Actuators, drives and controls for laboratory equipment

The Sorby Environmental Fluid Dynamics Laboratory (SEFDL), based at the University of Leeds, was established in 1988 to study and understand the sedimentary flow processes of the earth-surface both naturally and through industrial or man-made interaction. A recently completed 1.2million expansion programme has enabled the facility to become one of the best equipped and leading environmental fluid dynamics laboratories in the world.

Research undertaken at SEFDL includes laboratory modelling, field study and computational fluid dynamics (CFD) across a vast range of environmental studies, such as river and coastal erosion, pollution analysis, dredging studies, pipe flow, and oil and gas exploration. One of the largest projects involves the study of large moving submarine channels, thousands of kilometres in length and hundreds of metres high, that transport huge volumes of course sediments along the ocean floors and are increasingly important for hydrocarbon exploration and production.

The SEFDL facility has a wide range of flume tanks and measuring equipment to model these sedimentary processes. The most powerful is capable of moving 250 litres of water every second, enabling flows half a metre deep to move at a metre per second along the flume. Detailed two and three-dimensional flow velocity measurement systems and powerful computing systems analyse the results. Some flume tanks are equipped to model several layers of quite different sedimentary material, thereby improving overall accuracy and drastically reducing measurement timescales.

Automated X-Y actuators

MiniTec, the machine building and motion system specialist, has worked closely with SEFDL in supplying a number of automated belt-driven X-Y actuators complete with micro-stepping drives and motion controls for the flume tanks. These are used to position flow velocity measurement probes and to synchronise readings to and from data logging equipment.

The scope of supply included the development of Visual Basic front-end software to allow users to input scanning speeds and measurement intervals, trigger data collection and provide an output of all the information to a data logging system. The program integrated all communications routines between the intelligent micro-stepping drives, a PC host, measurement probes and data logging equipment. Motion control covered simple selection of pre-calculated scanning routines and other positioning modes, along with manual axis jogging, integrated diagnostics and status windows.

To simplify and standardise the SEFDL processes and improve data consistency, a key specification requirement called for the program to be used with all of the department's flume systems and to ensure that each shared identical user units and operational parameters. As the flume positioners had been supplied over a number of years, many had differing mechanics, with correspondingly different positioning resolutions. To ensure identical input and output values, MiniTec included scaling functions that required only the variable resolution information to be entered at the initial set-up.

For each flume positioning system, a MiniTec LR series X-Y actuator is typically mounted above a working section of the flume tank and provides a positioning window of up to 5m along the length of the flume and 0.5m across its width. The depth of the probe is adjusted manually.

Aluminium profiles

The LR series actuator and carriage assembly is based on standard MiniTec aluminium machine framing profiles with the addition of double-row angular contact bearings on hardened and ground precision shafts. With the possibility of creating extremely long travel lengths, the units are capable of carrying heavy loads with high accelerations. The positioners may be combined with other machine framing components to provide extremely robust and durable framing structures.

A typical MiniTec actuator used at SEFDL has a fundamental resolution of 190mm linear travel to 1 revolution of the input shaft, which is driven by a 50,000 steps/rev micro-stepping motor and a 4:1 gearbox; the final theoretical resolution is therefore in the order of just one micron. Each motor is also fitted with a rotary encoder and scaled within the motion control system to effectively record real-time position and speed in increments of 0.1mm for the data logging system. Also included are over-travel limits, datum switches and all interfacing cables within a chain-type cable management system.

MiniTec provided the complete on-site installation for each flume tank in accordance with the EN 954-1 safety standard, and wall-mounted control enclosures complete with stepper drives, power supply, relays and EMC filtering equipment. The specification also included a separate mains isolation and supply system with an emergency stop.