Head and ribbon driving mechanism for thermal printer

A head-driving and ink ribbon feeding mechanism for an ink-transfer thermal printer comprises a print carriage mounted for parallel and non-rotational movement in a direction parallel to the platen of the printer. A support element carrying a thermal print head at a free end thereof is pivotally mounted on the carriage and is normally resiliently biased to press the thermal print head against the platen in a head-down position. Mechanical actuating means are switched selectively between a first position for advancing a thermo-ink ribbon in a cartridge received on said carriage past the thermal print head in the head-down position and to a second position in which the drive for the ribbon is disengaged and in which the elongated support element is engaged and pivoted to switch the thermal print head to a head-up position.

BACKGROUND OF THE INVENTION 
The present invention relates to an ink-transfer thermal printer, and, more 
particularly, to an improved head driving and ink ribbon feeding mechanism 
for an ink-transfer thermal printer. 
The use of non-impact printers as medium and low speed printer output 
terminals of electronic business machines in business offices is becoming 
increasing prevalent, a large factor of their appeal being the silent 
printing operation afforded thereby, particularly in comparison with 
conventional impact printers. At present, ink-jet printers and thermal 
printers comprise the two major types of such non-impact printers. 
As is well known, ink-jet printing is performed by ejecting micro-ink drops 
from micro-nozzles of an ink-jet head toward the recording paper; the 
micro-nozzles of ink-jet printers, however, are known to present 
maintenance problems. 
Thermal printers, utilizing thermal energy as the basic printing method or 
technique, avoid the maintenance problem of ink-jet printers but introduce 
yet other problems. In this regard, there are two basic categories of 
thermal printing techniques. 
The first thermal printing technique is known as thermal-sensitive 
printing, and employs a thermographic paper coated with a thermo-sensitive 
coating which, when heated above some predetermined minimum temperature, 
undergoes a color change. The thermographic paper employed in such 
thermo-sensing printing, however, is rather costly and the printed images 
tend to fade or become discolored over time. 
A second category of thermal printing is known as ink-transfer thermal 
printing, wherein a thermo-ink, coated as a layer on a base ribbon of 
plastic film, is transferred selectively to the recording paper in 
accordance with the images or characters to be reproduced. The thermo-ink 
is solid at room temperature, but changes rapidly to a softened or molten 
state above a predetermined temperature. A thermal head, which may be of a 
dot matrix variety, is rapidly heated and caused selectively to contact 
the thermal-ink ribbon against the recording paper at a predetermined 
pressure, such that the selectively heated printing elements arranged on 
the thermal head cause the corresponding, contacted areas of the 
thermo-ink to become softened or molten and to selectively transfer from 
the ribbon to the recording paper as spots, or dots, of the thermo-ink 
material, the transferred dots providing a durable printed image on the 
recording paper. The thermo-ink is usually a carbon black powder or 
pigments which are mixed with a binder such as wax. As is readily 
apparent, the thermo-ink ribbon can be used only once in a given area, 
because the selective transfer of dots of the thermo-ink to the recording 
paper necessarily leaves the corresponding portions of the base ribbon 
exposed, or depleted of further thermo-ink material. Since it is somewhat 
expensive, the thermo-ink ribbon should be used as efficiently as 
possible; particularly, and by way of example, during spacing operations 
in which no printing is performed, the thermo-ink ribbon should not be fed 
or advanced, since otherwise the advanced portion of the thermo-ink ribbon 
is needlessly consumed and thus wasted. Accordingly, it is important that 
a thermo-ink ribbon feeding mechanism be designed to be coordinated with 
the movement of the thermal head and the circumstance of whether printing 
is or is not to be performed at any given position in which the print 
carriage is moved; particularly, the ribbon should be advanced by the 
required pitch (i.e., of the next print function, whether a full character 
or a column of selected dot positions) when printing is to be performed, 
and alternatively it should not be advanced when no printing is to be 
performed (i.e., as in a spacing operation). 
Mechanisms have been proposed in the prior art for the purpose of achieving 
this efficient use of the thermo-ink ribbon and particularly to avoid 
advancing same during carriage movement for a spacing operation in which 
no printing is to be performed. FIG. 1 is a schematic, perspective view of 
such a prior art ink-transfer type thermal printer, FIG. 2 comprising a 
cross-sectional elevational view of the thermal printer of FIG. 1 
illustrating the printer carriage mechanism and associated elements. With 
concurrent reference to FIGS. 1 and 2, recording paper 7 is wrapped 
partially about a cylindrical platen 6 and advanced thereby to receive 
successive lines of print, as desired, along the horizontal, printing 
direction illustrated by the line x--x in FIG. 1, the line x--x extending 
generally parallel to the axis of the cylindrical platen 6. 
