Valve pin position and velocity control method and apparatus

An injection molding apparatus comprising a manifold that receives an injection fluid (F) from an injection molding machine, the manifold distributing the injection fluid to a fluid delivery channel that delivers the injection fluid under an injection pressure to a gate of a mold cavity, and a valve pin having an axis (A) and a tip end, the valve pin being slidably mounted for movement along the axis (A) within the fluid delivery channel,

• wherein the valve pin is interconnected to an actuator in an arrangement wherein the actuator is adapted to drive the valve pin upstream and downstream along the axis and to drive the tip end of the valve pin upstream and downstream between a first closed position (GC) where the tip end of the valve pin obstructs the gate to prevent the injection fluid from flowing into the cavity, a full open position (FOP) where the injection fluid material flows freely without restriction from the tip end of the pin through the gate, and one or more intermediate positions (RP, RP2) between the first closed position and the full open position wherein the tip end of the valve pin restricts flow of the injection fluid along at least a portion of the length of the drive path extending between the first closed position and the intermediate position,
• the apparatus including a controller with instructions to first controllably operate the actuator to drive the valve pin upstream beginning from the first closed position to be moved to and held in a first selected position for a first selected period of time during the course of an injection cycle, the first selected position being an intermediate position, wherein the instructions to first controllably operate comprise instructions to drive the valve pin upstream from the first closed position to the first selected position at a maximum rate of travel at which the actuator is capable of driving the valve pin,
• the controller including instructions to second controllably operate the actuator to drive the valve pin, during the injection cycle, downstream beginning from the first selected position to be moved to and held in a second closed position for a second selected period of time;
• the controller including instructions to third controllably operate the actuator to drive the valve pin, during the injection cycle, upstream beginning from the second closed position to be held in a second selected position for a third selected period of time, the second selected position being an intermediate position, wherein the instructions to third controllably operate comprise instructions to drive the valve pin upstream from the second closed position to the second selected position at a reduced rate which is less than the maximum rate of travel at which the actuator is capable of driving the valve pin for a least a portion of the upstream travel from the second closed position to the second selected position;
• the controller including instructions to fourth controllably operate the actuator to drive the valve pin, during the injection cycle, downstream beginning from the second selected position to a third closed position.