- Published 29 Oct 2024
- Last Modified 29 Oct 2024
- 6 min
A Guide to Ball Screws
Ball screws play important roles in controlling everything from high-precision machine tools to jumbo jet wings. But just what are they, and how do they work? Read our article to find out.
The ball screw was invented by Rudolph G. Boehm in the late 1920s and is used in everything from robots to aerospace components and space hardware today. Ball screws are valued for their versatility, ability to cope with large loads, and accuracy and efficiency.
Want to learn about ball screws and how they work? Read on.
What is a Ball Screw?
Just what is a ball screw? All ball screws convert rotational motion into linear motion. These nifty mechanical devices are used for many reasons. Ball screw advantages include high accuracy, high efficiency, lack of friction, and repeatability, and they bring all this to aerospace, robotics, and machine tool applications.
Ball screws are a type of mechanical ball screw linear actuator (or power-transmission screw). They comprise a threaded screw and nut containing ball bearings. When the threaded shaft turns, the bearings move along it, making the nut move in a linear fashion up and down the shaft.
The mechanism of a ball screw actuator is designed to cut friction as much as possible, which means power conversion is more efficient. The efficiency of ball screws, or the ball screw torque calculation, is measured by their effectiveness in converting rotational movement into linear movement.
What are Ball Screws Used for?
What are ball screws used for? Some applications are literally out of this world. For example, as the largest telescope in space, the James Webb Telescope, goes about capturing distant images of stars and other cosmological phenomena, it relies on a ball screw to function. The ball screw moves the telescope’s deployable tower assembly, the component that made the James Webb compact enough to launch back in 2021.
Ball screws are also widely used in the defence industry and commercial aerospace. Common applications for ball screws in commercial aircraft are positioning aircraft flaps and thrust reversers. Ball screws are also used in military landing gear, to control engine inlets, and in exhaust nozzles.
Industrial applications of ball screws include milling machines and equipment such as steppers for semiconductor production. They are also widely used in automotive applications – particularly in ABS braking systems and power steering.
Ball Screw vs Lead Screw
When it comes to ball screw vs lead screw, just like a ball screw, a lead screw creates linear motion from rotational motion. Lead screws feature a sliding screw shaft and nut threads, but no ball bearings. They are more prone to creating friction than ball screws, which means more energy is lost in operation. Lead screws tend to be a lot less efficient than ball screws but are often cheaper. They are also noisier and more prone to vibration.
Ball Screw vs Ball Spline
And what’s the difference in terms of ball screw vs ball spline? Ball splines are compact designs that are also capable of providing linear and rotary motion. They consist of a ball screw and rotary ball spline, with spline grooves cut into the length of the shaft. The grooves prevent the bearing (known as a ‘spline nut’) from rotating, while allowing the ball spline to transfer power.
The ball spline also comes in rotary ball types that feature a rotating part such as a bearing or gear, enabling the spline to produce linear and rotational movement. Ball splines are capable of dealing with heavy loads and are widely used in robotics and transport applications.
Ball Screw Advantages
Ball screws have numerous advantages. They:
- Are high speed, high efficiency, and highly accurate. Ball screws are approximately 90% efficient. In comparison, lead screws have an efficiency of just 20% to 25%.
- Can carry big loads. Ball screws are used in industry for applications with high loads, whereas lead screws are suitable for lower loads.
- Have a long lifespan. In machine tool uses, ball screws can operate for thousands of hours without need for repair or replacement.
How Does a Ball Screw Work?
How does a ball screw work? All ball screws work by converting rotary movement of the shaft into linear movement of the nut. The ball bearings in a ball screw roll along the shaft on a track. The ball bearings are continually recirculated through the nut. As the ball recirculation system recycles the ball bearings, the nut is driven in a linear motion up the shaft. And because the screw uses ball bearings, friction is much lower than in some comparable systems, like lead screws.
Ball Screw Components
All ball screw assemblies contain the following components:
- Threaded shaft (screw). This is a cylinder that rotates, featuring helical grooves. A motor generates the power to rotate the shaft.
- Ball bearings. Bearings are situated within the helical grooves on the shaft and the nut. When the system rotates, the bearings drive the linear movement of the nut.
- Nut. The nut is a cylindrical component that moves up the shaft. The nut contains both the ball bearings and their recirculation system.
- Recirculation system. The recirculation system allows the bearings to move continuously between the grooves on the screw.
- End supports. A ball screw assembly has end supports to fix the shaft in position. They provide support throughout the process.
- Seals. Seals shield the ball bearings and the recirculation system from external contaminants such as dust. This helps to keep the bearings lubricated, reducing wear and friction.
Ball Screw Types
There are a number of different ball screw types available, depending on the application. Heavy-duty ball screws are capable of bearing particularly large loads and are used in everything from semiconductor manufacture to forging equipment and air compressors. High-speed ball screws, meanwhile, are used in applications such as machine tools where very high-speed feeding of workpieces is required.
The dynamic stresses on the ball screw can also generate a lot of heat, which is why some manufacturers offer ball screws with integral cooling systems to reduce wear. Ball screws can also be noisy in operation, which means low-noise types have been developed to improve the environment for production operators.
Using Ball Screws
Ball screws are a highly efficient way of converting rotary motion to linear motion. Because ball screws are so efficient (as well as being accurate and suitable for heavy-duty use) they can help save power. That’s because you may not need the same amount of energy from the motor to drive the screw as with a conventional screw system, an important factor to consider in any ball screw calculation.
If you’re thinking about the energy efficiency of your application, then, it may be time to consider using a ball screw. These versatile industry workhorses really do have a lot of advantages.
Looking for ball screws or lead screws? RS carries a wide range of mechanical power transmission equipment.
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