CUP-SHAPED FLEXIBLE EXTERNALLY TOOTHED GEAR AND CUP-TYPE STRAIN WAVE GEARING

摘要

The present invention provides a flexible external toothed gear, which has a cup-shape, has a small size, and has a sectional shape allowing stress concentration to be relieved. An outline of an external end of a diaphragm (22) of the flexible external toothed gear having the cup-shape is formed by a first concave circular arc (34) with a first radius (R1), a second concave circular arc (35) with a second radius (R2), which has a smooth shape continuously formed from the first concave circular arc (34), and an inclined straight line (36), which has a smooth shape formed continuously from the second concave circular arc (35) and is slightly inclined toward an inner straight line (31) with respect to a central axis (21a). The second radius (R2) of the second concave circular arc (35) is bigger than the first radius (R1) of the first concave circular arc (34). A thickness of the diaphragm (22) is gradually reduced as approaching from a boss (23) toward a body part (21) having a cylindrical shape. Stress concentration of a part attached to the boss of the diaphragm (22) can be relieved, thereby improving fatigue strength of the flexible external toothed gear.