Electricity: motive power systems – Positional servo systems – Multiple mode systems
Reexamination Certificate
2000-03-24
2001-08-28
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
Multiple mode systems
C318S595000, C341S144000, C341S141000
Reexamination Certificate
active
06281652
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to magnetic disk drives and, more particularly, to a method of using two lower-resolution digital-to-analog converters (DACs) for converting higher-resolution digital demands into analog signals that monotonically drive an actuator motor in a disk drive.
BACKGROUND OF THE RELATED ART
FIG. 1
is a block diagram of certain portions of a disk drive that are relevant to the present invention. With reference to
FIG. 1
, it is well known that magnetic disk drives generally read and write data on the surface of a rotating magnetic disk with a transducer or head
81
that is located at the far end of a moveable actuator that is moved with a voice coil motor (VCM)
80
. A sampled-data servo control system uses servo control information recorded amongst the data, or on a separate disk, to controllably move the actuator from track to track (“seeking”) and to hold the actuator at a desired position (“track following”). It is unnecessary to provide a detailed discussion of the sampled servo control format, the servo control loop, or servo control systems in general because such systems are well known.
Of relevance to this invention, however, it can be seen in
FIG. 1
that the control loop includes an N-bit digital-to-analog converter (DAC)
31
′ that is used to drive the VCM
80
via a suitable drive circuit
70
′. In operation, the DAC
31
′ receives a coded value in the form of an N-bit demand and then produces an analog output signal having a magnitude corresponding to the value coded into the N-bit demand.
The particular system of
FIG. 1
includes a controller
10
and a VCM driver chip
30
′ that are conventionally provided as separate elements. Other arrangements are possible, but it is important to note that, in order to accommodate the requisite power requirements, a coarser semiconductor fabrication technology is generally used to make the VCM driver chip
30
′ than is used to make the controller
10
. As such, it is generally considered important to minimize the logic embedded within the VCM driver chip
30
′ because of costs associated with an increase in die size.
In general operation, the controller
10
outputs a sequence of N-bit demands to the DAC
31
′, over a serial interface
20
, in accordance with host commands that are received from a host computer (not shown) and in accordance with sampled-servo information that was detected by a head
81
and communicated to the controller
10
via a channel
90
.
Each N-bit demand in the sequence is coded (typically in the form of a binary code) to represent a demanded amount of current to flow through the actuator motor
80
. The DAC
31
′ converts each N-bit demand into an analog output signal in the form of a voltage having a magnitude that corresponds to the N-bit demand. The drive circuit
70
′ suitably receives the analog output signal and controls the current in the coil of the actuator motor
80
accordingly.
The disk drive industry is highly competitive and manufacturers are continuously striving to increase areal density while reducing costs. One of the most common approaches to increasing areal density is to increase track pitch (tpi). In order to effectively track follow in the presence of more and more tightly packed tracks, however, it is necessary to provide finer and finer control of the VCM
80
with a higher resolution DAC. As an example, a 14-bit DAC is needed in order to provide the desired control resolution for contemporary areal density requirements.
Providing a 14-bit DAC on the VCM driver chip
30
, however, uses a relatively large amount of die space as compared with a lower resolution DAC. Consuming more die space, of course, is contrary to the need to reduce costs.
There remains a need, therefore, to provide the higher resolution control needed to satisfy the market's ever increasing TPI requirements at a competitive cost.
SUMMARY OF THE INVENTION
In a first aspect, the invention resides in a method of converting a sequence of N-bit demands into analog output signals that drive an actuator motor in a magnetic disk drive using two lower-resolution digital-to-analog converters (DACs) including a first DAC of at least X-bits of resolution that produces a coarse output signal (where X<N) and a second DAC of at least Y-bits of resolution that produces a fine output signal (where Y<N), the method comprising the steps of: receiving a new N-bit demand derived from a range of N-bit demand values; converting the new N-bit demand into an X-bit command and a Y-bit command by: selecting the X-bit command corresponding to a prior N-bit demand if the new N-bit demand is near enough to the prior N-bit demand such that the new N-bit demand may be attained by re-using the X-bit command which corresponds to the prior N-bit demand and varying the Y-bit command; else selecting a new X-bit command, and subtracting (
114
) the selected X-bit command from the new N-bit demand to calculate a new Y-bit command; producing a coarse output signal with the first DAC based on the selected X-bit command; producing a fine output signal with the second DAC based on the calculated Y-bit command; and combining the coarse and fine output signals to produce the analog output signal that drives the actuator motor.
In a second aspect, the invention resides in a method of converting a sequence of N-bit demands into analog output signals that drive an actuator motor in a magnetic disk drive using two lower-resolution digital-to-analog converters (DACs) including a first DAC of at least X-bits of resolution that produces a coarse output signal (where X<N) and a second DAC of at least Y-bits of resolution that produces a fine output signal (where Y<N), the method comprising the steps of: (a) receiving a new N-bit demand derived from a range of N-bit demand values; (b) converting (
120
) the new N-bit demand into an X-bit command and a Y-bit command wherein X is equal to N−Y+1 such that there are 2
N−Y+1
possible X-bit commands and 2
N−Y+1
operational segments that are each defined by a locus of commands corresponding to one of the 2
N−Y+
possible X-bit commands and a set of 2
Y
Y-bit commands, the converting step including the sub-steps of: (i) selecting the X-bit command corresponding to a prior N-bit demand if the new N-bit demand is near enough to the prior N-bit demand such that the new N-bit demand may be attained by re-using the X-bit command that corresponds to the prior N-bit demand and varying the Y-bit command; else selecting (
113
) a new X-bit command, and (ii) subtracting the selected X-bit command from the new N-bit demand to calculate a Y-bit command; (c) producing a coarse output signal with the first DAC based on the selected X-bit command; (d) producing a fine output signal with the second DAC based on the calculated Y-bit command; (e) scaling the coarse and fine output signals into first and second scaled output signals by using first and second scaling factors that are provided in a ratio of 1:2
N−Y
so that the 2
N−Y+1
operational segments collectively span the range of N-bit demand values by successively overlapping one another by 50 percent, with an endpoint of each operational segment ending near a center of an overlapped operational segment; and (f) summing the first and second scaled output signals together to produce the analog output signal that drives the actuator motor.
REFERENCES:
patent: 3449741 (1969-06-01), Egerton, Jr.
patent: 3850105 (1974-11-01), Aronstein et al.
patent: 3995206 (1976-11-01), Aronstein et al.
patent: 4063236 (1977-12-01), Amemiya et al.
patent: 4149200 (1979-04-01), Card
patent: 4149201 (1979-04-01), Card
patent: 4375636 (1983-03-01), Stack et al.
patent: 4429267 (1984-01-01), Veale
patent: 4599547 (1986-07-01), Ho
patent: 5172115 (1992-12-01), Kerth et al.
patent: 5223771 (1993-06-01), Chari
patent: 5229772 (1993-07-01), Hanlon
patent: 5339299 (1994-08-01), Kagami et al.
patent: 5444582 (1995
Bouchaya George S.
Ryan Robert P.
Ip Paul
Shara Milad G
Western Digital Corporation
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