Dual voltage servo system and method.

<b>RELATED APPLICATION</b>

0001This application is a continuation-in-part of U.S. Patent Application S.N. 07/764,590, filed September 24, 1991, entitled High Capacity, Low Profile Disk Drive System, which is incorporated herein by reference.

<b>FIELD OF THE INVENTION</b>

0002This application relates to disk drives generally, and particularly relates to servo systems for removable disk drives.

<b>BACKGROUND OF THE INVENTION</b>

0003Notebook computers have become commonplace both in the workplace and in the home. However, one difficulty which continues to exist is how to transfer data from a notebook system to a desktop system.

0004Many users of notebook computers rely on floppy diskettes to transfer their data. However, floppies suffer from a number of limitations, including low capacity, low speed and relatively poor reliability. Cable based file transfers are also commonplace, but require the presence of both machines, as well as knowing precisely which files are to be transferred.

0005Removable disk drives installable in both the portable and the desktop machine offer perhaps the most effective method of transferring data, because it allows users to compactly transport all of their programs and data in exactly the proper arrangement. In this manner no files are forgotten, no directories or partitions have to be relearned, and capacity is comparatively huge.

0006One problem with removable disk drives is that portable computers typically provide only a five volt supply, which tends to limit the performance of the disk drive when installed in a portable. Desktop machines, on the other hand, provide both five and twelve volt supplies, and users of desktop machines quickly become accustomed to the higher disk performance available with a twelve volt supply. Those skilled in the art will recognize that the voice coil motor used to position the heads over the disk in most modern disk drives offers significantly better performance when driven with a twelve volt supply than with a five volt supply.

0007As a result, while it is necessary in the current state of the art for a disk drive to function on five volts in the environment of a portable computer, it is highly desirable for the disk drive to function on twelve volts in the environment of a desktop computer.

<b>SUMMARY OF THE INVENTION</b>

0008Embodiments of the present invention resolve the limitations of the prior art by providing a removable disk drive which is capable of determining whether the available supply voltage is twelve volts or five volts, and providing a performance characteristic in accordance therewith.

0009The performance improvements provided by these embodiments are primarily directed to operation of the actuator in seeking mode which is controlled using gray code information from the servo demodulator. Once the actuator arrives close to the target track, a combination of gray code and fine servo burst positioning information is used to accurately position the actuator on track. To simplify design, in a presently preferred embodiment the read/write logic and spindle driver use only a five volt supply regardless of the availability of twelve volts.

0010More specifically, a simple voltage sensing circuit determines what the available supply voltage is. If only five volts are present, the micro-controller is set for a moderance performance characteristic, stored in EPROM, and during recalibration the various parameters that primarily determine access time are set to match the five volt supply.

0011On the other hand, if a twelve volt supply is sensed, the micro-controller selects a higher performance trajectory, also stored in EPROM, and during recalibration sets the various parameters accordingly. The result is that the actuator is driven with larger currents, causing faster response times.

0012Thus embodiments of the present invention provide a voltage sensing disk drive wherein the actuator may be driven either by five volts or twelve volts.

0013Embodiments of the present invention also provide a disk drive which provides higher performance when supplied with both twelve and five volts than when supplied with only five volts.

0014In addition embodiments of the present invention provide a removable disk drive which may be used in either a notebook computer or a desktop computer and automatically provides performance characteristics optimized for the particular environment.

0015These and other embodiments of the present invention may be better appreciated by the following Detailed Description of the Invention, taken together with the attached Figures.

<b>BRIEF DESCRIPTION OF THE DRAWINGS</b>

0016Figure 1 shows in perspective view a removable disk drive embodying the present invention.

0017Figure 2 shows in simplified schematic diagram form a dual voltage sensing and control circuitry embodying the present invention.

0018Figure 3 shows in schematic diagram form a more detailed view of the dual voltage sensing and control circuitry.

0019Figures 4A-F show in detailed schematic block diagram form the dual voltage sensing and control circuitry.

