U.S. patent number 3,789,378 [Application Number 05/256,022] was granted by the patent office on 1974-01-29 for transducer positioning mechanism.
This patent grant is currently assigned to Ing. C. Olivetti & Co. S.p.A.. Invention is credited to Giorgio Bonzano, Pier Carlo Lesca, Luigi Ponzano.
United States Patent |
3,789,378 |
Bonzano , et al. |
January 29, 1974 |
TRANSDUCER POSITIONING MECHANISM
Abstract
In a magnetic disc store system, transducers are positioned over
tracks on the discs by a stepping motor controlled by a central
unit which sends signals over three channels commanding first and
second pulse frequencies to be emitted from a pulse generator,
which frequencies are applied to a bidirectional counter. The
counter controls the motor and the pulses are fed back to the
central unit and are there counted to indicate actual transducer
position. When the transducers reach the selected position, fine
positioning is effected by a push rod which engages a wedge between
teeth of a rack attached to the transducers. There is further
disclosed an improved mechanism for interchanging disc cartridges
with automatic opening and closing of the shutter through which the
transducers are introduced and positioned.
Inventors: |
Bonzano; Giorgio (Montalto
Dora, IT), Lesca; Pier Carlo (Palazzo Canavese,
IT), Ponzano; Luigi (Ivrea, IT) |
Assignee: |
Ing. C. Olivetti & Co.
S.p.A. (Ivrea (Torino), IT)
|
Family
ID: |
11310427 |
Appl.
No.: |
05/256,022 |
Filed: |
May 23, 1972 |
Foreign Application Priority Data
|
|
|
|
|
May 24, 1971 [IT] |
|
|
68737 A/71 |
|
Current U.S.
Class: |
360/77.02;
G9B/5.193; G9B/5.187; 360/133 |
Current CPC
Class: |
G11B
5/5552 (20130101); G11B 17/041 (20130101); G11B
5/5521 (20130101) |
Current International
Class: |
G11B
5/55 (20060101); G11B 17/04 (20060101); G11b
005/56 () |
Field of
Search: |
;340/174.1B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Canney; Vincent P.
Attorney, Agent or Firm: McMahon; Kevin
Claims
What we claim is:
1. In a system for positioning a transducer over a selected
recording track of a peripheral magnetic disc store, the
combination including:
means for storing the desired position of the transducer and means
for storing the actual position of the transducer;
means for comparing the actual and desired positions, said
comparing means being connected to said actual and desired position
storing means and producing a fast and slow positioning signals
depending on the magnitude of the difference between the desired
and actual positions and further producing a direction signal;
pulse generator means, responsive to said slow and fast signals,
for producing pulses of relatively low or high frequencies, an
output of said pulse generator being connected to said actual
position storing means;
a bi-directional counter, connected to an output of the pulse
generator, for counting the pulse produced, the direction of
counting being controlled by said direction signal;
a stepping motor, connected to an output of the bi-directional
counter for positioning said transducer;
an odd-even counter means, connected to the output of the pulse
generator for recording whether the number of pulses produced by
said generator is odd or even;
a fine positioning device, responsive to said odd-even counter, for
positioning said transducer.
2. The system according to claim 1, wherein said fine positioning
device includes a rack fast with said transducer, at least two stop
latches having a fixed position with respect to the direction of
movement of said transducer and movable in a transverse direction
to engage with said rack, the pitch of said rack being equivalent
to an even multiple of the radial distance between two recording
tracks while the pitch between said two latches is equivalent to an
odd multiple of the radial distance between two recording tracks,
said latches being selectively activated by said odd-even counter
means.
3. The system according to claim 1, wherein said pulse generator
comprises a transistor connected across a bias voltage in parallel
with a first and a second branch, said first branch including a
resistor R1 and a capacitor C1 while said second branch includes a
resistor R2 and a capacitor C2, C1 being connected in parallel with
switch V1 and C2 being connected in parallel with switch V2 and
resistor R3, R3 and V2 being in series, the points between R1-C1
and R2-C2 being connected, the opening of V1 causing low frequency
oscillations, the opening of both V1 and V2 causing high frequency
oscillations.
