Project Description

Ball Screw Assembly and Components

Ball Screw Assembly

The ball screw assembly is a combination of a ball screw and one or more nuts. It provides an efficient method of converting rotary motion to linear motion or linear motion to rotary motion. When the ball screw is used as the active part, the nuts will be converted into linear motion according to the lead of the corresponding specification with the rotation angle of the screw. The passive part can be connected through the nuts to achieve the linear motion. Precision ball screws have multiple bearing balls that transfer loads between nuts and screws. The thread grooves where balls rolling is an ogival shape formed from two arcs of the same radius with offset centers. This kind of shape is also known as Gothic arches. Ball screw assembly is one of the most commonly used transmission components in tool machinery and precision machinery. Due to its small friction resistance, it has the characteristics of high precision, reversibility and high efficiency.

There are two common circulation methods for ball screw assembly: outer circulation and inner circulation. Sometimes rolling balls in the nuts come out of contact directly with the lead screw during the cycle is called outer circulation; The balls inside the nuts are in contact with the lead screw all the time during the cycle is called inner circulation. The return modes for the ball circulation of the outer circulation ball screw assembly mainly include end cap type, intubation type and spiral groove type. The inner circulation ball screw assembly adopts an inverter to realize the ball circulation. There are two types of inverters: cylindrical convex key inverter and oblate block inverter.

Features of ball screw assembly:

1. High precision: strictly temperature and humidity controlled in each process like grinding, assembly and inspection during manufacturing;
2. Micro-feeding: the ball screw assembly uses a rolling ball movement, the starting torque is extremely small, and the creeping phenomenon like sliding movement will not occur. It can ensure accurate micro-feeding;
3. High rigidity: the ball screw assembly can be preloaded because the preload can make the axial clearance reach a negative value, and then get higher rigidity;
4. High-speed feed: the ball screw assembly can achieve high-speed feed movement due to excellent movement efficiency and heat generation feature;
5. No self-locking features and has reversibility of transmission.

ISUTAMI supplies standard type ball screws and nuts in different sizes and accuracy, including metric and inch specifications, such as miniature ball screws and ball screws with flange nuts, etc.

Ball Screw End Support

Ball screw end support is a bearing unit that supports and connects the ball screw and the electric motor. It is generally divided into the flange type support units FK/FF, and the pillow block type support units BK/BF and EK/EF. The support unit on the fixed side is mounted with a pre-adjusted angular contact ball bearing, which has high rigidity, high precision and stable rotation performance. A deep groove ball bearing is mounted in the support unit on the support side. The mounted bearings of these end supports are filled with a suitable amount of lithium soap-based grease, sealed with special sealing rings, and can be directly installed for long-term use.

The BK/BF and EK/EF end supports are referred to as pillow block style. Mounting holes are provided to bolt these to the base where your ball screw will operate.
The BK or EK fixed end support contains two angular contact bearings that provide both axial and rotational support for the ball screw.
The BF or EF floating support has only a standard ball bearing that provides rotational support on the end of the ball screw opposite of where the drive occurs (typically a motor or pulley).

The FK/FF end supports are referred to as “flange” style. Mounting holes are provided in flanges, and bores in brackets on your machine receive the round bearing body. Bolts fasten the flanges to secure in place.
The FK fixed end support contains two angular contact bearings that provide both axial and rotational support for the ball screw.
The FF floating support has only a standard ball bearing that provides rotational support on the end of the ball screw opposite of where the drive occurs (typically a motor or pulley).

ISUTAMI standard ball screws are supplied with machining that will work with all of these end supports without modification.

Shaft Coupling

In a linear motion system operating with the ball screw, shaft coupling is used to mechanically connect the driving shaft and the driven shaft in different units to rotate synchronously for purpose of transmitting motion. It is designed for motion control applications that require very smooth motion and high torsional stiffness. Shaft couplings can compensate for offsets between the two shafts due to inaccurate manufacturing or installation, deformation or thermal expansion during work, and can also mitigate shocks. As a safety device to prevent excessive loads on the coupled shaft, shaft couplings play the role of overload protection. Most of the commonly used couplings are standardized. Generally, you can choose the right type of coupling according to the items and sizes. When necessary, the load capacity of the vulnerable links can be checked and calculated. When the operating speed is high, the centrifugal force of the outer edge, as well as the deformation of elastic elements, needs to be checked, and the balance calibration should be performed.

Rigid shaft coupling:

Rigid shaft couplings do not have the abilities of damping and compensating the relative displacement between the two axes, and require a strict alignment of these two rigid shafts. However, this type of coupling has a simple structure, low manufacturing cost, convenient assembly and disassembly, and easy maintenance, also can ensure high alignment of the two shafts and high transmission torque, so that there is no relative movement between the shafts. This type is widely used among the couplings.

Flexible shaft coupling:

Connect two shafts with up to 15° of misalignment. flexible shafts in high-speed, low-torque applications. They’re also better than U-joints for applications requiring precise movement and directional changes.

Flexible shaft couplings connect two shafts with a maximum misalignment of 15°. They can be divided into flexible couplings without elastic components and flexible couplings with elastic components. The former type only has the ability to compensate the relative displacement of the two axes, but it can’t buffer and reduce vibration; The latter type contains elastic elements, besides the ability to compensate the relative displacement of two axes, it also has a buffer and damping effect, but the transmitting torque is generally less than that of coupling without elastic components due to the limitation of its elastic element strength. Flexible couplings are suitable for connecting flexible shafts in high-speed, low-torque applications, and they are widely used in applications requiring precise motion and direction changes.

ISUTAMI can supply a wide range of standard ball screw and nut assembly, ball screw supports and shaft couplings in both metric and inch sizes, with specific surface treatments. We also offer custom services for any required products.

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