Patent Grant
7275408
The present invention relates generally to an apparatus and method for simultaneously adjusting parameters of a head suspension through the application of a laser beam to the head suspension. More particularly, the present invention is an apparatus and method for simultaneously adjusting at least the gram load and radius geometry height of a head suspension by scanning a spring region of the head suspension with a plurality of laser beam scan lines.
Head suspensions are well known and commonly used within dynamic magnetic or optical information storage devices or drives with rigid disks. The head suspension is a component within the disk drive that positions a magnetic or optical read/write head over a desired position on the storage media where information is to be retrieved (read) or transferred (written). Head suspensions for use in rigid disk drives typically include a load beam that generates a spring force and that supports a flexure to which a head slider having the read/write head is to be mounted. The load beam includes a mounting region at a proximal end, a rigid region at a distal end, and a spring region between the rigid region and the mounting region for providing the spring force. Head suspensions are normally combined with an actuator arm or E-block to which the mounting region of the load beam is mounted with a base plate so as to position (by linear or rotary movement) the head suspension, and thus the head slider and read/write head, with respect to data tracks of the rigid disk.
The rigid disk within a disk drive rapidly spins about an axis, and the head slider is aerodynamically designed to “fly” on an air bearing generated by the spinning disk. The spring force (often referred to as the “gram load”) generated by the load beam (when the load beam is at its “fly height”) urges the head slider in a direction toward the disk opposing the force generated by the air bearing. The point at which these two forces are balanced during operation is the “fly height” of the head slider.
Another important attribute of head suspensions is referred to as radius geometry height or “RG height.” This attribute or characteristic of the head suspension is the offset or distance that specific points or area of the rigid portion of the load beam of the suspension are displaced from a mounting plate in the mounting region of the suspension. RG height is an important characteristic to control, because it affects the torsional resonance characteristics of the load beam and thus affects overall performance of the head suspension assembly.
In addition to “RG height,” the load beam may be characterized by a parameter referred to as Delta Radius Geometry or ARG or “Delta Height.” This parameter measures the twist of the load beam. It is measured by finding the difference between RG height measured on each of two radius legs or arms. A twisted load beam can result in a suspension with poor resonance characteristics, in addition to possible distortion in flying attitude of the head slider. The twist affects windage, bending modes and torsional modes of the suspension. The “Delta Height” is thus seen to be the incremental height between the pair of legs in the spring region of the suspension.
The flexure typically includes a slider bond pad to which the head slider is attached. The flexure provides a resilient connection between the head slider and the load beam, and permits pitch and roll motion of the head slider and read/write head during movement over the data tracks of the disk in response to fluctuations in the air bearing caused by fluctuations in the surface of the rigid disk. The roll axis about which the head slider gimbals is a central longitudinal axis of the head suspension. The pitch axis about which the head slider gimbals is perpendicular to the roll axis. That is, the pitch axis is transverse to the longitudinal axis of the load beam, and crosses the roll axis at or around the head slider.
In order to store and retrieve data from magnetic or optical disks on which data is densely packed, it is necessary for the head slider to fly closely above the surface of the spinning data disk (on the order of 0.1 μm) without colliding with the disk (“crashing”). Further, because of the dense packing of data on magnetic or optical disks, it is important for the read/write head attached to the head slider to be able to read from or write to a relatively small area or spot on the disk.
The gram load provided by the spring region of the load beam is transferred to the flexure via a dimple or other pivoting structure that extends between the rigid region of the load beam and the flexure. The structure that extends between the rigid region of the load beam and the flexure is referred to herein as the “gimbal region” to distinguish from the “spring region” which, as used herein, refers only to the region adjacent a rigid mounting region, usually between the mounting region and the rigid region of the load beam. In the prior art, the spring region (which in some instances may be part of the load beam) was mechanically deformed, using a process of roll bending to impart a curvature to at least a portion of the spring region, typically moving the load beam out of plane from the mounting region (where, typically, a base plate was attached).