4. Mechanism for positioning the transducers of a disc store,
comprising a coarse positioning device to control the shifting of
said transducers in a radial direction with respect to said discs,
and a fine positioning device to control in a fine manner the
positioning of said transducers over a selected track, said second
positioning device functioning as a locating device and being
constituted by a rack fast with said transducers, at least one stop
push rod having a wedge-shaped end fixed position with respect to
the direction of shifting of said transducers and an electromagnet
for moving said rod in a transverse direction to engage said
wedge-shaped end thereof with that space of said rack which is
brought into correspondence therewith by said coarse positioning
device, two transverse leaf springs supporting each push rod, a
lever fast with the armature of said electromagnet and opposing a
first spring to control said push rod, said armature in the
condition of energization of the electromagnet being maintained in
a first position by overcoming the action of the second spring
which tends to retain it in a second position corresponding to the
de-energization of the electromagnet, said second spring being
adapted to exert a resilient load greater than that of said first
spring, so that when the command of said fine position device
effects the de-energization of said electromagnet said second
spring, by shifting said armature towards the second position,
releases said rod from the control of said lever and permits said
first spring to act on the mass only of said rod and cause it to
engage with said rack.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a system for connecting a central
processing unit to a peripheral magnetic disc store and more
particularly to a positioning system for bringing a read/write
transducer over a selected recording track of a disc.
Owing to the capacity of modern electronic processors of large and
medium sizes for processing large masses of information, they
necessitate the availability of large mass stores outside the
processor, in which the data or instructions are easily to be found
in use. In other words, the need arises for types of external
stores the capacity of which can be increased at will and in which
searching and reading are rapid. These requirements are adequately
met by magnetic disc storage units, each of which includes a
single-disc cartridge or a cylindrical package of vertically
stacked discs, the cartridge or package being normally of
interchangeable type.
In magnetic discs, the information is recorded in serial digital
form on each face of a disc along a plurality of concentric
circular tracks laid down in the circular band between the outer
edge of the disc and a given central circular area. The tracks may
be subdivided into sectors, so that it is possible to select even a
single segment of track as a storage area for recording or reading.
One or more transducer elements may be selectively positioned over
a given portion of the recording surface to carry out a reading or
writing operation.
Rapid reading of the information sought is tied up with the means
permitting rapid positioning of the magnetic transducer on the
track of the disc which contains this information. Once the
transducer has reached the desired track, the codes recorded on the
said track will allow the identification and the reading of a given
sector.
Normally, read/write transducers are mounted facing one another on
a pair of arms movable in a radial direction with respect to the
disc and disposed in the form of a fork so as to operate on both
faces of the disc. Each transducer must be accurately positioned
both in a normal direction with respect to the surface of the disc
and in a radial direction with respect to the axis of the disc. The
disc is caused to rotate at high speed (for example of the order of
4,000 r.p.m.) so that there is created a thin layer of air which
accompanies the surfaces of the disc during the movement and on
which glides the head containing the transducer, which is thus kept
at a very small distance from the face of the disc. The form, type
of mounting and possibility of adjustment of the head therefore
constitute so many critical points for the use of these types of
store, inasmuch as contact between the transducer and the
magnetized surface of the disc may cause damage both to the disc
and to the transducer.
The positioning of the transducers is generally carried out by
means of systems of electromechanical type. It is obvious that the
closer the tracks are brought to one another and the smaller the
tolerance in the radial distance between two tracks (with a
consequent greater amount of information recordable on the surface
of the disc), the greater are the problems that arise as regards
the positioning mechanism, which must not only achieve a low time
of access to the information sought, but must also effect precise
positioning of the transducer over a predetermined track. That is,
the positioning mechanism requires tolerances not greater than
those of the recording disc, otherwise the electromechanical
tolerances of the positioning mechanism would have repercussions on
the storage capacity of the disc.
When a given item of information is required in a peripheral store
unit having interchangeable discs, the disc containing the
information is selected and is inserted in the unit itself, which
will then receive from the computer the indication of the track in
which the information sought is located. The peripheral unit must
therefore be able to execute the order from the computer by
positioning the magnetic transducers over the track addressed and
thereafter be able to perform the function of reading or writing
(or possibly of erasure) which the processor transmits to it.
Peripheral disc units are known which employ rather complex control
systems and relatively costly positioning mechanisms, these control
systems and positioning mechanisms being therefore unsuitable for
small, low-priced peripheral units, which require a particularly
simplified internal structure and, therefore, simplicity of
connection with the central processor and must allow reliable
operation without sacrificing too much to access time.