In typical operation, following printing on a given print line, the 
recording paper 7 is advanced in the direction of the arrow a by a 
corresponding, intermittent rotation of the platen 6; typically, guide 
means (not shown) are provided to guide the paper 7 during this advancing 
operation. A carriage 5 is mounted in sliding engagement on a main guide 
bar 8 for selective translational movement therealong, in the alternative 
or opposite directions shown by the arrows b and c, parallel to the axis 
of the platen and thus to the printing direction x--x. Carriage 5 is 
driven by a carriage feeding means, typically comprising driving cables 
with related pulleys and a driving motor (not shown), for the selective 
translational or sliding movement along main guide bar 8. Carriage 5, 
moreover, is selectively rotatable about the main guide bar 8 in the 
alternative or opposite direction shown by the arcuate arrows f and g. 
A thermo-ink ribbon 1 extends from a supply spool thereof (not shown) 
across the face of the cartridge 3, such that a length of the ribbon 1 is 
disposed adjacent the current print line x--x on the recording paper 7, 
and is advanced onto a take-up reel 2 which, as seen in FIG. 2, is 
received over and driven by a shaft 9. Shaft 9 is mounted on the carriage 
5 for rotary motion and extends downwardly therefrom, carrying at its 
lower end a roller 10 affixed thereto for rotatably driving the shaft 9. 
Carriage 5 supports a thermal head 4 which may be of conventional type, the 
ribbon 1, as best seen in FIG. 2, being interposed between the thermal 
head 4 and the recording paper 7 which in turn is wrapped about the platen 
6. 
A head driving mechanism for the carriage 5 comprises an electromagnetic 
solenoid 11 and associated plunger or spindle 13, a horizontal bar 12 
coextensive with and extending parallel to the main guide bar 8, and the 
aforenoted take-up spool drive shaft 9 and associated roller 10. The 
horizontal bar 12 is mounted for generally horizontal, reciprocating 
movement selectively in the opposite directions indicated by the 
double-head arrow e in FIG. 2. Particularly, the bar 12 is to be driven to 
the right (i.e., as seen in FIG. 2) by the spindle 13 of the solenoid 11 
when the latter is energized, to rotate the carriage to the so-called 
"head-down" position in which the thermal head 4 selectively engages the 
ribbon 1 against the recording paper 7 to perform a printing operation; 
conversely, spring means (not shown) normally bias the carriage 5 to 
rotate in the direction of arrow g, returning same to the so-called 
head-up position when the solenoid 11 is not energized. 
More specifically, when the solenoid 11 is energized, the spindle 13 pushes 
the horizontal bar 12 in a rightward direction as seen in FIG. 2, 
transversely to the axis of the platen 6, which operates in turn through 
the roller 10 and shaft 9 to rotate the carriage 5 in the direction of the 
arrow f shown in FIG. 2, and thus counterclockwise about the main guide 
bar 8, thereby rotating the thermal head 4 toward the thermo-ink ribbon 1 
and the recording paper 7. The thermal head 4 thus engages the thermo-ink 
ribbon 1 and the recording paper 7 against the platen 6 with a 
predetermined pressure. This rotaty motion of the thermal head 4 in the 
direction f is referred to as a "head-down" operation. 
In known manner, thermal printing elements (not shown) are arranged on the 
face of the thermal head 4 in a vertical line, perpendicular to the print 
line x--x. When the thermal head 4 is pressed against the thermo-ink 
ribbon 1 and the appropriate printing elements are selectively heated by 
their respective heaters, the corresponding, softened or molten portions 
of the thermo-ink layer are transferred to the recording paper 7, leaving 
a dot pattern thereon. Thereafter, the heaters for the selective elements 
are turned off. The roller 10 is engaged with the guide bar 12 and the 
carriage 5 is advanced in translational movement along the main guide bar 
8 in the direction of the arrow b, thereby rotating the roller 10 in the 
direction of the arrow d as a result of the frictional engagement of the 
roller 10 with the horizontal bar 12. This in turn rotates the shaft 9 of 
the take-up reel 2 mounted within the cartridge 3, advancing the 
thermo-ink ribbon 1 and winding up the used thermo-ink ribbon 1 onto the 
take-up spool 2. Thus, a fresh portion of the thermo-ink ribbon 1 is 
positioned in front of the thermal head 4, in preparation for the next 
printing operation. 
