Simplified printer drive mechanism

A printer for transferring colorant from a donor web to a receiver web, includes a rotatable platen roller and a printhead having an energy transfer portion engaging the donor web and pressing the donor web into engagement with the receiver web and the receiver web into the surface of the rotatable platen roller to form a nip so that as the rotatable platen rotates, both the receiver web and the donor web are translated. Applied energy to the printhead is transferred from the energy transfer portion of the printhead to the donor web to transfer colorant to the receiver web at the nip. The movement of the receiver web is sensed for controlling the rotation of the rotatable platen roller and energy application.

FIELD OF THE INVENTION 
The present invention relates to printers which cause the transfer of 
colorant from a donor web to a receiver web. 
BACKGROUND OF THE INVENTION 
One type of printer which transfers colorant from a donor web to a receiver 
web is a thermal printer that uses a dye transfer process. 
U.S. Pat. No. 5,266,976 describes an apparatus for multipass color 
electrostatic recording in which edge registration marks are printed on 
the edge of the print on the first pass and then read by a sensor on 
subsequent passes to register the colors in the final print. The apparatus 
is illustrated by a belt drive devise, and may be limited to a continuous 
web, and a latent image process. The printed registration marks may be 
objectionable in many kinds of printed images. 
U.S. Pat. No. 4,745,413 describes a thermal head printing apparatus, but no 
method of correction for registration is given. 
U.S. Pat. No. 4,953,994 describes a thermal printer which has a control 
apparatus to locate printing on a label. With this arrangement, mulitpass 
registration is a problem. 
U.S. Pat. No. 4,752,786 describes a thermal printer with a simplified drive 
mechanism using a single motor for all drive functions. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a simplified printer 
which effectively can transport a donor web and a receiver web through a 
nip wherein colorant is transferred from the donor web to the receiver 
web. 
Another object of the present invention is to provide a printer which 
translates the donor web and receiver web and does not need to use a 
complex capstan drive system. 
These objects are achieved by a printer for transferring colorant from a 
donor web to a receiver web, comprising: 
a) a rotatable platen roller; 
b) a printhead having an energy transfer portion engaging the donor web and 
pressing the donor web into engagement with the receiver web and the 
receiver web into the surface of the rotatable platen roller to form a nip 
so that as the rotatable platen rotates, both the receiver web and the 
donor web are translated; 
c) means for applying energy to the printhead which is transferred from the 
energy transfer portion of the printhead to the donor web to transfer 
colorant to the receiver web at the nip; and 
d) means for sensing the movement of the receiver web for controlling the 
rotation of the rotatable platen roller and the energy applying means. 
ADVANTAGES 
An advantage of this invention is that registration of the different colors 
is precise and accurate. 
Another advantage is that the transport arrangements for the donor web and 
receiver web is particularly effective for multipass registration 
situations.

