TD detection with enhanced HDIs signal

Abstract

A method of operating an HDD having a slider-mounted read/write head that is configured for dynamic fly-height operation (DFH) and includes at least one head-disk interference sensor (HDIs). By operating the DFH to lower the head and subjecting the HDIs signal to a power-law enhancement, a consistent and accurate determination of the touchdown power (TDP) can be obtained. Combining absolute TDP determination with a method for measuring relative changes of FH, an absolute determination of FH can be determined.

Claims

1. A method for operating a dynamic flying height (DFH)-configured read/write head to determine a touchdown power (TDP, or TD power), comprising: providing a slider-mounted DFH-configured, read/write head operationally installed in a system wherein said read/write head is configured to controllably approach the surface of a rotating recording medium; wherein said slider-mounted DFH-configured read/write head is mounted on a slider aerodynamically configured to support said DFH-configured read/write head at a stable flying height (FH) above a rotating magnetic recording medium; wherein said slider-mounted read/write head includes at least one head/disk interference sensor (HDIs) and associated electronic equipment for receiving and processing signals generated by said HDIs; wherein said slider-mounted read/write head further includes DFH apparatus to raise and lower said slider-mounted read/write head relative to a surface of said rotating recording medium; generating an HDIs signal, x(t), as power is applied to said DFH apparatus and said slider-mounted read/write head approaches said surface of said rotating recording medium; then enhancing said HDIs signal, x(t), by applying a power-law signal processing formula to x(t) to obtain y(t): y(t)=(abs(x(t))){circumflex over ()}np, np=2, 3, . . . , while said approach occurs; and determining a TDP using said enhanced signal y(t).

2. The method of claim 1 wherein said TDP provides an absolute reference point whereby a method of determining relative changes in slider height can be combined with said absolute reference point to create a method to determine a flying height (FH) of said slider-mounted read/write head.

3. The method of claim 1 wherein in said signal processing formula:
y(t)=(abs(x(t))){circumflex over ()}np, np=2,3, . . . , np can be chosen to produce an optimal comparison with an independent measuring device.

4. The method of claim 3 wherein np is an even integer and the absolute value of x(t) is its positive value.

5. The method of claim 3 wherein said independent measuring device is a laser doppler vibrometer (LDV).

6. The method of claim 1 wherein said signal processing further includes a step of filtering, either before or after said enhancement of the signal.

7. The method of claim 1 wherein said signal processing further includes a step of signal amplification either before or after said enhancement of the signal.

8. The method of claim 1 applied to the manufacture of active HDD components, said components including a slider and/or a head gimbal assembly (HGA) and said application occurring during electric or dynamic electric test (ET, or DET) during manufacturing of said HDD components (slider and/or HGA).

9. A dynamic flying height (DFH)-configured read/write head having an absolutely determined touchdown point (TDP), comprising: a slider-mounted DFH-configured, read/write head operationally installed in a system wherein said read/write head is configured to controllably approach the surface of a rotating recording medium; wherein said slider-mounted DFH-configured read/write head is mounted on a slider aerodynamically configured to support said DFH-configured read/write head at a stable flying height (FH) above a rotating magnetic recording medium; wherein said slider-mounted DFH-configured read/write head comprises at least one head/disk interference sensor (HDIs) and associated electronic equipment for receiving and processing signals generated by said HDIs; wherein said slider-mounted read/write head further comprises a DFH apparatus configured to raise and lower said slider-mounted read/write head relative to a surface of said rotating recording medium; wherein said HDIs is configured to generate a signal, x(t), as power is applied to said DFH apparatus and said slider-mounted read/write head approaches said surface of said rotating recording medium; wherein said HDIs signal is configured to be processed and enhanced signal y(t) while said approach occurs and a TDP is determined using y(t); and wherein said read/write head is configured to apply the following power-law transformation to said HDIs signal x(t) to obtain y(t): y(t)=(abs(x(t))){circumflex over ()}np, np=2, 3, . . . , .

