Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B21/00—Head arrangements not specific to the method of recording or reproducing
  • G11B21/02—Driving or moving of heads
  • G11B21/12—Raising and lowering; Back-spacing or forward-spacing along track; Returning to starting position otherwise than during transducing operation

Definitions

• the field of the present invention relates to removable cartridge disk drives in general and, more particularly, to a device and method for loading and unloading magnetic read/write heads onto a magnetic disk in a removable cartridge disk drive system.
• Removable cartridge disk drive systems have been available on the market for some time. Like fixed disk drives, removable cartridge disk drive systems provide large storage capacities with relatively rapid access times at low cost. However, unlike fixed disk drives, removable cartridge disk drive systems enable a user to easily replace a relatively high capacity disk, allowing for convenient exchange of large amounts of information between remote sites and for greatly increased system storage capacity.
• removable cartridge disk drive systems use magnetic read/write heads to read and write data stored as magnetic fields on a magnetic disk surface.
• the disk surface is divided into a number of concentrically arranged tracks where data is stored.
• the disk surface is rapidly rotated and the read/write head(s) pass over the surface, following the circumferential path of the track or tracks where the data is to be stored or read.
• the disk drive requires some means for positioning the read/write heads over the disk surface along a track wherein data is to be written or read.
• the read/write head is attached to a voice coil motor (VCM) actuator which loads and unloads the head from the magnetic disk surface.
• VCM voice coil motor
• a control current is passed through the voice coil producing an acceleration and resulting angular velocity in the VCM and the attached read/write head.
• the read/write head may be positioned over the disk wherein data is desired to be written or read.
• the read/write heads When a removable cartridge is inserted into a removable cartridge disk drive, the read/write heads must be loaded onto the disk surface to begin read/write operations. Conversely, while not in use, or when a cartridge is to be removed from the disk drive, the read/write heads must be unloaded from the disk surface. When the heads are unloaded, it is desired to secure them in a parked position where they will be restrained from inadvertently moving back onto the disk surface in response to shocks or vibrations.
• FIG. 1 shows a prior art movable ramp and latch mechanism for loading and unloading read/write heads onto a disk in a removable cartridge disk drive.
• a VCM actuator and head assembly 102 comprises read/write heads 104 attached to a VCM actuator 106 by means of load beams 108.
• the VCM actuator and head assembly 102 is attached to a disk drive base 110.
• a movable ramp 112 with a pair of ramp surfaces 114, 116 which are sloped relative to the surfaces of the cartridge disk.
• the read/write heads 104 are rotated by VCM actuator 106 down or up the ramp surfaces to load or park the heads.
• the movable ramp 112 has a pair of protuberances 118 on each ramp surface. While in a parked position, the VCM actuator and head assembly 102 is 3 restrained by the protuberances 118 from moving down the ramp 112 and onto the disk surface until locked by a linkage assembly.
• the movable ramp 112 may be moved into a fully retracted ramp back position while the read/write heads 104 are not in use, such as when a disk cartridge is being inserted or ejected from the drive.
• the movable ramp 112 is moved into the back position by means of a linkage assembly which is not shown.
• the movable ramp 112 also may be moved into a ramp forward position from which the read/write heads 104 may be loaded onto a disk surface. From the ramp forward position, the entire width of the head load beams 108 must proceed over the protuberances 118 before the torque required to move the heads toward the disk is significantly reduced.
• the load beams must completely clear the protuberances before the read/write heads are secured. It is further desired to reduce the torque requirements for the VCM actuator in the disk drive as this can reduce the cost of the associated electronics in the disk drive.
• a tradeoff exists between the velocity of the load beams as they approach the ramp 4 and the amount of actuator torque which is required to ensure that the load beams can climb the ramp and pass over the protuberances.
• the load beam velocity must be increased as the assembly approaches and climbs the ramp. The resulting vertical acceleration up the ramp and over the protuberances during the head unloading process can damage the delicate head assembly.
• the present invention comprises a device and method for loading and unloading magnetic read/write heads onto a magnetic disk in a removable cartridge disk drive system.
• a removable cart-ridge disk drive incorporates a magnetic latch to secure or latch a read/write head in a parked position on a movable ramp when the head is unloaded from a magnetic disk.
• the attractive force of the magnet tends to recapture the read/write head to its latched position even if a shock causes the head to move momentarily.
• an improved latch for securing a read/write head in a parked position allows the VCM actuator and head assembly to climb the ramp with relatively little kinetic energy or actuator torque.
