Miniature ball screws are very small devices composed of a screw and nut containing ball bearings that travel in the helical grooves of a threading, allowing rotational motion to be converted into horizontal movement. Miniature ball screws change torque into thrust.
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Miniature ball screws can be used with miniature linear slides and actuators to provide precise movement for small machines or equipment that is transported linearly. Because they carry heavy loads, miniature ball screws are usually made from steel. There are two main components: the screw, which is a threaded rod, and a nut whose internal threads match with the threading on the screw. The nut rotates around the screw by use of ball bearings held inside. The diameter of miniature ball screws ranges from 5 to 16 mm with lead distances, the linear distance the carriage on the nut will travel with one revolution, ranging from 2 to 5 mm; custom sizes are also available. It is not uncommon for miniature ball screws to be measured in metric units as well as in American standard labels. Medical instruments, lasers, gauge measurement, semiconductors and small devices rely on miniature ball screws for smooth, precise linear movement. The electronics, computer, automotive and aerospace industries also use these ball screws in places where space is tight or where the load is light.
As described above, miniature ball screws use a threaded rod; unlike the fasteners of the same name, the screws do not taper but maintain a consistent diameter. The nut is a cylindrical casing that contains threading that corresponds to the screw. The two parts do not make direct contact because of ball bearings that travel in the helical grooves, rotating inside the nut and allowing the spinning nut to smoothly glide along the screw. Miniature ball screws also use deflectors to keep the balls circulating inside the nut. In many ball return system, the balls are returned to the opposite end of the nut by a return tube that curves around the outside diameter of the nut. Miniature ball screws can be manufactured by rolling, milling or grinding. Rolled screws are cold rolled from a blank. They are relatively inexpensive but are the least accurate of the three. Milled ball screws are cut and machined by milling tools and presses and are moderately precise. Ground ball screws are machined to a general shape then case hardened. They are then ground to precise dimensions and generally have a 0.0005 inch per foot lead accuracy. Miniature ball screws are generally used in environments or in applications that require precise motion. To achieve greater control, miniature ball screws can be preloaded, which eliminates any axial clearance to increase stiffness. Backlash can be minimized by using oversized ball bearings or by preloading.
