Patent ID: 7311508

Claim:
A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: a current detection circuit for, in a process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value X(t) of a current flowing in the motor; a memory for storing, with said process being repeated A times, respective current values X(t) corresponding to each of the points in time; a mean-and-variance calculating means for calculating for each of the points in time a mean value Mx(t) and a variance value Vx(t) that correspond to current values X(t) that have been read from the memory; a threshold calculating means for calculating a current threshold Xf(t) for each of the points in time using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Xf ( t )= Mx ( t )+ N·{Vx ( t )} 1/2 where N is a constant and not less than 3; and a determining means for comparing the current threshold Xf(t) and the current value X(t) at each of the points in time to determine whether there is an abnormality according to whether the current value X(t) exceeds the current threshold Xf(t) a predetermined number m of times.