The oscillating hydraulic cylinder is the executive component of the output torque and the reciprocating motion. There are several forms, such as single leaf, double leaf, spiral swing and so on. Blade type: the stator block is fixed on the cylinder, and the blade and the rotor are connected together. According to the direction of oil intake, the blade will drive the rotor to swing. The spiral swing type is divided into two kinds: single spiral and double helix. Now the double helix is more commonly used, and the straight motion of the piston in the cylinder can be changed into a compound motion of linear motion and rotational motion by two screw pairs, so as to realize the swinging motion.