WO1998037557A1

WO1998037557A1 - Method and apparatus for in-drive monitoring of stiction by measurement of disk spindle motor starting current

Info

Publication number: WO1998037557A1
Application number: PCT/US1998/002993
Authority: WO
Inventors: Bill Higgins; Gregg Uhlendorf
Original assignee: Quantum Corporation
Priority date: 1997-02-20
Filing date: 1998-02-20
Publication date: 1998-08-27
Also published as: AU6328198A

Abstract

A method for in-drive monitoring of stiction in a hard disk drive and corresponding improved hard disk drive are provided. Stiction is monitored by measuring starting current of the spindle motor of the drive without having to remove the printed circuit board of the disk drive, open the disk drive, or remove the drive from a given test environment. The method includes steps of initializing the motor driver control chip (step 200), initializing the motor (step 202), determining an initial disk position (step 204), applying an initial current (step 206) and determining if the disk position has changed (step 208 and 210). If the disk position has not changed, then the method applies a next higher current (step 212) to the spindle motor, wherein the method repeatedly increases the current until the disk position changes (step 208, 210 and 212). The last applied current which caused the disk position to change becomes the starting current (step 208, 210, 212 and 214). The method is implemented as an on-board electronic torque meter (ETM) by integrating specialized firmware with the motor driver control chip, to produce an improved hard disk drive.

Description

METHOD AND APPARATUS FOR IN-DRIVE MONITORING OF STICTION BY MEASUREMENT OF DISK SPINDLE MOTOR STARTING CURRENT

Field of the Invention

The present invention relates to monitoring stiction in a hard disk drive system. More particularly, the present invention relates to a method and apparatus for in-drive measurement of the disk drive starting current in a non-invasive manner.

Background

• ir Accurate and reliable measurement of stiction in a hard disk drive system is an important goal in drive development, as this measurement can be used for head and media qualification, failure analysis of a drive, or even advance warning of rising stiction in a drive is nearing its end of life.

Currently, drive developers monitor stiction by performing contact start stop (CSS) testing on drives. In one method of CSS testing, referred to as mechanical torque measurement (MTM), a torque watch is used to measure a starting torque of the disk spindle. This procedure requires the cover of the drive to be removed in order to measure the disk stack starting torque with the torque watch.

The MTM method of CSS testing has several disadvantages associated with it. In particular, since the drive must be opened to perform the measurement, there is considerable time and human contact involved which greatly increases the risk of damage to the drive. Additionally, opening of the drive exposes the interior to chemical and particulate contamination. Furthermore, in order to perform the CSS testing with the torque watch, the drive must be removed from the test environment. This requirement reduces the relevance of the measurements taken since the data collected is from an environment which is not under test.

Another method of CSS testing involves measurement of the disk spindle starting current required to overcome stiction and initiate disk rotation. In this method, an external device referred to as an electronic torque meter (ETM) is electrically connected to the hard drive to measure the starting current. This procedure requires the printed circuit board (PCB) of the drive to be removed, and the drive to be removed from its test environment.

Use of an ETM also has a number of disadvantages associated therewith. Since the ETM is an external device which requires the drive to be removed from the test environment, the relevance of the test data is also called into question with this method. Additionally, while the drive does not need to be opened, there is still considerable handling of the drive during removal from the test environment, and also during removal of the PCB. Such handling increases the possibility of damage to the drive. Furthermore, the use of the external ETM to measure stiction relies on detection of back EMF which requires a considerable amount of skill and measurement optimization in order to obtain meaningful results.

Thus, there exists a need for an improved, simple, reliable and cost efficient method for CSS testing of disk drives which does not require excessive handling of the drive and removal of the drive from the test environment.

Summary

The present invention satisfies this need.

The present invention is directed to a method and apparatus for in-drive stiction monitoring of a hard disk drive which includes a spindle motor, a disk stack assembly mounted on the spindle motor, an actuator assembly having a head stack assembly, and controlling circuitry enclosed within an interior of a housing assembly, and a printed circuit board having a motor driver control chip. The method includes steps of initializing registers of the motor driver control chip and initializing the spindle motor, then determining a starting disk position by the circuitry of the motor driver control chip. The motor driver control chip is then used to apply an initial current to the spindle motor and a present disk position is then determined. If the present disk position has changed from the starting disk position, the initial current applied to the spindle motor is identified to be the starting motor current. However, if the present disk position has not changed from the starting disk position, a next higher current is applied to the spindle motor and the present disk position is again determined. These steps of applying a next higher current to the spindle motor and determining the present disk position are alternately repeated until the present disk position has changed from the starting disk position. When it is determined that the present disk position has changed, the last applied current is identified as the starting motor current. In an additional aspect of the method having features of the present invention, the current applied to the spindle motor is applied as stepwise increments which are a fraction of a maximum spindle current. Preferably, the stepwise increments are less than or equal to about 1 /32 of the maximum spindle current. More preferably, the stepwise increments are about 1 /256 of the maximum spindle current.

