Multi-path to data facility for disk drive transducer arms

An improved disk file is disclosed including multiple independent transducer/actuator arrays disposed about a common disk (stack) and adapted to afford a plurality of alternate "Data-paths" whereby (virtually any) track on any disk may be accessed for data-in/data-out using a selectible one of several "data paths". In one type embodiment, this is implemented by switching-over between electronic-control stages when one such stage fails. In another type embodiment, it is afforded by providing overlapping track coverage by multiple head-units. Here, for any given (pair of) disk faces, each of several actuator arrays is assigned a respective set of tracks to cover as its "primary responsibility", also being assigned another adjacent set of tracks as its "secondary" (back-up) responsibility. Such arrangements can provide such benefits as "multiple paths to data", and can convert "Hard" failure to "Soft" failure.

BACKGROUND, FEATURES OF INVENTION 
This invention relates to novel arrangements for manipulating 
electromagnetic actuator systems. 
Magnetic disk files for recording and storing data are widely used in data 
processing; e.g., as peripheral memory. Disk files have the advantage of 
facilitating data transfer at randomly selected address locations (tracks) 
and without need for the "serial seek" mode characteristic of magnetic 
tape memories. 
As workers are aware, the transducers used in association with disk 
recording surfaces must be reciprocated very rapidly between selected 
address locations (tracks) with high precision. It will be recognized as 
important for such a system to move a transducer very rapidly between data 
locations; and to do so with high positional accuracy between 
closely-spaced track addresses. This constraint becomes very tricky as 
track density increases--as is presently the case. Typically, such disk 
storage systems mount the transducer head on an arm carried by a block 
that is supported by a carriage. This carriage is usually mounted on track 
ways for reciprocation by an associated transducer actuator. 
Workers will recognize that the present trend is toward ever higher track 
density with increased storage capacity and decreased access time. Of 
course, as track density rises, closer control over the actuator mechanism 
is necessary to position transducer heads accurately over any selected 
track, lest signals be recorded, or read, with too much distortion, and 
without proper amplitude control, etc. 
Known Positioners: 
Such transducer actuators (linear positioners) employed with magnetic disk 
memory systems are subject to stringent requirements; for instance, these 
systems typically involve a stack of several magnetic disks, each with 
many hundreds of concentric recording tracks spanning a radius of about 12 
inches; and a head-carrying arm is typically provided to access each pair 
of opposing disk surfaces. This arm will typically carry two to four heads 
so that it need be moved only about 3 inches (radially) to position its 
heads adjacent any selected track. Thus, it will be appreciated that such 
applications involve extreme positioning accuracy together with very high 
translation speeds (to minimize access time--a significant portion of 
which is used for head positioning). Such a positioner must move its 
transducer heads very rapidly so that the associated computer can process 
data as fast as possible--computer time being so expensive that any 
significant delay over an extended period (of even a fraction of a 
millisecond) can raise costs enormously ("transition time", during which 
heads are moved from track to track, is "dead time" insofar as data 
processing is concerned, of course). Thus, computer manufacturers 
typically set specifications that require such inter-track movements to 
take no more than a few milliseconds. Such high speed translation imposes 
extreme design requirements: it postulates a powerful motor of relatively 
low mass (including carriage weight) and low translational friction. 
Another requirement for such head positioners is that they exhibit a 
relatively long stroke, on the order of 1-4 inches or more, in order to 
minimize the number of heads required per recording surface [pair]. 
The prior art discloses many such positioner devices, including some 
intended for use in magnetic disk memory systems: e.g., see U.S. Pat. Nos. 
3,135,880; 3,314,057; 3,619,673; 3,922,720; 4,001,889; 4,150,407; 
3,544,980; 3,646,536; 3,665,433; 3,666,977; 3,827,081; and 3,922,718 among 
others. 
Among prior art approaches are the "Head-per-Track" approach whereby (some 
or all) disk faces, or pair thereof, are provided with a head which is 
"dedicated" to a respective track. This will be contrasted with the more 
usual "movable head" systems, which may be used alone, or with such a 
"Head-per-Track" arrangement; the latter here covering some of the tracks 
in some or all of the disk faces. 
Workers recall that such actuator carriages are driven by various actuator 
mechanisms, including the well known "voice coil" motor (VCM, comprising a 
solenoid like those used to drive an audio speaker). Such are explained in 
my cited copending U.S. Ser. No. 106,847, as are various "flat-coil" 
actuators according to a feature hereof. 
FIG. 26 shows a simplified view of a prior art disk pack D-D understood as 
comprising an array of like recording disks mounted to be co-rotated on a 
common spindle and spaced uniformly therealong, each disk having a pair of 
recording faces with a plurality of concentric recording track sites (tr) 
and being accessible by read/write transducer such as those indicated. The 
indicated transducers are mounted in pairs from a common axis arm with a 
plurality of arms projecting in common from a single transducer actuator 
TA adapted to reciprocate the arms in common to position one of the given 
heads above an associated selected track site as well known in the art. 
A disk drive (DD) will be understood conventionally as a mechanism that 
holds several magnetic disks, keeps them spinning, and moves the 
read/write heads into position when information must be read from, or 
stored on, one of the disks. One presently popular form of DD technology, 
the "Winchester", is viewed as highly reliable by today's standards, yet 
has a mean time between failure (MTBF) of from 8,000-12,000 hours (see 
April 1981 Edition of Output Magazine, pages 24,25). The cited article 
mentions that the principle drawback for such technology (or for any form 
of "on-line mass memory") is "the lack of a secure backup system" raising 
the equation: How can a user protect against loss of (much or all of) a 
data base if his on-line memory is damaged by machine malfunction, by 
programming or operator error, by fire or any similar calamity? 
It is acknowledged that the excellent MTBF's of present (Winchester) 
technology offers a high degree of reassurance--but it is just not high 
enough for many users of DD memory who are troubled by the likelihood of 
"Hard" failure at 8,000-12,000 hours. Thus many workers now ponder how to 
secure a suitable backup. One suggestion is a backup system based on 
floppy disks; another is based on "Streaming" tape drives (which run 
continuously instead of in the conventional start-stop fashion); another 
are data cartridges or video cassettes. All these backup systems are 
typically more expensive then users care to indulge these days and (e.g., 
in the case of floppies) will very seriously degrade the operation of the 
DD unit. 
"Dual Path to Data" concept: 
A salient feature of this invention involves modifying a typical disk drive 
arrangement (e.g., like that above mentioned) so as to exhibit a "dual 
path to data" capability, analogous to (actually) having a plurality of 
head-actuator units available to provide "overlapping coverage" to (some 
or all) of the tracks in each disk stack. Thus, for instance, with each 
pair of disk faces having a related pair of transducer-actuator units 
available to access both faces, failure of any one unit can automatically 
invoke the substitution of the other unit. 
Similarly, each such actuator unit in the pair may include a similar 
control stage so that failure of one control stage can automatically 
invoke substitution of the other compensatorily. Thus, as further 
explained below, workers will appreciate that a "dual path to data" 
capability can be afforded either by multiple transducer actuators giving 
"overlapping coverage" or by multiple actuator controls which are 
"cross-switchable", or both implementations where feasible. It is an 
object to teach this. 
