• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Linear Motion Tips

Covering Linear Motion Systems, Components and Linear Motion Resources

  • New
    • Editor’s blog
    • Industry news
    • Motion Casebook
    • Video
  • Applications
  • Slides + guides
    • Ball + roller guides
    • Track roller (cam + wheel) guides
    • Crossed-roller slides
    • Linear bearings
    • Plastic + composite guides
  • Drives
    • Ball + lead + roller screws
    • Belt + chain drives for linear
    • Rack + pinion sets
  • Actuators
    • Ball + leadscrew driven
    • Belt + chain driven
    • Linear motors
    • Mini + piezo + voice coil
    • Rack + pinion driven
    • Rigid-chain actuators
  • Encoders + sensors (linear) + I/O
  • Stages + gantries
  • Suppliers

Linear motion basics: 13 fundamental topics you need to know

October 15, 2021 By Danielle Collins Leave a Comment

Whether you’re new to designing and sizing linear motion systems, or you could just use a refresher, we’ve gathered all the articles that cover mechanical concepts used in linear motion systems and put them together here, as a sort of “linear motion basics” reference guide.

Unlike our curated lists of articles that address sizing and selection for specific products, such as ball screws, the articles below address more fundamental topics, such as Hertz contact stress, torsion, and the difference between moment and torque. And while you may not use all of these in every linear motion design and sizing project, understanding these foundational concepts can help you make more robust and cost-effective design choices.


degrees of freedom
The six degrees of freedom (DOF) include three translational and three rotational.
Image credit: Newport

Degrees of freedom

Some multi-axis systems can have six degrees of freedom and seven (or more) axes of motion. This article explains the difference between “axes of motion” and “degrees of freedom,” and why it matters.

Cartesian versus polar coordinate systems

In linear motion, we typically use the Cartesian coordinate system, but some applications — particularly those that use articulated robots — use the polar coordinate system. In this linear motion basics article, we explain how each coordinate system works, the differences between them, and how to convert from one system to the other.

Moment or torque – which do I want?

A force applied at a distance can create a moment or a torque. A moment force is static, whereas torque causes a component to rotate, so it’s important to know the difference between them and what causes each.

Roll, pitch, and yaw

Rotational forces are defined as roll, pitch, and yaw, based on the axis around which the system rotates. For linear guides, roll, pitch, and yaw forces can cause deflection and errors in motion.

Hertz contact stresses
The type and area of contact between a ball (or roller) and raceway influences the amount of friction, heat, and wear the bearing experiences.
Image credit: E.V. Zaretsky, Glenn Research Center

Hertz contact stresses

When two surfaces of different radii are in contact and a load is applied, a very small contact area is formed, and the surfaces experience Hertz contact stresses, which have a significant effect on a bearing’s dynamic load capacity and L10 life.

Ball conformity

The location and shape of the contact area between a ball (or roller) and a raceway is determined by the amount of conformity between the surfaces. Understanding ball conformity is important, since it is closely tied to the amount of Hertz contact stress that a bearing experiences.

Differential slip

Because the contact area between a load-bearing ball (or roller) and its raceway is an ellipse, the velocity varies at different points along the contact area, causing the ball or roller to experience slip rather than pure rolling motion. This differential slip is directly related to friction, heat, and bearing life.

Tribology: Friction, lubrication, and wear

Lubrication helps to reduce friction in linear bearings, which is the primary cause of wear and, in many cases, failure. Tribology is the study of friction, lubrication, and wear, and explains the complex relationship between them.

Stress and strain

Tension and compression loads in linear motion systems lead to stress and strain in the materials. These concepts are especially important for components such as fasteners, which may reach their yield point or tensile strength limit before other signs of damage occur in a system.

linear motion basics stress and strain
There are five fundamental types of loading: compression, tension, shear, torsion, and bending.

Stiffness and deflection

Deflection in linear motion systems can lead to misalignment of components, excess forces, and premature wear and failure. In this article, we look at how a material’s stiffness and deflection are related, and how stiffness differs from strength.

Torsion

Shafts on ball screws, pulleys, gearboxes, and motors can experience significant torsion, which causes shear stress and shear strain in the shaft. This article explains the effects of shear stress and shear strain and how to determine when a shaft will yield.

Material hardness

The hardness of a shaft or bearing surface plays a key role in its load capacity and life. In this article, we explain the different methods for testing and defining hardness.

linear motion basicsInertia versus momentum

Two commonly interchanged terms in linear motion are “inertia” and “momentum,” but they have different effects on a system’s performance. This linear motion basics article explains the difference between them and how each one is used in linear motion design and sizing.

Feature image credit: Bosch Rexroth

You may also like:

  • Acme or trapezoidal
    Acme or trapezoidal? What’s the difference between lead screw designs?
  • dynamic load capacity
    What’s the difference between dynamic load capacity and static load…
  • calculate acceleration
    How to calculate acceleration
  • Lead Angle
    Examining screws from three different angles

  • Bearing lubricant: Choosing between grease and oil

Filed Under: Applications, FAQs + basics, Featured

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

DESIGN GUIDE LIBRARY

“motion
Subscribe Today

RSS Featured White Papers

  • Evaluating actuators for washdown in food & beverage applications
  • Identifying Best-Value Linear Motion Technologies
  • Introduction to accuracy and repeatability in linear motion systems

RSS Motion Control Tips

  • Schneider Electric launches Universal Automation Discovery Packs to foster industrial innovation
  • Encoders from SIKO support Industrial Ethernet
  • Draw-wire encoders from SIKO measure position, speed and inclination
  • Incremental encoders configurable via NFC (near-field communication)
  • Low-cost motion control offered with CLICK PLUS PLCs from AutomationDirect

Footer

Linear Motion Tips

Design World Network

Design World Online
The Robot Report
Coupling Tips
Motion Control Tips
Bearing Tips
Fastener Engineering

Linear Motion Tips

Subscribe to our newsletter
Advertise with us
Contact us
About us

Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy