WO1997007507A1

WO1997007507A1 - Magnetic latch for a movable ramp and associated servo control for head loading

Info

Publication number: WO1997007507A1
Application number: PCT/US1996/013242
Authority: WO
Inventors: David Michael Drouin; Donald Edward Adams
Original assignee: Syquest Technology, Inc.
Priority date: 1995-08-15
Filing date: 1996-08-15
Publication date: 1997-02-27
Also published as: TW307002B

Abstract

A magnetic latch for latching read/write heads on a moving ramp in a removable cartridge disk drive system includes a latch mechanism and a latch plate (318), at least one of which includes a magnetically-attractive plate. The latch mechanism is attached to a voice coil motor actuator and read/write head assembly (302). The magnetic attraction between the latch plate (318) and latch assembly (316) retains the read/write head (308) on the ramp (304) in the presence of shocks and vibration to the disk drive. An associated servo control algorithm (900) controls the read/write head velocity while the head (308) is loaded on a magnetic disk.

Description

DESCRIPTION

Magnetic Latch for a Movable Ramp and Associated Servo Control for Head Loading

Background of the Invention

Field of the Invention

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.

Background of the Related Art

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.

Like fixed disk drives, 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. To read or write data to the disk, 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. Thus 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.

Typically, the read/write head is attached to a voice coil motor (VCM) actuator which loads and unloads the head from the magnetic disk surface. To actuate the VCM, 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. By controlling the voice coil current, the read/write head may be positioned over the disk wherein data is desired to be written or read.

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.

Figure 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.

Also attached to the disk drive base 110 is a movable ramp 112 with a pair of ramp surfaces 114, 116 which are sloped relative to the surfaces of the cartridge disk. During head loading or unloading operations, the read/write heads 104 (one on each side of the disk) 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.

As shown in Figure 2A, 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. As shown in Figure 2B, 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. Similarly, for unloading and retraction of the heads, 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. When unloading a head during power-off conditions, 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. To reduce the torque, 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 prior art arrangement of Figures 1 and 2 suffers from other disadvantages. The restraining force of the protuberances is limited by the need to insure that under worst case conditions the read/write heads can pass over the protuberances as the heads are unloaded. This results in some loss of immunity to shock, especially rotational shock, increasing the possibility that the heads may inadvertently move off the ramp and onto the disk, if the holding force of the protuberances is too light and the ramp moves forward too quickly, the load beams can be flung off the ramp and the read/write heads may land on the disk.

Accordingly, it would be advantageous to provide a more secure latch for restraining read/write heads in a parked position in a removable cartridge disk drive system, it would further be advantageous to provide an improved latch which allows the VCM actuator and head assembly to climb the movable ramp with lower kinetic energy. It would still further be advantageous to provide a servo control algorithm for loading and unloading read/write heads in a removable cartridge disk drive incorporating an improved latch. Other objects and advantages will appear hereinafter.

Summary of the Invention 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.

In one aspect of the present invention, 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.

In another aspect of the present invention, 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. In yet another aspect of the present invention, 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.

Brief Description of the Drawings

The various objects, features and advantages of the present invention may be better understood by examining the Description of the Preferred Embodiment found below, together with the appended figures, wherein: 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 1.

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. Figure 4C 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.

Description of the Preferred Embodiment

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. In a preferred embodiment, the magnet 410 may be a samarium cobalt 80 magnet, such as part number 18DRE0704 manufactured by Magnet Sales Co.

While the movable ramp 304 is in a ramp forward position, the magnetic latch 306 holds the heads 308 on the ramp.

As shown in Fig. 3, as the heads are loaded onto a disk from the ramp, the magnet 410 begins to separate from the latch plate 318, opening the magnetic latch 306.

Although in the preferred embodiment, 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. In a preferred embodiment, the latch assembly 316 is located approximately 3, C-M from the closest point of the voice coil 311.

In a preferred embodiment, 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. Although in the disclosed preferred embodiment, 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. In one variation, 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. In another variation, 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. Conveniently, in the illustrated embodiment of Figs. 4A-4C, 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.

As seen to better advantage in Figs. 6A-6C, 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. Although 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. However, 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. The opening 616 in the bracket 414 allows the magnet 410 to remain in contact with the latch plate 318 when the spring 412 is compressed. 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.

When it is desired to execute a read and/or write operation with a magnetic disk, the voice coil motor actuator 310 loads read/write head 308 onto a disk surface. To accomplish this, 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.

To determine 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. 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. 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 .

In a preferred embodiment, a servo control algorithm according to one or more aspects of the present invention 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. During the velocity control phase, the voice coil control current is set to a value calculated to produce target read/write head velocity. During the measurement phase, 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.

