Thermal printer

A thermal printer which is designed to reduce costs by reducing the number of parts, and which can easily drive a carriage using an inexpensive low-power drive motor by reducing a load acting on the part of the carriage which carries a thermal head. The carriage is provided so as to travel reciprocatively along a platen. A thermal head is directly attached to the opposite side of the carriage to the platen without any intervening member. A biasing member is disposed for urging the carriage toward the platen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermal printer which records 
information on a recording medium, such as thermal sensitive paper, with a 
thermal head and, more particularly to, a thermal printer suitable for use 
with a recording type electronic desk-top calculator or an electronic cash 
register. 
2. Description of the Prior Art 
Recently, electronic desk-top calculators and electronic cash registers 
(ECR) are equipped with a small thermal printer which directly records 
information on a printing medium with a thermal head. A more compact and 
high-performance thermal printer of that type has been desired without an 
increase in price. 
A conventional thermal printer 1 is constructed as shown in FIGS. 13 and 
14. As can be seen from the drawings, a platen attachment section 8 is 
formed on a back frame 5, that is, a back frame of the thermal printer 1, 
so that a platen 7 can be attached to the platen attachment section 8. A 
support shaft 15 is supported by side frames 6L and 6R in parallel with 
the platen 7 in the vicinity of the front bottom of the platen attachment 
section 8. A carriage 14 is fitted around this support shaft 15 in such a 
way as to reciprocally travel along the platen 7. A worm fitting section 
16 is formed into a recess at the lower part of the carriage 14 for 
receiving a worm 17 which drives the carriage 14. The carriage 14 is also 
provided with two projections at both lower corners of the carriage 14 on 
the platen 7 side. The projections constitute respective supporting 
sections 40, where through-holes 41 are formed. The support shaft 15 
passes through the through-holes 41, so that the carriage 14 is supported 
so as to be able to travel as the worm 17 moves. Further, an opening (not 
shown) is formed in the surface of the carriage 14 facing the platen 7, 
and a coil spring 42 which acts as a biasing member is fitted into that 
opening for pressing the thermal head 10 against the platen 7. 
A flat thermal head mounting unit 44 is attached between the supporting 
sections 40 of the carriage 14 so as to face the plate 7 and to rotate 
around the support shaft 15. The thermal head 10 is attached to the 
thermal head mounting unit 44 at the position opposing to the platen 7. An 
opening 43 is formed in the surface of the thermal head mounting unit 44 
facing the carriage 14 for receiving the coil spring 42. The spring coil 
42 is fitted between the opening 43 formed in the thermal head mounting 
unit 44 and the opening (not shown) formed in the carriage 14, so that the 
thermal head mounting unit 44 is rotated around the support shaft 15 by 
means of a biasing force of the coil spring 42. As a result of the 
rotation of the thermal head mounting unit 44, the thermal head 10 
attached to the thermal head mounting unit 44 is pressed against the 
platen 7. 
A carriage drive shaft 18 is rotatively supported by the side frames 6L and 
6R in parallel with the platen 7 for transmitting torque from the drive 
motor 28 which is a drive source of the carriage 14. The worm 17 is 
connected to the carriage drive axis 18 by means of a spline. A rack plate 
20 having rack cogs 20a formed thereon is provided on the base frame 2 in 
parallel with the carriage drive shaft 18, so that the rack cogs 20a mesh 
with the worm 17. 
Projecting cams 13a and 13b are formed on both ends of the platen 
attachment section 8, that is, they are positioned outside the area in 
which the thermal head 10 can carry out a printing operation. The cam 
sections 13a and 13b include end edges 11a and 11b which project from the 
platen attachment section 8 toward the carriage 14 in parallel with the 
direction of movement of the carriage 14. The projecting cams 13a and 13b 
further include tapered portions 12a and 12b which are tapered in parallel 
with the direction of the movement of the carriage 14 so as to extend 
between the respective end edges 11a and 11b and the vicinity of the ends 
of the platen 7. With this structure, if the thermal head 10 carries out a 
printing operation beyond the printable range, the thermal head mounting 
unit 44 travels along the tapered portions 12a and 12b of the cams 13a and 
13b against the biasing force of the coil spring 42 as the carriage 14 
moves, whereby the thermal head 10 is moved away from the platen 7. 
The operation of the conventional thermal printer having the above 
mentioned structure will next be described. 
Upon receipt of torque imparted from the drive motor for driving the 
carriage 14 via a torque transmission means 50, the carriage drive shaft 
18 rotates, which in turn starts the rotation of the worm 17. Since the 
worm 7 meshes with the rack cogs 20a formed on the rack plate 20, it 
travels reciprocatively along the rack plate 20. Together with this 
movement, the carriage 14 starts to travel reciprocatively along the 
platen 7 while being supported by the support shaft 15. The thermal head 
mounting unit 44, rotatively attached to the support shaft 15 between the 
supporting sections 40 of the carriage 14, is constantly urged toward the 
platen 7 by the biasing force of the coil spring 42, so that the thermal 
head 10 attached to the thermal head mounting unit 44 is pressed against 
the platen 7 with a recording medium, e.g., heat sensitive paper, between 
them. The thermal head 10 prints one line on the heat sensitive paper 
within the printable range by heating a heating section (not shown) 
according to a predetermined print command. Subsequently, if the thermal 
head 10 moves beyond the printable range, the thermal head mounting unit 
44 travels along the tapered portions 12a and 12b of the cams 13a and 13b 
while being rotated toward the carriage 14 against the biasing force of 
the coil spring 42 as the carriage 14 moves. As a result, the thermal head 
10 is moved away from the platen 7. When the thermal head mounting unit 44 
reaches the end edges 11a and 11b of the cams 13a and 13b, the carriage 14 
stops moving, and the heat sensitive paper is fed by a feed roller (not 
shown). When the heat sensitive paper is fed, the drive motor starts to 
reversely rotate, so that the torque is transmitted to the carriage drive 
shaft 18 via the torque transmission means. As a result, the carriage 
drive shaft 18 also starts to rotate reversely, thereby causing the 
carriage 14 to move in the opposite direction. Then, the thermal head 10 
repeats printing operations in the manner as previously mentioned until a 
desired printing operation is completed. 
