US20090284861A1 - Dissipation of liquid droplets in a magnetic disk drive - Google Patents
Dissipation of liquid droplets in a magnetic disk drive Download PDFInfo
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- US20090284861A1 US20090284861A1 US12/120,171 US12017108A US2009284861A1 US 20090284861 A1 US20090284861 A1 US 20090284861A1 US 12017108 A US12017108 A US 12017108A US 2009284861 A1 US2009284861 A1 US 2009284861A1
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- magnetic disk
- slider
- disk drive
- removal process
- tfc
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
- G11B19/02—Control of operating function, e.g. switching from recording to reproducing
- G11B19/04—Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions
- G11B19/041—Detection or prevention of read or write errors
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B25/00—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus
- G11B25/04—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus using flat record carriers, e.g. disc, card
- G11B25/043—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus using flat record carriers, e.g. disc, card using rotating discs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B33/00—Constructional parts, details or accessories not provided for in the other groups of this subclass
- G11B33/14—Reducing influence of physical parameters, e.g. temperature change, moisture, dust
- G11B33/1446—Reducing contamination, e.g. by dust, debris
- G11B33/1453—Reducing contamination, e.g. by dust, debris by moisture
Definitions
- the invention is related to the field of magnetic disk drives, and in particular, to performing a droplet removal process to dissipate liquid droplets that form on a slider in a magnetic disk drive.
- Magnetic disk drives typically include one or more sliders having a read head and a write head.
- An actuator/suspension arm holds the slider above the surface of the magnetic disk.
- ABS air bearing surface
- VCM voice coil motor
- the read/write head may then read data from or write data to the tracks of the magnetic disk.
- the spacing between the read/write head and the surface of the magnetic disk is often referred to as the fly height of the read/write head.
- One factor contributing to the fly height is the shape of the ABS of the slider and the rotational speed of the magnetic disk.
- Another factor contributing to the fly height is the amount of protrusion of the read/write head toward the surface of the magnetic disk.
- the read/write head is fabricated from materials that are different than the rest of the slider body. These materials expand and contract at different rates than the slider body. Thus, disk drive manufacturers take advantage of these material properties by embedding one or more heating elements in the read/write head or proximate to the read/write head.
- the protrusion of the read/write head may thus be precisely controlled by the application of a heating power to the heating element. Controlling the protrusion of a read/write head through the application of a certain heating power to the heating element is referred to herein as Thermal Fly-height Control (TFC).
- TFC Thermal Fly-height Control
- the slider may collect a lubricant that is deposited on the surface of the magnetic disk, or may collect other liquids that condense from vapors in the magnetic disk drive. Air flow over the slider surfaces then causes these liquids to accumulate as liquid droplets on low pressure points of the slider. The low pressure points are typically on the ABS of the slider, or on the trailing end of the slider. When the liquid droplets grow to a sufficient size, they can detach from the slider and fall onto the surface of the magnetic disk. If the slider subsequently comes into contact with the liquid droplet, such as on the next revolution of the magnetic disk, the liquid droplet may cause the slider to “jump” temporarily.
- the read/write head is in the process of performing a read/write process when the slider jumps, then the data being read or written may be corrupted. Thus, it would be advantageous to remove these liquid droplets from the slider before the liquid droplets fall onto the surface of the magnetic disk.
- Another solution to the problem is to heat the slider through the write head in the slider. Because the write head is formed from a coil having a low resistance, it may again take more power than desired to heat the slider enough to dissipate the liquid droplet.
- Embodiments of the invention solve the above and other related problems with an improved process for dissipating liquid droplets that may accumulate on a slider.
- the slider having the liquid droplet is unloaded from the magnetic disk.
- the slider may be unloaded from the magnetic disk and onto a ramp assembly.
- a heating power is applied to a TFC heating element in the slider to increase the temperature of the slider.
- the temperature is increased to a threshold temperature which dissipates any liquid droplets that may have accumulated on the slider.
- the slider may again be loaded onto the magnetic disk.
- the invention may include other exemplary embodiments described below.
- FIG. 1 illustrates a magnetic disk drive
- FIG. 2 is a top view of a magnetic disk drive.
- FIG. 3 is a side view of a magnetic disk drive.
- FIG. 4 is a cross-sectional view of a trailing end of a slider.
- FIG. 5 is a side view of a slider in relation to a magnetic disk with no Thermal Fly-height Control (TFC).
