Back to Roger's Design Portfolio
Back to Roger's Main Web Page

The Axtrusion Linear Motion System

Roger Cortesi (rcortesi@alum.mit.edu)

Abstract:

The Axtrusion is a new linear motion element developed by Professor Alexander Slocum and Roger Cortesi of the Massachusetts Institute of Technology’s Mechanical Engineering Department Precision Engineering Research Group. It is an easy to manufacture non-contact linear motion system. The prototype uses porous graphite air bearings and an open face permanent magnet linear motor to support and propel the carriage. Since there is no contact between the carriage and the way, the Axtrusion is ideal for high speed applications where reliability is at a premium. Initial testing of the prototype carriage indicates that it has the following performance specifications: a vertical load capacity of 2000 N (450 lbs); horizontal load capacity of 4000 N (900 lbs); a carriage pitch error of 12 micro-radians (2.5 arc seconds); a yaw error of 7.7 micro-radians (1.6 arc seconds); a vertical straightness at the center of the carriage of 0.3 microns (0.000012 inches); and a vertical stiffness of the carriage of 422 Newtons per micron (2,400,000 lbs/in).

The Complete Thesis (pdf 3.7 Mb)

Patents

    US Patent 6,150,740, held by Slocum, covers the Axtrusion concept and its implementation.
  • US Patent 4,817,930, held by Van Deuren, is an earlier method of using magnets to preload an aero statically supported linear motion stage.
  • US Patent 5,488,771, held by Devitt and Slocum, describes the technique we used to accurately replicate the bearings into the carriage.

Articles:

Video Clips of the Axtrusion in Action (.mpg files)!!!

Sponsors:

Download the Thesis (PDF files)

straightnessetup2.jpg (77938 bytes)

The prototype Axtrusion undergoing pitch testing at Dover Instruments.

rogergluing.jpg (69944 bytes)

Roger replicating the airbearings in to the prototype carriage.
Prototype Axtrusion Performance Data Summary
Parameter Metric Value English Value
Vertical Load Capacity 2000 N 450 lbs.
Horizontal Load Capacity 4000 N 900 lbs.
Pitch Accuracy ±5.9 micro-radians ± 1.22 arc seconds
Pitch Repeatability <2.4 micro-radians <0.50 arc seconds
Yaw Accuracy ±3.8 micro-radians ±0.79 arc seconds
Yaw Repeatability <2.7 micro-radians <0.56 arc seconds
Linear Position Accuracy ±0.67 microns 0.000026 inches
Linear Position Repeatability <0.33 microns 0.000013 inches
Vertical Displacement Error (@ center) 0.3 microns 0.000012 inches
Approximate Vertical Stiffness 422 N / micron 2,400,000 lbs. / inch
For plots of the data and more details see the Detailed Presentation of Data