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A vacuum-ready precision positioning system

29 December 2015

LG Motion recently delivered a six-axis, vacuum-compatible precision motion system to AWE Aldermaston that is used to determine the properties of X-ray diffraction crystals prior to installation into X-ray sensitive diagnostics for fielding on laser plasma experiments.

The PC controlled ‘Two Crystal Characterisation Positioning System’ includes three stepper motor driven rotary tables and a 350mm travel stepper driven linear axis that combine to support optical diffraction mounts and sensors, with two 35mm travel, manually adjustable linear stages used to pre-position static optical equipment.

LG Motion’s pre-programmed user interface allows operator and supervisor level access in order to set-up and calibrate the optical system and to load and run coded, pre-defined characterisation routines that run across the PC and the motion controller, producing and storing characterisation data.

The complete system includes a control cabinet housing the motion controller and stepper motor drives, with all positioning mechanics mounted on an aluminium base-plate. AWE integrated the mechanics into the vacuum chamber with connections through their vacuum bulkhead to the cabinet via 5m cables.

The scope of supply included 10-6 bar vacuum preparation with special lubrication and holes (through-holes or bleeder cross holes) to avoid any possibility of cavities forming under vacuum. All the motorised axes use vacuum compatible micro-stepping motors from motor specialist Empire Magnetics Inc., a distribution partner of LG Motion, whose products are regularly used and specified for hostile environment applications. 

The rotary and linear stages were vacuum modified standard tables from LG Motion’s LG series – part of a wide range of standard linear, rotary and elevation stages that are available with stepper or servo motors to form complete multi-axis positioning systems. The specification for the positioning mechanics called for tolerances of better than 0.075mm for the linear stage and better than 0.1 degrees for the rotary tables. Repeatability, meanwhile, was specified to be better than 0.02mm and 0.05 degrees.

The assembly was fully tested and CE marked at LG Motion’s Basingstoke site, then transferred to the customer where site acceptance testing was carried out with AWE and LG Motion engineers in attendance.


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