In an alternative embodiment, an improved hard disk drive having features of the present invention includes a spindle motor, a disk stack assembly having at least one rotatable data storage disk mounted on the spindle motor, an actuator assembly having a head stack assembly, and controlling circuitry which are enclosed within an interior of a housing assembly. The housing assembly is defined by a base with integral side walls and a cover. The improved disk drive also includes a removably attached printed circuit board having a motor driver control chip and additional circuitry for controlling disk drive functions, and an in-drive, or on-board, electronic torque meter which includes firmware means for determining contact start stop testing of the drive. The firmware means preferably includes firmware code for initializing the control chip and the spindle motor, determining a starting disk position, applying an initial current to the spindle motor, alternately determining a present disk position and applying a stepwise increasing current to the spindle motor until the present disk position has changed with respect to the starting disk position, and identifying the disk spindle starting current to be a last applied stepwise current prior to change in the present disk position. A further feature of the improved hard disk drive includes firmware code for applying a current step which is a fraction of a maximum spindle current.

The present invention can be used in a variety of diagnostic applications to optimize or improve disk drive development. The present invention provides a non-invasive and unattended manner of obtaining accurate data related to the head disk interface of a hard disk drive. The present invention also provides a simple and cost efficient way to characterize stiction in an automated and non-destructive manner.

Brief Description of the Drawings

Other features and advantages of the invention will be understood and appreciated by those of ordinary skill in the art upon consideration of the following detailed description, appended claims and accompanying drawings of preferred embodiments, where:

Fig. 1 is an exploded view of a hard disk drive for carrying out a method for in-drive stiction monitoring in accordance with principles of the present invention;

Fig. 2 is a simplified block diagram for carrying out the method in accordance with principles of the present invention;

Fig. 3 is a pictorial illustration graphically showing stepwise application of current to a spindle motor in accordance with an embodiment of the present invention;

Fig. 4 is an example of a listing of firmware code for implementing the method in accordance with principles of the present invention; and

Fig. 5 is graph showing correlation between spindle motor starting currents obtained using an on-board ETM in accordance with principles of the present invention, and an prior art external ETM.

Detailed Description of a Preferred Embodiment

Fig. 1 shows an example of a hard disk drive 10 in which a method embodying aspects of the present invention can be implemented. The disk drive 10 typically is contained in a housing which includes a base 12, integrally connected sidewalls (not shown), and a cover 14 with a sound damper 16. The disk drive 10 includes a disk stack assembly 18 having at least one data storage disk 19 rotatably mounted on a spindle motor 20, and an actuator apparatus or assembly 30. The spindle motor 20 is typically a brushless spindle motor integrated into a spindle or hub that supports the data storage disk 19, such that the spindle motor 20 supports and directly rotates the storage disk 19 at a predetermined angular velocity. The actuator assembly 30 typically includes a magnetic structure 31 , an encapsulated positioning coil 32, a headstack assembly 34 with attached flex circuit and controlling circuitry 36, and an actuator lock and filter assembly 38. The disk drive 10 additionally includes a foam damper 40 and printed circuit board 42 mounted to the housing base 12. The printed circuit board 42 includes the drive electronics to allow the disk drive to communicate with the computer to which it is connected, and to control operation of the disk drive 10.

Specifically, the disk drive electronics can include a microprocessor, interface electronics, a controller chip or ASIC, a read channel and a motor driver control chip.

Referring to Fig. 2, operation of an embodiment of the in-drive stiction monitoring method according to principles of the present invention will now be described. The method is implemented by first initializing registers of a spindle motor driver control chip 200 on the printed circuit board 42. The registers are initialized with operating parameters for the spindle motor such as, for example, an initial starting current, current step size and maximum current. Next the spindle motor 20 is initialized 202 prior to a current being applied to affect spindle rotation. A disk rotor starting position is then determined 204 by the motor driver control chip. The disk rotor starting position can be determined using any known rotor position detection algorithm such as a current rise time differential method, or a like position detection algorithm. An example of such a known detection algorithm can be found in U.S. Patent No. 5,028,852 entitled Position Detection For A Brushless DC Motor Without Hall Effect Devices Using A Time Differential Method.

