# Automatic Decentralized Vibration Control System Based on Collaborative Stand-Alone Smart Dampers
## 1 Introduction  
Active vibration control (AVC) by means of electrodynamic proof-mass actuators (PMA) represents a valid alternative to traditional passive tuned mass dampers [1] in order to suppress vibrations. In AVC, the advantage is represented by the possibility to introduce damping on more than one vibration mode. To do so, proof-mass actuators (PMA) are widely used, due to their easy mounting since they do not need to react off the base structure [2; 3; 4]. Therefore, the number of PMA on a structure can be easily increased and then the capability of the overall system to introduced damping increases. For all these reasons, a control system based on PMA has been developed in [5], where vibration suppression on a large structure was required. The PMA prototype is driven by a printed circuit board (PCB). In the PCB, an accelerometer samples the structure acceleration providing the feedback signal. This signal is used by the microcontroller for the computation of the control action, which is amplified by an analog conditioning circuit and fed into the actuator. These embedded features allows the PMA to work autonomously, thus no centralized regulator is necessary. For this reasons, such actuators are also named \"Stand-alone smart dampers\". Moreover, one of the most interesting feature of the device is the wireless module integrated on the PCB. This allows information and data sharing between the smart dampers. To date, the development of wireless solutions is ongoing also in other fields, like the vibration monitoring of cargo trains and the wind-induced vibrations of HVTL conductors [6; 7; 8; 9]. This wireless data sharing between devices has been already used in a control system, where two wireless nodes were considered [10; 11]. A Selective Negative Derivative Feedback (SNDF) control law has been implemented in [10]. Such control law filters out thelocal acceleration measurement by means of a band-pass filter centered on the considered eigenfrequency. The filtered acceleration is then integrated and multiplied by a control gain in order to compute the control force. The SNDF makes the system more robust to spillover and instability phenomenon related to the low frequency PMA phase shift. Compared to the Direct Velocity Feedback (DVF) control law, SNDF provides higher control gains and then more damping can be introduced. Some different solutions have already been studied to solve the instability problems of PMA [12], but the SNDF represents one of the most reliable one. Some automated functionalities have been developed in order to allow the control system to recognize the structure on which is mounted on. Each wireless sensor can recognize the natural frequencies of the hosting structure and the actual vibration conditions and share the results with the other devices. The final target is to develop a smart control system able to extract as many information as possible from the structure and automatically tune the control action according to the information obtained. The information sharing between wireless nodes is used to get a global overview of the hosting structure and to define a coordinated control strategy. In this work, starting from the described system, some functionalities have been developed. In particular, a procedure to estimate the non-dimensional damping and modal amplitude for each wireless sensor location and each vibration mode is proposed. The information obtained by the structure and vibration identification phase are exploited to implement a coordinated control strategy, based on a modified version of the Efficient Modal Control (EMC) proposed by [13]. Such control strategy is based on the low level SNDF control law and modulates the control gains of each actuator-controlled mode pair in order to get an effective vibration reduction. The control gains are weighted according to the excitation state of the hosting structure and to the performance of the each actuator to introduce damping in each mode. The latter weighting feature represents the novelty with respect the traditional EMC.