The dynamic behavior of a vertical piano action mechanism is studied using a simulation model and compared qualitatively to observations obtained by high-speed imaging of a real action. The simulated response of all components is obtained for two different prescribed input force profiles applied at the key front. These inputs represent in simplified form the general shape of a typical force input by a pianist measured at the key surface for a strong (forte) strike, or two key strikes in rapid succession. The graph-theoretic multibody model constructed represents the components and their interactions. Explicit contact edges provide forces generated between two bodies as a function of their kinematic states, using a special contact model to represent the compression of felt lined interfaces that can separate during the key stroke. Masses and geometrical parameters of the action were measured by importing scanned images from a real action into CAD software. The highly nonlinear system of five ordinary differential equations of motion was derived symbolically and solved by a numerical stiff solver in Maple. The effects of two components not present in the horizontal grand piano action, the bridle strap and hammer butt spring, were examined using simulations. The butt spring is seen to serve an important function in assisting the return of the hammer to its rest position on key release. The model will be useful in future studies to compare vertical actions to horizontal grand piano actions, as these are known to exhibit quite different playing characteristics.

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