U.S. patent number 3,833,789 [Application Number 05/339,432] was granted by the patent office on 1974-09-03 for thermal printing head.
This patent grant is currently assigned to Toyo Electronics Industry Corp.. Invention is credited to Hideo Taniguchi.
United States Patent |
3,833,789 |
Taniguchi |
September 3, 1974 |
THERMAL PRINTING HEAD
Abstract
A thermal printing head comprising a plurality of thin
insulating layers each being provided on one surface thereof with a
plurality of lower slips made of an electrically conductive
material arranged in spaced parallel relation to one another. The
insulating layers are piled stepwise one upon another so that one
end portion of the upper surface of each of the layers with the
corresponding end portions of the conductive slips thereon are
exposed from beneath the end of the layer immediately above. A
square element made of an electrically resistive material is placed
on each of the exposed end portions of the lower conductive slips.
An upper slip made of an electrically conductive material extending
transversely of the exposed ends of the lower conductive slips on
each of the insulating layers covers the resistive elements so that
the elements are sandwiched between the upper and lower conductive
slips. Upon impression of a voltage between the upper and lower
conductive slips, the resistive elements sandwiched therebetween
are heated. By selecting the lower conductive slips between which
and the upper conductive slip a voltage is to be impressed it is
possible to heat those of the resistive elements which are combined
to take the shape of a symbol, and with a sheet of heat-sensitive
paper being applied onto the surface of the printing head, the
symbol is printed on the paper.
Inventors: |
Taniguchi; Hideo (Kyoto,
JA) |
Assignee: |
Toyo Electronics Industry Corp.
(Ukyo-ku, Kyoto, JA)
|
Family
ID: |
12203243 |
Appl.
No.: |
05/339,432 |
Filed: |
March 8, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Mar 16, 1972 [JA] |
|
|
47-4726795 |
|
Current U.S.
Class: |
347/208;
219/543 |
Current CPC
Class: |
B41J
2/3357 (20130101); B41J 2/3353 (20130101); B41J
2/33525 (20130101); H05B 3/00 (20130101); B41J
2/3351 (20130101) |
Current International
Class: |
B41J
2/335 (20060101); H05B 3/00 (20060101); H05b
001/00 () |
Field of
Search: |
;219/216,543
;346/76 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Albritton; C. L.
Attorney, Agent or Firm: Christensen, O'Connor, Garrison
& Havelka
Claims
What I claim is:
1. A thermal printing head comprising: a plurality of layers of an
electrically insulating material piled one upon another stepwise so
that one end portion of one surface of each said layer is exposed
from under the layer immediately above; a plurality of lower slips
of an electrically conductive material arranged in parallel spaced
relation to one another on said one surface of each said insulating
layer; a plurality of elements of an electrically resistive
material provided on the exposed end portions of said lower
conductive slips on each said insulating layer; and an upper slip
of an electrically conductive material provided on said resistive
elements; whereby upon impression of a voltage between said upper
and lower conductive slips an electric current flows through said
resistive elements in the direction of the thickness thereof so as
to heat said elements.
2. The thermal printing head of claim 1, wherein said resistive
elements are arranged in rows and columns equidistantly spaced from
one another.
3. The thermal printing head of claim 1, wherein selected ones of
said resistive elements can be energized to form a predetermined
symbol.
4. The thermal printing head of claim 1, wherein said conductive
slips and said resistive elements are formed by the method of
screen printing.
5. The thermal printing head of claim 1, wherein said insulating
layers are of a raw thin ceramic sheet sintered into a unitary
structure.
6. The thermal printing head of claim 1, wherein said insulating
layers are of a raw thin ceramic sheet having said conductive slips
formed thereon by the method of screen printing before said layers
are sintered.
7. The thermal printing head of claim 1, wherein said insulating
layers are piled one upon another stepwise also at the other end
portions thereof opposite to said end portions where said resistive
elements are provided, so that the corresponding end portions of
said lower conductive slips on each said insulating layer are
exposed from beneath the insulating layer immediately above for use
as terminals through which electric energy is applied to said
conductive slips.
8. The thermal printing head of claim 1, wherein a voltage is
impressed between said upper conductive slip and at least one of
said lower conductive slips so as to heat those of said resistive
elements sandwiched between said upper slip and said lower
slips.