• the kinetic energy required to climb the ramp is reduced both by the lack of a frictional engagement to be overcome due to the elimination of protuberances on the ramp, and by the attractive force of the magnetic latch urging the VCM actuator and read/write head assembly up the movable ramp.
• a servo control algorithm maintains a constant read/write head velocity during the head load process in a removable cartridge disk drive with a movable ramp having a magnetic latch.
• Figure 1 is a top view of a voice coil motor actuator and head assembly and a movable ramp with a prior art latch mechanism for parking read/write heads in a removable cartridge disk drive system.
• Figure 2A is a top view of a voice coil motor actuator and head assembly retracted in a ramp back position on the movable ramp with the prior art latch mechanism of Figure 1.
• Figure 2B is a top view of a voice coil motor actuator and head assembly in a ramp forward position on the movable ramp with the prior art latch mechanism of
• Figure 3 is a top view of a voice coil motor actuator and head assembly in a ramp forward position on a movable ramp incorporating one embodiment of a magnetic latch constructed according to one or more aspects of the present invention.
• Figure 4A is a front view of a latch assembly for securing a read/write head in a parked position on a movable ramp in a removable cartridge disk drive.
• Figure 4B is a top view of the latch assembly of
• Figure 4A is a side elevation of the latch assembler Figures 4A and 4B.
• Figure 4D is a perspective view of a magnetic latch.
• Figure 5 is a side view of a steel spring for a magnetic latch.
• Figure 6A is a front view of a bracket for a magnetic latch.
• Figure 6B is a top view of the bracket of Figure 6A.
• Figure 6C is a side elevation of the bracket of Figures 6A and 6B.
• Figure 7 is top view of a voice coil motor actuator and head assembly retracted in a ramp back position on a movable ramp with a magnetic latch.
• Figure 8 shows a servo control loop for controlling read/ write head velocity in a removable cartridge disk drive incorporating a magnetic latch.
• Figures 9A-9C show a flow chart for a servo control algorithm for controlling the velocity of a read/write head during a head loading operation.
• Fig. 3 shows a voice coil motor (VCM) actuator and read/write head assembly 302 in a ramp forward position on a movable ramp 304 with a magnetic latch 306 according to one or more aspects of the present invention, with the movable ramp in a ramp forward position.
• the VCM actuator and read/write head assembly 302 comprises read/write heads 308 attached to a VCM actuator 310 by means of load beams 312.
• the VCM actuator includes a voice coil 311.
• the VCM actuator and read/write head assembly 302 and the movable ramp 304 are each attached to a portion of the disk drive housing structure comprising a base plate 314.
• the magnetic latch 306 comprises a latch assembly 316 connected to the base plate 314, and a latch plate 318 connected to the VCM actuator and head assembly 302.
• a preferred embodiment of the latch assembly 316 is shown in Figs. 4A-4C.
• the latch assembly 316 comprises a magnet 410 attached to a spring 412.
• the magnet 410 radiates a flux field of sufficient strength to attract and hold the latch plate 318 on the VCM actuator and head assembly 302 while the read/write heads 308 are parked on the movable ramp 304 in a fully retracted position.
• the magnet 410 may be a samarium cobalt 80 magnet, such as part number 18DRE0704 manufactured by Magnet Sales Co.
• the magnetic latch 306 holds the heads 308 on the ramp.
• the magnet 410 begins to separate from the latch plate 318, opening the magnetic latch 306.
• the latch assembly 316 is mounted on the base plate 314, it is to be understood that the latch assembly may be attached to any suitable portion of the disk drive housing structure.
• the latch assembly 316 is located with respect to the movable ramp 304 such that the magnet 410 is in contact with the latch plate 318 when the read/write heads 308 are parked on the movable ramp.
• the latch assembly also must be located far enough away from the voice coil 311 so that the field of the magnet 410 does not influence the operation of the voice coil.
• the latch assembly 316 is located approximately 3, C-M from the closest point of the voice coil 311.
• the latch plate 318 is fabricated from a magnetically-attractive material, such as a steel plate, a steel f lat head screw, or a similar device, and is fastened to the actuator 310 on the VCM actuator and head assembly.
• magnet 410 is included in the latch assembly 316, it would be understood that other arrangements are possible without departing from the scope and spirit of the present invention.
• the latch plate 318 may be magnetized with a polarity opposite to the polarity of the magnet 410 such that latch plate 318 and magnet 410 attract each other.
