Thermal transfer printer with ribbon tensioning mechanism

A thermal transfer printer comprises a pair of fixed frames for rotatably supporting a platen, a pair of movable frames supporting a thermal head, the movable frames being connected to the fixed frames so as to be rockable around a shaft, between a position where the thermal head is pressed against the platen and a position where the thermal head is moved away from the platen. The ink ribbon is supported by a supply roll and a take-up roll and may be alternately transported in one direction such that the ink ribbon is directed toward the region between the thermal head and the platen or in the direction opposite thereto. The movable frame is provided with operating member adapted to drive the supply roll to move the ink ribbon in the opposite direction, thereby applying a tension of the opposite direction to the ink ribbon, when the movable frame is rocked so that the thermal head is pressed against the platen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermal transfer printer in which 
heat-fusible or -sublimable ink applied to a ribbon is transferred to a 
paper sheet by means of Joule heat produced by heating a thermal printing 
head, and more particularly, to a thermal transfer printer adapted for 
printing characters and bar codes on paper sheets, such as labels. 
2. Description of the Related Art 
As an example of the conventional thermal transfer printer of this type, 
there is a label printer which is disclosed in Japanese Patent Disclosure 
No. 61-266271 (corresponding to U.S. Pat. No. 4,744,680, issured on May 
17, 1988) assigned to the same assignee as the present application. 
In this label printer, characters and bar codes are printed on a label 
sheet by means of a line thermal printing head with a large printing 
width. In printing, the printing head is pressed against an platen with a 
ink ribbon and the label sheet between the head and the platen. This prior 
printer invention is characterized in that a printer unit, in which a line 
thermal head and ink ribbon supply and take-up spindles are mounted on a 
pair of frames, is rockably or movably attached to a fixed mechanism 
section of a casing of the printer. 
According to the prior art printer described above, when the thermal 
printing head is pressed against the platen, the ink ribbon between ink 
ribbon supply and take-up rolls may slacken, thus failing to produce a 
clear print and, therefore, entailing defective printing. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a thermal transfer 
printer capable of preventing an ink ribbon between ink ribbon supply and 
take-up rolls from slackening when a thermal printing head is pressed 
against a platen. 
According to the present invention, there is provided a thermal transfer 
printer which comprises: a platen; platen supporting means for supporting 
the platen; a thermal head; ink ribbon supply means for feeding an ink 
ribbon between the platen and the thermal head; thermal head supporting 
means movable relatively to the platen supporting means and supporting the 
thermal head, the thermal head supporting means being adapted to be moved 
so as to press the thermal head against the platen across the ink ribbon 
and a paper sheet; and ink ribbon looseness removing means for applying a 
tension of at least one direction to the ink ribbon, situated between the 
thermal head and the platen, by moving when the thermal head supporting 
means is moved so that the thermal head is pressed against the platen, the 
direction of the tension being an ink ribbon feeding direction or the 
direction opposite thereto. 
Thus, in the thermal transfer printer according to the present invention, 
when the thermal printing head is moved so as to be pressed against the 
platen, a tension is applied to the ink ribbon, thereby preventing the 
ribbon from slackening.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings of FIGS. 1 to 8, a thermal transfer printer 
according to an embodiment of the present invention will be described in 
detail. 
In these drawings, numeral 1 designates a roller-shaped platen which is 
rotatably supported, at both ends thereof, on a pair of fixed frames 
(fixed supporting means for a platen) which are opposed to each other at a 
predetermined distance. Timing gears 3 and 4 are fixed individually to the 
respective projecting ends of slender platen shafts 21 at either end of 
platen 1. Timing belt 7 is passed around timing gear 3 (FIG. 1A) and motor 
gear 6 so that the driving force of platen drive motor 5 can be 
transmitted to gear 3 by means of motor gear 6 and belt 7. Motor 5 is 
mounted on the inside of one of fixed frames 2 with its rotating shaft 
protecting from the frame, for rotation in both forward and reverse 
directions. The other timing gear 4 is connected to timing belt 8 (FIG. 
