Method and apparatus for injection molding machine control

A control for a motor driven element of an injection molding machine, the machine element being driven along an axis by a motor through a drive mechanism, the control comprising:

• a first sensor positioned to measure the actual position of the machine element along the axis;
• a second sensor for measuring angular position of the motor shaft;
• a position calculator for determining an expected position of the machine element from the angular position of the motor shaft;
• and
• a comparison unit adapted to receive the actual position and the expected position, wherein said comparison unit comprises a program controlled computing device and program storage having encoded thereon a program including:
• a first routine for determining the difference between the actual position and the expected position;
• a second routine for comparing the difference to a predetermined tolerance value;
• a third routine for resetting a counter to a set value and enabling counting of the counter at regular time intervals while the difference between the actual position and the expected position exceeds the predetermined tolerance value;
• a fourth routine for generating an error signal representing an aberrant operating condition of the machine when the value in the counter reaches a predetermined value different from the set value;
• and
• a fifth routine for resetting the counter to a predetermined initial value when the difference does not exceed the tolerance value.

A computer readable medium having encoded thereon programs for control of an element of an injection molding machine, the element being driven along an axis by a motor through a drive mechanism, the programs comprising:

• a routine for receiving signals representing linear position along an axis of a machine element connected to a motor;
• a routine for receiving signals representing rotary position of the motor;
• a routine for converting the rotary position of the motor to a linear equivalent;
• a routine for determining the difference between the element position and the linear equivalent;
• a routine for changing the value of a counter by a preset increment when the difference between the element position and the linear equivalent exceeds a predetermined tolerance value;
• a routine for generating an error signal representing an aberrant operating condition of the machine when the value in the counter reaches a predetermined value;
• and
• a routine for resetting the counter to a predetermined initial value when the difference does not exceed the tolerance value.