Measuring the six dof driving point impedance function and an application to RB inertia property estimation

An accurate driving point measurement is imperative in structural dynamic testing. For example, it is used to derive modal scaling, for experimental correlation of finite element models, impedance modelling and extracting the rigid body (RB) inertia properties of an object. A typical driving point measurement gives the linear force/displacement relationship at a single degree of freedom (dof), but any point on an object actually has rotational dofs as well. For example these rotational dofs must be measured in an impedance model where moments are transmitted at the connection point of two substructures. By ignoring the rotations, an inaccurate model will result. In the past, dynamic sensing technology has been limited to the accurate measurement of translational dofs. While rotational sensors do exist, their accuracy is called into question for certain applications. Rotational dofs have tended to be ignored in the measurement process. Applications, which require their use, such as impedance modelling and RB inertia property estimation, have suffered as a result. A process/sensor is being developed to accurately measure the driving point impedance function in all six dofs. The sensor as well as a calibration procedure will be presented here. In order to verify the validity of the calibration and measurement procedure, a new method for measuring the RB inertia properties of an object will be presented. This new method requires an accurate six dof driving point impedance measurement to provide accurate results. The inertia properties of an automotive brake rotor will be measured and compared with the results of a traditional pendulous swing test