Note: Descriptions are shown in the official language in which they were submitted.
FIELD OF THE INVENTION
The present invention relates in general to magnetic
imaging on a recording medium/ such as a drum or disk, and
particularly to a technique for improving the coupling between
a magnetic recording head and the surface of the recording
medium.
BACKGROUND OF THE INVENTION
The information recording mechanism of a magnetographic
recording apparatus may take on various configurations, such
as one using an optical exposure station for selectively
erasing (demagnetizing) a premagnetized recording medium ~e.g.
chromium oxide) r or a configuration employing a magnetic write
head through which a latent image of the information to be
recorded is directly magnetically written onto the recoxding
medium. (For a description of the gener~l configuration of
each of these types of xecording schemes, attention may ~e
dixected to the U.S. Patent to Edwards et al No. 4,216,282,
for example.) In these configurations and in magnetoyraphic
recording apparatus in general, the fidelity with which the
magnetic storage state of the magnetic recording medium can be
accurately controlled is the principal factor for determining
successful performance. While such fidelity is obviously ~n
a priori requirement in an apparatus in which the recording
mech~.~ism constitutes a magnetic recording head, it also holds
true in other configurations, such as one employing an optical
1~11~4
exposure station, mentioned above, since that mechanism still
requires a comple~e premagnetization of the entire recording
surface and, to datel the principal expedient for
accomplishing this task has been a magnetic head.
Now, although the manufacturing tolerances of the
recording head can be controlled with precision, the surfac2
o the recording medium, usually chromium dioxide, with which
the magnetic head is intended to have effective intimate
contact, usually does not have the desired, perfect geometric
profile for estahlishing such effective intimate contact for
any location on the recording surface. More particularly, the
surface of the recording medium, ~such as a CrO~ layer, formed
on the surface of a rotatable drum) typically contains
imperfections including bumps and seams in the recording
material itself, and contamination by foreign matter r such as
dust and toner particles ~hich, even with the provlsion of
cleaning devices such as vacuum knives, may not be perfectly
removed.
Because the quality of the image that is formed on th~
surface of the recording dr~m by the magnetic recording head
depends on the degree of coupling between the recording head
and the drum surface, imperfections on the surface of the
recording medium, such as those exemplified a~ove, may,
depending upon drum rotational speed, constitute a source of
degradation in both the image quality and the physical surface
of the drum and/or the recording head during the movement of
the drum past the head~ Not only are imperfections on the
drum surface a cause of head bounce, but because the head is
under pressure to maintain contact (and thereby maximum
magnetic coupling~ between head and drum, both the h~ad and
the drum are subject to wear, and plate-out (the dispo~ition
of magnetic medium onto the magnetic head) may occur.
At low rotational velocities of the recording drum, the
head can slide on the chromi~m dioxide layer without causing
damage and without losing contact with the recording surface,
so that the imperections are not a serious problem. Also, at
very high velocities, using a high quality magnetic disk or
drum surface medium~ the aerodynamic bearing that is created
by the high relative rotational velocity between the recording
surface and the head can be utilized in conjunction with the
high quality medium to diminish the above problems. At a
medium-range of velocities, however, (on the order of 50 to
150 inches per second, imperfections in the drum surface
cannot be ignored, but instead, subject the imaging process to
the ~bove-mentioned drawbacks.
SUMM~RY OF TRE INVENTION
In accordance with the present invention, the
above-discussed problems of wear and bounce created by
imperfections in the surface of a magnetic recording medium,
such as a chromium dioxide-coated drum, are circumvented by a
hydrodynamic magnetographic imaging technique that provides
the intended effective intimate contact between the recording
head and the magnetographic recording surface. Pursuant to
the inventive scheme a liquid le.g~ water~ is applied ts the
surface of the drum slightly upstream of the loca~ion of the
recording head r 50 as to create a liquid bearing against which
the recording head is urged, and thereby intimately
magnetically coupled wi~h the surface of the drum, except for
an extremely thin liquid film between the head and drum
surface.
