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

为研制将具有巨大可变阻尼的磁流体应用于机械元件阻尼器的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，最后论证了采用电流开关控制控制振动的可行性。澄清阻尼机理：由带有磁极的旋转轴和固定在基座上的气缸，在轴与气缸之间的间隙内填充磁流体，组成专用实验装置。利用该装置，测量了阻尼的变化量。研究发现，阻尼随间隙内磁场强度的增大而增大，最大可达磁流体饱和磁通密度的十倍。这表明阻尼的起源是磁粒子团簇的形成。量化阻尼特性：从使用磁性或非磁性气缸与间隙作为参数进行的实验中获得了新的发现。它们是a)阻尼变化率，即变化的灵敏度，随着振幅和频率的增加而降低；b)灵敏度随着间隙的减小而略有增加；c)存在一个临界速度，在这个临界速度下，阻尼开始随着速度的增加而迅速下降。确认振动控制：为了评估振动控制性能，装配了并联和摆振两种振子。利用振幅和速度的量来控制电流的通断，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.