More particularly, the known connecting systems use a peripheral
unit which receives the address of the selected track in binary
coded form from the central processor, for example in parallel on
eight channels. The address of the selected track is deposited in a
staticizing register of the peripheral unit and compared by means
of a comparator with the address of the track on which the
transducer is at that moment. The difference is utilized to command
the movement of the positioning motor until the track addressed is
reached. These systems therefore require a high number of command
channels on which the central processor sends the address of the
selected track; moreover, the peripheral unit must contain all the
logical measuring and comparison elements for processing signals
for the positioning of the transducers.
SUMMARY OF THE INVENTION
These drawbacks are obviated, thus achieving the pre-established
objects for low-cost peripheral disc units, in a system comprising
one or more read/write transducers positioned radially over a
selected recording track by a stepping motor controlled by a
bidirectional counter which indicates the position and the
direction in which the said transducers are to be shifted, the
counter being fed by a pulse generator. In the present invention,
the central unit is prearranged to send on three separate channel
signals respectively denoting first and second speeds and the
direction of the shifting, the first-speed and second-speed signal
being adapted to control the frequency of the pulse generator. The
direction signal controls the counting direction of the counter.
The central unit receives on a return line the pulses supplied by
the pulse generator and counts these pulses for the purpose of
obtaining an actual indication of the current position of the
transducers. The central unit compares the said actual indication
with the nominal indication of the selected track, i.e. the
indication of the track to which the transducer has to move, to
generate separate binary logical level signals denoting the first
or second speed and the direction, respectively, on the said three
channels on the basis of the amount and sign of the difference
between the said actual and nominal indications.
Therefore, a first object of the invention is to simplify the
peripheral unit and its connection with the central processor in
such manner that the commands coming from the latter may be carried
back on a few channels.
Another object of the invention is to control the transient
originating from the passage from one speed of shifting or movement
of the transducers to another speed.
A third object of the invention is to obtain a very precise control
of the position of the transducer with respect to the selected
track by means of a fine positioning device which is actuated at
the end of the execution of the track selection command by the
step-by-step motor.
A fourth object of the invention is to obtain improvements in the
command of this fine positioning device.
A fifth object of the invention is to have a method of loading and
regulating the transducers which allows easy adjustment of the
positioning system.
A further object of the invention is to facilitate the insertion
and withdrawal of the single-disc container into and from the
peripheral unit.
The invention will be described in more detail, by way of example,
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the system according to the invention
for connecting a central processing unit to a peripheral disc
store;
FIG. 2a illustrates an embodiment of the pulse generator included
in the diagram of FIG. 1;
FIG. 2b is a diagram illustrating the course in time of a number of
signals present in the generator of FIG. 2a;
FIG. 3 is a diagram illustrating the course in time of a number of
signals present in the system according to the invention;
FIG. 4 is a plan view of the peripheral disc unit according to the
invention;
FIG. 5 is a side view, partly in section, of a first detail of FIG.
4;
FIG. 6 is a section of a single-disc cartridge employed in the
peripheral unit of FIG. 4;
FIG. 7 is a transverse view, partly in section, of a second detail
of FIG. 4;
FIG. 8 is a side view, partly in section, of a third detail of FIG.
4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the system for connecting a central processing
unit, in particular a computer 1, to a peripheral unit 15
containing a magnetic-disc store is substantially constituted by
three command channels extending from the computer to the
peripheral unit and a return channel from the peripheral unit to
the computer.
The three command channels transmit the first-speed signals V1, the
second-speed signals V2 and the direction of movement signals A/I,
respectively. The return channel C feeds back to the computer the
stepping pulses which command the positioning of the read/write
transducers. The pripheral unit 15 comprises a pulse generator 5
which feeds a bidirectional counter 6; the output of this counter
commands a first positioning device constituted by a step-by-step
motor 7 adapted to position a system of transducers 11 and 12 with
respect to a recording support consisting of a magnetic disc 8.
Each of the transducers 11 and 12 is adapted to execute a reading
or writing operation on a face of the disc and is suitably
supported by arm 9 or 10. The shifting of the arms is controllable
by the stepping motor 7. The stepping motor 7 is bidirectional and
therefore can effect the positioning in both radial directions; it
is, of course, possible to employ two separate motors, one for
forward movement and one for backward positioning.
The peripheral unit according to the invention is also provided
with a second positioning device 16 of fine type which is
controlled by another counter 14 and is activated when the motor 7
has completed the coarse positioning.
The various circuits for reading and writing and for executing
auxiliary functions (such as, for example, the selection of the
transducer, the indication of the availability of the peripheral
unit, the signalling of an erroneous search for the track, etc.)
are not described, inasmuch as they are not related to the present
invention; the signals at the interface of the computer and
peripheral unit are represented by the line In, which line
indicates a plurality of transmitting and receiving channels.
