Multihead magnetic head assembly having a single piece faceplate of magnetic ferrite

A magnetic head assembly has a plurality of magnetic heads of magnetic ferrite bonded in a single piece faceplate of magnetic ferrite. The magnetic heads are substantially surrounded by the magnetic ferrite faceplate. The bulk shielding properties of the magnetic ferrite faceplate effectively shield each magnetic head from crosstalk produced by other heads. Preferably, the faceplate and magnetic heads are formed from the same magnetic ferrite. The magnetic head assembly of the invention has application for use in magnetic tape recorders and magnetic disc drives.

BACKGROUND OF THE INVENTION 
This invention relates in general to a magnetic head assembly for use in 
magnetic media reproduction systems such as magnetic tape recorders. More 
particularly, this invention relates to a magnetic head assembly which 
includes a plurality of magnetic heads bonded into a single piece 
faceplate of magnetic ferrite which provides effective magnetic shielding 
between magnetic heads and a stable and long life mechanical structure. 
Magnetic head assemblies used in magnetic tape recorders and magnetic disc 
drives must meet more demanding design specifications necessitated by high 
density recording formats. Thus, in a high density magnetic tape recorder, 
the tape bearing surfaces (such as magnetic head tips and non-magnetic 
faceplate surfaces) must be durable in order to provide long head life 
despite high pressure contact over the head gap area with highly abrasive 
magnetic tape media (such as chromium dioxide tape). The faceplate and 
heads should have compatible wear properties to prevent head undercut and 
separation loss. Moreover, the magnetic head assembly must have mechanical 
stability and be able to withstand environmental changes (temperature, 
humidity, shock and vibration) without performance degradation. The 
magnetic head core structure must be optimized to minimize crosstalk 
between heads in adjacent tracks and between read and write heads in the 
same track. The magnetic head assembly should also have a cost effective 
design in order to be competitive in a highly cost sensitive market. 
Numerous proposals have been made to utilize both magnetic and non-magnetic 
ferrite materials in magnetic head assembly design. High density ferrites 
are generally mechanically stable;are highly resistant to abrasion; and 
provide good magnetic signal recording and reproduction characteristics. 
Typically, a multi-channel magnetic head assembly has been formed from a 
large number of individual elements. A typical head assembly, which is 
made of two half brackets (or two half shells) screwed and epoxied 
together, would include individual ferrite (or metal) cores wound with the 
necessary turns of electrical conductor. The cores are then (1) loaded 
into the half brackets, (2) cemented in place, and (3) connected to 
electrical terminal boards or electrical connector plates inserted into 
the bottom of the half brackets. Tip plates (which form the front surface 
of the magnetic head assembly) are slotted to accommodate intertrack 
magnetic shields and grooved to receive magnetic head tip pieces which are 
especially hard and durable. The tip plates are then attached to the 
loaded half brackets providing intimate contact between the tip pieces and 
the top of the ferrite cores. The magnetic gap of each head is then formed 
by vacuum deposition of silicon monoxide and the two half brackets bonded 
together. The front surface contacting the tape is then contoured (see for 
example, the Bell & Howell publication entitled, "MAGNETIC TAPE RECORDING 
TECHNICAL FUNDAMENTALS", 4th printing revised, 1984, pp. 23 et. seq.; "THE 
COMPLETE HANDBOOK OF MAGNETIC RECORDING", by Jorgensen, 1980 ed., pub. by 
TAB Books, Inc., Blue Ridge Summit, PA, pp. 158 et seq.; and U.S. Pat. No. 
3,400,386, entitled "Multichannel Magnetic Read Assembly", issued Sept. 3, 
1968, by R.C. Sinnott). Such magnetic head assemblies are disadvantageous 
because of the difficulty and expense in producing them. Moreover, the 
number of assemblies which must be discarded due to incorrect component 
positioning is high. 
Multichannel magnetic head assemblies have also been proposed, in which a 
plurality of magnetic ferrite heads are bonded to a split non-magnetic 
ferrite faceplate. Individual magnetic shields are secured between 
adjacent heads to minimize crosstalk and the structure mounted in an 
aluminum shell (see for example, U.S. Pat. No. 3,668,775 issued June 13, 
1972, entitled "Method for Manufacturing Magnetic Heads", by Morita et al; 
and U.S. Pat. No. 3,789,505, issued Feb. 5, 1974 entitled "Method Of 
Making a Multi-Core Magnetic Head With A Non-Magnetic Holder" by R.L. 
Huntt). Such magnetic head assemblies are disadvantageous in the use of 
individual magnetic shields between adjacent heads and in the use of 
different ferrite materials in the faceplate structure thus increasing 
mechanical instabilities. 