DETAILED DESCRIPTION OF THE INVENTION 
The invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it will be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention to elements forming part of, or cooperating more directly 
with, apparatus and method in accordance with the present invention. It is 
to be understood that elements not specifically shown or described may 
take various forms well known to those skilled in the art. 
The receiver web used in this invention should be understood to refer in 
general to all types of receiver materials, including conventional papers 
made from wood pulp, synthetic papers made from polymer fibers and 
extruded plastics films. 
FIG. 1 shows a prior art capstan drive printer commonly used in thermal 
resistive head printers. In this kind of printer, a donor web 30 is 
transported past a thermal resistive print head 50 from a donor supply 
roll 10 to a donor take-up roll 20. A guide roller 40 is used to steer the 
donor web 30. The donor web 30 contacts the receiver web 5 at the energy 
transfer portion of the print head 50A, thus pressing the donor web 30 
against the receiver web 5 and thereby forming a nip where the energy 
applied to the print head will effect transfer of colorant from the donor 
web to the receiver web without blank spots or drop-outs. A pair of 
capstan rollers 60 geared to the platen drive roller 70 serve to drive the 
receiver web across the print heat 50, and the nip pressure caused by the 
energy transfer portion of the print head 50A pressing the donor web 30 
into the receiver web 5 and the receiver web 5 in turn into the platen 
drive roller 70 serves to move the donor web 30 along with the receiver 
web 5 in the direction of the arrow in FIG. 1. The materials used to form 
the capstan rollers 60 and the capstan drive mechanism 80 that connect the 
capstan rollers to the platen drive roller 70 must be manufactured with 
high precision tolerances to prevent slippage of the donor and to prevent 
positional error banding in the printed image. In addition, the distance 
"a" indicated in FIG. 1, which is necessarily of a significant size, 
requires an unprinted border at the edge of the printed image so that 
contact of the receiver web with the capstan rollers is maintained through 
the printing process. 
FIG. 2 shows the simplified and improved mechanism of this invention. A 
donor web 30 is transported past a thermal resistive print head 50 from a 
donor supply roll 10 to a donor take-up roll 20. A guide roller 40 is used 
to steer the donor web 30. The donor web 30 contacts the receiver web 5 at 
the energy transfer portion 50A of the print head 50, thus pressing the 
donor web 30 against the receiver web 5 and thereby pressing the receiver 
web onto the surface of the rotatable platen roller 70, thus forming a 
nip, so that rotation of the platen roller 70 urges both the donor and the 
receiver webs forward in the direction of the arrow in FIG. 1. Preferably, 
the rotatable platen roller 70 is incrementally rotated under the control 
of computer 90 (see FIG. 2). The pressure of the nip guarantees good 
contact between the donor and receiver so that the energy applied to the 
print head will effect transfer of colorant from the donor web to the 
receiver web without blank spots or drop-outs. A receiver web movement 
sensor 110 (which can be an encoder) monitors the position and movement of 
the receiver web. The sensor is connected to a computer 90 which sends 
electrical signals to the platen drive motor 120 and to the energized part 
of the print head 50 so that the incremental rotation of the rotatable 
platen roller may be controlled to move the receiver web into a position 
synchronized with the application of energy from the print head 50 so that 
the different colors of a full color image may be transferred in accurate 
positional association, sometimes referred to as "in registration". The 
receiver web movement sensor 110 may take any one of several forms. A 
simple encoding wheel driven by the movement of the receiver web may be 
used to monitor the position of the receiver web. Alternatively, a non 
contact sensor utilizing a light signal or an electrical capacitance 
signal may be devised. 
FIG. 3 shows a view of the print head 50 and platen roller 70 across the 
receiver web 5. The donor web 30 is omitted from this drawing for clarity. 
Both a right hand 110R and left hand 110L receiver web movement sensor are 
shown. Signals from these two sensors are communicated to the computer 90 
which can thereby detect a skew in alignment of the receiver web 5 with 
the print head 50. The two head position controllers 130 receive signals 
from the computer 90 to control the position of the print head 50 in a 
direction normal to the rotatable platen roller 70. By controlling the 
position of the print head the pressure of the nip between the donor web 
and the receiver web may be increased or decreased thus causing more or 
less slippage of the receiver web 5 against the rotatable platen roller 70 
so that skew errors in the receiver motion may be corrected. 
FIG. 4 is a drawing showing how the computer 90 receives a digital image 
from memory, and receives signals from the right hand receiver web 
movement sensor 110R and the left hand receiver web movement sensor 110L, 
and sends corresponding signals to the right and left hand head position 
controllers 130, to the print head 50, and to the belt drive 100 of the 
rotatable platen roller 70. The energizing signals to the print head are 
sent when the receiver web movement sensors determine that the receiver 
web 5 is in the correct position for colorant transfer from the donor web 
30 to the receiver web 5. 
The invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it will be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention. 
TS LIST 
5 receiver web 
10 donor supply roll 
20 spent donor take-up roll 
30 donor web 
40 guide roller 
50 print head 
60 capstan rollers 
70 rotatable platen roller 
80 capstan drive mechanism 
90 computer 
100 belt drive 
110 receiver web movement sensor 
120 platen drive motor 
130 head position controller