Electric injection mechanism

An electric injection mechanism, comprising:

• a pair of front and rear support plates disposed on machine base by linking by means of a plurality of guide bars, a pair of right and left ball screw shafts disposed rotatably in parallel with the guide bars over the front and rear plates, a screw driver provided right and left inside with a pair of ball nut members meshing with said ball screw shaft, and inserted movably into the guide bars between the front and rear plates, and an electric motor of a driving means comprising said ball screw shaft and ball nut member, wherein:
• a shaft between a ball screw portion and a bearing portion said ball screw shaft is partially formed with a diameter smaller than a root diameter of a ball screw groove, forming a stress relaxation groove having a bottom face with a flat concave curbed face at the shaft.

An electric injection mechanism, comprising:

• a pair of support plates disposed in front and behind an installation member on a machine base, a pair of right and left ball screw shafts juxtaposed rotatably over the front and rear plates, a screw driver provided right and left inside with a pair of ball nut members meshing with said ball screw shafts, and put slidably on the installation member between the front and rear plates, and an electric motor of a driving means comprising said ball screw shaft and ball nut member, wherein:
• a shaft between a ball screw portion and a bearing portion of said ball screw shaft is partially formed with a diameter smaller than a root diameter of a ball screw groove, forming a stress relaxation groove having a bottom face with a flat concave curbed face at the shaft.