As a resul~ of ~his extremely thin liquid bearing,
continuous pressure can be applied to the head to maintain the
head in effective intimate contact with the surface of the
recording medium without the fear of scratching the medium or
causing wear on the head. Thus, the sliding characteristics
between head and drum attained at low velocities are achieved
without the problems associated with the higher xelative
tangential speeds. Also the movement, per se, of the fluid
past the head creates a Bernoulli suction effect that acts to
urge the he~d toward the recording sur~ace; this action is
further aided by the hydrostatic action of the fluido
Moreover, within the fluid bearing~ foreign matter that might
otherwise accumulate between the head and the recording
surface, is placed in solution, so that the bearing helps
to clean the head and th~ drum.
Preferably the bearing is generated by a simplified
spon~e/squeegee water applicator that rests on the drum
upstream of and adjacent to the recording head. Water i~
supplied to the sponge from a fluid inlet line, to create a
trickle flow from the sponge. This trickle of water is
converted into a thin film by a squeegee blade that rests
ag~inst the drum. For the purpose of controlling the flow of
water to the applicator the fluid inlet line may be positioned
to be selectively pinched and relaxed by the mechanism that
displaces the rec~rding head relative to the recording
surface. When the head is r~tracted from the surface (as
after imagining) the fluid (water) supply line is pinched off,
to interrupt the water supply to the applicator, so that the
liquid film/bearing is not generated. Conversely, when the
head is urged toward the recording surface, the head
displacement mechanism relieves its grip on the water feed
line and the bearing is applied to the recording surface just
prior to the head reaching its recording position, so that the
head will come into contact with the bearing at that location.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts a schematic side view of a
magnetographic recording apparatus employing the hydrodynamic
imaging device of the present invention;
Figure 2 is an enlarged illustration of the details of
the li~uid ~earing applicator shown schematically in Figure l;
and
Figure 3 i8 ~n exaggerated illustration of the coupling
of ~ magnetic recording head and a fluid bearing on the
surface of a recording medium.
DETAIL~D DESC~IPTION
Referring now to Figure 1, their i6 shown a general
schematic side view of a magnetographic recording appar~tus
employing the hydrodynamic imaging de~ice of the present
invention. Such an apparatus may include a single ~tation
both imaging (recording) and reproduction (hard copy
generation), as is conventionally employed in both
electrographic and magnetographic apparatus- (as described in
the above-referenced Edwards el ~1 patent). In
the description to follow and in the illustration of Figure 1,
it will be assumed that lmaging station and printing station
are separated from one another with the multiple
magnetographic drums being interchanged between the two
stations for ~he separate functions performed thereby, as
de~cribed in the ~bove-ldentif~ed copending ~ppllcation. For
fiuch an environment, the ~chematic illustration of the
,; . ~
configuration of the recording station may be simplified since
the details of the printing sector (decorator, web transfer
mechanism, e~c.) are unnecessary for an understanding of the
present invention and, accordingly, are not shown or described
here.
In Figure 1, a recording drum 10 is shown as being
rotatable in a clockwise direction R by a suitable drive
mechanism (not shown) about the axis 8 of a drum axle 11~ The
surface of drum 10 is made of magneti.cally r~sponsive
recording material~ such as a layer of chromium dioxide, as is
standard practice in the art. Circumferentially disposed
around drum 10 are a record head 14 d cleaning station 15 and
an erase head 23. These components, per se, are of
conventional configuration (e.g. clean station 15 includes the
usual roller brushes~ vacuum knives, magnet pick-up
elements etc.~ and not, per se, constituting the present
invention, will not be described in detail hexe. They are
shown simply to illustrate some of the components of a
magnetographic recording environment~ familiar to the skilled
artisan, in which the present invention may be employed.
Recording head 14 is displaceable, in a radial direction
relative to the axis of drum 10, toward and away from
surface 12 by a head positioning mechanism 17. As described
briefly above for the record modP magnetic recording head 14
is urged by head positioning mechanism into effective intimate
contact with the surface 12 of drum 10, whereby information
signals that are coupled to head 14 may be recorded on
surface 12 in the Eorm of modulated magnetic regions in the
chromium oxide layer representative of those information
signals.
