Note: Descriptions are shown in the official language in which they were submitted.
638
1 PHN 9348
The invention relates to a device for
determining a complete track number or address(s)
of a track which forms part of a set of tracks
present on a disc-shaped record carrier, said set
consisting of (n) groups of (sg) tracks, the record
carrier being divided into alternating sectors with
groups of data tracks and sectors with groups of
servo tracks, each track comprising per group of
servo tracks its own identification code which
includes a number of the track within the group and
which can be read by a transducer device provided
on a positioning member.
A device of this kind is notably used in
disc memories in which one or more discs provided
with or made of a storage material (for example,
magnetic, optical, ceramic) are used for the writ-
ing, storage and reading of data. An important
component of such a disc memory is formed by the
positioner, i.e. the movable support of the write
and/or read transducer (for example, a magnetic
head) which is to be accurately positioned over a
desired track of the disc at the highest possible
speed.
Many versions of disc memories are known.
A disc memory comprising a device for determining a
number of a track of the kind described is known
from United States Patent Specification 3,812,533
Kimura et al - May 21, 1974. In this disc memory,
the radial position of the write/read transducer is
controlled by utilizing the servo signals incorpor-
ated in a limited number of narrow sectors on each
disc. It is thus possible to determine a track
number of each track per group of tracks on the
disc (so termed "coarse" positioning) and, more-
over, to realize the accurate positioning over a
~5~638
11.1.80 2 P~L~ g348
given track of a group (so-termed "fine" positioning).
The determination of the track number per group, how-
ever, is not sufficient. It must be possible to dis-
tinguish each track from all other -tracks. In com-
bination with the number of the group of which a
track forms part, the track number within a group
must form an unambiguous data for the complete ad-
dress number of the relevant track. Complete po-
sitioning of the positioner over a track can be
achieved only on this basis. In order to make this
possible in the described disc mernories without in-
creasing the servo sectors (i.e. without loss of
effective data storage capacity), there is provided
a separate optical position transducer which con-
trols at ~east the positioning per group of tracks.
This separate transducer makes the solution of` the
positioning problem expensive and requires special
structural steps -to ensure proper and reliable
operation.
An object o- the inven-tion is to enable
direct control by means of the signal detected frorn
the servo sectors during each phase of the po-
sitioning, using servo signals which are recorded
in a limited number of (narrow) servo sectors on
each disc, witho-ut these servo sectors, being en-
larged.
In order to achieve this objeG-t, the in-
vention provid0s a first means f`or f`orming a com-
plete track number composed of firstly the track
nurnber read in a group and secondly a trial group
number which is formed in second means and which
is variable in an increasing or decreasiIIg sense,
third means for determining the dif`ference between
a complete track number formed in the f`irs~ means
and a complete track number es-timated in f`ourth
means on the basis of the displacement speed of`
the positioning member body, fifth means for com-
paring the magnitude of` the dil`ference obtained in
,
~152638
11.1.80 3 PHN 9348
the third means with a value determined by half (Sg),
a signal being produced if said magnitude is smaller
than half (Sg), said signal validating the complete
track number present in the first means at the rele-
vant instant.
This set-up of the device enables the cor-
rect track number to be determined after each servo
sector by utilizing the calculated estimate of the
new track number. Hereinafter, it will be demonstrat-
ed that a comparatively inaccurate estimate can suf-
fice for determination of the correct complete track
number. A separate position transducer can thus be
dispensed with. The calculation of said estimate
can be performed in various manners. When the sys-
tem incorporating the device in accordance with thepresen-t invention includes a speed transducer, the
speed signal can always be integrated with respect
to time to generate a position signal which is an
estimate of` the track number reached. In order to
achieve this, an embodiment of the device may com-
prise fourth means for estimating a cornplete track
nurrlber which consist of an integrator, an analog-
to-digital converter, and an adder, and in which a
speed signal determined by the positioning member
is applied to the integrator, the output thereof
being connectedt via the analog-to-digital con-
verter, to an input of the adder, a further input
of the adder receiving the value of the preceding
complete track number, so that the estimated value
of a next complete track number appears on the out-
put of the adder.
Thus~ an analog-to-digital converter is
required for obtaining the result in binary form
for further processing. A further embodiment of`
the device in accordance with the invention offers
an alternative solution in that the fourth means
f`or estimating a complete track number Collsist of
a voltage-frequency converter, a counter and an adder,
.