- TFC Thermal Fly-height Control
- FIG. 6 is another side view of a slider in relation to a magnetic disk with Thermal Fly-height Control (TFC).
- TFC Thermal Fly-height Control
- FIG. 7 illustrates a liquid droplet that has accumulated on the trailing end of a slider.
- FIG. 8 is a flow chart illustrating a method of performing a droplet removal process in a magnetic disk drive in an exemplary embodiment of the invention.
- FIG. 9 is a top view of a magnetic disk drive with a slider unloaded from a magnetic disk in an exemplary embodiment of the invention.
- FIGS. 1-9 and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents.
- FIG. 1 illustrates a magnetic disk drive 100 in an exemplary embodiment of the invention.
- Magnetic disk drive 100 includes a spindle 102 that supports a magnetic disk 104 .
- the spindle 102 is connected to a spindle motor 106 that is operable to rotate spindle 102 responsive to a motor current in order to rotate magnetic disk 104 .
- Magnetic disk drive 100 further includes an actuator/suspension arm 110 that supports a slider 114 over the surface of magnetic disk 104 .
- slider 114 includes a read/write head proximate to its trailing end.
- Actuator/suspension arm 110 is connected to a voice coil motor (VCM) 108 that is operable to pivot actuator/suspension arm 110 responsive to a VCM current in order to position the read/write head of slider 114 over desired tracks of magnetic disk 104 .
- VCM voice coil motor
- Magnetic disk drive 100 may include other devices, components, or systems not shown in FIG. 1 .
- magnetic disk drive 100 may include a plurality of magnetic disks 104 connected to spindle 102 and a plurality of actuator/suspension arms 110 supporting sliders 114 over the surface of the magnetic disks 104 .
- FIG. 2 is a top view of magnetic disk drive 100 in an exemplary embodiment of the invention.
- magnetic disk drive 100 further includes a control system 200 .
- Control system 200 includes a spindle motor controller 202 that is operable to apply a motor current to spindle motor 106 (not visible in FIG. 2 ), which controls the rotational speed of magnetic disk 104 .
- Control system 200 further includes a TFC controller 204 that is operable to apply a heating power to one or more TFC heating elements (not shown) in slider 114 in order to control the amount of protrusion of the read/write head.
- Control system 200 further includes a VCM controller 206 that is operable to apply a positional voltage to VCM 108 to control the position of actuator/suspension arm 110 .
- VCM controller 206 is illustrated in this embodiment, those skilled in the art will appreciate that any type of motor controller may be used to control the position of actuator/suspension arm 110 .
- Control system 200 further includes a ramp assembly 230 .
- magnetic disk drive 100 uses ramp load/unload functionality.
- ramp load/unload functionality slider 114 is moved off of magnetic disk 104 by VCM controller 206 prior to power down, as indicated by the arrow. Slider 114 is moved onto a ramp assembly 230 and safely positioned on ramp assembly 230 while magnetic disk drive 100 is powered down. Moving slider 114 from a position proximate to the surface of the magnetic disk 104 to ramp assembly 230 is referred to as “unloading” the slider 114 from magnetic disk 104 .
- When magnetic disk drive 100 subsequently powers on slider 114 is again moved off of ramp assembly 230 when magnetic disk 104 reaches the appropriate rotational speed. Moving slider 114 from ramp assembly 230 to a position proximate to the surface of the magnetic disk 104 is referred to as “loading” the slider 114 onto magnetic disk 104 .
- FIG. 3 is a side view of magnetic disk drive 100 in an exemplary embodiment of the invention.
- Slider 114 is supported above the surface of magnetic disk 104 by actuator/suspension arm 110 .
- Slider 114 includes a front end 302 and an opposing trailing end 304 (which is also referred to as a deposited end).
- Slider 114 also includes an air bearing surface (ABS) 306 that faces toward the surface of magnetic disk 104 .
- a read/write head is fabricated proximate to the trailing end 304 .
- Slider 114 also includes one or more TFC heating elements that are fabricated in slider 114 proximate to the read/write head, which is illustrated in FIG. 4 .
- FIG. 4 is a cross-sectional view of the trailing end 304 of slider 114 in an exemplary embodiment of the invention.
- Trailing end 304 includes the read/write head of slider 114 .
- the read functionality is performed by a read sensor 404 (e.g., a magnetoresistance sensor) that is sandwiched between a front shield 402 and a back shield 403 .