In the foregoing conventional thermal printer 1, the carriage 14 merely 
moves the thermal head 10 in parallel with the platen 7. In order to move 
the thermal head 10 toward the platen 7 and to press it against the front 
face of the platen 7, it is necessary to separately provide the thermal 
head mounting unit 44 that can pivot toward the platen 7 while having the 
thermal head 10 attached thereto. Further, in order to move the thermal 
head mounting unit 44 and the carriage 14 in an integrated fashion, the 
thermal head mounting unit 44 must be rotatively fitted around the support 
shaft 15 to which the carriage 14 is also fitted. The thermal head 
mounting unit 44 must be provided with two projecting supporting sections 
40, each having the through-hole 41 respectively formed therein, so that 
the support shaft 15 passes therethrough. Furthermore, it is necessary to 
form the fitting opening 43 and the counterpart opening in the thermal 
head mounting unit 44 and the carriage 14, respectively, for receiving the 
coil spring 42. With all the requirements described above, the 
conventional thermal printer 1 has such a problem that additional costs 
are incurred by manufacturing the thermal head mounting unit 44 and the 
supporting sections 40 of the carriage 14 for receiving the thermal head 
mounting unit 44. 
When the carriage 14 travels along the tapered portions 12a and 12b of the 
cams 13a and 13b, the thermal head mounting unit 44 also moves while 
remaining in slidable contact with the tapered portions 12a and 12b of the 
cams 13a and 13b, as well as pivoting from the platen 17 toward the 
carriage 14 against the biasing force of the coil spring 42. As a result, 
the biasing force of the coil spring 42 is accordingly increased. 
In order to move the thermal head mounting unit 44 against the load imposed 
by the cams 13a and 13b, the carriage 14 must be driven by a drive motor 
with larger torque, which makes it impossible to use an inexpensive 
low-powered motor. 
SUMMARY OF THE INVENTION 
The present invention is conceived to reduce the number of parts and 
associated costs by integrating together a thermal head mounting unit and 
a carriage so that the carriage itself can be pressed against a platen by 
a biasing force of a biasing member. Another object of the present 
invention is to provide a thermal printer which can easily drive the 
carriage using an inexpensive low-power drive motor by reducing the load 
acting on the thermal head carrying portion of the carriage by means of a 
structure formed so as to reduce the biasing force of the biasing member 
which increases as the carriage carrying the thermal head travels along 
the cam. 
Still another object of the present invention is to provide a thermal 
printer comprising a carriage provided so as to be movable along the 
platen, a thermal head attached to the carriage so as to be opposite to 
the platen, and a biasing member for urging the carriage toward the platen 
to press the thermal head against the platen. 
A further object of the present invention is to provide a thermal printer 
comprising a leaf spring having one end fixed to the opposite side of the 
carriage to the side where the thermal head is attached and the other end 
remaining in slidable contact with a leaf spring abutment section formed 
on the base frame of the main body parallel to the direction of the 
movement of the carriage. The latter end moves reciprocatively while 
remaining in slidable contact with the leaf spring abutment section as the 
carriage travels reciprocatively. 
Still further object of the present invention is to provide a thermal 
printer comprising two cams formed in the vicinity of both ends of the 
platen outside a printable range of the thermal head so as to move the 
thermal head away from the platen against the biasing force of the leaf 
spring when the thermal head travels beyond the printable range as the 
carriage moves, and tapered sections formed in the leaf spring abutment 
section which are tapered in such a direction as to progressively reduce 
the biasing force of the leaf spring as the carriage travels along the 
cams towards their respective ends. 
In the present invention, the thermal head is directly attached to the 
carriage, and the thermal head is pressed against the platen by urging the 
carriage toward the platen using the biasing member. As a result, it is 
possible for the thermal head to carry out a printing operation with such 
a simple construction. 
Further, the biasing member is made up of the leaf spring, and one end of 
this leaf spring is fixed to the carriage while the other end thereof is 
in slidable contact with the leaf spring abutment section formed on the 
base frame of the main body. As a result, it is possible to urge the 
carriage toward the platen. 
According to the present invention, when the thermal head travels beyond 
its printable range as the carriage moves, the carriage travels along 
tapered portions of the cams on both ends of the platen against the 
biasing force of the leaf spring, thereby causing the thermal head to move 
away from the platen. In this event, the biasing force of the leaf spring 
is normally increased, and hence large torque becomes necessary to move 
the carriage because the load acting on the carriage becomes greater due 
to the increasing biasing force. However, in the present invention, the 
leaf spring travels along the tapered sections formed in the leaf spring 
abutment section which are tapered so as to reduce the biasing force of 
the leaf spring as the leaf spring approaches both ends of the leaf spring 
abutment section. For this reason, the biasing force of the leaf spring 
does not increase, and hence there is no need to increase the torque 
required to move the carriage. As a result of a spring tape cassette being 
set in a cassette housing, the torque transmission mechanism is connected 
to a platen drive gear for rotating a platen roller, and it is possible to 
deliver the torque from the motor to a platen roller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will now be described with 
reference to the drawings. 
