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Method to achieve increased filter flow while minimizing flow-induced disk vibration in a hard disk drive Disclosure Number: IPCOM000228509D
Publication Date: 2013-Jun-14
Document File: 4 page(s) / 132K

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Crucial components of every hard disk drive (HDD) are the particulate and chemical filters. A well known method to achieve both excellent cleanup and low vibration is through the use of an aerodynamic bypass, see Hendriks et al. [2]. Small form factor (SFF) HDDs usually have little room for a bypass channel, which emphasizes the urgency to optimize traditional (so-called "11 o'clock" ) filters. Our invention describes how to improve the functionality of the particle filter (PF) by placing one edge of the PF as close as possible to the cover gasket. Our measurements show that both PF filter pressure and the resulting particle drain rate respond favorably to this arrangement. A welcome side benefit is that no additional cover gasket material is required resulting in no additional cost. Our preferred embodiment combines this PF location with a narrow inlet / narrow outlet implementation of the filter pocket.

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Method to achieve increased filter flow while minimizing flow -induced disk vibration in a hard disk drive

  Particle filters for HDDs are usually stuck in a filter pocket in which the filter media is held by friction. Enterprise drives have chemical filters that are sometimes integrated with a breather filter.

As note in Brown [1], air flow plays a dominant role in the transport and capture of particulate matter in HDDs. Good particle filtration benefits from turbulence and high dynamic air pressure inside the HDD. The number of disks inside the drive has a strong effect on the achievable cleanup rates. The more disks the better. On the other hand, high turbulenec is undesirable from the point of view of minimizing vibrations of the disks, actuator, suspension, etc. The filtration design problem involves getting the fastest cleanup rate for the smallest amount of turbulence.

The considerations that drive the design of the filter pocket take into account the following factors

1. maximization of the the pressure drop across the filter media (see FILTER in Fig.1 )

2. minimization of the disk shrouding

The preferred embodiment of our invention is shown in Fig. 1. The spinning disk creates a pressure buildup

on the upstream side of the filter media. A well designed filter pocket may reach 50 Pa of ram air pressure differential across the PF.. In prior art PF installations air can leak around the filter, thus reducing the filter flow through the media. the velocity of that flow is of the order of 5 cm/sec which is very much smaller than the typical air velocity near the disk rim, about 40 m/sec. Therefore, the inlet and outlet of the filter pocket can be very narrow and still easily carry the air flow through the filter. Limiting the interruption of the cylindrical shroud surrounding the disk pack limits turbulence near the filter inlet and outlet. Limiting turbulence limits flow induced vibration (FIV) and thus track misregistration (TMR).

Note that both inlet and outlet are approximately tangential to the disk pe...