Patent Application
20080241367
The present invention relates generally to a method of and apparatus for applying lubricant vapor to hard magnetic disks, and more particularly, to such a method and apparatus wherein a flow path for the vapor includes a selectively opened and closed shutter.
Hughes et al., U.S. Pat. No. 6,183,831 (incorporated by reference herein), discloses a method of and apparatus for coating hard magnetic disks with a lubricant film by applying the lubricant (preferably a perfluoropolyether (PFPE) disclosed in U.S. Pat. No. 5,776,577) in vapor, that is gaseous, form to a magnetic layer on the disks in a vacuum chamber. The magnetic disks are sequentially loaded into a flow path of the vapor by a carrying blade that lifts the disks out of cassettes that are transported into and out of the vacuum chamber. The vapor is obtained by supplying sufficient heat to a liquid form of the lubricant in a source located in the vacuum chamber. The resulting vapor flows through a gas diffuser plate prior to being incident on the magnetic disk. A single quartz crystal microbalance (QCM) is included in a gauge for monitoring the flow rate of the lubricant vapor being evaporated from the liquid lubricant source to control the amount of heat applied to the liquid lubricant source and thereby control the temperature of the liquid lubricant and the mass flow rate of vapor lubricant evaporated from the liquid lubricant source.
The foregoing arrangement described in the Hughes et al. patent has performed satisfactorily, but can be improved. There are frequent and prolonged idle or lull intervals during which there is no processing of the hard magnetic disks. During these intervals vapor is continuously evaporated from the liquid lubricant source because of the instabilities associated with starting the evaporation process. Consequently, there is a considerable amount of unused, wasted lubricant that is consumed during the idle periods, causing substantial expense and inefficiencies resulting from frequent shutdowns of the facility applying the coatings to the hard magnetic disks. The shutdowns occur due to the need to replenish the lubricant more often than would be the case if the lubricant were turned off during the idle periods.
Because a vapor flow path continuously exists in the prior system and the disk is raised and lowered into the vapor flow path at the beginning and end of each deposition cycle, the top of the disk has more vapor deposited on it than the bottom of the disk. Consequently, the lube coating is thicker at the top of the disk than the bottom of the disk.
It is, accordingly, an object of the present invention to provide a new and improved method of and apparatus for applying lubricant vapor to hard magnetic disks.
Another object of the invention is to provide a new and improved method of and apparatus for applying lubricant vapor to hard magnetic disks so that the amount of liquid lubricant that is consumed during idle periods is minimized even though heat is continuously applied to the liquid lubricant during the idle periods.
An additional object of the invention is to provide a new and improved method of and apparatus for applying lubricant vapor to hard magnetic disks that achieves a substantial reduction in the amount of wasted liquid lubricant.
A further object of the present invention is to provide a new and improved method of and apparatus for applying lubricant vapor to hard magnetic disks that achieves a substantial reduction in the cost of liquid lubricant.
An added object of the present invention is to provide a new and improved method of and apparatus for applying lubricant vapor to hard magnetic disks in such a way as to provide a lube coating having a substantially uniform thickness.
In accordance with one aspect of the invention, an apparatus is provided for applying lubricant coatings to magnetic disks selectively held in place on a holder in a vacuum chamber while vapor that can form the lubricant coatings is applied to one of the disks while the disc is held in place on the holder. The apparatus comprises a reservoir for liquid that can be vaporized to form the vapor; and a heater for heating the liquid in the reservoir to a lubricant vapor. A flow path for the flow of the lubricant vapor from the reservoir to the disk while the disk is in place on the holder is provided. The flow path includes (a) an apertured diffuser between the reservoir and the holder while the disk is in place in the flow path, and (b) a vapor chamber between the reservoir and the apertured diffuser. The flow path is arranged to be in a vacuum condition while liquid in the reservoir is heated to a lubricant vapor. A shutter that selectively blocks the flow path is arranged so that (1) while the shutter is closed the lubricant vapor is confined to the vapor chamber and (2) while the shutter is open the lubricant vapor flows via the flow path from the reservoir to the disk while the disk is in place in the flow path.
Preferably, the vapor chamber has a volume such that in response to the shutter being closed for a relatively long time, while vaporizing heat is applied to the liquid in the reservoir, pressure in the vapor chamber is such as to cause the volume of liquid in the reservoir to remain substantially constant.
The first and second apertures, as well as the diffuser and shutter, are preferably arranged so that all of the first apertures are simultaneously unblocked and blocked by the shutter being opened and closed, respectively. Consequently, substantially the same amount of lube vapor is deposited on all portions of the face of the hard magnetic disk facing the lube source, resulting in a lube coating having a substantial uniform thickness.