FIG. 1 is a plan view showing the principal elements of a thermal printer 
according to a first embodiment of the present invention. FIG. 2 is a left 
side view showing the inside construction of the principal elements with 
some omitted. FIG. 3 is an exploded perspective view showing the 
construction of a carriage 14 and its surrounding. FIGS. 4 to 6 are 
explanatory views of the construction of the carriage 14 and its 
surrounding when a thermal head 10 is pressed against a platen 7. FIG. 7 
is a right side view showing the principal elements. FIG. 8 is an enlarged 
partial view showing the construction of a roller drive gear 24 and its 
surrounding. FIG. 9 is an explanatory view of the construction of torque 
transmission means 37. 
The same elements as those used in the description of the prior art are 
assigned the same reference numerals. 
As shown in FIG. 1, the thermal printer according to a first embodiment of 
the present invention has an external frame made up of a plurality of 
frames as a top face of a rectangular parallelepiped is opened. The frames 
include a base frame 2 which is disposed as the bottom of the frames. 
Among the frames, a face frame 3 comprising a rectangular plane is 
provided at a front side FS of the thermal printer 1 as it is shown in a 
lower part of FIG. 1. A record plane of heat sensitive paper 4 which 
serves as a recording medium can be visually recognized from the front 
side FS of the face frame 3. 
As shown in an upper part of FIG. 1, a back frame 5 having a substantially 
rectangular cross section is disposed on a back side BS from which the 
heat sensitive paper can be fed. This back frame 5 also serves as a platen 
attachment section 8 for receiving the platen 7. 
As shown in FIG. 1, a pair of side frames 6L and 6R are positioned on the 
both longitudinal ends of the base frame opposite to each other for 
supporting the front and back frames 3 and 5. 
A platen attachment recess 9 is formed at the longitudinal center of the 
front side FS of the platen attachment section 8, and a substantially 
planar platen 7 is attached to the recess. A pair of cams 13a and 13b are 
formed on respective longitudinal ends of the platen attachment section 8 
for bringing the thermal head 10 into or out of contact with the platen 7. 
These cams 13a and 13b project from the platen 7 side toward the carriage 
14. End edges 11a and 11b are formed on the respective cams 13a and 13b 
parallel to the direction in which the carriage 14 moves. Tapered portions 
12a and 12b are formed so as to extend from the respective end edges 11a 
and 11b to the platen mounting recess 9. The tapered portions 12a and 12b 
are tapered in the direction in which the carriage 14 moves. 
As shown in FIGS. 1 and 2, a support shaft 15 is provided at a lower 
portion of the front side FS of the platen 7 in such a way as to extend 
parallel to the platen 7 for supporting the carriage 14 so as to oppose 
the platen 7 at a desired position. Both ends of the support shaft 15 are 
held by the side frames 6L and 6R, respectively. The carriage 14 is 
pivotally attached to the support shaft 15 so as to rotate around the 
support shaft 15, as well as to longitudinally travel reciprocatively 
along the support shaft 15. 
The thermal head 10 is attached to the back side BS of the carriage 14 
shown in an upper part of FIG. 1 so as to be opposite to the platen 7. The 
thermal head 10 includes a plurality of heating elements (not shown) which 
are regularly arranged on the thermal head and are selectively heated on 
the basis of desired print information. The thermal head 10 is designed to 
print the information on the heat sensitive paper 4 held by the platen 7 
in a so-called head down condition, that is, while it is pressed against 
the platen 7. 
As shown in FIG. 3, an arched worm fitting section 16 is formed in the 
bottom of the carriage 14, and a worm 17 is fitted into this worm fitting 
section 16. The worm 17 is connected to a carriage drive shaft 18 by means 
of a spline. The drive shaft 18 has a substantially rectangular cross 
section and extends parallel to the support shaft 15. The carriage drive 
shaft 18 is rotatively supported by the side frames 6L and 6R. A carriage 
drive gear 19 for rotating the carriage drive shaft 18 is disposed at the 
right end of the carriage drive shaft 18 shown in FIG. 1 so as to be 
positioned outside (on the right side of) the side frame 6R. 
As shown in FIGS. 1 to 3, the base frame 2 positioned below the carriage 
drive shaft 18 is provided with a rack plate 20 which extends parallel to 
the carriage drive shaft 18. The rack plate 20 has rack cogs 20a formed 
thereon for engaging with the worm 17. 
Rotation of the carriage drive shaft 18 causes rotation of the worm 17 
connected to the carriage drive shaft 18 by the spline. Then, the worm 17 
can travel reciprocatively in such a longitudinal direction as designated 
by the arrows D and E shown in FIG. 1 by means of the rack cogs 20a formed 
on the rack plate 20 which mesh with the worm 17. Associated with the 
movement of the worm 17, the carriage 14 is also designed to travel along 
the platen 7 and the platen attachment section 8 in the directions 
designated by the arrows D and E shown in FIG. 1 within a predetermined 
movable range. 
As shown in FIG. 3, a leaf spring 21 is provided on the front side FS of 
the carriage 14 so as to constantly urge the carriage 14 toward the platen 
7 and the platen attachment section 8 so that the thermal head 10 can be 
pressed against the platen 7. One end of the leaf spring 21 is fixed to 
the front side FS of the carriage 14, that is, the opposite side of the 
carriage 14 to where the thermal head 10 is attached. The other end (a 
free end) of the leaf spring 21 comes into contact with a leaf spring 
abutment section 45. This leaf spring abutment section 45 has a 
rectangular cross section and is formed on the front side FS of the base 
frame 2 parallel to the carriage drive shaft 18. The free end of the leaf 
spring 21 slides over the base frame 2 as the carriage 14 moves while it 
is bent like an arc. 
