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BEARINGS & LINEAR MOTION FEATURE Levitation: The key to clean production?

A major issue in the manufacture of semi-conductors and microchips used in PCBs is particle contamination, which can not only increase production costs but reduce the operational life of the end product. Paul Streatfield, an expert in linear motion systems at Bosch Rexroth, examines a potential solution which combines linear drives and magnetic levitation


uring the manufacturer of the semi-conductors and microchips

used in PCBs, an ultra-clean production environment is essential, such as an inline vacuum deposition process. Consumer products – ranging from televisions to portable systems, such as mobile phones, handheld game consoles and personal digital assistants – all contain sensitive electronics which are manufactured in this way. Even in vacuum, however, the production process can lend itself to the creation of tiny particles of dirt which can reduce production quality and the operational life of the end product. Particles are generated by the metal

to metal, or metal to grease, contact inherent in conventional methods of inline transport. Although electronics manufacturers are currently using a variety of methods – from chain drives to conveyor belts with linear motors – these can be complex, expensive and, crucially, particle generating. Typically, the layout includes a vacuum-sealed process chamber with the carrier inside a vacuum. But, as the bearings are also inside the vacuum, this results in metal to metal contact and the potential for particle ingress. Furthermore, this type of production is neither scalable nor flexible. Increases in demand cannot be quickly accommodated and the line will need extensive service and maintenance. There is therefore a need to avoid

any touching of components during the manufacturing process.

A POTENTIAL SOLUTION One potential solution that is currently being extensively tested is magnetic levitation. An example is the Bosch Rexroth LeviMotion concept, which combines inverted linear motion

technology with a completely contactless transportation system. With a standard linear motor system, there is one moving coil with the motion controlled by the switching of the current which activates the magnet. The carrier is then driven down the production line. The alternative is the use of an inverted

linear motor with magnets underneath the drive carrier, with the coil units mounted outside the process chamber. This type of system enables large air gaps between magnets and carrier which levitates above the permanent magnet tracks. In addition, a position sensor,

consisting of two hall sensor elements, controls the exact location of the carrier. Magnets moving over the sensor create a sinusoidal wave with the sensors spaced to ensure the phase difference is 90˚. Interpolation of the signals gives the exact carrier position. The carrier is also equipped with an automatic alignment procedure and advanced carrier control which offers full degrees of movement on five axes, including pitch, roll and yaw. This type of system has two advantages. Firstly, a series of coils can be constructed and up to 32 carriers can be used, rather than just the single carrier with the standard linear motor. Secondly, with the coils mounted underneath the carrier, any ingress particles fall away, improving product quality. There is therefore much less potential for particle ingress. With this method there is no friction

or wear and the movement of the carrier is contactless and clean, with no particle generation and no lubrication. What’s more, this method of transport is frictionless with no bearing related disturbances like sticking or slipping or fluctuating stiffness. In addition, only passive or sealed

components are located in the process chamber, leading to lower maintenance costs and a lower cost of ownership. Crucially, lines combining linear

motion and magnetic levitation can offer high speed, high positioning accuracy with constant speeds and low ripple. Testing has shown excellent planarity over long transportation distances with automatic alignment procedure in the bearings’ air gap.

The levitation system offers a wide range of benefits to manufacturers


Bosch LeviMotion concept combines

inverted linear motion technology with a

completely contactless transportation system”

PRODUCTION LEVELS In terms of production throughput, the carriers can achieve speeds of up to 5cm/s and can carry loads from 1kg to 1000kg. Most importantly, the carriers are capable of repeat positioning of 10-20µm along with exceptionally high positioning accuracy and minimal velocity ripple. While the combination of Bosch

Rexroth’s NYCe4000 LMS drive system and Mecatronix’s magnetic levitation is only currently being tested, it has already gained significant interest from electronics manufacturers.


A traditional system with the carrier inside the vacuum-sealed process chamber

Bosch Rexroth Enter 219


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