Stern ramp retracting and releasing device for ship and synchronous retracting and releasing method

The invention relates to a marine stern ramp retracting and releasing device and a synchronous retracting and releasing method.The retracting and releasing device is installed on the inner side bulkhead of a left board and the inner side of a right board of a cabin, and a transmission device serves as a power source, is composed of a variable frequency motor, a coupler, a speed reducer and a driving chain wheel and is installed on a deck platform on the front portion of the cabin; a driving chain wheel at the output end of the speed reducer drives the chain to reciprocate in a variable-frequency driving mode; a chain frame is arranged on a driving chain wheel and a driven chain wheel of the transmission device, the chain above the driving chain wheel and the driven chain wheel is connected with a cable dragging sliding block, the upper chain is supported and guided through a guide rail, and the lower chain is supported through a bracket. The two side traction devices are symmetrically distributed, the control