U.S. patent number 3,848,720 [Application Number 05/394,245] was granted by the patent office on 1974-11-19 for pressure spring for a thermoprinter.
This patent grant is currently assigned to Contex Calculators A/S. Invention is credited to Henning Gunnar Carlsen.
United States Patent |
3,848,720 |
Carlsen |
November 19, 1974 |
PRESSURE SPRING FOR A THERMOPRINTER
Abstract
A thermoprinter for use, for example, in electronic table
calculators and curve recorders, in which a thermosensitive
recording strip is advanced step by step across a printing plate
having a line of type of an electric resistance material, which are
selectively energizable by heating current, and is pressed into
contact with the printing plate during the printing of each line by
a pressing device including a leaf spring extending across the
printing plate with such a curvature in its unloaded condition that
a convex lateral surface of the spring faces the printing plate,
said leaf spring being relieved from the pressure contact when the
carrier is to be advanced by an actuator forming part of the
advancing mechanism and applying local bias forces in the direction
away from the printing plate in points on the leaf spring situated
at a short distance from either end thereof.
Inventors: |
Carlsen; Henning Gunnar
(Aalbaek, DK) |
Assignee: |
Contex Calculators A/S
(Birkerod, DK)
|
Family
ID: |
8101839 |
Appl.
No.: |
05/394,245 |
Filed: |
September 4, 1973 |
Foreign Application Priority Data
Current U.S.
Class: |
101/487; 101/408;
101/480; 346/136; 347/197 |
Current CPC
Class: |
B41J
25/312 (20130101) |
Current International
Class: |
B41J
25/312 (20060101); G01d 015/10 () |
Field of
Search: |
;197/1R,144 ;101/1,408
;346/76R ;219/216 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Crowder; Clifford D.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
What I claim is:
1. A thermoprinter comprising
a supporting frame;
a printing plate mounted in said supporting frame and including a
line of typing means of an electric resistance material for
printing line by line on a thermosensitive recording strip and
means for selectively supplying heating current to said typing
means;
pressing means for pressing said strip into contact with said
printing plate during the printing of each line, said pressing
means including a holder connected with said supporting frame, a
leaf spring supported at its end in said holder in operative
relation to the printing plate and extending in the line direction
thereof with such a curvature in its unloaded condition that a
convex lateral surface of the leaf spring faces the printing plate,
and means for locking said holder to said supporting frame in a
position in which said leaf spring is pressed against the printing
plate with a substantially uniformly distributed pressure in the
length direction of the leaf spring;
and an advancing mechanism for stepwise advancing said strip across
the printing plate, said mechanism including actuator means for
applying local bias forces in the direction away from the printing
plate in points on said leaf spring situated a short distance from
either end thereof supported in said holder, whereby the leaf
spring is relieved from pressure contact with the printing plate
when said strip is to be advanced.
2. A thermoprinter as claimed in claim 1, wherein the lateral
surface of the leaf spring facing the printing plate is provided
with a layer of a pressure-distributing material the extension of
which in the longitudinal direction of the leaf spring corresponds
to at least the maximum line length of the printer.
3. A thermoprunter as claimed in claim 2, wherein said pressure
distributing material is a felt-like textile material.
4. A thermoprinter as claimed in claim 2, wherein said pressure
distributing material is a velvet-like textile material.
5. A thermoprinter as claimed in claim 1, wherein the leaf spring
is supported in said holder so as to be pivotable through a small
angle about its longitudinal axis.
6. A thermoprinter as claimed in claim 1, wherein said holder is
provided with bearings for detachably mounting the ends of said
leaf spring.
7. A thermoprinter as claimed in claim 1, wherein said advancing
mechanism comprises an electromagnetic actuator.
8. A thermoprinter as claimed in claim 7, wherein means are
provided for energizing said actuator for advancing said strip and
relieving said leaf spring from pressure contact with the printing
plate immediately subsequent to the printing of each line on the
strip.
Description
The present invention relates to a thermoprinter of the type in
which a printing plate with controllable circuits actuates a
thermosensitive recording material line by line, said recording
material being advanced step by step across the printing plate by
means of an advancing mechanism and being pressed against the
printing plate during the recording process by a pressing
means.
