Product category:
Electric Linear Actuators
News Release from: Micromech | Subject: Alio stages
Edited by the Engineeringtalk Editorial
Team on 01 November 2007
Stages meet UHV requirements
Alio stages primarily use linear ceramic servomotors for demanding UHV applications with nonoutgassing and linear servomotors for less demanding HV applications.
Micromech's Alio stages are UHV-compatible (with exception of the air bearing systems) This means the linear, rotary, open centre X-Y, hexapods, tripods, goniometer stages and systems are manufactured in HV or UHV with ultra-low outgassing material
This article was originally published on Engineeringtalk on 26 Feb 2001 at 8.00am (UK)
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Nano-positioning equipment has to meet the toughest specifications, and the applications are further complicated when the management of motion is in a vacuum or when extended travel, finer repeatability, higher speed, greater uptime and lower cost are required.
Alio stages primarily use linear ceramic servomotors for demanding UHV applications with nonoutgassing and linear servomotors for less demanding HV applications.
Ceramic servomotors are unique in their motion, which acts as a spiralling friction motor, allowing unlimited travel without mechanical hysteresis while maintaining nanometre precision.
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Piezoelectric motor-driven stages offer shorter settling times, a constant velocity range, no drive inertia, no servo dither and no hysteresis.
They are also suitable for ultra-high-vacuum environments, due to the material's minimal heat generation and operating temperature range.
There are three main approaches that have been tried and proven to perform at single nanometre resolutions in UHV.
Optical encoders based on reading a physical scale can operate down to the nanometre level.
Although the scale has a 20 micron pitch, the signal has a sufficient signal to noise ratio to allow it to be interpolated down to 2.5nm to 5nm resolutions, depending on interpolator.
These encoders work well for most applications where low cost, accuracy and repeatability are needed.
The next level of performance to an optical encoder with tape or glass scale uses a similar read head with a novel scale.
Although using the same 20um pitch, it is etched directly into the stainless steel of a ring, for rotary applications or onto a nickel-plated invar spar for linear applications.
Beyond optical scale encoders, a laser interferometer can be used to provide resolutions to 38pm, which provides positioning stability on a suitable mechanical system to the sub-nanometer levels.
Using a plane mirror optical scheme in two axes also allows the Abbe error to be eliminated.
The added advantage of the interferometer is that only the plane mirror resides in the vacuum chamber.
Depending upon the required measurement, a single mirror can be placed in the chamber to measure from the stage to the chamber wall.
Alternatively, a differential measuring scheme can be employed to measure the distance between two plane mirrors within the vacuum chamber.
This eliminates all common mode noise sources between the stage and instrument.
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