is at a rest, at least in the vertical direction, from the output acceleration from the inertial sensing device together with the expected acceleration of gravity in the vertical direction of the global reference frame, to store this quaternion in the memory and to use it in deriving the quaternion corresponding to the rotation of the inertial sensing device.

52. A vertical jerk measuring apparatus comprising the apparatus according to claim 43 wherein the processor is programmed to differentiate the obtained acceleration with respect to time in the vertical direction to measure the jerk in the vertical direction in the global reference frame.

53. The vertical center of mass movement measuring apparatus according to claim 33, wherein the processor is programmed to use at least one of the estimate of vertical displacement and a derivative of vertical displacement of the center of mass, along with the input mass of the moving object, and also the direction of gravity, in calculating a measure of at least some of the energy used during the movement.

54. A computer program product containing instructions which when run on a processor connected to a memory and inertial sensing device provides the apparatus according to claim 33.

55. A vertical center of mass movement measuring apparatus comprising:

an inertial sensing device, for producing outputs relating to rotation and acceleration in its local frame of reference, a memory and a processor, wherein the processor is programmed to provide a rotation element, such as an Euler rotation matrix or a quaternion, corresponding to the rotation of the inertial sensing device and a first acceleration, both based on an output of the rotation sensing device, and the processor is programmed to combine the rotation element and the first acceleration and based on the result of the combination to provide a measure of vertical displacement, or a derivative of vertical displacement, in a global reference frame, wherein the apparatus is configured to apply a mathematical function, such a window, to the data from the combining of the first acceleration and rotation element to remove noise/errors that contribute to drift.

56. A method of measuring at least one of vertical center of mass displacement and a derivative of vertical displacement, of an object, in a global reference frame, the method comprising the steps of:

applying an inertial sensing device to the object;

calculating a quaternion corresponding to the rotation of the inertial sensing device and a first acceleration from the outputs of the inertial sensing device, and combining the quaternion and acceleration.