With the voice coil control current removed, there remains a residual current through the coil due to the decay time constant, L/R. The remaining voltage produced by this residual current after the delay period is subtracted from the measured voice coil voltage to obtain the back EMF which is proportional to read/write head angular velocity. From the measured back 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.

In the continuous low current velocity mode, the voice coil control current is continuously applied to the voice coil. Periodically, the algorithm samples the differential amplifier output to obtain the voice coil voltage. Using the known value of the voice coil control current measured during system calibration, the IR voltage is calculated and subtracted from the measured voice coil voltage to yield the back EMF. From 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. During the start of a head loading process, as the read/write heads are parked on the ramp, they are held in place by the magnetic latch. To overcome this force, 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. By operating in the chopped high current velocity servo control mode, the read/write head velocity may be measured and used in a servo control loop. Although an algorithm having a chopped velocity mode is particularly well suited to a disk drive having a movable ramp with a magnetic latch, it is also useful in conjunction with prior art movable ramp and latch mechanisms, for example, such as the system described above with respect to Fig. 1.

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.

In a first subroutine 910, shown in Fig. 9A, the algorithm 900 calibrates the servo control loop prior to loading or unloading the read/write heads from a magnetic disk. In the calibration routine, 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 . In a first series of steps from 912 through 934 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. In a second series of steps beginning at 936, and branching back to 916 through 934, both an offset value and a voice coil resistance value for the continuous low current velocity servo control mode are measured. As before, 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. Thus, 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. In a second subroutine 940, shown in Fig. 9B, the algorithm 900 operates in a chopped high current velocity servo control mode to control the velocity of the read/write heads. In a first series of steps 942 through 946, comprising a measurement phase, 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.

Next, 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. At steps 952 though 958, 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.

In a preferred embodiment, the measurement phase of subroutine 940 has a duration of approximately 300 μsec 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.

Following a first series of steps comprising the measurement phase, 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.

Also, 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.

In a third subroutine 972, shown in Fig. 9C, 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.

If 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.

Next, 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. In a preferred embodiment, each measurement period for the continuous low current velocity servo control mode is 200 μsec. The updated DAC voltage produces a voice coil current and a corresponding read/write head velocity during the measurement period. Also, 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.

Thus, 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.

Head load constants

C_hd_ref equ 00140H ; arget velocity

C_hd_calib equ 0FF00H ;Calibration Ivcm

ADC_P_LIMIT equ 00390H :+Vbemf saturation (chopped)

ADC_N_LIMIT equ 00020H ^■ -Vbemf saturation (chopped)

LOW-P-LIMIT equ 002A0H :+Velocity Limit (chopped)

LOW-N-LIMIT equ 0FC9CH -Velocity Limit (chopped)

HIGH-P-LIMIT equ 002AO0+80H ;+Velocity Limit (continuous)

HIGH-N-LIMIT equ 0FC9CH-80H -Velocity Limit(continuous)

INT-P-LIMIT equ 07C00H :+Integrator rail

INT-N-LIMIT equ 08400H -Integrator rail

UN-P-SAT equ 00180H ;+Vbemf saturatio (continuous)

UN-N-SAT equ -00180H ; -Vbemf saturation(continuous)

VEL-OFFSET equ 00080H ;Velocity offset

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

Copyright ^® 1995 Syquest Technology, Inc. stb cl,AVE_COUNT

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

Calibration and Setup for head load states

load_heads: ; VCM current ON state

Id al,AD_RSLT ;Read Vbemf shr al,#06H add hd_ofst,al Accumulate Vbemf for average ldb al,P2REG IF HGAIN is set calibration jbs all,BN_HGAIN,load_headsl0 at Ivcm = 0 is in progress add un,hd_calib,#dac_zero Set DAC = calibration level st un,dac (Ivcm ! = 0) load_heads10: ldb all,#05H ;Setup A/D to convert Vbemf stb all,AD_CMD

Id al,TIMER2 ;Setup EPA5 to initiate A/D add al,#usec400 ; conversion 400us from now st al,EPA TIME5 ldb state_lvl,#LOAD_HEADS20 Set next interrupt state br DONE_INTERRUPT END of INTERRUPT load -heads20: VCM current OFF state

Id al,AD_RSLT Read Vbemf shr al,#06H add hd_sns,al ;Accumulate Vbemf for average

Id un,#dac_zero ;Set DAC=0 (Ivcm = 0) st un,DAC

Id al,TIMER2 ;Compute time 400us from now add al,#usec400 ldb state_lvl,#LOAD_HEADS ;Set next interrupt state djnz AVE_COUNT,load_heads25 ;Repeat cycle 64 times

Process after calibration measurements shr hd_ofst,#06H ;Compute average Vbemf for lvcm=0