"Cross-switchable" actuator controls: 
For a simplistic showing of such a multiple actuator control arrangement 
please note FIGS. 21, 22 and 23, (described below in detail) where failure 
of one control unit is understood to automatically invoke a "substitution 
sequence" calling in the companion control unit and thus keeping the 
system "on the air". 
"Overlapping-coverage" by multiple transducer units: 
FIGS. 1A and 24 (described below in detail) schematically indicate the 
other approach whereby (selected) record faces are given "overlapping 
coverage" by a plurality (two are shown) of transducer actuator arrays, 
and to be cooperatively controlled and manipulated to afford such a "dual 
path to data" feature. That is, if one actuator unit fails, its companion 
unit may be called in to "cover" for it (i.e. to service the tracks 
primarily assigned to the failed unit). 
Vulnerability to failure of typical disk drive; (FIG. 25): 
Workers in the art of designing, making and/or using EDP systems are 
acutely sensitive to the problem of "catastrophic system failure" or 
"Hard" failure, where for some reason an entire EDP system or subsystem 
becomes essentially inoperative for a significant time. While an entire 
system is thus "off the air" some very bad things begin to happen: People 
in the user establishment typically rely very heavily on the EDP system 
(and it is typically too expensive to afford redundancy whereby a "standby 
system" is available for substitution--except in the case of a few 
ultra-large installations). Extreme pressure is brought to bear on the 
user's people every second the system is "down". 
These people in turn very quickly make the system's vendor (sales people, 
leasing agent and associated manufacturing people) acutely aware of how 
unpleasant their life has suddenly become. A parallel pressure is applied 
to the purveyor's management because of the loss of leasing revenue or the 
possibility of a system "return", loss of future sales, etc. Thus everyone 
concerned with an EDP system will go to enormous lengths to keep it "on 
the air", even if this means it might "limp along" for a time at reduced 
effectiveness (e.g., operating at reduced speed) this being known in the 
art as "Soft" failure. 
Now the disk drive (DD) components in such an EDP system are typically the 
most critical (present the greatest risk) viz a viz such a "Hard" failure 
of the entire system. This is because a DD unit is so used that it is 
usually "ON-Line" and it is not feasible to "bypass" it if it fails 
(unlike other different components, such as tape drives, card readers or 
printers, etc., which can themselves "go down" without dragging the whole 
EDP system down with them--this is partly because such input and output 
devices do not typically operate "on-line" with the CPU and in "real 
time", whereas a DD unit often does; thus if such off-line I/O unit fails, 
the system CPU may "busy itself", at least temporarily, by turning to 
other tasks; but this is not possible with a DD which typically may be the 
only "data-bridge" between the CPU and the outside world, spending much of 
its operating life linked "on-line" into the "data-paths" of the CPU while 
the CPU is manipulating and temporarily storing data; thus "Hard" failure 
of the DD unit by analogy "blows a fuse" in the on-line "data-path" of the 
CPU and so shuts down the entire system). 
Illustrative processing cycle of an EDP system, DD failure: 
An illustration may help clarify things. FIG. 25 is intended to very 
schematically and functionally depict such a typical EDP system with a 
pair of host central processors (CUP-1,-2) surrounded by clusters of 
servient peripheral units such as the array of card readers, CR, the array 
of cathod ray terminals CRT (typically with a keyboard for communicating 
to a CPU) an array of high speed printer units, PR, an array of tape 
drives, T, an array of Key-to-tape units KT, an array of optical reader 
units RP, an array of phone line connections, or modems, TM, and several 
disk drive units DD. The system is very sketchily shown, of course, but it 
will be understood as operating according to present good state-of-the-art 
practice. 
Briefly recounting a typical operating day for this EDP system in FIG. 25 
may be instructive, assuming the system is used in a large commercial 
bank, for example. During business hours, system operators will typically 
keep the CPUs busy, e.g., access either to provide current business 
information to management or to customers such as a daily summary of the 
latest status of bank finances and those of major customers or similar 
summary reports to large customers on the state of their accounts (e.g., 
to minimize their "float" and maximize profits on the use of their money). 
Also they may answer specific real-time queries of bank management or 
customers (e.g., a new customer wants a very large loan for 10 days: Can 
the bank swing it?--or the creditor of a customer inquires after his 
credit status, payment record, etc.). For instance, in a time-sharing 
mode, the two CP units might be capable of handling questions from 10 CRT 
units and several modem terminals, while also plugging-in and -out with 
one of the DD units in the course of answering questions and manipulating 
data. During the day company business and customer account changes 
typically involve a massive real time traffic demands on the system. 
For this reason other, less pressing tasks are deferred; e.g., such tasks 
as updating accounts, receiving reports from satellite bank branches 
reconciling debits and credits for the whole bank network to arrive at an 
accurate overall balance. These tasks are relegated to the non-business 
hours (e.g., late evening) when the CP units are not otherwise busy--then 
the CP may attend to these and other "housekeeping" duties. 
Thus, during the evening, input is received from branch banks and 
customers, etc.; e.g., being provided through the telephone modem units 
(perhaps being stored temporarily on a DD for fast transmission off the 
wire, then later dumped at a slower rate into tape drive units). Night 
workers may feed in results from the day's mail and from the day's 
transaction receipts (e.g., via card reader units CR or Key-to-tape) and 
these may be fed to similar slow-speed archival memory (tape drive). The 
CP units may then, in their own good time, call-up such input data once it 
has been fully received, organized and stored in local memory, doing this 
at the usual fast efficient rate (e.g., when the CP is ready to summarize 
the day's transactions or to begin updating customer accounts, etc.). Just 
before this, it will direct the appropriate tape drive to make a memory 
dump to a specific DD, the CPU keeping busy meanwhile on other things 
during the slow-speed dump--and later turning to the DD for high-speed 
data interchange in "real time". As workers know, it is more efficient for 
a CP to talk to a DD with the usual "fast data rate" then to a much 
slower, serially-organized tape drive--hence the TD uses the DD as its 
"middleman". 
In this manner, all the input data for the previous business day may be 
digested and stored in the system, with accounts reconciled and status 
reports prepared (printed) prior to the beginning of the next day's 
business day. 
Workers will recognize that in all these typical system operations the DD 
is the only peripheral unit that is so co-operative with the CP units 
operation in real time that it can actually "pull down" the CPU if it 
fails. That is, if a CP unit is working on a given block of data 
temporarily stored on a given DD and the DD fails during some manipulating 
sequence (e.g., while figuring a certain payroll--with all the hours, 
rates, latest deductions, etc., etc., stored on the DD for real-time use 
by the CP) this DD-failure will typically block further operation (on this 
sequence at least) by the CP. Of course in certain instances it may be 
possible for the CP to abort the entire sequence and start anew with a 
second DD unit, but this would mean an extravagant waste of time and money 
and few operations allow for this. 
Objects: 
Thus, I have discovered that preventing "Hard failure" of a DD unit is 
especially critical to operation of an entire EDP system. (Presently 
workers say that DD failure accounts for almost all of the urgent service 
calls to an EDP site). Accordingly, by this invention, I have addressed 
the problem of DD Hard failure and attempted to ameliorate this, 
converting it to a "Soft" failure to the obvious benefit of an entire 
associated EDP system. 
