Linear magnetorheological brake with serpentine flux path as a high force and low off-state friction actuator for haptics

In robotics and haptics, actuators that are capable of high force output with compact size are desired for stable and stiff interfaces. Magnetorheological brakes are viable options for such implementations since they have large force-to-volume ratios. Existing linear magnetorheological brakes have limited strokes, are relatively large, and have high off-state friction forces mainly due to the piston-cylinder internal design. The main contribution of this research is a new alternative internal design for linear magnetorheological brakes. The proposed approach uses the serpentine flux path concept to eliminate the piston-cylinder arrangement. It leads to significantly less off-state friction and infinite stroke. To the best of our knowledge, this is the first such linear magnetorheological brake. Our new brake can produce 173-N force. In comparison, a conventional linear magnetorheological brake with the same size can only produce about 27-N force. Our results showed that the ratio of the off-state friction force to the maximum force output in the prototype linear brake is about 3% compared with more than 10% for most similar devices in the literature and 27% for a commercial brake. At the same time, the compactness was improved as our prototype is about half the size of a commercially available product.