<b>DETAILED DESCRIPTION OF THE</b><b>PRESENTLY PREFERRED EMBODIMENTS</b>

0020Referring now to Figure 1, a disk drive 10 (of the type shown in U.S. Patent Application S.N. 07/764,590, filed September 24, 1991, entitled High Capacity, Low Profile Disk Drive System, and incorporated herein by reference) may be seen to comprise a head and disk assembly 20 together with a controller 30. The controller 30 basically drives a spindle motor 40, an actuator 50 which typically includes a voice coil motor 60 for positioning a set of heads 70 over one or more disks 80, and read/write logic 90 for writing to and reading from the disk(s).

0021Certain embodiments of the present invention are concerned primarily with apparatus and methods for driving the actuator. More particularly, these embodiments are directed to driving the actuator during seeking with performance characteristics matched to the supply voltage. More specifically, the DAC scaling range is altered depending on the available voltage, and the seek trajectory and servo coefficients are similarly selected based on the available voltage. However, because the disk drive must operate on both five volts and twelve volts, the spindle motor and read/write logic operate using only a five volt supply.

0022Referring next to Figure 2, which is a simplified schematic of the actuator drive circuitry, supply voltage VCM_VCC is provided by the host system (either a portable or a desktop computer) at line 100. Five volts is supplied at line 102 for use with the rest of the machine. A voltage divider comprised of R1 and R2 serves as a scaling network, with the supply voltage being sensed by an A/D converter 104 connected at point A between the two resistors. The particular values of R1 and R2 are selected to match the input characteristics for the A/D converter 104, which in an exemplary embodiment forms a portion of a Zilog Z86C95 microcontroller. Thus, for the A/D converter portion of a Z86C95 where an input of 3.00 volts indicates both twelve and five volt supplies are available while an input of 2.60 volts indicates only a five volt supply is available, the values of R1 and R2 may be 27.4K and 2.0K ohms, respectively.

0023The voltage sensed by the A/D converter 104 at point A is supplied to a digital signal processor portion 106 of the Z86C95, which sets the scaling of a D/A converter portion 108. Although the particular scaling values are subject to design choices, good success has been achieved in the presently preferred embodiment by choosing a scalar of two for 12 volt operation, and a scalar of one for five volt operation. In addition, the DSP 106 sets a seek trajectory and servo coefficients based on the voltage sensed at the point A, and supplies those parameters to a microcontroller 110.

0024A voltage to current converter 112, responsive to signals from the D/A converter controls a VCM driver circuit 114. A transconductance amplifier is typically used to control current. The VCM driver circuit is required to work over a relatively wide voltage range, to accommodate both five volt and twelve volt operation, and may for example be an Allegro 8958.

0025Referring next to Figure 3, the circuitry of Figure 2 may be understood in somewhat greater detail. To assist in understanding the circuitry, a discussion of the key parameters which control access time may be helpful. There are five dominant parameters in the seek operation that substantially control access time. TACH_GAIN is a constant multiplier that determines velocity feedback.

0026V_LEAD represents a velocity correction factor for the velocity estimator during acceleration, and is typically added to multiple of TACH_GAIN and the absolute value of the gray code difference. V_LAG, or Velocity Lag, represents a velocity correction factor for the velocity estimator during deceleration, and is typically subtracted from the multiple of TACH_GAIN and the absolute value of the gray code difference. FEED_FORWARD represents an anticipated deceleration characteristic. DAC_GAIN represents a programmable characteristic of the Zilog Z86C95 device, which permits scaling depending on whether low vold or high voltage is sensed.

0027The operation of the controller 30 during seeking initially involves determining a desired tract T_D at start point 300. The absolute value of the number of tracks between the existing track and the desired track ("tracks to go") is calculated at 310, and that value is supplied to a velocity table 312. The velocity table 312, which scales its output so that full scale is 90 ips for twelve volts and 53 ips for five volts, outputs a V_cmd signal which is summed at 314 with a negative velocity feedback signal 316. The velocity table typically defines a curve where the Y axis represents a velocity command and the X axis represents tracks to go, with the value of X being a maximum at the origin.