The leaf spring abutment section 45 includes tapered sections 46 which are 
opposite to the cams 13a and 13b. While the carriage 14 is moving along 
the cams 13a and 13b, the free end of the leaf spring comes into contact 
with the tapered sections. The tapered sections 46 are tapered to 
progressively reduce the increasing biasing force of the leaf spring as 
the carriage 14 approaches the respective ends of the cams. The cone angle 
of the tapered section 46 is substantially the same as that of the tapered 
portions 12a and 12b of the cams 13a and 13b. 
FIG. 4 is a side view showing the carriage 14 and the leaf spring when the 
thermal head 10 is pressed against the platen 7. FIG. 5 is a side view 
showing the carriage 14 and the leaf spring when the carriage 14 is 
pressed against the end edges 11a and 11b of the cams 13a and 13b. FIG. 6 
is an explanatory view of the carriage 14 and the leaf spring obtained by 
superimposing these elements shown in FIGS. 4 and 5 on each other. In 
these drawings, the angle between the free end of the leaf spring that is 
in contact with the leaf spring abutment section 45 and the front face of 
the thermal head 10 is designated as .alpha. in FIG. 4 and .beta. in FIG. 
5. In this embodiment, the height of the plate spring abutment section 45 
is determined such that .alpha. becomes smaller than .beta., or 
.alpha.&lt;.beta.. With this arrangement, the biasing force of the leaf 
spring can be prevented from increasing when the carriage 14 travels along 
the tapered portions 12a and 12b of the cams 13a and 13b. As a result, an 
extra force necessary to move the thermal head 10 away from the platen 7 
can be reduced. 
As shown FIGS. 1 and 2, a roller drive shaft 22 is rotatively provided at a 
lower portion of the platen attachment section 8 on the back side BS of 
the thermal printer 1 in such a way as to extend parallel to the platen 7. 
A paper feed roller 23 is fitted around the roller drive shaft 22 for 
feeding the heat sensitive paper 4 to the position opposite to the thermal 
head 10. A roller drive gear 24 for transmitting torque to the roller 
drive shaft 22 is attached to the right end of the roller drive shaft 22 
as shown in FIG. 1 in such a way as to situate outside of the side frame 
6R by way of a one-way clutch 36. Specifically, the roller drive gear 24 
acts as a clutch gear by virtue of the one-way clutch 36, and it transmits 
a rotational force (torque) to the roller drive shaft 22 only when it is 
rotated in one direction. 
As described above, the carriage 14 is capable of traveling along the 
platen attachment section 8 as the worm 17 moves, and it presses the 
thermal head 10 attached to the carriage 14 against the platen 7 for 
printing. Further, when the heat sensitive paper sheet 4 is fed by the 
paper fed roller 23 after the thermal head 10 has finished printing one 
line, the carriage 14 travels along the respective tapered portions 12a 
and 12b of the cams 13a and 13b toward their end edges 11a and 11b, 
whereby the thermal head is brought into a position away from the platen 
7. 
Torque transmission means 37 of the first embodiment will now be described. 
As shown in FIG. 1, a stepping motor 28 serving as a drive motor is 
disposed in the vicinity of the right end of the front side FS of the base 
frame 2 with its output shaft 28a directing towards the right. The output 
shaft 28a is positioned so as to pass through the side frame 6R, and a 
carriage output gear 29 is attached to the leading end of the output shaft 
28a so as to situate outside (on the right side of) the side frame 6R. 
Further, a spur idle gear 33 for transmitting rotations of the carriage 
output gear 29 to the carriage driving gear 19, and a transmission gear 34 
for transmitting rotations of the carriage driving gear 19 to the roller 
drive gear 24 are also provided outside the side frame 6R. The stepping 
motor 28 can be driven at a desired drive frequency by a controller 35. 
The carriage driving gear 19 and the roller driving gear 24 will now be 
described in more detail, including the operational relationship between 
them and the idle gear 33 and the carriage transmission gear 34. 
The carriage driving gear 19 is attached to the right end of the carriage 
drive shaft 18, as shown in FIG. 1. The carriage driving gear 19 consists 
of two gears, as is shown in FIG. 7, namely, a fully cogged gear 19A for 
constantly engaging with the idle gear 33, and a partially cogged gear 19B 
capable of engaging with the carriage transmission gear 34. The partially 
cogged gear 19B has a cogged part 19a formed around half of the 
circumferential edge thereof, and a cogless part 19b formed around the 
other half. The partially cogged gear 19B has a smaller diameter than that 
of the fully cogged gear 19A. The external edge of the cogless part 19b of 
the partially cogged gear 19B is positioned closer to the center of the 
fully cogged gear 19A than the root circle of the same. 
The roller driving gear 24 is attached to the right end of the roller drive 
shaft 22 via the one-way clutch 36, as shown in FIG. 1. 
When the roller driving gear 24 rotates in such a counterclockwise 
direction as designated by arrow A shown in FIG. 8, the counterclockwise 
rotation of the roller driving gear 24 is transmitted as a drive force 
(torque) to the roller drive shaft 22 via the one-way clutch 36, so that 
the heat sensitive paper 4 is fed (in a transmission direction). On the 
other hand, when the roller driving gear 24 rotates in such a clockwise 
direction as designated by arrow B, the clockwise rotation of the roller 
driving gear is interrupted by the one-way clutch 36, so that the rotation 
is not transmitted to the roller drive shaft 22 as a rotating force 
(torque), as a result of which the roller driving gear 24 only idles 
without feeding the heat sensitive paper 4 (in an idling direction). 