The prior art also included adjusting the spring region using a diode laser to thermally bulk heat the load beam in the spring region while the load beam was mechanically moved in an attempt to “trim” or correct radius geometry height. Also, reverse bending or “back bending” typically occurred in the process of manufacture of the head suspension, where the part was intentionally bent or plastically deformed one time, in a direction opposite to and after the rolling process is applied to the part to form the spring region. When the part was subsequently integrated into a head stack assembly, the suspension is “bent back” again to fit the heads between the discs. Lack of care in this subsequent bending process has been known to plastically deform the part, resulting in an error in gram load known as “load loss” or more particularly, “suspension gram load loss.” The phenomenon of suspension gram load loss is to be distinguished from “gram creep” or more properly “elastic recovery instability.” The term “recovery instability” refers to the portion of the strain that remains immediately after the stress is removed and disappears after a period of time. The phrase “elastic recovery instability” refers to instability in the “recovery” after adjustment of the head suspension. The present invention overcomes a substantial amount of the elastic recovery.
Moreover, the prior adjustment method described above was typically performed using three stations, with the individual head suspension entering a first station dedicated to measuring the head suspension radius geometry height and gram load, then passing the individual head suspension to a second station in which adjustments were made, after which that particular head suspension was transferred to a third station which measured the head suspension again. If the radius geometry and gram load were not both within specifications as measured by the third station, the part was rejected, because cycle times would be unacceptably long if the part were to be recycled through the series of stations. Furthermore, such parts are typically carried in a strip of, e.g., 12 for ease of processing. If one or some, but not all, of the parts in a strip were out of spec, the in-spec parts would be subject to additional handling if the strip were to be “recycled” through the stations, thus exposing good parts to potential degradation because of the additional handling.
From the above, it can be seen that there has been a continuing need to develop more efficient methods for correcting the RG height (more particularly the radius geometry height) and for adjusting the gram load. A method that provides precise error corrections for both height and gram load in a timely fashion, and that can be achieved without significant impact on other performance criteria of the head suspension is highly desirable. It is further desirable to be able to adjust delta radius geometry, if necessary, to eliminate or at least reduce twist in the load beam.
Techniques for adjusting only the gram load of the head suspension assembly after it has been rolled are generally known and disclosed, for example, in the Girard U.S. Pat. No. 5,832,764 and the Schones et al. U.S. Pat. No. 5,297,413. Briefly, one such method is a laser adjust technique. A known property of stainless steel members such as load beams is that the force they exert in response to attempts to bend them can be reduced through exposure to thermal energy. The functional relationship between the amount of force reduction and the amount of heat to which a member is exposed can be empirically determined. The light adjust method makes use of this empirically determined relationship to “downgram” or lower the gram load of load beams that have been purposely manufactured (e.g., through rolling operations of the type described above) to have an initial gram load greater than the desired gram load value.
Equipment for performing the light adjust method includes a clamp for clamping the mounting region of the suspension to a fixed base or datum, and a load cell for measuring the gram load of the suspension. A computer controlled actuator moves the load cell into engagement with the flexure and elevates the flexure to a z-height or offset with respect to the datum which corresponds to the specified fly height for the suspension (i.e., the gram load is measured at fly height). In practice, the measured gram load quickly rises toward its then-current value as the flexure is elevated. When the measured gram load reaches an upper range specification, the computer actuates or turns on a high intensity light to apply heat to the load beam. Since the applied heat reduces the actual gram load of the suspension, the measured gram load quickly peaks. Continued application of laser energy causes the measured gram load to decrease with time. The computer deactuates or turns off the light when the measured gram load has decreased to a predetermined set point, typically a load between the nominal or desired gram load and the lower range specification. Once the light has been turned off, the decrease in gram load quickly slows and reaches its minimum value (often at a gram load below the lower range specification) as the heat in the suspension dissipates. However, as the load beam continues to cool, the measured gram load increases and stabilizes at an equilibrium or final load value that is preferably within the specification range, and ideally close to the nominal specification. The final gram load is also measured following the light adjust procedure. This measurement is used by a computer to update a stored model (e.g., the setpoint) of the functional relationship between the amount of heat applied (e.g., light “on” time) and the gram load reduction, to optimize the accuracy of the results obtained by the light adjust procedure. It is to be understood that the above described light adjust procedure does not use any scanning movement to accomplish its goal. The light source in the above procedure is thus a general energy source, applying heat generally to the spring region.