When a space is designated in a line of print, the solenoid 11 is 
de-energized and simultaneously the plunger 13 and the horizontal bar 12 
are withdrawn by spring means (not shown), thus disengaging bar 12 from 
the roller 10. Particularly, the carriage 5 is rotated about the main 
guide bar 8 in the direction of the arrow g (i.e., clockwise in FIG. 2) by 
springs (not shown) to the "head-up" position illustrated in FIG. 2. In 
the "head-up" position, the thermal head 4 is spaced apart from the 
thermo-ink ribbon 1; moreover, since the bar 12 is spaced from the roller 
10 of the shaft 9, the take-up reel 2 is not driven and thus the 
thermo-ink ribbon 1 is not advanced during subsequent translation of the 
carriage 5 along the main guide bar 8, thus completing a space operation. 
Since the thermo-ink ribbon 1 is not advanced during the space operation, 
improved economy is achieved since the expensive thermo-ink ribbon 1 is 
not wasted by being advanced during the space operation, thus decreasing 
the operating costs of the thermal printer. 
The prior art mechanism for an ink-transfer thermal printer head, as 
illustrated in FIGS. 1 and 2 and described above, will be seen to perform 
a mechanical switching operation, for moving the thermal head 4 between 
the head-down and head-up states or positions. The mechanism is of 
substantial mass and includes the entirety of the printing carriage 5, a 
thermo-ink ribbon cartridge including the ribbon and its supply and 
take-up spools, and the shaft 9 and roller 10 for driving the latter; 
likewise, the lengthy horizontal bar 12 must be moved for each switching 
operation. In view of the mass of these moveable members, it is difficult 
for such prior art mechanisms to perform the above-described mechanical 
switching operations rapidly, thus limiting the printing speed of the 
printer. Moreover, the electro-magnetic solenoid operation and the related 
mechanical engaging functions involving the horizontal bar 12 produce 
substantial operating noise, detracting from the advantage of the "silent" 
printing operation of the thermal printer itself. 
Various other carriage drive and thermo-ink ribbon winding mechanisms are 
known for thermal head printers. One such prior mechanism, disclosed in 
Japanese Laid-Open Patent Application TOKU-KAI-SHO No. 57-92180, published 
June 7, 1982, employs a small rocking arm which is mounted pivotally on 
the carriage and carries the thermal head on a free end thereof. As in the 
above described prior art structures, the carriage is mounted for sliding, 
translational movement along a guiding means, parallel to the platen. 
However, the carriage is not actuated in rotary fashion as aforedescribed, 
and instead it remains stable and only the rocking arm and thermal head 
are moved during printing operations. By thus minimizing the mass of the 
moveable elements, rapid head-down and head-up switching operations are 
possible permitting high-speed printing operations. Whereas high speed 
operation is obtained with this mechanism, the feeding of the thermo-ink 
ribbon and the transportation of the thermo-head cartridge are controlled 
independently, resulting in a somewhat complicated mechanism which also is 
costly to produce. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a head 
driving and ink ribbon feeding mechanism for an ink-transfer thermal 
printer which is compact in size and affords higher speed printing 
operations at reduced noise levels, relative to prior art such mechanisms. 
A further object of the present invention is to provide a head driving and 
ink ribbon feeding mechanism for an ink-transfer thermal printer having 
improved switching rates, or speeds, between head-up and head-down 
positions and which generates a reduced level of mechanical operating 
noise in performing those operations, relative to prior art such 
mechanisms. 
Another object of the present invention is to provide a head driving and 
ink ribbon feed mechanism for an ink-transfer thermal printer employing 
mechanical switching means for switching the thermal print head between 
head-up and head-down positions and, automatically and substantially 
simultaneously, actuating the feed of the thermo-ink ribbon in the 
head-down position of the thermal print head for successive print 
operations and deactivating the feed of the thermo-ink ribbon in the 
head-up position of the thermal head during spacing and other operations 
in printing is not performed, thereby to avoid unnecessary advancing and 
thus waste of the unused thermo-ink ribbon. 