The roller driving gear 24 has a cogged part 24a formed along the 
circumference thereof except for its substantially opposite portion to the 
roller driving gear, as it is shown in FIG. 8. The part of the 
circumference other than the cogged part 24a is formed into a recessed 
cogless part 24b, and this recessed cogless part prevents interference 
with a cogless part 34b of a second transmission gear 34B of the carriage 
transmission gear 34 which will be described later. 
The carriage transmission gear 34 is made up of two gears, as is shown in 
FIG. 9; namely, a first spur transmission gear 34A capable of engaging 
with the partially cogged gear 19B of the carriage driving gear 19, and a 
second spur transmission gear 34B capable of engaging with the roller 
driving gear 24. The carriage transmission gear 34 is arranged so as to 
rotate once for every three rotations of the carriage driving gear 19. 
The first transmission gear 34A has a cogged part 34a formed along its 
circumference, and a cogless part 34b is also formed for every one third 
of the circumference. The cogless part 34b is recessed so as not to 
interfere with the cogless part 19b of the partially cogged gear 19B of 
the carriage driving gear 19. 
The second transmission gear 34B has a smaller diameter than that of the 
first transmission gear 34A. The second transmission gear 34B has a cogged 
part 34c formed along one third of its entire circumference, leaving the 
other two thirds as a cogless part 34d. The external edge of the second 
transmission gear 34B is positioned closer to the axis of the first 
transmission gear 34A than the root circle of the same. 
The above mentioned gears, i.e., the carriage output gear 29, the idle gear 
33, the carriage driving gear 19, the carriage transmission gear 34, the 
roller driving gear 24, and the one-way clutch 36, constitute the torque 
transmission means 37. 
As shown in FIG. 2, a paper feed slot 26 through which the heat sensitive 
paper 4 is fed is opened in the lower portion of the plate attachment 
section 8 on the back side BS of the thermal printer 1. An urging spring 
27 is provided at the end of the base frame 2 in the vicinity of the back 
side BS for urging the heat sensitive paper sheet 4 fed through the paper 
feed slot 26 toward the paper feed roller 23 with an appropriate bias 
force. In other words, when the paper feed roller 23 is rotated, the heat 
sensitive paper 4 is conveyed (fed) in the direction designated by arrow C 
shown in FIG. 2 (a paper feeding direction). 
The operation of the first embodiment having the above mentioned 
construction will now be described, referring to FIGS. 1 to 12. 
FIGS. 1 and 2 and FIGS. 7 to 9 respectively show an initial condition where 
the carriage 14 is positioned at the home position on the left end of the 
movable range. FIG. 10 is an enlarged partial view showing the carriage 
transmission gear 34 and its surrounding when it is in the initial 
condition. FIG. 11 is an enlarged partial view showing the carriage 
transmission gear 34 and its surrounding when it is positioned at the 
right end of the movable range which is opposite to the home position. 
FIG. 12 is an explanatory view for explaining the operation of the 
principal elements of the thermal printer 1. 
In the initial condition where the carriage 14 of the thermal printer 1 
according to the first embodiment stays at the home position, the left end 
of the back side BS of the carriage 14 is urged to abut on the cam 
projection 11a of the cam 13a formed at the left end of the platen 
attachment section 8, by means of the biasing force of the leaf spring 21. 
The thermal head 10 is brought in a head-up state, i.e., it is lifted away 
from the platen, while being positioned opposite to the tapered portion 
12a of the cam 13a at the left end of the platen attachment section 8. At 
this time, the leaf spring abuts on the lowest portion of the tapered 
section 46 of the cam plate abutment section, as shown in FIG. 5. The 
biasing force of the leaf spring is in a reduced state, and hence the 
carriage 14 undergoes only a small load. 
When the torque transmission means 37 is in the initial condition, as is 
shown in FIG. 9, the idle gear 33 meshes with the carriage output gear 29 
attached to one end of the stepping motor 28. The idle gear 33 also meshes 
with the fully cogged gear 19A of the carriage driving gear 19. The 
partially cogged gear 19B of the carriage driving gear 19 is positioned 
such that the cogged part 19a thereof is directed to the lower right, as 
shown in FIG. 10. The cogless part 34b of the first transmission gear 34A 
of the transmission gear 34 is positioned adjoining the cogged part 19a of 
the partially cogged gear 19B so as to be opposite to its cogless part 
19b. As a result, the carriage driving gear 19 and the carriage 
transmisson gear 34 are not engaged with each other. Further, the second 
transmission gear 34B of the carriage transmission gear 34 is positioned 
such that the cogged part 34c is directed to the lower right, as shown in 
FIG. 8. The cogless part 24b of the roller driving gear 24 is positioned 
adjoining to the cogged part 34c of the second transmission gear 34B so as 
to be opposite to its cogless part 34d. As a result, the carriage 
transmission gear 34 and the roller driving gear 24 are not engaged with 
each other. 
The heat sensitive paper 4 is manually fed via the paper feed slot 26 and 
pressed against the paper feed roller 23 by means of the biasing force of 
the urging spring 27. 