10. The DFH-configured read/write head claim 9 wherein said TDP provides an absolute reference point wherein, by combining said absolute TDP with a method of determining relative changes in slider height a flying height (FH) of said slider-mounted read/write head is obtained.

11. The DFH-configured read/write head of claim 9 wherein in the use of the power-law signal processing formula:
y(t)=(abs(x(t))){circumflex over ()}np, np=2,3, . . . , np can be chosen to produce an optimal comparison with an independent measuring device.

12. The DFH-configured read/write head of claim 11 wherein said independent measuring device is a laser doppler vibrometer (LDV).

13. The DFH-configured read/write head of claim 9 wherein said signal processing further includes a step of filtering, either before or after said enhancement of the signal.

14. The DFH-configured read/write head of claim 9 wherein said signal processing further includes a step of signal amplification either before or after said enhancement of the signal.

15. A head-gimbal assembly, comprising: the DFH-configured read/write head of claim 9; a suspension that elastically supports said DFH-configured read/write head; a flexure affixed to said suspension and a load beam having one end attached to said flexure and another end attached to a base plate.

16. A hard disk drive (HDD), comprising: said head gimbal assembly of claim 15; a magnetic recording medium positioned opposite to said DFH-configured read/write head; a spindle motor that rotates and drives said magnetic recording medium; a device that positions said DFH-configured read/write head relative to said magnetic recording medium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a graphical illustration of the application of DFH (dynamic flying height) power during a TD process, showing the stair-like shape of the applied power.

(2) FIG. 1B is a graphical illustration showing a measurement of TD vibration using an LDV (laser doppler vibrometer) during the TD process of FIG. 1A.

(3) FIG. 1C is a graphical illustration showing the HDIs signal time history with a 200 mV BHV (bias voltage) during the TD process of FIG. 1A.

(4) FIG. 1D is a graphical illustration showing the HDIs signal time history with a 280 mV BHV during the TD process of FIG. 1A.

(5) FIG. 2 is a set of graphs showing the RMS values of the TD vibration and HDIs signal of the graphs in FIGS. 1A, B, C and D.

(6) FIG. 3 is a set of graphs showing the RMS values of HDIs. With different np values (w/o PE means no signal enhancement)

(7) FIG. 4 is a set of graphs showing the RMS values of the TD vibration and HDIs signal with np=10.

(8) FIG. 5 is an illustration of the HDIs signal time history before power enhancement.

(9) FIG. 6 is an illustration of the HDIs signal time history with np=10.

(10) FIG. 7 is a graph of the RMS value of the HDIs signal with different np values.

(11) FIG. 8 is a graphical illustration of TDP (TD power) detected using HDIs with different np values.

(12) FIGS. 9, 10 and 11 are schematic illustration showing the system incorporated within the components of an operational HDD.

DETAILED DESCRIPTION

(13) The presently disclosed method begins with the use of a slider-mounted read/write head (the head) configured for dynamic fly height (DFH) operation, with the head possessing at least one HDIs (head-disk interference sensor). The head is operationally installed in a hard disk drive (HDD) or spin-stand wherein it is allowed to approach the surface of a disk by applying power to the DFH apparatus and whereby the HDIs produces a signal indicating the closeness of the approach.

(14) In the present method, however, the HDIs signal is enhanced by being first subjected to a processing step that raises its absolute value to an integer power. It will be demonstrated in the following that the processed signal provides a more accurate and reproducible indication of the approach than does an unprocessed signal. Assuming the unprocessed HDIs signal, as a function of time, t, is denoted x(t), the enhancement transformation y(t), which is a power-law operation, is applied to it as follows:
y(t)=(abs(x(t))){circumflex over ()}np, np=2,3, . . . ,(1)
where y(t) is the enhanced HDIs signal, abs(x(t)) is the absolute value of the signal, np is a positive integer, np=1, 2, . . . , and y(t) is given by equ. (1) above, where (abs(x(t))){circumflex over ()}np is the exponentiation of the absolute value of x(t) to the integer power np.