~l~Z638
11.1~80 4 PHN 934
a speed signal which is determined by the position-
ing member being digitized in the converter and be-
ing coun-ted in the counter, after which the count-
ing result and the value of the preceding complete
track number are applied to inputs of the adder, so
that the estimated value of a next complete track
number appears on the output thereof`,
A further possibility which may be suffi-
ciently accurate and may be attractive because of
its simplicity consists in estimating the complete
track number s = s(t2) by a linear extrapolation
bet-ween track numbers determined during previous
measurements i.e. between the last number s(t1),
and the last but one, s(to). In order to utilize
this aspect, a further embodiment of the device in
accordance with the invention may comprise fourth
means consisting of a subtractor in which, after
the doubling of the value of tlle latest (last de-
termined) complete track number, the doubledvalue
is reduced by -the value of the preceding cornplete
track number.
The advent Or :Large scale integrated cir-
cuits is accompanied by the airn to utilize their
features in many applications. A f`requently used
integrated circuit for general use, known as a
microprocessor, can also be used for reali~ing
the device in accordance with the inverl-tion. ~
plurality of "peripheral" circuits in the form of
memories (ROM, RAM), input/output circuits etc.
can then be accommodated on the sarne chip. Micro-
computer is a frequently used term in this res-
pect. For the principle of the invention it is not
important ~ se how the data processing capacity
of the circuits - integrated or not - is composed,
the important aspect being that use is made of this
data processing capacity. In order to indicate this,
the greneral terrn programmed digital signal proces-
sor is used hereinafter.
.
11~;2638
11.1.80 5 PHN 9348
A preferred embodirnent of the device in
accordance with the invention comprises a programmed
digital signal processor which comprises said first,
second, third, fourth and fifth means in the form of
register function means and arithrnetic logic function
means which act as counting/adding functiOn means,
subtraction function means and comparison function
means.
In order to obtain even more certainty
as regards the estimate, the flexibility of a pro-
grammed digital signal processor offers extra-
polation using a plurality of previously found com-
plete track numbers (and notably the difference
therebetween). In order to achieve this, the fourth
means which are included in the programmed digital
signal processor for determining the estimate of a
complete track number are adapted to extrapolate
over the latest (last determined) complete track
number and one or more preceding complete track
numbers. The fourth rneans incorporated in the pro-
grammed digital signal processor for determining
the estimate of a complete track number may be
adapted to find s' (estimated track number) on the
basis of the relationship
s = 1 0 0 + s(t )
in which s(t1) is the latest (last determined) com-
plete track number, s(tO) is the preceding complete
track number, and dss(tO) is the difference between
the preceding complete track number and the preced-
ing complete track number but one. Nornlally speaking,
the programmed digital signal processor will also be
adapted to determine the difference between a desir-
ed target track number and a complete track numberreached.
A further explanation and embodimen-ts of
the device in accordance with the invention will be
?2638
- 6 - PHN. 9348.
described, by way of example, hereinafter with reference
to the accompanying Figures. Notably the use in a mag-
netic disc-memory is shown. However, it is to be noted
that the invention is by no means restricted to the
examples given.
Figure 1 shows a disc-memory system comprising
a device in accordance with the invention.
Figure 2 shows a curve of the displacement of a
transducer between two servo sectors at instants tl and
10 t2.
Figure 3 shows an embodiment or a device in
accordance with the invention.
Figure 4 shows a separate embodiment of means for
estimating a complete track number.
Figure 5 shows a further separate embodiment of
means for estimating a complete track number.
Figure 6 shows a device comprising a programmed
digital signal processor.
Figures 7a and 7b show flow diagrams concerning
the operation of the device comprising a programmed
digital signal processor.
Figure 8, which is on the same sheet as Figure 6,
shows a time diagram.
Figure 1 shows how a device in accordance with the
invention can be included in a disc memory system. Figure
1 and the accompanying description serve to provide a
better insight into the nature of the environment in which
the device in accordance with the invention can be used.
However, it is intended merely as an example of such an
environment; it is to be noted that other embodiments of
disc-memory systems can utilize the invention equally
advantageously.
