Patent ID: 8229592

Claim:
An apparatus for controlling pressure in an electric-motor driven injection molding machine having an injection and pressure application mechanism in which rotation of a servomotor is transferred to rotation of a ball screw through a reduction gear and rotation of said ball screw is converted to a linear motion of a nut of said ball screw and said nut drives a moving part and a linear motion of a screw is realized through said moving part and pressure application to a melted polymer stored at the end of a barrel and fill-up of a cavity with polymer melt are realized by a movement of said screw, comprising: an injection controller operative to provide a motor current demand signal for said servomotor to external, which comprises a high-gain observer operative to execute at a constant time interval discrete-time arithmetic expressions obtained by applying a standard method of forward rectangular rule to continuous-time calculation procedures which are derived from a continuous-time mathematical model of an injection mechanism representing motion equations of said injection and pressure application mechanism and consisting of state equations having three state variables of a screw position variable, an injection velocity variable and an injection pressure variable, one input variable of a motor current demand signal applied to said servomotor or an actual motor current signal and output variables of measured state variables, an injection pressure setting device operative to feed an injection pressure command signal, a subtractor operative to feed a difference signal between said injection pressure command signal from said injection pressure setting device and an estimate of injection pressure which said high-gain observer outputs by using a screw position signal detected by a rotary encoder mounted on a servomotor axis and said motor current demand signal applied to said servomotor or said actual servomotor current signal as inputs and by executing said discrete-time arithmetic expressions built in, and a pressure controller operative to derive said motor current demand signal for said servomotor by using said difference signal from said subtractor operative so that said estimate of injection pressure follows said injection pressure command signal; and a motor controller fed said motor current demand signal from said injection controller.