A LOAD CELL OF A DISK BURNISHING MACHINE

BACKGROUND

[0001] Disk burnishing/wiping machines are often used to burnish/wipe both sides of a disk surface (such as a fabricated disk substrate for a magnetic recording system of a hard disk drive) to ensure particles and other debris are removed and thereby make the disk surface cleaner. In this process, a disk is clamped to a spindle which rotates the disk during the burnishing process. While the disk is being rotated, two sides of a contact roller (pad) of the burnishing unit with a very fine abrasive tape move toward the disk surface simultaneously, and bring the tape surface against the disk surface with a certain pressure/force to burnish both sides of the disk surface. The particles on the disk surface are thereby removed and/or reduced. In a subsequent processing step that operates in a similar way, a wiping unit with a woven cotton tape can be applied to remove the debris on the burnished disk surface, making the disk surface smoother and cleaner consequently.

[0002] During the burnishing/wiping process, a significant parameter for process quality is the loading force which is exerted on the disk surface by the burnishing/wiping unit through the contact roller or pad. For high product yield and positive testing results, it is best that the applied loading force is very accurate and consistent. More specifically, it is best that side-to-side loading force variations and machine-to-machine loading force variations are minimal or non-existent. To achieve this, the load cell, which measures the loading force, needs to be calibrated accurately and repeatedly.

[0003] In commonly used burnishing/wiping machines, a small load cell is tightly glued in a load cell bracket which is attached in a vertical orientation to a load force adjustment mechanism. The control and feedback wiring of the load cell are routed through various machine components, and are thus hidden inside. As such, it can be difficult to calibrate the load cell for a number of reasons. First, space limitations in the burnishing machine often do not allow existing load cell calibration tools to be used. Second, the load cell is small and often positioned vertically in the burnishing machine, which can make calibration extremely difficult or virtually impossible without dismantling it. At the same time, the load cell is tightly glued to the load cell bracket, and thus dismantling it will most likely damage the load cell. Third, the load cell control/feedback wiring is hidden inside the machine and it is troublesome to disconnect this wiring. Fourth, a small protrusion on load cell surface, which effectively is the force measuring surface of the load cell, can make it difficult to balance any calibration tool on the protrusion. No calibration method or tools have been developed that effectively address these problems.

[0004] For these reasons, a calibration method for this kind of load cell is highly desirable for the disk fabrication industry. In addition, it is desirable that any such calibration method be practicable with high accuracy and good repeatability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a schematic cross sectional view of a calibration system for performing in situ testing of a load cell of a disk burnishing machine, where the calibration system includes a weight holder, a weight, and various components of the disk burnishing machine in accordance with one embodiment of the invention.

[0006] FIG. 2 is a cross sectional view of the weight of the load cell calibration system of FIG. 1 in accordance with one embodiment of the invention.

[0007] FIG. 3 a is a top perspective view of the weight holder and the weight of the load cell calibration system of FIG. 1 , where the weight holder includes a machined hole and an adjustment screw and is spaced apart from the weight in accordance with one embodiment of the invention.

[0008] FIG. 3b is a bottom perspective view of the weight holder and the weight of the load cell calibration system of FIG. 1 in accordance with one embodiment of the invention.

[0009] FIG. 3c is a top perspective view of the weight holder and the weight of the load cell calibration system of FIG. 1 after the weight has been inserted into the machined hole of the weight holder in accordance with one embodiment of the invention.

[0010] FIG. 4a to 4d illustrate a sequence of perspective views of a disk burnishing machine, a weight holder, and a weight during an in situ process for testing a load cell within the disk burnishing machine in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

[0011] Referring now to the drawings, embodiments of systems and methods for performing in situ testing of a load cell disposed within a disk burnishing machine are illustrated. The systems can include a load cell bracket attached to a component of the disk burnishing machine, where the load cell to be tested is mounted within the load cell bracket and has a force measuring surface. The load cell bracket can be positioned such that the force measuring surface of the load cell faces a direction that is about opposite to a direction of gravity. The systems can further include a preselected weight and a weight holder configured to receive the preselected weight, where the weight holder is configured to be mounted to the load cell bracket and aligned with the load cell. The preselected weight can be positioned within the weight holder, once it has been mounted and aligned, and on the force measuring surface of the load cell. The load cell can then be tested, calibrated, and/or replaced if necessary.

