Precision ball screws are devices that use a nut that rotates up and down a screw by use of ball bearings that spin in the matching helical grooves. The radial motion, or torque, is converted into linear motion called thrust.
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Precision ball screws are often combined with linear slides and linear actuators to provide smooth motion in one direction when moving devices, parts or equipment. The threading of the screw and the threading of the nut match one another. Ball bearings roll in the grooves of the threads to provide a rolling friction and precise controllable motion. The screw is made from a strong metal such as steel; the ball bearings are usually made of chrome steel while the nut itself can be either plastic or metal. Precision ball screws have a number of benefits. When powered by a motor they are up to 90% efficient and require only low levels of energy. Precision ball screws perform critical functions in the manufacturing industry because of the level of control they allow operators to exert while transporting heavy loads. Precision and miniature ball screws are used in medical equipment, material handling equipment, conveyors and machine tools, robotic lines, precision assembly equipment, semiconductor manufacturing and fly by wire aircraft and missile control among many other product applications. Numerous industries, including aerospace, computer, electronic, automotive and medical industries, utilize precision ball screws in product applications.
Ball screws in general are manufactured by rolling, milling or grinding. Rolled screws are relatively inexpensive but are the least accurate of the three. Milled ball screws are cut by milling tools and are moderately precise. Ground ball screws are machined to their gross shape then case hardened and ground on machines with abrasive materials that spin at rapid speeds. This process allows the resulting ball screws to withstand high temperatures that would otherwise distort the shape and efficiency of the screw. Once the screw is manufactured, a nut is added. 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. They circulate through the nut by use of deflectors and return. Precision ball screws generally have a 0.0005 inch per foot lead accuracy or up to ten microinches per turn. To achieve greater control, precision ball screws can be preloaded with extra weight, eliminating any axial clearance and increasing stiffness. Backlash can be minimized by using oversized ball bearings or by preloading.
