Working principle of ball screw 

I. Main structural elements of a ball screw

High precision motion transmission in the ball screw is ensured by a precisely matched integrated design. A ball screw consists of a ball screw shaft, a ball screw nut, steel balls, a ball circulation system, a ball return device, and dust seals—six major components. All elements work in harmony, forming a closed motion transmission system with ball circulation.

High-precision arc-shaped raceways are made on the surface of the ball screw shaft, which serve as the main guides for the movement of the balls. The ball screw nut is a mating movable element, inside of which there are also corresponding raceways that precisely interact with the shaft tracks.

A plurality of high-precision steel balls are located between the inner and outer raceways and serve as the main rolling element. The circulation and return system of the balls ensures their continuous repeated movement along a closed circuit. Seals installed on both sides prevent the entry of dust and contaminants, ensuring consistent motion accuracy.

II. Basic Working Principle of Ball Screw

The basic operating principle of the ball screw is to replace the traditional sliding friction with rolling friction, and effectively convert the motor torque into linear force and linear movement through closed circulation of the balls. In a conventional screw drive, the thread surfaces directly contact and slide against each other, resulting in significant frictional resistance, rapid wear and relatively low gear efficiency.

In a ball screw, high-precision steel balls are placed between the helical raceways of the shaft and nut. When a servo motor or stepper motor drives the ball screw, the helix angle of the raceway creates an axial force on the steel balls, causing them to roll continuously along the raceway. As a result, the ball screw nut makes a smooth reciprocating linear movement. In the process of transmitting motion, the “sliding surfaces” contact is replaced by point contact and rolling, due to which the friction resistance is significantly reduced.

At the same time, a special ball circulation and return device directs the balls that have reached the end of the stroke back to the initial part of the raceway. After this, they are again included in the circulation, forming a continuous closed system of ball movement. This ensures long-lasting, stable and high-speed linear motion transmission.

Depending on the installation method, two options for transmitting motion are possible: the screw is fixed, the nut rotates and moves linearly; the nut is fixed, the screw rotates and makes reciprocating movement. These options make it possible to adapt ball screws to different design and installation conditions of automated equipment and machine modules.

III. Preload principle: high-precision motion transmission without backlash

Conventional screw gears have backlash, which reduces positioning accuracy and cannot meet the requirements of precision equipment. In precision ball screws, backlash in the gear is virtually eliminated by using a preload design. This is one of the key factors to ensure positioning with micron precision.

Technologies such as dual-nut preload, pitch-difference preload, and oversized ball preload ensure that the balls remain in constant, tight contact with the inner and outer raceways without play or loosening.

When switching the direction of movement of the equipment, there are no problems associated with idling, position shifting, jamming and vibration. Combined with precision grinding, this results in ultra-high positional repeatability of up to ±0.003 mm, ideal for high-precision applications such as precision machining, IC inspection, and precision assembly positioning.