Versatile printing mechanism

A wide format versatile printing mechanism is provided which has ribbon tensioning means to equalize the surface tension forces across the ribbon and remove all wrinkles. In one embodiment a cambered rod is introduced between the print head and the ribbon feed roll to apply an uneven force across the ribbon's width from its uncoated side. The cambered rod is fixed between two lateral lid side plates by two screws having their axis coaxial with the axis of the cambered rod which have at one of the end cut some radial grooves. The cambered rod can be rotated around its axis and positioned under different angles around its axis by means of a set screw through the lid side plate which corresponds with the radial grooves of the cambered rod's end, offering a variation of the tensile forces in the ribbon. In another embodiment, a second rotating cambered rod is located between the print head and ribbon take-up roll to apply an uneven tensile force across the ribbon's width from its uncoated side. This provides an alternate and a versatile additional means for equalizing the tensile forces across the ribbon as it is transported within the device and adapting with different types of ribbon.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus and a method for producing 
uniform tension in a wide roll of waxed based ink ribbon during printing, 
to remove all wrinkles due to uneven surface tension across the ribbon. As 
ribbons increase in width they become more difficult to handle as a force 
must be applied across their width of varying magnitude to eliminate 
wrinkles. This is generally due to the nature of the polyester based 
carrier onto which the wax formula ink coating is uniformly applied. 
Unwinding of the ribbon for printing purposes onto a base paper requires 
this uneven force applied across the width, as the center has a tendency 
to sag and wrinkle under a uniform force applied across the width. Hence, 
a cambered circular or elliptical rod having a smooth surface is 
introduced acting against the ribbon to apply an uneven force, with an 
increment towards the center, counteracting the inherent sag in the ribbon 
as it is unwound. Wrinkled ribbons do not transfer ink onto the base paper 
at locations of these wrinkles, affecting the overall image quality. 
Prior art in this field would involve thermal transfer printing mechanisms 
which use a waxed based ribbon to transfer an electronic image onto a base 
paper. A thermal print head is used as the heat source to melt the 
ribbon's ink coated on a carrier film, usually polyester, transferring ink 
to the base paper as selected heating elements comprising picture 
elements, or pixels, are individually addressed and heated to produce a 
tangible image on base paper. 
The main problem associated with most prior art systems for this particular 
application is the narrow width of ribbon commonly found in most thermal 
transfer printing mechanisms. For printing widths of 8 1/2 inches or less, 
the thermal transfer ribbon handles suitably without the need for any 
ribbon tensioning devices. As printing widths increase to 24 inches and 
greater, there is considerable sag in the center of the ribbon which leads 
to printing problems as the ribbon wrinkles, also impairing document 
handling. 
An example of a conventional printing mechanism related to the prior art, 
is shown in FIG. 1a to 1f of the accompanying drawings, according to 
Sakuragi et al. in U.S. Pat. No. 4,910,602. 
In this printing mechanism according to FIG. 1a, a ribbon ink 1 unwounded 
from a core 2 is superposed on a recording paper 3 wound on a core 4. The 
ribbon ink 1 is directed between a thermal head 5 and a platen roller 6 
via a tension roller 7 and is taken-up by a take-up shaft 8. 
The prevention of ribbon 1 wrinkling conforming to Sakuragi's patent is 
accomplished by the tension roller 7. According to FIG. 1b, the roller 7 
can rotate around its axis, having a bulged portion at its center, and 
gradually tapers lengthwise in both directions from the center. 
In this case, as shown in FIG. 1c, the roller 7 induces in the ribbon ink 1 
some tensile forces F1. The shape of the tensile forces F1 is determined 
by the gradual increase and decrease of the roller 7 diameter which is 
manufactured in such a way that the tensile forces F1 cannot be changed 
during rotation of the roller 7, thus lacking the ability to adapt the 
tensioning profile to various ribbon's elasticity. This is a major 
drawback of Sakuragi's patent. 