I have learned that DD failure is very often due to failure of a motor; 
less often because of a head crash; even less often due to failure of the 
actuator or the head electronics, (as workers know, once any head impacts 
a disk in a typical fixed DD all the other heads will "crash" against 
their confronting disk, gouging the disk and themselves, and of course 
destroying data in the process). Indeed I have found that the DD units are 
the most prone to serious failure of a type which interrupts the overall 
EDP system and "brings it down", resulting in expensive down-time and 
service calls. Here, I address the problem of DD failure and associated 
blockage of a "DP path" in an EDP system, and attempt to alleviate this by 
providing for "soft-failure" of a DD unit via a "multi-path to data" 
capability. That is, this approach focuses on the criticality of 
head-actuator units and provides "alternate paths to data", at least for 
all critical tracks in a disk file. A preferred way is to do so by 
providing alternative modes of "soft-failure" for the head actuator 
portions of a disk file. 
One preferred soft failure results from providing a novel "cross-bar" 
arrangement between a plurality of like head actuator arrays serving a 
common disk file whereby the electronic-control stage for each array is 
connected to be "cross-coupled" to one or several other arrays for 
emergency servicing thereof. 
"Soft-failure": is also here taught as implemented by providing a plurality 
of head-actuator units for all (critical) tracks, these units having a 
capability for overlapping track coverage, in case of emergency. That is, 
this "multi-path to data" approach provides two or more transducer units 
for each recording disk face, or pair of faces. The above mentioned flat 
coil actuator design will be seen to facilitate this. This may be 
optimized by apportioning transducer coverage across each given disk face 
and providing for "emergency mode" overlapping coverage by adjacent 
transducer units. 
Multiple overlapping transducer coverage; Ex. I: 
An Example of this multiple overlapping transducer coverage may be 
understood as follows with a given conventional Fixed Disk Drive with the 
disk file thereof presenting like disk recording faces, each with 1,000 
tracks and with three (3) associated transducer arrays: array i, array ii 
and array iii. Each array is conventionally adapted to be translated 
radially to a selected track in its associated track set. Array i is 
assigned to normally cover a first group of tracks, namely outermost 
tracks 1-100, these being the most frequently used; array ii is assigned 
to normally cover tracks 101-300, the next most "popular" tracks; array 
iii is assigned to cover the rest: namely tracks 301-1000. Each transducer 
array will, according to this invention, be adapted to also cover the 
adjacent track span in a prescribed "emergency mode" of operation. In this 
emergency mode, for example, if transducer array i fails for any reason, 
the adjacent array ii can be (automatically) thrown into emergency mode 
and operated to cover the tracks of array i (i.e., tracks 1-100) as well 
as its regularly assigned span. 
Similarly, if the array ii goes down, either adjacent array i and/or array 
iii can be thrown into emergency mode to cover its track span (#101-300) 
and so forth. This characterizes this kind of "Soft failure" capability 
(as well as a "multi-path to data" or "overlapping transducer coverage") 
since the failure of any one transducer array does not cause catastrophic 
failure of the DD unit or of the associated EDP system. Rather it merely 
throws the DD into an emergency mode which will characteristically operate 
a bit slower and less efficiently but nonetheless keep the entire EDP 
system "on the air"--something very desparately desired in the art now as 
workers know. 
Similarly, in certain operating modes, such a "multiple overlapping 
transducer coverage" can be advantageously used in regular, non-emergency 
operations. For instance, to reduce access time and improve DD 
performance. That is, the hardware and software can be arranged in such a 
DD so that while any one transducer array (array i) is operating on a 
given assigned track (e.g., #11) and where the "next track up" (e.g., #91) 
happens to lie in the same span of tracks (e.g., #1-100) covered by this 
"busy" array, the system will turn to the adjacent transducer (array ii) 
invoking an "assist mode" and, translating it to that track, to service it 
as soon as the first array i is finished (with track #11; e.g., while the 
"busy" transducer i is awaiting completion of a disk revolution, as it 
sometimes must). This second transducer will now be used, rather than the 
first, to operate on this "next-up" track. Workers in the art will 
appreciate how such multiple track coverage and how such anticipation of 
"translation time" can reduce access time, since translation time is the 
biggest obstacle to fast access in a DD unit. Other variants of this 
"assist mode" and overlapping transducer coverage will be appreciated by 
those skilled in the art. 
"Cross-bar" feature: 
Another related implementation of the "multi-path to data" capability 
involves such a system having a plurality of transducers per disk file 
(stack), each with associated control means, wherein a control means for 
one transducer unit may be switched to operate another unit in the 
file--e.g., where one control unit fails, the associated transducer may 
still be operated (albeit somewhat slower) perhaps while awaiting field 
repair; the system thus going "fail-soft" and not going down completely! 
To this end the control means are inter-coupled with "cross-bar" means 
allowing them to be so switched. 
Workers will see that this implementation can even be used to dispense with 
the abovementioned redundant transducer coverage or overlapping 
transducers while yet keeping many of its salient advantages. That is, it 
may be preferable to use the overlapping multiple transducer feature 
together with this "cross-bar" coupling control unit;--however, it will be 
apparent that for a cost-reduced DD one may dispense with the overlapping, 
while yet still achieving "Soft-failure" and multi-path to data capability 
by just cross-coupling the actuator control units, (for instance, as 
indicated in FIG. 23, further described below). With this feature, the DD 
will "Fail-soft" and keep the system on the air when one of several head 
actuator control units fails. Of course, this "cross-coupling" of control 
stages (cross-bar feature) is preferably used together with the multiple 
actuator per face implementation for a more comprehensive fail-soft 
capability. 
Thus, one object of this invention is to provide the mentioned and other 
features and advantages. A related object is to do so providing a 
"multi-path to data" capability in a disk drive, converting "Hard" failure 
thereof to "Soft" failure. A related object is to do this using 
"cross-coupling" of actuator control stages. Another object is to do so 
providing multiple-transducer per track capability. Yet a further object 
is to teach the use of such modules with independent multiple transducer 
control whereby transducers can be operated independent and in parallel 
(e.g., one engaged in "read/write" while one or several others are 
"seeking" their next read/write address; or some heads positioned over 
oft-used tracks while others "seek" randomly). 
Another object is to do so providing "multiple paths to data" (multi-port 
flexibility), with multiple transducer assemblies arranged to cover the 
same addresses, at least in "emergency mode" (and/or in an "assist mode").

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1B is an idealized perspective view of salient portions of a novel 
"dual-path" disk drive comprising a rotatable multi-disk pack Pk arranged 
to be controllably rotated, e.g., by motor m.sub.p, and otherwise operated 
relatively conventionally, except that it is operatively associated with a 
plurality of like actuator modules MA to be described hereafter. According 
to one feature hereof, this arrangement comprises a first stack of 
actuators MA-1 comprising 16 identical stacked actuators ("odd gap" stack) 
each designed to service one of the odd-numbered gaps in the 64 disk stack 
Pk, while a like "even stack" MA-2 comprises similar array of actuators, 
each designed to service one of the even-numbered gaps. Workers will 
appreciate that, here, two stacks rather than one are shown; this 
illustrating a feature of convenience with the invention. That is, rather 
than being stacked in a single vertical array, the flat coil actuators 
according to the invention are preferably broken up and organized into two 
stacks (as here) or into four stacks, etc., etc., as one may prefer. 
