Control method for preventing pinch roll of sizing machine from being not gripped

The invention relates to a control method for preventing a pinch roll of a fixed width machine from not biting, which comprises the following steps of: a, calculating a first roll gap of an inlet pinch roll based on a theoretical plate blank thickness, and performing closed-loop control on the inlet pinch roll at a position corresponding to the first roll gap to wait for entering of a plate blank; b, after the plate blank enters the inlet pinch roll, calculating a second roll gap based on the pressure of the inlet pinch roll, and controlling the inlet pinch roll at a position corresponding to the second roll gap under the condition that the pinch roll is judged to bite steel; and c, the inlet pinch roll is controlled at the position corresponding to the second roll gap for a preset time. By means of the method, the problem that when the actual thickness of the plate blank is much larger than the actual roll gap of the pinch roll, pressure control pressing is immediately input when the plate blank impacts the