Bar cooling bed output roller way control method

The invention belongs to the technical field of bar cooling bed output control, and particularly relates to a bar cooling bed output roller way control method, two cold metal detectors are installed on the basis of an original cold metal detector, multiple-length rolled pieces on an output roller way are detected at the same time, and only when the three cold metal detectors do not have detection signals, the three cold metal detectors can detect the multiple-length rolled pieces on the output roller way. The PLC control system controls the steel moving trolley to act only when the double length of the correlation grating is not detected before cold shearing; the PLC control system controls starting and stopping of a frequency converter controlled by a roller way motor in a segmented mode. The cold shear shears the first shear as a shear head, the cold shear shears the third shear, the cold bed output roller way first-section cold detection detects a steel-free signal, and the cold bed output roller way secon