Research Of A Novel Magnetorheological Damper And Six-axis Semi-active Vibration Isolation Platform

Precision instruments and equipments mounted on moving carriers, including: vehicles, ships, aircrafts and rockets, suffer greatly from the vibration exactions. Disturbances in the form of vibrations can degrade the performance of sensitive equipments or cause failure. It has been proved, resonance caused by vibration disturbance is the main reason for instruments failure. This work is motivated by the need for a property semi-active vibration control device and parallel platform that can isolate six-axis vibration disturbances.Aiming to develop a compact and lightweight magnetorheological(MR) damper, a novel double-piston structure has been proposed. This novel MR damper has simple structure and minimum diameter when has a large stroke on the same time. Most of this damper’s parts could be made by all kinds of high strength and lightweight materials, which will result in a minimum damper weight. The first prototype damper fully satisfied previous design requirements. The test results show that the damper can work smoothly. Compared with existing MR dampers, it has a more wide dynamical working range.The new MR damper has a unique velocity boundary conditions in the annular duct. Herschel-Bulkley constitutive model has been used to describe MR fluid’s rheological behavior. Flow field in the annular duct has been analyzed. Relationship between the damper structure parameters and damping force has been acquired. Parallel plates model using Bingham constitutive model has been studied in order to simplifies the calculation equations. Results form the simplified equations fit the testing results quite well. The damper force versus velocity plots show hysteresis in both pre- and post-yield regions, and asymmetric forces in jounce and rebound. A model that takes advantage of the models proposed for MR dampers in earlier studies is proposed for representing the force-displacement, force-velocity, and asymmetric forces observed in test results. A comparison of the modeling results and test data indicates that the model accurately represents the force characteristics of the damper.As the vibration disturbances could come form all directions, the vibration isolator should have six-axis vibration isolation ability under this situation. This is where cubic structure Stewart platform mechanisms emerge as an ideal candidate for six-axis vibration isolation. This platform using six proposed novel MR dampers. MR damper model has been developed in the interested frequency range. Dynamical model of this platform using six of this new double-piston MR dampers has been built and simulated. The passive isolation performance of this platform have been acquired under fix drive currents. When drived by fix currents, this platform have typical passive vibration isolation system properties. It can efficiently control the resonance with increase currents, but this will also reduces the high frequency vibration isolation performance.Properties of semi-active vibration isolation system using MR damper has been discussed. Three semi-active control laws, including equivalent skyhook damping control law, equivalent skyhook damping fuzzy logic control law and acceleration feedback fuzzy logic control law, have been proposed for six-axis platform semi-active control using six MR dampers. Simulation results from single degree of freedom(SDOF) and double degree of freedom(DDOF) vibration isolation systems proved the efficiency of these three control laws. Numerical simulation results in frequency domain indicate that the parallel semi-active vibration isolation platform has desirable vibration isolation properties in all six axes. It can efficiently depress the resonance without reduce performance in high frequency domain.Six-axis vibration isolation platform based on cubic Stewart platform and using six of modified novel double-piston MR dampers has been designed and fabricated. A six channels power source has been developed for MR dampers driving. Using rapid control prototype technology, semi-active control system has been used for platform performance testing. Testing results shows that the resonances along all three axis have been suppressed significantly without degrade high frequency domain performance, which show a good agreement with the simulation results.