The computer 1 is a general purpose processor set up in such manner
as to effect the connection with the peripheral unit 15 in the
manner hereinbefore indicated through three outgoing channels (V1,
V2, A/I) and one return channel (C). Only those elements of the
computer which develop a function connected with the command for
positionng at a selected track are illustrated, that is two
registers 2 and 3, the desired-position and actual-position
registers, respectively, and a comparator 4; the register 3 is
arranged to function as a counter.
The problem preliminary to reading or writing in a magnetic disc
store is represented by the positioning of the transducers 11 and
12 from the position in which they are located at the instant of
initiation of a new search phase to the position in which the
addressed track is located.
The search cycle may start after the peripheral unit has supplied
the computer with the available machine signal and commences with
the introduction of the address of the selected track into the
desired position register 2. Register 3 contains the current
(actual) address of the track over which the transducers are
located. The two addresses are compared in the comparator 4, which
gives an indication of the difference between the registers; the
comparator sends a signal on either the channel for the first speed
V1 or the second speed V2 according to whether the error resulting
from the comparison is smaller than or greater than a predetermined
quantity. Comparators of this type are, of course, entirely
conventional and, besides being commercially available, are found
in all digital computing machines.
The comparator 4 sends a forward or backward shifting level A/I
which indicates the direction of error.
The channels for low speed V1 and high speed V2 activate the pulse
generator 5 (which is of conventional construction) and it begins
to send stepping clock pulses with a frequency which depends on the
speed channel which effects the activation (for example 200 c/s for
V1 and 500 c/s for V2).
The stepping clock pulses M are applied directly to the
bidirectional counter 6 which commands the stepping motor 7. The
bidirectional counter 6 totals algebraically the pulses which it
receives; the direction of counting depends on the presence of the
forward or backward signal (transmitted on the channel A/I) which
enables either the input A (through the inverter 13) or the input
I. The output E of counter 6 controls stepping motor 7. The advance
commands E that the stepping motor reeives from the counter 6 are
in the form of decoded binaries of the numeric content of the
counter itself and are used to energize the position windings
concerned. The E commands have the same frequency and correspond to
the stepping clock pulses M produced by the pulse generator 5, as
is illustrated in the diagram of FIG. 3.
Each stepping clock pulse commands an advance equal to the radial
pitch or step of the tracks of the disc and therefore the total of
the stepping clock pulses generated in a certain interval of time
represents the number of tracks traversed. Since the stepping clock
pulse M are also sent through the channel C to the actual position
indicator 3 in computer 1, this indicator varies its numeric
content by one unit for each pulse received so as to represent the
address of the actual position of the transducers. As long as the
speed signals V1 and V2 remain, the generator 5 remains activated
and the indicator 3 continues to advance, so that the difference
found by the comparator 4 decreases progressively with each pulse
received by register 3. The high speed signal V2 is disenabled
first and the fine difference signal V1 is disenabled thereafter
when the difference between the counters 2 and 3 reaches the value
0, that is, when the selected track has been reached. At this
instant, the comparator disenables both channels V1, V2, and pulse
generator 5 stops, causing counter 6 to cease stepping the motor 7
(see the pulse diagram of FIG. 3).
In FIG. 3, the series of the last five command pulses for the
advance of the transducer carriage carry an indication of the
distance in track pitches from the selected track at the instant
corresponding to each of the said pulses. In the same diagram,
there is moreover assumed the simultaneous initial presence of the
signals V1 and V2, as will be explained hereinafter, and the
change-over (cancellation) of the machine-available signal in
synchronism with the appearance of the low-speed signal V1.
For the purpose of improving the positioning of the transducers
over the addressed track and ensuring a predetermined precision,
the peripheral unit according to the invention employes the fine
positioning device 16 of electromechanical type, which can come
into action only after the generation of the stepping clock pulses
M has been turned off. The fine positioning device 16, which will
be described in more detail hereinafter, consists of a rack
parallel to and fast with the transducer carrying arms; the rack
can be engaged and arrested in the adjusted position with respect
to each of the tracks of the disc by means of a push rod actuated
by an electromagnet. More particularly, if the rack has symmetrical
saw teeth and its pitch is twice the radial track pitch and the
fine positioning device is equipped with two push rods disposed in
fixed radial positions and separated by a distance equal to an odd
number of track pitches and movable selectively in a direction
perpendicular to the rack, it is possible to control the
positioning of the successive odd or even tracks with the precision
ensured by the push rod and rack coupling.
