Refrigeration – Using electrical or magnetic effect – Thermoelectric; e.g. – peltier effect
Reexamination Certificate
1999-06-25
2001-09-18
Bennett, Henry (Department: 3744)
Refrigeration
Using electrical or magnetic effect
Thermoelectric; e.g., peltier effect
C361S689000
Reexamination Certificate
active
06289678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved environment system for sealed hard disk assemblies, and more particularly to a system that extends the operating life of the hard disk assembly when subject to high operating temperatures.
2. Description of the Prior Art
FIG. 1
schematically illustrates a commercially available sealed, hard disk drive and its environment control enclosure that makes the disk drive suitable for use in rugged applications where it is subject to high temperature and mechanical shock and/or vibration. One such sealed hard disk and environment control enclosure is available from Miltope Corporation and referred to by Miltope as the LPC Series of rugged high capacity, low profile, shock and vibration resistant disk drives employing sealed, disk drive cartridges. These products are ruggedized for operation in severe field environment where extremes of temperature, shock, vibration, humidity and air pressure are common. They are designed for “on-the-move” operation in tracked and wheeled vehicles, as well as airborne and shipboard applications. As illustrated in
FIG. 1
, this prior art disk drive includes a commercially available sealed hard disk drive
10
, such as the sealed hard disk drive available from Toshiba, IBM Corp., Seagate and others. Such hard disk drives include a disk housing
12
, which is sealed except for a very small opening
14
that allows a small amount of gas sealed in the housing
12
to egress and ingress during disk start up and shut down respectively. A hard disk
16
within the housing
12
rides on a spindle
17
driven by a motor
18
, both of which are also located within the housing
12
. A flying head
20
is servo positioned over a desired track on the disk
16
in order to read from and write data onto the disk. The housing
12
is supported in a sealed environmental housing
22
by resilient mounts
24
, i.e. device to mechanically isolate rapid acceleration due to shock or vibration, for example, of the environmental housing
22
from the disk housing
12
. The environmental housing
22
is an air tight aluminum housing filled with an inert gas or, if desired, with dry or low humidity air. This sealed aluminum housing
22
can also house a control electronics module
30
. An embedded closed loop servo system compensates for temperature variation, ensuring reliable head positioning. An air tight connector
32
provides a signal and power interface between the components inside the sealed environmental housing
22
and connections (not shown) outside of the housing. As will be appreciated by those skilled in the art, hard disk drives of the type shown schematically in
FIG. 1
, store multi-gigabytes of data on a 2.5 inch or 3.5 inch disk, with the environmental housing
22
having a foot print of approximately 5 inches by 8 inches by 1.5 inches deep for a 3.5 inch disk, or appropriately smaller for a 2.5 inch or smaller hard drive. The expected mean time between failures is normally in excess of 100,000 hours in a normal environment application.
While quite satisfactory in normal office type operation, the hard disk drive systems of the type shown in
FIG. 1
have experienced a significant increase in failures when operating at very high temperatures.
SUMMARY OF THE INVENTION
An object of this invention is the provision of a hard disk drive system with a small footprint and rugged shock resistance (i.e. of the type described in connection with
FIG. 1
) but which can operate in a high temperature and/or high humidity environment without a significant decrease in mean time between failure.
Applicant has identified the cause of an increase in failure rate of hard disk systems operating in high temperature environments as the lubricant used to lubricate the disk drive motor
18
. Oil from the spindle motor has been found to wick and/or vaporize out of the motor bearing when operated at high temperatures. The lubricant has been found to form a deposit on the flying head and disk surface, eventually causing it to contact the disk and cause permanent damage as well as cause spindle motor bearing failure which causes permanent damage. In addition, when the hard drive is turned on, internal air is expelled as the air is heated through the breathing hole/filter generally used in disk drives of the magnetic media type due to the high speed rotation of the disk platter. When a drive is powered off, and cools down, make-up air is drawn in. If humidity is present, the make-up air can contain humidity or other contaminants which can deposit residue on the read/write head and disk platters, which can cause unstable flying of the read/write head and cause damage to the unit which can result in permanent failure. In addition, the disk drive electronics have caused circuit drifts and failures at temperatures above 135° F. Applicant's solution to the problem that applicant has identified is to provide arrangement inside the environmental housing to transfer heat away from the hard disk drive without necessarily increasing the overall footprint of the system or coupling shock or vibration from the environmental housing to the disk drive. In some embodiments of the invention, the arrangement includes a thermoelectric heat pump module that uses the Peltier effect to move heat. As will be appreciated by those skilled in the art, such solid state heat pumps are commercially available, for example from Melcor corporation. These heat pumps consist of a number of p type and n type pairs connected electrically in series and sandwiched between two ceramic plates. When connected to a d.c. source, current causes heat to move from one plate to the other, creating a relatively hot side and a relatively cool side. In one embodiment of the invention, the cool side of the solid state heat pump engages the hard disk housing, and resilient heat conductors thermally connect the hot side to the environmental housing without materially coupling shock or vibration. In another embodiment, the hot side of the solid state heat pump contacts the inside wall of the environmental housing, and a fan circulates the gas in the environmental housing across the cool side of the heat pump and the hard disk housing. In yet another embodiment, a fan circulates the gas along a wall of the environmental housing, and the cold side of the heat pump is in heat conducting contact with an exterior surface of the wall. The hot side of the heat pump is in heat conducting contact with a heat sink.
In still another embodiment, the heat pump is omitted in favor of a heat pipe. Heat pipes have been used to cool aircraft power supplies and densely packed electronics in portable computers. One particular type of heat pipe, manufactured by Thermacore, Inc. of Lancaster, Pa., consists primarily of a porous material soaked in a low vapor-point liquid, such as acetone or methanol. When the liquid is heated, it vaporizes and is forced to the center of the pipe. It then travels to one end, where it condenses and releases its heat. At that point, the cooled liquid is wicked back to where it started, and the process repeats. The heat pipe can be generally U-shaped, with one side being secured to the hard disk housing, and the other side being secured to an interior surface of the environmental housing. Flexibility is provided in the heat pipe by, for example, a flexible bellows between the two sides of the heat pipe. Heat from the side in contact with the hard disk housing flows through the heat pipe to the side in contact with the environmental enclosure.
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patent
Anderson Chad C.
Bennett Henry
Jiang Chen Wen
Phoenix Group, Inc.
Shannon John P.
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