The present invention relates to an injection molding machine having an injection device and a mold opening and closing device, particularly to a motor-driven injection molding machine using motors as drive sources in the injection device and the mold opening and closing device.
As is well known, according to a motor-driven injection molding machine, respective functions of injection, mold opening and closing, measurement and ejector, are realized by individually installed motors. Induction motors are normally used for such motors. An explanation will be given of an example of a motor drive for such a motor in reference to FIG. 1. In FIG. 1, a motor drive 10 is for a three phase induction motor IM and includes an inverter section 20 and a rectifying circuit section 30. The inverter section 20 includes a plurality of switching elements 21 for carrying out switching operation for respective phases of three phases. The rectifying circuit section 30 is realized by a condenser input type diode rectifying circuit. The diode rectifying circuit includes a plurality of diodes 31 for carrying out rectifying operation for respective phases of a three phase power source PS.
Meanwhile, the induction motor IM for the injection device or the mold opening and closing device generates regenerated electric power in deceleration thereof. Heretofore, in the motor drive, regenerated electric power of the induction motor IM is dissipated as heat by a resistor 41 provided to a dynamic brake circuit section 40. That is, when the induction motor IM generates regenerated electric power, the switching element 42 is switched on and the regenerated electric power is dissipated by the resistor 41. From a view point of reduction of electric energy, wasteful electric energy is dissipated. In addition thereto, there is constituted a heat radiating device for radiating generated heat of the resistor 41 and therefore, there poses a problem of an increase in dimensions.
As a measure with regard to the above-described regenerated electric power, there is provided even a system enabling power source regeneration by replacing the rectifying circuit section 30 by a power source regenerating converter. However, the power source regenerating converter is expensive.
Further, other than the above-described, it is the current situation that heretofore, according to the injection molding machine, no measure has been taken for electricity interruption except a necessary minimum power source backup function. Therefore, when molding operation is stopped by electricity interruption in the midst of a molding cycle during the operation, in the case in which resin is not sufficiently charged in a mold, an ejector mechanism cannot eject unmolded product in the mold. In this case, the unmolded product, that is, a failed molded product must be taken out by manual operation. Time and labor is required in taking it out and depending on cases, the mold must be disassembled. Further, when the operation is stopped in the midst of the molding cycle by electricity interruption, much time and labor is required and skill is needed in resetting peripheral apparatus of the injection molding machine in restarting thereof.
Hence, it is an object of the present invention to provide an injection molding machine capable of reducing power consumption by achieving effective utilization of regenerated electric power of a motor.
It is another object of the present invention to provide an injection molding machine capable of utilizing regenerated electric power of a motor to operation in electricity interruption.
An injection molding machine according to the present invention comprises a drive source comprising at least one motor and a motor drive, a charger for storing regenerated electric power of the motor and electric power from a power source, a charging and discharging circuit connected to the charger for charging electric power to the charger and for discharging electric power therefrom, and a controller for controlling the charger to charge electric power and for controlling the charger to supply electric power to the motor. The controller controls the charger by controlling the charging and discharging circuit based upon an operating condition of the injection molding machine.
According to another aspect of the present invention, a method of providing drive power to an injection molding machine is provided. The method comprises the steps of controlling a charger to charge electric power from a power source and to supply electric power to a motor of the injection molding machine. A controller provides control signals to a charging and discharging circuit based upon an operating condition of the injection molding machine.