[0001] The present invention relates to a magnetic head for recording a still image on a
magnetic medium and displaying an image based on printing information sent from an
external host unit.
[0002] Hitherto, there has been known a magneto-sensitive magnetic display sheet as a display
medium for developing/erasing colors in response to the direction and strength of
a magnetic field (as disclosed in Japanese Unexamined Patent Publications JP-A 48-56393
(1973) and JP-A 2-146082 (1990) for example).
[0003] Because simple letters and graphics can be drawn on such a magnetic display sheet
by touching the surface of the sheet with a magnetic pen containing a magnet and it
can be used over and over again by erasing them, it has been put into practical use
as a simple notepad.
[0004] Lately, an electronic information display apparatus records and displays a still
image on a magnetic display sheet by a recording head generating a dot matrix magnetic
field based on printing information sent from an external host unit is being developed.
Because the electronic information display apparatus allows contents to be displayed
to be arbitrarily changed by remote control from the external host unit, a great variety
of information may be given and advertised widely to pedestrians when it is installed
at public facilities, train stations, shops and the like. Further, because it requires
no work in repapering posters and contributes in saving resources such as paper, it
is considered to be promising as a future bulletin board.
[0005] In such electronic information display apparatus, a magnetic head is used to generate
the dot matrix recording magnetic field based on printing signals (as disclosed in
Japanese Unexamined Patent Publications JP-A 63-259678 (1988) and JP-A 7-281621 (1995)
for example). The magnetic head is composed of a plurality of magnetic cores arranged
in a row or in a plurality of rows for example, a plurality of electromagnetic coils
mounted to each magnetic core, a yoke provided around each magnetic core with an air
gap for leaking magnetism formed therebetween and others.
[0006] Semi-ringed lines of magnetic force are formed between an edge of the magnetic core
and the yoke in such magnetic head, and the strength of the magnetic field is maximized
at the position slightly separated in the radial direction from the extension of an
axis of the magnetic core. Therefore, when the space between the edge of the magnetic
core and the yoke is set longer than a certain extent, a printed dot whose circumference
is vague is formed.
[0007] The printed dot is preferred to be a circular dot having a diameter slightly larger
than a size of a pixel corresponding to a recording density and for that end, it is
ideal for the recording magnetic field to have a columnar distribution. However, it
is difficult in reality because the distribution of the magnetic field largely changes
depending on the dimension of the magnetic core and the air gap.
[0008] It is hence an object of the present invention to optimize the distribution of the
magnetic field generated by the magnetic core to provide a magnetic head for magnetic
display and a magnetic display apparatus which can realize high quality magnetic printing.
[0009] Various aspects of the present invention are specified in the independant claims.
Some preferred features of the independant claims are claimed in the dependant claims.
[0010] The invention provides a magnetic head for magnetic display comprising:
a yoke having a printing face which faces to a magnetic display medium and an air
gap hole formed in the printing face;
a magnetic core whose edge is inserted into the air gap hole, for generating a dot-like
recording magnetic field by magnetically coupling with the yoke; and
an electromagnetic coil for supplying a magnetic field to the magnetic core based
on printing signals,
wherein a diameter d of the edge of the magnetic core is smaller than a diameter D
of the air gap hole, a difference between the diameter D and the diameter d is less
than 0.9 mm and the diameter D is 2.0 mm or less.
[0011] According to the present invention, since the diameter d of the edge of the magnetic
core is smaller than the diameter D of the hole, the difference between the diameter
D and the diameter d is less than 0.9 mm, and the diameter D is 2.0 mm or less, the
expansion of the foot slope in the distribution of the magnetic field can be eliminated.
As a result, the printed dots formed on the magnetic display medium become less blurred
on the outline and have a high contrast.
[0012] In the present invention, it is preferable that the magnetic display medium to which
the magnetic field from the magnetic head is applied is constructed so that micro-capsules
containing magnetic powder and non-magnetic powder are distributed in plain and that
the size of the micro-capsule is in a range from 10 µm to 1,000 µm.
[0013] According to the invention, since the clear printed dots can be obtained, high recording
density and high quality magnetic printing may be realized.
