Patent Application
20060262451
1. Field of the Invention
The present invention relates to a liquid bearing between a head and a disk of hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads can magnetize and sense the magnetic fields of the disks to write and read data, respectively. The heads each have an air bearing surface that cooperates with a flow of air generated by the rotating disk to create an air bearing. The air bearing prevents mechanical wear between the head and the disk.
The strength of the magnetic flux and the corresponding electrical signal sensed by the head is inversely proportional to the height of the air bearing. The higher the air bearing, the lower the signal. It is generally desirable to minimize or even eliminate the gap between the head and the disk. Unfortunately, minimizing or eliminating the gap increases the mechanical wear between the head and the disk surface. Consequently, when designing an air bearing there is always a tension between increasing the signal strength and minimizing mechanical wear. It is therefore desirable to provide a bearing between the head and disk that optimizes signal strength while minimizing mechanical wear.
A hard disk drive that has a liquid bearing between a head and a disk of the disk drive. The drive includes a spindle motor and an actuator arm assembly coupled to a base plate. The disk and the head are coupled to the spindle motor and actuator arm assembly, respectively. The liquid bearing is formed between the head and the disk.
Disclosed is a hard disk drive that has a liquid bearing between a head and a disk of the disk drive. The drive includes a spindle motor and an actuator arm assembly coupled to a base plate. The disk and the head are coupled to the spindle motor and actuator arm assembly, respectively. The liquid bearing is formed between the head and the disk. By way of example, the liquid bearing can be formed by the condensation of a vapor within the disk drive assembly. The liquid bearing can minimize mechanical wear while optimizing signal strength in the signal detected by the head.
Referring to the drawings more particularly by reference numbers,
The disk drive 10 may include a plurality of heads 20 located adjacent to the disks 12. Each head 20 may have separate write (not shown) and read elements (not shown). The heads 20 are gimbal mounted to a corresponding flexure arm 26. The flexure arms 26 are attached to an actuator arm 28 that is pivotally mounted to the base plate 16 by a bearing assembly 30. A voice coil 32 is attached to the actuator arm 28. The voice coil 32 is coupled to a magnet assembly 34 to create a voice coil motor (VCM) 36. Providing a current to the voice coil 32 will create a torque that swings the actuator arm 28 and moves the heads 20 across the disks 12. The actuator arm 28 and flexure arms 26 can collectively be referred to as an actuator arm assembly.
The hard disk drive 10 may include a printed circuit board assembly 38 that includes a plurality of integrated circuits 40 coupled to a printed circuit board 42. The printed circuit board 42 is coupled to the voice coil 32, heads 20 and spindle motor 14. The cover 18 and base plate 16 enclose the disk 12 and heads 20 of the disk drive 10.
As shown in
F≈g·γL·cos θ (1)
Where;
F is the adhesive force;
g is a geometry dependent variable;
γL is the surface energy of the liquid;
θ is the contact angle of the liquid that is formed on the surfaces of the head and the disk.
From equation (1) it can be seen that the height and the stiffness of the liquid bearing (i.e. adhesive force F) can be varied by changing the type or composition of the liquid, γL the geometry of the head 20, and/or the chemical composition of the head and disk surfaces.
It may be desirable to create a negative load L on the head to somewhat offset the adhesive force F. The liquid bearing 44 will remain intact if the load L is less than the adhesive force F. The negative load L can be created by either the flexure (26 in
To control the formation of the liquid bearing 44, the head 20 can provide a DC voltage to strengthen the attraction between the head 20 and the disk 20. The negative load L may be greater than the adhesive load F but less than the combined effects of the DC voltage and the capillary pressure. When the DC voltage is not applied, the negative load L pulls the head 20 away from the disk 12 and breaks the liquid bearing 44.
The head 20 may include a heating element (not shown) that varies the temperature of the liquid. The adhesive force is inversely proportional to the temperature such that a rise in temperature will decrease the force F. The temperature may be raised to decrease the adhesive force to a level that is less than the load L, whereby the head 20 is pulled away from the disk 12 and the liquid bearing 44 is broken.
The liquid may be applied in bulk on the disk to create the liquid bearing. Unfortunately, the centrifugal force of the rotating disk will cause the liquid to become un-evenly distributed toward the outer diameter of the disk. As an alternate embodiment a vapor may be formed within the hard disk assembly. The vapor may be formed from a reservoir of liquid in the hard drive assembly that vaporizes under normal operating conditions.
Due to the high pressure between the head 20 and the disk 12 the vapor may condense between these two components to form the liquid bearing. This state of supersaturation occurs when the partial pressure of the vapor is greater than 1.
The following is an example of a vapor based system. One milligram of a hydrocarbon-based oil such as squalene may be applied to an activated carbon absorbent patch 48 (see
The read/write channel circuit 58 is connected to a controller 64 through read and write channels 66 and 68, respectively, and read and write gates 70 and 72, respectively. The read gate 70 is enabled when data is to be read from the disks 12. The write gate 72 is to be enabled when writing data to the disks 12. The controller 64 may be a digital signal processor that operates in accordance with a firmware and/or software routine(s), including a routine(s) to write and read data from the disks 12. The read/write channel circuit 58 and controller 64 may also be connected to a motor control circuit 74 which controls the voice coil motor 36 and spindle motor 14 of the disk drive 10. The controller 64 may be connected to a non-volatile memory device 76. By way of example, the device 76 may be a read only memory (“ROM”). The non-volatile memory 76 may contain the firmware and/or software routine(s) performed by the controller.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