Computer controlled mechanical bending procedures have also been used to adjust the gram load on load beams. The mechanical bending method makes use of an empirically determined relationship between the amount that the load beam is mechanically bent and the associated change in gram load. For a range of gram load adjustments that are typically performed by this technique, a simple linear regression line has been found to accurately describe this relationship. In practice, this technique is implemented by a computer coupled to a stepper motor-driven bending mechanism and a load cell. A model of the relationship between changes in gram load and the number of motor steps (i.e., the associated amount or extent of bending required) is stored in the computer. After the then-current gram load of the suspension is measured by the load cell, the computer calculates the required load correction (i.e., the difference between the measured and desired loads). The computer then accesses the model as a function of the required correction to determine the number of motor steps required to achieve the required load correction, and actuates the stepper motor accordingly. Once the load beam has been bent, the then-current gram load is again measured and used to update the model. Measured data from a given number of the most recently executed mechanical bends is used to recompute the regression line data prior to the execution of the next mechanical bend.
The air bearing head slider assembly is mounted to the flexure and the lead wires clamped to the load beam after the gram load of the suspension has been initially set using methods such as those described above. Unfortunately, the mechanical handling and assembly procedures involved in this manufacturing operation sometimes forces the gram load of the assembled head suspension assembly beyond the specification range. Since the gram load specification is so critical to proper disk drive operation, these out-of-specification head suspension assemblies cannot be used unless the gram load is readjusted to the specification range. A machine which uses both light-adjust and mechanical bending procedures to “regram” suspensions is shown in the Schones et al. U.S. Pat. No. 5,297,413.
RG height and ΔRG are important because of its relationship to head suspension resonance characteristics. In order for the head slider assembly to be accurately positioned with respect to a desired track on the magnetic disk, the suspension must be capable of precisely translating or transferring the motion of the positioning arm to the slider assembly. An inherent property of moving mechanical systems, however, is their tendency to bend and twist in a number of different modes when driven back and forth at certain rates known as resonant frequencies. Any such bending or twisting of a suspension causes the position of the head slider assembly to deviate from its intended position with respect to the desired track. Since head suspension assemblies must be driven at high rates of speed in high performance disk drives, the resonant frequencies of a suspension should be as high as possible.
As discussed in the Hatch et al. U.S. Pat. No. 5,471,734, the position, shape and size of the roll or bend in the spring region of a suspension, sometimes generally referred to as the radius geometry or profile of the suspension, can greatly affect its resonance characteristics. The radius geometry of a suspension must therefore be accurately controlled during manufacture to optimize the resonance characteristics of the part.
The present invention is intended to overcome the shortcomings of conventional methods for adjusting performance characteristics of a head suspension, particularly the radius geometry height and gram load of the head suspension. The technique of the present invention can provide sufficiently precise corrections to meet increasingly tight performance requirements on radius geometry height and gram load, while at the same time reducing the effect of suspension gram load loss on the head suspension. The present invention can also be performed at relatively fast cycle times, and can provide corrections that have limited impact on other performance parameters of the head suspension. In addition, the present invention is advantageous in that it involves minimal mechanical contact with the suspension.
The present invention includes a method of scanning a predetermined region (preferably the spring region) of the head suspension with a relatively narrow laser beam, in contrast to the prior art approach of using a relatively broad beam. Scanning the predetermined region of the head suspension with the narrow laser beam imparts heat to a very localized path in a controlled manner, to simultaneously adjust the radius geometry height (RGH) and gram load performance parameters of the head suspension by controlling the location and number of lines scanned by the laser beam in the spring region. In addition, the delta radius geometry (ΔRG) may be simultaneously adjusted by controlling the location and number of lines scanned with respect to the lateral (left and right) sides of the spring region. In the practice of the present invention, the spring region typically has one or more generally centrally located apertures or cutouts separating a first scan region from a second scan region transversely disposed with respect to the first scan region. A plurality of lines can be scanned in the first and second scan regions, with the lines being adjacent to each other and parallel to the transverse (pitch) axis of the head suspension. In such an embodiment, the lines preferably extend across the entire width of a first scan region and the second scan region, both located in the spring region, and each line causes a discrete amount of adjustment in the spring region to introduce an adjustment to the gram load and radius geometry height of the head suspension. The location of the central line of the plurality of lines and the number and spacing of the lines enables simultaneous or concurrent control of radius geometry height, delta radius geometry, and gram load, all based on stored data previously acquired for that type of head suspension.
Another aspect of the present invention includes an iterative, closed loop process for providing precise adjustments to the radius geometry height and gram load of a head suspension. In this aspect, a coarse adjustment is performed by scanning the scan region of the head suspension with the laser beam. The result obtained by the coarse adjustment is measured and a fine adjustment is performed by scanning the scan region a second time with the laser beam.