(15) The following brief example will show how the method is applied:

(16) The typical measured HDIs AC signal includes two portions: noise and a slider/disk contact signal (or TD signal). If there are n measurement points in a complete disk revolution and if the slider contacts the disk at point i (the slider/disk contact usually starts at a local point), then the measured AC signal will be:

(17) noise(1), noise(2), noise(i)+TD signal(i), noise(+1), . . . , noise(n). If we set np=2 in Eq. 1, the transformed signal will be

(18) noise(1){circumflex over ()}2, noise(2){circumflex over ()}2, [noise(i)+TDsignal(i)]{circumflex over ()}2, noise(i+1){circumflex over ()}2, . . . , noise(n){circumflex over ()}2. Or

(19) noise(1){circumflex over ()}2, noise(2){circumflex over ()}2, noise(i){circumflex over ()}2+2*noise(i)*TDsignal(i)+TDsignal(i){circumflex over ()}2, noise(i+1){circumflex over ()}2, . . . , noise(n){circumflex over ()}2.

(20) Thus, the signal at point i will be enhanced. With a large value of np, the signal will have more enhancements. That is shown in FIGS. 5 and 6.

(21) The RMS of the enhanced signals will show a larger difference between before the contact and after the contact, whereby the RMS curve will have a sharper change around contact point (contact power) with a larger np, as shown in FIG. 3.

(22) If values of np=2, 4, 6, . . . , are used, there is no need to calculate absolute value of x(t) (as is shown in Eq. 1). This is preferred, as it is easier to implement with a hardware circuit. If odd values of np=3, 5, 7, . . . , are used, the absolute value of x(t) must be calculated first, and then the power-law calculation is done.

(23) FIGS. 1A-1D show various aspects of an entire TD process. A ramping up of DFH power was applied in FIG. 1A, and TD vibration on a gimbal (see 200 in FIG. 9 for illustration of a gimbal) was measured in FIG. 1B using a laser doppler vibrometer (LDV). HDIs signals were captured at different bias voltages (BHV), as shown in FIG. 1C (BHV=200 mV) and FIG. 1D (BHV=280 mV). The different BHV values were used to simulate a spacing variation effect of the HDIs.

(24) As can be seen in the figures, as DFH power increases, both TD vibration increases (FIG. 1B) and HDIs signals increase until about 2.0 seconds or 62 mW (FIGS. 1C and 1D). This indicates that a TD occurred at around this point in time.

(25) FIG. 2 shows the RMS of both the TD vibrations and HDIs signals. It can be seen that the TD power (TDP) detected by TD vibration or by LDV is about 62.0 mW. Although the LDV can detect the true TD, it can only be used in a spin-stand component test and it cannot be used in the HDD. We want to use HDIs to do the TD detection in the HDD. However, it is difficult to determine the TDP from HDIs signals because they are ramping (or not sharp). If we use a threshold 0.1 for the detection, the detected TDP will be about 58.0 mW with the 280 mV BHV, and about 60.5 mW with the 200 mV BHV. Thus, there are two issues:

(26) a) the 58.0 and 60.5 mW are different from the LDV detection (62.0 mW), or they are not the true TD power;

(27) b) the results depend on BHV, i.e., HDIs spacing that has a large variation.

(28) Therefore, HDIs detection is not good, even though the HDIs signal is strong in this case. However, when we enhanced the HDIs with a power-law calculation (operation) shown in Eq. 1, the RMS curves become very sharp, as shown in FIG. 3. Using a large value of np in Eq. 1, detection becomes very easy and consistent.

(29) FIG. 4, which graphs the results of several different np values, shows that with np=10, an identical TDP can be found when using the HDIs signal with a BHV of 280 mV or 200 mV, and the value is very close to LDV detected TDP. Therefore, detection is accurate and not sensitive to BHV or HDIs spacing variation.

