Apparatus and method for detecting a position of an actuator piston

In an injection molding system, an apparatus for detection of position of a piston disposed within an actuator cylinder, the actuator cylinder comprising a body portion having an interior surface surrounding and defining a bore within which the piston is adapted to move to a plurality of travel positions extending between upstream and downstream positions contained within the bore, the body portion of the actuator cylinder having an exterior surface extending between the interior and exterior surfaces, the apparatus comprising:

• a magnetic member having a north N pole end and a south S pole end defining a N-S axis and generating a magnetic field, the magnetic member being mounted to the piston for movement together with the piston between the upstream and downstream positions,
• wherein movement of the piston modifies the magnetic field to a modified degree or quality that is dependent on the travel position of the piston relative to a detection position;
• the body of the cylinder being substantially non-magnetic and/or magnetically permeable;
• a hall effect sensor circuit, including one or more hall effect sensors, attached to the exterior surface of the substantially non-magnetic and/or magnetic magnetically permeable body portion of the cylinder, wherein the body portion of the cylinder is disposed between each sensor and the magnetic member,
• each sensor being disposed at a position where the magnetic field of the magnetic member is detectable by the one or more hall effect sensors at all travel positions of the piston between the upstream and downstream positions,
• the hall effect sensor circuit detects the modified degree or quality of the magnetic field and generates a changing output signal unique to each travel position of the piston based on the detected modified magnetic field,
• a processor receiving the changing output signal generated by the hall effect sensor circuit, the processor using the received signal to determine the travel position of the piston;
• wherein each sensor is disposed adjacent either the north N pole end or the south S pole end of the magnetic member, and wherein the magnetic member's N-S axis is disposed transverse to the direction of travel of the piston in the bore.

In an injection molding system, an apparatus for detection of position of a piston disposed within an actuator cylinder, the actuator cylinder comprising a body portion having an interior surface surrounding and defining a bore within which the piston is adapted to move to a plurality of travel positions extending between upstream and downstream positions contained within the bore, the body portion of the actuator cylinder having an exterior surface extending between the interior and exterior surfaces, the apparatus comprising:

• a magnetic member having a magnetic field, the magnetic member being mounted to the piston for movement together with the piston between the upstream and downstream positions,
• wherein movement of the piston modifies the magnetic field to a modified degree or quality that is dependent on the travel position of the piston relative to a detection position;
• the body portion of the cylinder being substantially non-magnetic and/or magnetically permeable;
• a hall effect sensor attached to the exterior surface of the substantially non-magnetic and/or magnetically permeable body portion of the cylinder at the detection position wherein the body portion of the cylinder is disposed between the detection position and the magnetic member,
• the detection position being disposed at a position where the magnetic field of the magnetic member is detectable by the hall effect sensor at all travel positions of the piston between the upstream and downstream positions,
• the hall effect sensor detects the modified degree or quality of the magnetic field and generates a changing output signal unique to each travel position of the piston based on the detected modified magnetic field,
• a processor receiving the changing output signal generated by the hall effect sensor, the processor using the received signal to determine the travel position of the piston;
• wherein the processor includes a triggering signal that can be used in providing instructions that control a drive mechanism that drives the piston, the instructions comprising an algorithm that use the determined travel position of the piston to instruct the drive mechanism to drive the piston in a predetermined manner during the course of an injection cycle, and wherein the processor includes a triggering signal that can be used in providing instructions that instruct the drive mechanism to drive the piston such that the piston travels continuously upstream from a gate closed position an intermediate upstream travel position at first travel velocity and such that the piston travels continuously upstream from the intermediate travel position to a predetermined upstream position at a second travel velocity that is higher than the first travel velocity.

A method of determining the position of a piston of an actuator piston driving a valve pin in an injection molding apparatus, wherein the actuator comprises:

• an actuator housing having a body portion, surrounding an axial bore, of a substantially non-magnetic and/or magnetically permeable material,
• a piston, movable within the axial bore for driving the vale pin, the piston including a magnetic member having a north N pole end and a south S pole end defining a N-S axis and generating a magnetic field such that axial movement of the piston in the bore modifies the magnetic field according to the position of the piston relative to a detection position,
• a hall effect sensor circuit, including one or more hall effect sensors, attached to an exterior surface of the substantially non-magnetic and/or magnetically permeable body portion, wherein the sensor circuit detects the position of the piston relative to the sensor(s) position(s) on the body portion by detecting the magnetic field of the magnetic member as modified by axial movement of the piston and generates a changing output signal that is unique to each travel position of the piston in the bore based on the detected modified magnetic field,
• wherein each sensor is disposed adjacent either the north N pole end or the south S pole end of the magnetic member, and wherein the magnetic member's N-S axis is disposed transverse to the direction of axial movement of the piston in the bore
• the method comprising:
• detecting the magnetic field of the magnet member with the hall effect sensor circuit upon axial movement of the piston in the bore,
• determining the position of the piston according to the detected magnetic field of the magnet member as modified upon axial movement.