Takafumi Asada

Characteristic analysis of hydrodynamic bearings for HDDs

We discuss the technical distinctions of hydrodynamic bearings (HDBs) in the application of HDDs. We also report on numerical analysis and experiments aimed at solving the characteristic problems of HDDs and high-speed HDDs.

Design of Hydrodynamic Bearing for Miniature Hard Disk Drives

This paper has two specific goals to achieve. The first goal is to address major challenges encountered in design and development of miniature hydrodynamic bearings for small form factor hard disk drive spindle motors. These challenges include extremely small thickness of the spindle motors, mass productivity of tiny bearing parts, and bearing reliability and performance in relation to changes in atmospheric pressure. To overcome these challenges, we have developed a prototype hydrodynamic bearing that is resistant to environmental changes, free from oil film disruption, and tolerant of variations in processing precision. The prototype hydrodynamic bearing has two special features: an oil circulation function and a gas/liquid separation function. The oil circulation function is achieved by using asymmetric hydrodynamic grooves together with circulation passages. The gas/liquid separation function is achieved by using tapered capillary seals in the circulation passages. As a result of these two special features, the prototype hydrodynamic bearing can successfully expel air bubbles out of the bearing, thus enhancing the performance and reliability of the hydrodynamic bearing. The second goal is to evaluate the prototype hydrodynamic bearing in a miniature spindle motor for small form factor hard disk drives. Two specific bearing designs are evaluated. The first bearing design is a pushing type that generates no low-pressure area. However, the flow rate increases at high temperature. The second design is just the opposite. It is a pulling type design that generates a low-pressure area. But the flow rate is constant and is independent of temperature changes. To accommodate manufacturing tolerances, a parametric study is conducted to identify the effects of manufacturing tolerance on bearing performance.

Vibration of 1.8-in Hard Disk Drive Spindle Motors at Various Ambient Temperatures

In this paper, vibration of 1.8-in hard disk drive (HDD) spindle motors is studied experimentally and theoretically. In the experimental study, vibration of 1.8-in HDD motors is measured at 5degC, 25degC, and 70degC in a thermal chamber. Experimental results reveal two important phenomena. First, vibration of 1.8-in HDD spindle motors is dominated by a (0,0) unbalanced mode that has a significant bending deformation of the base plate. Second, the natural frequency of the (0,0) unbalanced mode and the static gain of the frequency response function change significantly as the ambient temperature varies. To explain these experimental observations, we apply a mathematical model developed at the University of Washington to analyze the vibration of the 1.8-in HDD spindle motors. The analysis shows that (0,0) unbalanced mode shifts its natural frequency because membrane stresses are developed in the base plate during temperature changes as a result of a significant mismatch of coefficients of thermal expansion between the base plate and the fixture. Moreover, the change of the static gain results from reduction of fluid-dynamic bearing coefficients as the temperature varies.

Development of a 3-dimensional precision measuring method by optical endoscope (Evaluation of measuring accuracy of inner wall based on quartz pipe surface)

Newly developed 3D scanning optical endoscopic probe consists of φ1.5mm quartz pipe and 2 micro motors that run inside and conduct helical 3D scanning. This research looks into the possibility of accurately measuring the inner wall of extremely small diameter object by combining 3D scanning endoscopic optical probe and OCT (optical coherence tomography). Conventionally, precision measurement of such extreme inner diameter size was not possible due to influence of what is called “fluctuation of light” and “mechanical run-out of the measuring instrument itself” in axial and radial direction. In the new method, the inner wall of quartz pipe is measured in advance by calibration work, and the inner wall of the object is measured based on the quartz pipe. Applying this method, we succeeded in measuring with standard variation 0.07μm(σ) repeatedly. This new method also features auto-correction of the incline angle between the optical probe and the measuring object by computing, which prevents setting error and variation.

Design of Hydrodynamic Bearing for Miniature HDDs

This paper discusses major challenges in miniature hydrodynamic bearings, and covers the thinness of their structure, the mass-productivity of small bearing parts, and the improvement of bearing performance and reliability in relation to changes in air pressure. The basic design of a new type of this miniature bearing with an oil circulation mechanism that has the function of expelling air and eliminating bubbles inside the bearing cavity that would otherwise break the oil film find its potential application in mobile equipment and in spindle motors that require long-term reliability

Vibration of 1.8-In HDD Spindle Motors at Various Ambient Temperatures

The purpose of this paper is to identify critical parameters that govern vibration of 1.8-in hard disk drive (HDD) spindle motors at different thermal environments. The mechanisms that the change of static gain results from temperature dependence of fluid bearing coefficients are identified through the use of experimental measurements and numerical simulations developed at the University of Washington

Design of hydrodynamic bearing for mobile HDDs

This paper reports on the basic design of a Hydrodynamic bearing with an oil circulation mechanism that has the express function of eliminating bubbles that remain inside the bearing cavity that would otherwise adversely affect the disruption-free nature of the oil film in the bearing.[1]-[2].