[Development of posture measuring apparatus using goniometer and inclinometer. 2. Fixation, precision and calibration...

A new posture measuring apparatus was developed for time and motion study in the field of industrial health. This apparatus records working postures by measuring angles of joints and trunk inclination. The angles of joints were measured by the newly developed goniometers which use the bending loss of rubber optical fibers. This paper presents results of studies made on the fixation, precision and calibration of goniometers which are important in the actual application of this apparatus. Six freedoms of five joints were examined, i.e. elbow (flexion/extension), shoulder (abduction/adduction and horizontal adduction/abduction), hip (flexion/extension), knee (flexion/extension), ankle (dorsi-flexion/plantar-flexion). The results obtained were as follows; 1) Goniometers should be fixed according to the characteristics of each joint. 2) The output errors were calculated from the measured data, excluding the effects of flexed angles, subjects and fixations. The mean output error of all joints was 0.189 V (14.3 degree). 3) The output errors by the three calibration methods using logistic curves were calculated. The output errors for 2-point method (calibrated by the data of minimum and maximum angles) and 3-point method (calibrated by the data of minimum, medium and maximum angles) were 1.34 and 1.22 times larger than the output errors (0.139 V) for all-point method (calibrated by all measured data), respectively.