Thermal printer

A thermal printer includes a fixed planar thermal head composed of heating elements disposed in an area corresponding to one page, a detachable unitary ink donor ribbon assembly including a frame and an ink donor ribbon movably disposed in the frame and having a plurality of color zones, the ink donor ribbon being positioned in confronting relation to the planar thermal head, and a detachable unitary print paper storage assembly composed of a paper cartridge and print paper stored therein, and including a presser for holding the print paper in contact with the ink donor ribbon in a printing mode and for keeping the print paper out of contact with the ink donor ribbon in a non-printing mode. The planar thermal head and the print paper are prevented from relative movement in the printing mode until one-page printing is effected on the print paper. The print paper may comprise a stack of separate sheets or a roll of continuous print paper.

BACKGROUND OF THE INVENTION 
The present invention relates to a printing mechanism in a thermal printer 
having a planar thermal head. 
Thermal printers include a thermal head having heating elements selectively 
heated to melt ink on an ink donor ribbon and to apply the melted ink to a 
sheet of print paper for thereby forming a desired image on a print sheet. 
The conventional thermal printers are classified into two printer types. 
One of these printer types is a serial-type thermal printer having a 
thermal head composed of 9, 18 or 24 vertical dots, the thermal head being 
transversely movable in increments to print data on a sheet of print 
paper. The other printer type is known as a line-type thermal printer in 
which a line thermal head has one line of dots for printing data by 
feeding a sheet of print paper therepast. 
The conventional serial-type thermal printer capable of color printing 
includes an ink donor ribbon of multiple colors movable in plural strokes 
in the direction in which the thermal head traverses the sheet. Each time 
the ink donor ribbon is moved in its stroke, the thermal head selectively 
heats and melts the ink donor ribbon partially to print a multiple-color 
image on the sheet. 
To effect such a printing operation, the serial-type thermal printer has a 
mechanism for enabling the thermal head, the ink donor ribbon and the 
print sheet to move relatively to each other in plural strokes. 
Such relative movement however tends to give rise to friction due to 
sliding engagement between the thin ink donor ribbon which has a thickness 
ranging from 3 to 10 microns and the thermal head. The ink donor ribbon is 
therefore liable to wrinkle, be broken, or elongated. 
For color printing, the thermal head and the print paper must be 
positionally controlled with respect to each other in their relative 
movement in repeated strokes, since such positional control is directly 
related to the accuracy of combining color images printed in different 
colors dependent on the dot density of the thermal head or the resolution 
of a printed image. It has been highly difficult to obtain the desired 
accuracy of such positional control. 
Conventional efforts to achieve the desired positional control accuracy 
include a mechanism for accurately feeding the thermal head and members 
for transmitting movement from the feeding mechanism to the thermal head, 
drive motor control and feedback control, precise diameters of various 
feed rollers employed to feed the print paper, and a correcting mechanism 
to guard against a skew of the ink donor ribbon. 
Therefore, in order to determine the relative positions of the thermal head 
and the print paper, the prior thermal printers have to meet the specified 
tolerances of the various mechanisms, parts, and their movements, which 
are quite difficult to achieve. The conventional thermal printers are 
therefore complex in construction. 
The conventional thermal printers are also disadvantageous in that they 
have no effective means for preventing the ink donor ribbon from 
wrinkling, tearing, and elongating due to the relative frictional movement 
of the ink donor ribbon and the thermal head. 
Examples of prior art thermal printers are disclosed in Japanese Laid-Open 
Patent Publication No. 57-84871 published on May 27, 1982 and Japanese 
Laid-Open Patent Publication No. 58-20482 published on Feb. 5, 1983. 
SUMMARY OF THE INVENTION 
In view of the difficulties of the prior art, it is an object of the 
present invention to provide a thermal printer having a simple printing 
mechanism composed of a fixed planar thermal head having an area covering 
one page, a unitary ink donor ribbon assembly, and a unitary print paper 
storage assembly, so that the ink donor ribbon and the print paper can 
easily be positioned with respect to the planar thermal head. 