1B) so that the rotation of motor 5 can be transmitted to timing gear 9 
through belt 8. Gear 9 is mounted on one end of sheet feeding roller 10 
which is rotatably supported, at both ends thereof, on fixed frames 2. 
Thus, roller 10 can be rotated in the same direction as platen 1. 
A pair of movable frames (movable supporting means for a thermal head) 11 
are rockably mounted on the top portions of their corresponding fixed 
frames 2 by means of frame shaft 12 so that the top of platen 1 can be 
exposed. Shaft 12 is rockably supported, at both ends thereof, on fixed 
frames 2, and frames 11 are mounted on the opposite end portions of shaft 
12 for associated rocking motion. Thus, movable frames 11 are rockable 
together with frame shaft 12 around the axis thereof, between an open 
position, where the top portion of the printer between fixed frames 2 is 
open, as shown in FIG. 1A, and a closed position where the top portion is 
closed, as shown in FIG. 2. Auxiliary frame 11a is pivotally mounted on 
each movable frame 11, and tension spring 13 is stretched between frame 
11a and its corresponding fixed frame 2. A slit is bored through each 
auxiliary frame 11a, and guide pin 11b protrudes from each fixed frame 2. 
As pins 11b are loosely fitted in the respective slits of their 
corresponding auxiliary frames 11a, movable frames 11 are urged toward the 
open position by the action of springs 13. When movable frames 11 engage 
their corresponding stopper shafts 14 on the inside of fixed frames 2, 
they are retained in the open position. 
Head unit 16 is rockably supported on the front end portions of movable 
frames 11 by means of support shaft 17. Elongated line thermal head 15, 
which is adapted to be pressed against platen 1, is swingably held on unit 
16 with the aid of the means mentioned later. The head unit includes a 
pair of head arms 18 facing each other and head base 19 fixed to the 
inside of arms 18. Arms 18 are rockably supported on movable frames 11 by 
means of support shaft 17. 
Head holding portion 20, having a U-shaped cross section and open at the 
bottom, is formed at the central portion of the front end of head base 19. 
Holding portion 20 extends along the longitudinal axis of head base 19 
(parallel to support shaft 17). 
Line thermal head 15 has an elongated configuration extending along the 
longitudinal axis, and head bracket 23 is fixed to the back of the head. 
Bracket 23 has engaging recesses 22 individually at its opposite ends, 
which are adapted to releasably engage platen shaft 21 of platen 1. The 
engaging portions protrude forward from thermal head 15. U-shaped head 
coupling portion 24, which is open at the top, is provided on the central 
portion of bracket 23. Coupling shaft 27, which extends at right angles to 
the longitudinal axis, is passed through holes 25 and 26 in the center of 
coupling portion 24 and head holding portion 20, respectively. Thus, line 
thermal head 15 is mounted on holding portion 20 so as to be swingable 
around shaft 27. In other words, head 15 is mounted on head base 19 so 
that it is swingable around an axis parallel to its front face and 
perpendicular to the direction of its length. The respective central 
portions of a pair of leaf springs 28 having a U-shape are coiled around 
support shaft 17 (FIGS. 2 and 5A to 5C). One end of each spring 28 is held 
against the rear end of head base 19, thereby urging head unit 16 to rock 
around shaft 17 toward the platen. Each movable frame 11 has arcuate slot 
29 whose center of curvature lies on the axis of support shaft 17. Cam 
shaft 30 is rockably attached to head unit 16. As both end portions of 
shaft 30 are fitted in their corresponding slots 29, the rocking motion of 
head unit 16, i.e., line thermal head 15, relative to movable frames 11, 
is restricted within a predetermined range. 
