Magnetorheological fluid has attracted considerable attention in the recent past, particularly in mechanical control and electronic systems. This is owing to its unmatched ability to create the magnetorheological effect. This magnetorheological effect is in the sense that the rheological attributes of the related materials, for example, shear modulus and viscosity, can be tuned by an external applied magnetic field.
Magnetorheological fluid is made of micron-sized magnetizable particles, additives and carrier fluids. These particles are suspended in the carrier fluids forming columns, chains and complex networks when a magnetic field is applied to the fluid. However, when the magnetic field is removed the fluid turns back to the liquid state within milliseconds. In light of this mechanism, many research works have featured the application of magnetorheological fluid based gadgets such as dampers, valves, mounts, brakes, etc. Within these fluid-based devices, magnetorheological dampers have been applied widely in vibration control systems owing to their long range tunable damping force, low energy consumption, and fast response.
Researchers led by Professor Weihua Li University of Wollongong in Australia proposed a magnetorheological damper integrating a self-sensing mechanism composed of cylindrical permanent magnets as well as self-sensing coils, aiming to function as a controllable damper and velocity or displacement sensor together. In the proposed structure, the magnetic interference was isolated without extra elements. Their research work is now published in Sensors and Actuators A: Physical.
In the damper parts proposed by the authors, there were two chambers in the cylinder separated by a floating piston. They filled the chamber with the piston with magnetorheological fluid and the other used as an accumulator to take care of the volume changes that occurred as the piston moved. The accumulator was designed with a compression spring, which was used to support the movement of the floating piston. The magnetorheological fluid in the cylinder flowed through the annular gap between the head of the piston and the cylinder. The damper was identified to function consistently with the direct shear model.
The research team installed an excitation coil winding around the piston head and insulated it electrically. When they applied a direct current to the coil, a magnetic field was produced around the coil and the piston head. The annular gas was activated, changing the viscosity of the magnetorheological fluid in the gap. Therefore, the required change in the damping force was achieved.
The proposed damper used the piston as a sharing component between the self-sensing mechanism and the magnetorheological damper. This shared element could isolate the magnetic field between two function areas. For this reason, the authors were able to minimize magnetic field interferences without an extra shield and guild layer. Therefore, they were able to simplify the structure of the proposed damper.
The damper could however determine the velocity and displacement by implementing the sensing algorithms. The researchers evaluated experimentally the self-sensing performance under various excitation amplitudes and frequencies. The outcomes of the experiment indicate that the velocity curve had a little deviation between theoretical and experimental data based on 3Hz and 5nm frequency and amplitude respectively. When the excitation frequency and amplitude were increased to 4Hz and 15mm, respectively, the experimental curve was in agreement with the theoretical one, therefore, the efficiency and the feasibility of the self-sensing capability were confirmed. The damping performances were analyzed and it was observed that damping force ranged from 200N at 0A and 750N at 0.6A, and the dynamic range was approximately 3.75.
The theoretical analysis and the experimental data obtained in their study for the proposed magnetorheological damper had excellent self-sensing capacity and tunable damping capability.
Guoliang Hu1,2, Yun Lu2, Shuaishuai Sun2, Weihua Li2. Development of a self-sensing magnetorheological damper with magnets in-line coil mechanism. Sensors and Actuators A, volume 255 (2017), pages 71–78.Show Affiliations
- 1Key Laboratory of Conveyance and Equipment, Ministry of Education, East China Jiaotong University, Nanchang, Jiangxi 330013, People’s Republic of China.
- 2School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522, Australia.