Once the initialization steps 200, 202 are completed and the disk rotor position is determined 204, an initial current is applied 206 to the spindle motor 20 under the control of the motor driver control chip. The initial current applied to the spindle motor 20 is chosen by the end user and is dependent on the end user's specific needs. After the initial current is applied 206 to the spindle motor, the disk rotor position is again determined 208 to see if the initially applied current was sufficient to affect spindle rotation and change the disk position 210. If the disk position is unchanged from the previously determined starting position, a next higher current level is applied 212 to the spindle motor 20. Alternatively, if the disk position is changed or altered, the last applied current is provided through a head disk interface and reported to the end user as the starting current 214 of the disk drive 10.

In the event that the disk rotor position remains unchanged after current is applied to the spindle motor 20, the steps of applying a next higher current level 212 and determining the present disk position 208 are alternately repeated until the disk position has changed. When it is determined that the disk position has changed in response to an applied current, that current is reported as the starting current 214 of the disk drive 10, as described above.

As described above, a current waveform is applied to the spindle motor 20 as determined by the end user. Within the basic concept of the method there are several adjustments which can be made to this current waveform. As already described, during the initialization steps of the method, the initial current, maximum current and current step size are defined by the user. Additionally, the current ramp, current application and rest timings can be defined by the user. This flexibility in the applied current waveform provides a method that can be tailored to a specific application for which the user requires stiction monitoring. In a preferred embodiment of the method, the current waveform is defined such that the current applied to the spindle motor 20 is in stepwise increments which are a fraction of the maximum motor current. Such a current application is shown pictorially in Fig. 3, where the total current applied at each step is shown in bar graph form. In this embodiment, the stepwise increments are preferably less than or equal to 1 /32 of the maximum motor current. More preferably, the stepwise increments are about 1 /256 of the maximum motor current.

Alternatively, the current application can be defined such that the current level applied to the spindle motor 20 is a predetermined or user defined current level. This embodiment would be useful, for example, in a start/no start determination at a specific current level. Other current applications are also possible.

In another embodiment of the invention, the above described method is implemented as an in-drive, or on-board, electronic torque meter, which provides an improved hard disk drive. The electronic torque meter includes the motor driver control ASIC on the PCB 42 of the disk drive 10, and firmware means for carrying out the described method steps. The firmware means is firmware code and can be any known programming language/code, such as, for example, assembler code shown in Fig. 4.

In operation, the above method and apparatus are shown to provide similar test measurements as compared to prior art external electronic torque meters. Fig. 5 shows the correlation between measurements taken with an external ETM and those taken by the on-board ETM of the present invention. In the figure, the measured starting current of the on-board ETM is shown on the y-axis, and the measured starting current of the prior art external ETM is shown on the x-axis. The on-board ETM current is measured in DAC steps where the full scale current is 255 DAC steps, which roughly corresponds to 1 500 mAmps. As depicted by the figure, the in-drive ETM of the present invention can provide reliable measurements comparable to those obtained using an external ETM.

As described hereinabove, the stiction monitoring method and apparatus incorporating features of the present invention have a number of useful applications that provide several advantages over the prior art. First, the method and apparatus can be used for measuring spindle motor starting current of a disk drive during CSS testing in an automated, non-invasive manner. Such automated measurements of CSS performance can significantly enhance the ability to gather high quality data related to the head disk interface. In turn, this data can be used to qualify the head disk interface during preproduction of drive development, and as a diagnostic indicator of the head disk interface. Further, the present invention can be integrated into a selfscan CSS test procedure in which the spindle motor is repeatedly spun up and down. Here, the invention can be implemented to measure the spindle starting current as frequently as desired. These more frequent starting measurements can provide greatly improved CSS test data. Additionally, the integration of the on-board electronic torque meter and its operation into the selfscan CSS testing can significantly reduce the amount of time required for CSS testing and the amount of drive handling during CSS testing. Lastly, the non-invasive and automated manner of the present invention significantly reduces human handling of the disk drive, thus allowing testing in any ambient environment and reducing the possibility of damaging the drive. The present invention therefore provides a more efficient and less error prone CSS test procedure which is shown to produce reliable measurements comparable to prior art external CSS test procedures.

While the present invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The disclosures and description herein are purely illustrative and are not intended to be in any sense limiting.