9. The thermal printing head of claim 1, further including an
additional conductive slip electrically connected to said upper
conductive slip on each said insulating layer to be used as a
terminal for application of electric energy to said upper
conductive slip.
10. The thermal printing head of claim 1, wherein said upper
conductive slips extend in the same direction as said lower
conductive slips so as to cover those of said resistive elements
which are aligned in said direction on said insulating layers.
11. The thermal printing head of claim 1, wherein said upper
conductive slips are formed into a single sheet.
12. The thermal printing head of claim 1, wherein a projection made
of a thermally conductive material is formed on those portions of
said upper conductive slip on each said insulating layer which
correspond to said resistive elements beneath said slip, the upper
end surfaces of said projections being arranged at substantially
the same level.
13. The thermal printing head of claim 12, wherein said projections
are formed by the method of screen printing.
14. The thermal printing head of claim 13, wherein said projections
comprise a plurality of layers of a thermally conductive
material.
15. The thermal printing head of claim 12, wherein each said
projection comprises a bump of a thermally conductive material.
16. The thermal printing head of claim 1, wherein said resistive
elements on each said insulating layer are formed into a single
slip extending transversely of said lower conductive slips.
17. The thermal printing head of claim 1, wherein said upper
conductive slips extend transversely of said lower conductive slips
so as to contact those resistive elements associated with one
insulating layer.
18. The thermal printing head of claim 1, wherein said upper
conductive slips are arranged to contact said resistive elements
such that each of the plurality of resistive elements is
electrically common to one another.
Description
This invention relates to a rprinting head for use in thermal
printing.
Recently there have been in wide use thermal printers which employ
a thermal printing head to record information obtained from, say,
an electronic computer in the form of various symbols printed on
heat-sensitive recording media. The thermal printing head includes
those elements which produce heat when electric energy is applied
thereto. For printing, the elements are selectively heated to form
a required symbol to be pressed onto the heat-sensitive paper so
that the symbol is recorded on the paper. It is required of such a
printing head that a single head should be capable of selectively
printing a plurality of different symbols (including characters,
pictures, etc).
In one known printing head, there are provided many dot-like
heating elements arranged in rows and columns and spaced
equidistantly from one another. When a symbol is to be printed by
the printing head, those of the elements which correspond to the
symbol are selectively energized to be heated, so that the heated
elements are combined to form the shape of the symbol. Therefore,
when the head is brought into contact with a sheet of
heat-sensitive paper, those dot-like portions of the paper which
are contacted by the heated elements become colored, and the
colored dots are combined to appear as the required symbol.
One prior art printing head having such dot-like heating elements
comprises a plurality of thin layers of an insulating material
laminated into a single block each layer being provided on one side
surface thereof with a plurality of separate thin heating elements,
so that on the side or surface of the block there appear a
plurality of dot-like heating elements arranged in rows and columns
and spaced a predetermined distance apart from one another. For
supply of electric energy to each of the elements, on one surface
of the insulating layer there is provided a thin layer of an
electrically conductive material, through which electric current is
supplied to the heating element.
For manufacture of the printing head of the above-mentioned type,
it is necessary to provide dot-like heating elements on one side
surface of each insulating layer, and these heating elements are
film resistors formed on the surface by chemical deposition. The
manufacturing process is rather complicated and time-consuming and
requires a high degree of skill and precision.
Accordingly, the primary object of the invention is to provide a
thermal printing head which is provided with a plurality of
dot-like heating resistive elements.
Another object of the invention is to provide such a thermal
printing head as aforesaid in which the heating resistive elements
and the electrically conductive elements for supplying electric
energy to the resistive elements are composed of a thick film.
Still another object of the invention is to provide such a thermal
printing head as aforesaid wherein the terminals through which
electric energy is supplied to the resistive elements are arranged
in a substantial plane.
The thermal printing head of the invention comprises a plurality of
thin layers of an electrically insulating material each being
provided on one surface thereof with a plurality of slips of an
electrically conductive material arranged on the surface in spaced
parallel relation to each other. These insulating layers are piled
stepwise one upon another into a unitary structure. The word
"stepwise" means that the layers are so piled one upon another that
one end portion of the upper surface of each layer with the
corresponding end portions of the conductive slips thereon is
exposed from beneath the corresponding end of the layer immediately
above as if those exposed end portions of the layers formed stairs.
