Gear machining apparatus, cutter and strain wave gearing device

A cutter applied to a gear machining apparatus, comprising:

• a skiving mechanism positioning a work to be machined and the pinion type cutter on axes skewing from each other, the skiving mechanism rotating the work at a predetermined position and feeding the cutter while rotating in a direction of a tooth trace of a gear to be formed at the work synchronously to the rotation of the work for producing the gear from the work;
• the cutter including a tooth surface which is formed with an involute region having an involute curve in an area including a pitch circle in a tooth depth direction, an addendum region continuously formed from the involute region to an addendum, and a dedendum region continuously formed from the involute region to a dedendum, the addendum region and the dedendum region being shaped in a configuration different from the involute region;
• and wherein
• in a case where a tooth number of a gear to be formed on the work is defined as Zw and a tooth number of the cutter is defined as Zc, a ratio Zc/Zw between the cutter tooth number Zc and the work tooth number Zw is set within a range of being greater than ¼ and being smaller than ⅔ when the gear to be formed on the work is an internal gear and a ratio Zc/Zw between the cutter tooth number Zc and the work tooth number Zw is set within a range of being greater than ½ and being smaller than 3 when the gear to be formed on the work is an external gear.

A strain wave gearing apparatus, comprising:

• an internal gear;
• an external gear having a reduced number of teeth compared to the internal gear, the external gear being flexible;
• the internal gear being produced by a gear machining apparatus including a skiving mechanism positioning a work to be machined and a pinion type cutter on axes skewing from each other, the skiving mechanism rotating the work at, a predetermined position and feeding the cutter while rotating in a direction of a tooth trace of a gear to be formed at the work synchonously to the rotation of the work for producing the gear from the work, and the cutter including a tooth surface which is formed with an involute region having an involute curve in an area including a pitch circle in a tooth depth direction, an addendum region continuously formed from the involute region to an addendum, and a dedendum region continuously formed from the involute region to a dedendum, the addendum region and the dedendum region being shaped in a configuration different from the involute region;
• wherein
• a part of teeth of the internal gear is engaged with a part of teeth of the external gear by flexing the external gear;
• and wherein
• the internal gear and the external gear relatively rotate by rotating a flexed portion of the external gear.