Thermoprinters can be utilized in connection with many different
devises, for example, for writing out measuring and calculating
results. With the present-day continuous technological advances,
ever-increasing demands are made with respect to the speed of
printing and the uniformity of the blackening of the printed
characters while, at the same time, increasing demands for a
reduction in the noise level are also put forward.
It is known that the printing speed is increased and the uniformity
of the blackening is improved if, in the writing out process, the
total number of figures or other individual characters or symbols
in a line are written out in two or more stages in stead of being
printed one by one, by employing types for the recording which are
composed of a few uniform type segments that are constructed as
electric resistors, e.g., by thin film technology, having a shape
corresponding to the type segments desired. The individual types on
the printing plate may be composed identically of the same number
of type segments and the printing of a symbol in the form of a
given figure is then carried out by actuating the segments of the
type in question corresponding to the shape of this figure.
When writing out line by line in the above-mentioned manner
energization will first take place of those resistors in all the
types located on a line on the printing plate which, in each
character, cause specific, uniform elements to be written and,
subsequently other resistors are energized which, in each type,
cause other, specific type elements to be written and so forth,
until every single character in the line has been built up and
recorded. Since the electric signals necessary for scanning the
character elements are fed into a store, the scanning of the
characters in a line is carried out electronically and at such a
fast rate that no significant loss of time occurs. Moreover, by
arranging the writing out process in such a way that -- in
successive stages within the individual types -- type segments are
energized with the longest intervals feasible, a good heat
distribution in the printing plate is attained during the recording
process.
As the recording is effected by means of heat transfer from the
electric resistors on the printing plate to the thermosensitive
recording material, it is desirable to have a direct mechanical
contact between the printing plate and the recording material, the
electric resistors being, however, covered with a wear -- resistant
layer such as quartz, which can be applied by a sputtering process,
in order to reduce wear and tear.
The thermosensitive recording material normally consists of paper
which is provided on one side with a thermosensitive coating which,
in case of local heat transfer contact with a type segment
constructed as an electric resistor, melts or evaporates on the
spot in question. In order to obviate that the thermosensitive
coating material is hereby deposited on the printing plate which --
in the course of time may result in a substantial non-uniformity of
the blackening due to the differences in the frequency with which
the individual types on the printing plate are used for recording,
provision is normally made for the thermosensitive coating of the
recording paper to face away from the printing plate. As a matter
of fact, it is possible to obtain a satisfactory recording by the
action of heat from the back of the paper when using a suitably
thin recording paper material.
It has been found, however, that even when taking such
precautionary measures, there is nevertheless a tendency for
disparities to occur in the blackening and it is the solution of
this problem which is the subject-matter of the present
invention.
The invention is based on the recognition of the fact that the
problem is chiefly to be sought in the pressing means which, in
prior art thermoprinters, is constituted of a rigid rail member of
a pivotable, frame-shaped holder which, precisely with a view to
obtaining a good and uniform contact with the printing plate is of
strong construction and is actuated by a relatively powerful
spring, against the spring force of which the frame has to move
when the pressure on the paper is relieved in order to advance the
paper.
The thermoprinter according to the invention is characteristic in
that the pressing means is a leaf spring supported at its ends in a
holder, said spring having in its unloaded condition a curvature
with the convex lateral surface facing towards the printing plate
and being adapted for being biased in the direction away from the
printing plate at a short distance from the supporting
elements.
It has been found that by this measure the above-mentioned drawback
of contrast differences disappears and simultaneously the necessary
secure and uninterrupted contact with the printing plate is
achieved during the recording process. In the thermoprinter
according to the invention, the relief and springing movements are
left solely to the pressing means proper which is self-adjusting in
its longitudinal direction. Thus, only the leaf spring is moved
during the operation. The result of this is that the masses to be
accelerated and retarded become significantly smaller, which is
also reflected in a substantial noise level reduction.
In an expedient embodiment of the thermoprinter according to the
invention the leaf spring is fitted in the holder so as to be
rotatable a small angle around its longitudinal axis. Hereby it
becomes self-adjusting not only in the longitudinal direction but
also in the transverse direction. In addition, the leaf spring is
preferably detachably mounted so that it can be easily replaced.
This is particularly important if the spring is coated with a
softer material that is susceptible to damage or ageing. Such
damage may occur, for instance, if the thermoprinter is operated
without any recording material so that the soft material, e.g.,
felt or foam plastic, burns or melts when coming into contact with
the heated printing plate or as a consequence of contact between
said soft material and the prepared side of the recording
material.
