ROLLER SCREWS   |   BALLSCREWS   |   VIDEO   CALCULATIONS   |   ACCESSORIES

Ballscrews and roller screws

Welcome to this Motion Control Classroom on roller screws and ballscrews.


Absolutely core to linear-motion designs are the three types of rotary-to-linear screw drive types:

  • Simple leadscrews (sometimes called ACME or trapezoidal, though profiles and flank geometries abound) — based on sliding contact between the linear screw and nut

  • Ballscrews — based on rolling contact between the linear screw and nut (via ball bearings)

  • Roller screws — also based on rolling contact between screw and nut (via rollers).


In this Classroom, we present information on the last two linear-motion drive types.


Determining the most suitable rotary-to-linear screw drive for a given machine axis depends on the loads it will move, travel speeds, duty cycles, cost constraints, and the environment in which the machine will run.


In this Classroom, you’ll learn about ballscrew load-life characteristics — and why ballscrews excel where high speeds and loads are present … even while maintaining 90% efficiencies. You’ll also learn how roller screws leverage multiple sets of rollers for exceptional internal contact to withstand high loads and shock even while providing distinct stiffness advantages over ballscrews — and maintaining 84% efficiency or better. In fact, electric thrust actuators incorporating both screw types (but especially roller screws) have come to rival hydraulic cylinders for some applications — capable of delivering hundreds of kN.


Thank you for reading — and be sure to check out our other Classroom installments at designworldonline.com/mc2.


Lisa Eitel

Editor, Design World

Ballscrews and roller screws Classroom sponsored by: 

BASICS OF ROLLER SCREWS

Planetary roller-screw basics

Differential versus planetary roller screws

Update on roller-screw applications


Benefits of recirculating roller screws

More on the performance of roller screws 

Screw drives are some of the most common methods of mechanical linear actuation. And planetary roller screws are one of several screw types, including lead screws and ball screws. Planetary roller screws use threaded rollers that are toothed to mesh with geared rings at each end of a nut.

Traditional roller screws — sometimes referred to as planetary roller screws — can produce axial forces comparable to hydraulic cylinders, with the speed and precision capabilities of ball screws, at a price point that falls between the two.

Roller screws are also called planetary roller screws or sometimes satellite roller screws for how their nut-encased rollers orbit the drive-shaft axis during operation. These mechanical rotary-to-linear devices work in an increasing number of electromechanical actuators. 

Screw assemblies that use rollers as the load-carrying element come in several varieties, with the most common being the traditional planetary roller screw, which provides high load capacities and very high rigidity, capable of outperforming ball screw and hydraulic actuators in some heavy-duty applications.

Planetary roller screws — also called satellite roller screws — have long been the primary choice for applications that involve heavier loads and higher forces than traditional ball screws can withstand, or that require better speed and positioning accuracy than hydraulic cylinders can provide.

BASICS OF BALLSCREWS

What’s the difference between ball screw critical speed and characteristic speed?

Ball screw standards: What you need to know about DIN, ISO, and JIS

Ground vs. Rolled Ball Screws: Does manufacturing method matter?

Examining screws from three different angles

Ball screw preload: What you need to know


Ball screw drives incorporate two primary moving components: the rotating screw shaft and the nut that traverses the screw. (The radial bearings that support the screw shaft play a minor role for the purposes of this discussion.) This means that to

If you’re involved in ball screw sizing or selection, you’ve probably noticed that there are several different standards that govern various aspects of ball screw design, from lead accuracy and load capacity to ball nut tolerances and rigidity. Fortunately, in many cases, these standards are in harmony

When a linear motion application requires high thrust force and rigidity along with good positioning accuracy, a preloaded ball screw assembly is often the best choice. Manufacturers offer ball screw preload amounts ranging from just 1 or 2 percent for applications where backlash would be detrimental

The thread design of a power transmission screw—whether a lead screw or a ball screw—plays a critical role in the screw’s function. Aside from the basic thread form (acme, trapezoidal, etc.), the three main aspects of the thread geometry—helix angle, lead angle, and thread angle

There’s much debate among manufacturers, and sometimes among users, regarding the superiority (or lack thereof) of ball screws with ground threads over those with threads that are formed by rolling. Ground ball screws have traditionally been the choice

Hiwin Ballscrews

Animation of a planetary (satellite) roller screw from Rollvis

CALCULATIONS

How to account for screw inertia during motion system design

What is screw whip and why does it happen?

