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Gap-Size Effect of Compact MR Fluid Brake

MRF are kinds of functional fluids, whose rheological properties, especially shear stresses under shear rates, can be rapidly and repeatedly controlled with application of magnetic fields. CMRFB in which the MRF between multilayered disks works as a torque generator was developed in our previous works. The CMRFB has advantages in its small size and high torque. One of the objectives of this article is to find the cause of the unignorable errors between the estimated torque and the experimental torque in the CMRFB with 50 -µm gaps that we found in the previous report. And the other is to evaluate the case with the different gap size. In this article, a testing device to evaluate rheological properties of the MRF was developed. Experimental results with the testing device were utilized as basic data to design the CMRFB. Three sets of two types of the CMRFB that have two different gap-sizes (50 µm and 100 µm) were also developed, and their performances are compared analytically and experimentally. Analytical results derived 20% less braking torque of the 100 -µm gap brakes than that of the 50 -µm gap brakes. The comparison of analytical and experimental results for 50 -µm gap brakes shows bigger error than those of the 100 -µm gap brakes. Filling tests show a possibility that the magnetic particles are not sufficiently filled between the 50 -µm gaps.