Ambulatory measurement of arm orientation

The definitions of the segment reference frame. The unit y-axis are defined along the segment, upwards. In anatomical position, the z-axis point in dorsal direction and the x-axis laterally.

Attachment of Vicon markers and inertial sensing units to the forearm and upperarm. Sensors are adhered to the segment using double sided adhesive tape and secured using Leukoplast.

Angular velocity as measured in the coordinate frame of the IMU during an endorotation/exorotation movement (top graph). This endorotation/exorotation movement was used to find the y-axis of the upper arm. The same angular velocity, now expressed in the upperarm coordinate frame, is given in the bottom graph.

The error of the orientation of the upperarm with respect to the forearm for a morning routine task and an eating routine task, obtained using the method described in the text (arm filter). The error is compared to the case in which the orientation is not corrected using the constraint on the abduction angle (without arm filter).

Adduction angle as measured using the reference system (top) and inertial sensors (bottom) during a morning routine task. The adduction angle in the bottom graph was found using a standard deviation of the elbow abduction angle (square root of R) of 10°.

(A) RMS of estimated adduction angle during a morning routines trial and an eating routines trial. The trials were processed for several values of the model parameter R, the assumed variance of the elbow adduction angle, expressed in the figure as a standard deviation. For comparison, the RMS of the abduction angle obtained with the reference frame is given, as well as the RMS for the situation in which only the gyroscopes and accelerometers are used without assumptions concerning the elbow angle. The estimated adduction angle is smaller for lower values of the standard deviation of γ, (B) RMS errors of elbow orientation without and with the application of elbow constraints at several values of the standard deviation of γ (square root of model parameter R). The errors were determined with respect to the Vicon reference orientations.