(30) FIG. 5 shows another case. Here, the HDIs signal is very weak and smooth (not sharp) as compared to FIGS. 1C and 1D, and it is very difficult to find the TD point from the RMS plot shown in FIG. 7. However, after the HDIs signal is enhanced with np=10 in Eq. 1, the TD signature is very clear in both time history shown in FIG. 6 and RMS curves shown in FIG. 7. Detected TDP with different values of np are shown FIG. 8. In this case, when np>6, detected TDP is consistent and very close to the LDV detection.

(31) Referring finally to FIGS. 9, 10 and 11, there is shown an exemplary magnetic recording apparatus, such as a PMR configured hard disk drive (HDD), through whose use a PMR read/write head configured for DFH operation described above will meet the objects of this disclosure.

(32) FIG. 9 shows a head gimbal assembly (HGA) 200 that includes a slider-mounted PMR read/write head 100 configured for DFH operation and having at least one HDIs. A suspension 220 elastically supports the head 100. The suspension 220 has a spring-like load beam 230 made with a thin, corrosion-free elastic material like stainless steel. A flexure 231 is provided at a distal end of the load beam and a base-plate 240 is provided at the proximal end. The head 100 is attached to the load beam 230 at the flexure 230 which provides the read/write head with the proper amount of freedom of motion. A gimbal part for maintaining the read/write head at a proper level is provided in a portion of the flexure 230 to which the read/write head 100 is mounted.

(33) A member to which the HGA 200 is mounted to arm 260 is referred to as head arm assembly 220. The arm 260 moves the read/write head 100 in the cross-track direction y across the medium 14 (here, a hard disk). One end of the arm 260 is mounted to the base plate 240. A coil 231 to be a part of a voice coil motor is mounted to the other end of the arm 260. A bearing part 233 is provided to the intermediate portion of the arm 260. The arm 260 is rotatably supported by a shaft 234 mounted to the bearing part 233. The arm 260 and the voice coil motor (not shown) that drives the arm 260 configure an actuator.

(34) Referring next to FIG. 10 and FIG. 11, there is shown a head stack assembly and a magnetic recording apparatus in which the slider-mounted read/write head 100 is contained. The head stack assembly is an element to which the HGA 200 is mounted to arms of a carriage having a plurality of arms. FIG. 10 is a side view of this assembly and FIG. 11 is a plan view of the entire magnetic recording apparatus.

(35) A head stack assembly 250 has a carriage 251 having a plurality of arms 260. The HGA 200 is mounted to each arm 260 at intervals to be aligned in the vertical direction. A coil 231 (see FIG. 9), which is to be a portion of a voice coil motor is mounted at the opposite portion of the arm 260 in the carriage 251. The voice coil motor has a permanent magnet 263 arranged at an opposite location across the coil 231.

(36) Referring finally to FIG. 11, the head stack assembly 250 is shown incorporated into a magnetic recording apparatus 290. The magnetic recording apparatus 290 has a plurality of magnetic recording media 14 mounted on a spindle motor 261. Each individual recording media 14 has two PMR elements 100 arranged opposite to each other across the magnetic recording media 14 (shown clearly in FIG. 10). The head stack assembly 250 and the actuator (except for the read/write head itself) act as a positioning device and support the PMR heads 100. They also position the PMR heads correctly opposite the media surface in response to electronic signals. The read/write head records information onto the surface of the magnetic media by means of the magnetic pole contained therein.

(37) We wish to point out here that the present method of determining TD's can be applied not only to an operational HDD, but also to the fabrication and testing of HDD components such as the head gimbal assembly (HGA) described above. Moreover, it can also be applied in electric or dynamics electric test (ET, or DET) during manufacturing of HDD components (slider and/or HGA, head-gimbal assembly). During ET or DET, TD detection is required, and the present method should be very helpful also.

(38) As is understood by a person skilled in the art, the present description is illustrative of the present disclosure rather than limiting of the present disclosure. Revisions and modifications may be made to methods, materials, structures and dimensions employed in operating a HDD-mounted slider configured for DFH recording that uses processed signals from an HDIs to ensure that accurate FH measurements of HDIs can be taken during TDs while still operating such a device in accord with the spirit and scope of the present disclosure as defined by the appended claims.