This page contains a Flash digital edition of a book.
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


D


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


“The


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.


Left:


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


Bosch Rexroth www.boschrexroth.com Enter 219


/ DESIGNSOLUTIONS DESIGN SOLUTIONS | SEPTEMBER 2014 27


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52