The letters VSPN in Figure 1 denote the device in
which a complete track number s is determined in accord-
ance with the invention. D denotes a disc of the memorysystem which may comprise one or more-discs which may be
removable from the memory system. Disc D is provided
with tracks in which SSP
~152638
7 PHN g348
are the servo tracks which are situated in servo
sectors SS distributed over the disc and DSP are
data tracks which are situated in so-termed data
sectors DS. The servo sectors contain data SSPI
which, by using the device VSPN, is sufficient to
provide complete positioning of the positioning body
or positioner denoted by the letter P. The data
sectors contain the data DSPI stoxed in the memory
system. Said data SSPI of the servo sectors gen-
erally consists of at least two components which
are contained in the servo sectors in combined form
or not. The first component is the track number
data of the tracks Sm in each group of Sg tracks
(there are _ groups, so N = n x sg tracks in total)
and the second component is the fine-positioning
data which enables accurate positioning of the posi-
tioner over a given track. In this respect, refer-
ence is made to disc memory systems comprising such
servo sectors which are described in said United
States Patent 3,812,533 and United States Patent
4,027~338 Kril - May 31, 1977.
The positioner P is shown, by way of
example, as a rotatable body which can describe an
arc Bg across the disc D. All tracks of the disc
can thus be covered by the read/write transducer
WRIH. (A positioner of this kind is known, for
example, in British Patent Specification 1,342,495
IBM - March 13, 1971).
Because of the rotatable arrangement of P,
the sectors shown on the disc D are arc-shaped in
order to provide a parallel relationship between
said arc Bg and the sectors. Thus, there is no dif-
ference between signals written and read by the
transducer WRIH when this arrangement is compared
with the more generally used arrangement comprising
a positioner which is arranged on a carriage and
.. ~
~1~2638
11.1.80 8 PHN ~348
which moves radially across the disc.
It is to be noted that, without extensive
modifications being required, the device in accord-
ance with the invention can also be used in disc me-
mory systems which do not use concentric tracks buthelical tracks.
Positioners are displaced and positioned
over a desired track in known manner by a position-
ing apparatus PA which is controlled by a positioning
control device P~. The transducer SIH serves to sup-
ply fixed "clock" data and SI is the data concerning
the subdivision of the disc D into sectors DS and SS.
To this end, in this example a sector ring SIR is
shown at the outer circumference of the disc D. This
ring SIR comprises the parts SII which indicate the
location of the servo sectors on the disc. The data
SI is processed to form a signal TS in a pulse-shap-
ing network PV in known manner. The signal TS con-
sists of pulses having a length which equals the
time during which a part SII of SI is detected by
~IH. Via the selected location (on arc Bg), the
pulses TS indicate when and f`or how long a servo
sector passes the transducer WRIH. The signal WRI
is then read and applied to a switching device SW.
During the pulse signal TS, SW is in the lower po-
sition in the drawing and ensures that WRI, then
specifically containing the servo sector data SSPI,
is applied to the positioning control device PC. If
TS is absent, the data WRI, then specifically con-
taining the data DSPI, is applied to the user device(for example, a computer) which is not shown. The
control device PC may be a known control device
(compare the embodiments in the Patent Specifica-
tions cited above). The most important signals ap-
plied to PC area: Sd which is the target track onwhich positioning must take place as requested by
the user device (for example, a computer), and (b)
SSPI which is the servo sec-tor data wherefrom, in a
~;2638
11.1.80 9 PHN 9348
part DET of PC, in the first instance the track num-
ber sm of a servo track passing the transducer WRIH
at that instant is derived. This data sm is applied
- to the device VSPN for deternlining the complete track
number. The pulse signal TS is also applied to the de-
vice VSPN. Depending on the construction of VSPN, the
complete track number s is determined, with or without
use of the signal vp which indicates the speed of
displacement of the positioner P and which is ge-
nerated in PA in this embodiment. The data s, sd and
the servo signal data SS~I can be used to generate
unambiguous control signals (for coarse as well as
fine positioning) for the positioning apparatus PA
and hence for the positioner P.
Figure 2 shows a curve C which represents
the path actually followed by a write/read transducer
across a memory disc between the passage of two ser-
vo sectors at sampling instants t = t1 and t = t2 ~
t1 + T. At the starting instant t1, the complete
track nurnber 5 = 51 is known. At t2 = t1 ~ T, the
track number s of the track reached is measured
m
only on the basis of the code content of the servo
track. The group number is unknown. This means that
the transducer could be present in any of the points
of Figure 2 denoted by a cross. Because the speed
of the positioner is limited, the maximum nurnber
of groups which can be passed from the previous po-
sition is also limited. This maximum number of groups
is m, for which:
v
m~ f S a ~-m - 1 ;
therein, v is the maximum speed of the positioner,
s is the number of tracks per group, f is the re-
volution frequency of the memory disc in H~, S is the
total number of servo sectors, and a is the centre-to-
centre distance between two tracks in meters. It is to
be noted that said pulse T has a duration T = 1/f.S.
