Ribbon cassette for a printer

A cassette for ribbon for a printer, particularly a thermal printer, is disclosed. The cassette is configured to be stably mounted to a print carriage of a thermal printer, or to a storage turret mounted to the printer for storing a number of cassettes, and to be transferred by a passive transfer system between the print carriage and the storage turret simply in response to movement of the print carriage. A smooth, low friction path is provided for the ribbon within the cassette with no acute angle changes in the path when the cassette is in a printing position and being acted upon by the printer's print head. The cassette is provided with a brake mechanism which automatically engages the supply and take-up reels in the cassette when the cassette is removed from the print carriage, and automatically disengages the brake mechanism when the cassette is mounted to the print carriage. The cassette is provided with a bar code so that cassettes on the storage turret may automatically be identified, particularly for use in an automatic cassette transfer system. The cassette housing is plastic and is provided with an anti-static additive.

The invention disclosed in this application may be employed in the thermal 
printer disclosed in the following U.S. patent applications, all filed on 
Jul. 24, 1992: Ser. No. 07/920,186 titled "STRIP MODE PRINTING AND 
PLOTTING APATUS AND METHOD"; Ser. No. 07/919,666 titled "THERMAL STRIP 
MODE PRINTER COMPONENTS AND SUBASSEMBLIES; Ser. No. 07/920,115 titled 
"SHEET MEDIUM TRANSPORT SYSTEM, TICULARLY FOR PRINTERS AND PLOTTERS"; 
and with the cassette storage and transfer apparatus and described in the 
'116 Application. The reel diameter determining method and apparatus, and 
the ribbon tensioning method and apparatus disclosed in Ser. No. 
07/920,117 now U.S. Pat. No. 5,267,401 titled "METHOD and APATUS FOR 
GAUGING REEL DIAMETERS IN A REEL-TO-REEL SHEET MATERIAL TRANSPORT SYSTEM", 
filed Jul. 24, 1992 may be used with the cassette disclosed herein. The 
disclosures of all of the five patent applications referenced above 
(collectively referred to herein as "the cited applications") are 
incorporated herein by reference. The cited applications and this patent 
application are commonly owned. 
BACKGROUND OF THE INVENTION 
The invention disclosed herein relates to a cassette containing strip, tape 
or ribbon material (hereafter referred to simply as "ribbon") containing, 
for example, pigment, wax, resin, ink, etc., particularly for use with 
printers and plotters. However, the invention is not limited to cassettes 
containing ribbon for use in printing or plotting. 
While the cassette disclosed herein may be used in any suitable printer or 
plotter, the cassette finds particular application in the thermal strip 
mode printer described in the cited applications. The cassette disclosed 
herein may be stored an a turret device, carried by a print carriage 
during use and moved between the turret storage device and the print 
carriage as described herein and in the cited applications. 
The thermal printer described in the cited applications is capable of 
thermal transfer printing in wide formats of up to about 36 inches. In 
doing so, that thermal printer prints in a strip mode of printing where 
the print or plot is printed one strip at a time in widths (Y-axis 
direction) of about one inch to about four inches, with strips of about 
two inches being presently preferred. To print in strips of about two 
inches in width requires a thermal transfer ribbon of slightly more than 
two inches in width. In order to provide enough ribbon to print 
approximately 50 typical color, graphic D size plots, and approximately 
100 color typical line art D size plots, width, about 500M of ribbon of 
each of the four colors in the four color yellow, magenta, cyan and black 
system are typically required. As a result, reel-to-reel cassettes 
incorporating that amount of ribbon will have considerable size. 
The thermal printer described in the cited applications is a color printer 
which automatically prints in different colors to provide a composite 
color print or plot. In order to automatically print in color, the thermal 
printer incorporates a number of reel-to-reel cassettes each containing 
ribbon of a different color. In the presently preferred embodiment, the 
four color system referred to above is used for color printing, which 
requires four ribbons. Also as presently preferred, the thermal printer 
includes a primary four color system and a redundant four color system, 
and therefore incorporates a total of eight reel-to-reel cassettes. 
The thermal printer described in the cited applications incorporates an 
automatic transfer system for transferring ribbons between a storage 
location and a printing location on a movable print carriage which carries 
a thermal print head. As described in the cited applications and herein, 
the transfer system is passive in that the transfer mechanism itself is 
not servo controlled and operates simply in response to movement of the 
print carriage towards and away from the cassette storage device, which in 
the preferred embodiment is a rotatable turret. 