[0014] The invention provides a magnetic display apparatus comprising a magnetic head for
magnetic display; and a magnetic display medium which is writable and erasable by
magnetism,
the head comprising:
a yoke having a printing face which faces to the magnetic display medium and an air
gap hole formed in the printing face;
a magnetic core whose edge is inserted into the air gap hole, for generating a dot-like
recording magnetic field by magnetically coupling with the yoke; and
an electromagnetic coil for supplying a magnetic field to the magnetic core based
on printing signals,
the edge of the magnetic core having a diameter d smaller than a diameter D of the
air gap hole, a difference between the diameter D and the diameter d being less than
0.9 mm, the diameter D being 2.0 mm or less,
wherein a plurality of printed dots are formed to continuously overlap each other
when writing a dot pattern on the magnetic display medium.
[0015] According to the invention, since the high contrast printed dots having less blur
outline are continuously overlapped, high quality magnetic printing can be realized.
[0016] The invention provides a magnetic head for magnetic display comprising:
a yoke having a printing face which faces to a magnetic display medium and an air
gap hole formed in the printing face;
a magnetic core whose edge is inserted into the air gap hole, for generating a dot-like
recording magnetic field by magnetically coupling with the yoke; and
an electromagnetic coil for supplying a magnetic field to the magnetic core based
on printing signals,
wherein in comparison between a rate of change in magnetic flux density and a rate
of change in position from an outer peripheral end position of the edge of the magnetic
core to an inner peripheral end position of a front portion of the air gap hole, a
value of ratio of the change in flux density to the change in position in a vicinity
of a reaction threshold value of the magnetic display medium is 1(T/mm) or more.
[0017] According to the invention, high contrast printed dots having less blur outline can
be obtained with the result that high quality magnetic printing can be realized.
[0018] Other and further objects, features, and advantages of the invention will be more
explicit from the following detailed description taken with reference to the drawings
wherein:
Fig. 1 is a sectional view showing an electronic information display apparatus in
which a magnetic head of the present invention is used;
Fig. 2 is a partial perspective view showing an internal structure of the electronic
information display apparatus shown in Fig. 1:
Fig. 3 is a partial sectional view showing structures of a magnetic display sheet
10 and a magnetic head 30;
Figs. 4A through 4C, Figs. 5A through 5C, and Figs. 6A and 6B are graphs showing measured
results of distribution of a magnetic field generated by a magnetic core 37;
Figs. 7 through 10 are an enlarged photograph showing a print sample on a magnetic
display sheet; and
Fig. 11A through 11D are explanatory charts showing printing conditions which correspond
to dots printed on the photographs.
[0019] Now referring to the drawings, preferred embodiments of the invention are described
below.
[0020] Fig. 1 is a sectional view showing an electronic information display apparatus in
which a magnetic head of the present invention is used and Fig. 2 is a partial perspective
view thereof. A driven roller 50 is disposed within the upper part of a housing 1
and a driving roller 60 is disposed within the lower side thereof. A flexible endless
magnetic display sheet 10 is spanned between the two rollers 50 and 60. The roller
50 is urged upward by an elastic member (not shown) such as a spring to give certain
tension to the magnetic display sheet 10 to stably run the sheet and to maintain the
flatness of the surface of the sheet. The roller 60 is rotationally driven by a motor
63 via gears 61 and 62. The magnetic display sheet 10 is circulated so as to move
from the bottom to the top on the front side of the housing 1 (the left side in Fig.
1 or the back side in Fig. 2) and from the top to the bottom on the rear side of the
housing 1 (the right side in Fig. 1 or the front side in Fig. 2) when the roller 60
is driven. A display window 2 made of a transparent material such as acrylic resin
or glass is formed on the front of the housing 1.
[0021] A recording head 30 is provided at the lower part of the rear moving side of the
magnetic display sheet 10 and generates a dot matrix type recording magnetic field
toward the surface of the magnetic display sheet 10 based on printing signals sent
from an external host unit (not shown). The recording head 30 has a plurality of electromagnetic
coils disposed in stagger, for example, and is mounted on a carriage 31 which reciprocates
in the direction of the width of the sheet. The carriage 31 is fixed to part of an
endless belt 33 spanned between two pulleys 34 and 35 and is driven, while being guided
by two guide shafts 32, by a motor 36 which rotationally drives the pulley 35.