How to account for shock and vibration loads in screw drives

How to calculate the effect of preload on screw axial deflection

When sizing a motion system with a ball or lead screw drive, the first step is to determine the screw diameter and lead that can meet the application requirements for thrust force, speed, and compressive (buckling) loads. Once the screw diameter and lead are determined, the next step is to choose a motor that can deliver the required torque and speed, while also providing sufficient control

Ball screws are often the drive mechanism of choice in applications that require high thrust forces with excellent positioning accuracy and repeatability. But one of the drawbacks of ball screw technology is that speed is inversely related to length — the longer the ball screw shaft, the more likely it is to whip, like a jump rope, as it turns. This behavior limits the maximum travel distance

Calculations of ball screw service life and permissible static load take into account loads and forces that are predictable and quantifiable — thrust loads due to acceleration, process forces, and forces generated when holding a load in place, for example. But some applications are also susceptible to loads caused by shock 

In a recent post, we looked at the methods for inducing preload in a ball screw assembly and the effects it has on performance. One of those effects is that preload reduces axial deflection (displacement) and increases rigidity. But preload also increases the applied load

BALL SCREW ACCESSORIES

How to protect ball screws in harsh environments

Harsh environments can wreak havoc on motion system components — especially rolling element systems such as linear guides and ball screws. And while protective devices such as rail covers, wipers, and scrapers are widely available for linear guides, protecting ball screws in harsh environments is a bit more tricky.

Ball screw seals: Types, options,and applications

Ball screws are used in a wide range of applications, many of which expose the screw and nut assembly to harmful contamination in the form of dust, chips, or liquids. And like any bearing that uses metal balls (or rollers) on metal raceways, ball screws can experience abrasive wear when exposed to solid contaminants can interfere with proper lubrication — with both conditions reducing the expected life of the assembly and potentially causing catastrophic failure.

How to protect ball screws in harsh environments

Harsh environments can wreak havoc on motion system components — especially rolling element systems such as linear guides and ball screws. And while protective devices such as rail covers, wipers, and scrapers are widely available for linear guides, protecting ball screws in harsh environments is a bit more tricky.

What makes miniature ball screws unique?

Ball screws are used in a wide variety of applications, but some of the most challenging are those on the extreme ends of the performance spectrum – from large diameter, large lead screws for machine tools, to screws with small diameters and very fine leads for optical and medical applications. For very small, high-precision movements, designers and engineers often turn to miniature ball screws.

ROLLER SCREW ACCESSORIES

Support Bearings

Rollvis has designed a specialized family of support bearings for high load screw applications. These are available from shaft diameters of 12 to 100mm. These units are well sealed and greased for life. Using universally matchable angular contact ball bearings Rollvis is able to offer units with a stack up to 6 bearings and can configure the orientation of each bearing to match the loading requirements.


Getting straight on roller screws

Planetary roller screws – also referred to as satellite roller screws – have long been the primary choice for applications that involve heavier loads and higher forces than traditional ball screws can withstand, or that require better speed and positioning accuracy than hydraulic cylinders can provide. But some roller screw designs – specifically, recirculating roller screws – are also well-suited for high-precision applications, where resolution and positioning accuracy are of utmost importance.

Roller screws for any application article

As a relatively young technology, and with their initial applications being in heavy industries such as injection molding, roller screws are often considered to be best suited for applications where they replace hydraulic cylinders or other high-load drive mechanisms.


Roller screws unlock peak performance

You may not be familiar with roller screws, but these compact, high-efficiency screw drives are an important technology in the production of everyday devices and products. In fact, there were probably more than 20 roller screws involved in the manufacture and assembly of your vehicle – performing functions such as punching, tube bending, and riveting.



HIWIN is the world leader in motion control and system technology, providing high quality and reliable standard and custom components and complete motion control solutions with precision quality, at competitive prices. With an extensive inventory in Chicago, our products are widely used in industrial equipment, lab equipment, semi-conductor and more.

Rollvis SA was founded in 1970 in Geneva and our production site is in Plan-les-Ouates, the cradle of high-precision mechanics in Geneva.

Benefiting from more than half a century of experience and growth, our company has managed to maintain a human scale, offering our customers an ability to listen and optimal responsiveness.

Our satellite roller screws are today the reference for high precision linear motion applications.