Fluid bearings

It was the first to invest in the development and development of liquid bearings.

We will continue to accelerate the development of HDDs (hard disk drives) in the direction of high density and quietness.

The best performance of a server or PC depends on the performance of the HDD* (hard disk drive). So far, major manufacturers have made major breakthroughs in various key technical issues such as how to improve the smoothness of the surface of optical discs, switch to magnetic recording methods, and improve the sensitivity of magnetic heads, which have rapidly promoted the development of HDD products in the direction of high density and large capacity. However, since the end of the 90's, a new technical problem has emerged, that is, when the HDD spindle motor is rotating at high speeds, the vibration generated by the internal bearings seriously affects the reading and writing accuracy of the head.

Japan Densho Co., Ltd. is ahead of all other competitors and has been the first to mass-produce HDD spindle motors with FDB (Liquid Bearing) technology since 1994. Around 2000, as the production of this type of spindle motor continued to rise, by 2002, FDB had become the mainstream product of bearings for spindle motors. The main reason for this is that with the rapid increase in data storage density of HDDs, traditional ball bearings cannot completely unify the size of each ball in principle. In other words, NRRO (Non Repetitive Run Out) (NRRO) is generated by the difference in size between the balls, which causes the head to be unable to accurately record/read data on high-precision, high-density tracks.

FDB technology is a technology in which oil and other fluid carriers are injected between the shaft and the bearing, so that the shaft floats away from the bearing under the hydrodynamic pressure generated by itself when it rotates, thereby achieving smoother rotation. At the same time, the use of the damping characteristics of the oil itself can also bring us a spindle motor with low noise and vibration.

As early as 1883, Tawa, a United Kingdom railway technician, discovered the basic principles of liquid bearings. When HDD manufacturers realized that by applying this technology, which had been disclosed for a long time, to HDD spindle motors, they could break through the accuracy limit of ball bearings caused by NRRO problems and produce bearings with higher accuracy, so they began to research and develop these types of bearings. Among them, Japan Densan Corporation was the first to apply this technology to the mass production of HDD spindle motors, and has maintained a leading position in the world in this product field for a long time, and now has a global market share of 80%.

Limitations of ball bearing technology in terms of accuracy

Pattern diagram of a ball bearing. Even if the size of the balls is not very different, there will still be deviations, and when the inner wheel rotates, there will be a deviation of the central axis that is not synchronized with the number of revolutions. This is called "NRRO" (Non-Repetitive Run Out).

When the shaft rotates, it floats away from the bearing due to the hydrodynamic pressure generated by the shape of its own surface. At the same time, the characteristics of the oil itself can also bring us the effect of reducing vibration and slowing down the impact.

FDB has the characteristics of low noise, low power consumption, low vibration, shock resistance, and long life, and can be used not only in HDDs, but also in other fields, such as in fan motors installed in servers and notebook computers. Japan Denco Corporation (Nidec) is expanding the above application fields and is also striving to further improve the performance of FDB. The company has developed its own software to simulate the motor action, so that it can complete the development and design of a thinner and more powerful HDD spindle motor in a short time. At the same time, the company has also carried out research on the lubricants used in FDB, and strives to develop lubricants that can meet the requirements of lower friction and longer life of bearings.

Fluid bearings

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