In modern industrial automation, CNC machine tools and robotics, the ball screw is known as the “core bone of precision transmission”. By converting rotating motion into high-precision linear motion, it solves the problems of short life and poor accuracy caused by large friction and low efficiency of traditional sliding lead screws.Next, we will conduct in-depth analysis of the core structure and working principle of the ball screw.
What is a Ball Screw?
A ball screw (or ballscrew) is a mechanical linear actuator that converts rotational motion into linear motion with little friction. A threaded shaft creates a helical raceway for ball bearings, which function as precision screws. They can apply or endure large thrust loads while generating minimal internal friction. They are manufactured to precise tolerances and hence appropriate for high-precision applications. The ball assembly serves as the nut, while the threaded shaft functions as the screw.
What Are The Components Of A Ball Screw?
Screws
Screw is an important part of Ball Screws and is usually made of high strength alloy steel to ensure sufficient rigidity and wear resistance. The outer surface of the screw is machined with a specific shape of thread, and common types of threads include trapezoidal threads. The pitch of the thread is a key parameter that determines the distance the nut moves in a straight line for each revolution of the screw. The screw acts as a power source in the whole system, providing driving force for the linear movement of the nut through its own rotational movement.
Nut
The nut is closely matched to the screw, and its internal structure is more complex. The inner surface of the nut also has a threaded shape that matches the threads of the screw to ensure precise engagement between the two. Inside the nut, there are also specialized ball circulation channels.
The design of these channels ensures that the balls are able to circulate smoothly between the nut and the screw for efficient energy transfer and motion conversion. The nut, driven by the screw, moves in a straight line along the axis of the screw, which in turn leads to a corresponding linear displacement of the working parts connected to it.
Balls Bearings
Balls, as the core element of Ball Screws to realize efficient transmission, are generally made of high-quality bearing steel with extremely high hardness and surface finish. The dimensional accuracy of the balls is very strict, and any small deviation from the dimensions may affect the performance of the whole system. When working, the ball is evenly distributed in the threaded raceway between the screw and the nut, which greatly reduces the friction and improves the transmission efficiency by rolling friction instead of sliding friction in traditional sliding screws. The balls are continuously circulated within the nut’s recirculation channel, continuously providing support for the nut’s movement.
Return System
The Return System is a key mechanism in Ball Screws that allows the ball, after rolling from one end of the nut to the other, to return to its starting position and begin the cycle again. This ensures that the ball can continue to work without breaking away from the nut.
How Do Ball Screws Work?
A ball screw functions similarly to a traditional lead screw, but it has the considerable benefit of transmitting the load via ball bearings moving in the helical channel. In high precision applications, it is frequently essential to convert the rotational motion of a motor to linear motion for the payload. One method to accomplish this is to use a ball screw.
Ball bearings in a ball screw roll down the track in the same way as ball bearings do in a typical rotary ball race, reducing the sliding friction associated with lead screws. The ball bearings are constantly recirculated via the ball nut, dispersing the load and collecting lubricant along the route. The use of rolling ball bearings within a ball screw reduces internal friction, allowing ball screws to provide high levels of efficiency and positional precision even under high torque and force loads.
Applications of Ball Screw
Ball screws are well suited to applications in extreme environments such as high-performance machine tools, or very delicate and sensitive applications including medical devices.
Ball screws are generally suited to applications where the following elements are required:
- High Efficiency
- Smooth Motion and Operation
- High Accuracy
- High Precision
- Prolonged continuous or high-speed movement
Some specific applications for Ball Screws are;
- Electric vehicles – the ball screw can be used to replace a common hydraulic system.
- Wind turbines – ball screws are used in blade pitch and directional position.
- Solar Panels – the ball screws help to provide two or three axis movements.
- Hydro Electric Stations – ball screws are used to control gates.
- Motorised inspection tables – a ball screw will be used within the mechanism which helps to achieve the desired position of the tables for a given application.
- Lithography equipment – ball screws are used within step photolithography machines in microscopic integrated circuits.
- Automotive power steering systems – ball screws are used in automatic steering systems.
Type Of Ball Screws
Ball Screws are available in a variety of designs. According to their structural characteristics and application requirements, the common types can be classified into the following three types:
- Single Nut Ball Screws: Single Nut Ball Screws are designed with a single nut, which is simple in structure, light in weight and low in cost. Single Nut Ball Screws are widely used in a variety of industrial automation equipment, general machine tools, medical equipment and so on.
- Double Nut Ball Screws: Double Nut Ball Screws are designed with two nuts, which are usually pre-tensioned together to eliminate loosening and improve the rigidity and accuracy of the system. Bidirectional Ball Screws are mainly used in applications requiring high accuracy and rigidity, such as high-precision machine tools, aerospace equipment, and precision measuring equipment.
- High-Speed Ball Screws: High-Speed Ball Screws are designed with optimized thread shapes and ball return systems to meet the demands of high-speed motion. These design improvements reduce heat build-up and noise while maintaining smoothness and accuracy of motion. They are mainly used in applications that require fast movements, such as high-speed machine tools, automated assembly lines, and production equipment in the automotive industry.
Read More What Are The Different Types Of Ball Screws?
How to Select a Ball Screw
Before choosing which ball screw to utilize, it is important to consider the different factors that may play a role in the decision process. A few of the considerations include:
- Lead accuracy
- Axial clearance and preload
- Critical speed
- Rotational speed of the nut
Read More: 10 Steps To Selecting The Right Ball Screw
Lead Screw vs. Ball Screw
A lead screw is a threaded shaft designed to convert rotational motion into linear motion. It functions similarly to a ball screw, except rather than utilizing ball bearings, it employs sliding friction to move the nut down the shaft. Because of this, lead screws are less precise and efficient than ball screws.
The primary benefit of lead screws is that they are simpler and less expensive to manufacture. They are often employed in applications where accuracy is less important, such as 3D printers and other low-cost CNC equipment.
Read More Ball Screw vs Lead Screw: Everything You Need to Know
How to productions Ball Screw?
Read More Manufacturing Process of Ball Screws: From Raw Materials to Finished Products