US Patent 10052747 Hammer tool

A hammer tool for hammering on a workpiece by a tool bit moving at least linearly in a longitudinal direction of the tool bit, configured so that a hammering element moves toward the tool bit to hits the tool bit by way of air pressure fluctuation in an air chamber when a driving element is moved from a first position to a second position. In addition, the stroke center position of the reciprocating movement of the driving element moved between the first position and the second position is configured to be changeable.