A still further aspect of the present invention includes an iterative process for providing precise adjustments to the delta radius geometry height in addition to the radius geometry height and gram load of the head suspension. In this aspect, separate adjustment of the left and right sides of the spring region is performed by scanning the left and right sides of the scan region in different locations with the laser beam. Additionally, the scanning may be performed in two steps, with a coarse adjustment typically on both sides followed a fine adjustment on one or both sides, if necessary and desired. In the practice of this aspect of the present invention, measurement of gram load and radius geometry height after each coarse adjustment is preferably used in a dynamic regression for optimizing gram load and RG height, and for adjusting the gram load and height interaction. If fine adjustment is made, a subsequent measurement of gram load and RG height is preferably used in a dynamic regression to optimize parameters for fine adjustment of the gram load and RG height.
In the practice of this aspect of the present invention, the amount of scanning, e.g., the number and location of the scan lines necessary to provide coarse correction of the RG height, ΔRG, and gram load is determined and memorized. Determining the location and number of scan lines necessary to correct the RG height, ΔRG, and gram load errors on subsequently processed head suspensions of the same type is accomplished by referencing stored data describing the relationship between angular deflection and the number and location of lines scanned in the various parts of the spring region of a head suspension load beam of that type. It is particularly to be understood that stored data is ordinarily maintained on a model by model (or type) basis, for retrieval and use with subsequent load beams of the particular type or model for which data has been stored.
The fine adjustment can be performed in a similar fashion, wherein the remaining RG height, ΔRG, and gram load error between the desired values and the actual values present in the head suspension after the coarse adjustment are first determined, and the amount of scanning necessary to compensate for the remaining errors is predicted. The prediction can be made by consulting stored fine adjustment data describing the relationship between the angular deflection and the number of scan lines scanned in the scan region of the head suspension. The number and or location of scan lines for the fine adjustment can be upwardly or downwardly adjusted based upon the stored data. It is to be understood that the stored data (in either a single data set or plural data sets) is to preferably encompass a range of values sufficient to enable both the coarse and fine adjustments to be carried out in this version of the present invention. It is to be further understood that segmenting or “binning” may be used in the process of updating the stored data. In this aspect, the data is partitioned into segments covering the expected range of values for unprocessed parts, so that historical data will be maintained for all segments of the range of possible values of the stored data, even when a long run of parts falls within a band considerably narrower than the full range of possible values.
Additionally, it has been found desirable to provide an indirect nitrogen purge during laser scanning, to enable the use of higher power levels without discoloration of parts scanned.
With reference now to the Figures, a disk drive 2 having a head suspension 10 suspended over a disk 4 is shown in
In use, a read/write head on head slider 22 reads and/or writes data to and from disk 4 in disk drive 2, and the head suspension 10 supports and aligns the head slider 22 over a desired location on disk 4 in response to signals received from a microprocessor (not shown). Disk 4 rapidly spins about an axis 9, and an air bearing is created by rotating disk 4. Head slider 22 is aerodynamically designed to “fly” on the air bearing between the surface of the disk 4 and the head slider 22. As head slider 22 flies over the air bearing, it is urged away from the surface of the disk 4 by the air bearing. Head suspension 10 provides a gram load spring force that counteracts the force of the air bearing and urges the head slider 22 toward the surface of the disk 4, reaching stable equilibrium at the “fly height” of the head slider 22. The specific positional orientation of head slider 22 provided by head suspension 10 at the fly height in relation to the surface of the disk 4 is commonly referred to as the “dynamic attitude” of the head slider 22.
As shown in greater detail in
Spring region 26 of load beam 12 provides a desired gram load that opposes the force exerted upon head slider 22 by the air bearing generated by rotating disk 4. Toward this end, spring region 26 can include a bend or radius that provides the desired gram load or force. The gram load generated by spring region 26 is transmitted to flexure 40 through rigid region 24 of load beam 12. A load point dimple 9 (not shown) that extends between the rigid region 24 and the flexure 40 can be used to provide a point of transfer for the gram load generated by spring region 26. The load point dimple also provides a point about which the head slider 22 attached to flexure 40 can gimbal in response to fluctuations in the air bearing.