According to a related feature, each of these stacks MA-1, MA-2 is 
replicated in a second set: "even stack" MA-3 and second "odd stack" MA-4, 
these equivalent to MA-1, MA-2, respectively, except that where the first 
two stacks cover the outer disk tracks principally, the second stack pair 
are designed to cover the inner (half of the) disk tracks. As a 
supplemental feature, all stacks preferably have a secondary ("backup") 
capability to service the entire track array (e.g., in case a companion 
actuator is disabled or otherwise occupied). 
Attention is directed to FIGS. 1B-8 (especially FIGS. 3 and 4) where a 
single one of the actuator assemblies MA according to the invention, is 
shown. Each stack MA is arranged to provide a stacked module, or array of 
actuators and associated magnets and to provide positioner arm means for 
an associated set of transducer heads. Each stack MA will be understood as 
comprising a prescribed number of independent actuator strips A-m stacked 
vertically, each being adapted to be reciprocated along a prescribed 
carriage-way between a respective array of opposed permanent magnet pairs 
(see magnets m, FIG. 2) to position associated transducer means in a 
respective inter-disk gap. In FIG. 3, four illustrative actuator strips 
A-m1 to A-m4 are shown by way of example, with their forward, 
transducer-carrying ends adapted to project respective heads h into the 
disk stack (indicated in phantom and well known in the art). 
FIGS. 7 and 8 give a perspective view of a preferred embodiment of "flat 
coil" linear positioner A-m in accordance with this invention. Such an 
embodiment can be considered as comprised of two primary assemblies: the 
mobile armature-carriage assembly A-c essentially including the flat 
coils, head mount, roller bearing and support means; plus the fixed 
housing and permanent magnet structure A-g with the magnet shunts, sides, 
etc. 
As shown in the drawings for purposes of illustration, the invention is to 
be understood as incorporated in a magnetic disk memory system, including 
a plurality of disks D in a conventional stacked array Pk, arranged in 
vertical spaced relation with a related stacked array of head assemblies 
h. Each head assembly h is mounted at the distal end of an armature 
carriage A-m to be reciprocated back and forth in its disk-gap relative to 
a respective pair of magnetic recording disk surfaces. 
With selective positioning of each head assembly in a conventional manner, 
the "flat armature" (coil) means provided according to the invention, may 
be electrically energized to move into a retracted or extended position as 
known in the art (relative to the associated pair of disk surfaces) and 
read or record information on any selected track thereof. Thus, the head 
assemblies h are supported in pairs on actuator strip A-m, to be projected 
in cantilever fashion as part of a rolling carriage supported by rollers r 
and movable along track rails R. The reciprocating actuator assembly A-m, 
carrying coil C, is operable when coil C is current-energized in a 
conventional manner, to move the carriage along the associated cavity, 
toward and away from the disk stack between a plurality of precisely 
located addresses, these addresses, or track positions, determine the 
position of heads within the stack in the known manner. 
FIG. 4 indicates the opposite (rear) end of the actuators including their 
flexible connector (head cable) means CB-1, etc., and associated 
connections, these being provided conventionally and as known in the art. 
For illustration purposes, one such actuator assembly module MA is 
indicated schematically in FIG. 1A where, for simplicity of illustration, 
the actuator strips, associated permanent magnets m, etc., are removed, 
except for magnets m shown in phantom. Actuator array MA is arranged 
according to the invention to house a prescribed number of identical 
stacked actuator assemblies (here, four places shown, each assembly being 
separated by a prescribed metal shield-support or partition 1-p, 1-p', 
1-p"). Array MA is peripherally defined by a pair of metal sides 1-1, 1-1' 
connected and closed by a pair of (upper and lower) magnetic shunt plates 
(1-2, 1-2', respectively). Shunts 1-2, 1-2' are preferably comprised of 
cold rolled steel or other low reluctance material so as to offer a low 
resistance magnetic (shunt) return path for actuator flux. 
The inner portions of sides 1-1, 1-1' are cut-out to form slots 1-cv, etc., 
or elongate linear grooves for receiving guide rails (see rails R in FIG. 
8); these rails, in turn, to be engaged by a respective pair of roller 
assemblies r projecting from frame A-m--as indicated in more detail in the 
sectional view of FIG. 8, and the perspective of FIG. 7, for instance. The 
structure MA is preferably formed in a standard module with a prescribed 
standard height, width and length (h,w,l, respectively), such that these 
actuators may be stacked vertically. Thus, where a larger array of 
actuators is desired, the appropriate number of such modules may be added 
on, being stacked adjacent their associated gaps, (the number of 
compartments per stage is optional). 
As detailed in FIGS. 5, 6 and 7, each actuator strip A-m includes two 
double roller assemblies r on each side thereof (or two such opposed by a 
single third roller as an option, see FIG. 7). These dual-opposed wheels 
are adapted, as known in the art, to engage a respective guide rail R as 
indicated in FIG. 8, in rolling contact when the assembly A-m is 
translated along its elongate axis (in moving head assembly h relative to 
track addresses on a respective pair of disks D as well known in the art). 
Each actuator strip A-m is adapted to be so-reciprocated along a 
respective actuator cavity between opposed sets of permanent magnet poles 
m (here, four such pole pairs are shown in FIG. 6A at P-1/P-1'; P-2/P-2'; 
P-3/P-3'; P-4/P-4'; see also FIG. 2 where four such actuator strips A-m1 
through A-m4 are illustrated schematically as apt for reciprocation, when 
energized, along the strip's axis and between opposed sets of pole pairs). 
FIGS. 5-7 also illustrate details of such a flat coil actuator strip A-m 
where, according to various further features of novelty, the strip is 
formed into a relatively thin, light-weight, planar body and is adapted to 
receive flat coil windings; (--preferably as a printed circuit board PCB, 
with two or more flat, overlapped coils C printed thereon). Electronic 
circuit means e is also preferably mounted on each strip A-m at the 
designer's option, (e.g., read/write electronics for the associated 
actuator). 
Such a "flat armature" A-m will be understood to comprise a "planar 
trolley" carrying read/write heads h at its distal end and mounted on 
bearings to be reciprocated freely along a track between upper and lower 
relatively flat opposing pole pairs. The arrangment of magnets and 
housing, including magnetic shunts 1-2, 1-2' will be understood as forming 
a "closed" flux loop (return path) as mentioned, with flux direction as 
indicated in dotted line .phi.. Here, as opposed to a VC motor, the flux 
return path will be seen as "contained" (not "uncontained" or 
substantially in-air, as with a VC motor), lying principally across the 
working gap, so that return flux participates as working flux. This design 
dispenses with the tubular bobbin and helical coils of a VCM--in favor of 
the flat mandrel or support on which the several flat conductor loops are 
placed. These loops will comprise one or several turns (preferably eight 
coils of eleven turns each and staggered with a 0.625" pitch, as indicated 
in FIGS. 9A-9F--these loops comprising a moving coil through which the 
activating current passes to generate the "working flux" which moves the 
unit. 
Workers will be surprised how thin such an actuator can be (e.g., a 
thickness of about 3/4" is readily achieved using 1/16" PC board with 
copper cladding plus 1/2" thick magnets on 1/16" sheet steel, leaving an 
air gap of about 0.1"). 