The apertured diffuser preferably includes many first apertures and the shutter includes second apertures in registration with at least some of the first apertures while the shutter is open. The apertured diffuser and the shutter are arranged so none of the first and second apertures are in registration while the shutter is closed. Preferably, the first and second apertures, as well as diffuser and shutter, are arranged so that all of the first apertures are simultaneously unblocked and simultaneously blocked by the shutter being opened and closed respectively. Consequently, the same amount of lube vapor is deposited on all portions of the face of the hard magnetic disk facing the lube source, resulting in a lube coating having a substantially uniform thickness.
In a preferred embodiment, the apertured diffuser includes many first apertures, and the shutter has second apertures in registration with at least some of the first apertures while the shutter is open. The apertured diffuser and the shutter are arranged so none of the first and second apertures are in registration while the shutter is closed.
A further aspect of the invention relates to a method of applying lubricant coatings to magnetic disks. The method includes loading the magnetic disks onto a holder in a vacuum chamber, and applying vaporizing heat to liquid lubricant so vaporized liquid lubricant is supplied to the disks while the disks are in place on the holder. The vaporized liquid is supplied to the disks via a flow path including a vapor chamber and an apertured diffuser and an open shutter. The shutter is closed while no disk is in the flow path and while vaporizing heat continues to be applied to the liquid lubricant and the liquid lubricant continues to be vaporized.
When there is a substantial idle or lull in the application of the disks to the flow path, the the shutter is maintained in a closed condition during the lull and vaporizing heat is continuously applied to the liquid lubricant during the lull so that pressure in the vapor chamber during the lull is such as to cause the volume of liquid in a liquid reservoir in the vapor chamber to remain substantially constant.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings.
Reference is now made to the drawings that includes lubricant (frequently referred to as lube) source 10 and housing 12 including vacuum chamber 14 that is maintained by a suitable vacuum pump (not shown) at a suitable vacuum pressure. Located in chamber 14 is holder 16 for hard magnetic disk 18 that includes a substrate layer overlaid by a chromium layer, in turn overlaid by a magnetic layer, as disclosed in the aforementioned patents. Holder 16 sequentially lifts different hard magnetic disks from cassettes that are sequentially moved into and out of vacuum chamber 14 so that the disks are brought to the position illustrated In
Source 10 includes an atmospheric portion 20, maintained at atmospheric pressure, and a vacuum portion 22, maintained at approximately the same vacuum pressure as the vacuum in chamber 14 by virtue of a gas flow path that frequently exists between vacuum portion 22 and chamber 14. Liquid lube reservoir 24, that is carried by housing 25, is in vacuum portion 22 as are (1) vapor volume 26, (2) selectively opened and closed diffuser shutter 28 and (3) diffuser plate 30.
Vapor volume 26 is a cavity having a cylindrical sidewall 32 extending at right angles to planar faces 34 and 36 that are parallel to each other and define boundaries of the vapor volume. One face of reservoir 24 occupies a substantial portion of face 34, and a first planar face of diffuser shutter 28 (
As illustrated in
The liquid lube in reservoir 24 is heated to a vapor by resistive heater coil 50 in atmospheric portion 20 of source 10. The vaporized lube flows from reservoir 24 into vapor volume 26, thence through open diffuser shutter 28 and diffuser plate 30 toward hard disk 18 and holder 16 while the holder has lifted the hard disk from a cassette to the position illustrated in
When diffuser shutter 28 is closed, as occurs during substantial idle or lull periods in the operation of source 10 while no hard magnetic disks are being processed, none of the apertures in the diffuser shutter and diffuser plate 30 are in registration so the vaporized lube quickly fills vapor volume 26. As a result of the vaporized lube filling vapor volume 26 while diffuser shutter 28 is closed, the pressure in the vapor volume increases sufficiently so that additional vapor is not evaporated from reservoir 24, even though the amount of heat applied to the liquid lube in reservoir 24 by heater coil 50 remains approximately constant. As a result, there is a minimum amount of wasted lube evaporated from reservoir 24 during the substantial idle or lull periods. By continuously applying heat to the liquid in reservoir 24, instabilities in the evaporation of liquid from reservoir 24 that have a tendency to occur as result of starting and stopping the heating process of the liquid lube in reservoir 24 are avoided.