[0022] An erasing head 20 is composed of a permanent magnet and the like having a length
longer than the sheet width and is disposed so as to contact closely to the back of
the magnetic display sheet 10 at the upper part of the front moving side of the magnetic
display sheet 10.
[0023] Fig. 3 is a partial sectional view showing a structure of the magnetic display sheet
10 and the recording head 30. Coated and fixed around the whole surface of the magnetic
display sheet 10 are micro-capsules 15 which develops colors in response to magnetism.
Each micro-capsule 15 is composed of high viscous liquid and a spherical shell which
encloses and holds the liquid. Dispersed within the liquid are magnetic particles
which are nearly black and non-magnetic particles which are nearly white. For example,
particle of black iron oxide (FeO) having a size of 0.1 to 5 µm is used as the magnetic
particle and particle of white titanium oxide having a size of 0.1 to 5 µm is used
as the non-magnetic particle. Further, as the high viscous liquid, organic solvent
including aqueous solution, fat and oil and surface active agent type solvent is used
and as the material of the shell, gelatin is mainly used. The size of the micro-capsule
15 is distributed within a range from 10 to 1,000 µm.
[0024] In case the particle size is less than 10 µm, the micro capsule 15 can include just
a few magnetic particles and non-magnetic particles. When printing by attracting the
nearly black magnetic particles to the surface of the sheet 10, the nearly white non-magnetic
particles can be seen through the sheet because the amount of the magnetic particles
is small. This causes an undesired result that low contrast gray dots are printed.
When the particle size is more than 1,000 µm on the other hand, it becomes difficult
to create an adequate printed dot because the particle size becomes close to a diameter
d of an edge of a magnetic core 37 and a diameter D of a air gap hole in a recording
head 39 and the number of micro-capsules 15 which represent one printed dot decreases.
Further, it is not preferable that the recording head 39 as described later requires
a large quantity of current because the larger the size of the micro-capsule 15, the
longer the distance for moving the magnetic particles becomes. From these reasons,
it can be said that the suitable size of the micro-capsule 15 is within the range
from 10 to 1,000 µm.
[0025] The micro-capsule 15 is mixed with binder 14 made of highly transparent synthetic
rubber type adhesive and the like and is coated to a base 11 made of a transparent
material such as polyethylene terephthalate to form a capsule coating layer 12 of
40 to 1,000 µm thick, for example.
[0026] A protection sheet 13 made of polypropylene long-fibre unwoven cloth and the like
is adhered on the back of the capsule coating layer 12 so as to be 30 to 1,000 µm
thick, for example, to smoothly run the sheet.
[0027] Meanwhile, the recording head 30 comprises the box type yoke 39 made of a material
of high magnetic permeability, the magnetic core 37 made of a material of high magnetic
permeability uprightly provided within the yoke 39 and an electromagnetic coil 38
attached to the magnetic core 37. A plurality of magnetic cores 37 and electromagnetic
coils 38 are provided corresponding to a plurality of printed dots. While the magnetic
core 37 is formed into a columnar shape, the diameter of the edge thereof is smaller
than that of the middle part and a tapered portion in which the diameter changes linearly
is formed therebetween.
[0028] Numbers of circular air gap holes are formed on the printing face 39a of the yoke
39 and the edge of the magnetic core 37 is positioned at the center of each air gap
hole. Leakage magnetic field is generated because there exist the air gap between
the magnetic core 37 and the air gap hole. As shown in Fig. 3 as to the distribution
of the magnetic field, semi-ringed lines of magnetic force are generated between the
edge of the magnetic core 37 and the yoke 39 and the strength of the magnetic field
is maximized at the position slightly separated in the radial direction from the extension
of the axis of the magnetic core 37. Therefore, in the case where an interval between
the magnetic core 37 and the yoke 39 exceeds a certain amount, dots with blurred peripheries
are printed.
[0029] When the electromagnetic coil 38 is energized selectively corresponding to printing
signals, a magnetic field is generated along the axial direction of the magnetic core
37. It passes through a magnetic circuit composed of the magnetic core 37, the air
gap and the yoke 39 and generates a recording magnetic field from the air gap toward
the magnetic display sheet 10. That is, the magnetic field generated by the electromagnetic
coil 38 passes through the magnetic circuit composed of the magnetic core 37 (front
end), the air gap, the edge of the yoke 39, the yoke 39 and the magnetic core 37 (rear
end) and generates the magnetic field having a high magnetic flux density toward the
surface of the sheet around the edge of the magnetic core 37 because there exists
the air gap.
