Magnetorheological Damper Specifications

Each viscous damper has its limits and so does the one with magnetorheological fluid inside it. Some of the most significant concerns concerning the magnetorheological damper features are the two of these: How fast could it be? How powerful could it possibly be?

I will address these issues in this article.

Magnetorheological Damper Reaction Time

There are tests put together by a research group in Aalto University with a rectangular reference signal on actuators containing magnetorheological fluid. During these studies, the rising edge response time changed from 0.8 ms to 1.9 ms depending on if the experiment involved a valve or a membrane actuator paired with the valve. The falling edge response time varied respectively from 1.5 ms to 7.4 ms. From what I know, these are by far the best response times reported for actuators counting on magnetorheological fluid.

In my personal findings, the vibration pitch that I finally kill, is 25 Hz. My actuator per se can run at a lot higher frequencies - I have tested it up to 70 Hz - yet the resonance peak in my actual situation is especially distressing at this frequency. But what is fantastic in dampers with magnetorheological fluid, is that they can be programmed to eliminate whatever frequency you want as long as you stay underneath the highest possible frequency the damper can attenuate.

The groundhook control rule is applied in my application by presuming that the floor continues to be still. If we even further expect the vibration of the motor unit being sinusoidal, the control law then produces that the damper should stiffen itself during the negative half of the vibration acceleration curve. At 167 Hz (the absolute highest frequency to be dampened), the period for the magnetorheological fluid to get its firm state, is roughly 3 ms.

This establishes a prerequisite for the damper response time. It would have 1/4 period time (ca. 1,5 ms) to rise and another 1/4 period to go down (despite the fact that typically rising edge is faster than declining edge).

Magnetorheological Damper Force Prerequisite

As indicated by my estimations, damping a motor of 800 kg vibrating at 167 Hz involves a counteracting damper force of 19.6 N if 60% attenuation will be reached. When this force is split into four sustaining corners of a motor bedplate, the strength requirement for a single actuator would be roughly 5 N. Nonetheless, due to superposition of the frequencies, the force at a single instant would be increased. Therefore, the force requirement here was multiplied with the factor 10 since after conversations with the damper developer, I learned that it is still in the range that magnetorheological fluid dampers of this overall size are able to achieve.

As a summary, the following damper specs may be set for this sort of an example motor:

Force 50 N

Response time 1.5 ms

As it turns out, a damper that contains magnetorheological fluid complies with these kind of specs.