ALIO Industries' headquarters in Colorado
ALIO Industries have endorsed the publication of the ASME B5.64 standard “Methods for the Performance Evaluation of Single Axis Linear Positioning Systems.” The piece symbolises a significant step towards the redefinition of precision measurements in motion systems. A subject matter that ALIO have claimed to have been championing over the last decade.
Key information:
- The ASME B5.64 standard "Methods for the Performance Evaluation of Single Axis Linear Positioning Systems" has been published.
- ALIO Industries applauds the publication, which covers a subject matter the company has been championing over the last decade.
- The piece makes a significant step towards the redefinition of precision measurements in motion systems.
The publication suggests moving away from conventional planar methodologies and instead opting for 6D point precision specifications when defining the precision of ultra-precise single-axis linear motion systems. This specifically relates to ALIO as the company produces these systems.
“When analysing motion control solutions that provide sub-micron and nanometer-level accuracy, ALIO has contended for a number of years that a new language is necessary, and new standards are required to indicate the real levels of precision that different motion control solutions can achieve,” said Bill Hennessey, President of ALIO Industries. “So, saying, nearly 12 years ago, ALIO trademarked the phrases Point Precision and 6D Point Precision to protect its position in the market.”
All motion systems operate in 3-dimensional space and have errors in 6 degrees of freedom (6-DOF). But motion systems tend to be characterised by performance data of a single (or subset) of these 6-DOF. However, this process could lead to errors being unaccounted for in the performance data and specifications. To combat this issue, ALIO points out that repeatability performance for metrology inspection and manufacturing systems must be analysed, as it will provide an accurate representation of nanometre-precision performance. The ASME publication agrees with ALIO’s finding.
Typically, specifying repeatability as a single number representing the variation in linear displacement along an axis of travel was valid as repeatability specification was large enough that other errors would only come to a small percentage of the error total and could be disregarded (e.g., plane repeatability).
In plane repeatability, this method would assume that the plane only moves in one dimension and the axis is perfectly straight, but at the nanometre level, this assumption is not realistic. At that level, the axis of travel should be shown as bending and twisting through three-dimensional space. This results in plane visualisation becoming meaningless, as it will tip, tilt, and twist, as it travels along an axis. The stage moves in 6D space, which could misrepresent actual stage repeatability as additional error sources are neglected.
The ASME publication recognises that in nanometre-level precision systems, ‘other’ errors previously disregarded by less accurate systems can become equal or greater contributors to the 6D repeatability performance.
Each linear (or angular) direction the stage moves (or rotates) in results in a positional error in that direction. During nanometre-precision, this motion cannot be ignored as it will have an associated repeatability of that error motion. Additionally, every point on a stage mounting surface will move in a 3D space as a result of this motion error in 6-DOF. Point repeatability of an infinite number of points attached to a stage must be characterised by testing and specification data. Each point of repeatability will result in a spherical repeatability range.
“ALIO applauds the new ASME standard officially published and made available a few days ago. In our view, this is a very important step towards True Nano Positioning, allowing customers the ability to choose the best motion system for their applications based on a common standard rather than believing misleading, single-dimensional specifications that vary from supplier to supplier. Because ALIO has already been applying these newly published measurement procedures for over a decade, our customers find themselves in the lucky position of not having to worry about the true performance of their products,” said Hennessey.
He concludes, “ALIO will continue to be at the forefront of innovation and progress in the precision positioning industry. The new standard methods for the performance evaluation of single-axis positioning systems can only be the beginning though. Today’s motion systems are more complex, usually consisting of not just one linear axis, but combining multiple axes to 2, 3, 4 or 6 or more degrees of freedom. ALIO is ready to drive these next steps with the ASME and all other contributors to the ASME B5.64 to further improve the transparency and creditability of the precision motion world.”