The selective actuation of the said push rods is controlled by a
bistable element 14 which acts as an odds and evens counter for the
number of tracks traversed or crossed under the command of the
stepping pulses M. When the generation of these pulses stops, the
counter 14 has stored in it the odd or even position of the track
reached. After the M pulses stop, the machine produces a pulse S
which opens gate 17 allowing the odd or even indication of device
14 to be communicated to positioning device 16. Depending on the
contents of counter 14, the odd or even push rod of device 16 is
activated. This operation will be described in detail
hereinafter.
It is obvious that in the positioning system described the number
of commands required by the peripheral unit is reduced to a minimum
and that more speed commands are available; moreover the
electronics associated with the positioning of the selected track
are exceedingly simplified inasmuch as the capacities of the
central computer are exploited. This peripheral disc unit is
therefore simple and of low cost, without the complexity of
circuits and the connecting interface normally present in similar
servo-systems and without sacrificing speed or precision in the
positioning.
The positioning devices of read/write transducers for disc stores
are generally provided with a circuit which signals when the
transducers are on the reference track (normally the outermost of
the disc) called "track 0" and with another circuit which detects
an erroneous search or positioning, understood as an overstepping
of the number of tracks possible (for example 202) towards the
central part of the disc. When the condition of erroneous search is
produced, the computer, by methods entirely similar to those
hereinbefore described for a generic track, causes a positioning,
at low speed and with a direction of movement towards the outside
of the disc, of the track 0.
For the purpose of facilitating the finding of the reference track
(track 0) and the maximum distance track (track 202) and in order
to prevent damage to the machine due to command errors, the initial
and final parts of the travel of the transducers carriage are
controlled by end-of-travel microswitches. The activation of the
said microswitches takes place, for example, six tracks before the
end of the travel and causes the exclusion of the high-speed
command V2 if still present. The approach to the end-of-travel
track then takes place at low speed under the control of an
auxiliary end-of-travel counter which, activated by the said
microswitches and fed with the stepping clock pulses, signals the
reaching of the first and last tracks when by counting six pulses
it reaches a well-defined configuration.
There will now be described, with reference to FIGS. 2a and 2b, a
particular embodiment of the pulse generator 5 which, according to
a further characteristic of the invention, enables the passage from
the low to the high speed and vice versa to be effected with
controlled acceleration and deceleration.
We have seen that in the case in which the difference obtained in
the comparator 4 between the desired position and the actual
position gives a result less than or equal to a predetermined value
(for example 4) the channel enabled is the channel for the first
speed V1, which sets the pulse generator 5 in operation at the
lower frequency (for example 200 c/s).
In the case in which the difference obtained from the comparator 4
is greater than the predetermined value, both speed channels V1 and
V2 are enabled and the pulse generator 5 is obliged to pass over to
operation at the higher frequency (for example 500 c/s). During the
passage from one frequency to the other, there is a transient which
it is necessary to control. To this end, it is possible to use a
control circuit with a fixed time constant which comes into
operation every time the second-speed signal V2 is switched over.
This control of the transient is also necessary during the final
positioning phase, since on the reaching of that distance from the
selected track which is equal to the predetermined value (for
example 4, which defines the change-over point from slow to fast)
and after which only the first speed remains enabled the second
speed is switched off, with the consequent passage from the greater
frequency to the smaller one. The deceleration transient must
involve a time less than that necessary for covering the number of
tracks intervening before the selected goal is reached.
FIG. 2a shows a single-junction sawtooth oscillator constituted by
the single-junction transistor T (biased with voltage Va), the
resistor R1 and the capacitor C1. In addition, this oscillator has
a delay circuit represented by the group C2, R2, R3. The signals V1
and V2 control the short circuit of the capacitors C1 and C2,
respectively.
In the phase of arrest (low speed absent), the switch V1 is closed
and short-circuits C1, thus preventing the oscillations of the
circuit and keeping the output U at voltage O.
In the low-speed phase, the switch V1 is open, so that C1 is
charged with a time constant equal to C1R1. The oscillations of the
sawtooth oscillator, represented in FIG. 2b by means of the voltage
V.sub.B on the capacitor C1, are triggered. Pulses in
correspondence with each cycle of the oscillator are present at the
output U.
