Magnetic disk drive

Details Magnetic disk drive Magnetic disk drive

1996-12-31

2002-03-19

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S077030

Reexamination Certificate

active

06359746

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk drive.
A magnetic disk drive is used to record information in a plurality of concentric circular tracks and reproduce recorded information by rotating a magnetic recording medium of a disk type called a magnetic disk and by means of a magnetic head placed in an arbitrary radius position on the magnetic disk.
In such a magnetic disk drive, as a system of flying the magnetic head on the magnetic disk extremely slightly, e.g. 100 nm, by using the dynamic pressure effect of air, a fixed magnetic disk drive and a magneto-optical disk drive are available. In a drive like these, a given load is mechanically applied to a magnetic head in the direction of a magnetic disk by a suspension which supports the head, and this magnetic head is flied at flying height in which a force produced by a dynamic pressure bearing and the load given by the suspension are balanced.
The magnetic head moves to an arbitrary position on the magnetic disk. However, since the speed of an air flow passing through an air bearing increases more in an outer peripheral position than in an inner peripheral position, a flying force produced by a dynamic pressure air bearing increases and flying height also increases. There is a problem that reduction in a recording density is greater closer to the outer circumference as there is a negative correlation between this head flying height and the recording density. As methods of solving this problem and maintaining the recording density uniform in inner and outer circumferences, one to keep the flying height constant by providing an angle between the magnetic head and the air flow and one to attain the same purpose by adding some effective changes to the form of the bearing are known. However, by the former method variations in the flying height cannot be reduced so much though the air bearing section is simplified, and by the latter processing of the form of the air bearing section is difficult and besides the flying height cannot be made accurately constant.
In addition to the difficulty of making uniform the flying characteristic of a single magnetic head in every track position, it is difficult to make uniform the flying characteristics of a plurality of heads. That is, other than the air bearing section there are a great number of factors in which differences are generated, such as a suspension attaching position, a suspension load and the like, making it practically impossible to remove a difference in flying height among the heads. Thus, under the circumstances, some freedom is given to designing of a drive expecting such nonuniformity in characteristics.
As for cases where the head flying height variations due to a change with the lapse of time after the magnetic disk drive is assembled and the drive is set in an environment in which atmospheric pressure is extremely low, such as in highlands or the like, conventionally there have been no methods found to make the head flying height optimum.
The above-described magnetic disk drive in which the magnetic head is flied generally uses a method called CSS (contact/start/stop) of bringing the head into contact with the magnetic disk when the disk starts rotating and flying the head only when the number of rotations thereof increases. Since a load on the magnetic head is given by the suspension, almost the same load is applied at the time of contact as at the time of flying. As a result, there is a possibility that the magnetic disk may be destroyed by the load on the magnetic head at the time of performing the CSS. It is preferable for the load on the magnetic head to be big in order to improve stability against external disturbances, etc., at the time of flying. Generally, however, a light load of 3 to 10 grams is used so as to prevent destruction of the head.
Also, the dynamic pressure air-bearing mechanism has a sort of equivalent spring characteristic. In the case where acceleration is exerted from a source external to the drive due to a disturbance such as vibrations, therefore, the resulting shock fluctuates the flying height (i.e., the position) of the magnetic head slider. In recent years, the recording density has been increased with the increasing storage capacity of magnetic disk drives. A very low-flying structure has been developed with the flying height minimized. As a result, fluctuations of flying height due to disturbances causes an unstable write/read operation of the magnetic head for an increased error rate.
On the other hand, a method in which the magnetic head is not borne in air but kept in contact with the magnetic disk is available as a technique for increasing the recording density. A representative method is a floppy magnetic disk. A contact system has recently been employed, however, also for a fixed magnetic disk drive. In the contact system which has no fluctuations of flying height relatively stabilizes the position of the magnetic head. Nevertheless, air undesirably intrudes into a gap which is unavoidably formed between the magnetic head and the contact surface due to the fluctuations (surface roughness) of the surface of the magnetic disk.
With this reason, there are other methods by which the magnetic head is not flied but always brought into contact with the magnetic disk. Representative of them is a floppy disk and recently even for a fixed magnetic disk drive the use of this contact method has been proposed. Even in a case where the magnetic head is brought into contact with the magnetic disk, however, since air flows into spaces produced by ruggedness on a contact surface, contact surface pressure may be reduced when a sliding speed increases depending on the position of the magnetic head, the head touching may be deteriorated and S/N of a reproducing signal may be reduced. Thus, though a given pressing load is necessary for the magnetic head of a contact type, it is difficult to apply a sufficient load in order to prevent reduction in quality of the magnetic disk caused by sliding.
A load on the magnetic head is mechanically applied by a supporting spring such as a suspension and the like supporting the head. For this reason, if here are errors in manufacturing the magnetic head, the magnetic disk, etc., the load varies and this makes variations of flying height and pressure in contact surface, etc., to be big.
The contact system, like the air-bearing system, requires a certain degree of pressure load. It is necessary, however, to limit the load in order to avoid deterioration of the magnetic disk which otherwise might be caused by the sliding operation with the magnetic head. For this reason, the suspension (support spring member) for supporting the magnetic head and applying a minute load to it is very low in mechanical strength, resulting in a low resonance frequency due to the magnetic head and the suspension. Consequently, the magnetic head jumps up from the surface of the magnetic disk, especially when it is subjected to an external disturbance (a force such as a vibration having an acceleration) of a such a low frequency as to affect the mechanism of the magnetic disk and the magnetic head. The resulting increased distance between the magnetic head and the magnetic disk increases what is called the magnetic spacing, thereby making it difficult to produce a sufficient write/read signal characteristic. Also, due to the presence of fluctuations on the surface of the magnetic disk, the magnetic head is liable to jump up from the magnetic disk according as the resonance frequency due to the magnetic head and the suspension approaches the fluctuation frequency, thereby causing an unstable write/read signal characteristic.
In addition to the drive for mechanically obtaining the pressing force of the flying head, as disclosed in Japanese Patent Publication KOKAI No. 61-151839, there is available a drive for controlling flying height to be low by applying a voltage across the flying head and the disk in a device for eliminating a projection on the surface of the magnetic disk. According to this paper, the

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