The operation of such a novel, "flat coil" ("flat armature") actuator will 
be apparent to those skilled in the art; that is, the motor or linear 
positioner so formed will be understood as comprised of four flat plates 
(PC boards) supporting eight flat overlapped coils C with the head h and 
associated electronics e mounted at the front end of board A-m, and with 
bearings and associated rollers supporting the board edge for movement 
along respective rails. In operation, only one of the two overlapped 
coil-sets is energized at one time. Each coil set, when current is 
applied, interacts with four adjacent surrounding magnets (of the 
eight-magnet assembly see also FIG. 9AB). The magnets provide alternating 
flux in the air gap between themselves and the coil turns, such that a 
coil's "front" wire experiences flux that is directed oppositely to that 
experienced by its "back" wire. Thus, as the coil moves it will reach the 
boundaries of the flux area covered by these four driving magnets--at 
which time the second coil is enabled and takes over using the same four 
magnets. This action will be understood as providing a capability for 
"stepping" the flat coil actuator through the magnet assembly while still 
keeping a "linear region" associated with each step (Note: when such a 
coil is energized it moves in some direction until it reaches a "magnetic 
boundary"; then if the current is reversed, the coil moves in the opposite 
direction until reaching another "magnetic boundary"--the distance between 
these boundaries is the "linear mode region"). 
Workers will appreciate how compact, light and advantageous such a 
staggered multi-turn actuator coil array can be. For instance, as provided 
for a typical stack of magnetic recording disks, each such actuator would 
service the gap between associated disks; while stacked sets of such 
actuators will be grouped in modules wherein a common magnetic housing and 
circuit is provided (between shunts 1-2, 1-2', for instance, as noted in 
FIG. 1A, etc.). 
Thus, for a typical disk stack with a typical inter-disk spacing or gap 
g.sub.d (see FIG. 6) of about 3/8" and with one such "flat-coil" actuator 
arrangement servicing each inter-disk spacing, the performance and 
dimensional constraints for practical, optimal head translation are 
readily accommodated. (E.g., in one embodiment using 1/16" PC board with 
20 mil copper clad coils, and assuming inner gap clearance of about 1/10" 
inch, fast translation was seen.--Note above that the magnet poles P may, 
for instance, be formed of one-half inch thick ferrite, having a permeance 
coefficient of about 2.8; while shunts 1-2, 1-2' can be 3/8" cold rolled 
steel, with supporting plates 1-p, etc., comprising non-magnetic 1/16" 
steel sheet). The coils are preferably "overlapped" as illustrated. 
With rare earth-cobalt magnets in such an array (90 gm. actuator) and with 
a gap flux of about 4 kilogauss, a very surprisingly low leakage has been 
observed (e.g., about 5 gauss at 3/4" vs. ordinary VC motor similarly 
used: 5 gauss at about 7"). Also, the excursion characteristics are 
surprisingly "flat". Preferably, the coils are "reverse-wound" and 
connected at centers (see below). The flux loops (see .phi.) will be 
observed as nicely "contained" between adjacent opposed-polarity magnets 
(e.g., P-3, P-3'; P-4, P-4' shown) and the magnetic keepers or end plates 
1-p, 1-p'. Thus, the magnetic potential (M.P.) as shown will be zero at 
the top, bottom and center of the array (FIG. 6A). 
The working excursion of this actuator (FIG. 6A) should be viewed as: 
1: from extreme left (c-1, c-1' in phantom) across P-1/P-1' to P-2/P-2' 
with coils c-1, c-1' working; 
2: then, as coils c-2, c-2' (oppositely poled from c-1, c-1') start to 
sweep across P-2/P-2'-P-3/P-3' 
Except as particularized, workers will understand that the foregoing 
elements are constructed and operated as known in the art (e.g., as 
specified in the cited references). Workers may be surprised to learn that 
embodiments like that here indicated have involved a total moving mass of 
only about 90 grams--this comprising the actuator strip, or PC board, pair 
of head assemblies, and pair of R/W integrated circuits, along with the 
four sets of double bearings, or rollers--a surprising low mass! 
It will be apparent to workers how such a "flat armature" linear positioner 
simplifies the moving coil structure, compressing it and flattening it 
out, as well as making it possible to greatly reduce mass and volume. 
(E.g., as compared to a VC motor with its "open" (air traversing) flux. 
path; see FIG. 11). 
Such a "flat coil" actuator will also be seen as allowing for a relatively 
unlimited stroke length (according to the number of magnets strung out) 
this facilitating radical miniaturization and compression of the actuator 
stack (and thus allowing one simplified actuator between each pair of 
recording disk surfaces--i.e. per gap--according to a related 
feature)--the flat shape facilitating the close and intimate stacking of 
actuators in a rather surprising novel manner. 
--One plus" actuators per surface-pair; "multiple path to data" 
As is evident from the above (see FIG. 2 especially) this "flat armature" 
concept facilitates the use of one, or more, transducer assemblies per 
recording surface (pair). The evident reduction in actuator mass, cost, 
power, etc., will obviously encourage this. And workers will readily see 
advantages in such an "actuator-per-disk" array. For instance, no longer 
is it necessary to translate a heavy multi-transducer load, servicing "n" 
pairs of record surfaces, to shift one head on one surface! Also, while a 
first head is transducing, one (or several) other may, the-while, be 
shifted to a new address--thus avoiding wasted "access time" when the 
other head begins transducing (and the first ends). 
This, in turn, facilitates a "multiple path to data" concept, whereby some, 
or all, tracks may be serviced by more than one head, and by more than one 
associated actuator--preferably having two heads per surface. 
Such a "multi-ported" disk file concept is very schematically illustrated 
in FIG. 14, where one illustrative disk D.sub.n in a stack is shown to be 
comprised of 150 recording tracks--t.sub.1, t.sub.50, t.sub.100 and 
t.sub.150 being shown, in phantom, for illustration purposes. Certain 
groups of these tracks are to be serviced by a respective one of a trio of 
transducer heads h.sub.1, h.sub.2 and h.sub.3, the heads to be actuated 
and controlled by appropriate mechanisms as known in the art (not shown 
here--it being understood that each of the disks D in a subject stack 
would be similarly provided). 
Now, as indicated by the solid arrows, head h.sub.1 is arranged to 
primarily service tracks t.sub.1 -t.sub.50 (being positioned closely 
adjacent this group of tracks and normally reciprocated only across 
them--however being also adapted to be further translated to service 
tracks t.sub.50 -t.sub.100 as a "backup" transducer. In a similar manner, 
head h.sub.2 is disposed to primarily service tracks t.sub.50 -t.sub.100, 
as well as arranged to also service t.sub.1 -t.sub.50 as a "backup" to 
h.sub.1 (and/or t.sub.100 -t.sub.150 ; likewise head h.sub.3 is adapted to 
principally service tracks t.sub.100 -t.sub.150, while also optionally 
covering tracks t.sub.50 -t.sub.100 (and/or t.sub.1 -t.sub.50) as a 
"backup" head. 