- the write functionality is performed by a write coil 408 .
- one or more TFC heating elements 412 are fabricated in or proximate to trailing end 304 .
- TFC heating element 412 can control the amount of protrusion of read/write head relative to the ABS 306 of slider 114 .
- the use of TFC heating element 412 allows for more precise spacing between the read/write head and magnetic disk 104 .
- FIG. 5 is a side view of slider 114 in relation to magnetic disk 104 with no TFC.
- TFC heating element 412 see FIG. 4
- FIG. 5 shows that there is no protrusion of the read/write head due to TFC.
- FIG. 6 is another side view of slider 114 in relation to magnetic disk 104 with TFC. Due to the protrusion of the read/write head, the spacing between the read/write head and the surface of magnetic disk 104 is reduced. Thus, the spacing can be controlled by the amount of heating power applied to TFC heating element 412 by TFC controller 206 (see FIG. 2 ).
- slider 114 may collect a lubricant from the surface of magnetic disk 104 , or may collect other liquids that condense from vapors in magnetic disk drive 100 . Air flow over the slider surfaces may cause these liquids to accumulate as liquid droplets on low pressure points of slider 114 .
- the low pressure points are typically on ABS 306 of slider 114 , or on trailing end 304 of slider 114 .
- FIG. 7 illustrates a liquid droplet 702 that has accumulated on the trailing end 304 of slider 114 .
- FIG. 7 is a view from the ABS 306 of slider 114 .
- the air flow across ABS 306 typically causes the liquid droplet 702 to accumulate on trailing end 304 .
- liquid droplets may form on other low pressure areas of slider 114 , such as on ABS 306 .
- FIGS. 8-9 and the following description provide an improved process for removing liquid droplets that have formed on the trailing end of sliders.
- FIG. 8 is a flow chart illustrating a method 800 of performing a droplet removal process in a magnetic disk drive in an exemplary embodiment of the invention.
- the droplet removal process may be used to remove a droplet as formed on the trailing end 304 as illustrated in FIG. 7 , or to remove a droplet formed on other surfaces of slider 114 , such as surfaces on ABS 306 .
- Method 800 will be discussed in relation to the magnetic disk drive 100 shown in FIGS. 1-7 , although the method may be implemented in other types of disk drives.
- the steps of the flow chart in FIG. 8 are not all inclusive and may include other steps not shown.
- FIG. 9 is a top view of magnetic disk drive 100 with slider 114 unloaded from magnetic disk 104 in an exemplary embodiment of the invention.
- VCM controller 106 may apply the appropriate voltage to VCM 108 (see FIG. 1 ) to cause actuator/suspension arm 110 to swing off of magnetic disk 104 and onto ramp assembly 230 .
- slider 114 is moved off of magnetic disk 104 and onto ramp assembly 230 , slider 114 is considered “unloaded” from magnetic disk 104 .
- slider 114 may be lifted off of the surface of magnetic disk 104 a threshold distance, such as 1 micron. This type of action may be considered as “unloading” the slider 114 .
- slider 114 may be moved off of magnetic disk 104 , but not onto ramp assembly 230 . This type of action may also be considered as “unloading” the slider 114 .
- a heating power is applied to the TFC heating element 412 in slider 114 to heat slider 114 (or more particularly the trailing end 304 ) to a threshold temperature to dissipate the liquid droplet 702 .
- the operating parameters used in this step may vary based on a number of factors.
- the heating power that is applied to TFC heating element 412 and the threshold time period that the heating power is applied are two operating parameters that are determined or defined for the droplet removal process.
- the heating power may vary based on the composition of the liquid droplet 702 , the size of the liquid droplet 702 , the temperature inside of magnetic disk drive 100 , etc.
- TFC controller 204 may use a percentage of the normal operating power of TFC heating element 412 for fly height control.
- the heating power for the droplet removal process may be in the range of 100-120% of the normal operating power of TFC heating element 412 for fly height control.
- experimentation may be used to determine the heating power needed to dissipate a liquid droplet 702 of varying compositions as a function of time.
- the threshold time period that the heating power is applied may vary based on the composition of the liquid droplet 702 , the size of the liquid droplet 702 , the temperature inside of magnetic disk drive 100 , etc.
- experimentation may be used to determine how long on average it takes to dissipate a liquid droplet 702 of varying compositions as a function of heating power.
- control system 200 such as in a database structure, so that control system 200 can quickly determine how long to apply a heating power during the droplet removal process.
