Abstract: A control method of an injection molding machine includes the steps of advancing a screw 2, injecting and filling the resin in a barrel cylinder 3 into a mold 4 to fill the mold, and then applying a predetermined holding pressure to the resin in the mold 4. The control method further includes the steps of performing an injecting and filling by using an injection cylinder 5 having a double-rod piston 6 which can advance and retreat the screw 2, and then controlling the injection cylinder 5 by a controlling signal Dc including a predetermined alternating current signal in such a manner that the screw 2 is reciprocated in a longitudinal direction as a center with an advance finish and. stop position Xs and a position at which the screw is moved so as to retreat by a predetermined distance from the advanced finish and stop position Xs. Thereby, the mold failure such an overpack and a burr is eliminated.

Abstract: An hydraulic control circuit for an injection molding machine feedback-controls the operations of an injection cylinder by connecting an hydraulic source and an oil tank to a hydraulic actuator through a plurality of servo valves. The plurality of servo valves, such as four-port servo valves, are connected in parallel and a servo valve control function unit is used which controls the servo valves preferentially to the feedback control to permit series or parallel control of the servo valves. Thus, even when the specifications of an injection molding machine require a larger size and higher speed, the size of the injection molding machine is prevented from increasing, the cost is decreased, the response speed and the stability are remarkably improved, and fine control is realized over a wide control range.

Abstract: A first direction shifting valve adapted to supply pressurized hydraulic oil to a hydraulic chamber on the rearward displacement side and discharge hydraulic oil from the hydraulic chamber on the rearward displacement side, and moreover, discharge hydraulic oil from a hydraulic chamber on the forward displacement side is disposed in a hydraulic path extending between a hydraulic pump and an injection cylinder. In addition, a second direction shifting valve adapted to supply pressurized hydraulic oil to a chamber on the forward displacement side is disposed in the foregoing hydraulic path. Additionally, a third direction shifting valve is disposed to build a bleeding-off circuit in cooperation with the second direction shifting valve. While a hydraulic path on the rearward displacement side is blocked by the third direction shifting valve, a hydraulic path on the forward displacement side is hydraulically connected to the tank side.