Servo electric driven stretch rods for blow molding machine

Apparatus for forming a hollow plastic article, which comprises:

• a blow mold for forming a hollow plastic article from a parison;
• holding means for holding the parison within the blow mold including channel means within the holding means communicating with the parison;
• blow means having a channel communicating with the parison for transmission of high pressure fluid to the parison to expand the parison into conformity with the blow mold and form a blown article therein;
• means for transmitting fluid pressure to the blow means;
• a stretch rod for stretching the parison movable in the holding means channel from a retracted position outside the blow mold to a forward position within the blow mold;
• a servo electric drive for moving the stretch rod in the holding means channel separate from the high pressure fluid operative to move the stretch rod with a programmable rate of change of speed while the parison is in the blow mold;
• means for determining the position of the stretch rod in the holding means channel operatively connected to said servo electric drive;
• and
• a programmable controller means operatively connected to the means for determining the position of the stretch rod and to the means for transmitting fluid pressure for synchronizing the movement of the stretch rod and the transmission of high pressure fluid to the parison based on the position of the stretch rod in the holding means channel to synchronize the movement of the stretch rod with the transmission of high pressure fluid while the parison is being expanded into conformity with the blow mold wherein the servo electric drive operatively moves the stretch rod with a rate of change of speed which is synchronized to the blowing operation.