- experimentation may show that a liquid droplet 702 primarily composed of Z-Tetraol (a disk lubricant) is dissipated when a heating power of 90 mW-120 mW is applied to TFC heating element 412 for one minute.
- Z-Tetraol a disk lubricant
- step 806 When the liquid droplet 702 is dissipated from slider 114 , slider 114 is loaded back onto magnetic disk 104 in step 806 (see FIG. 8 ).
- the heating power may be removed from TFC heating element 412 to allow slider 114 to cool. Alternatively, the heating power may be returned to the normal operating power that is used for fly height control.
- spindle motor controller 202 applies the desired motor current to spindle 102 so that magnetic disk 104 reaches the desired rotational speed. With magnetic disk 104 spinning at the desired rotational speed, VCM controller 206 may apply the appropriate voltage to VCM 108 (see FIG.
- FIG. 2 illustrates slider 114 loaded back onto magnetic disk 104 .
- the droplet removal process may be controlled in magnetic disk drive 100 by droplet removal process (DRP) controller 902 .
- DRP controller 902 is operable to execute the logic to perform the droplet removal process, and to control TFC controller 204 and VCM controller 206 appropriately.
- DRP controller 902 may be comprised of instructions that are stored on storage media. The instructions can be retrieved and executed by a processor. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to operate in accordance with the invention.
- the term “processor” refers to a single processing device or a group of inter-operational processing devices. Some examples of processors are computers, integrated circuits, and logic circuitry.
- the droplet removal process as described in FIG. 8 may be activated, initiated, or performed in a variety of scenarios.
- the droplet removal process may be performed upon power up of magnetic disk drive 100 .
- slider 114 is automatically unloaded from magnetic disk 104 because magnetic disk drive 100 implements ramp load/unload functionality.
- DRP controller 902 may instruct TFC controller 204 to apply the heating power for the droplet removal process before loading the slider 114 back onto magnetic disk 104 . This advantageously ensures that liquid droplets are removed from slider 114 each time magnetic disk drive is powered on.
- the droplet removal process may be performed periodically based on threshold time periods. Experimentation may show that a liquid droplet having a size of consequence is formed on the trailing end 304 of slider 114 every 50 minutes of operation. Thus, the droplet removal process may be performed by DRP controller 902 every 50 minutes to dissipate any droplets. In another alternative, the droplet removal process may be performed responsive to detecting the liquid droplet of a threshold size having formed on slider 114 . DRP controller 902 may implement laser technology or some other detection means for detecting when a liquid droplet of a threshold size has formed on slider 114 . When DRP controller 902 has detected such a liquid droplet, the droplet removal process is performed. Those skilled in the art will appreciate that any combination of the above scenarios for performing the droplet removal process may be used, and that other scenarios for performing the droplet removal process exist that are not discussed for the sake of brevity.
Abstract
Description
- 1. Field of the Invention
- The invention is related to the field of magnetic disk drives, and in particular, to performing a droplet removal process to dissipate liquid droplets that form on a slider in a magnetic disk drive.
- 2. Statement of the Problem
- Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders having a read head and a write head. An actuator/suspension arm holds the slider above the surface of the magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the slider to fly a particular height above the magnetic disk. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read/write head over selected tracks of the magnetic disk. The read/write head may then read data from or write data to the tracks of the magnetic disk.
- As the density of magnetic disks increases, it has become more important to precisely control the spacing between the read/write head and the surface of the magnetic disk. The spacing between the read/write head and the surface of the magnetic disk is often referred to as the fly height of the read/write head. One factor contributing to the fly height is the shape of the ABS of the slider and the rotational speed of the magnetic disk. Another factor contributing to the fly height is the amount of protrusion of the read/write head toward the surface of the magnetic disk.
- The read/write head is fabricated from materials that are different than the rest of the slider body. These materials expand and contract at different rates than the slider body. Thus, disk drive manufacturers take advantage of these material properties by embedding one or more heating elements in the read/write head or proximate to the read/write head. The protrusion of the read/write head may thus be precisely controlled by the application of a heating power to the heating element. Controlling the protrusion of a read/write head through the application of a certain heating power to the heating element is referred to herein as Thermal Fly-height Control (TFC).