Thus, data along any particular track will have at least one alternate 
"port" (for data input/output), or transducer head arrangement for 
servicing it in case its primary transducer is unavailable (e.g., being 
busy elsewhere or damaged and inoperative, etc.). Thus, for example, head 
h.sub.1 might be transducing on track t.sub.49 and the current program 
call for track t.sub.47 to be transduced next--in which case an optimized 
program could call head h.sub.2 into service for this rather than head 
h.sub.1 (assuming head h.sub.2 was not otherwise occupied and was then 
available); thus head h.sub.2 would be translated to track t.sub.47 during 
the time h.sub.1 was transducing on t.sub.49. Quite evidentially this 
would avoid the "dead time" that would have resulted if head h.sub.1 were 
used to service both tracks (avoid need to suspend data processing and 
input/output while h.sub.1 was translated from t.sub.49 to t.sub.47). 
Workers will, of course, conceive of many other instances in which such 
"multi-head servicing" of data tracks is particularly advantageous. Also, 
it will be apparent that the aforementioned "flat armature" design for 
transducer-actuators is particularly apt for providing this. 
--Formation and Operation of flat coil armatures; FIGS. 7, 9A-9F and 9AA, 
9AB: 
A preferred construction and mode of assembly for flat coil armature 
embodiment A-m in FIG. 7 is indicated in a form of a layup in exploded 
view in FIG. 9A, with the several parts thereof being indicated in FIGS. 
9B, 9C, 9D, 9E and 9F, while an operational representation is indicated in 
FIGS. 9AA and 9AB, FIG. 9AB also illustrating the preferred coil offset or 
overlapped relation. 
More particularly, in FIGS. 9A and 9B will be seen an upper view of the 
frame f (of expoxy-glass, about 0.6 inches thick) to which the PC boards, 
coils, rollers and connectors, etc., are to be attached (for a non-ferrous 
metal may be used, preferably with all "rings" gapped with a dielectric). 
The structure and operation of these and other parts described will be 
understood as conventional, except as otherwise described. Frame f will be 
seen to be cut-out along its cross-section wherever possible (wherever the 
necessary rigidity and cross-sectional strength admit). A pair of PC 
boards, B.sub.1, B.sub.2 are to be placed respectively above and below 
frame f, each board carrying two pair of flat printed-circuit 
"overlapping" coils C (one on its top, the other on its bottom face) in 
opposed offset relation (though this is optional). That is dual-coils C-1, 
C-2 are disposed on the top and bottom of upper board B.sub.1 and coils 
C-4, C-3 disposed atop and below the bottom PC board B.sub.2. Opposed 
pairs of rollers r (bearings) support the frame for rolling reciprocation. 
A conventional head assembly (pair) is carried (not shown) along with 
associated electronics (e.g., see R/W chip 7-5). Flexible cables 7-3 
couple the structure electrically to the outside and may include 
return-spring means. 
In operation, and as very generally indicated in FIG. 9AA, each such flat 
coil C (only one coil shown for simplicity) will preferably comprise a 
multi-turn printed circuit exhibiting a rather advantageous mode of 
interaction with adjacent magnetic flux (intersecting the coil turns and 
emanating preferably from sets of surrounding permanent magnet poles as 
indicated in FIG. 9AB and elsewhere). Thus, once an energizing voltage 
V.sub.c is applied across the terminals to coil C, current will flow in 
the directions indicated by the arrows, and, with oppositely directed flux 
.phi. (indicated as .phi..sub.+ and .phi..sub.- in FIG. 9AA), the 
actuation impulses will be additive, tending to thrust the overall 
structure f unidirectionally as indicated by arrow aa. 
This is indicated rather diagrammatically in FIG. 9AB, where a flat coil 
armature A-m of the type described in the above embodiment is shown very 
schematically and in cross-section. Here, A-m includes a pair of 
opposed-offset coils C-1, C-2 disposed on opposite sides of a supporting 
board. Coils C-1, C-2 are identical and shown in schematic operative 
relation with a linear array of opposed permanent magnet pole pairs of the 
indicated polarity (see arrows). Each coil has an inner diameter 
(C.sub.1D) approximating the common length (P.sub.L) of any pole along the 
translation path (arrows aa), less a coil width (C.sub.w)--i.e. C.sub.1D 
=P.sub.L -C.sub.w. The pole pairs should be an even number and may, 
advantageously, extend virtually any distance with such a construction--a 
decided advantage over conventional actuators such as a VCM. Low 
reluctance shunt caps MK, MK' (e.g., of steel) help close the flux paths 
efficiently, minimizing the in-air flux-paths. 
In operation, coil C-2 may be assumed to be energized with a certain drive 
current (+i.sub.d) to begin translating armature A-m in the direction of 
arrow aa. When coil C-1 passes beyond the poles P-1, P-1' and reaches 
position C-1', or before, the current (+i.sub.d) to coil C-2 is terminated 
and an opposite-polarity current pulse (-i.sub.d) is sent through C-1 
(while C-1 passes pole P-2, P2'). Coil C-1 then goes "quiescent" and C-2 
is re-activated--and so on, until the armature reaches the end of this 
excursion (indicated here as the position of C"-1, C"-2--however, if less 
than "full power" is acceptable, the excursion may be extended somewhat in 
both directions, as workers know). 
Workers will recognize many features of novelty in such a "flat linear 
actuator"; for instance, its thin planar cross-section (tailored to disk 
gap dimensions), the aligned magnet pairs, the overlapping coils. 
Results: 
Such a "flat armature" (printed circuit) actuator will be seen as 
advantageous by those skilled in the art, whether developed according to 
the above described embodiment or in a different related manner according 
to the subject teaching. Such a "flat actuator" is obviously apt for use 
in a "multi-actuator" array, with a plurality of actuators (and heads) 
available for each disk surface (or pair thereof)--i.e., with a plurality 
available per track as a preferable option. Such a "flat actuator" lends 
itself readily to the "multi-actuator" concept (e.g., as suggested in FIG. 
1A) especially as opposed to existing designs. 
As a qualitative example of the kind of results that can be achieved, 
consider FIG. 10, a plot of actuator force vs. head position for an 
actuator using (2.0 ampere excitation current). NOTE: a translational 
force of 250 to 300 grams is quickly developed and sustained to be 
relatively constant over a translation excursion of about 0.3 to 1.3 
inches--the next cycle beginning about 1.5 inches wherein the second set 
of coils takes over. 
VC Actuators compared; FIGS. 12, 13: 
FIG. 12 depicts, very schematically, a relatively conventional cylindrical 
solenoid 15-M (of the VC-M type, as in FIG. 11 also) comprising a 
permanent magnet source of magnetic flux comprised of a cylindrical, or 
semi-cylindrical, shell 15-1, with an inner core 15-2, core 15-2 being 
encircled by a moving solenoid coil 15-4. Coil 15-4 will be recognized as 
conventionally translated along core 15-2 when energized with current (due 
to inductive interaction with the magnetic flux--see arrows emanating 
between core 15-2 and peripheral magnet parts 15-1). Force arrow F 
indicates the resultant reciprocal translation forces so developed--the 
force direction being determined by direction of current through coil 
15-4, as well known in the art. 