To change to high speed, it is necessary for the switch V1 to be
open; the change takes place by means of the opening of the switch
V2. In this case, the voltage at the point A which was about O
begins to rise with a law determined by the time constant C2R2. As
long as the voltage at A is lower than that at C1, R2 does not
intervene to charge C1; when this value is exceeded, C1 is charged
with a new time constant represented by (R1 .sup.. R2/R1 + R2) C1.
In the meantime, C2 is charged until it reaches the maximum voltage
at which C1 can arrive in the course of the cycle of oscillations
and from this instant the diode D2 excludes it from the oscillator
circuit. The effect produced by the gradual passage of the
oscillator circuit from the initial time constant C1R1 to the final
one (R1 .sup.. R2/R1 + R2) C1 is illustrated in FIG. 2b by means of
the voltage diagram VB: there is a gradual reduction of the period
of the oscillator and therefore an increase in the frequency of the
pulses at the output U.
To pass from high to low speed, it is necessary to close the switch
V2. In consequence of the discharge of C2 through R3 and when the
voltage at C2 decreases, the proportion of current which is
required from the branch R3V2 to the resistor R2 increases. This
resistor therefore no longer contributes to the charging of C1, so
that an effect reciprocal to that which was obtained in
acceleration is achieved.
CARTRIDGE INSERTION AND WITHDRAWAL DEVICE
The embodiment of the invention described here relates to a
peripheral store unit having interchangeable discs and more
precisely to the so-called single-disc type of store contained in a
cartridge of standard type.
Rferring to FIGS. 4 and 5, the peripheral unit comprises a base 20
(FIG. 5) on top of which there is arranged an insertion and
withdrawal device 21 for a disc cartridge 22 and a positioning
device 23 (FIG. 4) for a pair of transducers 11 and 12 (FIG. 8)
adapted to read and write on a selected recording track of the disc
8 contained in the cartridge.
Each of these disc cartridges 22 (FIG. 6) is provided with a
shutter or door 51 openable to allow the introduction and
positioning of the transducers 11 and 12 with respect to the disc 8
contained therein and is moreover provided with a pair of locating
surfaces 52 and 53 adapted to couple up with corresponding guides
46 and 47 included in the insertion and withdrawal device 21.
Moreover, in these cartridges, the disc 8 is mounted concentrically
on a hub 40 having a conical cavity 45 adapted to engage a
like-wise conical tip 55 of a spindle 80 of electromagnetic type
supplied by a motor 81 positioned below the base 20.
The hub 40, which also acts as a flywheel, is provided at the
bottom with a ring 60 in which there is formed a series of notches
65 adapted to co-operate with a photoelectric assembly constituted
by a lamp 70 and a phototransistor 75 for the control of the speed
and the signalling of the angular position of the disc.
The insertion and withdrawal device 21 for the disc cartridge 22
comprises a supporting platform 26 (FIG. 5) parallel to which,
supported by the posts 28, there is arranged a plate 27 provided in
its central portion with a recess 25 (FIG. 4) in which it is
adapted to accommodate the shutter 51 of the cartridge 22.
The platform 26 has a circular hole 30 in its central portion which
is adapted to permit the spindle 80 to engage the hub 40 of the
cartridge.
The supporting platform 26 is pivoted by means of two pins 29 and
31 (FIG. 4) on two first blocks 32 and 33, respectively, of the
base 20 and is inclinable with respect to the normal working
position (shown in FIG. 5) by means of a manually operated arm 34.
This arm 34 is constituted by two L-shaped levers 36 and 36 (FIG.
4) interconnected by a handle 37 and pivoted by means of two pins
38 and 39, respectively, on two second blocks 41 and 42,
respectively, of the base 20. Each of the levers 35 and 36 is
provided with two rollers 43 and 44, respectively, adapted to
cooperate with the bottom part of the supporting platform 26. Two
guides 46 and 47 are arranged on the top of this platform 26, while
on a rod 48 disposed on the plate 27 transversely of the recess or
opening 25 there is arranged a pair of vertical references 49 and a
rubber-cover roller 50 adapted to exert a resilient pressure on the
upper surface 53.
At the edges of the opening 25, in the upper part of the plate 27
(FIG. 5) and at right angles thereto, there are arranged two side
pieces 54 and 56 which are parallel to one another and in which
there are formed two slots 57 and 58 (FIG. 4), respectively,
adapted to produce a compulsory path for a movable carriage 59
constituted by two shafts 61 and 62 slidable in the said slots and
between which there is arranged a central body 63 provided with a
hook 64 at one end.