- As the slider flies over the surface of the magnetic disk, the slider may collect a lubricant that is deposited on the surface of the magnetic disk, or may collect other liquids that condense from vapors in the magnetic disk drive. Air flow over the slider surfaces then causes these liquids to accumulate as liquid droplets on low pressure points of the slider. The low pressure points are typically on the ABS of the slider, or on the trailing end of the slider. When the liquid droplets grow to a sufficient size, they can detach from the slider and fall onto the surface of the magnetic disk. If the slider subsequently comes into contact with the liquid droplet, such as on the next revolution of the magnetic disk, the liquid droplet may cause the slider to “jump” temporarily. If the read/write head is in the process of performing a read/write process when the slider jumps, then the data being read or written may be corrupted. Thus, it would be advantageous to remove these liquid droplets from the slider before the liquid droplets fall onto the surface of the magnetic disk.
- One solution to the problem is to heat the slider while the slider is in an operating position. The heating of the slider can cause the liquid droplets to dissipate before they fall onto the surface of the magnetic disk. Unfortunately, the air flow caused by the rotation of the magnetic disk and the thermal transfer of energy from the slider to the magnetic disk affects the heating of the slider. It may thus take more power than desired to heat the slider enough to dissipate the liquid droplet.
- Another solution to the problem is to heat the slider through the write head in the slider. Because the write head is formed from a coil having a low resistance, it may again take more power than desired to heat the slider enough to dissipate the liquid droplet.
- Yet another solution is to stop the rotation of the magnetic disk, and to land the slider on the surface of the magnetic disk. Such a process of landing the slider on the stationary magnetic disk is traditionally referred to as Contact Start-Stop (CSS). When the slider is parked on the surface of the magnetic disk, a current is passed through the slider body which in turn heats the whole slider. The heating of the slider helps to dissipate the liquid droplets that have accumulated. Unfortunately, heating the slider while it is parked on the surface of the magnetic disk may be harmful to the magnetic disk. Also, passing a current through the entire slider body can damage some components in the slider.
- Embodiments of the invention solve the above and other related problems with an improved process for dissipating liquid droplets that may accumulate on a slider. For a droplet removal processes of the embodiments described herein, the slider having the liquid droplet is unloaded from the magnetic disk. For example, the slider may be unloaded from the magnetic disk and onto a ramp assembly. While unloaded from the magnetic disk, a heating power is applied to a TFC heating element in the slider to increase the temperature of the slider. The temperature is increased to a threshold temperature which dissipates any liquid droplets that may have accumulated on the slider. After the liquid droplets have dissipated, the slider may again be loaded onto the magnetic disk.
- The invention may include other exemplary embodiments described below.
- The same reference number represents the same element or same type of element on all drawings.
-
FIG. 1 illustrates a magnetic disk drive. -
FIG. 2 is a top view of a magnetic disk drive. -
FIG. 3 is a side view of a magnetic disk drive. -
FIG. 4 is a cross-sectional view of a trailing end of a slider. -
FIG. 5 is a side view of a slider in relation to a magnetic disk with no Thermal Fly-height Control (TFC). -
FIG. 6 is another side view of a slider in relation to a magnetic disk with Thermal Fly-height Control (TFC). -
FIG. 7 illustrates a liquid droplet that has accumulated on the trailing end of a slider. -
FIG. 8 is a flow chart illustrating a method of performing a droplet removal process in a magnetic disk drive in an exemplary embodiment of the invention. -
FIG. 9 is a top view of a magnetic disk drive with a slider unloaded from a magnetic disk in an exemplary embodiment of the invention. -
FIGS. 1-9 and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. -
FIG. 1 illustrates amagnetic disk drive 100 in an exemplary embodiment of the invention.Magnetic disk drive 100 includes aspindle 102 that supports amagnetic disk 104. Thespindle 102 is connected to aspindle motor 106 that is operable to rotatespindle 102 responsive to a motor current in order to rotatemagnetic disk 104.Magnetic disk drive 100 further includes an actuator/suspension arm 110 that supports aslider 114 over the surface ofmagnetic disk 104. Although not visible inFIG. 1 ,slider 114 includes a read/write head proximate to its trailing end. Actuator/suspension arm 110 is connected to a voice coil motor (VCM) 108 that is operable to pivot actuator/suspension arm 110 responsive to a VCM current in order to position the read/write head ofslider 114 over desired tracks ofmagnetic disk 104.Magnetic disk drive 100 may include other devices, components, or systems not shown inFIG. 1 . For instance,magnetic disk drive 100 may include a plurality ofmagnetic disks 104 connected to spindle 102 and a plurality of actuator/suspension arms 110 supportingsliders 114 over the surface of themagnetic disks 104. -
