For those more demanding applications, the ALIO stages now available from Micromech 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 (e-7 Torr) or UHV (e-10 Torr) with ultra low outgassing material and where all components are carefully prepared and baked.
Nano-positioning equipment has to meet the toughest specification that are often further complicated when the management of motion is in a vacuum or when requiring extended travel, finer repeatability, higher speed, greater uptime and of course at the right price. The challenges of engineering and selecting components that must work together in perfect harmony to achieve such precision are not to be under estimated. The drive mechanism, bearings, feedback system, motion controller, kinematic structure and the environmental conditions must be considered for the perfect design to meet this accuracy in atmospheric or vacuum environments. These vacuum challenges can vary from 10e-3 Torr to 10e-10 Torr from positioning performance to outgassing challenges.
The various ALIO stages primarily use the Linear Ceramic Servo Motors for demanding UHV applications with non outgassing and Linear Servo Motors for less demanding HV applications. Ceramic Servo Motors are unique in their motion, which acts as a spiralling friction motor allowing for unlimited travel without mechanical hysteresis while maintaining nanometre precision. Other beneficial performance features from using piezoelectric motor driven stages include shorter settling times, constant velocity range (from less than 1 micron per second to 250mm/s with less than 0.5 % variation), no drive inertia, no servo dither and no hysteresis. They are also ideal for ultra high vacuum environments (10e-10 Torr) due to the materials minimal heat generation and operating temperature range.
The position feedback systems used in a vacuum chambers have special designs to insure performance and no outgassing. 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 resolve 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 the single digit nano-metre. (2.5nm to 5nm resolutions depending on interpolator) These encoders work well for most applications where low cost accuracy and repeatability is needed. The next level of performance to an optical encoder with tape or glass scale utilises 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 on a nickel-plated invar spar for linear applications.
Beyond optical scale encoders, a laser interferometer can be used to provide resolutions to 38 picometers 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 would reside 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.
The nanometre management of motion has become more pervasive throughout industry as leading edge technology pursues a common trend of working on smaller and smaller scales. This trend is prevalent in numerous positioning sensitive industries, such as fibre optics, bio-medical, micro-machines, electronics, semiconductor, energy, optics, aerospace, and synchrotrons as well as in other research and development establishments. The demand has resulted in the ALIO stages becoming a world leader in nano-precision vacuum equipment.