Ball Spline

A ball spline is a spline bearing with a rolling guide.
This is a revolutionary product that can also transmit torque while performing linear motion. The permissible load is greater than that of a linear bushing because balls roll in a groove on the shaft.

Precautions on Use

Types

The use of a ball cage maintains the aligned circulating motion and enables high-speed operation. In addition to preventing balls from impacting each other and causing mutual friction, the cages enable low noise and low dust generation. They also allow for long-term maintenance-free operation by improving grease retention.

The spline shaft has three crests positioned equidistantly at 120°, and along both sides of each crest, two rows of balls (six rows in total) are arranged so as to hold the crest so a single spline nut provides a preload to eliminate angular backlash and increase the rigidity.

This ball spline has a large load capacity in the radial and torque directions because the spline shaft has two to three crests on the circumference, and along both sides of each crest, two rows of balls (four to six rows in total) are arranged to hold the crest so that a reasonable preload is applied.

These models are unit types that have gear teeth on the flange circumference and radial and thrust needle bearings on the spline nut, all compactly integrated. The ball spline is optimal for torque transmission with a spline nut drive.

A compact unit type ball spline whose support bearings are directly integrated with the outer surface of the spline nut.

Features

Structure and Features

The Ball Spline is an innovative linear motion system in which balls accommodated in the spline nut transmit torque while linearly moving on precision-ground raceways on the spline shaft.
Unlike the conventional structure, a single spline nut can provide a preload with THK’s Ball Spline. As a result, the Ball Spline demonstrates high performance in environments subject to vibrations and impact loads, locations where a high level of positioning accuracy is required or areas where high-speed kinetic performance is required.
In addition, even when used as an alternative to a linear bushing, the Ball Spline achieves a rated load more than 10 times greater than the linear bushing with the same shaft diameter, allowing it to compactly be designed and used in locations where an overhung load or a moment load is applied. Thus, the Ball Spline provides a high degree of safety factor and long service life.

Curved Grooves That Approximate the Ball Shape

The linear bushing has a long history of use as a rolling guide, and it is still widely used today.It utilizes point contact, so although it achieves smooth linear motion with minimal friction resistance, its low permissible load presents challenges. The biggest difference between ball splines and linear bushings lies in the raceways.Ball splines have curved raceways that approximate the shape of the balls, which makes for alarger contact surface in comparison with point contact.

Higher Load Capacity

While it would take 13 linear bushings to bear a 1,000 N load, for example, the same feat could be accomplished by a single ball spline with the same shaft size, ball diameter, and number of balls.

Significantly Extended Service Life

For example, if you took a linear bushing and ball spline with the same shaft diameter, ball diameter, and number of balls and loaded the linear bushing with an object that it would strain to carry, a ball spline could carry 2,200 of the same object.

Achieve Compact Designs

For example, if you were to design two devices that would bear the same load, the spline nut used for one would have an external diameter about 1/3 the size of the linear bushing used for the other.