WAVE GENERATOR OF STRAIN WAVE GEARING DEVICE

An outer-ring lubrication groove pattern (6) formed in an outer-race raceway surface (47a) and an inner-race lubrication groove pattern 5(5) formed in an inner-race raceway surface (46a) of a wave generator bearing (45) of a strain wave gearing device (1) are patterns in which linear lubrication grooves (53, 54, 60) having very small widths and depths of several micrometers or less are arranged at fine pitches of several micrometers or less. The inner-race lubrication groove pattern 10(5) includes a second groove pattern (52) formed in long-axis-side inner-race raceway surface portions (46B1, 46B2) to hold the lubricant, and a first groove pattern (51) formed in short-axis-side inner-race raceway surface portions (46A1, 46A2) to hold the lubricant and guide the lubricant to the second groove pattern (52). This configuration 15 improves the contact state between balls (48) and the inner-race and outer-race raceway surfaces (46a, 47a) of the wave generator bearing (45), thus reducing the coefficient of friction therebetween.