Development of an identification method for the minimal set of inertial parameters of a multibody system

The inertial properties of an object (mass, center of gravity, and inertia tensor) are fundamental parameters that considerably affect the accuracy of motion control and simulation results. Therefore, an accurate identification of inertial properties is crucial. All inertial properties of individual links modeled with multiple links cannot be identified via link motion, interjoint torque, or external force data because they are redundant to the multibody dynamics model. The minimum dynamic parameters necessary to represent the multibody dynamics model have been defined and identified. These dynamic parameters are obtained by combining the geometric parameters and inertial properties of the counterpart elements and are called the minimal set of inertial parameters (MSIP). Conventional identification methods use a set of measured link motions and ground reaction forces. MSIP for a sagittal plane can be identified from motions such as the walking motion of human bodies. However, applying these methods to three-dimensional identification is challenging. The primary difficulty lies in the large number of parameters involved, making it challenging to find motions that appropriately excite all MSIP in three dimensions to be identified. In this study, a new method for identifying the MSIP of a multibody system is developed by expanding and applying the identification method based on free vibration measurements, which is the identification method for the inertial properties of a single body. This method shows that MSIP for three dimensions can be identified theoretically and experimentally with high accuracy via considerably simple motion measurements.