Injection apparatus and related methods

An injection apparatus for an injection molding machine, comprising:

• a) a barrel extending along an axis;
• b) a nozzle at a front end of the barrel for discharging melt;
• c) a screw in the barrel, the screw rotatable about and translatable along the axis;
• d) a shot chamber in the barrel axially intermediate the screw and the nozzle for holding melt;
• e) a drive assembly for driving translation and rotation of the screw, the drive assembly comprising:
• i) a housing having a front end coupled to the barrel;
• ii) a spindle in the housing, the spindle extending along the axis and fixed to the screw;
• iii) a first motor in the housing, the first motor having a hollow first rotor through which the spindle passes, the first rotor rotationally fixed to the spindle for driving rotation of the screw about the axis, and the spindle axially translatable relative to the first rotor for accommodating translation of the screw along the axis;
• iv) a second motor in the housing, the second motor having a hollow second rotor through which the spindle passes, the second rotor coupled to the spindle and rotatable relative to the spindle in a rotational first direction for advancing the screw along the axis and in a rotational second direction opposite the first direction for retracting the screw along the axis;
• and
• f) a controller configured to operate the drive assembly to, for each injection cycle:
• i) apply a holding torque to the first rotor for inhibiting rotation of the screw about the axis relative to the housing;
• ii) during (i), apply an injection torque to the second rotor in the first direction to exert an axial force on the spindle for urging the screw to advance toward the nozzle;
• iii) during (ii), determine an injection pressure value based on the holding torque, the injection pressure value corresponding to a reactionary pressure of melt in the shot chamber during application of the holding torque and the injection torque;
• and
• iv) adjust the injection torque to bring the injection pressure value toward a target pressure value, the target pressure value corresponding to a target pressure for the melt in the shot chamber during injection of the melt into a mold.

A method of operating an injection apparatus drive assembly to regulate melt injection pressure, comprising:

• (a) applying a holding torque to a hollow first rotor to inhibit rotation of a spindle about an axis, the spindle passing through the first rotor along the axis and fixed to an injection screw;
• (b) during (a), applying an injection torque to a hollow second rotor to exert an axial force on the spindle, the spindle passing through the second rotor along the axis and the axial force urging the injection screw to advance toward a nozzle;
• (c) during (b), determining an injection pressure value based on the holding torque, the injection pressure value corresponding to a reactionary pressure of melt in a shot chamber axially intermediate the screw and the nozzle during application of the holding and injection torque;
• and
• (d) adjusting the injection torque to bring the injection pressure value toward a target pressure value, the target pressure value corresponding to a target pressure for the melt in the shot chamber during injection of the melt into a mold.