ERF: a step change in intelligent dampers
01 June 2012
New technology from German manufacturer, Bansbach has resulted in a range of fully automatic dampers that can adjust damping characteristics at any point along the stroke in a matter of milliseconds.
Combining smart PID systems with the latest in electro-rheological fluid (ERF) technology, a fully autonomous active damping system may be realised by simple adjustment of ERF viscosity in response to a control signal. The result is virtually instantaneous control of damping characteristics corresponding to the demands of a system’s real time dynamics.
Available through Bansbach’s UK distributor, Albert Jagger, these intelligent dampers were initially developed for the ‘active suspension’ systems that are much in demand by top marque automotive sector manufacturers. However, it was quickly recognised that this technology had a much broader scope of applications, particularly those in industry involving machine suspensions, precise motion control actuators or self adaptive end-of-stroke damping systems.
Highly energy efficient and with low power consumption of between 2 and 20W, the Bansbach range of ‘easyERF’ dampers can be adjusted using a variety of control inputs, both digital and analogue. Silent in operation (no throttling effects or turbulent flows), the system has the additional benefit of no moving parts (control valves, for example) and is therefore virtually maintenance free. Forces range from 100 to 2,500N, with strokes from 25mm to 125mm, and a positioning accuracy of +/- 0.1mm.
Electro-rheological (ER) fluids belong to the group of Bingham materials and are dispersions of solid polymer particles in oil (mineral or silicone). The viscosity of such fluids can be modified by the application of an electrical charge; the greater the charge, the greater the viscosity - even to the point where the liquid changes to a solid state. Fully reversible, this effect of changing the fluid’s properties is achievable within just a few milliseconds, and the ER fluid remains unaffected by the number of times its viscosity changes. Indeed, Bansbach’s range of easyERF dampers has been tested to over half a million cycles with no deterioration of performance detected.
A Bansbach Smart PID system consists of at least one adjustable easyERF damping cylinder and one amplifier with an integrated controller. In its basic form this ‘open loop’ system requires manual adjustment in order to modify its damping properties. For fully autonomous ‘closed loop’ systems, sensors can easily be integrated into the system to provide measurement of controlling parameters such as acceleration, displacement or weight. Of course, that’s not all; a variety of parameters may be used - the possibilities are limited only by the imagination of the design engineer.
The system itself comprises a piston with a defined gap, known as the ‘annular gap’ between housing and piston, and two chambers filled with a silicone oil based electro-rheological fluid (see Figure 1). With no electrical charge applied, the fluid flows through an annular valve as in a standard damper. The inherent resistance is caused by the hydraulic drag coefficient of the laminar fluid flow. When an electrical charge is applied, the viscosity of the fluid increases, thus choking the annular valve, resulting in an increase in the resistance force of the damper. Moreover, the electrical charge can be increased to a point where the ERF actually solidifies, achieving a ‘zero velocity’ or ‘clamping’ action.
There are a number of advantages in using controlled dampers of this kind, including the ability to adjust the force or damping characteristics at any point along the stroke. Using the Bansbach easyERF with smart PID System also offers the advantage of speed of response; it needs only a few milliseconds to adjust damping force, so it is possible to control highly dynamic processes and those operating at high frequencies.
A particularly useful feature is the damper’s ability to provide a
holding force. As described above, at velocity zero (when the ERF becomes a solid) it is possible to clamp or block an ER damping cylinder by suitable adjustment of the electrical charge. The effect is similar to that of a friction clutch, but without the need for additional clamping elements. And as the fluid in the damper is effectively controlled via an analogue or digital signal, this feature, as well as the reactive damping characteristics, can be managed remotely.
Some application examples
Clearly, there are many ways in which these dampers can improved the reliability and efficiency of industrial processes. One example might involve a conveyor transporting objects that differ one from another in terms of their weight. By sensing the weight of each load as it passes a certain point and using this measurement to calculate an appropriate signal for the damper control system, an ERF damper deployed as an end stop to arrest the movement of loads may be adjusted automatically - and virtually instantaneously - according to the weight of the approaching load. Conveyor speed can be increased, as a result, because no human intervention is needed to mechanically increase or decrease the end damper force.
A more demanding example in terms of machine dynamics might involve a high-speed industrial centrifuge, on which multiple sensors are installed to monitor machine vibration. These measurements may be gathered in real time and processed to provide control inputs for an array of ERF dampers strategically sited on the centrifuge to limit potentially damaging structural movements.
This group of dampers would be capable of working independently one from another, with the supervisory control computer sending different voltages to each damper simultaneously. As in the previous example, the centrifuge’s efficiency and speeds are significantly improved as the risk of mechanical damage is substantially reduced by the independent action of the dampers.
Electro-rheological technology offers new scope for mechatronic system design. By incorporating systems like Bansbach’s Smart PID it may be possible to achieve quite dramatic improvements in the performance efficiencies of a diverse range of applications, from automated materials handling equipment such as conveyors, crushers, dryers or centrifuges, to production machinery carrying out drilling, forming, or milling operations. There are even applications within the medical equipment sector, such as exercise machines typically used in resistance training regimes for heart attack patients or victims of congenital or acquired limb loss.
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