A square patch or element of an electrically resistive material is
placed on the end portions of the conductive slips on the exposed
end portion of each of the insulating layers. A slip of an
electrically conductive material extending transversely of the
exposed ends of the conductive slips on each of the insulating
layers is placed in contact with all the square resistive elements
so as to electrically connect the elements. In the following
description those conductive slips which are directly placed on the
insulating layer will be referred to as the lower conductive slips
and that which is placed on the resistive elements, as the upper
conductive slip.
If one of the lower conductive slips on one of the insulating
layers is selected and a voltage is impressed between the selected
lower conductive slip and the upper conductive slip, an electric
current flows through the resistive element sandwiched between the
upper and lower slips in the direction of the thickness of the
elements so that the element is heated. The heat is transferred to
that local portion of the upper conductive slip which corresponds
to the resistive element.
If more than one of the lower conductive slips on each insulating
layer is selected so as to impress a voltage between the selected
slips and the common upper conductive slip, the corresponding local
areas of the upper slips are heated. The heated areas are separate
and dot-like, but when all the heated dot-like areas on the exposed
surface of all the insulating layers are taken as a whole, they
express a symbol or character. Therefore, if a sheet of
heat-sensitive paper is applied onto the surface of the printing
head, the symbol appears or is printed on the paper.
As previously mentioned, the insulating layers are piled stepwise.
However, since each of the layers, the slips and the resistive
elements is as thin as 0.015 mm, the upper surface of the printing
head is practically flat. However, if the stepped surface causes
any trouble to clear printing, projections of a thermally
conductive material may be provided on those portions or areas of
the upper conductive slip which correspond to the resistive
elements below the slip. The projections are of such a height that
their upper surfaces are in substantially the same plane. With this
arrangement, the surfaces of all the projections can be applied to
a sheet of heat-sensitive paper with substantially the same
pressure so that a clear printing is obtained.
The insulating layers are piled stepwise also at the side opposite
to that where the resistive elements are provided so that the
corresponding ends of the lower conductive slips on the insulating
layers are exposed at that side, which can be used as terminals
through which electric energy can be applied to the slips. With
this arrangement there is no need for provision of particular
terminals or leads for the purpose.
On each of the insulating layers there is further provided an
additional electrically conductive slip extending alongside the
lower condsuctive slips. This additional slip may be referred to as
the common conductive slip. The slip has its one end electrically
connected to the upper conductive slip on that insulating layer and
its opposite end exposed at the opposite exposed end of the
insulating layer in the same manner as the exposed terminal ends of
the lower conductive slips. The exposed end of the common
conductive slip can advantageously be used as the terminal of the
upper conductive slip on that insulating layer. The invention will
be described further in detail with reference to the accompanying
drawings, wherein:
FIG. 1 is a top plan view of one form of the thermal printing head
of the invention, with its middle portion being eliminated for ease
of illustration;
FIG. 2 is a schematic enlarged perspective view of a portion of
FIG. 1;
FIGS. 3 - 5 are perspective views similar to FIG. 2 but showing
different embodiments;
FIG. 6 is an enlarged side view, in vertical section, of a
projection formed on the heat-producing portion of the printing
surface of the head; and
FIG. 7 is a view similar to FIG. 6 but showing a modified form of
the projection.
Referring in detail to the drawings, there is shown a printing head
comprising a plurality, say, seven, layers 1A - 1G made of a
suitable insulating material such as alumina or the like ceramic
piled one upon another. The layers 1A - 1G are supported by a base
10 made of a suitable material. The base and the layers thereon
form a unitary structure. If the base is made of an insulating
material, the lowest layer 1A may be eliminated.
