Test actuator development

Libertine’s Linear Power Systems are being developed for a range of high performance dynamic test actuators whose applications range from road load simulators to materials testing.

Dynamic test actuators are used to determine material and component durability, and to characterise the performance of systems in response to input vibrations. In the case of automotive testing this can include the road load inputs to wheels and axles. Unlike servo-hydraulic actuator systems, linear electrical machines are oil-free and offer simple installation, which makes them ideal not only for R&D applications but also for in-line quality testing of medical devices, elastomers and composite materials. But perhaps the biggest advantage offered is the dynamic performance made possible by the reduced moving mass and simplified control of direct acting linear electrical machines.

Libertine has partnered with a leading automotive test systems business to develop a family of actuators operating at frequencies up to 300Hz, well above the performance limit of today’s servo-hydraulic systems. In automotive applications this higher level of performance will permit accurate reproduction of road load vibration inputs so that OEMs can evaluate noise and vibration performance of suspension and structural components. The design of these sub-systems can then be optimised earlier in the development cycle, well before these are integrated into complete vehicles.

Libertine is developing a new linear electrical machine for this application, designed to offer high force per unit of moving mass for high-frequency performance. This machine is integrated with gas bearings and a variable pneumatic pre-load for reliable, low-friction, oil-free operation. Variants of this new machine can be configured for loads of up to 25 kN, and strokes of up to 200 mm.


ApplicationSuspension test systems
Move diameter75 mm
Maximum Stroke40 mm
AccelerationUp to 50g with 2kg test subject
Operating frequencyUp to 300 Hz
Specific force0.6 kN/kg

“Direct acting linear electrical machines are ideally suited to high-frequency test actuator applications. Testing of Libertine’s linear actuator prototype by our lead customer has exceeded initial performance expectations, and has already generated interest from automotive OEMs looking to apply this technology in their new product development programmes.”

CEO, Libertine FPE Limited