When there is a problem, the upper dead center signal will be lost, which will lead to not yielding and not changing steps.Stop at the upper dead center slide, is the root cause of the loss of the upper dead center signal, will work into the back pressure from 9MPa modulation of 10.5MPa, work into the loose foot pedal has been a little bit of rebound, but will still slide, slide a little slower.Multiple tests have found that, stopped at the upper dead center sliding, Y_UDP signal will be lost (due to the cancellation of the fast down loose foot pedal return, will not automatically return to the upper dead center), if then this stage, do not switch to the stop page, C_NCRDY signal has always been there, this state of action is normal, if the signal is lost in the upper dead center, switched to the stop page and then start again, the C_NCRDY signal will be lost, thisstate will result in no yielding and no step change.Modify the PLC program to replace the X_IP and R_IP signals in the fast down with the C_NCRDY signal so that the slider will not fast down after the C_NCRDY signal is lost.Eliminate the fast down release pedal from returning, so that the slider will automatically return to the upper dead center after the upper dead center signal is lost.