Comparison of properties of electromagnetic clutches with ferromagnetic powder and magnetorheological fluid for low frequency control signals
The article presents the results of laboratory tests for the two electromagnetic clutches of controllable: powder clutch and clutch fluid MR. The research was aimed at comparing the opportunities for coupling the power supply conditions in the low-frequency signals of 1 to 5 Hz. The system uses proprietary software written in Visual Studio C#. The program allows for controlled, laboratory power supply ATTEN PPS3205T-3S.
A novel SMA drive based on the Graham Clock escapement and resistance feedback
Abstract This paper describes a novel concept of a rotary drive actuated by two SMA springs working in an antagonistic way. The conversion of mechanical power from linear oscillations to rotary movement is based on the Graham Clock Escapement which is typically used as a rate regulation mechanism in mechanical clocks. The position of the SMA moving joint was estimated using a resistance feedback loop. Resistance feedback is a kind of sensorless loop and it is based on families of displacement vs. the resistance characteristics which were measured for different mechanical loads. The Graham Clock Escapement mechanism has been taken into account as an innovative gear system. In a typical application the mechanism reduces the force. In the solution presented it has worked as a gear, converting linear force into a rotary stepper movement. The prototype demonstrates that the mechanism is able to generate movement. The velocity of the drive was poor, it is driven by SMA thermal activation and natural convection cooling. As a result, the presented prototype is a very low-speed stepper motor which moves about 1 rotation per 77 min or slower. The prototype drive was constructed, and the resultant mechanical force of two SMA springs were measured and calculated and the gear ratio of the Graham Clock Escapement was also calculated. The resistance vs. position characteristics were converted to relative ones for linearization and they were applied for a sensorless control system using an 8-bit microcontroller, finally the velocity of rotation for the idle mode of the drive was measured.
Microstructural investigations of the yielding behaviour of bidisperse magnetorheological fluids
Particle level simulations were used to investigate the effects of size bidispersity and particle size ratios on the static and yielding behaviour of magnetorheological fluids (MRF). The MRF were treated as linearly magnetisable, neutrally buoyant particles dispersed in a viscous carrier liquid. In the quiescent mode (static structures), the bidisperse suspensions were found to have a higher tendency to form straight chains than the monodisperse suspensions; this is consistent with previous findings. Under steady shearing, the bidisperse suspensions exhibited higher stress enhancement than the monodisperse systems. The stress enhancement in bidisperse suspensions is likely to be due to the population and orientation of interacting large particles in the bidisperse suspensions.