[0012] The methods can involve providing a load cell bracket attached to a component of the disk burnishing machine, where the load cell is mounted within the load cell bracket and has a force measuring surface, moving the load cell bracket such that the force measuring surface of the load cell faces a direction that is about opposite to a direction of gravity, aligning and mounting a weight holder on the load cell bracket, installing a preselected weight within the weight holder and on the force measuring surface of the load cell, and determining whether a weight measurement of the load cell is within a preselected tolerance of a weight of the preselected weight. In some embodiments, if the load cell is not within the preselected weight tolerance, then the load cell can be replaced.

[0013] The systems and methods can provide a fast, on-site accurate calibration with good repeatability. In several embodiments, the weight holder is configured to receive the calibrated weight in a precisely machined circular hole. This hole holds the weight and also enables the weight to balance on a protrusion (e.g., force measuring surface) of the load cell. The precisely machined hole and ability to properly balance on the protrusion can enable accurate and repeatable loading force readings.

[0014] It shall be appreciated by those skilled in the art in view of the present disclosure that although various exemplary fabrication methods are discussed herein with reference to magnetic recording disks, the methods, with or without some modifications, may be used for fabricating other types of recording disks, for example, optical recording disks such as a compact disc (CD) and a digital-versatile-disk (DVD), or magneto-optical recording disks, or ferroelectric data storage devices. [0015] FIG. 1 is a schematic cross sectional view of a calibration system 100 for performing in situ testing of a load cell 102 of a disk burnishing machine, where the calibration system 100 includes a weight holder 104, a weight 106, and various components of the disk burnishing machine in accordance with one embodiment of the invention. The weight holder 104 includes a circular hole 104a, precisely machined, for receiving the weight 106. The weight holder 104 is mounted on a load cell bracket 108 of the burnishing machine. The load cell bracket 108 is mounted to one or more other components 110 of the disk burnishing machine. The load cell 102 is glued and thereby effectively embedded in the load cell bracket 108. The load cell 102 is coupled to a digital indicator 112 by cell wiring 114. The weight 106 has been placed within the machined hole 104a of the weight holder 104 and rests on a force measuring surface 102a (e.g., a top surface of the small centrally located protrusion) of the load cell 102. From this position, a user of the calibration system can determine whether the measured weight of the load cell 102 is within a preselected tolerance of the weight 106 (e.g., a preselected weight having a well known and accurately determined weight). If the measured weight is not within the preselected tolerance, the user can replace the load cell. In some embodiments, the user may instead recalibrate the load cell 102 and/or digital indicator 110 to have a more accurate reading based on the degree of error in the load cell 102.

[0016] FIG. 2 is a cross sectional view of the weight 106 of the load cell calibration system 100 of FIG. 1 in accordance with one embodiment of the invention. The weight 106 is precisely machined to have a height (H) and a diameter (D) suitable for a clearance fit with the machined hole 104a of the weight holder 104. In a number of embodiments, the weight 106 has a flat or substantially flat top surface to support an additional weight 116.

[0017] FIG. 3a is a top perspective view of the weight holder 104 and the weight 106 of the load cell calibration system 100 of FIG. 1, where the weight holder 104 includes a machined hole 104a and an adjustment screw 104b and is spaced apart from the weight 106 in accordance with one embodiment of the invention. In operation, the adjustment screw 104b can be used to secure the weight holder 104 to the load cell bracket 108. Once the weight holder 104 is mounted to the load cell bracket 108, the weight 106 can be placed in the hole 104a and on the load cell 102 (see the configuration of FIG. 1 for example) such that the load cell can be tested for accuracy. [0018] As to the design of the circular machined hole 104a of the weight holder 104, the machined hole 104a functions as both a weight housing and a guide for the weight 106. Therefore, in several embodiments, it can be precisely machined. For example, in several embodiments, the hole should be precisely machined with the allowable size tolerance (diameter, height), form tolerance and position tolerance (e.g., circularity, cylindricity, and perpendicularity tolerances) to ensure that the weight 106 is balanced or about balanced on the load cell 102a.

[0019] In some embodiments, the side surfaces defining the hole 104a should be machined sufficiently smooth as to allow the weight to be inserted inside in a smooth fashion with relatively small clearance. In several embodiments, the hole's height should be controlled properly (not too high and not too low) to avoid allowing the weight to tilt and thereby generate inaccurate readings on the load cell indicator.