Magnetic head assemblies are also known in which magnetic ferrite cores are 
mounted in non-magnetic ferrite holders and individual magnetic ferrite 
shields are inserted between adjacent magnetic heads (see for example, 
U.S. Pat. No. 3,909,932, issued Oct. 7, 1975, entitled "Method of 
Manufacturing A Multi-Track Magnetic Head", by W.L. Kroon; U.S. Pat. No. 
3,842,494, issued Oct. 22, 1974 entitled "Multi-Channel Magnetic Ferrite 
Head And A Method For Making The Same", by H. Chiba et al; and U.S. Pat. 
No. 3,761,641 issued Sept. 25, 1973, entitled "Magnetic Head With 
Demountable Face Part Assembly", by T.A. Mlinarick). Each of the magnetic 
head assemblies disclosed in these patents is disadvantageous because of 
the large number of parts required to form the magnetic head assembly and 
because of the difficulty in properly aligning the magnetic head gaps 
across the width of the assembly. Such magnetic head assemblies are also 
complex and expensive to produce. 
In order to reduce the number of individual parts used in a multi-head 
magnetic head assembly and in order to effect exact alignment of magnetic 
head gaps across the width of the head assembly, it has been proposed to 
form a plurality of individual heads from blocks of magnetic ferrite. The 
magnetic ferrite blocks are ground down to form individual magnetic head 
core pieces. The structure is lapped, gapped and bonded to form a 
multi-head magnetic assembly. The individual heads may be commonly joined 
together by a portion of the magnetic ferrite block which is not removed. 
Such assemblies are disclosed in U.S. Pat. No. 3,544,982, issued Dec. 1, 
1970, entitled "Multi-Head Magnetic Assembly", by J.J. Hanak. As 
disclosed, the rear portion of the magnetic heads is commonly joined by a 
solid magnetic ferrite piece which is integral with the individual head 
cores. U.S. Pat. No. 3,543,396, issued Dec. 1, 1970 entitled "Method Of 
Multi-Track, Two-Gap, Ferrite Magnetic Heads Design Especially For Digital 
Recording", by Z. Illg et al, discloses a magnetic head assembly in which 
three blocks of magnetic ferrite are lapped, gapped and bonded together. 
The bonded structure is ground down to provide a multi-track magnetic head 
assembly in which each track has a pair of in line heads separated from 
each other. In the embodiments shown in FIGS. 6 and 7, a centrally 
disposed solid magnetic ferrite piece runs the width of the head assembly 
and is integral with the inner core leg of each head in the assembly. 
These magnetic head assemblies are disadvantageous (1) in using separate 
magnetic shields between adjacent heads and between in-line heads and (2) 
in using an integral magnetic ferrite shunt between adjacent heads in the 
magnetic assembly which increases the likelihood of crosstalk between 
heads in the same track and between heads in adjacent tracks. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a multi-head magnetic 
head assembly which substantially solves the problems of known multi-head 
magnetic head assemblies, as, for example, disclosed in the above patents. 
The mult-head magnetic head assembly of the present invention has the 
following advantages: (1) effective magnetic shielding optimization so 
that crosstalk between heads in different tracks and between heads in the 
same track is substantially suppressed; (2) increased durability and 
resistance to highly abrasive magnetic media such as tape with which the 
head assembly comes into contact; (3) high degree of mechanical stability 
and resistance to environmental changes (such as temperature, humidity, 
shock and vibration) without performance degradation; (4) cost effective 
design for competitiveness in a highly cost sensitive market through the 
use of a minimum of head assembly components; and (5) consistent 
performance between heads within a track and between heads in adjacent 
tracks. 
According to an aspect of the present invention, these advantages are 
achieved by means of a magnetic head assembly which includes a single 
piece faceplate of magnetic ferrite in which are bonded a plurality of 
magnetic heads of magnetic ferrite. Preferably, the faceplate and magnetic 
heads are of the same magnetic ferrite. According to another aspect of the 
invention. The single piece magnetic ferrite faceplate surrounds each 
head, thus effectively shielding each magnetic head from crosstalk from 
other magnetic heads. According to a further aspect of the invention the 
magnetic head assembly includes a minimum number of components, thus 
greatly increasing the cost effectiveness and reliability of the assembly. 