Flexure 40 provides a resilient connection between head slider 22 and load beam 12, and is designed to permit head slider 22 to gimbal in response to variations in the air bearing generated by rotating disk 4. That is, minute variations in the surface of disk 4 will create fluctuations in the air bearing generated by the rotating disk 4. These fluctuations in the air bearing will cause slider 22 to roll about a longitudinal axis 11 of head suspension 10, and to pitch about a transverse axis 15. Longitudinal axis 11 is defined to extend along the center line of head suspension 10 and through the load point dimple, while transverse axis 15 is defined to be orthogonal to axis 11 and intersect axis 11 at the load point dimple between load beam 12 and flexure 40. Flexure 40 is designed to permit the slider 22 to gimbal in both pitch and roll directions in response to these air bearing variations. In the embodiment shown, flexure 40 is separately formed from load beam 12. It is to be understood that the head suspension assembly 10 shown here is a three-piece design made up of the base plate 14, load beam 12, and flexure 40. Flexure 40 preferably includes a flexure mounting region (not shown in detail) that overlaps and is mounted to the rigid region 24 of load beam 12 using spot welds or other known techniques. Flexure 40 also includes a gimbal region (not shown) that can extend beyond the distal end of load beam 12, to provide the compliance that permits slider 22 to gimbal in pitch and roll directions.
Flexure 40 may also include a trace assembly (not shown) that provides electrical interconnection between slider 22 and read/write drive circuitry (not shown) of disk drive 2 for connecting read and write signals to and from the read/write head on slider 22.
During the manufacture of suspensions 10, elongated carrier strips having a plurality of flat and unformed load beam blanks extending therefrom are chemically etched from thin sheets of stainless steel or other spring material. Carrier strips with flat and unformed flexure blanks are etched in a similar manner from sheets of stainless steel. During subsequent manufacturing operations any side rails 30, wire lead captures 32, load point dimples (not visible) and any other structures which extend upwardly or downwardly from the generally planar surface of the load beam 12 (i.e., in what is known as the z-height direction), along a z-axis 16 are formed on the load beam blanks by conventional mechanical forming procedures. Any structures on the flexure blanks requiring z-height deformation (e.g., load point dimples, not shown) are formed in a similar manner. After forming, the flexures 40 are welded to the distal ends of the load beams 12. The carrier strip is then cut or “detabbed” from the flexures 40. Baseplates 14 also are welded to the mounting regions 13 of the load beams 12 following the forming operations.
In another suspension design known as a two-piece design or integrated gimbal suspension (not shown), the flexure is etched in the distal end of the rigid region of the load beam. Portions of the integrated gimbal which extend from the planar surface of the load beam in the z-height direction are formed along with other structures on the load beam during the forming operation. A baseplate is typically welded to the mounting region after these load beam and integrated gimbal etching and forming operations.
As shown in
The result of forming the load beam 12 and assembling the flexure 40 and base plate 14 to the load beam 12 is shown in
High performance disk drive operation requires the air bearing head slider 22 to closely follow the rotating magnetic disk surface at a constant fly height. To meet this critical requirement, the gram load of the head suspension assembly 10 must be adjusted to a relatively tight specification range (defined in terms of upper and lower range specification gram loads above and below, respectively, the desired or nominal gram load).
Additionally, the radius geometry height (or RG height) is critical to proper operation of the head suspension assembly, particularly with respect to resonance characteristics, as has been mentioned above. As shown in
It is to be understood that
To measure RG height, the suspension is clamped to a datum or reference level in the region of the suspension where the base plate is located. In at least one prior art approach, variations in the thickness of the base plate affected the measurement for the reverse base product because the load beam was spaced away from the datum level by the thickness of the base plate.
Referring now to
In
Referring now also to
In a preferred embodiment, laser beam 62 is a continuous wave, focused laser beam which traverses and irradiates the spring region 26 to impart heat energy to the load beam and to provide precise adjustment of that portion of the spring region irradiated. Laser beam 62 preferably has a focused diameter of 30 micrometers.
A continuous wave fiber laser such as is available from SDL, Inc., of San Jose, Calif., model number SDL-FL20-4211-001, is preferred for laser 41, and a focused spot size diameter of between about 15 and about 60 micrometers have been found to be useful in the method of the present invention. Other lasers, such as, but not limited to an SDL FL 10 laser may be used in the practice of the present invention, as desired. Higher power levels have been found desirable to obtain more part response per scan line. However, such higher power levels can also result in discoloration of the part being scanned. To avoid discoloration, it has been found desirable to introduce an inert gas, preferably nitrogen, into the area where scanning is performed. To avoid mechanically disturbing the part being scanned, the inert gas atmosphere is preferably introduced indirectly, with one arrangement calling for introduction of 200 cubic feet per hour into the shroud around the part to be scanned, on each side, through ¼ inch tubing, taking care to avoid directing the flow at the part to be scanned.