~SZ638
.; , . . .. .
11.1.80 10 PHN 9348
number of feasible transducer positions is thus li-
mited to m. If the direction of movement of the trans-
dicer is not known in advance, the number of feasible
positions is twice as high, so 2m. According to the
idea of the invention, the correct position of the
transducer can still be unambiguously determined,
i.e. the new complete track number 52- To this end,
the position of the transducer at the instant t1 + T
is estimated. The error in this estimate must not be
greater than the range of sg tracks around the ac-
tual value, see Figure 2. In view of the movernent
direction (which need not be known), -therefore, the
maximum absolute error in the estimate may not ex-
ceed 2 S . In this respect, see the description given
with reference to Figure 3.
Fi~re 3 shows a diagram of an embodiment
of a device in accordance with the invention. The
reference numeral 1 deno-tes the i`irs-t means for form-
ing a complete track number. In this embodiment,
these f`irst means consist of a register. The reference
numeral 2 deno-tes the second meansfor supplying a
group number which varies in an increasing or de-
creasing sense. These second means in this embodi-
mcnt consist of an AND-function gate E1 and flipflop
FF, a counter TR, an adder AD and a group number re-
gister GR. The reference numeral 3 denotes the third
means for determining the difference ~etween a com-
plete track number formed in the register 1 and a
complete track number estirnated in the fourth means
which are denoted by the reference 4. In this embo-
diment, 3 is shown to be a subtractor. The fourth
means 4 in this embodiment provide the above es-
timate on the basis of a linear extrapolation of
previously obtained complete track numbers. These
fourth means 4 comprise: a subtractor SB and three
registers R1, R2 and VRA. The reference numeral
denotes the fifth means, which in this embodiment
is a comparison device in uhich the magnitude of
~15i2~38
11.1.80 11 PHN 9348
the difference determined in 3 is compared with the
value s . Also shown is CD which is a code conver-
ter which, if necessary, converts the track number
s read from a group into a preferably binary code.
This track number as read may be expressed, for
example, in the so-called Gray code. This Gray code
is a suitable code for incorporating track numbers
in servo tracks. Also shown are two AND-function
gates E2 and E3. The result of the comparison in 5
of the magnitude of the result of 3 may be that it
is larger than sg/2; this results in a 1-signal on
line VNOK, which indicates that the correct complete
track number is not yet present in register 1. If
said result is smaller than s /2, a 1-signal is
supplied on line VOK, which indicates that the cor~
rect complete track number s(t2) is present in the
register 1. The comparison device 5 may be a simple
subtractor in which it is checked whether the sub-
traction result is positive or negative.
The further operation of the device shown
in Figure 3 is as follows. When the pulse TS appears
(see Figure 1), a clock signal CL can reach the
counter TR, via gate E1, if the line VNOK also car-
ries a 1-signal. TR successively passes through
the positions 0, 1, 2, ... m, assuming it starts
from the position 0. Therein, m is the said maximum
number of groups which can be traversed from a pre-
ceding position. (The starting position "O" or an
other value chosen as a starting position can be
adjusted, for example, each time at the first clock
pulse passed by E1). The successive counting posi-
tions are applied from TR to the adder. AD. From the
group number register GR, the group number "g" pre-
sent therein is also applied to AD. AD is controlled
on further inputs "+" and "-": a clock signal 2CL
(double the pulse frequency of CL) is applied to
the flipflop FF. The E-input of this FF al~ays
carries a 1-signal. In reaction to 2CL, the outputs
. _
11.1.80 12 PHN 9348
F1 and F2 of FF change over once within the duration
of a pulse from clock CL. F1 is connected to the "+"
input of AD and F2 is connected to the "-" input of
AD. 'rhus, within each pulse ~L, the counter eontent
of' TR is suceessively added to and subtracted from
the value "g": (g + O), (g - O), g + 1, g - 1, g + 2,
g - 2, ... g + m, g - m. The procedure described be-
low is performed for each of these values until the
correct value of s(t2) is found. Before this proce-
dure is elaborated, it is to be noted that in mostsystems it is known in which direction the displaee-
ment of the positioner will oecur. In that ease, the
"+" input or the "-" input is directly activated
from outside the device ( for example, by a com-
puter).