Given the relatively large size cassette required to hold 500M of about two 
inch wide ribbon, and given the stringent requirements for thermal 
transfer printing described in the cited applications and herein, unwanted 
movement of ribbon could cause serious problems. 
The cassette disclosed herein and in the cited applications was invented in 
consideration of the factors mentioned in the cited applications and 
herein, including: size constraints for mounting eight relatively large 
cassettes in a printer incorporating automatic cassette transfer; 
configuration constraints on the cassette so as to efficiently mount a 
number of them on the turret, and one on the print carriage in an 
efficient print position; preventing unwanted movement of the ribbon in a 
simple and efficient manner; a simple automatic cassette transfer system; 
providing for smooth and efficient ribbon delivery to the print head and 
back to the cassette; protecting the ribbon from contamination and 
physical damage; possible recycling of the entire cassette or parts 
thereof; providing an accessible customer interface which protects the 
customer and reduces difficulties that the customers will have in handling 
the cassettes; and identifying the cassettes on the turret in a simple 
manner. 
There is therefore a need for ribbon cassettes which satisfy all or various 
combinations of the factors discussed herein and in the cited 
applications. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention disclosed herein to provide an improved 
ribbon cassette for a printer or plotter. 
Another object of the invention is to provide a ribbon cassette having a 
bar code which identifies the cassette and/or at least one characteristic 
thereof and a means for reading the bar code on the cassette while the 
cassette is mounted to a rotating storage turret. 
Another object of the invention is to provide a ribbon cassette in which 
the status of ribbon available for use (and/or status of used ribbon) may 
be visually detected. 
Another object of the invention is to improve the mounting in a ribbon 
cassette of the ribbon supply and take-up reels. 
Another object of the invention is to contain and/or dissipate static build 
up on a ribbon in a ribbon cassette. 
Another object of the invention is to minimize friction in a ribbon 
cassette between the ribbon and the cassette. 
Another object is to prevent wrinkling of the ribbon during the printing 
process and to optimize the ribbon path for use in a thermal printer. 
Another object of the invention is to improve transfer of a ribbon cassette 
between a use location on a print carriage and a storage location off the 
print carriage. 
Another object is to improve the mounting of a ribbon cassette to a print 
carriage of a thermal printer; 
Another object of the invention is to stably secure a ribbon cassette both 
to a print carriage and to a storage device off the print carriage. 
Another object of the invention is to prevent movement of the ribbon in a 
cassette when not printing. 
The invention disclosed herein in its various aspects achieves the above 
and other objects of the invention by providing a cassette having two 
major opposed sides and a peripheral side therebetween in which holes on 
one side are used to mount the cassette to a mounting structure from one 
side of the cassette, and holes on the opposing side are used to mount the 
cassette to a mounting structure from the other side of the cassette. The 
two mounting structures may be different mounting structures, one being on 
a print carriage carrying a print head which acts on the ribbon carried by 
the cassette to print on a sheet medium, and the other being a storage 
element for holding cassettes for transfer to the mounting structure on 
the print carriage. This allows the storage element and the print carriage 
to be mounted side by side so that transfer of a cassette between the 
print carriage and the storage element may be effected passively as 
described herein simply by moving the print carriage so that its mounting 
structure engages the mounting structure of the storage element. The 
number and locations of the holes are selected so that the cassette may be 
stably guided during a transfer and stably mounted to both the print 
carriage and the storage element. 
In the preferred embodiment, there are first and second spaced holes in the 
first major side for receiving respective pins projecting from a mounting 
structure (e.g., on a print carriage) for mounting the cassette to the 
mounting structure with the first major side facing the mounting 
structure, and third and fourth spaced holes in the second major side for 
receiving respective pins projecting from a mounting structure (e.g., a 
storage element) for mounting the cassette to that mounting structure with 
the second major side facing that mounting structure. 