In the region scanned by the laser, an elevated temperature isothermal is created on the irradiated surface along the path or scan line that the laser traverses. The scan line region is constrained by the cooler material surrounding the scanned area causing it to yield in compression. In this manner, the surface of the material irradiated will “curl” or bend towards the laser beam upon cooling. Through the selective scanning of the spring region, the spring region can be caused to bend in a predetermined and desired manner, which will in turn provide a desired adjustment to both the gram load and radius geometry height of the head suspension 10.
It is to be understood that the load beam is preferably initially formed with the spring region intentionally formed to an “overgram” condition, such that the gram adjust procedure performed in the practice of the present invention is used to reduce the gram load. The direction of RG height change is dependent on the scan location. To decrease RG height, the scans are located between the base plate 14 and the low point location. To increase RG height, the scans are located between the low point location and the rigid region 24. It has been found preferable with the one-sided gram adjust to have a minimum gram adjust for obtaining a maximum RG height adjustment. Typically, for every 20 milligram change in a gram load, 1 μm change is possible in RG height. However, it is to be understood that such adjustment parameters are dependent on material type, thickness, and width, part design and laser specifications.
It has been found preferable to make the length of the spring region 26 in the longitudinal direction 1.5 mm for full thickness load beams, and about 0.8 mm for load beams having a partially etched spring region. Other values may be used, depending upon the amount of adjustment required. The location of the bend radius affects the range in the positive or negative direction for adjusting Radius Geometry height. For equal ranges, the low point location is preferably located in the middle of the spring region. It is to be understood that the area available for scanning is a factor in determining the adjustment range.
In the practice of the present invention it is desired that each individual load beam will be rolled to a higher than desired gram load in a conventional forming machine. The entire radius region is then preferably stabilized using a diode laser to bulk heat the spring region rolled. This is done to keep the gram creep during the bake test the same as what would be expected if the entire part was heat treated to stabilize it. The load beam can be subjected to intentional back bending after the rolling operation and prior to laser stabilization to reduce suspension gram load loss at the time of head stack assembly. It is to be understood that this intentional back bending takes place prior to processing according to the present invention, when the load beam is elevated to the offset height in a machine 90 which adjusts dynamic gram and height (the “DAGH” or Dynamic Adjust Gram and Height station). It is to be further understood that elevating the load beam to the offset height does not cause suspension gram loss in the short term.
The amount of scanning performed on the head suspension, and thus the amount of adjustment that is obtained, is dependent upon a number of variables, each of which can be controlled as needed by a desired application to optimize the scanning process. One constraint on the amount of scanning performed on a head suspension in a compensation process is the amount of correction that is needed to overcome errors in the gram load and radius geometry height of the head suspension. A second constraint on the amount of scanning performed is that the head suspension is preferably not permanently marked during the correction process, which will diminish the aesthetic appearance of the part. In
The physical configuration of the arms 28 of the spring region 26 of the head suspension (i.e. part width and thickness) will also play a part in the amount of angular deflection the head suspension experiences for a given amount of scanning. For a specific suspension configuration, the beam size, intensity, number of scan lines, and scan rate can be optimized as necessary to induce the proper amount of correction while not permanently marking the head suspension part.
The amount of scanning that needs to be performed on a head suspension to effect a desired adjustment of gram load and radius geometry height is experimentally obtained and stored for later reference by holding certain of the variables described above that affect the heat imparted to the component constant while varying other variables. For example, using the head suspension of
Referring now most particularly to
Referring now to
The four points of the system 88 can be arranged in a variety of configurations.
Delta RG height=(P1−P3)−(P2−P4) (1)
Delta RG height=(P1−P2) (2)
where P1 is the measurement by sensor 92 of the distance from the end of the sensor to the suspension 10 at location 92 in
Referring now to
RG could be a few micrometers off the target. In
While it is possible to repeat scanning more than twice per part, it is preferable to limit the number of scan cycles to two, so as to avoid significantly reducing the production rate for processing parts using the present invention.
The DAGH station 90 will adjust parts to the nominal gram by decreasing gram on the incoming (overgrammed) parts. For partially etched load beams, the change in gram per laser scan line will be more (at equal laser power) due to the decreased material thickness for such parts.