Similarly, in another embodiment of Sakuragi's patent according to FIG. 1d, 
he uses two fixed side walls 9 and 10 in front of and behind the print 
head 5, which induce in the ribbon ink 1 some tensile forces F2 as shown 
in FIG. 1f. The variation of tensile forces F2 is determined by the 
profile of the side walls 9 and 10. 
As shown in FIG. 1e, he uses a shaped edge profile peaking in the center 
for his walls. This solution does not conform exactly to the distribution 
of tensile forces in ribbon foils of a variety of compositions, as the 
device has no ability to adapt to various ribbons. 
Further, the inclination of the sided walls 9 and 10 against ribbon's 1 
surface is fixed; this also lacks the ability to adapt to the tensioning 
profile of various ribbon's elasticity. In his case, using a preset 
distribution of said forces will not necessarily work for different ribbon 
types. 
In other words, Sakuragi's solution does not allow the flexibility of 
choosing different types of ribbon materials, limiting the user to type 
that works well with his device. 
Hence, the primary function of the present invention is in the adapting to 
a variety of wide format ribbons to avoid any sag related complications 
affecting the image quality, allowing the flexibility of choosing 
different types of ribbon materials conforming to variations in 
elasticity. 
SUMMARY OF THE INVENTION 
In a principle aspect of the present invention, a versatile printing 
mechanism using a cambered rod is provided as a waxed ribbon is unwound 
from a feed roll before printing on a base paper due to the applied 
rotational force of a drive roller, to counteract the uneven surface 
tension encountered in wide format thermal transfer ribbon rolls. 
In a further aspect of the present invention, the cambered rod which is 
located between the print head and the ribbon feed roll applies an uneven 
force as it contacts the ribbon in unwinding, with a greater force applied 
to the center of the ribbon across its width where there is much less 
surface tension compared to the ends. 
In a further aspect of the present invention, the cambered rod is an 
integral part of the thermal transfer mechanism providing a means for 
smooth document handling and wrinkle free printing, as ribbon is released 
from a feed roll and collected on a take-up roll after the printing 
process. 
The cambered rod is cylindrical in shape, having a fixed radius of 
curvature throughout its entire length. The cambered rod also has an axis 
which passes through its both ends. 
Furthermore, the cambered rod ends are cut in parallel planes and 
perpendicular to the axis of the cambered rod, one of the ends having cut 
some radial grooves. The cambered rod is fixed between two lateral lid 
side plates with two screws having their axis coaxial with the axis of the 
cambered rod. 
Moreover, the cambered rod can be rotated around its axis and positioned 
under different angles by means of a set screw through the lid side plate 
locking into a radial groove of the cambered rod's end. 
By rotation of the cambered rod around its axis, uneven tensile forces are 
applied across the ribbon's width decreasing or increasing proportional 
with rotation angle. 
In another embodiment of the present invention, a second cambered rod is 
applied between the print head and ribbon take-up roll to apply an uneven 
tensile force across the ribbon's width from its uncoated side, allowing a 
greater displacement of ribbon towards the center of the roll applying the 
most force at this location, gradually decreasing towards the ends 
symmetrically about the center. 
This provides a versatile alternate means for equalizing the tensile forces 
across the ribbon as it is transported within the device which adapts to 
the different types of ribbon, and acts in conjunction with the force 
applied by the ribbon take-up roll and the first cambered rod, to remove 
all wrinkles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
For a better understanding of the invention's operation, reference is first 
made to FIG. 2, which represents a schematic side view of the versatile 
printing mechanism using a rotating cambered rod, in accordance with a 
first embodiment of the present invention. 
Referring to FIG. 2, a drive roller 11 is used to transport an ink ribbon 
12 and a base paper 13 simultaneously without any slippage as printing is 
performed by a thermal print head 14. The base paper 13 is stored in a 
roll 15 and is released at the same rate as the ribbon 12 from a feed roll 
16. The ribbon 12 is constructed of a carrier material, usually polyester, 
coated with a wax and or resin formula uniformly on one first side of the 
ribbon, having an uncoated second side opposite to the first waxed side. 
