A low vibration type compressor for refrigerators using a Self-standing support method

In household refrigerators, the rotational speed of a reciprocating compressor can be appropriately adjusted according to the temperature inside of the refrigerator. The lower rotational speed reduces the power consumption of the compressor. However, several natural frequencies of the compressor exist in the low rotation region, and besides, the unbalance force arising from the piston motion acts on the internal drive unit. Thereby the vibrations of the compressor are likely to be larger due to the resonance in the low rotation region. Although the compressor on the refrigerator is supported by vibration-proofing materials, such as rubber bushes, it is difficult to fully suppress the vibration transmission from the compressor to the refrigerator. In this study, therefore, a method for supporting the drive unit inside the shell, which is called “the self-standing support” is newly proposed in order to reduce the vibration of the compressor drastically. In the proposed method, a spherical support element is utilized instead of coil springs to support the drive unit. And the drive unit can maintain a stable self-standing state by acting restoring moment due to the gravity while it is directly placed on the shell. The natural frequencies of the compressor can be greatly reduced by decreasing the support stiffness for the drive unit in comparison with the support method using coil springs. Furthermore, in designing the drive unit, the application point of the exciting force is matched with the center of percussion to the contact point on the spherical support. As a consequence, the periodic restraining force acting on the contact point can be minimized. By these two features, it is possible to considerably reduce the vibration transmission from the drive unit to the shell. In the present study, a simplified model for a reciprocating compressor is treated, and the effectiveness of the self-standing support is investigated analytically and experimentally

Suppression Effect of Two Flexible Joints for Underwater Sound Propagation

Recently, noise problems often accur in a building that has been repurposed and reused, so-called conversion architecture. One of the causes of this probrem is structure-borne sound in pump piping system. Vibration reduction method that involves installing two flexible joints in series has been found to be useful for countermeasures against structure-borne sound in pump piping system. This technique is very useful compared to the general noise reduction method which installs many vibration isolators in the whole system. However, the effect of reducing sound wave propagation in piping has not been completely explained yet. In this study, the simple apparatus having the straight-line piping is treated, and the reduction of sound wave propagation in piping by installing flexible joints is verified analytically and experimentally. The numerical analysis and experimental results confirm that sound wave propagation in piping is reduced by the difference in sound velocity between the pipe and joint. Furthermore, the length of the joint and between joints is important reducing sound wave propagation in piping

Countermeasure against Frictional Vibration in Electric Sander by Dynamic Absorber

The symptoms of Raynaud’s disease, a hand-arm vibration syndrome, are caused by long-term use of hand-held electric tools or vibrating tools and by excessive exposure to hand-arm vibrations. The purpose of the present research is to develop a passive vibration suppression system using electric tools in order to address the problem of the handarm vibration syndrome. We focus on the development of a dynamic absorber for a electric sander used to grind the surface of wood or steel. After measuring and analyzing the vibration in the tools, it was proven that the fiction force acting between tools and work materials is one of the causes of an increase in the tool’s vibration. Consequently, the suppression effect of the dynamic absorber on frictional vibration was verified experimentally. As a resuls, it was confirmed that when the dynamic absorber with the natural frequency of 10 Hz or less is installed on the sander, the daily vibration exposure values become lower than 1.0 m/s2

Development of Borehole Seismometer Using Conical Pendulum to Three-Component Velocity Measurement

The aim of this study is to develop a small, inexpensive borehole seismometer that can accurately measure the shot-period velocity signal of three directions. The prototype developed in prior research is composed of a biaxial horizontal electromagnetic sensor in conical pendulum form and a vertical electromagnetic sensor installed on the pendulum axis. The performance of the prototype has been verified experimentally, however, the accuracy of the measurement became degraded due to the elastic vibration and residual vibration of the pendulum axis. As a countermeasure for this problem, the prototype has been improved such as increasing the rigidity of the pendulum axis and adding a magnetic attenuation. In the paper, the performance of the improved prototype was evaluated based on the verification experiment results