What is the difference between ball spline and ball screw?

A ball screw spline is a combination of two components--a ball screw and a rotating ball spline.By combining drive elements(ball screw)and guide elements(rotary ball spline),ball screw splines can provide linear and rotational motion as well as helical motion in a highly rigid,compact design.

一、The component of a ball spline

1. Ball screw

Ball screw uses a cyclic steel ball in a precision machined nut to drive the load to a precise position.In most designs,the screw is fixed at one or both ends and prevents the nut from rotating through a keyed housing or other anti-rotation device.Motor drives or rotates the screw.But because the lead screw is restricted to linear movement,the motion is transmitted to the ball nut,which moves along the length of the lead screw axis.Another ball screw design contains radial angular contact bearings on the outer diameter of the nut,allowing the nut to be actuated - usually via a belt and pulley assembly connected to the motor-while the screw remains completely stationary.When the motor turns,it rotates the nut so that it crosses the length of the screw.This setup is often referred to as a"driven nut"design.

2. Ball spline

A ball spline is a linear guide system similar to circular shaft and cyclic ball bearings,but with spline grooves precisely machined along the length of the shaft.These grooves prevent the bearings(called spline nuts)from rotating and also allow the ball spline to transfer torque.A variation of the standard ball spline is the rotary ball spline,which adds a rotating element- gear,cross-roller,or angular contact ball bearing-to the outer diameter of the spline nut.This allows rotating ball splines to provide both linear and rotational motion.

二、How ball splines work

When a driven nut type ball screw assembly is combined with a rotating ball spline,the resulting configuration is often referred to as a ball screw spline.The shaft of a ball spline has threads and spline slots along its length that"cross"each other.

  A ball spline has a ball nut and a spline nut,each nut having a radial bearing in the outer diameter.  

三、Ball spline motion: straight,spiral,and rotational motion

Ball screw spline assembly limits the linear motion of ball screw nuts and ball spline nuts.By driving the ball and spline nuts together or separately,three different types of motion can be generated:straight,spiral,and rotational motion.To generate linear motion,the spherical nut is driven while the spline nut remains stationary.As the nut cannot move in a straight line,the shaft passes through the nut.However,the fixed spline nut prevents the axis from rotating,so the axis motion is purely linear and there is no rotation.Alternatively,when the spline nut is driven and the ball nut remains stationary,the ball spline induces a rotational motion,and the thread through which the ball nut is fixed causes the shaft to move linearly as it rotates,resulting in a helical motion.When both nuts are driven,the rotation of the ball nut essentially cancels the linear motion induced by the ball spline,so that the shaft rotates without any linear stroke.

In a ball spline assembly,the ball screw nut and spline nut can be driven individually or together to produce linear,helical,or rotational motion.

https://www.autolinearmotion.com/ball-screws.html