MOLD PROTECTION DEVICE FOR INJECTION MOLDING MACHINE

A mold protection device for an injection molding machine capable of automatically setting a reference value for detecting an abnormal load exerted on a mold in a mold closing process. A load exerted on a servomotor for driving a mold clamping mechanism is estimated by a disturbance estimating observer provided in a control system of the servomotor. The estimated disturbance torque is sampled at every predetermined period in a mold protection region and cyclically stored in a table TA as data DA (0, 0) to (i, j) in mold closing processes of the number (i+1). A predetermined amount is added to an average value of data DA (0, n) to (i, n) to define an upper limit DC(n) for the disturbance torque and stored in the table TC. If the estimated disturbance torque at each sampling period exceeds the upper limit DC(n) of in the mold protection region in a present mold closing process, an alarm is issued to indicate abnormal load. An optimum reference value for determining an abnormal load is automatically set for securely protecting the mold without requiring an operator to manually set the reference value.