Self-braking ball screw, ball screw, also known as self-limit, limit ball screw, ball screw terminal clutch, is the traditional ball screw and rolling bearing composite use. The ball screw generally include the following components - ball screw, a special ball nut, retaining sleeve, stop off and so on. Rotary screw generally place the nut axially movable manner. At this point, there are two screw assembly running: First, when the nut is located in a position between the two ends of the trip limit when the ball screw ball screw is equivalent to the average; Second, when the nut is located at both ends, and the ball kept the limit set under the action of turning off the place, together with the screw when the screw vice screw nut is equivalent to the limit position supported on rolling bearings, which remains the case even if the screw rotating state , the nut does not move axially.