In another expedient embodiment of the thermoprinter according to
the invention the leaf spring is adapted for actuation by an
electromagnetic activator.
As the recording material is released to be advanced by a slight
movement of the leaf spring it is preferred according to the
invention that the actuating mechanism be adapted to be controlled
in such a way that the pressing means is relieved as soon as
recording has been effected on the thermosensitive material.
Moreover, this results in the advantage that the softer,
pressure-equalizing material on the leaf spring is automatically
relieved when the thermoprinter is inoperative so that a permanent
deformation of this material during prolonged rest periods is
avoided.
The invention will now be explained in greater detail with
reference to the accompanying drawings, in which
FIG. 1 is a perspective view of the parts of an embodiment of a
thermoprinter according to the invention which are necessary for
understanding the invention,
FIGS. 2, 3 and 4 show the interaction between a printing plate and
a pressing means for the recording material in FIG. 1 in a purely
schematic manner,
FIG. 5 is a schematic sectional view illustrating an actuating
mechanism for advancing the recording material and relieving the
pressing means,
FIG. 6 shows a drive means for the actuating mechanism in FIG.
5,
FIG. 7 shows a supporting element for the pressing means, and
FIG. 8 shows a modification of the actuating mechanism in FIG.
5.
The recording process in the thermoprinter shown in FIG. 1 which is
intended to be employed in an electronic table calculator, is
carried out in that a thermosensitive recording material -- which
is not shown in FIG. 1 -- while being advanced step by step, is
kept in contact line by line with a printing plate 1 having a
plurality of character types arranged thereon in alignment, as
shown with dotted lines at 2. Each character type in the embodiment
shown consists of seven rectilinear elements of electric resistance
material which, in combination, form two squares located above one
another so that the character type has the shape of a square figure
eight whereby it becomes possible, with such a type, to print any
figure in the decimal system by supplying current to different
combinations of the rectilinear type elements. The recording
material may, for example, be paper which is prepared on one side
with a material that evaporates locally when it is exposed by
current being supplied to a type element to heating at the point in
question, whereby a blackening of the material takes place.
In order to avoid to the greatest extent possible contrast
differences stemming from the varying background heating of the
printing plate, which are caused by the fact that a different
number of type elements are utilized for printing different
figures, the printing process may be divided into two or more
stages as mentioned in the foregoing in each of which current is
supplied to resistor elements forming identical type elements of
the types. By way of example, those type elements located in upper
half of all types which are intended to be printed may be energized
in a first stage and, in a subsequ3nt stage, energization of the
type elements intended for printing which are located in the lower
half of the types can take place together with energization of one
out of a number of additional resistor elements (not shown) located
between the character types so as to produce a decimal comma.
Thereby, a substantially inform heating of the printing plate is
achieved during said recording stages.
As mentioned in the foregoing, the printing plate is constructed by
employing known thin film technology and is provided, in addition
to the character elements, with controllable electric circuits for
selectively energizing the character elements. The character
elements and said circuits can be applied to a supporting plate by
means of a vapour deposition or sputtering process. In order to
protect the resistance elements and to reduce wear and tear, the
printing plate may be provided with a wear-resistant surface layer
consisting of, for example, a quartz layer applied by
sputtering.
In the embodiment shown of the thermoprinter the printing plate is
in contact during the recording process with the unprepared side of
the recording paper so that the atomic components of the
preparation evaporated during the printing process cannot attack
the printing plate.
In order to obtain a good contact between the recording paper and
printing plate 1 the thermoprinter is equipped with a pressing
means which, according to the invention, is constituted by a leaf
spring 3 which is supported at its ends in a frame-shaped holder 4
and is adapted to be actuated during paper advancement in a
direction away from pressing plate 1 at a short distance from the
supporting elements.
The interaction between printing plate 1 and pressure spring 3
appears from FIGS. 2-4. FIG. 2 shows the pressure spring in its
unloaded condition, in which holding frame 4 is pivoted away from
the printing plate, said holding frame being pivotably connected by
means of a shaft 5 to the side plates of the thermoprinter as shown
at 6, and being locked in said unloaded condition relative to said
side plates with the aid of snap means, as shown with dotted lines
at 7, engaging locking flanges which project perpendicularly from
the side plates as shown with dotted lines at 8. It appears from
FIG. 2 that the pressure spring is shaped so as to have, in said
unloaded condition, a curvature with the convex lateral surface
facing towards the printing plate.