[0030] Next, the principle of the magnetic recording/displaying and erasure will be explained.
When the recording head 30 approaches the surface of the magnetic display sheet 10
where the base 11 is positioned, and generates the recording magnetic field based
on printing signals, the magnetic particles dispersed within the micro-capsule 15
are attracted to the side of the base 11 and due to the pressure, the non-magnetic
particles move to the side of the protection sheet 13. Then, the part to which the
recording magnetic field has been applied is observed as if it has developed nearly
black color seeing from the surface side of the magnetic display sheet 10. That is,
letters and symbols may be recorded by applying magnetic fields in dot matrix by using
the recording head 30.
[0031] Next, when the erasing head 20 approaches the back of the magnetic display sheet
10, i.e. the side where the protection sheet 13 is positioned, the magnetic particles
dispersed within the micro-capsule 15 are attracted to the side of the protection
sheet 13 and due to the pressure, the non-magnetic particles move to the side of the
base 11. Then, the part to which the erasing magnetic field has been applied turns
nearly white seeing from the surface side of the magnetic display sheet 10. That is,
the sheet may be erased uniformly by applying the erasing magnetic field across the
whole surface of the sheet width.
[0032] Liquid having a predetermined viscosity is selected for the above-mentioned high
viscous liquid within the micro-capsule 15 so as to hold the state of display caused
by the magnetic particles moved to the back or the front side when the magnetic field
has been applied. That is, it is selected to prevent the state of display from being
collapsed which might otherwise occur when the particles moved once to the front or
the back side settle or move due to vibration and the like when the viscosity of the
liquid is low. Accordingly, the magnetic attracting force of the recording head 30
and the erasing head 20 must exceed the yield value of the above-mentioned liquid
defined by the viscosity. Writing/erasure of the display is thus implemented.
[0033] Next, an operation of the whole apparatus will be explained. Making reference to
Figs. 1 and 2, the magnetic display sheet 10 is circulated at a constant speed to
erase the whole surface with the erasing head 20 before starting printing at first.
Next, printing is carried out magnetically by receiving printing signals from the
external host unit and feeding pulse current of several hundred microseconds to several
tens miliseconds to the electromagnetic coil 38 while moving the recording head 30
in the direction of the sheet width every time when the development of image data
of one printing line ends and applying the dot matrix magnetic fields to the surface
of the magnetic display sheet 10.
[0034] When one line of printing is finished, the magnetic display sheet 10 is shifted by
a predetermined feed pitch and is stopped to print based on image data developed for
the next printing line. One sheet of image is then formed by repeating the development
of the image data, the serial printing by the recording head 30 and the intermittent
feed of the magnetic display sheet 10 as described above.
[0035] When a new image is to be printed, serial printing is carried out by the recording
head 30 after erasing the whole face with the erasing head 20 by circulating the magnetic
display sheet 10 at the constant speed in the same manner as described above.
[0036] Next, a result of changes of the printed dots studied by variously changing the diameter
d of the edge of the magnetic core 37 and the diameter D of the air gap hole formed
in the yoke 39 will be explained. Table 1 shows whether or not a blur is generated
in the periphery of the printed dot formed on the magnetic display sheet 10. In Table
1, "○" represents those printed dots whose periphery is clear, " × " represents those
printed dots whose periphery is blurred, and [-]represents impracticable settings
Table 1
Diameter d of edge portion of magnetic core 37 (mm) |
Diameter D of hole (mm) |
|
0.8 |
1.1 |
1.4 |
1.7 |
2.0 |
0.5 |
O |
O |
X |
X |
X |
0.8 |
O |
O |
O |
X |
X |
1.1 |
- |
O |
O |
O |
X |
1.4 |
- |
- |
O |
O |
O |
1.7 |
- |
- |
- |
O |
O |
2.0 |
- |
- |
- |
- |
O |
[0037] Accordingly, since the diameter d of the edge of the magnetic core 37 is smaller
than the diameter D of the hole, the difference between the diameters D and d is less
than 0.9 mm, and the diameter D is less than 2.0 mm, expansion at the foot of the
magnetic field distribution can be eliminated. As a result, each printing dot formed
in a magnetic display body is a clear and high-contrast printing dot in which there
is little blurring of the contours can be attained. Also, although the printing dots
exhibit ring-shaped density distribution in which the density in the center of the
printing dot is low, this does not present a problem in practical applications.