Diffuser plate 30 includes many rows of closely spaced, relatively small circular openings (not shown) that are aligned and in register with corresponding openings 52 (
Piezoelectric crystals 70 and 72 (both located in housing 71) selectively monitor the deposition rate of vapor lube flowing through vapor volume 26, such that during a first time interval crystal 70 is coupled to vapor volume 26 to the exclusion of crystal 72, and during a second time interval crystal 72 is coupled to the vapor volume to the exclusion of crystal 70. During a third time interval, neither crystal 70 nor crystal 72 is coupled to the vapor volume. During the first and second intervals, particles of lube vapor in vapor volume 26 are incident on crystals 70 and 72. During the third interval, no vapor lube particles are incident on the crystals.
Shutter 73 is selectively interposed in fluid flow paths between volume 26 and crystals 70 and 72 to achieve these results. Shutter 73 reduces the exposure time of crystals 70 and 72 to the lube vapor during lull or idle periods to reduce maintenance expenses by prolonging the useful life of the crystals. The use of plural deposition rate monitoring crystals 70 and 72, rather than a single deposition rate monitoring crystal, helps to achieve the same beneficial result.
To these ends, sidewall 32 of vapor volume 26 includes aligned openings 74 and 76 that are displaced from each other along the length of the wall between reservoir 24 and diffuser shutter 28. Openings 74 and 76 are respectively in fluid flow relationship with cylindrical passages 78 and 80 having outlet apertures respectively in close proximity to piezoelectric crystals 70 and 72, preferably of the QCM type that is available from Maxteck Inc. of Beaverton Oreg. Rotary shutter 73 is in the form of a rotatable disk driven by shaft 84, in turn driven by pneumatic motor 86 and linkage 88 so shutter 73 is selectively located between the outlet apertures of passages 78 and 80 and crystals 70 and 72. Motor 86 is in the atmosphere and is carried by housing 89 that is connected to flange 60. Crystals 70 and 72, shutter 73, shaft 84 and a portion of linkage 88 are in the vacuum of chamber 14, while motor 86, housing 89 and the remainder of linkage 88 are at atmospheric pressure.
Housing 71 for crystals 70 and 72 progressively heats up to the temperature of process chamber 14 after chamber 14 has been in operation for a while. However, initial calibration of the deposition rate detected by crystals 70 and 72 and indicated by the frequency derived by oscillator 122 (
To mitigate this potential vulnerability in control of vapor flow rate, the temperatures of crystals 70 and 72 are actively controlled by controlling the temperature of housing 71 so it is constant. To this end, a cooling mechanism is included in housing 71 to maintain crystals 70 and 72 at a constant temperature so the reading derived from crystals 70 and 72 is always with reference to a constant temperature of fluid coolant (air or water as appropriate). The coolant fluid flows to and from housing 71 by tubes 75, 77 and 79 such that the coolant fluid in tubes 77 and 79 respectively provide primary cooling to crystals 70 and 72. The heated coolant flowing through tube 79 flows back to heat exchanger 81, where it is cooled and recirculated back to tubes 77 and 79. The amount of cooling imparted by heat exchanger 81 to the recirculated coolant fluid is controlled by temperature detector 83 that is imbedded in housing 71 to effectively monitor the temperature of crystals 70 and 72. Detector 83 is electrically connected by a suitable cable (not shown) to the heat exchanger.
Cylindrical sidewall 32 of vapor volume 26 is part of heater block 90, having a high thermal conductivity, made preferably of copper or some other relatively inexpensive, high thermal conductivity metal that aids in reducing condensation of vapor lube on block 90. Because block 90 is made of a high thermal conductivity material the entire length of each wall of block 90 is at a substantially uniform temperature so differential condensation of vapor on the same wall surfaces of block 90 is minimized.
Block 90 includes circular base 92 that provides a high thermal conductivity path for heat from resistive heating coil 50 to the liquid in reservoir 24. Block 90 includes heat choke 94. Heat choke 94 is a portion of block having a high thermal impedance compared to the rest of block 90. Heat choke 94 is a circular groove 102 between base 92 and circular flange 96, the inner periphery of which forms cylindrical sidewall 32 of vapor volume 26 to enable block 90 to have two thermal zones, one formed by base 92 and a second formed by flange 96. Block 90, in combination with resistive heating elements and a temperature detector arrangement, causes sidewall 32 of vapor volume 26 to be at a predetermined temperature, such as 5° C., above the temperature of base 92 of block 90 that provides the high thermal conductivity path for heat from resistive heating coil 50 to the liquid in reservoir 24. As a result, condensation of lube vapor in vapor volume 26 onto sidewall 32 is minimized, to provide more efficient operation of source 10.