A result from AD, "g + i", arrives inthe register 1 (left part of the drawing). The re-
gister 1 also receives (right part of the drawing)
the value of thr track num'ber s measured. This eon-
stitutes a eomplete track mlrnber for which it is yetto be determined whether it is the correct number.
To this end, in subtractor 3 it is subtracted from
an estimated value s' from 4. The absolute value of
this difference (i.e. the sign is omitted) is com-
pared with the value sg/2 in comparison device 5.If a 1-signal occurs on VNOK, the result is not yet
correct (the said absolute value is larger than
s /2). Meanwhile, for example, "g + i - 1" or
(llg + i + 1") is input into the register 1. Sub-
sequently, the same is done with the content ofthe register 1 etc., until a l-signal appears on
the line VOK (said absolute value is smaller than
sg/2. This means that the result in register 1 is
correct because the correct group number is then in
AD or in the left part of the register 1. Ullder the
control of the 1-signal on VOK the following talces
place: the content of ~he register 1 is output, via
the gate E3, to the environment (user) as the correct
Z638
11.1.80 13 PHN 9348
complete track mlmber s(t2). At the same time, s(t2)
is input in the register R1, the value s(tl) is
transferred from R1 to R2. Furthermore, the new
group number present in the left part of the re-
gis-ter 1 is applied, via the gate E2, to the group
register GR in order to replace the previous value.
The determination of the estimate is of
major importance for this procedure. In Figure 3
this is realized in the means 4 by means of said
linear extrapolation. In this embodiment, this is
realized as follows: the latest complete track num-
ber s(t1) is stored in the register R1. The content
s(t1) of R1 is doubled (ln this binary example, this
can be simply realized by adding a bit "0" behind
the least-significant bit : see indication Z in
Figure 3). In the subtractor SB, the subtraction
takes place and the result g s'(t2), is stored in
the register VRA where s'(t2) = 2 s(t1) - s(to).
The error of this estimate is maximurn when the ab-
solute value of the acceleration of the positioneris maximum. It can be calculated that this maximum
error ~ , expressed in track numbers, is given by
= am . T /a, in which a is the maximum acce-
; leration in m/sec . As has already been stated, the
; 25 maximum error may not exceed 2 Sg in an absolute
sense. In all practical cases the estimate obtain-
ed by means of this extrapolation satisfies this
requirement. Example: a system in which f = 50 re-
volutions per second; a = 85 /um; S = 58; s = 8;
~r = 0.83 m/sec; a = 70 m/sec. 0 The maximum num-
ber of groups m which can be traversed is
m>~ 0.43 ~/ m - 1, so in practice m = 1. The per-
missible estimate error is -2 S = 4 track numbers.
The maximum estimate error is ~ = 0.1 track num-
35 bers~ A further example: a disc memory comprising
very narrow tracks and involving a small s-torage
capacity loss due to comparatively few servo sec-
tors; f = 40 Hr~; a = 10 /um; S = 50 ; s = 32;
1~52638
11.1.80 14 PHN 9348
v = 2rn/sec; a = 200 m/sec . The maximum number of
groups m which can be traversed is then m~/ 3.1
~ m - 1, so in practice m = 4. The maximum per-
missible error is -2 Sg = 16 track numbers. The
maximum error of the extrapolation amounts to ~ = 5
track numbers, which is well within the acceptable
limit.
It is to be noted that wi-thin the scope
of the foregoing the mean speed between the passage
Or the last two servo sectors can be determined. This
mean speed can be derived from the difference between
the latest (i.e. last) and the last but one complete
track number determined. The signal presenting this
difference can in principle replace a speed trans-
ducer present in such disc memory systems. The speedsignal thus obtained has a bandwidth which is limit-
ed by the sampling (only at the area of the servo
sectors). If this bandwidth is insufficient for use
in the control system of the memory, the si~nal can
be increased by a second signal which represents on-
ly the high frequency fluctuations of the speed.
United States Patent Specification 3,8Z0,712 describes
a method of generating such a high frequency signal,
based on integration of the positioning current, and
~5 of forming a continuous speed signal.
Figure 4 separately shows an embodiment of
the fourth means for estimating a complete track
number. When the memory system comprises a speed
transducer (see Figure 1), the speed v can be in-
tegrated to form each time a position signal whichis an estimate of` the complete track number:
s' (t ) = s (t + 1 . ~ v (t) dt
In the embodiment shown in Figure 4, integration
takes place in an integrator with an operational
amplifier OP and an integration capacitor ~I. The
integration time is given by the pulse TS (see Figure 1)
~ l~Z638
11.1.80 15 PHN 9348
which controls the switch SW1o The integration result
is converted, in an analog-to-digital converter ADC~
into a binary value, after which the binary inte~ra-
tion result is added, in an adder 6, to the value of
the complete track number found one period T (_ t2 ~ t1)
earlier i.e. s(t1).