Copyright ^® 1995 Syquest Technology, Inc. shr hd_sns,#06H Compute average Vbemf forlvcm!=0 ldb all,P2REG If HGAIN is not set (low gain) jbc all,BN_HGAIN,Load_heads23 calibration is complete andb all,#not B_HGAIN ELSE setup to calibrate at stb all,P2REG low gain st hd_ofst,hd_ofst_h Store high gain offset value call vsnsl_setup Repeat calibration for low gain br DONE_INTERRUPT END of INTERRUPT

; Setup for head load velocity control load_heads23 : sub hd_cc,hd_ofst,hd_sns Compute Voffset - Veal ldb state_lvl,#LOAD_HEADS30 ,-Set next interrupt state ldb all,#Offh /Initialize integrator reset stb all,xh_tmp ; flags clr X2 _/Initialize velocity add un,#dac_zero /Initialize DAC output st un,DAC ldb all,P2REG /Set high gain mode_^ orb all,#B_HGAIN stb all,P2REG

Id al,TIMER2 _/Set A/D conversion start add al,#usec500 ,-500us from now

; Enable next A/D conversion load_heads25:

St al,EPA_TIME5 _/Set A/D conversion start time ldb all,#05H /Setup A/D to convert Vbemf stb all,AD_CMD br DONE-INTERRUPT /END of INTERRUPT

High VCM current "chopped" velocity control servo

load_heads30: VCM current OFF state Id hd_sns,AD_RSLT Read Vbemf (unused) Id un,#dac_zero Set DAC=0 (Ivcm = 0) st un,DAC ldb all,#05H /Setup next A/D cycle stb all,AD_CMD / to convert Vbemf Id al,TIMER2 / 300us from now add al,#usec300 st al,EPA_TIME5 ldb state lvl,#LOAD HEADS40 /Set next interrupt state

Copyright ^® 1995 Syquest Technology, Inc. br DONE_INTERRUPT END Of INTERRUPT load_heads40: VCM control state

Id hd_sns,AD_RSLT Read Vbemf shr hd_sns,#06H sub hd_sns,hd_ofst_h Adjust Vbemf by offset level

VELOCITY = Vbemf - Voffset mul a,hd_sns,#256 Scale velocity shral a,#4

Id x2,al /Save scaled velocity clr bh /Compute velocity error sub bl, d_ref,#VEL_OFFSET sub bl,al subc bh,ah

Id un,bl Id al,#HIGH_N_LIMIT /Saturate velocity

Id ah,#Offffh / for velocity limits exceeded cmpl b,a jit load_heads43

Id al,#HIGH_P_LIMIT cLr ah cmpl b,a jle load_heads44

Id un,#HIGH_P_LIMIT sjmp load_heads44 load-heads43 :

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 x4,#INT_P_LIMIT sjmp load_heads46

load_heads45:

Id x4,#INT N LIMIT

load_heads46 :

Id al,x4 _/Apply integrator gain shra al,#05H

Copyright ^® 1995 Syqueεt Technology, Inc. add un, al /Add proportional term / to integrator cmp un,#HIGH_N_LIMIT /Saturate UN jle load_heads47 cmp un,#HIGH_P_LIMIT jle load_heads48 Id un,#HIGH_P_LIMIT sjmp load_heads48 load_heads 7:

Id un,#HIGH_N_LIMIT load_heads48: ldb all,xh_tmp Skip high-velocity reset jbc alt,0,dac_output if reset occurred before cmp x2,#VEL_TRIP Check for velocity outside jgt null_integrator trip limits cmp x2,#-VEL_TRIP jit null_integrator sjmp dac_output null-integrator: Id x4,RO /Reset integrator if velocity

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 , TIMER2 add al,#msec001 st at,EPA_TIME5 ldb state_lvl,#LOAD_HEADS30 /Set next interrupt state br DONE-INTERRUPT /END of INTERRUPT

Low VCM current "continuous" velocity controL servo

Id hd_sns, D_RSLT /Read Vbemf shr hd_sns,#06H cmp hd_sns,#ADC_P_LIMIT /Process saturation of Vbemf jnh load_heads51 cmp un,#UN_P_SAT je load_heads510

Id un,#UN_P_SAT sjmp load_heads65 load_heads51: cmp hd_sns,#ADC_N_LIMIT jh load_heads52 load_heads510:

Id un,#00H sjmp load_heads65 load_heads52: sub hd sns,hd ofst h /Adjust Vbemf by offset level / VELOCITY = vbemf - Voffset mul a,hd_sns,#256 /Scale velocity mul b,un,hd_cc /Compute velocity adjustment sub al,bl /Velocity=hd_sns_(un*hd_cc) subc ah,bh shral a,#4

Id x2,al /Save velocity clr bh sub bl,hd_ref,al /Compute velocity error subc bh,ah / VE = hd_ref - velocity