According to the present invention, there is provided a thermal printer 
including a planar thermal head composed of heating elements disposed in 
an area corresponding to one page, a unitary ink donor ribbon assembly 
including a frame and an ink donor ribbon movably disposed in the frame 
and having a plurality of color zones, the ink donor ribbon being 
positioned in confronting relation to the planar thermal head, a unitary 
print paper storage assembly composed of a paper cartridge and print paper 
stored therein, and including a presser for holding the print paper in 
contact with the ink donor ribbon in a printing mode and for keeping the 
print paper out of contact with the ink donor ribbon in a non-printing 
mode, and a control unit for holding the planar thermal head and the print 
paper against relative movement until one-page printing is effected on the 
print paper. The planar thermal head is fixed, and the unitary ink donor 
ribbon assembly and the unitary print paper storage assembly are 
detachable with respect to the fixed planar thermal head. Since the planar 
thermal head and the print paper are in fixed positions with respect to 
each other in the printing mode, they can easily be controlled in position 
with respect to each other. The unitary assemblies serve to simplify the 
construction of the thermal printer. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which preferred 
embodiments of the present invention are shown by way of illustrative 
example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIGS. 1 and 2, a thermal printer according to a first 
embodiment of the present invention includes a planar thermal head 1 
composed of heating elements arranged in an area corresponding to one page 
of a sheet of print paper, the planar thermal head 1 having a heat 
applying lower surface 1a and a connector 1b. A control unit 2 connected 
to the connector 1b contains a memory, a driver, a microcomputer, and 
other components for controlling the heat applying surface 1a of the 
planar thermal head 1 and also the overall thermal printer. 
A rolled ink donor ribbon 3 has a width corresponding to one page of the 
print paper and is composed of a plurality of color bands indicated by 
respective marks 3a , 3b that can be detected by a detector 4. The ink 
donor ribbon 3 and the detector 4 are housed in a ribbon frame 5. A motor 
6 is also housed in the control unit 2 for driving the ink donor ribbon 3. 
The rolled ink donor ribbon 3 is thus disposed in a unitary assembly. 
A stack 7 of separate sheets of print paper each cut to one page is 
accommodated in a paper cartridge 8 including a presser roller 9 disposed 
at the bottom of the paper cartridge 8. The pressure roller 9 is biased by 
a bow-shaped spring 10 for pressing the sheet stack 7. A pair of drive 
belts 11 is rotatably mounted on the bottom of the paper cartridge 8, the 
drive belts 11 having pins 11a engaging ends of the presser roller 9. Both 
drive belts 11 are driven by a motor 12. 
A pair of paper feed rollers 13 is held against the upper surface of an end 
of the sheet stack 7 housed in the paper cartridge 8, the paper feed 
rollers 13 being rotated by a motor 14. The print sheets are therefore 
disposed in a unitary print sheet storage assembly. 
Therefore, the planar thermal head 1 and the paper cartridge 8 housing the 
sheet stack 7 are fixedly positioned with respect to each other. The 
unitary assemblies or units can easily be detached from the thermal 
printer. 
Operation of the thermal printer of the first embodiment thus constructed 
is as follows: 
The control unit 2 depresses the pressure roller 9 with a release 
mechanism, not shown, to keep the sheet stack 7 out of contact with the 
rolled ink donor ribbon 3. Therefore, the rolled ink donor ribbon 3 can 
freely move with respect to the planar thermal head 1 and the sheet stack 
7. The thermal printer is therefore in a non-printing mode. 
Then, the control unit 2 energizes the motor 6 to rotate so as to feed the 
rolled ink donor ribbon 3, and selects a yellow-ink zone upon detection of 
the mark 3a with the detector 4, whereupon the rolled ink donor ribbon 3 
is stopped. 