The magnetic flux field set-up by coil current will flow mainly through the 
"path of least reluctance" (as indicated by flux loops 15-3 through magnet 
15-M). I have found that "flat armature actuators" of the type described 
above operate somewhat differently. As indicated rather diagrammatically 
in FIG. 13, one may, simplistically, consider such "flat-armature" devices 
as comprised of a flat coil CCL (any number of turns) arranged to be 
energized and movable along a path between opposed magnet pairs, such as 
pairs A, B and C, in line. (Loop CCL here indicated as spanning section B 
and part of C). Considering the inductive energy stored in the air gap 
between these magnet poles, and intersected by the loops of coil CCL, the 
total energy in the system may be described as the sum of energy across 
segments A, B and C. 
Now, if coil system CCL is moved "Forward" (in the direction indicated by 
the arrow, to the position CCL', shown in phantom), it will obviously span 
less of the working cross-sectional flux through segment C, while adding a 
corresponding amount from segment A, with that through segment B remaining 
unchanged. Thus, when the volumetric inter-gap flux densities are summed 
after such an incremental step, it will be found that the new energy is 
the same. 
Hence, one can say that such movement of a "flat coil" armature involves no 
transfer of energy, unlike the "cylindrical actuators" indicated in FIG. 
12 above. Workers will appreciate this advantage. 
Alternate coil configurations; FIGS. 14, 15: 
FIG. 14 indicates very generally, and in plan view, a pair of 
opposed-offset (overlapping) coils C-A, C-B, mounted on a "flat-armature" 
A-m and adapted to function in the manner of the above described 
embodiments. That is, the two opposed "end segments" of coil C-A (see 
arrows) are shown as relatively directly intersected by the flux of an 
adjacent pole pair (at this point in the translation cycle); while the end 
segments of companion coil C-B will intercept little or no such magnetic 
flux. Thus, one can say that coil C-A is "active", here; while coil C-B is 
now "quiescent" (during this portion of their excursion cycle). 
Thereafter, as the coils move and the flux leaves the confines of the C-A 
segments, it will begin to more directly intersect the end segments of 
coil C-B--then coil C-A will have turned "quiescent" and coil C-B become 
"active", to thereby maintain the driving force and continue the 
translation of armature A-m. Thereafter, upon further coil movement, coil 
C-A will again turn "active" and C-B "quiescent", etc., etc., as described 
above. 
Workers in the art will perceive that while the "opposed-offset", 
overlapping printed coil construction indicated in described embodiments 
is rather advantageous and practical for many applications, there are 
other ways of implementing this concept and achieving similar results. One 
such alternate way is (very schematically) indicated in FIG. 15, (in the 
manner of FIG. 14). Here, a related "flat coil" armature A-m will be 
understood to include one or several adjacent coil "loops" L-1, L-2 shown 
for wires CC disposed thereon (as opposed to the "single-loop" coils C-A, 
C-B in FIG. 14, each of which is drawn about a common perimeter). As 
indicated in FIG. 15 each such printed circuit wire is to be extended 
along the actuation direction to define this "Multi-loop" version of such 
"flat armatures". 
Coil-coupling variations; FIG. 16: 
FIGS. 16A, 16A' show schematically (perspective and section respectively) a 
single coil (replicated each side) 2 layer construction wherein the 
(printed circuit) coils will be understood as "reverse-wound" and 
through-connected (C-a to C-b) at their centers. FIGS. 16B, 16B' are 
similar and show a variation: a "dual coil" (2 separate coils); single 
layer assembly wherein C-d and C-e are connected to separate input 
terminals. 
FIGS. 16C, 16C' are similar and show another, highly preferred variation: a 
"dual coil/4 layer" assembly yielding eight coils effectively and deriving 
more turns per coil. (C-f through-connected to C-g at center; then C-g to 
C-m at ends; thence C-m to C-n at centers; and C-h to C-j at centers; 
thence C-j to C-k at ends; thence C-k to C-l at centers). 
Different magnet arrays; FIGS. 18: 
FIG. 18A shows, schematically, a 4 magnet (2 opposed pair) actuator array 
comparable to that of FIG. 2. FIG. 18B similarly shows an 8-magnet (4 
opposed pairs) array comparable to that of FIGS. 5 and 6--both having 
magnetic keeper plates, mk, mk' as above mentioned for flux conservation. 
FIG. 18C shows three actuator compartments, each with a 6-magnet array (3 
opposed pairs) plus a side-keeper sk for closing the magnetic circuit. 
Such an "odd pair" configuration is less preferable than "even-pairs" 
(multiples of 4 magnets preferred). 
FIG. 18D is another variation comprising (for each actuator) a 
bi-functional array of magnets: one set of high-performance magnets (e.g., 
rare-earth/cobalt magnets M-RC) for "normal" fast operations, over a 
normal excursion; plus a second set of inexpensive, low-performance 
magnets (e.g., ceramic magnets M-C) for exceptional or emergency 
operations. For instance, as used in a "dual path-to-data" disk drive, as 
noted above, such actuators would be understood as normally operating over 
a short (e.g., 50 track) excursion--this defined by high strength 
expensive magnets M-RC. But for optional occasional use, over an extended 
stroke (e.g., 100 tracks, when companion actuator is "busy" or 
"disabled"), the actuator (coils) would travel beyond the region M-RC into 
that of magnets M-C as well. For such occasional, emergency operations the 
degraded performance to be excepted with magnets M-C (e.g., slower 
translation) is acceptable, and justified by the cost-savings. 
Various actuator-stack configurations; FIG. 19: 
FIG. 1B shows schematically, a 4-compartment stack, for four "flat coil" 
actuator units, with top and bottom flux-shunt plates. Compare the 
7-compartment unit of FIG. 19A and the 8-unit array of FIG. 19B and 19C. 
FIG. 19B really combines two 4-unit modules as in FIG. 1B; but in 19C the 
(redundant) center shunting plates (mk", mk'") are eliminated, with 
reduction in height, weight and cost, but no sacrifice in performance. 
Multi-arm "flat coil" actuator; FIG. 20: 
FIG. 20 shows in very schematic perspective, a variant use of the "flat 
coil actuator" of the invention. Here, a plurality of arms (3 shown, 
number optional): aa-1, aa-2, aa-3 are shown all mounted in common from a 
single "PCB coil" actuator comprising broad A-1 with coils (C, etc.) as 
before indicated. Large permanent magnet plates M-I, M-II surround the 
(coil portion of) board A-I and are adapted to cause it to reciprocate 
(arrow c-o) when the coils are energized, as before. This will, of course, 
drive associated head assemblies to a prescribed common position adjacent 
respective disk surfaces (D-1, D-2, D-3). 
However, according to a related feature board A-I is mounted and arranged 
(by conventional means, not shown) to also be reciprocated vertically 
(arrow v-d) by conventional means (not shown). 
"Cross-bar" feature: 
According to another feature of invention, another way of providing 
"multi-path to data" and "Soft-failure" capability (besides the "multiple 
actuator per face" implementation indicated above) is to provide the 
"cross-bar" feature for a disk drive system, e.g., as very schematically 
indicated in FIG. 23. 