In FIG. 3, pressure spring 3 is shown in contact with printing
plate 1. In order to ensure pressure equalization over the entire
printing width, the spring is provided on the side facing towards
printing plate 1 with a coating 9 of a soft material, e.g., a felt
or velvet-like textile material.
In the condition illustrated in FIG. 4 pressure spring 3 is
subjected to biasing forces in the direction away from the printing
plate at a short distance from each of its ends supported in holder
4 by means of actuating arms 10 forming parts of an actuating
mechansim described in the following in order to effect paper
advancement. As a consequence of this biasing, the spring acquires
a curvature with the concave lateral surface facing towards
printing plate 1.
As shown in FIG. 5 each of actuating arms 10 constitutes one arm of
a two-armed lever which is rotatably supported on a through shaft
11 upon which a paper advancing roller 12 is mounted. The other arm
13 of the lever which forms an angle of approximately 90.degree. to
arm 10 is provided of its outer end with a flange 14 acting as a
cam follower by being engaged by a cam disc 15 which is rigidly
mounted on a drive shaft 16 which can be turned by a driving means
described in the following through an angle of approximately
75.degree. between the positions shown in solid and dotted lines,
respectively, in FIG. 5.
The circumference of cam disc 15 describes approximately a quarter
ellipse limited by a minor axis half and a major axis half. In the
position shown in solid lines, cam follower flange 14 is located
opposite the portion of the cam disc circumference at the minor
axis so that pressure spring 3 is not biased by actuating arm 10.
In the position shown in dotted lines, cam follower flange 14 is
resting on the portion of the cam disc circumference at the major
axis, whereby actuating arm 10 biases the pressure spring in the
direction away from the printing plate as shown in FIG. 4.
In addition, a pivot arm 17 is rigidly connected with cam disc 15,
said arm constituting one part of a two-armed crank connection, the
second part of which consists of an arm 18 which is connected in
one end with the free end of pivot arm 17 and engages in its
opposite end one end 19a of a coil spring 19 wound around advancing
roller shaft 11. By turning cam disc 15 from the position shown in
solid lines to the position shown in dotted lines, spring end 19a
is moved to the right-hand side of arm 18 in FIG. 5, whereby spring
19 is tightened and turned together with shaft 11. The rotation is
restricted by the other end 19b of spring 19 impinging upon a stop
flange 20 projecting from side plate 5. By returning cam disc 15 to
the position drawn in solid lined, spring 19 is again relieved from
driving engagement with shaft 11 and turned back into the starting
position without participation of shaft 11 in this return movement
due to the fact that roller 12 is subjected through the recording
paper, to pressure from a plurality of resilient paper pressing
elements 21 mounted on shaft 5 in holder 4.
As illustrated in FIG. 6, the driving means for cam disc shaft 16
comprises two electromagnetic activators 22 and 23 having U-shaped,
lamellated soft iron yokes 24 and 25 the legs of which carry
series-connected coils 26, 27 and 28, 29, respectively, and at the
ends of which legs pole pieces are formed with circular recesses
matching the terminal faces of two lamellated soft iron armatures
30 and 31, respectively, which are rigidly secured on shaft 16.
Armatures 30 and 31 are mounted in such a way on shaft 16 that
their planes of symmetry through the shaft are mutually displaced
by an angle of approximately 75.degree. so that, in the position
shown in which armature 30 has its terminal faces located in
recesses in yoke 24, armature 31 assumes a position in which a
small portion of its terminal face extends into the recess in
25.
The position shown in FIG. 6 corresponds to the solid line position
of the actuating mechansim shown in FIG. 5 in which pressure spring
3 presses the recording paper against printing plate 1. When the
actuating mechanism in FIG. 5 is to be activated for paper
advancement and for biasing pressure spring 3 in the direction away
from printing plate 1, the coils 28, 29 on yoke 25 are supplied
with current while coils 26, 27 are without current whereby
armature 31, under the influence of the magnetic field produced, is
turned in the direction of the arrow into the position which, in
the figure, is shown for the other armature 30, and hereby shaft 16
and cam discs 15 are turned through an angle of approximately
75.degree. into the position shown by dotted lines in FIG. 5. When
a recording is once more to be made, current is supplied to coils
26, 27 while coils 28, 29 are de-energized, whereby the position
shown in FIG. 6 is reassumed. When no current is supplied to either
coils 26, 27 or coils 28, 29, armatures 30 and 31 and, thereby,
shaft 16, assume a position determined by that activator 22 and 23
which was energized last.