[0038] Figs. 4A through 4C, Figs. 5A through 5C and Figs. 6A and 6B are graphs showing the
measurement results of the distribution of the magnetic field generated by the magnetic
core 37. The distribution of magnetic flux density is measured assuming that the capsule
coating layer 12 of the magnetic display sheet 10 is positioned on a plane separated
from the printing face 39a of the recording head 30 by a certain distance (ex. 50
µm) and by scanning a magnetic probe along this plane. The ordinate represents the
flux density (unit T: tesla) and the abscissa represents position (mm) from the center
of the magnetic core.
[0039] Fig. 4A shows a case when the diameter d of the edge of the magnetic core 37 is 0.5
mm and the diameter D of the air gap hole is 0.8 mm. It shows a "caldera volcano"
type distribution in which the magnetic flux density is slightly dented around the
center of the magnetic core, is maximized around the circumference of the edge of
the magnetic core and drops sharply as the position is separated therefrom.
[0040] Although the reaction threshold value of the magnetic display sheet 10 differs depending
on the diameters and amounts of the magnetic particles and the viscosity of the liquid
within the micro-capsules 15, since the reaction threshold value of the magnetic display
sheet 10 put to use is approximately 0.3T, in places where a flux density of 0.3T
or more can be applied, the magnetic particles within the micro-capsules 15 are drawn
toward the front surface of the magnetic display sheet 10 to impart a black coloring,
and in places where only a flux density of less than 0.3T can be applied, the magnetic
particles in the micro-capsules 15 do not react and the display remains white. Also,
in the vicinity of the reaction threshold value (in the vicinity of approximately
0.3T in the case of the magnetic display sheet 10 used in this experiment) the magnetic
particles slightly react and look gray. Where these gray colored portions in the vicinity
of the reaction threshold value are numerous in the contoured portions of the printing
dots, in other words where the flux density variation rate in the vicinity of the
reaction threshold value of the contoured portions of the printing dots is low, the
contours of the printing dots are blurred.
[0041] In the case where the diameter d of the edge portion is 0.5 mm and the diameter D
of the hole 0.8 mm, the ratio of change in flux density in the vicinity of the reaction
threshold value is calculated at a large ratio of change in flux density to position
change of Ya/Xa = 2.2(T/mm), so that a clear printing dot without blurring of the
contour can be attained at a diameter of approximately 0.8 mm.
[0042] Fig. 4B shows a case where the diameter d of the edge portion of the magnetic core
37 is 0.8 mm and the diameter D of the hole is 1.4 mm, the flux density exhibiting
a distribution which is slightly dented in the vicinity of the center of the magnetic
core, is maximum in proximity to the peripheral portion of the edge of the magnetic
core, and abruptly decreases further away therefrom.
[0043] In the case where the diameter d of the edge portion is 0.8 mm and the diameter D
of the hole 1.4 mm, the ratio of change in flux density in the vicinity of the reaction
threshold value (approximately 0.3T) of the magnetic display sheet 10 put to use is
calculated at a somewhat large value of Yb/Xb = 1.1(T/mm), so that a clear dot without
blurring of the contour can be attained at a diameter of 1.3 mm.
[0044] Fig. 4C shows a case when the diameter d of the edge of the magnetic core 37 is 1.1
mm and the diameter D of the air gap hole is 1.4 mm. It shows a distribution in which
the flux density is slightly dented in the vicinity of the center of the magnetic
core, is maximized around the circumference of the edge of the magnetic core and drops
abruptly as the position is separated therefrom.