Figure 5 separately shows a further embodi-
ment of the fourth means for estimating a complete
track number. The essential difference consists in
that the integration of the speed signal vp takes
place in a digital manner only after it has been con-
verted into pulses in a voltage/frequency converter
SFC. During periods T these pulses are counted in a
counter 7 and are applied to an adder 8. Then:
v ( t1 )
S (t2) = s(t1 ) f . T .
a
This is actually a refinement of the extrapola-tion
rnethod used in the embodiment of the Means 4 describ-
ed with reference to Figure 3. As has already been
noted, a refinement of this kind will not always be
necessary, because the error remains substantually
within the permissible limits during extrapolation.
~igure 6 shows a device comprising a pro-
grammed digital signal processor which is denoted by
the reference MPU. In this example, MPU is a micro-
processor (for exarnple, of the type Intel 8085)
which forms a so-termed microcomputer system MCS
in conjunction with the memory system MS. The sys-
tem bus B corrects the microprocessor MPU and the
mernory system MS via the lines AD 0 - 7 as well as
the registers BR1, BR2, ... BR6, HSU and the gate
TRSP. The registers BR1, BR2 and BR3 serve to trans-
fer data from an electronic data processing system
EDP (not shown), of which the device in accordance
with this application forrns a subunit, to the micro-
computer system MCS. This data is the following: in
reaction to a command CS, causing an interrupt in the
~1~;2~38
11.1.80 16 P~ 9348
system MCS (see hereinafter), the data concerning a
desired target track number Sd is present on the inT
puts ACB O - 10. Because the width of the bus B is
only 8 bits in this example, 11 target track number
bits (on ACB O - 10) are entered into the system MCS
in two operations in this embodiment. This means that
in a first cycle the first 8 bits are transferred
from the inputs ACB O - 7, via the register BR1, to
the bus B (lines AD O - 7) and are applied to MCS.
The sarne is done in a second cycle f`or the remain-
ing 3 bits on the inputs ACB 8 - 10 which are applied,
via register BR2 and bus B (lines ADO - 2), to MCS.
Eor a complete understanding, ~his Figure 6 also
shows how, in the case of a disc memory, not only
the target track number Sd but also the desired head
number is input from the EDP system. A command HS,
causing an interrupt in the MSC system, indicates that
the desired head nurrlber is present on the inputs ACB
O - 3, In a "fetching" cycle generated by MSC for this
purpose, the head number is input into the MSC systern
via the register BR3 and the lines AD O - 3. The head
selection can thus be realized.
Further da-ta to be input, obviously, is the
data originating frorrl the record carrier of the disc
memory, notably the servo sector data:SSE'I (see Fi-
grure 1) during the passage of a servo sector along
a head (instant TS), At TS, another interrupt occurs
in MCS to indicate that the servo sector data is
available. SSPI supplies the measured track number
Sm via DET (see Figure 1). This number is stored in
the register BR4. In practice this takes place twice
and since s = 8, so needing 3 bits, BR4 is at least
a 6-bit register, so that the same s or, in the case
of a rounding situation, possibly two dif`ferent s
values are stored. Via lines AD O - 5, the s data
is transferred to the MCS system via the bus B by
means of a f`etching cycle. On the basis of all said
data, the programmed digital sig~lal processor (MPU)
~152638
11.1.80 17 PHN 9348
is capable of supplying the necessary control sig-
nals for the positioning apparatus PA and hence for
the positioner P. In this embodiment, these control
si~lals for PA (or P) are (see Figure 1): vp, which
is the positioning speed control signal, and some
commands CMDS. On the basis of the difference deter-
mined between the target track number Sd and the
complet~ track number s obtained in the MPU (see
hereinafter), the MPU determines the speed to be
;~ l0 reached by the positioner P in order to reach the
desired position in the shortest period of time. The
relationship between the distance yet to be covered
(in track numbers) and the speed is stored for this
purpose in a suitable memory section and this data
is applied to output register BR5 via the bus B (lines
AD 0 - 7). The control signal vp then occurs after
digital - to - analog conversion in D/A. If the dif-
ference between sd and s is large enough (for example,
more than 1 track number), coarse control is concerned.
