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Product category: Ballscrews, Linear Guides, Jacks, Dampers
News Release from: THK UK | Subject: Linear motion guides
Edited by the Engineeringtalk Editorial Team on 18 August 2004

Small, but perfectly formed

Bob Love, Assistant Branch Manager at THK, examines the challenges facing linear motion guide manufacturers as they attempt to keep pace with demand for everything small.

Small may be beautiful, but it can also be extremely practical and very desirable Electronics products, for example, are downsizing at a rate of knots, the results of which can be seen on every high street, office and coffee shop in the UK

Palm-top computers are ubiquitous, and with consumer demand for these type products gathering pace, miniaturisation is increasingly the preferred option.

The notion of miniaturisation has been with us since the 1970s, when significant technological breakthroughs gave us the first digital wristwatches and portable TVs.

The growth of everything small has had an impact on almost every facet of our lives.

Today, you can take a picture from an in-built camera in your phone, send an e-mail from palm-top computer and choose from literally thousands of songs stored your own personal pocket-sized jukebox.

The influence of miniaturisation, however, extends further than simply consumer goods, where there is undoubtedly a degree of novelty.

The long-term impact of miniaturisation has been most keenly felt in the development of manufacturing processes, systems and components.

Here, size isn't the primary factor; control is.

In the field of linear motion, for example, the latest generation of miniaturised technologies are enabling the control of linear and reciprocating devices to reach submicron or nanometre levels.

This degree of control is essential if component and chip sizes are to be reduced sufficiently to enable the next breed of miniaturised consumer products to be unleashed on an evermore gadget-hungry public.

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

Available in a variety of styles that meet the almost limitless requirements of linear motion, these adaptable mechanisms can be installed on level surfaces, vertical planes, inverted positions, slopes and walls.

In short, linear motion guides can be commissioned in any location that requires equipment to be moved from one place to another.

With this level of flexibility, linear motion guides have become an important factor in a number of manufacturing processes, ranging from high-precision environments found in pharmaceutical and biotechnology research, to the harsh working conditions of industrial and process-oriented applications.

Typically, linear motion guides are constructed of rails, or raceways, and guide blocks, or platforms, which transport materials or components along specified routes.

Most systems use steel ball bearings held within the block to support the mechanism.

The bearings run along a groove in the rail creating an efficient and precise movement.

As with most technologies, this basic principal has been refined and improved to incorporate the latest innovations that promote greater levels of efficiencies and performance.

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

More importantly, these developments have encouraged the use of linear motion guides in a wider range of industrial environments.

Manufacturers of semiconductors, silicon wafers, electronics and laboratory test equipment, for example, incorporate the latest guides to enhance accuracies and improve system control.

Indeed, as the market for semiconductor and electronics products slowly recovers from the global slump witnessed a couple of years ago, so demand for the latest production systems is also picking up.

Inevitably, this will manifest itself in fresh demand for compact and accurate linear devices.

In many ways, the challenge confronting linear motion component manufacturers isn't simply reducing the physical size of the products, but rather finding suitable technologies that will support the cost-effective manufacture of these devices.

For instance, there are a number of technical issues that need to be addressed before the size of linear motion guides can be reduced further.

Stainless steel balls - the elements on which the system literally rests - are typically configured to provide as smooth and as controllable movements as possible, ideally with minimal friction or noise.

However, as the physical dimensions of linear guides diminish, so the size of these balls has to reduce accordingly.

With the potential for ball diameters reaching tens of microns, conventional manufacturing techniques and materials could well become redundant.

Through research carried out by companies like THK, it is possible to create stainless steel balls that measure less than 1mm in diameter.

Admittedly, these tiny elements are used for prototype systems that incorporate guide rails that are just 1mm wide, and have been created by pushing existing production techniques to their very limits.

To go any further would require a reappraisal of the constituents used and/or control methods employed, with the very real possibility of introducing systems based on piezoelectric, electrostatic or electromagnetic techniques.

With balls diminishing in size and the possibility of alternative methods of controlling motion and positioning being required, it may also be necessary to develop new lubricating materials, which are often overlooked as one of the most important elements of linear motion guides.

For instance, most conventional lubricants would be incapable of supporting the delicate component parts or low levels of friction demanded by miniaturised guides to achieve the desired levels of accuracy.

To overcome these is a new generation of lubricants are being introduced: for example THK's latest AFF grease has a smaller, flatter molecular structure that provides a stable, consistent and frictionless medium on which miniaturised components can move.

