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Motion control proves an exacting science

Motion control proves an exacting science

When Diamond Light Source required a customised beamline detector positioning system to increase flexibility on one of its primary beamlines, it turned to LG Motion for a solution.

The I24 beamline at Diamond Light Source provides an important research facility, with a system that illuminates miniscule crystal samples with an X-ray beam and the detectors are positioned to a precision of just a few tens of microns to capture scattered light that reveals the complexities of protein structure and their functions. 

In a recent automation project, the objective for the scientists at the national facility was to increase flexibility and research throughput on the I24 beamline. The design specification called for an XZ positioning rig with the ability to load multiple detectors up to 280kg mass with a volume of around 1m3 over a 1.55m horizontal and 0.85m vertical travel range.

The custom-built detector positioning system is based around precision linear rails with integrated linear encoder and precision ground ballscrews that are connected to a servo motor via flexible couplings. The vertical axis includes a safety brake and further in-line planetary gearhead reduction to ensure that it does not back-drive under power off conditions, even if the fail safe brake is disengaged for any reason. Both axes also include datum and over-travel limit switches as a part of the specification.

The 280kg detector load is evenly distributed on the horizontal stage carriage plate using a welded steel framework with four vertical precision linear bearing rails which guide the vertical translation of the detector mounting platform. Each horizontal rail has three bearing carriages that support the upper moving horizontal stage carriage plate which is approximately 1000mm square and 20mm in thickness. The large base plate of the detector system was bolted to the experiment hutch floor after some precision laser alignment, levelling and grouting on installation.

The vertical axis uses one pair of bearing rails utilising three bearing carriages, with the opposing pair just one carriage. This design is much preferred to a more conventional dual bearing arrangement for overhung loads, but this design allowed the use of smaller linear bearings and simplified the power transmission mechanics to be used.

A Schneeberger Monorail AMS series linear motion guide with linear encoders was selected for its compact, integrated design that offered exceptional loading characteristics, smooth motion and precision feedback. The Schneeberger solution was selected as it is used extensively on large scale precision machine applications with advantages of ‘close to load’ measurement and simplified installation, plus cost benefits over separately supplied bearings and encoders.

The beamline detector mounting platform is fabricated from Minitec modular aluminium profiles ideal for design flexibility and fixing mounting brackets onto.

In this case one of the most critical aspects of the challenge was to be able to ensure exact positioning motion control down to microns.  If this could not have been achieved then the institute would not have been able to advance their research into protein structure, proving the point of the pun that motion control is indeed an exacting science.

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