FIG. 2 is a top view ofmagnetic disk drive 100 in an exemplary embodiment of the invention. In this view,magnetic disk drive 100 further includes acontrol system 200.Control system 200 includes aspindle motor controller 202 that is operable to apply a motor current to spindle motor 106 (not visible inFIG. 2 ), which controls the rotational speed ofmagnetic disk 104.Control system 200 further includes aTFC controller 204 that is operable to apply a heating power to one or more TFC heating elements (not shown) inslider 114 in order to control the amount of protrusion of the read/write head.Control system 200 further includes aVCM controller 206 that is operable to apply a positional voltage toVCM 108 to control the position of actuator/suspension arm 110. Although aVCM controller 206 is illustrated in this embodiment, those skilled in the art will appreciate that any type of motor controller may be used to control the position of actuator/suspension arm 110. -
Control system 200 further includes aramp assembly 230. Instead of using Contact Start-Stop (CSS) functionality,magnetic disk drive 100 uses ramp load/unload functionality. For ramp load/unload functionality,slider 114 is moved off ofmagnetic disk 104 byVCM controller 206 prior to power down, as indicated by the arrow.Slider 114 is moved onto aramp assembly 230 and safely positioned onramp assembly 230 whilemagnetic disk drive 100 is powered down. Movingslider 114 from a position proximate to the surface of themagnetic disk 104 to rampassembly 230 is referred to as “unloading” theslider 114 frommagnetic disk 104. Whenmagnetic disk drive 100 subsequently powers on,slider 114 is again moved off oframp assembly 230 whenmagnetic disk 104 reaches the appropriate rotational speed. Movingslider 114 fromramp assembly 230 to a position proximate to the surface of themagnetic disk 104 is referred to as “loading” theslider 114 ontomagnetic disk 104. -
FIG. 3 is a side view ofmagnetic disk drive 100 in an exemplary embodiment of the invention.Slider 114 is supported above the surface ofmagnetic disk 104 by actuator/suspension arm 110.Slider 114 includes afront end 302 and an opposing trailing end 304 (which is also referred to as a deposited end).Slider 114 also includes an air bearing surface (ABS) 306 that faces toward the surface ofmagnetic disk 104. A read/write head is fabricated proximate to the trailingend 304.Slider 114 also includes one or more TFC heating elements that are fabricated inslider 114 proximate to the read/write head, which is illustrated inFIG. 4 . -
FIG. 4 is a cross-sectional view of the trailingend 304 ofslider 114 in an exemplary embodiment of the invention. Trailingend 304 includes the read/write head ofslider 114. For the read/write head, the read functionality is performed by a read sensor 404 (e.g., a magnetoresistance sensor) that is sandwiched between afront shield 402 and aback shield 403. The write functionality is performed by awrite coil 408. In addition to the read/write head, one or moreTFC heating elements 412 are fabricated in or proximate to trailingend 304. Because the materials used to form the read/write head have a different thermal rate of expansion than the remainder of the body ofslider 114,TFC heating element 412 can control the amount of protrusion of read/write head relative to theABS 306 ofslider 114. The use ofTFC heating element 412 allows for more precise spacing between the read/write head andmagnetic disk 104. -
FIG. 5 is a side view ofslider 114 in relation tomagnetic disk 104 with no TFC. When no heating power is applied to TFC heating element 412 (seeFIG. 4 ) inslider 114, there is no protrusion of the read/write head due to TFC. There may still be protrusion as a result of heating of the trailingend 304 due to other factors, such as heating due to a current throughwrite coil 408, but it is not controlled as with TFC. - When a heating power is applied to
TFC heating element 412, theTFC heating element 412 causes the read/write head to protrude from theABS 306 toward the surface ofmagnetic disk 104 in a controllable fashion.FIG. 6 is another side view ofslider 114 in relation tomagnetic disk 104 with TFC. Due to the protrusion of the read/write head, the spacing between the read/write head and the surface ofmagnetic disk 104 is reduced. Thus, the spacing can be controlled by the amount of heating power applied toTFC heating element 412 by TFC controller 206 (seeFIG. 2 ). - As
