Screw jack, also known as a helical drive mechanism.It is primarily used to convert rotary motion into linear motion or vice versa. There are those primarily for transmitting energy, such as spiral presses and jacks; others for transmitting motion, like the feed screws on machine tool tables; and still others for adjusting the relative positions of parts, such as spiral drive mechanisms. Screw jacks are differentiated by their sliding friction mechanisms and rolling friction mechanisms.

Features of screw jack:

1The working principle involves ball bearings placed between the screw thread raceways of the lead screw and nut.

2When the screw or nut rotates, the ball bearings roll along the thread groove, resulting in rolling friction between the screw and nut during relative motion. To prevent the ball bearings from rolling out of the groove, return guide devices are installed at both ends of the nut's spiral slots.

3They form a circulation loop with the threaded raceway, allowing the ball bearings to circulate within the nut's raceway.

The transmission forms of screw jack are based on the relative movement combinations between the screw and nut. There are essentially two types of basic transmission forms for screw jacks.

(1)Nut fixation, screw rotation and movement; this type of transmission is simple in structure due to the nut's inherent supporting function, which eliminates the additional axial movement that might occur in screw shaft bearings. It achieves high transmission precision. However, its axial dimensions should not be too long, as this would reduce rigidity. Therefore, it is only suitable for applications with short travel distances.

(2)The screw shaft rotates, and the nut moves. This type of transmission requires limiting the nut's rotation, thus necessitating a guiding device. Its features include a compact structure, good rigidity of the screw shaft, and suitability for applications with large working travel.