• the latch plate 318 may be magnetized and the latch assembly may comprise a nonmagnetized magnetically-attractive plate in place of the magnet 410.
• Fig. 4D shows a preferred embodiment of the magnetic latch 306 comprising the latch assembly 316 and the latch plate 318.
• Fig. 5 shows a preferred embodiment of the spring 412.
• the latch assembly 316 also is provided with a bracket 414.
• the spring 412 is fastened to the bracket 414 by fastening means 416, which may be a bolt and nut, a threaded screw, a spot weld, or a similar device.
• Bracket 414 is in turn attached to the base plate 314.
• bracket 414 has a first arm 610 including a slot 612 for receiving a screw or bolt for attachment to the base plate 314.
• the bracket also has a second arm 614 including an opening 616 through which the magnet 410 may pass to make initial contact with the latch plate 318.
• the preferred embodiment includes the bracket 414 it will be understood that the spring 412 may be directly fastened to the base plate 314 without the bracket 414.
• the bracket improves the operation of the magnetic latch 306 by restraining the forward movement of the magnet 410 and spring 412 toward the latch plate 318 when the read/write heads 308 are being loaded onto a disk.
• Fig. 7 shows the VCM actuator and read/write head assembly 302 retracted on the movable ramp 304 with the magnetic latch 306 of Fig. 3, while the movable ramp itself is retracted in a ramp back position.
• the ramp 304 is moved into a back position by a linkage assembly as discussed above, not shown or forming a part of the present invention.
• the magnet 410 and latch plate 318 are in contact with each other while the read/write heads 308 are in a fully retracted position, with the ramp 304 in the back position, the spring 412 is compressed.
• the voice coil motor actuator 310 loads read/write head 308 onto a disk surface.
• the disk drive passes a control current though the voice coil 311, producing a force which translates to an acceleration and resulting angular velocity in the read/write head 308.
• a servo control loop may be used to control the read/write head velocity.
• the voltage developed across the voice coil of the VCM actuator 310 is measured.
• the measured voice coil voltage is the sum of two components: the back electromotive force (EMF) , which is proportional to the read/write head angular velocity, and the IR voltage drop across the coil's wiring resistance.
• EMF back electromotive force
• the IR voltage drop across the coil's wiring resistance By subtracting the IR voltage drop from the measured voice coil voltage, the EMF is obtained and the read/write head angular velocity is calculated.
• An appropriate control current then may be applies to the voice coil to maintain a target velocity. More details regarding this method of controlling read/write head velocity be found in U.S. Patent No. 4,864,437, entitled "HEAD LOADING VELOCITY CONTROL" assigned to the assignee of the present invention and hereby incorporated herein by reference.
• Fig. 8 shows a preferred embodiment of a servo control loop 800 for controlling read/write head velocity in a disk incorporating a magnetic latch.
• the servo control loop includes differential amplifier 802 which measures the voltage across the coil in the voice coil motor 804. The measured voltage is provided to an analog- to-digital converter (ADC) 806 where it is periodically sampled and converted into a digital word, suitable to be processed by a digital microprocessor 808.
• ADC analog- to-digital converter
• the digital microprocessor 808 executes an algorithm to periodically update an output digital control voltage word, based on the measured voice coil voltage.
• the digital control voltage word is provided to a digital-to- analog converter (DAC) 810 to produce an analog voltage signal.
• the analog voltage signal is provided to a transconductance amplifier 812 which in turn supplies the control current to the voice coil .
• ADC analog- to-digital converter
• DAC digital-to- analog converter
• a servo control algorithm controls the read/write head velocity by switching between two control modes, depending upon the magnitude of the voice coil control current through the voice coil. In response to the magnitude of the control current exceeding a predetermined threshold, the algorithm operates in a chopped high current velocity control servo mode, as will he explained in more detail below. Otherwise, the algorithm operates in a continuous low current velocity control servo mode.
• the algorithm operates in the chopped high current velocity servo control mode in response to the magnitude of the voice coil control current being sufficient to cause the differential amplifier input to saturate on the resulting IR component of the voice coil voltage.
• the chopped high current velocity control mode prevents saturation of the differential amplifier input during measurement of the voice coil voltage by removing the voice coil current.
• the chopped high current velocity servo control mode operates in two phases, i.e., a velocity control phase and a measurement phase.
• the voice coil control current is set to a value calculated to produce target read/write head velocity.