slider 114 flies over the surface ofmagnetic disk 104,slider 114 may collect a lubricant from the surface ofmagnetic disk 104, or may collect other liquids that condense from vapors inmagnetic disk drive 100. Air flow over the slider surfaces may cause these liquids to accumulate as liquid droplets on low pressure points ofslider 114. The low pressure points are typically onABS 306 ofslider 114, or on trailingend 304 ofslider 114. -
FIG. 7 illustrates aliquid droplet 702 that has accumulated on the trailingend 304 ofslider 114.FIG. 7 is a view from theABS 306 ofslider 114. The air flow acrossABS 306 typically causes theliquid droplet 702 to accumulate on trailingend 304. However, liquid droplets may form on other low pressure areas ofslider 114, such as onABS 306. - When the
liquid droplet 702 grows to a sufficient size, it can detach fromslider 114 and fall on the surface ofmagnetic disk 104. Ifslider 114 subsequently comes into contact withliquid droplet 702, such as on the next revolution ofmagnetic disk 104, then theliquid droplet 702 may causeslider 114 to “jump” temporarily which can cause read/write errors. Thus,FIGS. 8-9 and the following description provide an improved process for removing liquid droplets that have formed on the trailing end of sliders. -
FIG. 8 is a flow chart illustrating amethod 800 of performing a droplet removal process in a magnetic disk drive in an exemplary embodiment of the invention. The droplet removal process may be used to remove a droplet as formed on the trailingend 304 as illustrated inFIG. 7 , or to remove a droplet formed on other surfaces ofslider 114, such as surfaces onABS 306.Method 800 will be discussed in relation to themagnetic disk drive 100 shown inFIGS. 1-7 , although the method may be implemented in other types of disk drives. The steps of the flow chart inFIG. 8 are not all inclusive and may include other steps not shown. - In
step 802, theslider 114 is unloaded frommagnetic disk 104 to initiate the droplet removal process.FIG. 9 is a top view ofmagnetic disk drive 100 withslider 114 unloaded frommagnetic disk 104 in an exemplary embodiment of the invention. To unloadslider 114 frommagnetic disk 104,VCM controller 106 may apply the appropriate voltage to VCM 108 (seeFIG. 1 ) to cause actuator/suspension arm 110 to swing off ofmagnetic disk 104 and ontoramp assembly 230. Whenslider 114 is moved off ofmagnetic disk 104 and ontoramp assembly 230,slider 114 is considered “unloaded” frommagnetic disk 104. There may be other ways of unloadingslider 114 frommagnetic disk 104. For example,slider 114 may be lifted off of the surface of magnetic disk 104 a threshold distance, such as 1 micron. This type of action may be considered as “unloading” theslider 114. Alternatively,slider 114 may be moved off ofmagnetic disk 104, but not ontoramp assembly 230. This type of action may also be considered as “unloading” theslider 114. - In
step 804 ofFIG. 8 , a heating power is applied to theTFC heating element 412 inslider 114 to heat slider 114 (or more particularly the trailing end 304) to a threshold temperature to dissipate theliquid droplet 702. The operating parameters used in this step may vary based on a number of factors. For example, the heating power that is applied toTFC heating element 412 and the threshold time period that the heating power is applied are two operating parameters that are determined or defined for the droplet removal process. - The heating power may vary based on the composition of the
liquid droplet 702, the size of theliquid droplet 702, the temperature inside ofmagnetic disk drive 100, etc. To determine the heating power to use for the droplet removal process,TFC controller 204 may use a percentage of the normal operating power ofTFC heating element 412 for fly height control. For example, the heating power for the droplet removal process may be in the range of 100-120% of the normal operating power ofTFC heating element 412 for fly height control. Alternatively, experimentation may be used to determine the heating power needed to dissipate aliquid droplet 702 of varying compositions as a function of time. - Likewise, the threshold time period that the heating power is applied may vary based on the composition of the
liquid droplet 702, the size of theliquid droplet 702, the temperature inside ofmagnetic disk drive 100, etc. To determine the threshold time period to use for the droplet removal process, experimentation may be used to determine how long on average it takes to dissipate aliquid droplet 702 of varying compositions as a function of heating power. These time periods may then be stored incontrol system 200, such as in a database structure, so thatcontrol system 200 can quickly determine how long to apply a heating power during the droplet removal process. For example, experimentation may show that aliquid droplet 702 primarily composed of Z-Tetraol (a disk lubricant) is dissipated when a heating power of 90 mW-120 mW is applied toTFC heating element 412 for one minute. - When the
