Patent ID: 7767119

Claim:
A method for controlling an amount of gas injected into a barrel of an injection molding machine, comprising the steps of: a) opening a needle valve of an actuator to allow the gas to be injected from a gas compressor to a gas line until a pressure of the gas line rises to a first predetermined level, when a gas injecting device of the injection molding machine is turned on; b) closing the needle valve of the actuator when the pressure of the gas line rises to the first predetermined level, followed by detecting whether or not a screw is rotated through analysis of a detection signal from a screw rotating detection sensor; c) detecting a pressure of the gas line and a pressure of the barrel changed according to the rotation of the screw if it is determined that the screw starts rotating, followed by detecting whether or not a pressure difference between the gas line and the barrel reaches a second predetermined level; d) opening a gas control valve to allow the gas to be injected from the gas line to the barrel while monitoring changes in pressures of the gas line and the barrel, if it is determined that the pressure difference between the gas line and the barrel reaches the second predetermined level; and e) closing the gas control valve while opening the needle valve of the actuator to allow the gas to be injected from the gas compressor to the gas line, if it is determined that the pressure difference between the gas line and the barrel reaches a third predetermined level.