ACTUATOR MECHANISM FOR DISK STORAGE APPARATUS

ACTIONNEUR POUR MEMOIRE A DISQUES

English Abstract

ACTUATOR MECHANISM FOR DISK STORAGE APPARATUS


ABSTRACT


The invention relates to an actuator mechanism suitable for positioning
a recording head over the surface of a recording disk. The actuator
consists of a planar coil etched from a copper laminated board. The
board is pivoted at one end and carries a recording head supported on
an extended arm. Magnets produce a flux perpendicular to the plane of
the laminate so that current through the coil produces limited motion of
the board about its pivot. The actuator mechanism is located in relation
to the disk so that the limited motion of the board moves the head over
the disk from one transducing position to another. The mechanism is
included in a closed loop servo system which derives position information
from servo tracks on the disk and enables track access and track following
operations to be conducted.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. An actuator mechanism for disk storage apparatus
comprising a planar conductive coil on an insulating lamina
substrate mounted on a pivot means to permit movement in
the plane of the substrate, a recording and playback head
assembly mounted on said pivot means for movement with the
substrate, a magnetic assembly positioned with respect to
the substrate so that current through the coil causes
movement of the substrate about the pivot means, and a
control circuit for controlling the magnitude and direction
of current supplied to the coil.
2. An actuator mechanism as claimed in claim 1, in
which the magnetic assembly consists of at least one gen-
erally C-shaped magnetic structure having facing pole
pieces at the open ends thereof, the structure or structures
being positioned so that portions of the coil are located in
the gaps between the poles.
3. An actuator mechanism as claimed in claim 1, in
which the magnetic assembly consists of two generally C-
shaped magnetic structures each having facing pole pieces at
the open ends thereof, the structures being positioned one
on each side of the substrate with portions of the coil
located in the gaps between the poles.
4. An actuator mechanism as claimed in claim 2 or
claim 3, in which the portions of the coil between the pole
pieces extend substantially parallel to a line or lines
drawn through the pivot.
5. An actuator mechanism as claimed in claim 1, in
which the planar conductive coil is electrically connected
to a further planar conductive coil on the opposite surface
of the substrate so that current supplied to the coil



is supplied to the further coil, the construction and
arrangement being such that current through the coil causes
movement of the substrate in the same direction.
6. An actuator mechanism as claimed in claim 5, in
which the shape of one planar coil is identical to the shape
of the other planar coil and is connected in series there-
with by means of a plated-through hole through the sub-
strate.
7. An actuator mechanism as claimed in claim 1, claim
2 or claim 5 in which the or each coil is disposed to one
side of the pivot means and is symmetrically about a line
drawn through said pivot means.
8. An actuator mechanism as claimed in claim 1, claim
2 or claim 5 in which the recording and playback head
assembly consists of an arm extending from said pivot means
with the recording and playback head mounted at the free end
thereof.
9. An actuator mechanism as claimed in claim 1, claim
2 or claim 5 in which the substrate is a multi-layer lami-
nate having incorporated therein an aluminium layer of
sufficient thickness to produce eddy current damping of
actuator movement.

Description

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1 The invention relates to an actu~tor mechanism for
disk storage apparatus and is a modification of the trans-
ducer arm assembly disclosed in our U.K. patent specifica-
tion No. 1,342,495, published January 3, 1974.
According to the present invention an actuator mech-
anism for disk storage apparatus comprises a planar con-
ductive coil on an insulating lamina substrate pivoted to
permit movement in the plane of the substrate, a recording
and playback head assembly mounted on the ~ubstrate, a
magnetic assembly positioned with respect to the substrate
so that current through the coil causes movement of the
substrate about the pivot, and a control circuit for con-
trolling the magnitude and direction of current supplied to
the coil.
In order that the invention may be fully understood
a preferred embodiment thereof will now be described with
reference to the accompanying drawings.
In the drawings:
Figure 1 shows the actuator mechanism subject of this
invention; and
Figure 2 shows schematically the actuator mechanism
forming part of a disk storage apparatus.
The actuator mechanism shown in Figure 1 consists of
an approximately triangular-shaped insulating lamina sub-