Adjacent to and upstream (in terms of direction of
rotation R of drum 10) of magnetic recording head 14 is a
liquid bearing applicator 16 (shown in detail in Figure 2,
described below) which creates a liquid bearing between
head 14 and surface 12 so that the degree of coupling between
the transducer surface of head 14 and surface 12 may be
significantly improved compared to conventional schemes
wherein no such bearing is provided. Applicator 16 is coupled
to a liquid supply source 13 by way of a fluid supply line 21,
through which the bearing liquid (e.g. water) is supplied, as
by gravitational flow. As will be explained below, with
reference to Figure 2, 10w line 21 may be mechanically
coupled with head positioning mechanism 17 so that water flow
therethrough is selectively controlled in response to the
displacement of he~d 14 relativè to surface 12. For the
purpose of the description of Figure 1, it is to be understood
that water is supplied from water source 13 through line 21 to
applicator 14, so that a thin film or liquid (water) layer is
formed on surface 12 of drum 10 and is carried on drum 13 past
the position of magnetic recording head 14~ As head 14 is
urged toward surface 12 of drum lO i.t encounter3 thi~ liquid
film which acts as a bearing on which head 14 rides as the
drum is rotated therepast in the direction of drum rotation R.
Referring now to Figure 2/ the details of the liquid
beaxing applicator are shown as incLuding a sponge 31 and a
squeegee rubber strip 32 against which sponge 31 abu~s, so
that water released thereby will be directed onto the
surface 12 of drum 10 to form a thin liquid bearing 51 that is
carried past the position of recording head 14. Water is
supplied to applicator'14 from a water supply reservoir (not
shown), corresponding to source 13 of Figure 1. As water
flows, as under the in1uence o gravity ~hrough line 21,
sponge 31 becomes saturated and emits a trickle 3ufficient to
create a thin film 51 by the action o squeegee rubber
strip 32, the edge portion 36 of which rides on the water
bearing 51 as it is carried along drum 10.
Downs~ream of applicator 16 is the magnetic recording
head 14. Head 14 is affixed to one end of a flat spring or
band 33, the other end of which is held hy a rigidly-fixed
support block 38~ Band 33 may comprise a strip of beryllium
that is cantilevered at block 38 so that heaa 14, in turn, is
supported in a cantilevered fashion at block 38. Displacement
of head 14 toward and away from surface 12 is accomplished by
a positioning rod 42 which engages head 14 and is displaceable
in a radial direction (rela~ive to the axis of drum 10~ by a
L6~L
drive motor 44 in the direction of arrows 47. Positioning
rod 42 engages a pinch bar 41 such that displacemen~ 5f rod 42
causes a corresponding displacement of pinch bar 41.
Disposed adjacent to but spaced apart from pinch bax 41
is a head support base 47 through which a guide pin 36 passPs.
Water flow feed line 21 passes in a space or channel between
~upport base 47 and pinch bar 41 so that in the position shown
in Figure 2, line 21 is not constricted and water is permitted
to flow through line 21 to the applica~or 16. When drive
source 44 is opera~ed t'o retract recoxding head 14 away from
drum 10, pinch bar 41 is displac~d towards support base 47,
whereby line 21 becomes constricted or pinched between pinch
bar 41 and support base 47, to ther~by in~errupt the flow o~
water to applicator 16. Such displacement of head 14 takes
place subsequent to the record mode of operation of drum 10
prior to its use as a printing drum at a printing station (not
shown). By mechanically coupling water flow line 21 with the
displacement mechanism for head 17 in the manner shown in
Figure 2, a simple scheme for synchronizing liquid bearing
generation to head engagement with drum 10 is provided. ~hen
head 14 is to be displaced from its retracted position to
effective contact with drum 10 for imaging, displacement of
rod 42 moves pinch bar 41 away from support base 42 prior to
head 14 reaching surface 12 of drum 10, so that the
hydrodynamic bearing is formed between head 14 and surface 12 t
beore head 14 would oth~rwise contact drum 10.