This situation is made known to PR by way of a rele-
vant command CMD1 which is applied from MPU to the
register B~6. In the case of fine control, a command
CMD2 is present on a relevant OUtpllt of BR6. Depend-
ing on the direction in which the positioned must be
positioned (determined by the si~n of the dif`-
ference between sd and s), a further command CMD3
~ill have a given value. ~n practice more commands
CMDS will be available (for example, even/odd track),
but these commands are not of importance for a proper
understanding of the present invention and will not
be elaborated herein. The same is applicable to the
head selection: on the basis of the head number in-
put (see above) and a track number reached, the pro-
cessor MPU applies this head number, via the bus B
(lines AD O - 3)~ to the head selection unit HSU.
The various heads H1, H2, ... can thus be select-
ed.
As regards the above interrup-ts requested
115Z638
11.1.~Q 18 PHN 9348
by the signals CS, HS and TS, the following explana-
tion can be given. The interrupt requests CS, HS and
TS are applied to inputs of a priority encoder PRE.
In reaction to a request, an output INT provides a
signal which is applied to MPU. When the interrupt
request is accepted, MPU supplies a signal on out-
put INTA. The interrupt having the highest priority
of all interrupts requested is granted priority (in
this case, TS always has the highest priority). In
`~ lo reaction to the signal INTA, the interrupt releas-
ed by PRE and coded in a number is applied, via a
tri-state buffer gate TRSP and the bus B, to MCS
which reacts by starting an associated instruction
(so-termed RESTART instruction).
The operation of the system shown in Fi-
, gure 6 is illustrated on the basis of flow diagrams
in Figures 7a and b.
On the basis of the interrupt commands INT
(CS/HS), the data of the EDP system (see ~i~ure 6)
concerning the desired target track number Sd and
the head number l~i are input in the system MCS :
sdIN and I-IiIN. In block 700 a, it is indicated that
the head selection unit HSU is loaded: LHSU. In
block 701 it is indicated that in MCS the difference
is determined between the desired sd and a pre-
viously determined actual (or possibly startin~
position) track number: D = sd - s. Tllis difference
may be positive or negative. The latter data is in-
put in register BR6: LBR6 (block 7O4). The command
CMD3 is thus laid down. The magnitudc of the dif-
ference D is used i-n block 7O2 for determining the
speed vp at which the positioner is to be controlled
(see the description with reference to Figure 6).
The digital value of vp is loaded into the register
35 RB5: LBR5 (block 703). The positioner can be con-
trolled therefrom v~a the D/A conversion. In block
7O5 it is determined whether synchronization with
the sector pulses exists: it is thus ensured that the
~1~i;2638
11.1.80 19 PHN 93~8
processing of the data in the programmed digital
signal processor takes place in the correct periods
Or time, so that the results of the processing are
applied at the correct instants in the positioning
process. If the synchronization is correct, the
command CMD3 from register BR6 to the positioning
control apparatus (PA in Figure 1) is released
(block 706).
The determination of the track number in
the MCS system commences at this instant. Block 707
Fs indicates that the latest (last determined) com-
plete track number s ( = s(t1)) is prepared for use.
(The s-value is normally stored in the table of a
memory section). Block 708 provides a delay conditional
on whether a servo sector pulse TS appears. If not,
"N", there is a delay. If yes, "Y", the process may
proceed to block 709. Said yes means that there are
servo signals i.e. SSPI is present (Figures 1 and 6).
Therefrom, a measured track number smis derived
(DET) and is stored in the register BR4 and applied
to the MSC system. Subsequently, block 710 is reach-
ed. Therein, the (variable) group number ~ in a
group number register is combined with the value sm
(compare Figure 3, register GR and 1). In block 711,
the dif~erence ~\ = g/s - s' is determined. (s' is
again available from the last processing cycle
thereof). In block 712, it is checked whether the
magnitude, ~ of said difference ~ is less
than s /2. If not, "N", the group number value is
increased or decreased by 1 in block 713 (depend-
ing on whether a positive or a negative direction
displacement is concerned, determined by the com-
mand CMD3). In this respect, also compare the
operation according to Figure 3, element 5 etc. If
la 1 ~ sg/2, "Y" occurs which means that the re-
sult of the combination of g and sm is ready for
further treatment. The result of the combination
of g/s is indicated by s which is the complete track
;
~i~2638
11.1.80 20 PH~ ~348
number found on the basis of the latest rneasured
value o:f s . The estimated value s' used for this
purpose is the result of an estimate calculation made
on the basis o~ measuring data obtained directly pre-
viously, notably the last value s = s(t1) determinedas indicated at the top of Figure 7b.
