Patent Application
20110034107
The present invention is directed to a method and apparatus for reciprocal or alternating polishing, and in particular, user-controlled preferential material removal.
Reciprocal excitation produces a relative motion responsible for material removal at the interface between an abrasive article and a work piece. The relative motion between the abrasive article and the work piece causes asperities to interlock and high stresses producing wear. During ultrasonic excitation a relative velocity is produced between the abrasives and the work piece that varies from zero to a maximum back to zero. The hydrodynamic film formed at the interface is negligible promoting maximum wear at the interface.
The present invention is directed to an ultrasonic assembly with user controlled preferential material removal. The present ultrasonic polishing has wide application to polishing slider bars for hard disk drives, optical fibers, lenses, and the like.
A series of air/fluid channels located behind an abrasive article. The fluid pressure in the fluid channels can be changed to deform the abrasive article, causing localized high stresses between the abrasive article and a work piece. The localized high stress preferentially removes more material from the work piece at specific locations. Interference between the work piece and the abrasive article is controlled by the magnitude of the air/fluid pressure applied at the interface. An ultrasonic generator applies ultrasonic energy to the abrasive article with negligible out of plane motion.
The present invention is also directed to a method of polishing a work piece. A polishing pad is located on an excitation generator. The polishing pad includes a plurality of discrete fluid channels. The excitations generated oscillate or energize the abrasive article. An abrasive article is located on the polishing pad. Fluid pressure in one or more of the discrete fluid channels is selectively altered to selectively deform the abrasive article to preferentially remove material from the work piece.
In one embodiment a series of air/fluid ports are fabricated on the polishing pad to selectively deform the abrasive article, thus increasing or decreasing interference between the polishing article and the bar. This process may be very desirable for controlled sensor material removal as is the practice in disk drives, such as disclosed in U.S. Patent Application No. 2005/0071986 (Lackey et al.), which is hereby incorporated by reference.
In another embodiment, a series of pressure hoses are connected from the fixed base to the polishing pad to control the pressure in each air/fluid channel. The spatial distance between a series of sensors can be matched to the polishing plate channels to produce customized stress management at each work piece sensor. If the desired amount of wear is achieved at each sensor then the pressure is removed from the pressure channel causing no interference.
Reciprocal motion imparts interference between the work piece and the abrasive article and minimizes formation of a hydrodynamic film to maximize polishing and burnishing. Multiple lubricant viscosities can be used without the concern of interference mitigation due to hydrodynamic film formation. A boundary lubrication regime is preferably maintained throughout the polishing process.
Controlled interference between the abrasive article and the work piece can be maintained using a hydrostatic air bearing and/or preloaded gimbaled work piece holder. The work piece is presented to the abrasive article is such a fashion that the cutting forces emanating from the interaction are balanced and minimize chatter and vibrations. The work piece holder maintains stability during the polishing process.
Substrate actuation can impart preferred concave or convex shapes (crown, camber, etc.) to the work piece. Compact lapping tools capable of atomically smooth polishing bars. The floor space required for housing this tool is extremely small compared to spindle base lapping tools.
A variety of abrasive articles are suitable for use with the present a reciprocal motion assembly 20, such as for example, abrasive charged polymers, diamond charged flexible plates, diamond-like-carbon coated flexible plates, and the like. In one embodiment, the abrasive article includes a DLC film with a thickness of 50-200 nm with integrated cutting asperities with a height of 5-50 nanometers to provide high stress sites, and a thin film lubricant to provide boundary lubrication. Since deformation of the abrasive article 32 is typically in the nanometer range, the abrasive article 32 can be flexible, rigid, or semi-rigid.
Electro-mechanical system 48 including a moving base 44 with a magnet that is actuated by alternating current applied to coil 46. Upon energizing of the coil 46, the springs 36, 38 are bent out of plane, which causes the attached moving base 44 to undergo a reciprocating motion. The motion of the moving base 44 can be elliptical, orbital, circular, and the like. Additional coils 46 can optionally be provided to generate irregular motions.
Controller 70 selectively adjusts fluid pressure in each of the discrete fluid channels 54. Upon activation the controller 70 adjusts the fluid pressure in the fluid channels 54 to deform the flexible abrasive article 64 and to increase or decrease interference with the work piece 72 being ultrasonically polished (see
Positive pressure is applied to fluid channels 54A, 54B, 54C and 54E, while no pressure is applied to fluid channel 54D. The present method and apparatus allows for selective polishing of the individual sliders 74. The read/write heads and/or sensors 76 can be adapted to provide a signal proportional to the progress of the polishing operation. In one embodiment, the sensors 76 are height sensors. Various control mechanisms are known for monitoring the progress of the polishing process, such as the closed loop feedback system disclosed in U.S. Patent Application No. 2005/0071986 (Lackey et al.), which is hereby incorporated by reference. Consequently, controller 70 can be programmed to automatically control the pressure in the fluid channels 54 in accordance with the polishing requirements for the work piece 72.
Interference control between the work piece and the abrasive article can be achieved using a variety of techniques, including hydrostatic or hydrodynamic fluid bearings, and/or a gimballed interface. Various methods and systems for interference control suitable for use with the present reciprocal motion assembly are disclosed in U.S. Provisional Patent Application Ser. No. 61/232,425, entitled Dressing Bar for Embedding Abrasive Particles into Substrates, filed Aug. 8, 2009; Ser. No. 61/174,472, entitled Abrasive Article with an Array of Gimballed Abrasive Members and Method of Use, filed Jun. 30, 2009, all of which are hereby incorporated by reference.
In one embodiment, the various work pieces discussed herein are supported by a gimbal mechanism.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the inventions.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.
Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.
This application claims the benefits of the filing date of U.S. Provisional Patent Application Ser. No. 61/232,525 filed Aug. 10, 2009, which is entitled “Method and Apparatus for Ultrasonic Polishing” which is hereby incorporated herein in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61232525 | Aug 2009 | US |
