Fixed width machine rhythm control method

The invention belongs to the technical field of steel rolling, and discloses a fixed width machine rhythm control method which comprises the following steps: synchronously acquiring a length value of a slab and a passing time threshold value corresponding to the length value when the slab is descaled by a descaling machine; a plate blank enters a width fixing machine after passing through a descaling machine, an inlet pinch roll clamps and conveys the plate blank in a walking and stopping mode to pass through an inlet guide roll, an outlet guide roll and an outlet pinch roll in a stepping mode, and in the stepping process of the plate blank, hammerheads on the two sides conduct extrusion width reduction on the plate blank; and when the head of the plate blank passes through the outlet pinch roll, a pressure signal generated by downward pressing of the outlet pinch roll is obtained, timing is started, and when the moving time of the plate blank reaches the passing time threshold value, the next plate blank is