A pair of head adjusting cams 31 are mounted on cam shaft 30. They serve to 
adjust the urging force of leaf springs 28 by stages. As shown in FIGS. 4A 
and 4B, a plurality of flat cam faces 32a, 32b and 32c are formed along 
the outer periphery of cam 31 so that they are situated at different 
distances from cam shaft 30. A flat face of each leaf spring 28 at the 
other end portion thereof is urged to be in plane contact with any of flat 
cam faces 32a to 32c. In this embodiment, each head adjusting cam has 
three cam faces. First cam face 32a is nearer to shaft 30 than the other 
two are, and third cam face 32c is the remotest. Thus, if spring 28 
engages first cam face 32a, as shown in FIG. 5A, it applies the smallest 
urging force to line thermal head 15 to be pressed against the surface of 
platen. If spring 28 engages second and third cam face 32b, 32c, as shown 
in FIGS. 5B, 5C, it applies a greater and the greatest urging forces to 
head 15, respectively. Since these cam faces are flat surfaces, they serve 
to lock cam 31 in position as they are engaged by spring 28, unless a 
lever of the cam is rocked. The selection of the cam face to be engaged 
depends on the thickness and quality of the paper sheet used. If the sheet 
is relatively thick or firm, cam 31 is set in the position shown in FIG. 
5C to produce the greatest urging force. If the sheet is thin or weak, on 
the other hand, the cam is set in the position shown in FIG. 5A to reduce 
the urging force. The urging force of spring 28 to press thermal head 15 
toward platen 1 is changed when the position of head bracket 23 relative 
to platen shaft 21 is slightly shifted. 
Paired head adjusting cams 31, which are fixed to cam shaft 30, are adapted 
to rock together therewith. Therefore, they need not always be two in 
number, and it is necessary only that at least one adjusting cam be 
provided for the purpose. Cams 31 are located exposed beside movable 
frames 11 in order that they can be manually operated from the outside. 
The respective lower ends of a pair of lock levers 33 are pivotally 
mounted on the inner surfaces of their corresponding fixed frames 2 by 
means of shaft 34. Both end portions of shaft 34 are rockably supported on 
their corresponding fixed frames 2. Thus, lock levers 33 are mounted on 
frames 2 so as to be rockable around the axis (indicated by line B--B in 
FIG. 3) of shaft 34. When movable frames 11 are brought to the closed 
position, levers 33 engage the top of support shaft 17 so that shaft 17 is 
fitted and retained in recesses 35 formed in the respective top edges of 
fixed frames 2, thereby preventing movable frames 11 from rocking. Each 
lever 33 is urged in the counterclockwise direction of FIG. 1A by means of 
tension spring 3b. Knob 37 is attached to one of lock levers 33. If knob 
37 is operated to rock levers 33 in the clockwise direction of FIG. 1A, 
against the urging force of springs 3b, movable frames 11 are released 
from the locked state. In rocking frames 11 to the closed position, 
support shaft 17 is held against the lateral faces of lock levers 33, and 
levers 33 are rocked against the urging force of springs 3b. When movable 
frames 11 are rocked in this manner, they are locked automatically. 
Sheet holding member 38 for holding wide label sheet P protrudes from the 
rear end portions of fixed frames 2. It comprises a pair of support arms 
spaced in the longitudinal direction of the printer. A bearing or recess 
is formed on the top surface of each support arm. Rolled label sheet P is 
wound around a support shaft, both end portions of which project 
individually from the opposite sides of sheet P. As the projecting end 
portions of the shaft are rotatably supported by the bearings of the 
support shafts, sheet P is held by holding portion 38 so as to be 
rotatable around the axis of the support shaft. The leading end of sheet P 
is drawn out from its outermost periphery. Thus, sheet P is guided to a 
printing section through sheet guide passage 39, which comprises of a pair 
of curved plates vertically spaced at a very short distance from each 
other and arranged below movable frames 11. Paper sensor 40 is attached to 
that portion of passage 39 situated between platen 1 and sheet feeding 
roller 10. Sensor 40 serves to optically detect the presence of label 
sheet P, that is, the leading end of the sheet. 
