Wednesday 31 March 2010

Nanopositioning mechanics and motion controls

Laser technology solutions specialist Altechna Co. (LT) is basing its Alt-SCA femtosecond laser micromachining system around Aerotech's ANT130 series linear motor driven nanopositioning stages in a customised 3-axis XYZ configuration that includes a granite bridge support structure and a unique pneumatically counterbalanced vertical axis. The synchronisation between the one nanometre resolution positioning system and the laser's firing pattern is precisely and crucially controlled with the advanced PSO (Position Synchronised Output) command from their software based A3200 motion controller which is built into Altechna's SCA (System Control Application) front end software using .NET class libraries. (What is a femtosecond? - Wikipedia!)

Altechna has developed its SCA software with C++ and C# to provide a flexible yet powerful control platform for laser micromachining that is capable of 3-levels of simple-to-complex micro-fabrication where, at the basic level, a WYSIWYG equipped GUI is able to convert complex positioning information from BMP or PLT files without the need for G-code programming. Moreover, SCA can be used to program multiplex trajectories using mathematical functions (Fig. 1). At the highest level, programmers may write micro-fabrication code directly in C++ and C#. Altechna's software has been applied to ultrafast-laser materials processing research at the University of Southamptons' Optical Research Centre (Fig 2.).

The AltSCA femtosecond laser machining system integrates the complete Aerotech motion sub-system including rack mounted linear servo-amplifiers with a 10W Yb:KGW (1030 nm) femtosecond laser source, machine vision, beam shaping optics and a galvo scanning head with resulting fabrication speeds up to 350000 pixels per second with 25400 DPI resolution (Fig. 3). Combining such high processing speed and large area positioning capability with nanoscale resolution and sub- micron accuracy, the AltSCA is aimed at both research and industrial users alike for development and/or high throughput manufacture of surface or 3D micro-nano structures for anything from MEMS sensors and optical micro-elements fabrication to microchip repairs and waveguide production.

Altechna is based in Vilnius, (LT) and works closely with the Laser Nanophotonics Group at Vilnius University where the Aerotech equipment is being used for research involving the fabrication of fully functioning microlenses in the order of 100 μm. These three dimensional structures are paving the way for integrated 3D optical micro-circuits.

They are also working on fully integrating Galvo-scanners with the ANT130 positioning system by using Aerotech's Nmark SSaM (Synchronized Scanner and Motion module). This will allow wide-format bitmaps to be processed continuously by enabling laser micromachining of structures and patterns that exceed the normal field of view for the Galvo scanner.

The AltSCA femtosecond laser machining system uses an integrated ANT130 XY series low profile X-Y stage that supports the object workpiece and a separate vertically mounted Z-axis stage for laser head manipulation. The Z-axis is fixed to the granite bridge structure and its pneumatic counterbalance is based upon a tried and tested design that Aerotech has developed over previous generations of micro-positioning stages. The large granite base provides high stability for the positioning system and the complete assembly includes all cabling and provision for air supply.

The ANT130 series has a nominal width of 130 mm and is available in travel ranges from 35 mm to 160 mm, in a choice of two accuracy grades up to +/-250 nanometres to suit high or ultra-high precision requirements. The performance characteristics (pitch, yaw and roll etc) ensure that the combined flatness, straightness, perpenicularity, abbe error, and all other critical geometric specifications do not compromise the nanometre level machining requirements for this application. The compact design includes anti-creep cross roller bearings and a centre driven brushless/non-cogging linear servomotor with 1 nanometre resolution encoders. Maximum speeds are up to 350 mm per second with acceleration to 1g. The non-contact linear servomotor and encoder system helps to ensure a very long working life with minimal maintenance..

The three-axis ANT130 is a part of Aerotech's nano Motion Technology (nMT) positioning range that brings together linear, rotary and goniometric stages to provide exceptional precision, rapid acceleration, high speed and ultra-fine resolution for nanometre resolution positioning. With zero-backlash and hysteresis in combination with high speed encoder feedback processing and real-time axis calibration, the nMT range is providing the enabling technology for many demanding applications where large area/high throughput positioning involves nanometre level structuring – a perfect solution for ultrafast-laser micromachining.

Aerotech’s PC-based A3200 Automation Platform is a software-only multi axis motion controller for up to 32 axes based on the IEEE-1394 Firewire® protocol network delivering fully deterministic, distributed and tightly synchronised motion and I/O control in combination with Aerotech’s Ndrive digital servo amplifiers. Further software expansion modules are available for additional machine control functions such as HMI, Vision and PLC. The flexibility and powerful advanced features of the A3200 include sophisticated commands such as the PSO along with diagnostics, commissioning and programming options that include AeroBASICTM, Visual Basic® C, C++, with higher levels including Windows® based ActiveX components with C++, VB and .NET class libraries.

For such high precision and high resolution applications Aerotech recommends its DSP based linear stage servo amplifiers rather than PWM drive stage alternatives to guarantee extremely low noise and jitter free stability. Its smooth current control also ensures ultra-smooth motion which is essential for sub nanometre applications.

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