[0020] In one embodiment, for example, the machined hole 104a has a roundness tolerance of plus or minus 15 microns (e.g., about 15 microns), a cylindricity tolerance of plus or minus 15 microns (e.g., about 15 microns), an average surface roughness (Ra) of less than 1.6 microns (e.g., about 1.6 microns), and a perpendicularity tolerance with respect to a bottom surface of the hole of plus or minus 15 microns (e.g., about 15 microns). The hole 104a can also have a position tolerance of plus or minus 20 microns (e.g., about 20 microns). Where the term "about" is used herein in describing a parameter, a 5 to 10 percent tolerance, or other customary tolerance in the art, might be expected.

[0021] In one embodiment, each of the surfaces of the weight holder 104 can have a flatness tolerance of plus or minus 25 microns (e.g., about 25 microns). In one embodiment, the weight 106 can have a roundness tolerance of plus or minus 15 microns (e.g., about 15 microns), a cylindricity tolerance of plus or minus 15 microns (e.g., about 15 microns), and an average surface roughness (Ra) of less than 1.6 microns (e.g., about 1.6 microns).

[0022] In other embodiments, the weight holder 104 and weight 106 can have other suitable tolerances.

[0023] The weight 106 can be designed as shown in FIG. 3 a and FIG. 2 (see also FIGs. 3b and 3c). In several embodiments, the illustrated weights provide a solution to calibrate the load cell with one or more weights. That is, additional weights can be placed on the top surface of the weight 106 to ensure proper calibration for greater overall weight. [0024] In the embodiment illustrated in FIG. 3a and FIG. 2, the weight 106 has a preselected shape defined by a first cylindrical portion and a second cylindrical portion, where a diameter of the first cylindrical portion (e.g., head portion) is greater than that of the second cylindrical portion (e.g., shaft portion). In such case, the second cylindrical/shaft portion is configured to fit within the hole 104a, and the first cylindrical/head portion includes a substantially flat top surface area configured to support a second weight.

[0025] As to the second cylindrical portion (e.g., shaft portion) of the weight 106, it can be precisely machined with allowable size tolerances, form and position tolerances, and good smoothness as described above. In several embodiments, the diameter of the shaft portion of the weight should be machined to be slightly smaller than that of the hole 104a of the weight holder 104, while the height of the shaft portion is expected to be slightly greater than that of the hole to avoid allowing the head portion to rest on the weight holder during calibration. In one embodiment, the weight 106 has a weight tolerance of plus or minus 0.1 grams (e.g., about 0.1 grams).

[0026] As described above, the weight 106 can be designed to have the flat top surface to allow additional weights to be added for calibrating a range of loading forces for the load cell 102. For example, in some embodiments, the calibration process may involve starting with a 20 gram weight and then adding additional 10 or 20 gram weights all the way up to about 100 grams. In one such embodiment, weights of 20, 40, and 60 grams can be used for calibration. In some embodiments, the weight top surface can have other shapes conducive to supporting one or more precise weights. For example, in one embodiment, the weight has a simple cylinder shape.

[0027] FIG. 3b is a bottom perspective view of the weight holder 104 and the weight 106 of the load cell calibration system 100 of FIG. 1 in accordance with one embodiment of the invention. As can be seen in FIGs. 3a and 3b, the weight holder 104 has a main body having a rectangular block shape having a top surface and a bottom surface, where the hole 104a extends from the top surface to the bottom surface, and where the top surface and the bottom surface each have a larger surface area than that of the other sides of the block shape. In addition, the weight holder 104 has two side walls extending from the bottom surface of the main body along the longer edges of the bottom surface. The hole 104a of the weight holder 104 includes a counter-bore portion 104c at the bottom surface. This counter-bore portion 104c can provide clearance to ensure that the weight holder 104 does not make contact with the load cell 102 after alignment and mounting (see FIG. 1). The adjustment screw 104b can be advanced through a threaded hole in one of the side walls of the weight holder 104 by turning the screw 104b.

[0028] As to the design of the locating surface (e.g., bottom surface coming into contact with the load cell bracket), it is shaped to effectively fit with the top surface of load cell bracket 108 (see FIG. 1). The adjustment screw 104b provides the capability to fine-tune and secure the weight holder 104 horizontally (see FIGs. 3a to 3c). More specifically, the adjustment screw 104b can provide a lateral force to the load cell bracket 108 to secure the weight holder 104 to the load cell bracket 108 and/or align the hole 104a of the weigh holder 104 over the load cell 102 (see also FIG. 4c).

