Travelling in style

The latest linear motion guides are not only fast and accurate, they are reaching almost maintenance-free levels of performance, says Bob Love, Technical Manager at THK.

The latest linear motion guides are not only fast and accurate, they are reaching almost maintenance-free levels of performance, says Bob Love, Technical Manager at THK.

It's been said that it's not the journey that's important, but the way in which you arrive.

This wisdom can be applied to host of different vehicles and scenarios.

Its relevance to linear motion guides may not, however, be immediately apparent.

Linear motion guides provide the means by which machinery and components can be moved or positioned to perform specified tasks.

These versatile transport mechanisms are available in a variety of styles that are designed to meet the almost limitless requirements of linear motion.

As a result, linear motion guides can be installed on level surfaces, vertical planes, inverted positions, slopes and walls - in fact, any location that requires equipment to be moved from one place to another.

With this level of adaptability, linear motion guides have, unsurprisingly, become important components in machinery used throughout industry.

These range from high-precision environments, found in pharmaceutical and biotechnology research, to industrial and process-orientated applications in manufacturing.

In particular, linear motion guides are used in heavy engineering, food processing and semiconductor manufacturing applications.

Generally speaking, linear motion guides comprise rails, or raceways, and guide blocks, or platforms that transport materials or components along specified routes.

Various techniques have been developed to support this mechanism, although most systems use steel ball bearings held within the block running along a groove in the rail.

The design creates a highly efficient unit delivering precise movement and pinpoint control.

This basic principal has been continually refined as advances in technology have enabled even greater levels of efficiencies and performance.

THK's Caged Ball design, for instance, relies on retainers to hold the ball bearings at an equal distance from each other, thereby enabling smoother movements, less friction and fewer maintenance requirements.

These advances have encouraged the use of linear motion guides in a growing number of applications.

However, as the UK economy buckles under the weight of falling demand and overseas competition, what operational advantages do these breakthroughs give manufacturers and OEMs?.

Early linear motion devices relied on gothic-arch-contact or point-contact designs to rotate the linear bearings in the raceway.

Although this technology is still used today, it has generally been superseded by the circular-arc design, which centres on a two-point contact construction between carriage and raceway.

Capable of self-adjustment, high capacities and consistently low friction, the design compensates within the elastic deformation of the balls for deviations in the installation's surface accuracy.

To meet demand for increased automation and performance, the circular arc design has evolved through advancements in the precision grinding of the circular arc grooves and ball to raceway conformity.

This enabled far greater stiffness and capacity, together with improved damping and lower profiles.

In essence, linear guides have got smaller, faster and more reliable.

Even at high speeds, the guides avoid all the known problems associated with sliding guides.

Indeed, compared with their sliding counterparts, ball-based linear motion guides provide considerable savings in terms of assembly man hours, due to the ease with which they can be installed and their ability to provide high-precision movements from unprepared surfaces.

This, combined with minimal maintenance requirements, means linear motion guides offer a practical and economical method of machine transport.

The current generation of linear motion products are so reliable that they are commonly regarded as fit-and-forget components.

For example, THK's latest ballscrews, which incorporate its caged ball technology within a ballscrew nut assembly, enjoy an operating life that can be three times that of traditional devices.

The caged ball system in the SBK and SBN ballscrews effectively eliminates the noise, friction, heat and wear that is common in conventional ball race configurations.

By enclosing the high-precision stainless steel balls within a separator cage with controlled density grease pockets, the caged ball configuration prevents contact between balls and improves lubrication, leading to significant improvements in overall performance and operating life.

The extended operating life of the SBK and SBN ballscrews is matched by the versatility of THK's new HCR guide, featuring an ingenious circular-guide design.

Suitable for medical, optical and industrial applications, the HCR is ideal for large rotary transport and positioning systems, such as turntables, rotary observation towers and swing cranes, providing equal load rating in radial, reverse radial and lateral directions.

Featuring four rows of balls, each with a 45-degree contact angle, the HCR is both stable and reliable and provides excellent load carrying capacities, with smooth, precise circular movement.

Modern linear motion guides provide a low-cost method of achieving highly accurate movements at exceptional speeds.

The latest innovations, however, focus on improving operating efficiencies by simplifying system setup and cutting maintenance requirements.

Breakthroughs, such as THK's caged ball technology, reduce rolling resistance variation to a tenth of that experienced by conventional models and extend performance levels to almost maintenance-free status.

Although the journey remains important, the level of maintenance and expense incurred during that journey might take the edge of your trip.

The latest innovations in linear motion systems ensure the arrival of extended system operation and reduced costs, with the luxury of increased reliability, speed and accuracy.

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