This work aims to investigate a novel MR brake with the ability to sense temperature, current and magnetic field. To achieve this goal, a novel adjustable gap MR brake controlled by an electrothermal SMA spring is designed and fabricated, which implements a double-disk transmission and adopts an electrothermal SMA spring to change the MRF working gap and control the braking torque. Based on the equivalent circuit method and the finite element method, the magnetic circuit and magnetic field distribution of the MR brake were theoretically analysed, and the squeezing force and braking torque were theoretically deduced and calculated. Then, the squeezing force of the electrothermal SMA spring at different temperatures was tested, and the braking performance of the MR brake was tested. The results show that the squeezing force of the electrothermal SMA spring is highly nonlinear during the temperature rise and that the squeezing force increases very rapidly between the austenite start transition temperature and the austenite end transition temperature, and maximum extrusion force output is 70.2 N when the SMA temperature reaches 100 degrees C. The proposed MR brake has a high braking torque and a wide adjustable braking range with a maximum braking torque of 125.08 N m. Increasing the braking torque of the MR brake by increasing the coil current is not effective due to the effect of the magnetic saturation phenomenon on the magnetic field. However, the method of controlling the torque of the MR brake by changing the thickness of the MRF working gap with an electrothermal SMA spring can reduce the energy required for control and increase the controllable torque ratio of the MR brake. This new adjustable gap MR brake has a large torque adjustment range. The proposed electrothermal SMA spring actuator overcomes the defects of slow response and difficult control of general SMA springs and gives the MR brake a temperature sensing capability. This paper provides a reference for the design and fabrication of MR brakes with multi-physical field sensing capability.
展开▼
