A ball screw is a mechanical device used to convert rotary motion into linear motion.
Compared with options under the same class, such as roller screws and acme screws, ball screws are one of the most economical ways of performing precision motion control in the industries. They are able to move heavy loads at high speeds with exceptional accuracy. Ball screws are also considered the more cost-effective alternatives of pneumatic and hydraulic actuators.
A ball screw consists of a ball nut and a threaded shaft, each of which can act as the traversing component. It functions in a similar fashion as ball bearings, where hardened steel balls traverse along an inclined-hardened inner and outer race. Ball screws are typically used for linear-motion applications which provide high efficiency, load capacity, as well as positioning accuracy.
Ball screws work very similarly to the standard lead screws, but they offer more benefits for using ball bearings that run in the helical channel to transmit the load. In high precision applications, they are needed to convert the rotary motion from a motor to linear motion for the payload.
Ball bearings in a ball screw traverse along the track in a similar fashion to ball bearings in a standard rotary ball race, thereby eliminating the sliding friction relative to the lead screws. The ball bearings recirculate through the ball nut continually, picking up lubrication and distributing the load along the way. Thanks to the utilization of roll bearings within a ball screw, the internal friction is kept at the minimum, which means the ball screw is able to provide superb efficiency and positional accuracy even at high force loadings and torque.
Attributed to ball screws’ more complicated mechanism and high precision requirement, they are often more costly compared with other types of lead screw. This is also due to the more sophisticated assembly technique revolving around the relative manufacturing process. With that said, the performance of a ball screw will generally justify the cost.
Following the above, despite the generally higher cost, ball screws do offer many advantages for your motion applications:
● A ball screw is very efficient and requires less torque, hence the smaller motor.
● A ball screw offers great positional accuracy.
● A ball screw has low friction, enabling it to run at cooler temperatures.
● Ball screws are available in ground or rolled types.
● A ball screw can be adjusted to increase or decrease preload.
● A ball screw does not require frequent replacement.
● Ball screws come in various diameters from 4mm to 80mm.
Despite the many benefits, a ball screw can be back-driven because of its low internal friction. For instance, the screw shaft can be driven linearly in order to rotate the ball nut. This makes ball screws undesirable for manually-fed machine tools, as the stiffness of a servo motor is needed to keep the cutter from grabbing the work piece and self-feeding. To elaborate, the cutter and work piece may be ruined when both exceed the optimum feed rate and jam together. Lastly, as we mentioned previously, the cost is another major factor that results in the replacement of cheaper alternatives, such as Acme screws.
Ball screws are ideal for applications that require efficiency, accuracy, precision, smooth motion, and prolonged continual, high-speed movement. On a broader scope, they are typically used in aircraft and missiles to control surfaces. They are also used in the power steering for automobiles to convert rotary motion from an electric motor to the axial motion of the steering rack. Furthermore, you can often see ball screws in machine tools, robots, and precision assembly equipment as well. High-precision ball screws are used in steppers in semiconductor manufacturing.
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