Such developments are inevitable, but once again, other factors may determine the rate at which these innovations are introduced.

Traditional mounting components, for example, will no longer be appropriate if the size of linear guides continue to diminish.

Unable to hold micro guides securely in place, alternative retaining methods, such as micro-clamps, adhesives or possibly materials that create molecular adhesions, may be needed to supersede current mechanisms.

Clearly, these are far-reaching projections of what might be required to facilitate linear motion on a much smaller scale.

However, these techniques aren't based on fanciful ideas or whimsical notions, but rather on technologies being developed today that may provide a stepping stone to the next generation of linear guides.

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

However, as well as focusing on improved operating efficiencies and simplified set-ups, the latest linear innovations are responding to a growing demand for smaller systems that also maintain reduced rolling resistance, heightened performance levels and almost maintenance-free operation.

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

For instance, THK's caged ball technology within a ballscrew-nut assembly effectively eliminates excessive noise, friction, heat and wear that commonly plagues conventional ball-race configurations.

By preventing contact between balls and incorporating improved lubrication, performance and operating lives can be significantly improved.

Small, compact and lightweight linear systems used for the positioning of CD/DVD mechanisms, automotive seating controls, systems for step-and-scan medical cell analysis or the production of semiconductors increasingly require component parts that are compact, easy to assemble and cost efficient.

In response to this emerging market, the latest generation of linear motion technologies are being integrated with other components enabling OEMs, machine builders and end users to purchase a single operating unit featuring a guide, controller, motor and interface.

Although this facility has been available for larger components, it has only recently been incorporated into smaller and more compact systems.

Innovative miniature linear motion modules that combine linear motors, linear guides, encoders and cabling with a standard drive can reduce specification and build times, while improving levels of reliability and performance.

More importantly, these systems can effortlessly transport significant loads, achieve high levels of accuracy and eliminate the problems associated with sourcing individual components from disparate suppliers.

For example, through a unique collaboration between THK, Parker, Renishaw and HMK, a number of combination systems have been launched that are supplied preprogrammed and ready to install.

For example, the RDM micro with a stroke range from 9 to 409mm and measuring only 49mm high by 60mm wide is ideal for applications where space is restricted, or where miniaturised equipment is required, such as in pick-and-place systems for electronics and telecommunications components, medical devices, test and measuring instruments and compact process lines.

As you would expect, the complex nature of linear guides and the critical role they perform requires accurate specification to achieve the best possible performance, not only from the components themselves, but also from the overall system.

Therefore, components of this nature should be carefully selected to meet the requirements of the intended process and the demands of the operating environment.

This is especially true when the component in question is only millimetres in width or height.

An important aspect that should be considered during the specification of a miniature linear motion system is the conditions under which the component will operate.

Extreme temperatures, humidity and airborne contamination generally have only a limited effect on standard equipment, but as component size decreases, so the impact of environmental conditions becomes increasingly important.

In particular, temperature changes can have dramatic impact on miniaturised guideways.

Even the smallest of thermal fluctuations can encourage expansion or contractions in the guide rail, resulting in a deterioration of production quality and reliability.

Therefore as the physical size of the linear guide decreases, so the environmental limitations on the system multiply.

Similarly, the materials used in the construction of the linear motion systems must also be considered: clean-room operations, for instance, can be hampered by emissions from grease or particles produced through wear and tear.

To address this issue, it may be necessary to create a pressure differential within the linear motion system, or consider vacuum operation in order to remove contaminants.

The buoyancy of sectors producing consumer electronics, automotive electronics and biotechnology equipment would suggest that demand for miniaturisation across a wider range of products is set to increase.

As a result, smaller linear guides will undoubtedly become increasingly critical in a growing number of products, testing procedures and manufacturing processes.

The initial signs of this demand are already being addressed by miniaturised packaged systems that are growing in popularity because they offer single-source solutions that can reduce design and assembly times, while reducing the need to deal with multiple suppliers.

Partnerships between different manufacturers indicate the significance attached to these latest combination solutions.

The momentum of miniaturisation in linear motion is increasing strongly and seems set to continue for the foreseeable future.

Specific products are being launched that meet existing requirements for small, compact and lightweight linear products.

However, as consumer expectations grow, even smaller systems will undoubtedly come to the fore.

The only limiting factors that will determine the rollout of these miniature guides will be the rate at which production technology can be evolved and the cost of bringing that new technology to market.

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