ACTIVITY MONITORING SYSTEM INSENSITIVE TO ACCELERATIONS INDUCED BY EXTERNAL MOTION FACTORS

• US 20110012759A1
• Filed: 03/05/2009
• Published: 01/20/2011
• Est. Priority Date: 03/14/2008
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Yin, Bin
• Granted Patent: US 8,416,102 B2
• Time in Patent Office: Days
• US Class Current: 341/20
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1118 Determining activity level
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths

Abstract

This invention relates to an activity monitoring system adapted to eliminate passive movement components caused by external forces from readout data produced by a first and a second motion sensor when attached to a subject during movement. The readout data include gravitational components, movement components caused by active movement of the subject or subject parts, and the passive movement components. A processor estimates first and second gravitational components produced by the at least first and a second motion sensors. It determines a rotation matrix based on the estimated gravitational components, the rotation matrix denoting rotation required for the first sensor to get aligned with the second sensor in orientation. It then multiplies the readout data produced by the first motion sensor with the rotation matrix when rotating the first sensor towards the second sensor. Finally, it subtracts the result of the multiplying from the readout data produced by the second motion sensor when rotating the first motion sensor towards the second motion sensor.

Claims

1. An activity monitoring system (100) adapted to eliminate passive movement components caused by external forces from readout data (105) produced by at least a first and a second motion sensor (101, 102) when attached to a subject (104) during movement, the readout data (105) including gravitational components, movement components caused by active movement of the subject or subject parts, and the passive movement components, the system comprising:

a processor (103, 203) adapted to;

estimating a first and second gravitational components produced by the at least first and a second motion sensors (101, 102),

determining a rotation matrix based on the estimated gravitational components, the rotation matrix denoting rotation required for the first sensor to get aligned with the second sensor in orientation,

multiplying the readout data produced by the first motion sensor with the rotation matrix when rotating the first sensor towards the second sensor, and

subtracting the result of the multiplying from the readout data produced by the second motion sensor when rotating the first motion sensor towards the second motion sensor.

2. An activity monitoring system according to claim 1, where the motion sensors (101, 102) are attached to the subject (104) at respective positions such that the orientation of the motion sensors coordinate system (401, 402) changes differently when the subject experiences a motion.

3. An activity monitoring system according to claim 2, wherein the respective positions are different body parts of the subject.

4. An activity monitoring system according to claim 1, wherein the motion sensors (101, 102) are three or more motion sensors forming two or more motion sensor pairs, the steps of eliminating the passive movement components being performed for each respective motion sensor pair.

5. An activity monitoring system according to claim 1, wherein the motion sensors (101, 102) are three or more motion sensors forming two or more motion sensor pairs, the processing further including selecting one motion sensor pair from the two or more motion sensor pairs as the first and the second motion sensor, the selection being based on monitoring which readout data differ most from the three or more motion sensors.

6. An activity monitoring system according to claim 1, wherein the motion sensors are tri-axial accelerometers.

7. An activity monitoring system according to claim 1, wherein the motion sensors (101, 102) are integrated into the system and form a hand-held device.

8. An activity monitoring system according to claim 1, wherein the system further comprises a receiver (203) adapted to be coupled to the processor (204), the motion sensors (101, 102) being externally located and adapted to transmit the readout data (105) to the receiver (203).

9. An activity monitoring system according to claim 1, further comprising a memory (205) for storing the readout data produced by at least a first and a second motion sensor.

10. An activity monitoring kit comprising:

a processor (103), and

at least a first and a second motion sensor (101, 102) adapted to be coupled to the processor (103),

the processor being adapted to eliminating passive movement components caused by external forces from the readout data produced by the motion sensors when attached to a subject during movement, the readout data including gravitational components, movement components caused by active movement of the subject or subject parts, and the passive movement components, the eliminating of the passive movement components comprising;

estimating a first and second gravitational components produced by the at least first and a second motion sensors,

determining a rotation matrix based on the estimated gravitational components, the rotation matrix denoting rotation required for the first sensor to get aligned with the second sensor in orientation,

multiplying the readout data produced by the first motion sensor with the rotation matrix when rotating a first sensor towards a second sensor, and

subtracting the result of the multiplying from the readout data produced by the second motion sensor when rotating the first motion sensor towards the second motion sensor.

11. A method of eliminating passive movement components caused by external forces from readout data produced by at least a first and a second motion sensor when attached to a subject during movement, the readout data including gravitational components, movement components caused by active movement of the subject or subject parts, and the passive movement components, the method comprising

estimating a first and second gravitational components produced by the at least first and a second motion sensors (601),

determining a rotation matrix based on the estimated gravitational components, the rotation matrix denoting rotation required for the first sensor to get aligned with the second sensor in orientation (603),

multiplying the readout data produced by the first motion sensor with the rotation matrix when rotating a first sensor towards a second sensor (605), and

subtracting the result of the multiplying from the readout data produced by the second motion sensor when rotating the first motion sensor towards the second motion sensor (607).

12. A computer program product for instructing a processing unit to execute the method step of claim 11 when the product is run on a computer.