In the inoperative position, the movable carriage 59 (FIG. 4) is
accommodated with its two shafts 61 and 62 in the lower end fof the
slots 57 and 58, where, pivoted on the side pieces 54 and 56, there
are arranged two stops 66 and 67 adapted to hold the carriage 59 in
this position through the action of two springs 68 and 69 when the
cartridge 22 is withdrawn.
When the cartridge 22 is fully inserted into the device 21, the
carriage 59 is accommodated with its shafts 61 and 62 in the upper
end of the slots 57 and 58 (FIG. 5), where it remains in stable
equilibrium since these slots have a sharp downward reversal of
direction.
Below the upper end of the slots 57 and 58 and pivoted on the side
pieces 54 and 56 there are arranged two levers 71 and 72 bearing at
one end two rollers 73 and 74 adapted, through the action of two
springs 76 and 77 to press against the locating or reference
surface 53 of the cartridge 22 and to co-operate with the
references 49 for the vertical centring of the cartridge.
A stop fork 143 receiving the disc cartridge 22 effects an
approximate centring of the disc 8 in the radial direction.
MECHANISM FOR POSITIONING AND ADJUSTING THE TRANSDUCERS
The positioning device 23 for the pair of transducers 11 and 12
(FIG. 8) comprises a base plate 82 (FIG. 4) on which there are
mounted two first posts 83 and 84 adapted to support a first guide
shaft 86 and two second posts 87 and 88 adapted to support a second
guide shaft 89, and a pin 91 of a command bar 92.
Slidable on the cylindrical guides 86 and 89 are two bushes 93 and
94 of a carriage 96 movable in a radial direction with respect to
the disc 8. One bush 93 carries an arm or flange 97 to which there
is fixedly connected a rack 98 meshing with a toothed wheel 99
driven by a step-by-step motor 101 arranged below the base 20.
Each transducer 11, 12 (FIG. 8) is supported by the resilient end
102 of an arm 103 mounted on the carriage 96 (FIGS. 8 and 4) and
movable manually with respect to this carriage in a direction
parallel and radial with respect to the surface of the disc by
means of an adjusting screw 104 connected to a lug 106 of the same
arm 103 and in engagement with a screw nut 107 of the carriage 96,
in such manner as to effect a centering of the transducer with
respect to the tracks of the disc 8.
The approach of each transducer to the surface of the disc, once
the predetermined working conditions have been achieved, is
produced by a loading member constituted by a lever 108 pivoted on
the carriage 96 by means of an eccentric pin 109 and provided at
one end 111 with a pin 112 adapted to transfer to the resilient end
102, as a bending load, an action applied at the other end of the
lever 108 by means of a cam 113 co-operating witn a small roller
114 fixed to the lever 108.
The eccentricity of the pin 109 is adjustable manually by means of
a screw 115 (FIG. 4) which, by rotation thereof, enables the axis
of the lever 108 to be shifted to adjust the distance of the
transducer with respect to the surface of the disc.
The cam 113 is mounted on a shaft 116 with its axis extending
transversely of the movement of the carriage 96 and is movable
axially between two predetermined positions under the command of
the command bar 92 (see also FIG. 7) co-operating with a collar
118. The command to the bar 92 is given by an electromagnet 119
arranged below the base 20. Through the medium of the toothed wheel
99 and the rack 98, the step-by-step motor 101 executes a first
approximate positioning of the transducers 11 and 12 in a radial
direction with respect to the disc 8. A more precise positioning is
effected by a second positioning device 121 constituted by a rack
122 fast with the bush 93 of the carriage 96 and adapted to
co-operate with two stop push rods 123 and 124 which are paralel to
one another and have one end wedge-shaped for penetration into one
of the sawtooth spaces of the rack 122.
The push rods 123 and 124 are each supported by two transverse leaf
springs 126 and 127 fixed at the bottom to the base plate 82 and
are controlled by two electromagnets 128 and 129, respectively. The
push rods 123, 124 cause the rack 122 to be moved by the action of
a rod being inserted into the sawtooth with the sawtooth gap not
being precisely alined with the rod tip. The insertion of the rod
tip will, of course, cause the rack to move so that the gap will be
alined with the tip.
Each of the armatures 130 of the electromagnets 128 and 129 is fast
with the arm 131 of a lever 132 pivoted on a shaft 133 and having
one of its arms 134 adapted to co-operate with a collar 136 of each
of the push rods 123 and 124. A spring 137 stretched between an arm
138 of the lever 132 and a lug 139 fast with the electromagnets 128
and 129, respectively, is adapted to keep each armature 130 spaced
from the corresponding electromagnet 128, 129, respectively, when
it is not energized.
