Linear guides with integral encoders chosen for positioner

LG Motion recently designed and supplied a large custom built X-Z detector positioning system for the I24 Microfocus Macromolecular Crystallography (MX) beamline at Diamond Light Source, the UK's national synchrotron science facility.

The design specification called for the ability to load the positioning rig with multiple detectors weighing up to 280kg with a volume of around 1m3 over a 1.55m horizontal and 0.85m vertical travel range to allow increased flexibility and research throughput on the I24 beamline. At acceptance testing, the system was actually loaded with 420kg - which is 1.5 times the rated load - and positioning repeatability for both axes was measured to better than 10 microns, which is well within the desired specification for the I24 detector.

Now it has been commissioned the upgraded I24 beamline is used by chemists and structural biologists for cutting-edge molecular-level studies in genomics, immune systems and membrane proteins, and groundbreaking research in drug design to combat major diseases and viruses.

Minuscule protein crystal samples are illuminated with the I24's intense 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 structures and their functions.

Positioning system construction

LG Motion's custom-built detector positioning system is based around Schneeberger Monorail AMS series linear motion guide bearings with magnetised track linear encoders built into the rails. This compact and durable bearing support and fully protected incremental position measurement system is used extensively on large-scale precision machine applications, providing the advantages of close-to-load measurement and simplified installation, as well as cost benefits over separately supplied bearings and encoders.

Two AMS bearing rails are fixed to a large 3000 x 1000mm horizontal base plate that is bolted to the experiment hutch floor with provision for alignment, levelling and grouting on installation. 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 280kg detector load is evenly distributed on the horizontal stage carriage plate using a welded steel framework with four vertical linear bearing rails that allow the vertical translation of the detector mounting platform - which is fabricated from MiniTec ProfileSystem machine framing components. With one pair of bearing rails utilising three bearing carriages and the opposing pair having just one carriage, this design is much preferred to a more conventional dual bearing arrangement with an inherent overhung load; the advantage is that smaller linear bearings and simplified power transmission mechanics can be used.

Each axis is driven by a servo motor with precision ball screws, bearing block type supports and a flexible coupling. 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 overtravel limit switches.

On budget and on time

During the design approval, manufacture and commissioning, LG Motion worked closely with scientists and support staff at Diamond to ensure that the detector positioning system was installed on budget and on time, and that it fully met relevant machinery directives, safety standards and performance specifications.

As a key distributor for leading motion control equipment manufacturers including Schneeberger, Agile Systems and SMAC, plus a full design service and in-house manufacturing capability along with its own range of linear and rotary stages, LG Motion provides a complete service for all types of customised positioning systems.

Follow the link for more information about LG Motion's design and build capabilities.