A method for controlling an injection molding machine that actuates a plurality of hydraulic actuators to perform injection molding, the injection molding machine including the hydraulic actuators, and a hydraulic supply device that supplies working oil to the hydraulic actuators to actuate the hydraulic actuators, wherein the hydraulic supply device includes:
- a first main hydraulic power source having a first constant rotational speed motor that rotates at a constant rotational speed, a first main hydraulic pump that is driven by the rotational driving of the first constant rotational speed motor to discharge working oil, the first main hydraulic pump having variable capacity, and a first main discharge pipe through which the working oil discharged from the first main hydraulic pump flows;
- at least one auxiliary hydraulic power source having a servo motor in which rotational speed is controlled by a servo control circuit, an auxiliary hydraulic pump that is driven by the rotational driving of the servo motor to discharge working oil, the auxiliary hydraulic pump that operates with a preset specific capacity, an auxiliary discharge pipe through which the working oil discharged from the auxiliary hydraulic pump flows, and a check valve that is provided at the auxiliary discharge pipe to regulate the inflow of working oil to the auxiliary hydraulic pump;
- a hydraulic control unit that controls the first main hydraulic power source and the auxiliary hydraulic power source;
- a junction pipe at which the first main discharge pipe and the auxiliary discharge pipe join;
- and a switching unit that has the junction pipe connected thereto, and switches the supply and non-supply of working oil to at least some of the plurality of hydraulic actuators, the method comprising:
- a hydraulic power source operation step of operating the first main hydraulic power source, and selectively operating the auxiliary hydraulic power source based on a required pressure or flow rate, when a request for inputting a hydraulic pressure is received so as to obtain a predetermined pressure or flow rate in the junction pipe, and
- a flow rate command outputting step of generating flow rate commands corresponding to the first main hydraulic power source and the auxiliary hydraulic power source, based on the flow rate control value of the hydraulic actuators targeted, and outputting the flow rate commands to the corresponding first main hydraulic power source and auxiliary hydraulic power source, wherein
- in the flow rate command outputting step, a flow rate command generating unit has a first flow rate range in which only the first main hydraulic power source is actuated, and a second flow rate range in which the first main hydraulic power source and the auxiliary hydraulic power source are actuated, the second flow rate range being greater than the first flow rate range,
- when the flow rate control value is within the first flow rate range, a flow rate command corresponding to the flow rate control value is output to the first main hydraulic power source, and
- when the flow rate control value is within the second flow rate range, the auxiliary hydraulic power source to be driven is selected based on the magnitude of the flow rate control value, a flow rate command is output to the selected auxiliary hydraulic power source, and a flow rate command corresponding to the shortfall in the flow rate of working oil which is generated in the selected auxiliary hydraulic power source with respect to the flow rate control value is output to the first main hydraulic power source.