Coupler

The coupler comprises a first half coupler body with at least one pair of convex teeth arranged at one end, and two pairs of sliding contact faces which are opposite in inclination direction and havethe same included angle with a radial plane are arranged on the two convex teeth belonging to the same pair respectively; the second half coupling is provided with end sections which are staggered with the convex teeth; the middle connecting piece is only connected to the end section in a sliding mode and can freely move in the axial direction, an inclined sliding groove is formed to be matched with the protruding teeth, and the second half coupler can be connected to the protruding teeth in the mode that the second half coupler can freely move in all directions along the sliding contact face.And meanwhile, each convex tooth is matched with at least one middle connecting piece, the middle connecting pieces matched with the two convex teeth belonging to the same pair are equal in mass, andthe common mass center of