The research objective of this award is to investigate a new magnetorheological (MR) brake actuator with an embedded Hall-effect sensor in its flux path to eliminate hysteresis using closed-loop control. The new actuator will also incorporate a permanent magnet, coil and serpentine flux path to reduce the overall size to improve its torque-to-volume ratio. MR-brake actuators have been implemented in many applications including civil engineering, haptics, exercise equipment, automobile suspensions and tactile displays. However, their hysteretic behavior makes control challenging. The research will result in a systematic methodology to identify the dominant parameters of the actuator and study their complex interactions. The research approach progresses from parameterized finite element simulations to analysis of the data with design of experimental techniques and to verifications with a prototype actuator.
If successful, the results of this research will transform the state-of-the-art MR-brake actuator technology into a smart actuator technology. Example applications include automotive industry, aerospace, robotics, civil engineering, prosthetics, haptics, vibration control, game industry and rehabilitation. The results will be disseminated to allow the creation of commercial devices. Graduate and undergraduate engineering students will benefit through classroom instruction and involvement in the research. A new workshop on smart fluids and actuators will be organized for the underrepresented middle and high school students during the annual MESA events on campus. The workshop will allow children to conduct experiments with magnets, coils and MR fluid and emphasize how research leads to development of new knowledge and products.
MR-brakes are passive actuators where the braking torque/force can be controlled electronically. They employ magnetorheological (MR) fluid. This fluid is a suspension of small iron particles in oil. The MR fluid can be activated using magnetic field. When activated, the viscosity of the fluid increases. MR-brake actuators have very desirable characteristics. Therefore, they have been used in many applications including civil engineering, haptics, exercise equipment, automobile suspensions and tactile displays. However, they have a major drawback: they exhibit hysteresis behavior. The hysteresis also leads to non-zero torque in the off-state of the brake, which is quite undesirable in applications such as haptics. This research explored a new MR-brake actuator concept with an innovative idea of embedding a sensor in the flux path to eliminate hysteresis using closed-loop control. Prototype MR-brakes have been designed and extensive experiments have been conducted. The results indicate that the new approach is very effective in significantly reducing the hysteresis. Another drawback with the existing MR-brakes is that the device size tends to be large due to the need to embed a coil inside the actuator to activate the fluid. In this research, another innovation was incorporated into the new brake. A permanent magnet has been embedded into the MR-brake to reduce the size of the coil needed to activate the fluid. The resulting brake produces the same amount of braking torque in a smaller device size. It also has a fail-safe feature since the brake remains engaged due to the magnet, if there is a power interruption. In May 2012, U.S. Patent has been filed to protect the intellectual property of the inventions. We expect significant broader impacts of the developed technology due to the wide range of applications of MR-brakes including, automotive industry, aerospace, robotics, civil engineering, prosthetics, haptics in virtual reality, vibration control, game industry and rehabilitation. An introductory presentation on MR fluids and actuators has been developed. This module was used to educate students about the technology in an undergraduate course. The project provided significant opportunities to develop the research skills and experience of two graduate students. Both students learned to become independent researchers who can now manage relatively large R&D projects on their own. They learned to write technical documents, including journal and conference papers, theses and both had opportunities to give research presentations at international conferences. Results of the research have been disseminated through 10 conference and journal publications. Also, two masters theses have been written.