In the practice of the present invention, it has been found preferable to develop response curves for each type of load beam or head suspension product to be adjusted by the method of this invention. In effect, the algorithm “memorizes” the center scan location and number of scans necessary to provide a desired combination of gram load and RG height adjustments. The change in RG height is a function of scan location and number of scans. It is to be understood that by “scan location” is meant the location of the center of a group of scans with reference to the top (flexure side) of the cut out of the spring region. It is to be understood that the adjustment range for gram load an RG height according to the present invention is affected by power and velocity combinations (P/V1/2), focus spot size, scan offset and material properties, particularly material thickness.
Referring to
Since the relation between the RG height and center scan location (CSL) is linear for a given number of scans, the RG height change for a given number of scans can be expressed as:
DeltaRG=InterceptCSL+SlopeCSL×CSL (3)
The InterceptCSL and SlopeCSL are each a function of the number of scans performed. Therefore, they can be expressed as:
InterceptCSL=Mc×(Number of Scans)+Cc (4)
where Mc is the Slope of the InterceptCSL, and Cc is the Intercept of the InterceptCSL and
SlopeCSL=Mm×(Number of Scans)+Cm (5)
where Mm is the Slope of the SlopeCSL, and Cm is the Intercept of the SlopeCSL.
This allows Equation (3) to be rewritten as:
DeltaRG=Mc×(Number of Scans)+Cc+[Mm×(Number of Scans)+Cm]×CSL (6)
Equation (4) can be further simplified by forcing Cc and Cm to 0. This can be done without making a significant compromise in accuracy, since (Number of Scans)=0 when there is no change. In that situation, Equation (6) can be rewritten:
DeltaRG=Mc×(Number of Scans)+Mm×(Number of Scans)×CSL (7)
Similarly, gram change can be plotted as a function of number of scans and scan location.
Change in RG height=SlopeNoS×CSL+InterceptNoS (8)
where NoS is the number of scans, and the Intercept is the point at which the individual curve intersects the ordinate on the graph. The relationships in illustrated in
SlopeNos=MSlope×NoS+CS (9)
InterceptNoS=Mintercept×NoS+C1 (10)
where MSlope is the slope of the Delta RG height versus CSL Slopes versus NoS, Mintercept is the slope of the Delta RG height versus CSL Intercepts versus NoS, and CS and C1 are constants that are set to zero since there is no change when the number of scans is zero.
By substituting [MSlope×NoS] in place of [SlopeNoS×CSL] and [MIntercept×NoS] in place of InterceptNoS in Equation (8), the change in RG height can be expressed as a function of both CSL (center scan location) and NoS (number of scans):
Incremental RG height=MSlope×NoS×CSL+MIntercept×NoS (11)
To adjust gram load and RG height simultaneously, the effect of CSL on gram needs to be considered. The change in gram load versus the number of scans at a given CSL can be derived from
Coarse Delta Gram=(SlopeCSL×CSL)+(SlopeCSL2×CSL2)+(SlopeNoS×NoS)+(SlopeNoS2×NoS2)+Constant (12)
Fine Delta Gram=(SlopeCSLcoarse×CSLcoarse)+(SlopeCSLfine×CSLfine)+(SlopeCSL2fine×CSL2fine)+(SlopeNoScoarse×NoScoarse)+(SlopeNoSfine×NoSfine)+(SlopeNoS2fine×NoS2fine)+Constant (13)
To adjust gram load and RG height at the same time, the Gram and RG height equations [(12) and (11)] and [(13) and (11)] are solved simultaneously.
After initial gram load and RG height measurements are made, and desired delta gram and delta RG height are calculated, an iterative method for the number of scans is used to determine how to best adjust gram load and RG height, where the number of scans is in the range of 1 to MAX, where MAX is a maximum number of scans which is the largest number of scans that can be performed within the adjust region. For each iteration of the number of scans, a “Best CSL” is calculated to move RG height as close to the target as possible. A gram load change is then calculated. The actual number of scans are chosen after iterating through all of the possible number of scans, and choosing the number that predicts moving gram load as close as possible to the target gram load. It has been found through experimentation, that this process converges, achieving an error minimization for gram load as it occurs. It is to be understood that RG height error may be chosen to be minimized, instead of gram load. Furthermore, a combined reduced error criteria for both gram load and RG height may be selected in a manner that blends both, if gram load and RG height are not able to simultaneously be minimized.