The mechanism of the present invention overcomes the problems of the prior 
art mechanisms as above described, in two significant respects. The first 
is that the mechanism of the invention comprises mechanical switching 
means which employ a substantially reduced number of elements of minimum 
size, relative to prior art such mechanisms, for switching the thermal 
print head between the head-up and head-down positions, thus minimizing 
the mass of the moveable elements and permitting substantially increased 
rates of switching operations thereof with corresponding increased 
printing rates. A supporting lever of small mass is pivotally mounted to 
the print cartridge and carries the thermal head at a free end thereof. 
Resilient biasing means, such as springs, normally maintain the head-down 
state of the thermal head. Mechanical switching, or actuating, means are 
provided which selectively engage the opposite end of the supporting lever 
to cause pivotal movement thereof relative to the carriage, against the 
biasing force of the springs, to switch the head to the head-up state. By 
appropriate selection of the pivotal support position of the supporting 
lever, the inertia about the pivot position is minimal; as a result, the 
mechanism of the invention is capable of achieving rapid switching of the 
thermal head between the head-up and head-down positions. This contributes 
significantly to achieving high printing speeds in a thermal printer. 
The second significant improvement relates to minimizing the noise caused 
by the switching operation. In the prior art mechanism described above, 
the switching operation is performed by an electro-magnetic solenoid which 
produces significant noise each time the plunger impacts the bar. This 
problem is avoided in accordance with the invention, through use of a cam 
mechanism instead of the prior art solenoid mechanism. The cam mechanism 
produces an essentially insignificant noise level during its operation. 
These and other objects and advantages of the invention are more readily 
apparent from the following detailed description of the invention and the 
accompanying drawings, wherein like reference numerals refer to like parts 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 is a schematic perspective view of an embodiment of an ink-transfer 
thermal printer according to the present invention, illustrating the 
structure of the head driving and ink ribbon feed mechanism thereof. FIGS. 
4(a) and 4(b) are cross-sectional views of the embodiment of FIG. 3, 
illustrating the thermal head and its associated mechanism when actuated 
to a head-down state and to a head-up state, respectively. In each of 
FIGS. 1 to 4, like reference numerals refer to like parts. 
A recording paper 7 is fed in the direction of the arrow a about a 
cylindrical platen 6, perpendicularly to the line of printing x--x (as 
illustrated in FIG. 1), which may be driven by a feed mechanism (not 
shown) in conventional fashion for advancing the paper 7 to successive 
print line positions. 
A print carriage 20 is mounted on a main guide bar 8 for translational, 
sliding movement selectively in the directions of the arrows b and c, and 
thus parallel to the axis of cylindrical platen 6 and transversely to the 
direction a of movement of the recording paper 7. The carriage 20 is 
affixed in sliding engagement with a clamping guide bar 23 for free 
translational movement therealong, the bar 23 preventing rotational 
movement of the printing carriage 20 relative to the axis of the main 
guide bar 8. The printing carriage may be driven in the aforesaid 
translational movement by a conventional driving mechanism (not shown). 
The frame of the printing carriage 20 supports a thermal print head 4 
mounted on a supporting lever 22, and a cartridge 3 containing a supply 
spool (not shown) and a take-up spool 2 for a thermo-ink ribbon 1, a 
cross-sectional segment of which ribbon 1 is seen disposed between the 
thermal print head 4 and the recording paper 7. The supporting lever 22 is 
pivotally mounted on the printing carriage 20 by a pivot pin 21 which 
permits pivotal movement of the lever 22 selectively in the directions 
indicated by the arrows h and i as shown respectively in FIGS. 4(a) and 
4(b), and thus in a plane perpendicular to the axis of the platen 6. The 
thermal head 4 is mounted at the upper, free end of the supporting lever 
22 as seen in FIGS. 4(a) and 4(b), so as to engage the thermo-ink ribbon 1 
against the recording paper 7 and platen 6 in the head-down position shown 
in FIG. 4(a). The opposite, or lower, free end of the supporting lever 22 
includes a rounded projection 27 for contacting the adjacent, outer 
sidewall of the elongated, U-shaped lever 25. 
The supporting lever 22 is biased normally by coil springs (not shown) to 
rotate in the direction of the arrow h shown in FIG. 4(a) and thus to 
maintain the head-down state. The thermal head 4 thus normally engages the 
thermo-ink ribbon 1 against the recording paper 7 and the platen 6 with a 
predetermined pressure established by the springs (not shown). 
