Posted to News on 23rd Sep 2008, 14:23
XLF ball screws designed for servo-controlled machines
Ball screws have become an integral to modern machine tools due to their positional accuracy, load-bearing characteristics and low friction when compared with lead screws. However, little has changed in design since the first use of the ball screw in machine tools some decades ago. A common misconception is that to improve a ball screw, all that is necessary is to improve lead accuracy. Although improvement in lead accuracy is important, there are many areas in which design improvements can have a significant impact on overall machine performance.
Therefore, the ball screw cannot be considered in isolation, but rather as one element influencing servo loop performance. In developing its new XLF range ball screws, Jena Rotary Technology has recognised the importance of the ball screw in servo loop performance and designed a ball screw to meet the demands of modern machine tool controls. One important factor to consider is reversal error (reversal error occurs when lost motion is apparent during change of rotational direction in the ball screw), which can affect positioning and surface finish in the workpiece. The reaction of the mechanical elements in a system can have a significant effect on reversal error.
Ball screws in the XLF range have a low coefficient of friction, yet they retain high system rigidity and eliminate reversal error. Due to the design and materials used, it has also been possible to reduce the preload in the ball nut while retaining rigidity. Ball screw life and wear accuracy have also been significantly improved. The ball screw is also quiet compared with traditional designs. Another benefit is thermal stability of the assembly due to the reduced preload, improved rigidity and low coefficient of friction, producing a ball screw with low levels of heat generation.
Detailed changes
These improvements have been achieved using hybrid materials and changes in the design of the raceway profile in the ball screw and the ball nut. The changes are not noticeable to the eye, with the exception of the blue-grey appearance of the ball screw. The reduced preload and super-smooth run can be felt when the ball nut is turned by hand.
Clearly these benefits are not restricted to the machine tool industry; any applications where high accuracy, extended life and low levels of noise are required would benefit from the XLF range ball screws.
