How do axial and radial loads affect linear motion systems?

In any moving system,it is important to know the type and direction of the applied and generated load in order to determine the bearing lifetime and analyze the deflection.In linear motion systems,we usually use Cartesian coordinates(X, Y, and Z)to define the position and direction of the load.But for rotating components such as screws,rack and pinion drives,or pulley systems,the load is often described as an axial or radial load,terms that employ spin-bearing techniques.These terms are also sometimes used to describe loads on linear guides,although their relationship to the load direction may vary depending on the manufacturer and type of guide.

The load on a rotating bearing is defined as axial or radial load.

Here we will investigate how radial and axial loads affect a system in linear motion and explain the terminology commonly used to describe loads on a linear wire.In this discussion,we use the following conventions to define the X,Y,and Z axes.The X-axis is oriented along the direction of travel,the Y-axis is horizontal and perpendicular to the direction of travel,and the Z-axis is perpendicular.(Note that in some cases,the manufacturer specified the Y and X axes along the direction of travel as horizontal and perpendicular to the direction of travel.)

A common convention for defining the axes of a system of linear motion is to name the direction of travel the X axis,the vertical horizontal axis the Y axis and the vertical vertical axis the Z axis.

Axial load: parallel to the direction of travel

The rotary bearing term defines axial load as a load parallel to the axis of rotation(X axis),and it is also used for rotary linear drives(such as screw,pulley system,or rack and pinion drives).Axial load is the load that the system has to overcome to generate motion,and is also commonly referred to as thrust load.In ball screw and screw drives, axial loads can also cause deflection or buckling of the lead screw shaft.

Axial loads occur parallel to the direction of motion,while radial loads occur perpendicular to the direction of motion.

Note that linear guides do not support axial loads because their individual degrees of freedom(motion)are along the X-axis.

Radial load: perpendicular to the direction of travel

As with rotating bearings,the linear drive term defines the radial load as the load in the Y or Z direction perpendicular to the axis of motion.(Note that a load occurring at an angle between three orthogonal axes can be resolved as a component occurring purely in X,Y,or Z.)

For linear guides,the terminology will vary when describing the load perpendicular to the axis of motion,depending on the type of guide and whether the load is operated in the Y or Z direction.For example,the term"radial load"is commonly used for circular axis linear guides because of their rotational capability.

Manufacturers sometimes use the term"radial"to describe the load that occurs vertically along a linear guide.

For non-rotating linear guides(such as shaped guides,cross-roller guides,or dovetail sliders),radial loads occurring along the Z axis are often described as "normal loads","tension loads"(for loads in the positive Z direction),or "compression loads"(for loads in the negative Z direction)

Loads occurring along the Y-axis(horizontal,perpendicular to the direction of motion)are often referred to as"lateral loads","lateral loads",or"lateral loads".It is important to note that while linear guides are designed to handle loads in the Y and Z directions,bearing types and raceway arrangements can result in different load capacities in different directions.

The load nomenclature on telescopic guides is usually installed on their sides,unlike other linear guides.When a telescopic guide is used,the radial load in the vertical direction acts on the side of the guide.Axial load occurs horizontally,perpendicular to the direction of travel,and acts on(or away from)the top of the guide.

For a telescopic guide,the radial load occurring in the Z-direction acts on the side of the guide,while the axial load occurring in the horizontal direction acts on the top of the guide.

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