When the stepping motor 28 in the initial condition is driven according to 
a control command (not shown), and the output shaft 28a of the stepping 
motor 28 is caused to rotate counterclockwise, as is shown in FIG. 9, the 
carriage output gear 29 attached to the end of the output shaft 28a starts 
to rotate counterclockwise. As a result, the rotating force (torque) of 
the stepping motor 28 is transmitted to the carriage driving gear 19 via 
the idle gear 33, whereby the carriage driving gear 19 starts to rotate 
counterclockwise as shown in FIG. 8. In conjunction with this 
counterclockwise rotation of the carriage driving gear 19, the carriage 
drive shaft 18 starts to rotate counterclockwise, thereby causing the worm 
17 connected to the carriage drive shaft 18 by the spline to rotate 
counterclockwise. Eventually, the worm 17 starts travel to the right over 
the rack plate 20 as designated by arrow D shown in FIG. 1. The rightward 
movement of the worm 17 causes the carriage 14 to move to the right, as it 
is designated by arrow D shown in FIG. 1. 
When the stepping motor 28 is rotated counterclockwise, the carriage 
driving gear 19 rotates counterclockwise first half rotation. As a result, 
the cogged part 19a of the partially cogged gear 19B of the carriage 
driving gear 19 comes to engage with the cogged part 34a of the first 
transmission gear 34A of the carriage transmission gear 34, as shown in 
FIG. 9. This engagement causes the carriage transmission gear 34 to rotate 
clockwise one-third turn, as shown in FIG. 8. At this time, the cogged 
part 34c of the second transmission gear 34B of the carriage transmission 
gear 34 engages with the cogged part 24a of the roller driving gear 24, 
thereby causing the roller driving gear 24 to rotate counterclockwise 
one-half turn, as shown in FIG. 9. Since the roller driving gear 24 is 
connected to the roller drive shaft 22 via the one-way clutch 36, as 
described above, the counterclockwise rotation of the roller driving gear 
24 designated by the arrow A shown in FIG. 8 is not transmitted to the 
roller drive shaft 22, thereby causing the roller driving gear 24 to 
simply idle. 
As a result of the first half counterclockwise rotation of the carriage 
driving gear 19 due to the counterclockwise rotation of the stepping motor 
18, the thermal head 10, which moves with the carriage 14, moves along the 
tapered portion 12a of the cam 13a formed at the left end of the platen 
attachment section shown in FIG. 1 toward the platen attachment recess 9 
before it enters into the printable range. The thermal head 10 is then 
brought into a head down position by means of the biasing force of the 
leaf spring 21. 
As a result of the next two and a half counterclockwise rotations of the 
carriage driving gear 19 caused by the counterclockwise rotation of the 
stepping motor 28, the carriage 14 further travels to the right while the 
thermal head 10 is retained in the head-down state, that is, it is pressed 
against the platen 7. When the thermal head 19 is located within the 
printable range during the movement of the carriage 14, the plurality of 
heating elements (not shown) regularly arranged on the thermal head 10 are 
selectively heated according to predetermined printing information, 
whereby the information is printed on the heat sensitive paper 4. 
At this time, one end of the leaf spring abuts on the uppermost face of the 
leaf spring abutment section 45 while the other end thereof urges the 
carriage 14 toward the platen 7. Accordingly, the thermal head 10 mounted 
on the carriage 14 is pressed against the platen with a desired bias 
force. 
Of two and a half counterclockwise rotations of the carriage driving gear 
19 resulting from the counterclockwise rotation of the stepping motor 28, 
the carriage transmission gear 34 rotates to its initial position during 
the first two rotations. During the next half rotation, the carriage 
transmission gear 34 stands still, because the cogless part 34b of the 
first transmission gear 34A of the carriage transmission gear 34 is 
positioned opposite to the cogless part 19b of the partially cogged gear 
19B of the carriage driving gear 19. 
In other words, the carriage transmission gear 34 is arranged so as to 
rotate one-third turn during the first half rotation of the carriage 
driving gear 19, so that the cogless part 34b of the first transmission 
gear 34A is positioned opposite to the cogless 19b of the partially cogged 
gear 19B of the carriage driving gear 19. During the next half rotation of 
the carriage driving gear 19, the carriage transmission gear 34 stands 
still. During two and a half counterclockwise rotations of the carriage 
drive gear 19 from this position, the carriage transmission gear 34 stays 
still during the first half rotation. Then, the carriage transmission gear 
34 rotates one-third turn during the second half rotation of the carriage 
drive gear 19. It again stays still during the third half rotation, and it 
again rotates one-third turn during the fourth half rotation. 
During these subsequent two and a half counterclockwise rotations of the 
carriage driving gear 19, the roller driving gear 24 stays still, because 
the cogless part 34d of the second transmission gear 34B of the 
transmission gear 34 is opposite to the cogless part 24b of the roller 
driving gear 24. 
As with the previously mentioned first half counterclockwise rotation of 
the carriage driving gear 19, the cogged part 19b of the cogless gear 19B 
of the carriage driving gear 19 engages with the cogged part 34a of the 
first transmission gear 34A of the transmission gear 34, as a result of 
the final half counterclockwise rotation of the carriage driving gear 19 
caused by the counterclockwise rotation of the stepping motor 28. Then, 
the transmission gear 34 rotates clockwise one-third turn, as shown in 
FIG. 8. At this time, the cogged part 34c of the second transmission gear 
34B of the transmission gear 34 engages with the cogged part 24a of the 
roller driving gear 24, thereby causing the roller driving gear 24 to 
rotate counterclockwise one-half turn, as shown in FIG. 9. As previously 
mentioned, the roller driving gear 24 is connected to the roller drive 
shaft 22 via the one-way clutch 36, and therefore the counterclockwise 
rotation of the roller driving gear 24 as designated by the arrow A shown 
in FIG. 8 will not be transmitted to the roller drive shaft 22. For this 
reason, the roller driving gear 24 simply idles. 