Circular base 92 has a planar circular face 98 that is in vacuum portion 22 of source 10 and abuts a planar, circular face of housing 25 for reservoir 24. Face 98 is in a plane at right angles to a straight-line path from reservoir 24 to face 36 of diffuser shutter 28 from which extends annular flange or ring 96. Base 92 includes a planar circular face 100 that is parallel to face 98. Resistive heating coil 50 includes a planar circular face that abuts face 100 to assist in providing the high thermal conductivity path between the resistive heating coil and reservoir 24.
Base 90 includes the deep annular groove 104 in face 100 that is in atmospheric portion 20 of source 10. Groove 102 extends from face 100 almost to face 102 to form a narrow neck (that constitutes heat choke 94) between base 92 and flange 94. Because of heat choke 94 it is possible, through the use of active temperature control, to maintain base 92 and flange 94 at different temperatures. The active temperature control is provided, inter alia, by embedding four mutually perpendicular resistive heating coils 111-114 in flange 94 in close proximity to wall 32. Only heating coils 111 and 113, that are diametrically opposite from each other, are illustrated in
Resistive temperature detectors 116 and 118 are respectively embedded in base 92 and flange 94 of block 90, to separately monitor the temperatures of the base and flange. Consequently, temperature detectors 116 and 118 effectively derive responses indicative of the temperatures of (1) the liquid lube in reservoir 24 and (2) wall 32 of vapor volume 26. A feedback controller of the type illustrated schematically in
Reference is now made to the schematic diagram of
The frequency of oscillator 122 is determined by the resonant frequency of the crystal 70 or 72, connected by switch 120 to the oscillator. Consequently, the frequency of oscillator 122 is generally indicative of the mass flow rate of the lube vapor being detected by the active one of crystals 70 or 72, as determined by the position of shutter 73. Frequency detector 124 responds to the frequency generated by oscillator 122, to derive a DC voltage indicative of the frequency derived by oscillator 122. Function generator 126 responds to the DC voltage derived by detector 124 to derive a voltage indicative of the mass flow rate of the lube vapor detected by the active one of crystals 70 or 72.
The output signal of function generator 126 is compared in magnitude with the output signal of mass flow rate set point signal source 128 in subtractor 130 that derives an error signal indicative of the deviation between the desired mass flow rate of vapor lube in vapor volume 26 and the actual flow rate of the vapor lube in volume 26. The error output signal of subtractor 130 is applied to function generator 132 that converts the mass flow rate error signal to an error signal for the temperature of reservoir 24, that is, an error signal that is influential in controlling the amount of current supplied to resistive heating coil 50.
Temperature controller 134, for the amplitude of current that is supplied to resistive heating coil 50, responds to (1) the output signal of function generator 132, (2) signals derived from reservoir temperature set point source 136, and (3) the temperature sensed by resistive temperature detector 116. In essence, temperature controller 134 responds to the signals resulting from resistive temperature detector 116 and set point source 136 to determine the difference between the actual and desired temperatures of base 92 of block 90 to derive a temperature error signal. The temperature error signal is modified by the signal from function generator 132 to compensate for the error in the mass flow rate of the vapor lube flowing through volume 22. Temperature controller 134 responds to the modified error signal to control the current amplitude flowing through resistive heating coil 50 that in turn controls the temperature of base 92.
Temperature controller 138, for the amplitude of current flowing through series connected resistive heating coils 111-114 in flange 94, is responsive to signals derived in response to the temperatures detected by resistive temperature detectors 116 and 118, respectively in base 92 and flange 94 of block 90. In addition, temperature controller 138 responds to (1) the set point signal that source 136 derives for the temperature of reservoir 24, and (2) a set point signal that source 140 derives for the desired temperature difference between flange 94 and base 92. In essence, temperature controller 138 determines the temperature difference between base 92 and flange 94 by responding to the signals derived in response to the resistive changes of resistive temperature detectors 116 and 118. The temperature difference between base 92 and flange 94 is compared with the desired temperature difference between the base and flange, as derived by set point source 140 to derive an error signal indicative of the change in the amplitude of current supplied by temperature controller 138 to resistive heating coils 111-114. The error signal is combined with the output signal of reservoir temperature set point source 136 to control the actual amplitude of current supplied by temperature controller 138 to resistive heating coils 111-114.
While there has been described and illustrated a specific embodiment of the invention, it will be clear that variations in the details of the embodiment specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims.