The control unit 2 inactivates the non-illustrated release mechanism to 
allow the bow-shaped spring 10 to act on the pressure roller 9 for moving 
the same upwardly. The pressure roller 9 thus displaced upwardly presses 
the bottom of the end of the sheet stack 7 upwardly until the upper 
surface of the sheet stack 7 is held against the rolled ink donor ribbon 
3. 
Thereafter, the control unit 2 energizes the motor 12 to move the drive 
belts 11. The pressure roller 9 is driven by the drive belts 11 to move 
from one end to the other of the sheet stack 7 while being held against 
the bottom thereof. Therefore, the upper surface of the sheet stack 7 is 
held against the rolled ink donor ribbon 3 at the one-line position which 
moves from one end to the other of the sheet stack 7. 
Simultaneously, the control unit 2 selectively energizes the heating 
elements on the heat-applying surface 1a of the planar thermal head 1 
according to the yellow printing data, the energized heating elements 
being in the one-line position where the sheet stack 7 and the rolled ink 
donor ribbon 3 are held against each other. The yellow ink on the rolled 
ink donor ribbon 3 is partly melted and transferred to the sheet 7. 
One line of data is now printed. The above printing cycle is repeated while 
the pressure roller 9 is moved successively through the lines over the 
sheet 7 until the desired characters are printed in yellow over the full 
page. 
Then, the rolled ink donor ribbon 3 is moved to select a blue ink zone and 
place the same in confronting relation to the planar thermal head 1. 
Thereafter, the pressure roller 9 is moved while at at the same time 
selected heating elements are energized according to blue printing data. 
Thus, the desired characters or image are printed in blue over the full 
page of the sheet 7. 
Likewise, desired characters or image are printed in red. The full page of 
the sheet 7 is now printed in all of the colors. The feed rollers 13 are 
rotated by the motor 14 to discharge the printed sheet 7 out of the 
thermal printer. 
While the separate sheets 7 are employed in the thermal printer of the 
first embodiment, roll paper can also be employed. A thermal printer, 
shown in FIG. 3, according to a second embodiment of the present invention 
is designed for use with such roll paper. Like or corresponding parts 
shown in FIG. 3 are denoted by like or corresponding reference characters 
in FIGS. 1 and 2, and will not be described in detail. 
Designated at numeral 15 is a roll of print paper. A roll core 16 is 
disposed at an end of the paper cartridge 8 for supporting the roll 15 
thereon. Also provided are a paper cutter 17, a base 18 of the paper 
cutter 17, and a magnet 19 for moving the paper cutter 17. 
The roll 15 is mounted in the paper cartridge 8, and has its end extending 
over the pressure roller 9 and between the paper cutter 17 and its base 18 
out of the thermal printer. The thermal printer of FIG. 3 operates in the 
same manner as the thermal printer of the first embodiment for printing 
characters in colors on one page of the roll paper 15. 
After the color characters have been printed, the motor 14 rotates the 
paper feed rollers 13 to discharge a one-page length of the roll paper 15. 
Then, the magnet 19 is activated to pull the paper cutter 17 toward the 
base 18 to cut off the one-page length of the roll paper 15 thereon. 
With the arrangement of the present invention, the planar thermal head and 
the print paper are set a fixed positions with respect to each other 
during a cycle of printing operation. Therefore, they can be positioned 
with a desired accuracy more easily and accurately than possible with the 
conventional thermal printers, thus preventing color shifts or mixtures on 
printed sheets. With the print paper pressed against the ink donor ribbon, 
the ink can be transferred from the ink donor ribbon to the print paper 
with high efficiency to thereby improve the printing quality. 
Since the ink donor ribbon moves while it is out of contact with the planar 
thermal head and the print paper, the ink donor ribbon is protected from 
wrinkles, breakage, or elongation, and can be moved stably. 
The unitary ink donor ribbon assembly and the unitary print paper storage 
assembly are effective in simplifying the thermal printer in construction. 
The ink donor ribbon and the print paper can easily be replaced simply by 
detaching their units from the thermal printer. 
Although certain preferred embodiments have been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.