An identification technique for evaluating static body segment parameters in the upper extremity

In this paper we present a method for identifying the static biomechanical parameters of all three upper extremity body segments. The experiment is based on coupling the human arm with an industrial robot which is then used for imposing a specified sagittal plane trajectory. Joint angles and forces in the contact point are collected during this process. An optimization based identification procedure was developed, which assumes the upper extremity model of a 3-degree of freedom (3DOF) rigid body planar structure in a closed kinematic chain configuration with the robot. The solution is based on fitting the joint torques calculated from contact forces to those predicted by the inverse dynamic model of the linkage. In order to verify the developed identification procedure the experiment was first performed on a 2DOF mechanical arm with dimensions similar to those of the actual arm. This mechanical model was designed using CAD software that provides an accurate assessment of all necessary dynamic parameters. A suitable low velocity trajectory was imposed into all joints, with very small angular deviations. The outcome of the identification is an estimate of masses and center of gravity (COG) coordinates for the lower arm and palm segments, their products for the upper arm and the passive moments around the measured angle of all joints in the sagittal plane. Finally, the results obtained for the human arm are compared to the literature estimates which are based on average population.