[0045] In the case where the diameter d of the edge portion is 1.1 mm and the diameter D
of the hole 1.4 mm , the ratio of change in flux density in the vicinity of the reaction
threshold value (approximately 0.3T) is calculated at a large ratio of change in flux
density to position change of Yc/Xc = 2.4(T/mm), so that a clear printing dot without
blurring of the contour can be attained at a diameter of approximately 1.4 mm. Also,
even in the case of printing wherein the central density of the printing dot exhibits
a somewhat concave ring-shaped density distribution and the central portion is blurred,
by printing with the dots overlapping each other favorable printing results can be
attained. In addition, where letters and diagrams are normally printed, essentially
favorable printing can be attained by overlapping a plurality of dots.
[0046] Fig. 5A shows a case when the diameter d of the edge of the magnetic core 37 is 1.1
mm and the diameter D of the air gap hole is 1.7 mm. It shows a distribution in which
the flux density is dented in the vicinity of the center of the magnetic core, is
maximized around the circumference of the edge of the magnetic core and drops abruptly
as the position is separated therefrom.
[0047] In the case where the diameter d of the edge portion is 1.1 mm and the diameter D
of the hole 1.7 mm, the ratio of change in flux density in the vicinity of the reaction
threshold value (approximately 0.3T) is calculated at a large ratio of change in flux
density to position change of Yd/Xd = 1.0(T/mm), so that a clear printing dot without
blurring of the contour can be attained at a diameter of approximately 1.4 mm. Also,
even in the case of printing wherein the central density of the printing dot exhibits
a somewhat concave ring-shaped density distribution and the central portion is blurred,
by printing with the dots overlapping each other favorable printing results can be
attained.
[0048] Fig. 5B shows a case when the diameter d of the edge of the magnetic core 37 is 1.7
mm and the diameter D of the air gap hole is 2.0 mm. It shows a distribution in which
the flux density is largely dented in the vicinity of the center of the magnetic core,
is maximized around the circumference of the edge of the magnetic core and drops abruptly
as the position is separated therefrom.
[0049] In the case where the diameter d of the edge portion is 1.7 mm and the diameter D
of the hole 2.0 mm, the ratio of change in flux density in the neighborhood of the
reaction threshold value (approximately 0.3T) of the magnetic display sheet 10 put
to use is calculated at a large value of Ye/Xe = 2.2 (T/mm) and a clear printing dot
without blurring of the contour can be attained at a diameter of 2.0 mm. Also, even
in the case of printing wherein the central density of the printing dot exhibits a
somewhat concave ring-shaped density distribution and the central portion is blurred,
by printing with the dots overlapping each other, favorable printing results can be
attained.
[0050] Fig. 5C shows a case where the diameter d of the edge portion of the magnetic core
37 is 1.4 mm and the diameter D of the hole is 2.0 mm, the flux density exhibiting
a distribution which is slightly dented in the vicinity of the center of the magnetic
core, is maximum in proximity to the peripheral portion of the edge of the magnetic
core, and abruptly decreases further away therefrom.
[0051] In the case where the diameter d of the edge portion is 1.4m and the diameter D of
the hole 2.0 mm, the ratio of change in flux density in the neighborhood of the reaction
threshold value (approximately 0.3T) of the magnetic display sheet 10 put to use is
calculated at a large value of Yf/Xf = 2.3 (T/mm) and a clear printing dot without
blurring of the contour can be attained at a diameter of 2.0 mm. Also, even in the
case of printing wherein the central density of the printing dot exhibits a somewhat
concave ring-shaped density distribution and the central portion is blurred, by printing
with the dots overlapping each other, favorable printing results can be attained.
[0052] Fig. 6A shows a case where the diameter d of the edge portion of the magnetic core
37 is 0.5 mm and the diameter D of the hole is 1.4 mm, the flux density exhibiting
the "caldera volcano"-type distribution which is slightly dented in the vicinity of
the center of the magnetic core, is maximum in proximity to the peripheral portion
of the edge of the magnetic core, and gradually decreases further away therefrom.
[0053] In the case where the diameter d of the edge portion is 0.5 mm and the diameter D
of the hole 1.4 mm, the rate of change in flux density in the neighborhood of the
reaction threshold value (approximately 0.3T) of the magnetic display sheet 10 put
to use is calculated at a small value of Yg/Xg = 0.53(T/mm), a printing dot having
a blurred contour is produced at a diameter of 1.0 mm.