The ribbon cartridge 3 may be of a conventional prior art type, as 
previously described, and thus accommodates the thermo-ink ribbon 1, a 
supply spool (not shown in FIG. 4(a)) and a take-up spool 2, the latter 
receiving the upper extremity of a drive shaft 9 which is rotatably 
mounted in the carriage 20. The thermo-ink ribbon 1 is drawn from the 
supply spool and wound onto the take-up spool 2 when the latter is driven 
in rotation by the shaft 9 in the direction of the arrow d shown in FIGS. 
4(a) and 4(b). The shaft 9 extends downwardly from the carriage 5 and 
carries a contact roller 10 at its lower end. 
The head driving mechanism, or switching mechanism, which provides for 
actuation of the thermal head between its up and down positions, comprises 
the roller 10, the U-shaped bar 25, and a cam 24. More particularly, the 
longitudinal, U-shaped bar 25 is of a length corresponding to the required 
length travel of the printing carriage 20 and extends in a direction 
parallel to the axis of the platen 6; it is mounted to the printer frame 
by the axially extending pivot elements 26, which permit it to perform a 
reciprocal rotary, or rocking, movement, in the directions indicated by 
the arrows j and k in FIGS. 4(a) and 4(b). As is clearly seen in FIGS. 
4(a) and 4(b), the U-shaped bar is mounted such that its interior recess, 
defined by the sidewalls of its U-shaped cross-sectional configuration, is 
inverted and thus extends downwardly relative to the pivot elements 26. A 
cam 24 mounted on a rotary shaft 28 is received in the U-shaped recess of 
the bar 25 and is selectively rotatable therewithin to engage one or the 
other of the interior sidewall surfaces 25a and 25b, the bar 25 thus 
acting as a cam follower with respect to the cam 24. Drive means (not 
shown) rotate the shaft 28 which in turn drives the cam 24 to the 
appropriate position in response to a drive signal, in accordance with 
whether a printing or a spacing operation is to be performed at any given 
position of the carriage 20. Thus, as shown in FIG. 4(a), when the cam 24 
is rotated to engage the interior surface of the sidewall 25b, the 
U-shaped bar 25 is rotated in the direction of the arrow j. The spring 
biasing means (not shown) thus rotates lever 22 to position the thermal 
print head 4 in the head-down position, the projection 27 at the opposite, 
lower end of the lever 22 thus following the movement of the sidewall 25a. 
Simultaneously, the outer surface of the opposite sidewall 25b of the 
U-shaped bar 25 engages the roller 10. Thus, when the printing carriage 20 
is driven in translation in the direction of the arrow b as shown in FIG. 
3, by an incremental distance corresponding to one pitch of the dot print 
format, the roller 10 is rotated in the direction of the arrow d shown in 
FIG. 4(a) by frictional engagement of the roller 10 and the outer surface 
of the sidewall 25b of the U-shaped bar 25. Shaft 9 thus is rotated and 
advances the thermo-ink ribbon 1 onto the take-up spool 2, thus presenting 
a fresh portion of the thermo-ink ribbon 1 between the thermal head 4 and 
the recording paper 7 in preparation for the next printing operation. 
Conversely, as shown in FIG. 4(b), when the shaft 28 is rotated to position 
the cam 24 at its opposite extreme, the U-shaped bar 25 is rotated in the 
direction of the arrow k, the outer surface of sidewall 25 engaging the 
rounded projection 27 of the supporting lever 22 for rotating the latter 
against the spring biasing force and switching the thermal head 4 to the 
head-up position. Simultaneously, the outer surface of the opposite 
sidewall 25b of the U-shaped bar 25 is displaced from the roller 10. 
Therefore, in the head-up state, during further translational movement of 
the carriage 20 such as for a space operation, no feeding of the 
thermo-ink ribbon 1 occurs. 
