1. Working principle
The ball screw nut pair is a transmission pair that puts balls between the screw and the nut, and the screw and the nut become a driving pair of rolling friction. Both the screw 1 and the nut 3 are formed with spiral grooves with arc-shaped surfaces, and they are assembled together to form a spiral raceway, and the ball 4 both rotates and rolls cyclically.
2. Features
Compared with ordinary screw nut pairs, ball screw nut pairs have the following advantages:
- (1) Small friction loss and high transmission efficiency. The friction factor of the ball screw nut pair is only 0.002～0.005; the transmission efficiency is 0.92～0.96, which is 3 to 4 times higher than that of the ordinary screw nut pair; the power consumption is only equivalent to that of ordinary screw and nut pairs. The lead screw is 1/4 to 1/3, so the heat is small and high motion can be achieved.
- (2) Smooth movement without crawling. Due to the low frictional resistance, the difference between dynamic and static friction is extremely small, so the movement is stable and crawling is not easy to occur.
- (3) It can be pre-tightened, and there is no lost motion ball screw pair in the reverse direction. After pre-tightening, the shaft gap can be eliminated, so there is no reverse dead zone, and the transmission rigidity and transmission accuracy are also improved.
- (4) Small wear, good accuracy retention and long service life.
- (5) The reversibility of motion. Because the friction factor is small and it is not self-locking, it can not only convert rotary motion into linear motion, but also convert linear motion into rotary motion. That is, the screw and nut can be used as active parts or from Moving parts.
The disadvantages of ball screw pair are:
- (1) The structure is complex, and the machining accuracy and surface quality of components such as screws and nuts are high, so the manufacturing cost is high.
- (2) It cannot be self-locked, especially when used as a vertically installed ball screw drive, it will automatically drop due to the weight of the component. When the component is driven downwards, due to the weight and inertia of the component, it cannot be immediately shut off when the transmission is cut off. To stop the movement, a braking device must be added.
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