[0054] Fig. 6B shows a case where the diameter d of the edge portion of the magnetic core
37 is 0.8 mm and the diameter D of the hole is 1.7 mm, the flux density exhibiting
a distribution which is slightly dented in the vicinity of the center of the magnetic
core, is maximum in proximity to the peripheral portion of the edge of the magnetic
core, and gradually decreases further away therefrom.
[0055] In the case where the diameter d of the edge portion is 0.8 mm and the diameter D
of the hole 1.7 mm, the rate of change in flux density in the neighborhood of the
reaction threshold value (approximately 0.3T) of the magnetic display sheet 10 put
to use is calculated at a small value of Yh/Xh = 0.5(T/mm), a printing dot having
a blurred contour is produced at a diameter of 1.3 mm.
[0056] As seen from these measurement results, in order to realize a print with little blurred
contours, it is preferable to set the diameter d of the edge portion and the diameter
D so that the ratio of change in flux density is Y/X ≧ 1.
[0057] It can be also seen that although the absolute value of the distribution itself of
the magnetic fluxes shown in Figs. 4 to 6 may change, the tendency of the distribution
is not changed so much even when the quantity of current to be fed to the electromagnetic
coil 38 in the recording head 39 is changed more or less. Accordingly, it is possible
to optimize the shape of the printed dot by controlling the quantity of current to
be fed and the feed time corresponding to the sensitivity of the magnetic display
sheet 10. It can be seen from these facts that it is important to set the diameter
d of the edge of the magnetic core 37 and the diameter D of the air gap hole at adequate
size in advance.
[0058] Next, experiments on evaluation of print will be explained. Figs. 7 through 10 are
enlarged photographs showing samples of prints magnetically printed on the magnetic
display sheet by changing the diameter d of the edge of the magnetic core 37 and the
diameter D of the air gap hole variously. Figs. 11A through 11D are explanatory charts
showing printing conditions corresponding to the printed dots on the photographs.
[0059] Fig. 7 is a printing sample in which the diameter D of the hole is 1.1 mm and the
diameter d of the magnetic core edge portion is 1.1 mm, and the right side is a printing
sample where the dots overlap each other at a printing pitch of 0.7 mm. In the enlarged
photograph, in contrast to the micro-capsules of the magnetic display sheet 10 being
observed in particle shape, there is little blurring of the contours and a favorable
printing result is achieved.
[0060] Fig. 8 is a printing sample in which the diameter D of the hole is 1.4 mm and the
diameter d of the magnetic core edge portion is 1.4 mm (upper sample) and 1.1 mm (lower
sample), and the right side is a printing sample where the dots overlap each other
at a printing pitch of 0.9 mm. Also in this photograph, there is little blurring of
the contours and a favorable printing result is achieved.
[0061] Fig. 9 is a printing sample in which the diameter D of the hole is 1.7 mm and the
diameter d of the magnetic core edge portion is 1.7 mm (upper), 1.4 mm (middle) and
1.1 mm (lower), and the right side is a printing sample where the dots overlap each
other at a printing pitch of 1.1 mm. Also in this photograph, there is little blurring
of the contours and a favorable printing result is achieved.
[0062] Fig. 10 is a printing sample in which the diameter D of the hole is 2.0 mm and the
diameter d of the magnetic core edge portion is 2.0 mm (upper), 1.7 mm (middle) and
1.4 mm (lower), and the right side is a printing sample where the dots overlap each
other at a printing pitch of 1.3 mm. Also in this photograph, there is little blurring
of the contours and a favorable printing result is achieved.
[0063] Here the printing pitch, where forming letters or diagrams, is able to be modified
within a range from a value larger than a formed dot/2 and less than a formed dot/1.414213
··· (root 2), and in particular a printing pitch calculated from the formed dot/1.414213
··· (root 2) is suitable. Although Figs. 7 through 10 were printed at the printing
pitch calculated by formed dot/1.414213 ··· (root2), even in cases where the central
density of the printing dot exhibits a concave ring-shaped density distribution as
shown in Fig. 9 and Fig. 10, a favorable printing result can be achieved by printing
with the dots overlapping each other. Also, where letters and diagrams are normally
printed, because printing is performed by overlapping a plurality of dots, essentially
favorable printing is attained.