The thermal print head 14 applies heat at addressed locations along a print 
line to the uncoated side of the ribbon 12, which then releases the ink as 
it melts at individual heating element locations, representing each 
picture element or pixel of a printed image. 
The melted ink is transferred from the ribbon 12 directly to the printing 
surface of the base paper 13 to form the printed image. After the printing 
process, the used ribbon is collected in a take-up spool 17 whilst the 
printed image appears on the output 18. 
A cambered rod 19 is provided as the ribbon 12 is unwound from the feed 
roll 16 before printing on the base paper 13 due to the applied rotational 
force of the drive roller 11, to counteract the inherent uneven surface 
tension encountered in wide format thermal transfer ribbon rolls. 
The ribbon's feed roll 16 is positioned to allow the ribbon 12 to flow over 
a cambered rod 19 which act s as a ribbon tensioner, prior to entering the 
thermal print head 14. 
The cambered rod 19 is cylindrical in shape having a fixed radius of 
curvature R through its entire length. The cambered rod also has an axis 
X-X which passes through its both ends (FIG. 3). 
The cambered rod 19 has two ends E1 and E2 which are cut in parallel planes 
and perpendicular to the axis X-X of the cambered rod 19. One of the ends 
E2 has cut some radial grooves 20 (FIG. 7). 
The cambered rod 19 is positioned with its axis X-X parallel to ribbon's 12 
surface and fixed to a printing mechanism between two lid side plates 21a 
and 21b (FIG. 7), by means of some fixing screws 22a and 22b which passes 
through said lid side plates 21a and 21b. The axis of fixing screws 22a 
and 22b are coaxial with the axis X-X of the cambered rod 19. 
The cambered rod 19 can be rotated around its axis X-X, it can be also 
positioned from a first position P1 to a second position P2 (FIG. 2 and 
2a) at a desired preset rotation angle .alpha. (FIG. 2 and FIG. 2a) by 
means of a set screw 23 through the lid side plate 21a. The set screw 23 
is positioned to fit with the radial grooves 20 at the end of the cambered 
rod 19 (FIG. 7, 8 and 9). 
As the cambered rod 19 rotates from its first position P1 to the second 
position P2 (FIG. 2a) representing a new profile 19a, the ribbon 12 
changes its position to a new position 12a. 
Corresponding to this rotation of the cambered rod 19, the ribbon's 12 
profile of the first position P1 represented in FIG. 3 and FIG. 5 changes 
to a new profile of the second position P2 represented in FIG. 4 and FIG. 
6. 
As presented in FIG. 10a corresponding to FIG. 5, the cambered rod 19 
applies over the ribbon 19 width an uneven forces f1, allowing a greater 
displacement towards the center of the ribbon where the greatest sag 
occurs. 
As presented in FIG. 10b corresponding to FIG. 6, as the cambered rod 19 
rotates from its first position P1 to the second position P2 (FIG. 2a), a 
different tensile forces f2, reduced in amplitude in this case, is induced 
across the width of the ribbon 12, better adapting with different types of 
ribbon. 
The variation of the tensile forces induced by the cambered rod 19 across 
the ribbon's 12 width, from f1 to f2 presents a different amplitude shape 
which is in this case less bulged corresponding to second position P2 of 
the cambered rod 19 (FIG. 10b). 
In another embodiment of the present invention conforming to FIG. 11, a 
second cambered rod 24 is applied between the print head 14 and ribbon 
take-up roll 17 to apply an uneven tensile force across the ribbon's 12 
width from its uncoated side. 
This provide an alternate and a versatile additional means for equalizing 
the tensile forces across the ribbon, acting in conjunction with the force 
applied by the ribbon take-up roll and the first cambered rod to remove 
all wrinkles. 
It is also understood that the following claims are intended to cover all 
of the general and specific features of the invention herein described, 
and all statements of the scope of the invention which, as a matter of 
language, might be said to fall therebetween.