• the voice coil control current is removed. After a delay period over which the coil current decays substantially to zero, voice coil voltage is measured. By removing the current, the voice coil voltage is measured without saturation of the differential amplifier.
• the voice coil control current is continuously applied to the voice coil.
• the algorithm samples the differential amplifier output to obtain the voice coil voltage.
• the IR voltage is calculated and subtracted from the measured voice coil voltage to yield the back EMF.
• the read/write head angular velocity is calculated and compared to a target value, producing a velocity error value.
• the voice coil control current is then adjusted to reduce the velocity error.
• An algorithm having a chopped high current velocity servo control mode is particularly well suited to a disk drive having a movable ramp with a magnetic latch more according to one or more aspects of the present invention.
• the read/write heads are parked on the ramp, they are held in place by the magnetic latch.
• the voice coil control current may be increased to a level where the resultant IR voltage voice across the voice coil saturates the differential amplifier.
• the read/write head velocity may be measured and used in a servo control loop.
• Figs. 9A-9C comprises a flow chart of an algorithm 900 for servo control of the velocity of a read/write head during a head loading operation according to one or more aspects of the present invention.
• the algorithm 900 may be executed whenever it is desired to load a read/write head onto a magnetic disk to initiate a data read or data write operation.
• a complete firmware code listing for a preferred embodiment of a servo control algorithm is provided at the end of this specification pursuant to 37 C.F.R. ⁇ 1.96.
• the firmware code may be executed using an 80C196KR microprocessor manufactured by Intel Corp.
• the algorithm 900 calibrates the servo control loop prior to loading or unloading the read/write heads from a magnetic disk.
• the algorithm measures the offset voltages produced by the servo control loop circuitry, such as the differential amplifier, and the voltage produced by residual current through the voice coil due to the L/R decay time constant .
• an offset value for the chopped high current velocity servo control mode is measured. With the control current set to zero, 64 periodic measurements of the voice coil voltage are taken. The 64 high current offset voltage measurements are then averaged to yield a high current offset value.
• both an offset value and a voice coil resistance value for the continuous low current velocity servo control mode are measured.
• 64 periodic measurements of the voice coil voltage are performed with the control current set to zero.
• the 64 low current offset voltage measurements are averaged to yield a low current offset value.
• the 64 low current offset measurements are alternate- with another 64 measurements of the voice coil voltage wherein the voice coil control current is set to a nominal value.
• the nominal voice coil control current is selected such that the voice coil is urged in a direction up the ramp and against the latch so that no net movement results.
• the measured voice coil voltage, with the voice coil control current set to the nominal value corresponds to the IR voltage loss through the voice coil windings.
• the 64 measurements are averaged to yield a low current IR correction factor.
• the algorithm 900 operates in a chopped high current velocity servo control mode to control the velocity of the read/write heads.
• the control current is set to zero and the back EMF across the voice coil is measured.
• the high current offset value is subtracted and the result is scaled to yield the read/write head velocity.
• the measured read/write head velocity is compared to a target velocity to generate a velocity error.
• the velocity error is then limited, if necessary, to insure that its magnitude does not exceed predetermined positive and negative error limits.
• the velocity error is proportionally integrated with previous error measurements to produce a servo loop filter response.
• the integrated error signal is limited, if necessary, to insure that its magnitude does not exceed predetermined positive and negative limits.
• the measurement phase of subroutine 940 has a duration of approximately 300 ⁇ sec and occurs with a period of approximately 1.3 msec. Part of the time for the measurement phase is a delay time corresponding to the L/R time constant required for the voice coil control current to dissipate toward zero.
• the subroutine 940 executes a second series of steps 966 through 970 comprising a velocity control phase.
• the integrated error signal is used to program the DAC in the servo control loop with a voltage to be applied to the voice coil during the velocity control phase.
• the updated DAC voltage produces an updated voice coil control current and a corresponding read/write head velocity during the velocity control phase.
• the updated voice coil control current is calculated and its magnitude is compared to predetermined saturation thresholds. As long as the magnitude of the current exceeds the thresholds, the algorithm continues to operate in the chopped high current velocity servo control mode. If the current is low enough to insure that the differential amplifier will not be saturated by the IR voltage across the coil, the algorithm switches to the continuous low current velocity servo control mode.
• the algorithm 900 operates in a continuous low current velocity servo control mode to control the velocity of the read/write heads.