On the upper surface of the lowest layer 1A there are provided a
plurality, say, six slips 11A - 16A of an electrically conductive
material arranged in parallel with and equidistantly spaced from
one another. In a similar manner, there are provided on the surface
of each of the insulating layers 1B - 1G six parallel conductive
slips 11B - 16B, 11C - 16C, 11D - 16D, 11E - 16E, 11F - 16F and 11G
- 16G. Of these conductive slips the slips 16A - 16G are the common
conductive slips while the rest are the lower conductive slips. The
insulating layers are piled stepwise one upon another so that the
one end portions of the conductive slips are exposed and the
exposed areas of the insulating layers appear as if they formed
stairs.
A square patch or element 21A - 25A made of an electrically
resistive material is placed on each of the exposed end portions of
the lower conductive slips 1A - 16A on the lowest insulating layer
1A. In a similar manner, resistive elements 21B - 25B, 21C - 25C,
21D - 25D, 21E - 25E, 21F - 25F and 21G - 25G are provided on the
exposed end portions of the lower conductive slips on the other
insulating layers 1B - 1G.
An upper conductive slip 3A extending transversely of the exposed
ends of the lower conductive slips 11A 14 15A on the lowest
insulating layer 1A is placed on the resistive elements 21A - 25A
in electrical contact therewith. The slip 3A has its one end also
placed on the common conductive slip 16A so as to provide an
electrical connection between the two slips 3A and 16A. In a
similar manner upper conductive slips 3B - 3G are provided on the
other insulating layers 1B - 1G and electrically connected to the
common conductive slips 16B - 16G. These slips and elements are
formed by the method of screen printing. Although in the drawing
there appears a gap between the under surface of the upper
conductive layer and the upper surface of the insulating layer,
this is merely for ease of illustration and actually there no such
gap between the two surfaces.
The end portions of the insulating layers opposite to those
portions where the resistive elements and the upper conductive
slips are provided are also arranged stepwise so that the
corresponding end portions of the lower and common conductive slips
are exposed so as to be used as terminals and leads through which
electric energy is applied to the slips.
As the material for the insulating layers a ceramic such as alumina
is used. On a sheet of alumina there are provided a plurality of
lower and common conductive slips which are formed by the method of
screen printing. A plurality of such sheets are piled one upon
another stepwise at the opposite end portions thereof and sintered
to form a unitary structure. At the stepped end portion of the
structure there are formed by the method of screeen printing a
plurality of resistive elements on the exposed end portions of the
lower conductive slips and then an upper conductive slip on the
resistive elements.
In one printing head manufactured in the above-mentioned manner,
the width of the conductive slips and the resistive elements, and
the gap between adjacent two of the conductive slips are all about
0.2 mm, the thickness of each of the conductive slips and the
resistive element is about 0.015 mm, and the distance between the
edge of each of the insulating layers and the upper conductive slip
thereon is about 0.1 mm. With these dimensions, each of the
resistive elements (which are heated) is a square one side of which
is 0.2 mm long, and these square elements exist as dots
equidistantly spaced from one another on the upper surface of the
printing head.
Suppose that a pulse-like voltage is impressed between, say, the
lower conductive slip 11A and the common conductive slip 3A so that
the element is heated. The heat is transferred to that local
portion of the upper conductive slip which coreesponds to the
resistive element. As will be easily understood, by selecting the
lower conductive slips between which a voltage is to be applied it
is possible to heat those of the resistive elements which are
combined to take the shape of a required symbol.
If in FIG. 1 those of the resistive elements which are hatched are
heated, the heated elements 21A - 25A, 25B, 24C, 23D, 24D, 25E,
21F, 25F, 22G and 24G as a whole take the shape of the reversed
numeral "3". In order to heat these hatched portions, a voltage is
applied between the common slip 16A and each of the lower
conductive slips 11A - 15A; the common conductive slip 16B and the
lower conductive slip 15B; the common conductive slip 16C and the
lower conductive slip 14C; the common conductive slip 16D and each
of the lower slips 13D and 14D; 16E and each of 11F and 15F; and
16G and each of 12G, 13G and 14G. With the printing head being
impressed onto a sheet of heat-sensitive paper, when these
resistive elements are heated in the above manner, the
corresponding portions of the paper change its color so that the
numeral "3" appears or is printed thereon.
Application of a voltage to the conductive slips is made through
those ends of the conductive slips which are opposite to the ends
thereof where the resistive elements are provided, that is, through
those ends of the lower conductive slips and the common conductive
slip which are exposed on the stepped end portions of the
insulating layers. Since the ends of all the conductive slips are
exposed, they can be used as terminals through which a voltage can
be applied to the slips with ease.