Individual magnetic shields separating adjacent magnetic heads are 
eliminated, since the single piece magnetic ferrite faceplate of the 
invention provides maximum shielding for each head. Moreover, the single 
piece faceplate can be easily electrically grounded at a single point to 
minimize buildup of static electricity on the head assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the Figures, a preferred embodiment of a multihead 
magnetic head assembly according to the present invention will be 
described. Such multihead magnetic head assemblies are used, for example, 
in magnetic tape recorders and magnetic floppy and hard disc drives used 
in computers. Although a specific embodiment of magnetic head assembly is 
illustrated, it will be understood that other embodiments of multihead 
magnetic head assemblies are within the scope of the present invention. As 
shown in FIG. 1, magnetic head assembly 10 includes a generally 
rectangular faceplate 12 having a plurality of magnetic heads 14, 16, 18 
and 20 respectively bonded in slots 22, 24, 26, and 28 which extend 
through the thickness of faceplate 12. Faceplate 12 has a generally curved 
upper face 30, lower face 32 and sides 34, 36, 38 and 40. Upper face 30 
has a plurality of ridges or rails 42, 44, 46, 48 and 50 for providing 
good head to face contact between magnetic media such as tape 52 and the 
head gaps of heads 14-20. Heads 14, 16, 18, 20 are arranged in a dual 
head, two track configuration. Thus, heads 14 and 16 are aligned in one 
track and heads 18 and 20 are aligned in another track. Moreover, the gaps 
of heads 16 and 18 are in alignment. According to the invention, the 
magnetic gaps of heads 14, 16, 18, 20, satisfy demanding gap azimuth 
specifications. 
As shown more clearly in FIG. 3, magnetic head 18 includes core elements 54 
and 56 having head tips 58 and 60 separated by a head gap 62 of 
non-magnetic material. Non-magnetic material (such as epoxy or glass) 
bonds elements 54 and 56 together (such as at 65) and also bonds head 18 
in slot 26 of faceplate 12 (such as at 67). A back bar 64 of magnetic 
ferrite shunts the ends of core elements 54 and 56. Electrically connected 
coils 66 and 68 are respectively wound on core elements 54 and 56. 
Similarly, magnetic head 20 includes core elements 70 and 72 having head 
tips 74 and 76 separated by head gap 78. Non-magnetic bonding material 
bonds elements 70 and 72 together (as at 71) and bonds head 20 in slot 28 
of faceplate 12 (as at 73). A back bar 78 of magnetic ferrite shunts the 
ends of core elements 70 and 72. Electrically connected coils 80 and 82 
are respectively wound on elements 70 and 72. 
The cross sectional areas of slots 22, 24, 26 and 28 broaden out below face 
30 in order to accommodate coils, such as 66 and 68 on head 18, and 80 and 
82 on head 20. According to the present invention, faceplate 12 is a 
single piece of magnetic ferrite (such as manganese zinc ferrite or the 
like). Faceplate 12 is preferably of the same magnetic ferrite material as 
magnetic heads 14, 16, 18 and 20. The thickness of faceplate 12 is 
preferably equal to or greater than the length of the core elements of 
heads 14-20. Thus, as shown in FIG. 3, the ends of core elements 54 and 56 
of head 18 and core elements 70 and 72 of head 20 are substantially 
coplanar with the lower surface 32 of faceplate 12. Since magnetic heads 
14-20 are substantially surrounded by magnetic ferrite faceplate 12, each 
head is effectively shielded from crosstalk produced by other heads in the 
assembly. 
As shown in FIG. 1, faceplate 12 is grounded by conductor 84 to an aluminum 
support member 86 which forms part of the magnetic head assembly support 
structure. Grounding minimizes static buildup and stray electric currents 
which produce localized magnetic fields. The head tips of heads 14-20 are 
flush with rails 44, 46 and 48 so that wear on heads 14-20 and faceplate 
12 is substantially the same. Face 30 of faceplate 12 can be either 
machined or molded to shape. The magnetic ferrite of both faceplate 12 and 
heads 14-20 is preferably of a high density, hot pressed or hot isostatic 
pressed material in order to provide long life and mechanical stability. 
The magnetic heads 14-20 may be individually supported relative to 
faceplate 12 prior to bonding or may be assembled with faceplate 12 
according to the method disclosed in copending U.S. Pat. No. 4,825,532, 
entitled "Method For Making A Multi-Head Magnetic Head Assembly". 
The magnetic head assembly of the present invention has the following 
advantages, among others: (1) the use of a single piece magnetic ferrite 
faceplate for supporting and shielding a plurality of magnetic heads 
significantly reduces the number of separate components in the magnetic 
head assembly by eliminating individual shields between magnetic heads and 
individual support structure for each magnetic head; (2) magnetic 
shielding between heads is optimized by the bulk shielding properties of 
the single piece magnetic ferrite faceplate structure and by the 
substantially uninterrupted head assembly to magnetic media interface 
which minimizes localized magnetization; (3) the single piece magnetic 
ferrite faceplate assembly has increased durability, increased mechanical 
stability, and increased ability to withstand environmental changes such 
as temperature, humidity, shock and vibration without performance 
degradation. 
It will be understood that the magnetic head assembly of the present 
invention may be configured to include any number of tracks and any number 
of magnetic heads within a track. Thus, for example, instead of having two 
tracks with two heads in each track, the magnetic head assembly may 
include three or more tracks with two, three or more heads within each 
track. Moreover, the dimensions of the magnetic head assembly are not 
critical. For example, the magnetic head assembly of FIG. 1 may be used 
with magnetic tape having a width of from 4-25 mm. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.