Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
`- 20 1 9265
THERMAL HEAD DEVICE
This invention relates to a thermal head device for
facsimile machines and the like, and more particularly to
a thermal head with an improved positioning means.
Conventional thermal head devices will be described
hereinbelow in conjunction with the drawings.
The present invention has been achieved with a view
to solving the above-mentioned problem of the prior art,
and has as its object the provision of a thermal head
device which can prevent deviations of the heating
element of the thermal head from the center axis of the
platen roller to guarantee production of prints of
satisfactory quality.
It is another object of the present invention to
provide a thermal head device employing a positioning
means which is far improved as compared with existing
counterparts in positioning accuracy and performance
quality and yet feasible at a relatively low cost.
It is a further object of the invention to provide a
thermal head device which permits improved positioning
accuracy without entailing complication or enlargement of
size of the thermal head device itself.
In order to achieve these objectives, the thermal
head device according to the present invention includes a
thermal head with a heating element, a platen roller held
in abutting engagement with the heating element of the
thermal head for scanning recording paper fed
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therebetween, and a positioning means mounted astride of
the rotational shaft of the platen roller for positioning
the heating element in alignment with the center axis of
the platen roller, the thermal head device being
- 5 characterized by the provision of a preload means adapted
to urge the positioning means into abutting engagement
with the shaft of the platen roller to preclude
fluttering motions or backlashes of the thermal head in
operation.
Namely, the thermal head device according to the
invention is provided with a preload means which holds
the positioning means in abutting engagement with the
platen roller in operation thereby maintaining the
heating element in a constant position relative to the
axis of the platen roller to ensure prints of
satisfactory quality.
The above and other objects, features and advantages
of the invention will be more fully understood from the
following particular description of the invention and the
appended claims, taken in conjunction with the
accompanying drawings, which are given for the purpose of
illustration only and therfore should not be construed as
limitative of the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
Figs. lA to lC are schematic sectional and enlarged
views of a conventional thermal head device;
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,
Figs. 2A to 2C are schematic sectional and enlarged
views of a thermal head device according to one
embodiment of the present invention; and
Fig. 3 is a schematic sectional view of a thermal
head device according to another embodiment of the
invention .
A conventional thermal head device is shown in
schematic sectional and enlarged views in Figs. lA to lC.
In these figures, numeral 1 designates a thermal head, 2
a heating element of the thermal head 1, 3 a platen
roller to be abutted against the heating element 2, 4 the
shaft of the platen roller 3, 5 a collar assembled on the
roller shaft 4, 6 a positioning member which is fixedly
secured to the thermal head 1 and abutted against the
collar 5 at its inner surfaces 6a and 6b to position the
heating element 2 of the thermal head 1 in alignment with
the axis of the platen roller 3, 7 a compression spring
serving to press the thermal head 1 against the platen
roller 3, 8 a frame, 9 recording paper which is driven by
the platen roller 3 and printed by the thermal head 1, W
the width of the positioning member 6, dl the outside
diameter of the shaft 4, d2 the inside diameter of the
collar 5, and d3 the outside diameter of the collar 5.
The collar 5 is formed of a material which is softer than
the shaft 4, and not rotatable during operation.
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Next, the operation will be described. By the
pressing force of the spring 7 acting on the thermal head
1, the platen roller 3 and recording paper 9 are held in
abutting contact with each other uniformly in the
longitudinal direction of the thermal head 1 or in the
direction perpendicular to the face of Fig. 1. The
spring 7 exerts a pressing force in the direction of
arrow Y to hold the thermal head 1 and platen roller 3
against fluctuating motions which might result from
rotation of the platen roller 3 by a drive source, which
is not shown, or from scanning of the recording paper 9,
for the purpose of enhancing the printing performance
quality together with the above-mentioned uniform
abutting contact.
As shown in Fig. 1, when the platen roller 3 is
rotated in the direction of arrow Z, the recording paper
9 is driven in the direction of arrow X and printed with
characters by the heat which is generated by the heating
element 2 according to signals from a heat controller,
not shown.
In the drawings, the anti-rotation mechanism for the
thermal head 1 is omitted for the sake of simplicity of
illustration.
