Indecisive material makes big step forward

Lord Corporation has joined forces with Biedermann Motech to produce a device that improves the mobility of leg amputees by recreating a natural gait.

US company, Lord Corporation, has joined forces with Biedermann Motech, a German manufacturer of spinal implants and prosthetic components, to produce a device that improves the mobility of leg amputees by recreating a natural gait.

The device is based on Rheonetic Systems technology pioneered by Lord which uses Magneto Rheonetic (MR) fluids to adapt and respond instantly to varying levels of vibration, shock or motion.

When exposed to a magnetic field, MR materials change consistency from fluid to a near-solid state. This is because the material consists of tiny magnetisable particles suspended in oil, and in the presence of a magnetic field, these particles align and resist flow. Real time control is made possible by the fact that MR particles respond to a magnetic field within milliseconds. Under normal conditions, a Rheonetic Magnetic Fluid is a free-flowing liquid with the consistency of motor oil.

Lord claims that conventional stepper motor-powered prosthetic devices lack the stability of Motech’s Smart Magnetix battery-operated and electronically controlled MR damper knee mechanisms. Lord’s MR damper is designed to perform in combination with sensors and software calculating the changes in walking speed, uphill and downhill motion, high and low loads, ramps, stairs and terrain adjustments. The system analyses the patients’ gait to adapt knee motion appropriately.

Combined with electronics and software, the MR-enabled responsiveness of the device is said to provide the closest ever match to human neural reaction time.

MR dampers are highly adjustable and instantly responsive to the changing needs of the user. Conventional hydraulic shocks are not real time adjustable, and controllable hydraulic shocks with stepper motors adjusting the valving provide less adjustability, speed and control.

Lord first applied its technology as a seat damper for trucks. Reported in DE (November 1999), this system uses Rheonetic fluid in an electronically controlled damper in place of conventional hydraulics to absorb vibration. Called the Motion Master Ride Management System, it allows driver selectable ride modes (soft, medium, or firm) to provide a smoother, more comfortable ride on suspended seats found in large vehicles. Lord has also developed solutions in primary automotive suspension shocks, and other industrial and automotive vibration and motion control applications.

In a similar move, automotive giant Delphi has developed a prototype semi-active suspension system that provides Continuously Variable real-time Damping (CV-RTD). Using valve-less, monotube struts and shock absorbers, Delphi’s MagneRide system has no moving parts and relies again upon the properties of magnetorheological fluid.

An electro-magnet in the damper piston uses signals from an on-board computer to change the flow properties of the damper fluid up to 1,000 times per second, providing an instantaneous adjustment of the ride characteristics of the vehicle. The result is a much smoother ride over rough roads, instantaneously adjusting to a stiffer suspension for more difficult or unexpected driving situations.

Delphi claims that the technology represents the industry’s most advanced variable damping system, with the system’s quick reflexes helping it to respond hundreds of times during a wheel’s up-and-down motion over a bump.

Expected to be available on production vehicles by 2002, Magnetoride is said to offer considerable improvements in ride quality, vehicle handling and stability, but it will come into its own when it is integrated with other chassis control systems.

Under peak loads, the system uses only about as much power as a 75 watt light bulb. Delphi claims that MagneRide will be cost competitive with existing valve-based real-time damping systems.

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