Id un,bl

Id al,#LO _N_LIMIT /Saturate velocity

Id ah,#Offffh / for velocity limits exceeded cmpl b,a jit load_heads55

Id al,#LO _P_LIMIT clr ah cmpl b,a jle load_heads57

Id un,#LOW_P_LIMIT sjmp load_heads57 load_heads55: Id un,#LO _N_LIMIT load heads57:

Copyright ^® 1995 Syquest Technology, Inc. add x4,un /Integrate X4 = X4 + UN cmp x4,#INT_N_LIMIT /Saturate X4 jle load_heads58 cmp x4,#INT_P_LIMIT jle load_heads59

Id x4,#INT_P_LIMIT sjmp load_heads59 load_heads58:

Id x4,#INT_N_LIMIT load_heads59:

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

Id un,#LO _P_LIMIT call switch2high /Switch to high gain "chopped" br load_heads49 / mode if saturated load_heads60:

Id un,#LOW_N_LIMIT call switch2high /Switch to high gain "chopped" br load_heads49 / mode if saturated load_heads65: add al,un,#dac_zero /Output control to DAC st al,DAC ldb all,#05H /Setup A/D to convert stb all,AD_CMD / Vbemf 200us from now

Id al,TIMER2 add al,#usec200 st al,EPA_TIME5 br DONE INTERRUPT /END of INTERRUPT

Switch from continuous to chopped velocity control

switch2high: st un,al /Initialize DAC Level st al,DAC lcb all,P2REG /Set high gain mode orb att,#B HGAIN

-- Switch from chopped to continuous velocity control

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

Claims

Claims:

1. An apparatus for latching a voice coil motor actuator and read/write head assembly in a parked position on a movable ramp mounted inside a housing structure in a removable cartridge disk drive comprising: a magnet; and a magnetically-attractive structure, one of said magnet and said magnetically-attractive structure attached to a portion of the disk drive housing structure, and the other of said magnet and said magnetically-attractive structure connected to the voice coil motor actuator and read/write head assembly, said magnet in contact with said magnetically-attractive structure while the read/write head is parked on the movable ramp in a retracted position.

2. The apparatus of claim 1, wherein said magnet is movably attached to the portion of the disk drive housing structure.

3. The apparatus of claim 2, further comprising spring means movably attaching said magnet to the portion of the disk drive housing structure.

4. The apparatus of claim 3, wherein said magnet has a magnetic pole perpendicularly oriented with respect to the portion of the disk drive housing structure.

5. The apparatus of claim 4, further comprising a bracket, said bracket having a first arm connected to the portion of the disk drive housing structure and a second arm, substantially perpendicular to the first arm, having an opening through which said magnet may pass to make contact with said magnetically-attractive structure.

6. The apparatus of claim 5, wherein said spring means movably attaches said magnet to the portion of the disk drive housing structure by connecting said magnet to said bracket.

7. The apparatus of claim 1 wherein said magnetic attractive structure comprises a second magnet having a polarity opposite to the polarity of said first magnet .

8. A removable cartridge disk drive comprising: a read/write head for reading data from and writing data to a magnetic disk; a movable ramp for parking said read/write head; and a magnetic latch for latching said read/write head while parked on said movable ramp.

9. The removable cartridge disk drive of claim 8, further comprising: a voice coil motor actuator connected to the read/write head for loading said read/write head from said movable ramp onto the magnetic disk; and a servo control loop for controlling the velocity of said read/write head by passing a voice coil control current through the voice coil of the voice coil motor actuator while loading said read/write head onto the magnetic disk.

10. The removable cartridge disk drive of claim 9, wherein said servo control loop operates in a chopped high current velocity servo control mode when the magnitude of the voice coil current exceeds a predetermined threshold, and wherein said servo control loop operates in a continuous low current velocity servo control mode when the magnitude of the voice coil current does not exceed the predetermined threshold.

11. A method of controlling an angular velocity of a read/write head as it is loaded onto a magnetic disk in a disk drive, comprising the steps of: passing a voice coil control current through a voice coil actuator connected to the read/write head to produce the angular velocity; in response to the voice coil control current exceeding a preselected threshold, setting the voice coil control current to zero while measuring a back EMF, scaling the back EMF by a proportionality factor to obtain a measured angular velocity, comparing the measured angular velocity with a target angular velocity to produce a velocity error signal, and integrating the velocity error signal to produce an updated voice coil current to control the angular velocity of the read/write head; and in response to the voice coil control current not exceeding a preselected threshold, measuring the voice coil voltage, subtracting an IR correction factor from the measured voice coil voltage to obtain the back EMF, scaling the back EMF by the proportionality factor to obtain the measured angular velocity, comparing the measured angular velocity with the target angular velocity to produce the velocity error signal, and integrating the velocity error signal to produce the updated voice coil current to control the angular velocity of the read/write head.