• the voice coil voltage is measured and its magnitude is compared to predetermined positive and negative saturation limits of the ADC in the servo control loop. If the limits are exceeded, the magnitude of the voice coil current is reduced and in steps 994 and 996 a new voice coil voltage measurement is made after a fixed delay. In a preferred embodiment, the fixed delay is approximately 200 //sec.
• the voice coil voltage is within the ADC saturation limits, then the low current voltage offset and low current IR correction factor are subtracted from the measured voice coil voltage and the result is scaled to yield the read/write head velocity.
• the measured read/write head velocity is compared to a target velocity to generate a velocity error.
• the velocity error is then limited, if necessary, to insure that its magnitude does not exceed predetermined positive and negative error limits.
• the velocity error is then proportionally integrated with previous error measurements to produce a servo loop filter response.
• the integrated error signal is limited, if necessary, to insure that its magnitude does not exceed predetermined positive and negative limits.
• the integrated error signal is used to program the DAC with a voltage to be applied to the voice coil during the next measurement period.
• each measurement period for the continuous low current velocity servo control mode is 200 ⁇ sec.
• the updated DAC voltage produces a voice coil current and a corresponding read/write head velocity during the measurement period.
• the new voice coil current is calculated and its magnitude is compared to predetermined saturation thresholds. As long as the magnitude of the current does not exceed the thresholds, the algorithm continues to operate in the continuous low current velocity servo control mode. If the saturation limits are exceeded, then the algorithm switches to the chopped high current velocity servo control mode.
• the algorithm 900 provides servo control of the velocity of a read/write head as it is loaded onto a magnetic disk.
• the algorithm 900 may also be executed when it is desired to unload a read/write head from a magnetic disk.
• the present invention has been set forth in the form of its preferred embodiment. It is nevertheless intended that modifications to the magnetic latch and associated servo control algorithm disclosed herein may be made by those skilled in the art without departing from the scope and spirit of the present invention.
• hdldy_setu clru un ;Initialize current DAC output ldb all,P2REG ;Set high gain mode orb all,#B_HGAIN stb all,P2REG ret
• vsnsl_setup Id c,#dac_zero ;Set zero VCM current st c,DAC Id c,#C_hd-ref /Initialize target velocity st c,D_hd_ref Id c,#C_hd-calib ;Initialize calibration current st c,D_hd-calib st RO,D_hd_ofst ;Clear Vbemf offset register st RO,D_hd-sns ;Clear Vbemf sense register ldb cl,#40H ;Average 64 conversions
• Id c,#05C4H Start A/D by OC on TIMER2 stb ch,AD_CMD Set A/D to convert Vbemf/ch5 stb Cl,EPA_CTRL5 Set EPA5 to start A/d on TIMER2
• Id CTIMER2 Get TIMER2 value add c,-#09C40H add to it 10 msec st C,EPA_TIME5 Set OC time to start A/D in 10 msec ldb state_lvl,#LOAD_ Set next interrupt state ret
• Id un,#HIGH_N_LIMIT load-heads44 add x4,un / Integrate X4 X4 + UN cmp x4,#INT_N_LIMIT / Saturate X4 jle load_heads45 cmp x4,#INT_P_LIMIT jle load_heads46
• Id un,RO / is outside trip limits stb RO,xh_tmp dac_output: add al,un,#dac_zero /Set DAC to control Level st al,DAC cmp al,#800H+80H /Check for VCM current over jh load_heads49z / threshold cmp al,#800H-80H jnh load_heads49z call switch21ow /Switch to low gain br load heads59 / "continuous" control load_heads49z : ldb all , #05H /Setup A/D to convert Vbemf stb all , AD_CMD / 1ms from now
• Id al,x4 /Apply integrator gain shra al,#05H add un,al /Add proportional term / to integrator cmp un,#LO _N_LIMIT /Saturate UN jle load_heads60 cmp un,#LOW_P_LIMIT jle load_heads65
• switch2high st un,al /Initialize DAC Level st al,DAC lcb all,P2REG /Set high gain mode orb att,#B HGAIN
• switch21ow ldb all,P2REG / Set low gain mode andb all,#not(B_HGAIN) stb all,P2REG ldb state_lvl,#LOAD_HEADS50 /Set next interrupt state ret

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• 1996
  • 1996-08-15 WO PCT/US1996/013242 patent/WO1997007507A1/en not_active Ceased
  • 1996-10-08 TW TW85109873A patent/TW307002B/zh active

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