Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-01-22
2001-07-10
Huson, Gregory L. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603010, C029S603070, C029S603130, C029S603140, C029S603150, C360S121000, C360S125330
Reexamination Certificate
active
06256864
ABSTRACT:
DESCRIPTION
1. TECHNICAL FIELD
The present invention relates to a process for producing an assembly having several magnetic heads and to a multiple head assembly obtained by this process.
A particularly preferred application occurs in general public video recording, but use is also possible in other fields, such as data backup or computer memories.
2. PRIOR ART
A magnetic recording support for video recording, data backup or computer memories comprises several tracks on which informations are written in the form of magnetic domains.
In order to increase the information density, there is a rise not only in the number of informations per length unit, but also the number of tracks. For this purpose the track width is reduced and simultaneously there is a reduction of the gap separating them until the tracks are contiguous.
In order to avoid any crosstalk problem on reading, the informations are written on two adjacent tracks in inclined manner with opposing inclination angles. These inclination angles are known as azimuth angles. The magnetic head gap must have an azimuth, whose value corresponds to the inclination of the recording.
Thus, the attached
FIG. 1
shows a recording support with two tracks
10
a
and
10
b
, whose writing directions, fixed by the gap and shown in oblique line form, form angles +i for track
10
a
and −i for track
10
b
with the normal to the general direction of the tracks.
The attached
FIG. 2
shows two magnetic heads
12
a
,
12
b
with gaps
14
a
,
14
b
having azimuth angles of respectively +i and −i. The head displacement direction is designated D.
In reality, an assembly of two heads azimuthed in opposite directions is not generally in the form of two juxtaposed heads as in
FIG. 2
, otherwise the tracks read would not be contiguous. It is in the form of two mutually longitudinally displaced or offset heads, as illustrated in FIG.
3
. This arrangement makes it possible to narrow the tracks. In this arrangement, each of the two heads
16
a
,
16
b
has an azimuthed gap of total width L, the two gaps being separated by a distance T. Each head can then browse a recording track of width e, said tracks being quasi-contiguous. The overlap of the heads is designated r.
In order to have contiguous tracks written with opposed azimuths and of the same width, it is necessary for the recording period P, i.e. the distance between two tracks recorded with the same azimuth, to be linked to L, r and e by the relation:
P=2(L−r)=2e or r=L−P/2=L−e.
For example, we obtain for P=10 &mgr;m e=5 &mgr;m for L=6 &mgr;m and r=1 &mgr;m, it obviously being possible to choose L=e and r=0.
In the case of heads having different pole widths, respectively L
1
and L
2
, the recording period is equal to: P=L
1
+L
2
−r−r′, in which L
1
is the pole width of head
1
, L
2
the pole width of head
2
and r′ the overlap due to the system parameters.
By acting on r and r′, it is possible to find two written tracks of the same width, even if the heads have different pole widths. The fact of having heads with different pole widths can be of interest for several reasons, i.e. as a parameter for adjusting the reluctances of the two heads (to have comparable efficiencies), or for tightening a tolerance on one of the two heads.
The two magnetic heads
16
a
,
16
b
also comprise not shown means, such as a magnetic flux closure circuit, which connects one pole piece to the other and a conductor coil magnetically coupled to the magnetic circuit. The assembly of all these means forms a double head with opposed azimuths carrying the general reference
18
in FIG.
3
. Its displacement direction is symbolized by the arrow D.
In order to obtain such a double head, production generally takes place of two independent heads having gaps inclined in opposite directions and said two heads are installed on a single support. An azimuth magnetic head is shown in exemplified manner in
FIG. 4
(in section). It is possible to see a monocrystalline substrate
20
, two pole pieces
22
1
,
22
2
separated by an amagnetic gap
24
, which is inclined by an angle i. This inclination is e.g. obtained by taking advantage of the monocrystalline nature of the substrate and by performing anisotropic etching in accordance with a crystallographic plane of the substrate. This process is described in FR-A-2 664 729 (or WO-92/02015).
This double head production process, consisting of regrouping two single heads, is not entirely satisfactory. Thus, it is difficult to correctly orient the two heads so that their gaps have in each case the desired azimuths and it is also difficult to correctly place the two heads with respect to one another, so that each of them cooperates correctly with the tracks. The dimensions given in connection with
FIG. 3
, more particularly the width of 6.7 microns, show that it is a question of extremely fine settings or adjustments.
FR-A-2 747 226 describes another process for producing an assembly having two magnetic heads with opposing azimuths. One of the variants of this process is illustrated in
FIGS. 5 and 6
.
FIG. 5
shows a header A with a first head, carrying the general reference
100
, with an assembly
102
comprising a magnetic circuit with an azimuthed gap and a conductor coil and two contact pieces
104
1
,
104
2
. Alongside said head is provided a first etched groove
120
.
On a counterheader B is provided the same means, namely a second head
130
, with an assembly
132
comprising a magnetic circuit with an azimuthed gap identical to the gap of the first head
102
, a conductor coil and contact pieces
134
1
,
134
2
. Alongside said second head
130
is provided a second groove
140
.
On reversing the counterheader B on the header A, the first head
100
is fitted into the second groove
140
and the second head
132
in the first groove
120
and then the assembly obtained is joined together. The result is diagrammatically illustrated in
FIG. 6
, where it is possible to see the first head
102
with its azimuthed gap g1, placed on a substrate
150
and covered by an insulating layer
160
and a second head
142
with its gap g2 azimuthed in an opposite direction, with its reversed substrate
150
and its insulating layer
160
. The two pieces are inserted in one another. As they are complimentary to one another, they form a one-piece head.
Although satisfactory in many respects, this process still suffers from certain disadvantages. Thus, it would appear more appropriate for an assembly by headers than for an entirely collective process. Thus, it is difficult on a complete plate to control etchings of a few dozen microns (for the fitting of one head in the other) on an already very complex stack and with a tolerance below
1
micron. Moreover, the electrical connection between the two heads is difficult. The junction of the two heads in the vertical portion may not be perfect, which makes dirtying possible. Finally, the cost of a double head of this type compared with a single head is at least multiplied by 4.
The object of the present invention is to obviate these disadvantages. The invention also aims at obtaining not only double heads, but more generally multiple heads.
DESCRIPTION OF THE INVENTION
To this end, the invention proposes a process, where operation once again takes place by reversing one piece on another, but where the coils or windings are produced after reversal and not before, which eliminates the contact renewal problem. There is also an avoidance of deep etching of grooves in the substrates, which simplifies the technology and eliminates the vertical portion of the assembly, where the adhesive joint caused problems. Finally, by using a common technology for both subassemblies, production costs are greatly reduced.
These objectives are achieved by the invention in the following way:
on a first substrate is formed at least one first subassembly, in each case comprising at least two first pole pieces sepa
Albertini Jean-Baptiste
Gaud Pierre
Sibuet Henri
Commissariat A l'Energie Atomique
Huson Gregory L.
Kim Paul
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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