On the move

Cutting-edge technology is being used to refine simple components such as bearings to help manufacturers move and position essential equipment. Colin Carter reports

The art of shifting stuff about has posed a perennial challenge for manufacturing. From the precision placing of electrical components to the moving of large items such as whole ships, the methodologies have revolved around guiding systems such as rails, and some means of moving the product along the system, such as belts and ball bearings.

Many everyday items have to be moved about at some point. Even the signs at McDonald’s rely on bearings to change menus.

Every morning, in McDonald’s restaurants around the world, the menu changes from a breakfast to a daytime meal. The power-driven menu boards use Micromech Spyraflo bearings to guide the boards to show whatever is being sold: the bearings need to cope with chassis manufacturing tolerances and misalignment caused during shipping and installation of the finished menu board assemblies to place the signs.

Even reading The Engineer, whether the online or print version, would be impossible without motion technology. For example, the online version relies on computers, which are generally made on production lines relying on a flow of components and products delivered automatically. The print version has to have a system for moving paper and ink heads to the right part of the press so the four colours are printed in the same place.

Printing environments are often dusty, dirty places and, as a result, the lubricants in moving parts such as bearings are prone to seizing up and contamination. One solution used in Codeology’s printer applicators are Igus’s iglidur polymer bearings in place of conventional, plain roller bearings.

Unlike conventional bearings, these are polymer, removing the need for lubrication and the need to be mounted in housings: their injection-moulded manufacture means they are self-lubricating and can fit straight on to a shaft.

Cleanliness can also be a problem for lubricated bearings. Germany-based Belimed Technik specialises in cleaning, disinfecting and sterilising equipment and services for the pharmaceutical industry, healthcare establishments and laboratories. It used SKF purpose-designed polymer ball bearings for its new PH 8xx.2 type range of cleaning machines, as they offer low friction and the ability to operate under high temperatures.

These machines use slide-out racks to hold the equipment to be cleaned, which originally rested on plain, non-lubricated bearing sheaves that rolled on rails. These were difficult to move in and out when fully loaded. Lubrication was not an option as it would have contaminated the items being cleaned.

The SKF solution involved designing a cageless polymer track-runner ball bearing, with two asymmetric sets of stainless steel balls. The rings are made of polyetheretherketone, which has a low coefficient of friction, and is slippery enough so the bearings do not need lubrication.

Moving items around does not always require manual effort, as in some other examples. For example, 18 Reliance Cool Muscle motors have been used on a Labman Automation automated bottle inspection system. Bottles travel to one of nine test stations and are photographed and weighed to check their condition and the filled volume as part of the inspection process.

Bottles are then barcode scanned and a ‘Cool Muscle’ (a small servo system, encompassing an integrated vector drive, amplifier, controller, H-infinity tuner, 50,000 count magnetic encoder and a 0-3000rev/min high-torque motor) lowers a mechanism to check the cap and to tighten it, if necessary. This intelligent motion control solution can measure and change the applied torque ‘on the fly’, which allows it to check and adjust bottle cap tightness.

These advances in the technology are not confined to motors. Even the humble bearing has been subject to some interesting twists in an attempt to reduce bearing friction to zero, which not only makes maintenance easy as there is limited wear, but also enables more precise positioning.

Netherlands-based IBS Precision Engineering recently announced the launch of its new range of porous air bearings that it claims combines virtually frictionless motion with high load-carrying capabilities and positional accuracy.

The air is supplied through porous media (which provides uniform air distribution) under the bearing to ‘float’ it, and the company claims this virtually eliminates static friction and enables accurate positional accuracy to be achieved with high repeatability.

The bearings also eliminate the need for oil lubrication and generate positive air pressure to produce a self-cleaning action in use. This makes them ideal for use in high-precision applications in industries such as optical lens or mirror polishing, lithography, precision gauging, metrology, silicon wafer manufacture and high-speed machinery.

Semiconductor manufacture (in addition to scanning microscopy and other demanding scan and positional applications) is also a target of Aerotech’s rotary air bearing positioning stages, which use near-frictionless air-bearings driven by linear motors to ensure smooth scanning performance and in-position stability.

The bearings allow a claimed calibrated positional accuracy of +/-1um, a resolution range between 1nm and 200nm and friction-free mechanics with zero-backlash and no wind-up, unlike conventional bearings. The lack of friction means that a long life is expected.

An alternative to carrying bearings on a bed of air is the development of magnetic bearing systems, which have specialist applications in areas where bearings are required to work in a vacuum.

One of the few producers of these bearings, the Barden Corporation (part of the Schaeffler Group), makes what it calls active magnetic bearings, which provide a method of suspending shafts (both axially and radially) in applications, such as turbomolecular vacuum pumps (used in semiconductor manufacturing), dry pump bearings, compressors, blowers, air conditioning systems, gas expanders (used as venting devices in gas pipelines) and in energy storage systems as emergency back up power.

The bearings use actively controlled electromagnetic forces to control the motion of a rotor or other ferromagnetic body in air.

The advantages of this non-contact style are similar to those of air bearings — reliability, low maintenance and the lack of the need for lubrication.

So when it comes to moving and positioning anything from components to larger items, the technological advances in what are essentially simple components such as bearings with air, and magnetic bearings are at the cutting edge.