In figure 7b, a check "ckl" is performed
in block 714 in order to check whether the result
obtained satisfies given requirements: the complete
-~ 10 track nwnber may not exceed a given maxirnum (because
there are only a given number of tracks). If this
check reveals an error, "N", block 715 becomes re-
levant. Therein~ the value s = g/s is simply re-
placed by a value of s found d-uring the preceding
measurement (the rejected latest measurement is thus
neglected). If the check is O.K, "Y", block 716 is
reached. For each latest determined value of the
complete track number s ( = s(t1)), the difference
D = sd - s is determined in block 716. If` D = 0,
the target track has been reached, "Y", the command
CMD2 appears and is stored in BR64 Fine control is
then initiated, and the processing of the position-
ing data is terminated at "END". If D is not yet zero
("N"), the process continues normally, beginning with
a coarse control command C~D1. Block 718 shows the
speed indication vp which is loaded f`rorn the MCS
into the regis-ter BR5 (LD~5) as a speecl control
signal, block 719. Therefrorrl, after D/A conversion,
it is applied to the positioning apparatus PA. A
-table of the memory MCS inter alia stores s(t1),
but also the preceding value s(to) and also the dif-
ference between this preceding value and -the preced-
ing value but one, that is, dss (to) ol the complete
track numbers. This is shown in block 720 (for com-
pleteness' sake, the target track number is alsoindicated therein). In block 711, a further check
is performed: the difference between the latest com-
plete track number (in this case s(tl)) and ~the pre-
~ 152638
11.1.80 21 PHN 9348
ceding one (in this case s(tO)) must be larger thanor at least equal to 0 for "forward" displacement,
that is to say positive displacement, (compare block
701 above). If "backward" (negative) displacement
takes place, this difference must be smaller or a
least equal to 0. If this check is O.K., "Y" block
722 is reached. If this check is not O.K., "N", a
read error has occurred, for example, due to an
oscillation. The system comprising the signal pro-
cessor can thus simply discover such an error and itcan even intervene : block 723. In block 723 the
preceding situation is returned to for the sake of
reliability, i.e. the value s(t1) is replaced by
s = s (t~) (the result of the preceding measurement).
Moreover, in block 723 the value s = s (to) is also
taken as the estimated value s'. This value can be
used for further processing and the error is automa-
tically corrected when a (the) next measurement (via
724 etc.) i8 performed. If the check in block 721
was O.K., "Y", the estimated value s' is determined
in block 722 by means of data from block 720 by extra-
polation:
s(t1) - s(to) + dss (-to)
This means an extrapolation over a plurality of
previous values of s or the differences thereof. This
possibility is offered by the use of the programmed
signal processor without a substantial number of
additional facilities heing required. After the cal-
culation of s' by extrapolation, block 724 is reach-
ed. In block 724, RDYs indicate that the data then
available is ready for further processing~ A next
servo pulse TS is awaited: block 725 (compare the
situation in block 708). If TS appears ("Y"), the
process continues at point A of Figure 7a.
Figure 8 illustrates the processing in the
time described with reference to the Figures 7a and 7b.
Z638
11.1.80 22 PHN 9348
Along the time axis t, the instants TS are indicated
as vertical strokes. At INT, the interrupt from CS
appears, HS with statement of the newly desired head
number and the target track number. At STPS, the
positioning starts, the estimated value being equal
to the present track number (the speed is still zero).
ENDPS indicates the instant at which the positioning
is terminated. In this segment, the processing phases
0 to 5 are completed. The phases 2, 3, 4 thereof are
; lO completed as many times as is required for reaching
the target track. Thc said phases can be found in the
Figures 7a and 7b as follows:
phase 0: processing of new head number and target track
number: blocks 700 to 707.
phase 1: waiting cycle for synchronization: block 708.
phase 2: reading from servo sector and forming of new
track number: blocks 709 to 715.
phase 3: determination of the difference between the
target track number and the new track number
and thus the speed and D/A value for po-
sitioner PA: blocks 716 to 719.
phase 4: det~rmination of new estimate s' and waiting
for next TS: blocks 720 to 725.
phase 5: switching over to fine control, end of po-
sitioning: from Y output of block 717.