0028The sum of the V_cmd signal and the feedback signal 316 is scaled at 318 by a factor K_error. The value of K_error is set for two if VCM_VCC is five volts, but set for one if VCM_VCC is twelve volts. The scaled results are then summed at adder 320 with a predicted signal from a feedforward generator 322, and the output is supplied to a DAC 324. The DAC 324 is scaled according to the value of VCM_VCC, with a factor of 0.5 if VCM_VCC is five volts, and a value of one if VCM_VCC is twelve volts. It will be appreciated that the respective values of K_error and DAC scaling multiply to unity for both values of VCM_VCC.

0029The output of the DAC is supplied to a transconductance amplifier 326 which is directly connected to VCM_VCC and has a gain of .55 a/v during seeking. In the "on track" mode, the gain of the amplifier 326 is reduced to one-fourth of its gain during seeking. The amplifier 326 drives the actuator 50 so that the heads are moved across the disk.

0030Gray code feedback 340 is provided from the servo demodulator in the ASIC and the absolute value of the gray code difference supplies the input to the velocity estimating logic 342. The velocity estimating logic 342 provides the velocity feedback signal 316 during both acceleration and deceleration, but difference equations are used to define the signal during the respective stages. During acceleration, the velocity estimate is derived by multiplying a constant, referred to as TACH_GAIN, times the absolute value of the gray code difference, and summing that multiple with the value of V_LEAD. During deceleration, the velocity estimate is the multiple of TACH_GAIN times the absolute value of the gray code difference, minus the value of V_LAG.

0031For a presently preferred embodiment, TACH_GAIN is set to 9.44 when VCM_VCC is five volts, and is set to 5.5 when VCM_VCC is twelve volts. The velocity estimate signal 316 is then fed back to the summing junction 314, as noted previously. Similarly, position data, X, is fed back to the absolute value adder 310, and the iterative process repeats.

0032The foregoing values are exemplary only, and apply particularly to a disk configured to have 3300 tpi and a sample rate of 143 microseconds. In such an embodiment, for a VCM_VCC of twelve volts the access time is on the order of eleven milliseconds, while for a VCM_VCC of five volts the access time is on the order of 16.5 milliseconds.

0033Referring next to Figures 4A-F, the circuitry for implementing the methodology of Figure 3 may be better understood. Figure 4A represents an overview of the circuit, and includes a disk controller 400, typically an ASIC, which communicates with a microcontroller 410, a read/write channel 420 and power drivers 430. Each of these devices communicates with the HDA, which connects at an HDA connector 440, while the disk controller 400 communicates with the host bus through a connector 450.

0034Referring next to Figure 4B, the read/write channel can be better understood, in which the read/write channel logic 420 is embodied in an IMP62C738 device. External to the channel logic are synthesizer and data separator phase locked loops 422 and 424, respectively.

0035Referring next to Figure 4C, the disk controller 400 may be better appreciated. The disk controller 400 externally communicates with a cache RAM device 402 and an appropriate oscillator 404. Turning next to Figure 4D, the microcontroller/DSP, typically a Z86C95 or equivalent, receives sense data from the resistors R1 and R2 as discussed in connection with Figure 2, and provides Valid High and Valid Low signals VAHI and VALO. Servo error signals are provided on a DAC line, while data is buffered through a 29C256 device 412.

0036With regard to Figure 4E, the spindle motor logic is shown in greater detail. The motor phase signals are provided at lines OA-OC and CT, while a pair of zener diodes provide isolation between VCM_VCC and five volts. Figure 4F illustrates in detail a notch filter used to eliminate most of the mechanical resonance in the system, and also illustrates the circuitry for providing high and low reference values for the D/A converter.