In the above example, the resistive element is sandwiched between
the upper and lower conductive slips at each of the intersections
thereof. In FIG. 3 a single slip made of an electrically resistive
material replaces the separate resistive elements on each of the
insulating layers. In the drawing three of such resistive slips are
shown at 2A - 2C, extending transversely of and in contact with the
exposed end portions of the lower conductive slips on each of the
insulaing layers. The arrangement of FIG. 3 is easier to
manufacture than that of FIG. 1 since a single resistive slip
suffices in FIG. 3 instead of the many elements separately provided
in FIG. 2.
In FIG. 2, the upper conductive slip makes a right angle with the
lower conductive slips on one and the same insulating layer. In
FIG. 4, however, an upper conductive slip 31A extends in the same
direction as the lower conductive slips 11A - 11G on all the
insulating layers, so that the upper conductive slip 31A covers the
resistive elements 21A - 21G in electrical contact therewith. In a
similar manner, upper conductive slips 32A - 34A are provided to
cover the resistive elements 22A - 22G, 23A - 23G and 24A - 24G,
respectively.
An improved modification of the arrangement of FIG. 4 is shown in
FIG. 5, wherein a single upper conductive sheet 3 replaces the
separate upper conductive slips of FIG. 4 and covers all the
resistive elements on the insulating layers. With this arrangement
it is possible to use the upper conductive sheet in common with any
of the lower conductive slips, and the manufacture of this
structure is much easier.
As will be easily understood, an electric current flows through the
resistive element in the direction of its thickness because the
element is sandwiched between the upper and lower conductive slips.
Therefore if the thickness of the resistive element is uniform all
over its area, the density of electric current per unit area of the
resistive element is uniform all over its area so that the amount
of heat produced per unit area of the element is uniform. However,
if a pair of conductive members were connected to the opposite
sides of the resistive leement, the current would flow in the
direction perpendicular to the direction of the thickness of the
element. In this case, if the length of the heated portion of the
element changes, the voltage to be applied must accordingly be
changed. In this invention, however, even if the heated area of the
resistive element changes, the voltage to be applied need not be
changed and the density of electric current per unit area remains
unchanged, so that uniformity in heating can be effected more
easily than otherwise.
In the above described embodiments, since the insulating layers are
piled stepwise, strictly speaking the upper surfaces of the
conductive slips are at different levels above the upper surface of
the base 10. In other words, the printing surface of the head is
not strictly flat or plane but rugged. The insulating layers are so
thin that the above-mentioned difference in level may be small.
However, when the printing surface of the head is applied onto a
sheet of thermally sensitive paper, the contacting pressure may
differ at different parts of the contacting surface of the head,
with resulting unevenness or obscruity in the print obtained.
To solve the problem, a projection made of a thermally conductive
material may be provided on those portions of the upper conductive
slip on each of the insulating layers to which heat is transferred
from the resistive elements beneath the slip, that is, those
portions of the upper conductive slip which overlap the exposed end
portions of the lower conductive slips on each of the insulating
layers. The upper surfaces of the projections on different
insulating layers are at substantially the same level above the
upper surface of the base 10.
In FIG. 6 the whole upper surface of the printing head except for
those portions at which the above-mentioned projections are to be
provided is first covered by an insulating layer 41 by the method
of screen printing, and then a metallic bump 42 is fixed in each of
the portions on which there is no overlying insulating layer
41.
In FIG. 7 a projection 43 is formed without initially forming no
such overlying insulating layer as 41 in FIG. 6. The projection 43
comprises three layers 44 of a metallic material screen-printed
three times on the upper conductive slip 3A. As previously
mentioned, all the bumps 42 or projections 43 are so formed that
their upper surfaces are at the same level.
In the illustrated embodiments, the printing head is designed so as
to print a single symbol or character. In order to print a
plurality of symbols at one time, a plurality of matrices each
comprising any one of the illustrated constructions may be arranged
side by side. In this case it is possible to use the insulating
layers and the upper conductive slips or sheet in common with
different matrices.
* * * * *