The Grand Piano Action Functioning Demystified thanks to the Multibody Approach

Piano actions are striking mechanisms whose functioning is based on dynamic principles. Producing a sound on a struck keyboard instrument by pressing a key slowly is impossible because the hammer needs momentum to hit the strings. For this reason, many modern studies on the piano take advantage of engineering tools in order to measure the exact behaviour of their actions in terms of time response, involved forces and displacement values. A complementary approach to study piano actions consists in modeling them, giving us a virtual mechanism to work with. In this case, the above-mentioned motion and behaviour are computed instead of being measured. The modeling approach used in this work, called multibody dynamics, consists in computing the motion and the forces acting upon each component of the action. Subsequently, the response of the mechanism to any key stroke can be computed and visualized. In this paper, the functioning of the most modern double escapement action found in grand pianos is demystified thanks to the multibody modeling features. The goal, which is mostly pedagogical, is achieved with three progressive models; the first one is a simplified version of the action to which components of the complete action have been (virtually) removed. The stepwise progression leads to a single escapement action for the second model, and finally to the full double escapement action for the third. Response to different types of touch are compared with literature