[0064] In addition, with regard to the size of the dots, as well as the number of dots forming
one screen image decreasing where the size is too large, in case where the printing
dot has a central density which exhibits a concave ring-shaped density distribution,
printing must be performed by adjusting the printing pitch more finely and overlapping
the dots, therefore there is a possibility that this may cause a reduction in the
printing speed, therefore to perform printing at an optimum printing pitch, the upper
limit is thought to be where the diameter D of the hole is approximately 2.0 mm.
[0065] Once the printing dot increases in the above manner, although the central density
has a tendency to exhibit a concave ring-shaped density distribution, by adjusting
the printing pitch and performing printing by overlapping each dot slightly, the concavity
in the central density can be reduced.
[0066] The invention may be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. The present embodiments are therefore
to be considered in all respects as illustrative and not restrictive, the scope of
the invention being indicated by the appended claims rather than by the foregoing
description and all changes which come within the meaning and the range of equivalency
of the claims are therefore intended to be embraced therein.
1. A magnetic head (30) for magnetic display comprising:
a yoke (39) having a printing face (39a) which faces to a magnetic display medium
(10) and an air gap hole formed in the printing face;
a magnetic core (37) whose tip is inserted into the air gap hole, for generating a
dot-like recording magnetic field by magnetically coupling with the yoke; and
an electromagnetic coil (38) for supplying a magnetic field to the magnetic core based
on printing signals,
wherein a diameter d of the tip of the magnetic core is smaller than a diameter D
of the air gap hole, a difference between the diameter D and the diameter d is less
than 0.9mm and the diameter D is 2.0 mm or less.
2. A magnetic head for magnetic display as claimed in claim 1, wherein the magnetic display
medium (10) to which the magnetic field from the magnetic head is applied comprises
micro-capsules (15) containing magnetic powder and non-magnetic powder, the size of
the micro-capsule being in a range from 10 µm to 1,000 µm.
3. A magnetic head as claimed in claim 2, wherein said range is from 10 µm to 200 µm,
or 200 µm to 400 µm or 400 µm to 600 µm or 600 µm to 800 µm or 800 µm to 1000 µm.
4. A magnetic display apparatus comprising a magnetic head (30) for magnetic display;
and a magnetic display medium (10) which is writable and erasable by magnetism,
the head comprising:
a yoke (39) having a printing face (39a) which faces to the magnetic display medium
(10) and an air gap hole formed in the printing face;
a magnetic core (37) whose tip is inserted into the air gap hole, for generating a
dot-like recording magnetic field by magnetically coupling with the yoke; and
an electromagnetic coil (38) for supplying a magnetic field to the magnetic core based
on printing signals,
the edge of the magnetic core having a diameter d smaller than a diameter D of the
air gap hole, a difference between the diameter D and the diameter d being less than
0.9 mm, the diameter D being 2.0 mm or less,
wherein a plurality of printed dots are formed to continuously overlap each other
when writing a dot pattern on the magnetic display medium.
5. A magnetic display apparatus as claimed in claim 4, wherein the magnetic display medium
comprises microcapsules (15) containing magnetic powder and non-magnetic powder, the
size of the microcapsules being in the range from 10 µm to 1.000 µm.
6. A magnetic display apparatus as claimed in claim 5, wherein the range is from 10 µm
to 200 µm, or 200 µm to 400 µm, or 400 µm to 600 µm, or 600 µm to 800 µm, or 800 µm
to 1000 µm.
7. A magnetic head (30) for magnetic display comprising:
a yoke (39) having a printing face (39a) which faces to a magnetic display medium
and an air gap hole formed in the printing face;
a magnetic core (37) whose tip is inserted into the air gap hole, for generating a
dot-like recording magnetic field by magnetically coupling with the yoke;
and an electromagnetic coil (38) for supplying a magnetic field to the magnetic core
based on printing signals,
wherein in comparison between a rate of change in magnetic flux density and a rate
of change in position from an outer peripheral end position of the tip of the magnetic
core to an inner peripheral end position of a front portion of the air gap hole, a
value of ratio of the change in flux density to the change in position in a vicinity
of a reaction threshold value of the magnetic display medium is 1(T/mm) or more.