Active vibration suppression of glide head suspension arm

Details Active vibration suppression of glide head suspension arm Active vibration suppression of glide head suspension arm

1999-09-23

2003-12-23

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

Reexamination Certificate

active

06667844

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to slider suspension arms, and more particularly to a slider suspension arm having a bimorph sensor and bimorph actuator used to suppress vibration in the suspension arm.
As the density of data recorded on magnetic discs continues to increase, the flying height of magnetic transducers with respect to the disc must be reduced to accurately read and write information on the disc. As a result, the magnetic recording disc must accommodate the lower fly height of the transducer and the slider supporting it, meaning that the disc surface must be extremely smooth and uniform. In order to certify that a magnetic disc is adequately smooth for use in a disc drive system, glide height tests are performed on the disc.
In addition to the general requirement of reduced fly height, magnetoresistive (MR) heads are extremely sensitive to small physical defects in the surface of the disc, such as undulations on the disc surface and microscopic debris on the disc. When the MR head strikes a defect, there is a momentary frictional heating of the MR element, known as a thermal asperity. This heating effect increases the resistance of the MR head, which causes data errors and loss of information in reading the disc. Thus, it is important to ensure the surface of any disc is relatively free of defects which may adversely affect the ability of the MR head to function.
Thus, one of the final steps in manufacturing a disc is to perform a glide height test. In conducting a glide height test, a single disc is placed on a spin stand and the disc is spun at extremely high speeds, often approaching over 10,000 revolutions per minute (rpm). A glide head suspended on a suspension arm is moved across the surface of a disc as the disc is spun. A typical glide head often comprises a piezoelectric transducer mounted on an air bearing slider. During the glide height test, the glide head “flies” over a disc surface at a predetermined height above the disc surface, known as the glide height. If contact occurs between the glide head and a disk asperity or a defect, the glide head is forced to vibrate and deform.
The slider deformation results in corresponding deformation of the piezoelectric transducer, and creates a potential difference between the electrodes of the piezoelectric element. When the contact occurs, many vibration modes of the piezoelectric element and slider are excited simultaneously, and each mode generates a voltage at its specific frequency. Signals generated by the piezoelectric element are fed to a pre-amplifier and a band pass filter. A digital data acquisition system on the glide tester then processes the filtered data, which can then be used to determine whether the disc passes or fails the glide height test. Should the disc fail a glide height test, it is possible to use a burnishing head to attempt to smooth out surface asperities.
One problem in performing a glide height test is the potential for the suspension arm to experience vibrations during the glide height test. Vibrations occur in the suspension arm during glide tests due to a variety of causes. First, the windage created by the disc as the disc is spun is very strong and can create vibration in the suspension arm. Vibration can also occur as the suspension arm is moved across the surface of the disc by an actuator motor. Finally, should a minor defect be encountered on the surface of the disc, such a defect may also cause the suspension arm to vibrate. If the suspension arm begins to vibrate during a glide test, the results of the glide test are much less actuate. Vibration in the suspension arm results in an uneven fly height of the glide head. Uneven fly height in turn results in the glide head missing some defects, or over-detecting minor defects which may not have an effect on the ultimate functioning ability of the disc.
In addition to glide head suspension assemblies, the same problem occurs in other slider suspension assemblies. Vibrations in the suspension arm which carries a magnetoresistive (MR) head will similarly result in an uneven fly height of the MR head over the surface of a disc, which in turn adversely affects the ability of the MR head to read data from the disc and write data to the disc. Vibrations may also occur in suspension arms which carry burnishing heads. Vibrations in a burnishing head assembly result in an uneven fly height of the burnishing head, which adversely affects the ability of the burnishing head to accurately burnish a disc asperity.
Thus, there is a need in the art for a slider suspension arm which can counteract the effects of vibration occurring in the suspension arm as the slider is flown over a rotating disc.
BRIEF SUMMARY OF THE INVENTION
The present invention is an improved slider suspension assembly which acts to control and suppress any vibration which may occur in the suspension arm as the slider is moved over the surface of a rotating disc. Included as part of the suspension arm are two bimorph piezoelectric elements. A first piezoelectric bimorph element is attached to the top of the suspension, and a second piezoelectric bimorph element is attached to the bottom of the suspension. One of the piezoelectric bimorph elements acts as an actuator while the other element acts as a sensor.
As the suspension arm vibrates, a first piezoelectric bimorph element acts as a sensor. The vibration in the suspension arm causes the first piezoelectric bimorph element to likewise vibrate. As the first piezoelectric bimorph element is deformed due to the vibration, it generates a voltage. The voltage indicates the bending vibration frequency and amplitude of the suspension arm. Because the bending vibration of the suspension arm is repetitive, the other piezoelectric bimorph element acting as an actuator can be used to actively damp the vibration by providing a voltage signal to the second element which is 180 degrees out of phase with the sensed signal. Once the vibration of the suspension arm is damped, a precise fly height of the slider can be achieved.


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