A remarkable device for the accelerated testing of highways or airport runways and developed in South Africa, features modular AC drives from Control Techniques.

The Accelerated Pavement Testing device (APT) – the MLS10 - produced by MLS Test Systems Pty Ltd of Stellenbosch, features contactless linear induction motors eliminating drive train fatigue and wear.  The MS10 can apply more than 100 000 wheel loads per day, each equivalent to a 12-ton axle load, onto a 3.6 metres long stretch of road.  The typical speed of the wheels is 6 m/s (22 kph).

The machine structure is a space frame 10 metres long, inside which four wheel bogies, each fitted with dual 295/65 R22.5 truck tyres, run in a vertical loop.  The wheel bogies, linked together in an endless chain, are guided by two concentric sets of steel guide rails.  Dual, counter-rotating, 250-mm diameter steel guide wheels on the bogies run between two sets of guide rails.  Whilst a bogie runs along the bottom section of the rails, the tyres are pushed down onto the pavement by a hydraulic and compressed nitrogen gas system.   In addition, whilst running, the entire machine can be translated sideways, about 500mm to each side, on computer-controlled hydraulic powered slides to simulate the lateral distribution of the wheel paths of different trucks on a highway.

The machine has an on board a 132kW diesel generator and is fitted with transport wheels on which it can be driven and steered at low speed under its own power.

The machine utilises Linear Induction Motors (LIM’s) from Force Engineering in the UK to drive the bogies inside the machine and these are controlled by specially configured modular Unidrive SPM AC drives.  LIM’s, with their no-contact characteristics and their high thrust and acceleration were the perfect choice for this application, but they do require control by specially configured inverter drives. Control Techniques has worked closely with Force Engineering for many years to produce the optimum control characteristics for LIMs.