Lock

Claim 1

A lock in an injection molding apparatus, having a fixed back pressure plate connected to one end of a plurality of tie bars extending in parallel with each other, a movable base slidably supported by said tie bars and adapted to receive a first mold, and a double toggle type toggle mechanism having at least one pair of link means each of which is pivotally connected between said fixed back pressure plate and said movable base for moving between extended and retracted positions, said lock being arranged to move said movable base with respect to a fixed base to which a second mold is fixed, until said link means becomes straight, so that the first and second molds are clamped by an elastic restoration force generated by extension of said tie bars, the improvement comprising: (a) a servo motor; and (b) a transmission mechanism having a nut mechanism rotatably supported by said fixed back pressure plate and a screw threadedly engaged with said nut mechanism and extending substantially in parallel with said tie bars, wherein said nut mechanism is adapted to be rotatively driven by said servo motor for rotatively driving said screw, said screw is adapted to be rotatively driven for reciprocal movement substantially in parallel with said tie bars to extend and retract said link means, and said servo motor operates to hold said link means straight when said link means is straightened.