Depending on the thickness of water bearing 51 as defined
by applicator 16, the pressure applied to head 14 is
established to maintain the desired magnetic coupling ~e,g.
physical spacing) between the transducer surface of head 14
and surface 12 of drum 10. This may be on the order of an
ounce or two of pressure provided by source 44 and beryllium
band 33, so that a slight pressure is exerted on head in a
direction normal to suxface 12. This slight pressure is
sufficient to keep head~ 14 riding on the bearing layer 51, but
insufficient to override the back pressure of bearing
layer 51, so that head 14 is prevented from actually touching
surface 12.
Figure 3 shows an exaggerated (not to scale) illustration
of head 14 as it rides on liquid bearing 51. As described
above, the thickness of the liquid film bearing 51 is
controllable by means of the water flow from and the
positioning of applicator 16 relative to surface 12 of
drum 10. The exact thickness of bearing 51 will depend, of
course, on the rotational speed of drum 10 past ~he
applica~or 16 and head 14 and the quality of surface 12.
These factors are readily established emperically based upon
station size and configuration and need not be precisely
determined prior to system set up. As mentioned above, water
flow rate based simply upon the influence of gravity has been
found to provide a bearing that meets the performance
objectiv~s of the present invention.
The ackion of bearing 51 as illustrated in Figure 3 not
only provides a slight separation D between the transducer
magnetic coupling face 56 of head 14 from the surfac~ 12 to
prevent contact between head 14 and imperfections in the
surface 12, such as bump 61 and seam 62, but maintains foreign
matter, such as a toner or dust particles 52, in solution,
away from transducer face 56 and surface 12. This latter
action prevents a buil~ up of foreign matter on these surfaces
which would otherwise detrimentally affect ~he intended
performance of the recorder, as mentioned previously. Not
surprisingly, s,ome of the foreign matter that is carried by
bearing 51 floats on the surface o the water and, over time,
forms a "bathtub ring~ 54 on the side surface of head 14.
However, this ring is at a location on head 14 that does not
affect performance or cause wear of the head, and can be
easily removed when the head itself is removed for cleaning.
As will be appreciated from the foregoing description, a
substantial improvement in performance and component 7ife of a
magnetographic recording apparatus can be achieved in
accordance with the hydrodynamic recording scheme of the
present invention. The structure for imp~rting the liquid
bearing to the drum surface is simple and does not affect the
`magnetic coupling forces between the recording head and the
6~
chromium dioxide surface, The benefits in recording
performance provided by the present invention are especially
noteworthy when considering the capabilities of a
magne ographic recording apparatus as contrasted to
electrographic systems, In the latter type of system,
reapplication or reganera~ion of the latent image on the
recording surface is required for each document to be pxinted.
In a magnetrographic apparatus, however, once the image has
been recorded, it is effectively permanent until erased.
Thu~, production yiel* for a magnetographic apparatus is
pot~ntially a greater than that for a electrographic system.
Prior to the present inventionl however, the performance of
and thereby quali~y of image recorded by magnètographic
apparatus have been limited by the head wear and bounce
problems, discussed abover that are solved by the inventive
hydrodynamic imaging scheme. Since effective intimate
magnetlc coupling between head and image recording surface
necessary to achieve any desired resolution is attainable
using the hydrodynamic imaging technique according to the
invention, a magnetographic recording apparatus employing the
same is cost and yield-wise superior to conventional
electrographic and magnetographic systems.
While we have shown and described one embodiment in
accordance with the present inven~ion, it is understood ~hat
the same is not limited thereto but is susceptible of numerous
changes and modifications as known to a person skilled in the
13
art, and we therefore do not wish to be limited to the details
sho~ and described herein but intend to cover all such
changes and modifications as are obvious to one of ordinary
skill in the art.
