Television – Special applications – Manufacturing
Reexamination Certificate
1999-11-01
2002-10-15
Kelley, Chris (Department: 2613)
Television
Special applications
Manufacturing
C348S094000, C382S151000, C382S218000
Reexamination Certificate
active
06466257
ABSTRACT:
FIELD OF INVENTION
This invention relates to the field of measurement of orientation and location of magnetic recording sliders within a head stack assembly.
BACKGROUND OF THE INVENTION
In a hard disk drive there are one or more disks rotating on a common spindle, which store magnetic information on their surfaces. For each magnetic surface a suspension or Head Gimbal Assembly (HGA) is provided. A HGA consists of a slider, a flexure, a load beam, a mount plate, and electrical leads, which carry signals to and from the head. The slider has a read/write head, which magnetizes small areas or domains on the surface of the disk. Typically, these magnetized areas are organized in the form of tracks (e.g., concentric tracks). The slider also has an air bearing surface (ABS) fabricated on the side facing the disk. The shape of the ABS generates a pressure distribution underneath the slider as air is dragged between the slider and rotating disk; this pressure distribution tends to push the slider away from the disk. The slider is connected to the load beam via a flexure, which is a flexible member that allows the slider to pivot in the pitch (transverse axis) and roll (longitudinal axis) directions. The load beam imposes a counteracting force onto the slider to balance the pressure force. The counteracting force is called the “gram load”. A method to support the HGA's over the disks is to attach them on a single metallic piece with multiple arms. The metallic piece commonly known as an actuator is pivoted around a bearing so that the magnetic read/write elements on the slider reach various areas of the magnetic surface of the disk. A set of HGA's mounted on an actuator is called a Head Stack Assembly (HSA). The actuator arm has a sufficient length such that the mounted HGA's reach to the very inside tracks of the disk. Every HGA within a HSA needs to be precisely aligned relative to each other to ensure that all sliders can access the maximum allowable area on the disk. The symmetry axis, at which each HGA emanates radially from the pivot axis of the actuator is called the longitudinal or x-axis. The y-axis as the second axis is perpendicular to the x-axis and parallel to the disk surfaces. The magnetic elements of all sliders in the HSA need to be aligned to the same y-position to a close tolerance. Any deviation from the specified y-position is called y-misalignment. It is caused either by misalignment of the slider on the load beam or misalignment of the HGA on the actuator arm. One of the objectives of the current invention is to measure any y-misalignment of the sliders.
The distance between the read/write head and the disk surface is called the “flying height”. It is typically below 100 nm. The main factors that affect the flying height are: the gram load, the nature of the ABS, the mounting of the slider on the flexure, the mounting of the HGA on the HSA, and the Roll Static Attitude (RSA) of the slider. RSA is a tilting of the slider around the x-axis in a free state before it is flying over the disk and can change during the HSA assembly process.
Magnetic recording is a “near-field” process, whereby the reading and writing by the read/write head occurs in close proximity to the disk surface. To increase the areal density, it is essential to reduce the average flying height and flying height variations of the sliders, which hold the magnetic recording heads. Unintentioned alterations of the RSA and the y-misalignment during the manufacturing of head stack assemblies change the aerodynamic properties of the air bearing surface and the even distribution of the gram load thereon. RSA and y-misalignment of the sliders occur especially during the handling and the swaging process by which the HGA is attached to the actuator. Both result in flying heights and flying height variations that can exceed the predetermined limits. To minimize these alterations, tight manufacturing tolerances and a reliable quality control are necessary.
U.S. Pat. No. 5,588,200 for instance describes a method and tool to examine individual suspension assemblies or HGA's. In the disclosed method an auto-focus vision system takes perpendicular distance measurements of several reference points of the air bearing surface of one slider. These reference points define a plane whose orientation and location are compared with control parameters. This method is space-consuming, because it requires the user to access the air bearing surface along at least one perpendicular or near-perpendicular direction. The close distance between the sliders in a head stack assembly make the air bearing surfaces inaccessible for the auto-focus vision system. The disclosed method is therefore of no use for post-assembly control.
U.S. Pat. No. 5,636,013 discloses methods to take measurements on the HGA level of orientation and z-location of sliders or suspension parts close to the slider. The z-location is recognized as a distance perpendicular to the air bearing surface of the slider. The reflection angle of a laser beam directed onto an optically reflective surface is thereby used to retrieve information about the sliders orientation. The z-location is measured simultaneously by an autofocusing system. This method is space-consuming, because it requires the user to access the air bearing surface along at least one perpendicular or near-perpendicular direction. This method is not useable for measurements on a head stack assembly for the same reasons as described under US. Pat. No. 5,588,200.
The general use of the air bearing surface as reference plane for control measurements is limited by additional incorporated three dimensional features. The air bearing surface controls the floating performance of the slider on the air stream driven by the spinning disk surface. It has more and more channels, pads and other three dimensional features added as the state of the art advances. Hence, the quality of the reflection is reduced. The reduced reflection quality in addition to limited available space between sliders within a head stack assembly make the direct optical access to the air bearing surfaces for maeasurements in the head stack assembly highly impractical.
An instrument based on U.S. Pat. No. 5,636,013 and marketed by Brumco Inc. performs the measurements on sliders within a head stack assembly. The instrument uses a miniature mirror placed between two air bearing surfaces. The mirror deflects a laser beam onto the air bearing surface, captures and transmitts the reflection via an optical lens system onto a scale. There it can be inspected. In the practical use of this instrument the variation of the measurement results exceeds the orientation and location tolerances of the sliders to be analyzed.
There is a need for a reliable and precise method and apparatus to measure the amount of RSA and the y-misalignment of each individual slider within the finished head stack assembly. The method and tool needs to be utilized for intermediate quality control within an industrial disk manufacturing. This application discloses such a solution.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide an apparatus and a method to measure the y-misalignment and roll static attitude of sliders within a head stack assembly.
It is a further object of the present invention to utilize a geometric element on the deposited end of the slider with a predetermined position and orientation to provide a reference for the measurement process.
It is another object of the present invention to provide a fixture having an assisting mechanism for aiding in the measurement process.
It is an additional object of the present invention to provide an automated apparatus to systematize the measurement process.
The above objects and advantages, as well as numerous improvements attained by the apparatus and method of the invention are pointed out below.
SUMMARY
The method and apparatus or tool for measurement of roll static attitude and y-misalignment of a magnetic recording slider within the head stack assembly
Baugh Eric Gordon
Flickner Myron Dale
Fontana, Jr. Robert Edward
Olson Stephen Arnold
Singh Gurinder Pal
International Business Machines - Corporation
Kelley Chris
Lumen Intellectual Property Services Inc.
Parsons Charles
LandOfFree
Method and tool for measurement of roll static attitude of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and tool for measurement of roll static attitude of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and tool for measurement of roll static attitude of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3000421