Development of a new driving impact system to be used in experimental modal analysis (EMA) under operational condition

Abstract

An automatic impact device system, which consists of a combination of computer controlled linear solenoid and force sensor was developed to replace an Integrated Circuit Piezoelectric (ICP) impact hammer in conventional Experimental Modal Analysis (EMA) procedure. A dedicated electrical circuit was constructed to transform an artificial signal generated by virtual instrumentation software into an analog output for driving and controlling the solenoid motion. Under the present configuration, the solenoid was positioned vertically above the force sensor that was mounted on a tested structure. The gap between the solenoid end-effector and the force-sensing pad was adjusted to obtain the optimum characteristics of the generated input force signal. This includes attaining the maximum amplitude from the impact along with the establishment of single impulse profile onto the tested structure under different operating conditions. For the validation purpose, the acquired input signal along with the natural frequency of the structure was systematically compared with the results generated under the conventional EMA procedure. The present results have demonstrated that the new system is capable to match the performance of the currently used impact hammer system in terms of providing reliable input force and modal parameter at static condition of the structure. Further, due to its capability to provide periodical impact onto the structure, the introduced system can also be extended to conduct EMA under operational condition which paves a new paradigm for vibration analysis of structures with running harmonics.