Ink ribbon supply roll 41 and ink ribbon take-up roll 42 are rotatably 
mounted on the inside of fixed frames 2. Supply roll 41 serves to feed 
wide ink ribbon R to the printing section, while take-up roll 42 is used 
to wind the used portion of the ink ribbon. Rolls 41 and 42 are removably 
held by their corresponding pairs of roll holders 43 and 44, which are 
mounted individually on the inside of frames 2. Ink ribbon R on supply 
roll 41 is wound around take-up roll 42 after being passed around a 
plurality of ribbon guide shafts 45 (three in this embodiment), which are 
fixed to head arms 18 and extend parallel to the longitudinal axis of the 
printer. One of paired roll holders 43 is pressed against one end face of 
roll 41 by means of a coil spring disposed between itself and its 
corresponding fixed frame 2. Likewise, one of roll holders 44 is pressed 
against one end face of roll 42 by means of another coil spring disposed 
in the same manner. Thus, rolls 41 and 42 can be easily mounted on or 
removed from their corresponding holders 43 and 44. The other of holders 
44 for take-up roll 42 is coaxially connected to take-up gear 47 by means 
of one-way clutch 48. As shown in FIG. 1A, take-up gear 47 is operatively 
connected, by means of a gear train, to take-up motor 46 which is fixed to 
the inside of one of fixed frames 2. Thus, as the driving force of motor 
46 is transmitted to ink ribbon take-up roll 42 via take-gear 47 and 
one-way clutch 48, roll 42 is rotated in a take-up direction or the 
clockwise direction of FIG. 2. Feed gear 49, which contains one-way clutch 
49a therein, is coaxially attached to the other of roll holders 43 which 
hold ink ribbon supply roll 41. Gear 49 is in mesh with a large-diameter 
portion of intermediate gear 50, a double gear. A small-diameter portion 
of gear 50 is in mesh with ribbon rewinding gear 51 which is coaxially 
fixed to frame shaft 12 between movable frames 11. Gear 51 is composed of 
a sector gear whose center is on the axis of shaft 12. Thus, when movable 
frames 11 are rocked to the closed position, rewinding gear 51 also rocks, 
thereby causing intermediate gear 50 to rotate through an angle 
corresponding to the rocking motion of frames 11. The rotation of gear 50 
is transmitted through feed gear 49 to the other roller holder 43. 
Thereupon, supply roll 41 is rotated through a predetermined angle in the 
clockwise direction of FIG. 2, i.e., in the direction opposite to a ribbon 
feeding direction. 
Head-up mechanism 52 is located beside sheet feeding roller 10. It serves 
to temporarily force up line thermal head 15, in pressure contact with 
platen 1, when movable frames 11 are in the closed position. As shown in 
FIG. 3, mechanism 52 includes cam shaft 53 and a pair of cams 54 fixed 
individually to the opposite end portions of shaft 53. Shaft 53, which 
extends in the longitudinal direction (line C--C) of the printer, is 
rotatably supported, at both ends thereof, to fixed frames 2. Gear 55 
(FIG. 1B) is coaxially mounted on one end of cam shaft 53. It is 
connected, by means of a gear train, to cam drive motor 56 which attached 
to the other fixed frame 2. Thus, cam 54 is rotated by means of motor 56. 
A pair of head-up rollers 57 are rotatably mounted on head arms 18, 
individually, so that they are situated in the paths of rotation of their 
corresponding cams 54 when movable frames 11 are in the closed position. A 
pair of sheet rewinding arms 59 are arranged inside those portions of 
fixed frames 2 near sheet feeding roller 10. Each end portion of shaft 60, 
which extends parallel to roller 10, is fixed to the central portion of 
each corresponding arm 59. Both ends of shaft 60 are movably supported on 
fixed frames 2, individually. As shaft 60 rocks, arms 59 can rock together 
therewith around the longitudinal axis (line A--A) of shaft 60. Pinch 
roller 62, which extends parallel to roller 10, is rotatably supported, at 
both ends thereof, on sheet rewinding arms 59. Tension spring 61 is 
disposed between each arm 59 and its corresponding fixed frame 2. As shown 
in FIG. 7, spring 61 urges arm 59 to rock in the counterclockwise 
direction, thereby pressing pinch roller 62 against sheet feeding roller 
10. Release rollers 58, which can engage cams 54, are rotatably mounted on 
sheet rewinding arms 59, individually. When cams 54 engage their 
corresponding rollers 58, arms 59 are rocked against the urging force of 
springs 61, so that pinch roller 62 is disengaged from roller 10. In FIG. 