liquid droplet 702 is dissipated fromslider 114,slider 114 is loaded back ontomagnetic disk 104 in step 806 (seeFIG. 8 ). For the process ofloading slider 114 back onto magnetic disk 104 (seeFIG. 9 ), the heating power may be removed fromTFC heating element 412 to allowslider 114 to cool. Alternatively, the heating power may be returned to the normal operating power that is used for fly height control. Also, ifmagnetic disk 104 was stopped, then spindlemotor controller 202 applies the desired motor current to spindle 102 so thatmagnetic disk 104 reaches the desired rotational speed. Withmagnetic disk 104 spinning at the desired rotational speed,VCM controller 206 may apply the appropriate voltage to VCM 108 (seeFIG. 1 ) to cause actuator/suspension arm 110 to swing off oframp assembly 230 and back ontomagnetic disk 104. Whenslider 114 is moved ontomagnetic disk 104 and off oframp assembly 230,slider 114 is considered “loaded” ontomagnetic disk 104.FIG. 2 illustratesslider 114 loaded back ontomagnetic disk 104. - The droplet removal process may be controlled in
magnetic disk drive 100 by droplet removal process (DRP)controller 902.DRP controller 902 is operable to execute the logic to perform the droplet removal process, and to controlTFC controller 204 andVCM controller 206 appropriately.DRP controller 902 may be comprised of instructions that are stored on storage media. The instructions can be retrieved and executed by a processor. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to operate in accordance with the invention. The term “processor” refers to a single processing device or a group of inter-operational processing devices. Some examples of processors are computers, integrated circuits, and logic circuitry. - The droplet removal process as described in
FIG. 8 may be activated, initiated, or performed in a variety of scenarios. For example, the droplet removal process may be performed upon power up ofmagnetic disk drive 100. Whenmagnetic disk drive 100 is powered down,slider 114 is automatically unloaded frommagnetic disk 104 becausemagnetic disk drive 100 implements ramp load/unload functionality. Thus, whenmagnetic disk drive 100 is powered on,DRP controller 902 may instructTFC controller 204 to apply the heating power for the droplet removal process before loading theslider 114 back ontomagnetic disk 104. This advantageously ensures that liquid droplets are removed fromslider 114 each time magnetic disk drive is powered on. - Alternatively, the droplet removal process may be performed periodically based on threshold time periods. Experimentation may show that a liquid droplet having a size of consequence is formed on the trailing
end 304 ofslider 114 every 50 minutes of operation. Thus, the droplet removal process may be performed byDRP controller 902 every 50 minutes to dissipate any droplets. In another alternative, the droplet removal process may be performed responsive to detecting the liquid droplet of a threshold size having formed onslider 114.DRP controller 902 may implement laser technology or some other detection means for detecting when a liquid droplet of a threshold size has formed onslider 114. WhenDRP controller 902 has detected such a liquid droplet, the droplet removal process is performed. Those skilled in the art will appreciate that any combination of the above scenarios for performing the droplet removal process may be used, and that other scenarios for performing the droplet removal process exist that are not discussed for the sake of brevity. - Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.
Claims (25)
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US12/120,171 US7609473B1 (en) | 2008-05-13 | 2008-05-13 | Dissipation of liquid droplets in a magnetic disk drive |
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US12/120,171 US7609473B1 (en) | 2008-05-13 | 2008-05-13 | Dissipation of liquid droplets in a magnetic disk drive |
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JP2010040084A (en) * | 2008-08-01 | 2010-02-18 | Toshiba Storage Device Corp | Recording medium driving device |
US8068306B2 (en) * | 2009-12-14 | 2011-11-29 | Hitachi Global Storage Technologies Netherlands B.V. | Write quality of HDD heads experiencing temporary fly-height problems |
CN102681571B (en) * | 2011-03-15 | 2015-02-04 | 神基科技股份有限公司 | Heating circuit, electronic device and method for entering operation mode under low temperature environment |
US8929008B1 (en) | 2013-03-14 | 2015-01-06 | WD Media, LLC | Systems and methods for testing magnetic media disks during manufacturing using sliders with temperature sensors |
US8817413B1 (en) | 2013-07-19 | 2014-08-26 | Western Digital Technologies, Inc. | Disk lubricant management in data storage device |
US8804273B1 (en) | 2013-07-23 | 2014-08-12 | Seagate Technology Llc | Head fly height testing and compensation |
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