In operation, in the head-down position, the thermal head 4 exerts a 
predetermined pressure against the thermo-ink ribbon 1 and the recording 
paper 7, as backed by the platen 6, in accordance with the force exerted 
by the coil spring (not shown) through the supporting lever 22. The actual 
printing is performed in accordance with the prior art process of transfer 
of the thermo-ink from the ribbon 1 to the recording paper 7. Following 
the print operation, the print carriage 20 is advanced by one pitch along 
the main guide bar 8 and the thermo-ink ribbon 1 is advanced 
simultaneously, being wound onto the take-up spool 2, and the mechanism 
thus is prepared for the next successive printing operation. If a space is 
to be provided at the next position in the print line, the mechanism 
switches the thermal head 4 to the head-up position, thus displacing the 
thermal head 4 from the thermo-ink ribbon 1 and the recording paper 7, as 
shown in FIG. 4(b); the cam 24 is rotated to displace the U-shaped bar 25 
from the roller 10 and thus shaft 9 is not rotated for advancing the 
thermo-ink ribbon, as before noted. As a result, economies in the use of 
the expensive thermo-ink ribbon 1 are achieved, since it is not needlessly 
advanced when the next character position in the print line is a space. 
Whereas the figures of the drawings discussed in the foregoing are 
schematic in nature to facilitate an understanding of the invention, the 
following FIGS. 5-9 provide a more detailed illustration of the actual 
structure of an embodiment of the invention, and wherein like reference 
numerals denote like parts. 
FIG. 5 is a plan view of an actual embodiment of the invention, 
illustrating the principal structure and components of a thermal printer, 
with the housing removed to better facilitate illustration of the internal 
components. FIGS. 6(a) and 6(b) are cross-sectional views of the thermal 
printer of FIG. 5 taken along the line Y--Y in FIG. 5 and respectively 
illustrate the mechanism in the head-down and head-up positions of the 
thermal head; FIGS. 6(a) and 6(b) are drawn on a larger scale than that of 
FIG. 5 for ease of illustration. Concurrent reference will be had to FIGS. 
5, 6(a) and 6(b) in the following. 
The printer is enclosed within a housing, shown by dash-dot lines in FIG. 
6(a), comprising a base plate 100 and a cover 111, the latter having in 
its upper horizontal portion two slots 111A and 111B through which 
recording paper 107, shown by a dash-dot line, enters and exits the 
printing mechanism in the direction shown by the arrow a. The recording 
paper 107 is received about the feed roller 131 which in turn is driven by 
a paper feed motor 132 through reduction gears 133, and passes from the 
roller 131 in a path between a fixed platen 106 and a thermo-ink ribbon 
101 (illustrated by a dotted line in FIG. 6(a)), the recording paper 107 
exiting from the printer through the slot 111B in the cover 111. It will 
be appreciated that the cylindrical platen 6 of FIGS. 3 and 4 thus is 
replaced by the flat platen 106 and the feed roller 131. A main guide bar 
108 and a clamping guide bar 123 are arranged in parallel axial 
relationship with each other and with the axes of the feed roller 131 and 
the platen 106, the guide bars 108 and 123 being secured rigidly to the 
frame 112. The printing carriage 120 is supported on the guide bars 108 
and 123 for sliding movement therealong, and is driven by a carriage 
driving motor 115, pulleys 116 and 117, and a closed loop cable 118. 
A supporting lever 122 is mounted pivotally on the printing carriage 120 by 
the pivot element 121 and is biased rotatably in the direction shown by 
arrow h by torsion coil springs 135 (see FIG. 5). A thermal head 104 is 
mounted on the upper, free end of the supporting lever 122 and disposed in 
facing relationship with the thermo-ink ribbon 101 and the recording paper 
107. A thermo-ink ribbon cartridge 103 of conventional type (shown in 
dot-dash lines) is received on the thermal head carriage 120 such that the 
take-up reel is disposed over and thereby connected with the shaft 109, 
which serves to drive same. The shaft 109 is mounted rotatably within and 
extends downwardly from the printing carriage 120, and carries a roller 
110 at its lower extremity. A U-shaped bar 125 is pivotally mounted on the 
main guide bar 108 and receives within its downwardly projecting elongaged 
recess, as before described, an eccentric cam 124 which, when rotated to 
the respective positions shown in FIGS. 6(a) and 6(b), causes the related 
mechanism including the U-shaped bar 125 and the support lever 122 to move 
the thermal print head 104 to the head-down and head-up positions, 
respectively. The mechanical switching operation of the structure shown in 
FIGS. 5, 6(a) and 6(b) is in accordance with that described previously in 
relation to FIGS. 3 and 4. The U-shaped bar 125 preferably carries a 
rubber plate 113 on the exterior of its sidewall which engages roller 110 
to enhance the frictional engagement therebetween in the head-down 
position as seen in FIG. 6(a), thereby to assure that the ribbon advance 
function is performed reliably. 