For determining the position of the thermal head,
the conventional device resorts to the positioning member
6 which has its inner surfaces 6a and 6b abutted against
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201 9265
the collar 5 on the platen roller 4. Due to the
existence of gap spaces in the mechanism, this
arrangement has a problem that the thermal head 1 is put
in fluttering motions during operation as a result of
S deviations from the center axis of the platen roller 3 by
an amount corresponding to:
(1) the difference between the outside diameter dl
of the platen roller shaft 4 and the inside diameter d2
of the collar 5; and
(2) the difference between the outside diameter d3
of the collar 5 and the width W of the positioning member
6.
Consequently, in case of intermittent facsimile
recording operations in or the like, the fluttering
motions cause fluctuating deviations of the heating
element 2 from the center axis of the platen roller 3,
impairing the quality of the print to be produced.
A preferred embodiment of the invention will be
described in detail referring to accompanying the
drawings.
Referring to Figs. 2A to 2C, there is shown an
embodiment of the thermal head device according to the
invention in schematic sectional and enlarged fragmentary
views, in which the component parts common to the prior
art counterpart of Fig. 1 are designated by common
reference numerals and their description is omitted to
avoid repetitions.
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In these figures, numeral 8b designates a frame,
and 10 a spring which is employed as a preload means for
biasing the thermal head 1 in the direction of arrow X.
The spring 10 which is provided between the frame 8b and
thermal head 1 pushes the thermal head 1 in the direction
of arrow X in such a manner as to substantially zeroing
gap spaces in the mechanism including the gap space
between shaft 4 and the collar 5 and the gap spaces
between the collar 5 and the positioning member 6. As a
result of application of the pressing force of the
spring 10 urging the thermal head 1 in the rightward
direction in the drawing, the inner surface 6b of the
positioning member 6, collar 5 and platen roller shaft
4 are tightly abutted against each other without leaving
a play gap therebetween. Namely, the pressing force of
the spring 10 directly acts on the thermal head 1 to
hold same against the shaft 4 of the platen roller 3
through the collar 5 for positioning the heating element
2 relative to the platen roller 5.
Next, operation of this thermal head with the
above-described construction will be described.
If the platen roller 3 is turned in the direction
of arrow Z by a drive source which is not shown, the
recording paper 9 is driven in the direction of arrow X
since the thermal head 1 is pressed in the direction of
arrow Y by the spring 7. At this time, as the thermal
head 1 which is preloaded in the direction of arrow X
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by the spring 10, the inner surface 6b of the
positioning member 6 is tightly abutted against the
platen roller shaft as explained hereinbefore.
Accordingly, even in intermittent recording operations,
the preload means suppresses the fluctuating deviations
of the heating element 2 of the thermal head 1 from the
center axis of the platen roller 3, holding the heating
element 2 in a constant position relative to the platen
roller 3 to ensure prints of satisfactory quality.
Instead of applying the thermal head 1 with a
preload in the direction of arrow X by the spring 10 as
in the foregoing embodiment, there may be employed an
arrangement in which the thermal head 1 is preloaded in
an oblique direction (in the direction of arrow H) as
-shown in Fig. 3 by the use of a spring 7a. In this
case, the thermal head 1 is preloaded in the direction
of arrow X by the component force I of the spring 7a to
produce the same effects as in the first embodiment.
Further, a tension spring may be employed as a
preload means in place of the compression spring 7a or
10 in the foregoing embodiments. Similar effects can be
obtained by a preload means in the form of a tensile or
compression spring which is provided in the first
quadrant instead of locating same in the second quadrant
as in the particular embodiments shown.
As clear from the foregoing description, the
thermal head according to the present invention ensures
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production of prints of satisfactory quality by the
provision of the preload means which is adapted to abut
the head positioning means against the platen roller
shaft in such a manner as to maintain the heating
element of the thermal head in a constant position
relative to the center axis of the platen roller.
The preload means which suffices to have simply a
function of biasing the head positioning means in a
predetermined direction can be realized at a low cost.
For the reasons stated above, the present invention
makes it possible to provide a simple and compact
thermal head.
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