During the final half counterclockwise rotation of the carriage driving 
gear 19 resulting from the counterclockwise rotation of the stepping motor 
28, the carriage 14 travels along the tapered portion 12b of the cam 13b 
formed at the right end of the platen attachment section 8 toward the end 
edge 11b of the cam 13 shown in FIG. 1. Together with the movement of the 
carriage 14, the thermal head 10 is gradually caused to move away from the 
platen 7 and is finally brought into a head-up position. Consequently, the 
carriage 14 completes its rightward movement as designated by the arrow D 
in FIG. 1. 
As described above, while the carriage 14 travels along the tapered portion 
12b of the cam 13b until it reaches the end edge 11b, the leaf spring 
travels downward along the tapered section 46 of the leaf spring abutment 
section 45 from the position shown in FIG. 4 to the position shown in FIG. 
5. Although the load that the carriage 14 receives from the cam 13b 
increases while the carriage 14 travels along the tapered portion 12a of 
the cam 13b, the biasing force of the leaf spring is reduced 
correspondingly. Accordingly, the carriage 14 can easily travel along the 
tapered portion 12b of the cam 13b with smaller torque. In other words, a 
low-power motor can be used as a stepping motor for driving the carriage 
14 without problems. 
When the carriage 14 is positioned at the rightmost end of the movable 
range opposite to the home position, the partially cogged gear 19B of the 
carriage driving gear 19 is positioned such that the cogged gear 19b 
thereof is directed to the upper left, as is shown in FIG. 11. The cogless 
part 34a of the first transmission gear 34A of the carriage transmission 
gear 34 is positioned adjoining to the cogged part 19a of the partially 
cogged gear 19B so as to be opposite to the cogless part 19b. As a result, 
the carriage driving gear 19 does not engage with the carriage 
transmission gear 34. 
At this time, the second transmission gear 34B of the carriage transmission 
gear 34 is positioned such that the cogless part 34c is directed to the 
lower left, as is shown in FIG. 11. The cogless part 24b of the roller 
driving gear 24 is positioned adjoining to the cogged part 34C of the 
second transmission gear 34B so as to be opposite to the cogless part 34d. 
Eventually, the carriage transmission gear 34 does not engage with the 
roller driving gear 24. 
As has been described, the movement of the carriage 14 in the direction 
designated by the arrow D in FIG. 1 is now completed, and thus the 
printing of one line onto the heat sensitive paper sheet 4 carried out by 
the thermal head 10 is also completed. 
On the assumption that the stepping motor 28 is driven by a control command 
from the controller 35 and the output shaft 28 of the stepping motor 29 
starts to rotate clockwise as being shown in FIG. 9 while the carriage 14 
is positioned at the rightmost end in the movable range opposite to the 
home position, the carriage output gear 29 attached to the leading end of 
the output shaft 28a also starts to rotate clockwise. As a result, the 
rotating force (torque) of the stepping motor 28 is transmitted to the 
carriage driving gear 19 via the idle gear 33. Eventually, the carriage 
driving gear 19 starts to rotate clockwise, as it is shown in FIG. 9. 
Associated with the clockwise rotation of the carriage driving gear 19, 
the carriage drive shaft 18 also starts to rotate clockwise, and the worm 
17 connected to the carriage drive shaft 18 by the spline also rotates 
clockwise. It also starts to travel over the rack plate 20 in the leftward 
direction as designated by the arrow E shown in FIG. 1. As the worm 17 
travels leftward, the carriage 14 also starts to travel leftward as 
designated by the arrow E shown in FIG. 1. 
During the first half clockwise rotation of the carriage driving gear 19 
resulting from the clockwise rotation of the stepping motor 28, the cogged 
part 19a of the partially cogged gear 19B of the carriage driving gear 19 
comes to mesh with the cogged part 34a of the first transmission gear 34A 
of the transmission gear 34. The carriage transmission gear 34 then 
rotates counterclockwise one-third turn, as shown in FIG. 10. At this 
time, the cogged part 34c of the second transmission gear 34B of the 
carriage transmission gear 34 meshes with the cogged part 24a of the 
roller driving gear 24. The roller driving gear 24 then rotates clockwise 
by a predetermined amount (until it reaches the cogless part 24b at the 
opposite position), as shown in FIG. 9. The clockwise rotation of the 
roller driving gear 24 in the direction designated by the arrow A shown in 
FIG. 8 is transmitted to the roller drive shaft 22 which is connected to 
the roller driving gear 24 via the one-way clutch 36. Consequently, the 
roller drive shaft 22 rotates clockwise one-half turn. As the roller drive 
shaft 22 rotates clockwise, the paper feed roller 23 rotates clockwise. As 
a result of the clockwise rotation of the paper feed roller 23, the heat 
sensitive paper sheet 4 is fed (conveyed) in such a direction as 
designated by the arrow C shown in FIG. 2, whereby line feed is 
implemented by a predetermined amount necessary to print the next line. 
During further two and a half clockwise rotations of the carriage gear 19 
resulting from the clockwise rotation of the stepping motor 28, the 
carriage 14 travels further to the left while retaining the thermal head 
10 in the head-down state, that is, while it is pressed against the platen 
7. The plurality of heating elements (not shown) regularly arranged on the 
thermal head 10 are selectively heated according to predetermined printing 
information so as to print the next line onto the heat sensitive paper 4. 