In addition to adjusting overall gram load and RG height for a load beam, it is within the scope of the present invention to simultaneously adjust those parameters for individual legs of the load beam. By “leg” (or “arm”) is meant the part of the spring region lateral of the aperture. In this aspect of the invention, left and right gram response can be individually adjusted, along with respective left and right radius geometry height adjustments. Such separate adjustability of the left and right legs of the spring region enable adjustment of delta height for the suspension. Example curves are shown in
The effect of stress due to elevation was investigated on particular models of load beams (identified as models QS and 3420 offered by the assignee of the present invention) by changing the offset height and comparing the change in gram per scan. The load beam was scanned with the center scan located at the maximum response location, at the center of the bend.
For just Gram and RG height adjust the scans on the part were symmetrical. To reduce a “twist” error where delta height is not equal to zero, the scan location on each leg is varied. RG height now is defined as Average Height since it is the average of the heights of both legs of the load beam.
For Coarse Adjust:
Delta Average Height=(Slope CSLavg*CSLavg+Constant)*NSc (14)
Delta Delta Height=(SlopeCSLbias*CSLbias+Constant)*NSc (15)
Delta Gram=SlopeNSc*NSc+(Slope NSc2+NSc2)+Slope Left CSL*Left CSL+Slope Right CSL*Right CSL+(Slope CSLbias0.5*CSLbias0.5)+Constant (16)
For Fine Adjust:
Delta Average Height=(SlopeCSLF*CSLF+Constant)*NSF (17)
Delta Delta Height=(SlopeCSLF*CSLF+Constant)*NSF (18)
Delta Gram=Slope NSF*NSF+(SlopeNSF2*NSF2)+Slope NSc*NSc+SlopeLeftCSLF*LeftCSLF+SlopeRightCSLF*RightCSLF+(SlopeCSLbias0.5*CSLbias0.5)+Constant (19)
Where NSc is the number of coarse scans and NSF is the number of fine scans.
The Center Scan Location is now an average of the left and right center scan locations as given by Equation (20):
CSLavg=(Left CSL+Right CSL)/2 (20)
In addition, to fully describe Center Scan Location, a bias value is given by Equation (21):
CSLbias=Left CSL−Right CSL (21)
The Maximum number of scans MaxNoScans that can be placed on a part is given by Equation (22):
MaxNoScans=(scan limit at the load beam end−scan limit at the base end)/scan spacing (22)
Procedure
Measure the part and compute the desired delta gram, delta average height and delta delta height.
Since Delta Average Height=(Slope CSLavg*CSLavg+Constant)*NS, where NS is the number of scans, for a given number of scans:
CSLavg=(Desired Delta Average Height/(Slope CSLavg*NS))−(Constant/SlopeCSLavg)
Choose CSLavg as close to base or load beam as possible if calculated CSL is outside the range (as in earlier procedure).
Since Delta Delta Height=(SlopeCSLbias*CSLbias+Constant)*NS
For a given NS:
CSLbias=(Desired Delta Delta Height/(Slope CSLbias*NS))−(Constant/CSLbias) (23)
Choose maximum or minimum CSLbias if calculated CSLbias is beyond a feasible location.
Min/Max CSLbias=+/−(load beam limit−base end limit)−(NS−1)*scan spacing. If NS=31 and (load beam limit−base end limit)=1.0 mm, and scan spacing equals 0.02 mm, then Min/Max CSLbias=+/−0.4 mm.
It is to be understood that there needs to be an option to choose which adjusted parameter is most important. When Average Height is most critical, CSLavg is given higher priority than CSLbias. When Delta Height is more critical, CSLbias is given higher priority than CSLavg.
Example: If NS=31 and (load beam limit−base end limit)=1.0 mm, and scan spacing=0.02 mm, then:
For Average Height priority:
If calculated CSL is <0.3 or >0.7, CSLbias must be 0
For Delta Height priority:
If calculated CSLbias is <−0.04 or >0.04, CSL must be 0.5 mm.
In the examples described above, the amount of scanning necessary to effect a desired adjustment is described in terms of the number of scans needed to accomplish the course and fine adjustments for a given beam power, beam diameter, scan velocity, and scan line spacing. The relationship between the adjustment achieved and the amount of scanning performed can also be determined as a function of a different laser operating parameters. For example, the number of scan lines could be held constant while the laser beam intensity is varied to determine the relationship between adjustment and beam intensity. Both coarse and fine adjustments can be determined in this manner.
It is within the practice of the present invention to adjust the suspension using double sided scanning, wherein the apparatus and method may be utilized by scanning a laser beam across both the top and the bottom of the spring region of the suspension.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
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