FIG. 7 is a perspective view illustrating in greater detail the U-shaped 
bar 125 and its pivotal mounting on the main guide bar 108. As 
distinguished from the structure of FIG. 4, in this embodiment the main 
guide bar 108 serves a dual purpose, both comprising the main guide for 
the carriage 120 and the pivotal support for the U-shaped bar 125. 
The illustrations of FIGS. 8 and 9 show the relative positions of the cam 
124 and the cam follower action of the U-shaped bar 125 in the head-down 
and head-up states, respectively. More particularly, FIGS. 8(a) and 9(a) 
are plan views of the cam 124 and the driving mechanism therefor, whereas 
FIGS. 8(b) and 9(b) are simplified cross-sectional elevational views taken 
along a plane generally perpendicular to the U-shaped bar 125 and passing 
through the axis of the cam 124. The cam 124 comprises an integral, 
toothed gear segment 124F which extends radially beyond the cam surface 
and engages a gear 119 which is driven by the cam driving motor 136 seen 
in FIGS. 6(a) and 6(b). With reference to FIG. 8(a), when the motor 136 
drives gear 119 in the direction of arrow 1, the cam 124 correspondingly 
is driven in the direction of arrow m, causing the eccentric cam 124 to 
bear against the interior surface of the sidewall 125a of the U-shaped bar 
125, displacing same in the direction indicated by the arrow D for 
switching to the head-down position as illustrated in FIG. 6(a), in which 
the U-shaped bar 125 is displaced from the lower extremity of the 
supporting lever 122 for the thermal head 104. In that position, the 
thermal head 104 presses against the thermo-ink ribbon 101, the recording 
paper 107, and the stationary plate 106 in accordance with the resilient 
biasing of the torsion coil springs 135. Simultaneously, the U-shaped bar 
125 operates through the rubber plate 113 to engage the roller 110 to 
produce the ribbon advance function during translational movement of the 
carriage 120. Conversely, as shown in FIGS. 9(a) and 9(b), when the gear 
119 is driven in the direction of arrow n, the arcuate toothed segment 
124F rotates the cam 124 in the direction of the arrow o, causing the 
eccentric cam 124 to engage the interior surface of the sidewall of the 
U-shaped bar, thereby pivoting the U-shaped bar 125 about the main support 
bar 108 and moving the sidewall 125b in the direction U. This corresponds 
to the head-up position of the mechanism shown in FIG. 6(b), in which the 
U-shaped bar 125 engages the supporting lever 122 to displace the thermal 
print head 104 from the thermo-ink ribbon 101, the recording paper 107, 
and the stationary platen 106, and in which the rubber plate 113 is 
displaced from the roller 110. 
The significant reduction in the number, and in the total mass, of the 
elements of the head driving and ribbon feeding mechanism of the present 
invention which must move to perform the mechanical switching operations, 
as compared with that of the prior art, readily will be apparent. Very 
briefly, as described above, the prior art mechanism required movement of 
a substantial number of relatively large components, including the 
carriage, the ribbon cartridge and a long horizontal bar, to accomplish 
the mechanical switching actuation between head-up and head-down positions 
of the thermal printing head. By contrast, the mechanism of the invention 
requires movement only of a minimum number of components having a very 
small mass. Moreover, by proper selection of the pivot position of the 
supporting lever 122, taking into account the inertia and force factors 
relevant to its actuation, the required actuating force transferred 
through the U-shaped bar 125 to switch the support lever 122 between its 
head-up and head-down positions can be minimized. Moreover, the U-shaped 
bar 125 performs only a limited pivotal or rocking movement to accomplish 
the mechanical switching of the support lever 122, yet provides for 
simulaneous and coordinated engagement or disengagement of the ink ribbon 
feed function. As a result, the mechanism can operate rapidly to switch 
the thermal head between the head-up and head-down positions, thereby 
permitting high speed printing operations. Furthermore, the mechanical cam 
action employed by the present invention to afford the mechanical 
switching operation is substantially silent and thus overcomes the noise 
problems of the switching mechanisms of the prior art thermal printers. 
Numerous modifications and adaptations of the head driving and ink ribbon 
feeding mechanism of the invention will be apparent to those of skill in 
the art, and thus it is intended by the appended claims to cover all such 
modifications and adaptations which fall within the true spirit and scope 
and the appended claims.