During the two and a half clockwise rotations of the carriage driving gear 
19, the carriage transmission gear 34 repeats a stopping action and a 
one-third rotation for every half rotation of the carriage driving gear 
19, beginning with the stopping action; namely, stop, a one-third 
rotation, stop, a one-third rotation, and stop, until it returns to the 
condition shown in FIG. 1. 
Further, during these two and a half clockwise rotations of the carriage 
driving gear 19, the roller driving gear 24 stands still, because the 
cogless part 34d of the second transmission gear 34B of the carriage 
transmission gear 34 is positioned opposite to the cogless part 24b of the 
roller driving gear 24. 
Similarly to the case of the rightward movement of the carriage 14 
described above, the leaf spring urges the carriage 14 toward the platen 7 
while having one end abutting on the top surface of the leaf spring 
abutment section 45, as is shown in FIG. 4. 
During the final half clockwise rotation of the carriage driving gear 19 
resulting from the clockwise rotation of the stepping motor 28, the 
carriage 14 travels along the tapered portion 12a of the cam 13 formed at 
the left end of the platen attachment section 8 toward the end edge 11a. 
As the carriage 14 travels, the thermal head 10 is gradually lifted away 
from the platen 7. It is finally brought into the head-up state, and the 
carriage 14 now completes traveling leftwards in the direction designated 
by the arrow E shown in FIG. 1. Concurrently, the heat sensitive paper 4 
is fed (conveyed). Similarly to the first half clockwise rotation of the 
carriage drive gear 19, the roller driving gear 24 and the roller drive 
shaft are rotated clockwise via the carriage transmission gear 34. The 
heat sensitive paper 4 is then fed (conveyed) by an amount necessary for 
the next printing operation. 
The leaf spring travels downward along the tapered section 46 of the leaf 
spring abutment section 45 in such a direction as to reduce the increasing 
biasing force of the leaf spring, from the position shown in FIG. 4 to 
that in FIG. 5. Consequently, the biasing force urging the carriage 14 
toward the platen is also reduced. 
As described above, the carriage 14 travels leftward as designated by the 
arrow E shown in FIG. 1, so that the thermal head 10 prints one line onto 
the heat sensitive paper 4. Thus, the feed line of the heat sensitive 
paper 4 is now completed. 
According to the embodiment of the thermal printer 1 of the present 
invention, the thermal head 10 is directly attached to the carriage 
without any intervening member, and the carriage 14 itself can be rotated 
toward the platen 7 by the biasing force of the leaf spring. With this 
arrangement, it becomes unnecessary to separately provide the conventional 
head mounting unit 44, which contributes to the reduction in the number of 
parts and thus associated costs. 
The plate sprint abutment section 45 is provided with the tapered sections 
46 opposite to the cams 13a and 13b, and these tapered sections are 
tapered in such a direction as to reduce the increasing biasing force of 
the leaf spring as the carriage approaches the respective ends of the 
cams. This makes it possible to reduce an increase in the biasing force of 
the leaf spring, which in turn reduces the load acting on the carriage 14. 
As a result, even a low-power inexpensive driving motor can reliably drive 
the carriage 14. 
By means of the torque transmission means 37 described in the first 
embodiment of the thermal printer 1 of the present invention, it is 
possible for the single stepping motor 28 to drive the carriage 14 and the 
paper feed roller 23. Further, it is possible to easily control the 
movement of the carriage 14 and the rotations of the paper feed roller 23 
by correlating them with each other. As a result, the thermal printer can 
be reduced in size and cost. 
In the present embodiment, the torque is transmitted from the stepping 
motor 28 to the paper feed roller 23 while the thermal head 10 is lifted 
from the platen 7 by means of the cams 13a and 13b, i.e., while it is in 
the head-up state. Thus, it is possible to ensure the prevention of 
interference between the movement of the thermal head 10 associated with 
the movement of the carriage 14 and the feeding of the heat sensitive 
paper 4 carried out by the paper feed roller 23 (i.e., it is possible to 
ensure the prevention of the feeding of the heat sensitive paper 4 during 
the movement of the thermal head 10). 
The present invention is not limited to the above embodiment but can be 
modified as required. 
For instance, in the above embodiment, the carriage 14 is moved from one 
end to the other by rotating the carriage driving gear 19 three and a half 
rotations. The carriage 14 travels during the middle two and a half 
rotations of the three and a half rotations of the carriage drive gear 19. 
As a result, the remaining one rotation comprising the first half 
clockwise rotation and the last half clockwise rotation that take place 
when the carriage 14 is positioned at the respective ends of the movable 
range are used for feeding (conveying) the heat sensitive paper 4. 
However, the number of rotations of the carriage driving gear 19 may be 
optionally selected by modifying the shapes of the gears 19, 24, and 34, 
all constituting the torque transmission means 37. In this case, the 
number of rotations of the carriage driving gear 19 for moving the 
carriage 14 from one end to the other may be set as N/M rotations, while 
the number of rotations for feeding the heat sensitive paper carried out 
by the paper feed roller 23 may be set as m/M rotations (wherein 
N=M.times.n+m, m&lt;M, and M, N, and n are integers). 
The torque transmission means 37 is constituted such that the carriage 
drive shaft 18 and the roller drive shaft 22 are both driven by the single 
stepping motor 28 via the plurality of gears. However, the carriage drive 
shaft 18 and the roller drive shaft 22 may be provided with specially 
designed drive motors, respectively, so that they are driven by a 
different driving motor. 
As described above, according to the thermal printer of the present 
invention, it is possible to reduce the number of parts for mounting a 
thermal head onto a carriage and thus the associated costs, as well as to 
reliably drive the carriage using a low-power drive motor without 
problems.