CA1209258A - Controlled rotational start of lubricated magnetic disks - Google Patents

Abstract

Abstract In a magnetic recording disk file in which one or more magnetic sliders rest on the surfaces of the disks when the lubricated disks are not rotating, the initial acceleration of the disks at the start of rotation is limited, this limited initial acceleration serving to free the slider or sliders from any stiction forces tending to bind them to the disk surface.

Description

- ~2~2~i8 CONTROLLED ROTATIONAL START OF LUBRICATED M~GNETIC DISKS

Background of the Invention Field of the Invention This invention relates to magnetic recording disk files and relates more particularly to methods for overcoming forces tending to bind the magnetic head sliders to the disk surfaces when the disX or disks have been at rest.

Description of Prior ~rt In current magnetic recording disk files there have been problems encountered with the sliders containing magnetic heads tending to adhere to the surface of the disk or disks after the disk has been at rest. This adhering or stiction problem is aggravated by the presence on the disk surface of lubricant material which - studies have shown tends to puddle up between the disk surface and the slider when the disk is not in motion and the slider rests on the disk surface.

This stiction problem is a relatively new one in magnetic disk files. In early magnetic disk files, as exemplified by the IBM 2311, 2314 and 3330 disk drives, for example, the magnetic sliders were never in contact with the magnetic record surface (except in the event of an inadvertent malfunction). Instead, the sliders were removed from the disk area prior to powering down the.
disk drive and, upon powering up, were not repositioned over the disk area until the disks were rotating at a speed sufficient to generate an air-bearing for supporting the sliders in a "flying" mode above the , ~Z09~
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rotating disk surface. Hence, disk files of this type had no "stiction" problems between the slider and disk.

With the advent of the IBM 3340 disk drive in 1973, the "start-stop in-contact" mode of disk file operation was introduced, with a lubricant applied to the disk surface. This disk file and subsequent files permitted the sliders to contact the recording disk surface (usually in a non-data portion thereof) when the file was powered down, and were in contact with the surfaces when the file was powered up. It is in this latter situation that possible problems with stiction arise. The sliders in these files were configured to establish a self-generated air bearing to support the sliders above the disks when the disks had reached a certain rotational speed.

~ n the disk files involved here, the sliders are movable radially on the disk to be positioned over a selected one of a group of concentric recording trac~s.
The sliders are carried on a suspension assembly connected ultimately to a~ actuator. The slider and its suspension are somewhat fragile when subjected to tangential force. Such tangential force is just wha~is applied to the suspension when stiction is encountered.
As the disk begins rotation, the lubricant under the ~5 slider face tends to hold the slider, and as the disk continues to rotate substantial forces can be applied tangentially of the slider and suspension, resulting in damage to or destruction of the suspension, and possible damage to the disk sur~ace. This problem can be aggravated in situations where the motor which rotates.
the disk has a relatively high starting tor~ue. Such high starting torque is desirable to enable the disks to quickly come up to a rotational speed which will permit the generation of air bearings to support the sliders ~Z09~5~3 above the disk surfaces, thereby reducing the in-contact wear between the sliders and the rotating disks. However, such high start torque does put increased stress on the suspension assemblies.

Summary of the Invention In accordance with the present invention, less than full torque is applied to the disk drive motor at file startup, this reduced starting torque being maintained for a minimum length of time sufficient to permit the sliders to move free of the lubricant wetted areas. This reduced torque has been found to be very effective in freeing the sliders from the stiction forces which tend to bind them to the lubricant layer on the disk surfaces, without damage to the slider assemblies.

Brief Description of the Drawings Figure 1 is a schematic diagram of one embodiment of circuitry for implementing the present invention; and Figure 2 is a timing diagram illustrating the operation of the invention.

Description of the Preferred Embodiment The present invention may be employed in a disk file of a suitable type such as that shown in U.S. Patent 4,136,293.
Such a disk file includes a head/disk assembly (HDA) which contains a plurality of magnetic recording disks mounted on a shaft for common rotation by a drive motor which is external to the HDA. The HDA also includes a plurality of sliders carrying magnetic heads for magnetically cooperating with different concentric recording tracks on the disk surfaces.
In the above .;

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patent, the heads in the HDA are moved to different tracks by two actuators having coils which are movable in separate gaps of a common voice coil motor (VCM) structure.

In Figure 1, a dislc drive motor ll is coupled through a belt 12 to a pulley 13a in an HDA 13. Pulley 13a is connected t0 a spindle (not shown) in the HDA on which the magnetic recording disks are mounted, so that rotation of motor 11 results in rotation of the disks.

In accordance with the present invention, the initial disk acceleration is reduced until the sliders have left the lubricant-wetted area. Preferably, this initial disk acceleration is kept at 4 radians/sec/sec or less until the disks have rotated a sufficient amount to free the sliders from the liquid lubricant. Tnis results in the maximum forces on the suspension system being held to an acceptable level.

Since the disk drive motor tor~ue is proportional to the applied voltage s~lared, the motor's acceleration can be controlled by the voltage applied. Any convenient method can be used to reduce the motor voltage, such as resistors, transformers, a solid-state controller, etc.
Circuitry shown in the drawin~ can be used in reducing the initial acceleration, using resistors 15 to drop the voltage applied to the motor. As shown in Figure 2, when Relay 1 closes, reduced power is applied to motor 11 through resistors lS. Followillg a time delay, Relay 2 closes, bypassing resistors 15 and applying full line voltage to motor 12.

The technique of the present invention has been found tG be extremely effective in reducing or eliminating damage to slider suspensions and disks caused by stiction problems at disk file start up.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for reducing the stiction force existing between an air-bearing slider member and a rotatable magnetic recording disk on whose surface said slider member rests when said disk is not rotating, said slider member being mounted in a suspension assembly extending radially of said disk, comprising the step of limiting the initial acceleration of said disk at the start of rotation of said disk to reduce the transverse forces on said slider assembly.

2. A method in accordance with claim 1 in which said initial acceleration is limited to 4 radians per second per second or less.

3. A method in accordance with claim 1 in which said initial acceleration is limited by reducing the voltage applied to electric motive means for rotating said disks.