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

为了将具有巨变阻尼特性的磁性流体应用于机械元件阻尼器，开发超精密振动控制装置，首先阐明了阻尼的表现机理，然后对阻尼特性进行了量化，最后论证了电流开关控制振动控制的可行性.澄清阻尼机制：由带磁极的旋转轴、固定在底座上的圆柱体和填充在轴与圆柱体之间差距中的磁流体组成了特殊的实验装置。使用该装置，测量阻尼的变化量。阻尼被发现增加成比例的磁场强度在差距高达十倍以上的饱和磁通密度的磁性流体。这揭示了阻尼的起源是磁性粒子团簇的形成.量化阻尼特性：新的发现，从实验中获得的间隙作为一个参数，使用磁性或磁性圆柱体。这些是a）阻尼的变化率，即，变化的灵敏度随着振幅和频率的增加而减小，B）灵敏度随着间隙的减小而略微增加，c）存在临界速度，在该临界速度处阻尼开始随着速度的增加而迅速减小。振动控制：为了评估振动控制性能，组装了平行和摆动模式的两个振动器。通过电流幅值和速度的大小来控制电流开关的实验表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.