According to the invention, the energization of activators 22 and
23 may advantageously be effected in such a way that, in the
inoperative periods of the device, pressure spring 3 will
invariably assume the condition shown in FIG. 4 so that deformation
of the recording paper during a prolonged rest period is avoided,
which means that the individual components of the actuating
mechanism will -- as a rest position -- assume the position shown
in dotted lines in FIG. 5. This can be achieved by arranging the
operating cycle of the recording process in such a manner that,
prior to the actual recording period where the printing elements
are actuated, there comes a period in which activator 22 is
energized so that the actuating mechanism is made to assume the
position shown in solid lines in FIG. 5 whereby pressure spring 3
is brought into the position shown in FIG. 3 and, immediately
subsequent to the recording period, there follows a period in which
activator 23 is energized so as to bring pressure spring 3 into the
position shown in FIG. 4 and to turn roller 12 one step.
With respect to the working speed of the thermoprinter it has been
found that 20 msec are available for each of the said actuation
periods since the remaining part of the total working cycle is
taken up by the recording process proper. In this connection, it is
a significant advantage of the thermoprinter according to the
invention that only small masses have to be moved and retarded when
removing the pressing means from the printing plate and returning
it into contact with the plate, that is to say, the masses of the
pressure spring 3 and the elements of the actuating mechanism which
may be constructed chiefly of light-weight materials, whereas the
movement of the relatively heavy holder 4 is avoided.
Since the coating 9 of pressure spring 3 is of soft material which,
in the course of time, may age and is also exposed to damage due to
the contact with the prepared side of the recording paper, the
spring in embodiment shown is mounted to be easily removable from
holder 4 in order to be replaceable in that its ends are supported
in nylon bearings 32 as shown in FIG. 7, which bearings are
inserted into recesses in the frame-shaped holder 4 as shown in
FIG. 1. Each of bearings 32 has an insertion aperture 33 the width
of which is greater than that of the leaf spring, said aperture
having in the central part of one of its longitudinal lateral faces
a projection 34. Thereby, it is achieved that the spring 3 mounted
in bearings 32 is rotatable through a small angle around its
longitudinal axis for ensuring pressure equalization in the
transverse direction of the spring.
FIG. 8 shows purely schematically a modification of the actuating
mechansim in FIG. 5, in which actuating arm 10' serving to bias
pressure spring 3 in the direction away from printing plate 1, and
a corresponding actuating arm on the opposite side of the
thermoprinter, are interconnected via a through flange portion 35
and are pivotably journalled on a shaft 36 which is mounted in the
side walls of the thermoprinter. Like the embodiment shown in FIG.
5, actuating arm 10' in FIG. 8 constitutes one arm of a two-armed
lever, the other arm 13' of which is constructed with a flange 14'
functioning as a cam follower by being engaged by a cam disc 15'
which is rigidly mounted on a drive shaft 16' which may be driven,
for example, by electromagnetic activators of a structure as shown
in FIG. 6. The shape of cam disc 15' in FIG. 8 corresponds to that
of the cam disc in FIG. 5, and by turning cam disc 15'
counter-clockwise from the position shown in FIG. 8, actuating arm
10' will be actuated to move pressure spring 3 away from printing
plate 1 and simultaneously cam disc 15' rotates advancing roller 11
through a crank and spring transmission in the same way as shown in
FIG. 5.
Compared to the embodiment in FIG. 5, the modification shown in
FIG. 8 has the advantage that cam disc 15' and lever 13 are present
only at one side of the thermoprinter the actuating arm at the
opposite side being actuated via through flange 36. It has been
found that this embodiment of the actuating mecahnism results in
reduced wear and tear of the movable parts, particularly the
actuating arms and their supporting elements as compared to the
construction shown in FIG. 5.
Even if the thermoprinter has been described in the foregoing with
reference to its utilization in electronic table calculators, it
will be apparent that the present invention is applicable also to
thermoprinters intended for curve recorders etc. Moreover, it will
be possible within the scope of the invention to bias the pressure
spring in other ways than by means of the actuating mechansims
described.
* * * * *