Dynamic modeling of a flexible hub-beam system with an eccentric tip mass including nonlinear hysteretic contact is studied in this paper. In reality, the model is intended to represent the mechanical finger of an actuator for a piano key. Developing a device to achieve a desired finger-key contact force profile that realistically replicates that of a real pianist’s finger is the main objective of this research. The proposed actuation system consists of a flexible arm which is attached to a DC brushless rotary motor thorough a hub. The compliant arm behaves as a cantilever beam to which an eccentric tip mass has been attached at its free end. During the piano key stroke, the contact force input from the tip causes the key to rotate and impact the ground through an interface lined with stiff felt to suppress vibrations and noise. Euler-Bernoulli beam theory in conjunction with Lagrange’s method is utilized to obtain the governing equations of motion for the system. The finite element method is used as the discretization procedure for the flexible cantilever beam, which can be considered a distributed parameter system. To include contact dynamics at the stop, the nonlinear hysteretic behavior of felt under compression is modeled in such a way that smooth transitions between loading and unloading stages are produced, thus ensuring accurate response under dynamic conditions, and particularly with partial loading and unloading states that occur during the contact period. Simulation results show excessive vibration is produced due to the arm flexibility and also the rigid-body oscillations of the arm, especially during the period of key-felt contact. To eliminate these vibrations, the system was supplemented with various dashpot models, including a simple grounded rotational dashpot, and a grounded rotational dashpot with a one-sided relation. The results of simulations are presented showing the effect on vibration behavior attributed to these additional components.

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