A sensorless method for measuring the point mobility of mechanical structures

This paper presents a convenient and cost-effective experimental tool for measuring the mobility characteristics of a mechanical structure. The objective is to demonstrate that the point mobility measurement can be performed using only an electrodynamic inertial exciter. Unlike previous studies based on a voice coil actuator, no load cell or accelerometer is needed. Instead, it is theoretically shown that the mobility characteristics of the structure can be accurately estimated from variations in the electrical input impedance of the actuator fixed onto it, provided that the electromechanical parameters of the actuator are known. A thorough discussion is provided to describe and justify the derivation of the mobility characteristics of the structure from the actuator impedances. The proof of concept is made experimentally using a commercially available inertial exciter on a simply supported plate, leading to a good dynamic range from 100 Hz to 1 kHz. Measured data are compared to a standard shaker testing and the strengths and weaknesses of the sensorless mobility measuring device are discussed. It is believed that this sensorless mobility measuring device can be a reliable and convenient experimental tool to determine the dynamic characteristics of a wide range of mechanical structures.