Development of Linear Oscillatory Actuator with 4 poles and 8 poles Movers.

Abstract

Recently, Inertia Force Generators (IFGs) was reported to reduce undesirable vibrations in automobiles and precision devices, which consists linear oscillatory actuators (LOAs), sensors and a controller. In the IFG, inertia force for reducing vibrations that generated by the LOA is controlled by a controller and sensors [1]. Here, the LOA should effectively generate inertia force at wide frequency range because the frequency range of undesirable vibrations is wide. However, the conventional LOA can effectively generate inertia force at narrow frequency range because of one mechanical resonance.In this abstract, a LOA with two movers which can effectively drive using two mechanical resonance is developed and the pole configuration is discussed.The proposed LOA mainly consists a stator, an outer mover (0.485 kg) and an inner mover (0.545 kg), as shown in Fig. 1. The stator and outer mover are connected by two leaf springs (totally 139.4 N/mm), and the stator and inner mover are also connected by two leaf springs (totally 44.4 N/mm). The stator is mainly composed of 16 coils and yokes, and the outer and inner movers are mainly composed of magnets and a yoke. Magnets are magnetized at positive or negative radial-direction, and these are axial-directionally arranged with 4 magnetic poles in outer mover, and these are arranged with 8 magnetic poles in inner mover. Coil 1, 2, 5, 6, 9, 10, 13 and 14 are wound clockwise and others are wound counterclockwise. Then, Coil 1, 4, 5, 8, 9, 12, 13 and 16 are connected in series that are called as coil group 1, and others are connected in series that are called as coil group 2. Same-phase or reverse-phase current is applied to coil groups. Here, the former is sinusoidal current with same-amplitude and same-phase in coil groups, and the latter is sinusoidal current with same-amplitude and reverse-phase in coil groups. The 4 poles outer mover is reacted with magnetic fluxes generated by same-phase current, and the 8 poles inner mover is reacted with magnetic fluxes generated by reverse-phase current. In this way, two movers can be independently driven by controlling current. Also, the two movers simultaneously oscillate by superimposing with same- and reverse-phase current. By driving of movers, inertia force is effectively generated at two frequency range because of two mechanical resonance.Next, it is compared between a LOA with 2 and 3 poles movers [2] and the proposed LOA which has 4 and 8 poles movers. In the former, unintentional attractive force was generated between a 3 magnetic-poles and 2 magnetic-poles movers when no current was applied at initial condition because pole-combination of movers is odd and even numbers. So, it must be canceled out by mechanical springs that may have manufactured error or deterioration. In the latter, unintentional attractive force is made to theoretically be zero because that is different even and even numbers. By electromagnetic analysis using 2-D EFM [3], attractive force in the former LOA was calculated as 28.5 N and -9.5 N at each mover, and that in the latter LOA was calculated as 0 N at all movers. Thus, it was verified that the pole combination of the proposed LOA is effective to reduce the attractive force.The prototype of the proposed LOA is manufactured as shown in Fig. 1. The accelerations of outer and inner movers are measured when same-phase or reverse-phase currents with amplitude 0.5 A is applied at each frequency. Then, inertia force is calculated by multiplying measured accelerations and mover’s mass together. As shown in Fig. 2, an outer mover was mainly oscillated when applying same-phase current, and an inner mover was mainly oscillated when applying reverse-phase current. Then, large inertia force was obtained with two frequency at 37 and 84 Hz because of mechanical resonances of the outer and inner movers.For comparison, each mover positions are calculated using motion equations with current thrust and detent characteristics that derived from electromagnetic analysis, and analyzed inertia force is calculated. As shown in Fig. 2, measured results almost agreed with analyzed results. **