Development of accurate vibration control devices applying magnetic fluid with variable damping

为开发机械元件阻尼器的超精密振动控制装置，将具有巨型可变阻尼力的磁流体应用于机械元件的阻尼器，首先阐明了阻尼器的减振机理，然后量化了阻尼器的减振特性，最后论证了电流开关控制减振的可行性。阐明减振机理：由带有磁极的转轴、固定在底座上的圆柱体和充填在轴体与圆柱体间隙中的磁性液体组成的专用实验装置。利用该装置测量了阻尼力的变化量。研究发现，磁隙中的磁阻尼值与磁场强度成正比，最大可达磁流体饱和磁通密度的十倍。这表明，磁粒子簇的形成是产生衰减的原因。对减振特性进行量化：新的发现来自以间隙为参数的磁柱体或非磁柱体的实验。它们是：a)阻尼的变化率，即变化的灵敏度随振幅和频率的增大而减小；b)灵敏度随间隙的减小而略有增加；c)存在一个临界速度，在该临界速度处，阻尼开始随速度的增大而迅速减小。振动控制的确定：为了评价振动控制性能，组装了两个平行和摆动模式的振子。通过对磁流体的幅值和速度进行电流开关控制的实验，证明了磁流体在振动控制中的适用性。

To develop ultra-accurate vibration control devices by applying magnetic fluid exhibiting giant variable damping to dampers for machine elements, first mechanism of manifestation of damping was clarified, then damping characteristics were quantified, and finally the feasibility of vibration control using the current on-off control was demonstrated.1. Clarifying damping mechanism : Special experimental apparatus was set up from a rotating shaft with magnetic poles, a cylinder fixed to a base and magnetic fluid filled inside the gap between the shaft and cylinder. Using this apparatus, the amount of variation of damping was measured. The damping was found to increase in proportion to magnetic field strength in the gap up to as much as ten times larger than the saturated magnetic flux density of magnetic fluid. This revels that the origin of the damping is the formation of clusters of magnetic particles.2. Quantifying damping characteristics : New findings were obtained from experiments performed using magnetic or nonmagnetic cylinders with the clearance as a parameter. Those are a) the variation rate of damping, i.e., sensitivity of the variation, decreases with increase in the amplitude and frequency, b) the sensitivity slightly increases with decrease in the clearance, c) there is a critical velocity where the damping begins to decrease rapidly with increase in the velocity.3. Confirming vibration control : To evaluate vibration control performance, two vibrators of parallel- and swing-modes were assembled. Experiments using the current on-off control by the amounts of the amplitude and velocity indicated the applicability of magnetic fluid to vibration control.