[0029] In a number of embodiments, the weight holder 104 is shaped (e.g., the locating surface with the hole 104a and the counter-bore portion 104c) such that the weight holder 104 does not make contact with the load cell 102 after alignment.

[0030] FIG. 3c is a top perspective view of the weight holder 104 and the weight 106 of the load cell calibration system 100 of FIG. 1 after the weight 106 has been inserted into the machined hole 104a of the weight holder 104 in accordance with one embodiment of the invention.

[0031] FIG. 4a to 4d illustrate a sequence of perspective views of a disk burnishing machine 200, a weight holder 204, and a weight 206 during an in situ process 300 for testing a load cell 202 within the disk burnishing machine 200 in accordance with one embodiment of the invention.

[0032] In FIG. 4a, the process 300 first provides (302) the disk burnishing machine 200 which is configured to burnish a disk and includes a load cell bracket 208 attached to a component of the disk burnishing machine 200. In such case, the load cell 202 (not visible in FIG. 4a but see FIGs. 4b and 4c) is mounted within the load cell bracket 208 and includes a force measuring surface 202a (not visible in FIG. 4a but see FIGs. 4b and 4c). In this stage of the process (302), the load cell bracket 208 is vertically oriented such that the load cell 202, though not visible, is vertically oriented to measure the force associated with the spring loaded shaft directed into the load cell bracket 208.

[0033] In FIG. 4b, the process moves/rotates (304) the load cell bracket 208 such that the force measuring surface 202a (e.g., central protrusion) of the load cell 202 faces a direction about opposite to the direction of gravity. In such case, the load cell bracket 208 and load cell 202 have effectively been horizontally oriented. In several embodiments, this adjustment of the load cell bracket 208 can prepare it to receive the weight holder and ultimately the calibration weight. In one embodiment, the movement/rotation of the load cell bracket 208 can involve slight dismantling of the bracket 208 and the related spring loaded shaft.

[0034] In FIG. 4c, the process aligns and mounts (306) the weight holder 204 on the load cell bracket 208. The adjustment screw 204b can be used to securely mount the weight holder 204 to the load cell bracket 208. A user, possibly using the adjustment screw 204b, can align the hole 204a of the weight holder 204 to be directly over the load cell 202.

[0035] In FIG. 4d, the process then installs (308) a preselected weight 206 within the weight holder 204 and on the force measuring surface (not visible in FIG. 4d but see 202a in FIG. 4b) of the load cell (not visible in FIG. 4d but see 202 in FIG. 4b). In several embodiments, the process then determines (310) whether the weight measurement of the load cell is within a preselected tolerance of the expected weight of the preselected weight 206. In a number of embodiments, if the measurement is not within a preselected tolerance of the expected weight, the load cell is replaced. In other embodiments, the load cell and or display may be calibrated and adjusted to compensate for the load cell inaccuracy.

[0036] In several embodiments, the calibration process 300 advantageously does not require the disk burnishing machine to be disassembled.

[0037] In one embodiment, the process can perform the sequence of actions in a different order. In another embodiment, the process can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously. In some embodiments, additional actions can be performed.

[0038] Embodiments of the invention can provide a number of advantages. For example, in several embodiments, the invention provides high accuracy and good repeatability where embodiments of the methods described herein use the calibrated weight as a gauge and the precisely machined circular hole as a weight guide to ensure accurate and repeatable calibration. In several embodiments, the invention enables in situ calibration without dismantling load cell. More specifically, these embodiments can accommodate the limited space of a disk burnishing machine and do not require fully dismantling the load cell and/or its control/feedback wiring which makes the existing machine's digital indicator for the load cell usable for calibration. Among other things, this avoids bringing in an additional indicator, and enables fast, in situ calibration. [0039] In several embodiments, the invention can also involve simplicity in design and fabrication where the calibration tools can effectively consist of a cylindrical weight and its holding fixture only. In such case, the calibration tools can be easily fabricated with relatively low cost. In several embodiments, the calibration tools described herein can be easily employed such that they provide an easy and practical way to locate (e.g., attach to) the load cell bracket. In several embodiments, the calibration tools described herein easily provide for calibration of a range of load forces by enabling the addition of standard weights directly onto a flat top surface of the weight.

[0040] While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.

[0041] The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event, state or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other suitable manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.