US Patent 9006549 Hammer device and keyboard device for electronic keyboard instrument

A hammer device of an electronic piano with keys which swing in accordance with key depression, includes a hammer support that is made of a synthetic resin and has a fulcrum shaft, and a hammer having a shaft hole part for being fitted on the fulcrum shaft and configured to pivotally move about the fulcrum shaft in a manner interlocked with the swinging key. The fulcrum shaft has an outer peripheral surface formed by a pair of arcuately-curved surface portions opposite to each other and a pair of planar surface portions each extending between the pair of arcuately-curved surface portions and parallel to each other.