wherein the slidably fixing device comprises a sliding track mounted at an end of the crane rail, two sides of the sliding track are respectively provided with sliding grooves, each of the sliding grooves is provided with a first sliding block and a second sliding block therein, and the first sliding block and the second sliding block are respectively connected to an end of the sliding track via a first sliding spring and a second sliding spring;

wherein the braking device comprises two front stop rods, side walls of each front stop rod are provided with braking grooves, a braking block which is slidable in the braking groove is mounted in each braking groove, and the braking block is connected to an end of the braking groove via a braking spring; an end of each front stop rod near the actuating device is provided with a wedge-shaped opening for seizing a pressed plate of the actuating device, and an end of each front stop rod near the slidably fixing device is connected to the first sliding block via a rotating shaft; the braking block is connected to one end of a rear support rod through the rotating shaft, another end of the rear support rod is connected to the second sliding block via the rotating shaft, a stop plate is connected between the two front stop rods, and a damping plate is adhered to a side of the stop plate near the crane wheel.