Common types of ball screws

phylogeny

Actually, it is not a long history for people to use screw for transmission. The traditional screw has been in poor positioning and easy damage. Until 1898, it was the first time that people tried to put steel balls between nuts and screws to replace sliding friction with rolling friction, so as to improve their poor positioning and easy damage. In 1940, the ball screw was put on the steering device of automobile, which was a great revolution in the application of ball screw and gradually replaced the traditional ACME screw. Until recent years, ball screw has become one of the most widely used components in the industry.

principle

1. according to the national standard GB/T17587.3-1998 and application examples, ball screw (which has basically replaced trapezoidal screw, commonly known as screw) is used to convert rotary motion into linear motion; Or an actuator that converts linear motion into rotary motion, and has high transmission efficiency, accurate positioning and the like.
2. When the ball screw is used as the active body, the nut will be converted into linear motion with the rotation angle of the screw according to the lead of the corresponding specification, and the passive workpiece can be connected with the nut through the nut seat, thus realizing the corresponding linear motion.

type

Ball screw

There are two common circulation modes: external circulation and internal circulation. In the process of ball circulation, sometimes it is out of contact with the lead screw, which is called external circulation; Always keep in contact with the screw is called internal circulation. Each ball circulating closed circuit is called a column, and the number of leads contained in each ball circulating closed circuit is called the number of turns. Each nut of the inner circulating ball screw pair has two columns, three columns, four columns, five columns and so on, and each column has only one circle;

There are 1.5, 2.5 and 3.5 cycles in each column of external circulation.

1) External circulation: The external circulation means that the balls return to the screw nut through the spiral groove or cannula on the outer surface of the nut and re-enter the circulation. As shown in Figure 2-3, the return modes of the external circulation ball screw nut pair according to ball circulation mainly include end cap type, cannula type and spiral groove type. Common external circulation mode: end cap type; Intubation type; Spiral groove type. End cap, a longitudinal hole is machined in the nut to serve as the return passage of the ball, and the cover plates at both ends of the nut are provided with return ports of the ball, from which the ball enters the return pipe to form a cycle. Intubation type, which uses bent pipe as return pipe. This structure has good manufacturability, but because the pipe protrudes out of the nut body, its radial size is larger. Spiral groove type, in which a spiral groove is milled on the outer circle of the nut, through holes are drilled at both ends of the groove and tangent to the thread raceway to form a return channel. This structure is smaller in radial dimension than the cannulated structure, but it is more complicated to manufacture. The external circulation structure and manufacturing process of the external circulation ball screw are simple and widely used. Its disadvantage is that the seam of the raceway is difficult to be smooth, which affects the stability of the ball raceway.

2) Internal circulation: The internal circulation adopts reversers to realize ball circulation. There are two types of reversers. The cylindrical key reverser, its cylindrical part is embedded in the nut, and its end is provided with a reversing groove 2. The reverse groove is positioned by the circular key 1 on the outer cylindrical surface and its upper end to ensure alignment with the direction of the thread raceway. Round insert reverser, which is a general round head Ping Jian insert. The insert is embedded in the groove of the nut, and its end is provided with a reverse groove 3, which is positioned by the outer contour of the insert. Compared with the two kinds of reversers, the latter is smaller in size, thus reducing the radial size and axial size of the nut. However, the outer contour of the reverser and the dimensional accuracy of the notch on the nut are required to be high.