FIG. 23 may be viewed as very schematically indicating a fixed disk drive 
unit DD.sub.A including a disk file F-B, similar to those discussed above 
and shown in FIGS. 21 and 22, being adapted to provide memory and be 
controlled by at least one host computer CP.sub.h. Disk drive unit 
DD.sub.A will be understood as conventional according to present good 
practice except where otherwise specified herein. Disk file F-B will be 
understood as comprising a plurality (two shown) of multi-arm transducer 
actuator arrays T-i, T-ii, each array being coupled via an associated 
actuator control stage (A-CU-i, A-CU-ii, respectively) to a host computer 
CP.sub.h, being coupled thereto however according to the novel "cross-bar" 
feature (stage CB) further described below. 
Such a two-actuator file is relatively conventional like file F-A in FIG. 
21, wherein the lower set of disks d are understood as accessed by 
associated arms and heads projecting in common from a lower actuator 
carrier A-1, while the upper disks d are similarly accessed by an 
associated upper carrier A-2. Each actuator array will, typically, also 
have a conventional servo arm and head as indicated, for instance in FIG. 
21 and at 128-S in FIG. 22. FIG. 22 also suggests that each arm a may 
carry (1 or) two pairs of transducer heads 128, one head in each pair 
being presented to a respective one of the two opposing disk faces in each 
subject file-gap g.sub.f. Thus, for instance, in the preferred embodiment 
of FIG. 23, file F-B may comprise a pair of head-actuators T, each of 
which presents five actuator arms, each arm having two pairs of opposed 
transducer heads and being projectible into one of the five associated 
gaps, as known in the art. 
Disk Drive embodiment DD.sub.A including "cross bar" stage CB will be 
understood as adapted to prevent "Hard", or catastrophic, 
electronic-control failure of the disk drive and the associated EDP 
system,--i.e., failure relative to "actuator electronics" (i.e., any 
electronic failure which impairs the actuator electronic supply-control 
means, such as the failure of a power amplifier or power supply in one of 
the control stages, A-CU, or the failure of an associated fuse, 
transformer, electronic packaging element, as understood by workers in the 
art--such being known by some as the most frequent cause of EDP "Hard" 
failure; the next most frequent being actuator motor failure). In one 
mode, such a failure, resulting in shut down of the drive unit, will 
automatically result in the switching-in of another ("live") 
electronic-control stage (substitution for the "dead" one) and the 
resumption of drive operation. 
Thus, this "cross-bar" feature allows one of the two electronic data paths 
associated with each of several disk file modules to be reconfigured so 
that they can access one another's actuators. For instance, if any 
electronic element (e.g., in electronic supply-control stage A) along one 
data path (path A) fails, the entire associated file would "go down" 
ordinarily so that the computer system would be blocked from access to the 
associated data (cf actuator A associated with this file A would be 
rendered inoperative). 
But with this "cross-bar" feature actuator A (and file A) can be "revived" 
by cross-coupling to the electronic control stage B of the companion file 
B--and so recoupled to the host CP, etc. 
Likewise, of course, if control stage B fails its associated file and 
actuator can be "revived" by connection with companion control stage A in 
similar fashion. The net result of this is that the system is relatively 
tolerant of electronic failure in either data path, the files in each data 
path being adapted to so "share" control stages. 
As a result of such "cross-bar" implementation a "Hard" failure can be 
turned "Soft"; thus, should one of the control units A-CU fail for any 
reason, the host CP.sub.h may for instance be programmed and arranged to 
induce switching, via cross-bar stage CB, to link the other control unit 
A-CU to the concerned actuator T (the software routine may act as the 
controller in this case through known programming techniques associated 
with such hardware). Workers are well aware of the means of effecting 
this. 
The significance of such a "cross-bar" implementation will be apparent to 
those skilled in the art; and it will be apparent that such may be used 
for many different kinds of fixed disk drives rendering them less 
susceptible to "Hard" failure, invoking instead a "Soft" failure, using 
the "multiple path to data" approach. Workers will see other incidental 
advantages to providing this "cross-over" capability. For instance, in the 
inspection test, checkout, etc. of the disk drive, a field engineer can 
pull or otherwise disable one of the two actuator control units A-CU, yet 
still keep the DD "on the air" by simply invoking the cross-over feature 
whereby the other control unit A-CU is made to handle the load during this 
test sequence. Workers will visualize other like applications and see how 
powerful a tool this "cross-over" capability is. 
Workers will also appreciate how simply and inexpensively this "cross-over" 
feature can be implemented, while yet preventing one of the most common, 
expensive sources of "Hard" failure in a DD. Such a solution can, for 
instance involve $10-20. added cost in a typical DD unit, while all but 
eliminating "Hard" failure from electronic sources and greatly increasing 
the MTBF of the unit (e.g., from a few 1000 hours to the order of ten 
times that level--then, due to motor failure). Workers will appreciate how 
powerful this cross-over feature is, yet how simple and inexpensive to 
implement. 
Combining "cross-bar" with "overlapping actuators"; FIG. 24: 
It was mentioned that this "cross-bar" feature can of course, be combined 
with the multiple overlapping actuator (per recording face) feature 
previously mentioned; such a combination is shown very schematically in 
FIG. 24. Here, in a much simplified representation, a single recording 
face of exemplary disk d is shown as "normally covered" by a pair of 
associated magnetic transducer heads and related actuator stages A-1, A-2, 
with one unit (A-1) covering the outer span of tracks and the other unit 
(A-2) covering the inner span (each unit is also arranged to additionally 
cover the other span of tracks in its "emergency mode", as mentioned 
above). 
The output from the two actuator units is sent to a host CPU along an 
associated data path (DP-1, DP-2) and via an associated control 
electronics stage (A1-CU, A2-CU), via a common "cross-bar stage" CB' of 
the type described above in FIG. 23. Thus it will be apparent that for 
instance, should control stage A1-CU fail, the host CP (or other means) 
can automatically direct the substitution of other control unit A2-CU to 
handle actuator A-1--this being the "emergency mode" for A-CU-2, which 
will also be handling its normal responsibilities on the inner tracks. In 
this fashion, there is provided a "multiple path to data" from the CPU to 
the recording tracks on disk d. 
Conclusion: 
Workers will appreciate how such a "cross-bar" feature can thus provide 
"Soft failure" and a "multiple path to data" capability in a fixed disk 
drive. In particular they will appreciate how such a disk drive may be 
provided with two or more actuator arrays, each with an associated control 
stage, and how these control stages may be cross-switched and "shared", 
via an intermediate "Cross-bar" stage, to provide these results at 
relatively simple cost and using simple state-of-the-art implementation. 
Workers will further appreciate how such a "multiple path to data" and 
"Soft failure capabilities" are rendered using multiple actuators per 
recording tracks, especially as combined with the mentioned "cross-bar" 
feature. 
It will be understood that the preferred embodiments described herein are 
only exemplary, and that the invention is capable of many modifications 
and variations in construction, arrangement and use without departing from 
the spirit of the invention. 
Further modifications of the invention are also possible. For example, the 
means and methods disclosed herein are also applicable to other disk drive 
units (e.g., Mass Memory therefrom). Also, the present invention is 
applicable for providing the positioning required in other related 
recording and/or reproducing systems, such as those in which data is 
recorded and reproduced optically (optical transducers replacing the 
described magnetic ones). 
The above examples of possible variations of the present invention are 
merely illustrative. Accordingly, the present invention is to be 
considered as including all possible modifications and variations coming 
within the scope of the invention as defined by the appended claims.