3, numeral 63 designates a cam detecting plate attached to one end of cam 
shaft 53. Numeral 64 designates a cam sensor for optically detecting the 
rotational position of cams 54 through detecting plate 63, while numeral 
65 denotes a ribbon sensor for optically detecting the presence of ink 
ribbon R. 
In printing on a wide label sheet P, in the printer with the arrangement 
described above, ink ribbon supply roll 41 and ink ribbon take-up roll 42 
are first set inside fixed frames 2. The leading end of ink ribbon R, 
wound around supply roll 41, is passed around ribbon guide shafts 45 
between head arms 18, and is then anchored to take-up roll 42. Meanwhile, 
the leading end portion of label sheet P, held by sheet holding portion 
38, is drawn out and passed through sheet guide passage 39 to be set on 
platen 1. Then, in this state, movable frames 11 are brought down to the 
closed position, where they are fixed to fixed frames 2, and line thermal 
head 15 is pressed against platen 1. As movable frames 11 rock in this 
manner, ribbon rewinding gear 51 also rock, thereby causing ribbon supply 
roll 41 to rotate in the counterclockwise direction of FIG. 2, through the 
medium of intermediate gear 50 and feed gear 49. Thereupon, ink ribbon R, 
which is drawn out long to cover ribbon take-up roll 42 via supply roll 41 
and thermal head 15, is rewound. Accordingly, a tension toward supply roll 
41 is applied to ribbon R, so that the ribbon can be prevented from 
slackening or be smoothed out. Ribbon rewinding gear 51 rocks also when 
movable frames 11 are raised from fixed frames 2. In this case, however, 
ribbon supply roll 41 never rotates, since one-way clutch 49a is contained 
in feed gear 49. 
When line thermal head 15 is pressed against platen 1, moreover, cam drive 
motor 56 is caused to rotate for a predetermined amount by means of a 
detection switch (not shown). Thereupon, cams 54, having so far been in 
engagement with release rollers 58, are caused to engage head-up rollers 
57. Thus, pinch roller 62 is pressed against sheet feeding roller 10, and 
thermal head 15 is forced up through the medium of head arms 18, as shown 
in FIG. 7. 
When line thermal head 15 is lifted from platen 1, platen drive motor 5 
rotates reversely. Thus, label sheet P, held between pinch roller 62 and 
sheet feeding roller 10, is retreated from platen 1 as roller 10 rotates. 
When paper sensor 40 detects passage of the leading end of sheet P, the 
rotation of motor 5 is stopped in response to an output signal from the 
sensor. Thereupon, the leading end of the sheet is set in a predetermined 
position behind sensor 40, whereupon its alignment is completed. In this 
state, platen drive motor 5 rotates forward, and cam drive motor 56 
rotates again for a predetermined amount in response to the output signal 
from sensor 40, after the passage of a predetermined time (or when sheet P 
is brought onto platen 1). As a result, cams 54, having so far been in 
engagement with head-up rollers 57, are caused to engage release rollers 
58. Thus, thermal head 15 is pressed again against platen 1 with the 
leading end portion of sheet P between the two, and pinch roller 62 is 
separated from sheet feeding roller 10, as shown in FIG. 2. Thereafter, 
thermal head 15 is heated to accomplish a specific cycle of printing 
operation, and platen 1 is rotated to feed label sheet P forward. 
FIG. 8 shows an electrical control system of the thermal transfer printer 
with the aforementioned construction. As seen from FIG. 8, a CPU is used 
as a principal control means for the printing operation. In this system, a 
ROM and a RAM are designed for label layout, just as in the case of the 
prior art printers.