strate 1 on each side of which is provided a planar con-
ductive coil 2. The coil on the underside is identical to
the coil visible in the figure and the two are connected
in series by a plated-through hole 3 at the inner extrem-
eties of the coils. Both coils are produced using con-


ventional printed circuit techniques. The substrate 1 i9mounted for oscillatory motion about a pivot 5 situated in
the vicinity o~ the apex of the triangular
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1 -shaped substrate. In the preferred embodiment the two
portions oE each coil 2 on either side o the pivot 3
extended substantially parallel to lines drawn through the
pivot.
Two C-shaped magnetic structures 6 are supported on
each side of the lamina substrate so as to produce flux per-
pendicular to the plane of the substrate. Each C-shaped
structure 6 consists of a magnet 7 with two laterally
extending pole pieces 8 and 9 the pole-faces of which
define a narrow magnetic gap 10. The structures 6 are
positioned so that the portions of the coils along the sides
of the substrate adjacent the pivot are situated symmetric-
ally in the gaps of the structures. The shape of the pole~
faces is such that practically the whole of the portions of
the windings are situated in the magnetic gaps. A head
support arm 11 is also mounted on the pivot 5 with its
longitudinal àxis parallel to the axis of symmetry of the
substrate 1 but extending in the opposite direction. A
magnetic record and playback head 12 is supported at the
free end of the arm 11.
In operation, current passed in one direction through
`~ the series connected coils 2 produces rotational motion of
` the substrate 1 and thus head 12 in one direction about the
pivot 5. Reversal of the current produces motion in the
opposite direction. Drive current to the coils is supplied
~- to one of the terminals 4 and returned through the other
via solder connected connecting wires (not shown). Movement
of the head over a limited arc of travel can therefore be
controlled by energisation of the coils 2 with currents of
appropriate magnitude and direction.
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1 In practice this may be achieved by including the actua~or
in a servo controlled loop supplied with information con-
cerning the actual position of the head 12. Such systems
are well known in the art and will not be described in this
specification.
Figure 2 shows schematically the actua~or described
with reference to Figure l forming part of a disk storage
apparatus. Members in Figure 2 corresponding to members
in Figure l have been given the same reference numerals.
The storage medium used in the present invention is a
magnetic disk 13 supported by a central magnetisable hub 14.
The disk is contained within a cartridge 15 of plastics
material. In use, the cartridge 15 is located in a main
frame (not shown) of the storage apparatus with the disk 13
rotatable supported on a spindle 16 of a drive motor 17
permanently maintained in the main frame. The magnetic
chuck 18 carried by the motor spindle 16 cooperates with
the hub 14 to lock the disk accurately in place. The
cartridge can either be fixed or can be interchangeable
with other cartridges. Details of how the cartridge is
supported have no bearing on the present invention and are
not included in this specification.
The actuator mechanism shown in figure l is also
permanently mounted in the main apparatus. The position
of the actuator within ~he frame is such that the head 12
projects into an elongated slot 19 in one wall of a
cartridge located in the frame to contact the surface of
the enclosed disk. The slot è~.tends in a radial direction
with respect to the disk and energisation Oe the actuator
moves the head su~stantiall~ radially across the disk
surface to access concentric data tracks on the disk

surface. The direction of movement of the head
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1 relative to the disk is not apparent from the drawiny in
figure 2 which is a schematic representation of the
apparatus. When a selected track has been reached the head
is maintained in a track following mode by control of the
energisation of the actuator drive current in a known
manner.
The actuator subject of the present invention is of
extremely low inertia and is capable of relatively high
performance with low drive current. Various modifications
to the preferred embodiment of the actuator structure des-
cribed above are possible. For example the substrate can
be made of a multi-layer laminate with printed circuit
coils provided between each layer of the laminate as well
as on the two outside surfaces. Clearly, the operation of
the actuator can be improved in this way by increasing the
number of turns of the composite coil supported by the
substrate in the magnetic gap of the two magnetic struc-
tures. In practice a trade-off has to be reached
between the number of layers and the resulting increased
mass of the substrate. Eddy current damping of the
actuator movement can also be provided by including an
aluminium layer in the multi-layer laminate.




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