Claims

What is claimed is:

1 . A method for in-drive stiction monitoring of a hard disk drive, the disk drive including a spindle motor, a disk stack assembly having at least one rotatable data storage disk mounted on the spindle motor, an actuator assembly having a head stack assembly, and controlling circuitry enclosed within an interior of a housing assembly defined by a base with integral side walls and a cover, and a printed circuit board having a motor driver control chip thereon, the printed circuit board removably attached to the housing assembly, the method comprising steps of: (a) initializing registers of the motor driver control chip; (b) initializing the spindle motor; (c) determining a starting disk position using the motor driver control chip; (d) applying an initial current to the spindle motor using the motor driver control chip; (e) determining a present disk position using the motor driver control chip; (f) applying a next higher current level to the spindle motor if the disk position is unchanged; (g) indicating a last applied current as the starting current of the disk drive if the disk position is changed, wherein the stiction monitoring is performed internally to the disk drive without opening the housing assembly or removing the printed circuit board such that damage, due to handling and contamination, to the disk drive is reduced.

2. The method of claim 1 wherein steps (e) - (g) are repeated until it is determined that the disk position has changed from the starting disk position.

3. The method of claim 2 wherein the next higher current level is a stepwise increment which is a fraction of a maximum motor current.

4. The method of claim 3 wherein the stepwise increments are less than or equal to 1 /32 of the maximum motor current.

5. The method of claim 4 wherein the stepwise increments are preferably about 1 /256 of the maximum motor current.

6. The method of claim 2 wherein the initial current and the next higher current level are user determined values.

7. A method of internally measuring disk spindle starting current of a disk drive device including a spindle motor, a disk stack assembly having at least one rotatable data storage disk mounted on the spindle motor, an actuator assembly having a head stack assembly, and controlling circuitry enclosed within an interior of a housing assembly defined by a base with integral side walls and a cover, and a printed circuit board having a motor driver control chip thereon, the printed circuit board removably attached to the housing assembly, the method comprising steps of:

(a) initializing the control chip and the spindle motor; (b) determining a starting disk position; (c) applying an initial current to the spindle motor; (d) alternately determining a present disk position and applying a stepwise increasing current to the spindle motor until the present disk position has changed with respect to the starting disk position; and (e) identifying the disk spindle starting current to be a last applied stepwise current prior to change in the present disk position, wherein the disk spindle starting current is determined in a non- invasive manner to the disk drive such that the housing assembly does not have to be opened and the printed circuit board is not removed.

8. The method of claim 7 wherein the stepwise increasing current is a fraction of a maximum motor current.

9. The method of claim 8 wherein the stepwise increasing current is less than or equal to 1 /32 of the maximum motor current.

1 0. The method of claim 9 wherein the stepwise increasing current is preferably equal to approximately 1 /256 of the maximum motor current.

1 1 . The method of claim 7 wherein the initial and stepwise increasing currents are user specified values.

1 2. An improved hard disk drive system comprising at least a spindle motor, a disk stack assembly having at least one rotatable data storage disk mounted on the spindle motor, an actuator assembly having a head stack assembly, and controlling circuitry enclosed within an interior of a housing assembly defined by a base with integral side walls and a cover, and a printed circuit board having a motor driver control chip and circuitry thereon for controlling disk drive functions, the printed circuit board removably attached to the housing assembly, wherein the improvement comprises: an in-drive electronic torque meter comprising firmware means for performing contact start stop testing of the drive, wherein disk spindle starting current is determined in a non-invasive manner to the disk drive such that the housing assembly does not have to be opened and the printed circuit board is not removed.

1 3. The improved hard disk drive system of claim 1 2 wherein the firmware means for performing contact start stop testing of the drive comprises: (a) firmware code for initializing the control chip and the spindle motor; (b) firmware code for determining a starting disk position; (c) firmware code for applying an initial current to the spindle motor; (d) firmware code for alternately determining a present disk position and applying a stepwise increasing current to the spindle motor until the present disk position has changed with respect to the starting disk position; and (e) firmware code for identifying a disk spindle starting current to be a last applied stepwise current prior to change in the present disk position.

14. The improved hard disk drive system of claim 1 3 wherein the firmware code for applying a stepwise increasing current to the spindle motor includes firmware code for applying a current step which is a fraction of a maximum motor current.

1 5. The improved hard disk drive system of claim 1 4 wherein the current step is less than about 1 /32 of the maximum motor current.

1 6. The improved hard disk drive system of claim 1 5 wherein the current step is preferably about 1 /256 of the maximum motor current.

1 7. The improved hard disk drive system of claim 1 3 wherein the firmware code for applying a stepwise increasing current to the spindle motor includes firmware code for applying a current step which is a user specified value.

1 8. The improved hard disk drive system of claim 1 3 further comprising: (f) firmware code for indicating the identified disk spindle starting current to a user.