Between the collar 136 and a fixed stop 141, concentrically with
each of the push rods 123 and 124, respectively, there is arranged
a compression spring 142. More particularly, the spring 137 is
adapted to exert a resilient load greater than that of the spring
142.
In the condition in which the machine is switched off and unloaded,
the handle 37 (FIGS. 4, 5) can be lowered and the arm 34 then holds
the supporting platform 26 inclined upwardly in a position suitable
for the introduction of a cartridge. In this position, moreover,
the movable carriage 59 is accommodated with its shafts 61 and 62
(FIG. 5) at the lower end of the slots 57 and 58 and has the hook
64 prearranged for engaging the shutter 51 of a cartridge 22.
Moreover, the two transducers 11 and 12 are at the end of their
travel and spaced from one another so as not to interfere with the
insertion and withdrawal device 21.
A cartridge 22 is then introduced into the device 21 by causing it
to slide with the locating surface 52 on the guides 46 and 47. The
cartridge 22 is guided at the top by the references 49 and the
resilient roller 50 (FIGS. 5, 4). Once the shutter 51 has been
gripped by the hook 64, pushing the cartridge 22 by hand to insert
it, the movable carriage 59 -- the stops 66 and 67 having been
raised -- is brought towards the upper end of the slots 57 and 58,
thus raising the shutter 51.
When the cartridge 22 has been fully inserted, the handle 37 is
raised, bringing the supporting platform 26 parallel to the base 20
and thus enabling the electromagnetic spindle to engage the disc
hub 40, centring it by means of the conical tip 55. The spindle 80
also exerts an upward thrust on the cartridge which is opposed
resiliently by the rubber-covered roller 50 and by the rollers 73
and 74 mounted on resiliently acting levers. Moreover, by lowering
the cartridge, the ring 60 is interposed between the source of
light 70 and the phototransistor 75.
The disc 8 contained in the cartridge 22 is thus prearranged for
correct reading and/or recording thereof. The transducers 11 and 12
can approach the surfaces of the disc 8 only after the latter has
been set in rapid rotation by the spindle; since the distance
between the transducer and the disc depends on the balance between
the aerodynamic force acting on the transducer invested by the
cushion of air carried along by the moving disc and the resilient
load imposed by the lever 108, until the speed of rotation of the
disc and, therefore, the bearing action of the air has reached a
predetermined value, the transducers 11 and 12 are kept spaced from
the surfaces of the disc 8. If it is assumed that this value is
reached within a predetermined interval starting from the switching
on the motor, at the end of this interval there is generated a
signal enabling the approach of the transducers 11 and 12 to the
surfaces of the disc 8. This signal energizes the electromagnet 119
(FIGS. 4, 7) which, causing the coomand bar 92 to turn clockwise,
shifts the shaft 116 to the right and causes the rollers 114 to
co-operate with the larger-diameter cylindrical part of the cam
113. Consequently, the lever 108 produces the approach of the
respective transducer to the surface of the disc.
Any possible track centring operations or adjustments of the
distance from the disc can be effected by acting on the devices
hereinbefore described for adjusting the transducer.
The operations which are required for effecting the positioning,
both approximate and fine, of the transducers over an addressed
track have been described in the section on the electronic
controls. FIG. 4 also illustrates the end-of-travel microswitches
144 and 145.
The mechanical simplicity of the positioning devices is obvious
from the foregoing description, this mechanical simplicity, by
reducing the number of mechanical components required by the known
systems, achieving reliable positioning operations and eliminating
plays and tolerances which have a direct repercussion on the
storage capacity of the disc. Moreover, the masses in movement for
the fine positioning by means of the rack and push rod coupling
have also been considerably reduced due to the new type of command
mechanism for the push rods which separates the release of the
armature 130 (restored by the spring 137) from the advance of the
push rod carried out thereafter by the spring 142, thus avoiding
the disadvantage of heavy blows of the push rod against the rack
and of repeated rebounds.
The peripheral disc unit is also provided with a system for the
forced circulation of air and the cleaning thereof. More
particularly, the air circulates in a close circuit and is
introduced by a fan into the cartridge, which has a cover openable
towards the interior in its lower face. In correspondence with this
cover, the platform 26 has an opening 146 in coincidence with which
an air filter is arranged in the base 20.
* * * * *