Safety and linkage are indispensable parts of door. They can ensure the normal performance of the door. Roughly, they can be divided into the following parts: running blocking, slow down blocking, lifting blocking, anti-broke lock, locality protection device, worm blocking, impulse blocking, gasbag blocking, photo-electricity blocking, mechanical blocking, over-load blocking and so on; the design will take into account the linkage part that require extremely high strength grade, matching-up accuracy, flexible function.