The cassettes have a pair of spaced projections on the peripheral edge of 
the housing for engaging arms on a mounting structure, and a cassette is 
mounted to the mounting structure by engagement of the arms on the 
mounting structure with the lugs on the cassette and entry of pins 
projecting from the mounting structure into the holes on the same side of 
the cassette which faces the mounting structure when the cassette is 
mounted thereto. The cassette is mounted in generally the same way from 
either side of the cassette, except that the holes are located differently 
on opposite sides of the cassette to optimize mounting of the cassette 
from one side and yet satisfy certain requirements for mounting the 
cassette from the other side. The cassette is structured such that there 
is space within the cassette for the pins to project within the cassette a 
distance sufficient to guide the cassette as it is being mounted to the 
mounting structure, and to stably mount the cassette to mounting structure 
from either side of the cassette. In the preferred embodiment, there is 
space within the cassette for all of the pins to project simultaneously 
within the cassette from both major sides substantially from major side to 
major side. 
The cassette has a center of gravity, and in the preferred embodiment, the 
first and second holes are positioned as follows: the first hole is 
positioned on one side of the center of gravity adjacent the peripheral 
edge of the cassette; the second hole is positioned on an opposite side of 
the center of gravity adjacent the peripheral edge; and the first and 
second holes are positioned such that a first line connecting the center 
of the first and second holes passes through a central part of the 
cassette. The third and fourth holes are substantially spaced apart with 
each positioned adjacent the peripheral edge of the cassette and such that 
a second line connecting the center of the third and fourth holes 
intersects the first line at an angle of from about 60.degree. to about 
120.degree., and preferably about 90.degree.. 
In the preferred embodiment, the housing comprises a body and includes 
spaced arms projecting from the body which terminate in the inlet and 
outlet, the first and second holes being positioned in the body spaced 
from the arms, and the third and fourth holes being positioned in or near 
the arms. The cassette comprises a first reel (e.g., a supply reel) 
rotatably mounted in the housing having an axis perpendicular to the major 
sides and a second reel (e.g., a take-up reel) rotatably mounted in the 
housing having an axis perpendicular to the major sides, the first and 
second reels being laterally spaced in the housing, and the first and 
second holes being positioned such that a first line connecting the center 
of the first and second holes passes between respective axes of the reels 
and a second line connecting the center of the third and fourth holes does 
not. 
The cassette has means associated at least with one of the reels (e.g., the 
take-up reel) for permitting that reel to be driven and means for guiding 
ribbon along a path from the first reel to the outlet of the housing and 
from the inlet of the housing to the second reel. The arms are configured 
to project ribbon exteriorly of the cassette spaced therefrom such that a 
print head may act upon the ribbon between the arms exteriorly of the 
cassette. The guiding means comprises a plurality of guides for guiding 
ribbon in the path from the first reel to and from the outlet, and a 
plurality of guides for guiding ribbon in the path from the inlet to the 
second reel. The guides are positioned and configured such that in a use 
configuration of the cassette with the print head acting upon the ribbon, 
the guides introduce only oblique angle changes in the path. The guides 
are positioned and configured such that in a non-use configuration of the 
cassette when the print head is not acting upon the ribbon, the guides 
introduce not more than one angle change which is approximately an acute 
angle. 
The reels are mounted for low friction rotation. The cassette includes 
means for rotatably mounting the reels in the housing including means held 
from rotating in the housing positioned in the housing adjacent the ends 
of the axles on which the ends of the axles bear and rotate. The reels 
each include structure which may be engaged through respective holes in a 
first of the major sides of the cassette by apparatus for rotating or 
braking a respective reel from a side of the reel opposite the one side, 
and guiding means for loosely guiding the reels at the ends opposite the 
one end while permitting the reels to rotate, whereby the reels are 
loosely captivated in the cassette when not engaged by the apparatus for 
rotating or braking. The axle end is rounded to provide an area of contact 
thereon which is substantially less than the cross-sectional area of the 
axle, and the means on which the ends of the axles bear and rotate 
comprise a planar surface having relatively low friction. The guiding 
means comprises respective holes in the first major side of the cassette 
which have a larger diameter than the diameter of the reels such that the 
holes loosely guide the outer periphery of the opposite sides of the 
reels, and means acting on the planar surfaces for resiliently urging the 
axles towards the first major side. 
The cassette according to the invention is provided with a brake mounted in 
the housing for frictionally engaging at least one of the reels in any 
angular position thereof in response to the cassette not being mounted to 
the mounting structure and for not frictionally engaging the reel in 
response to the cassette being mounted to the mounting structure. The 
brake does not frictionally engage the reel when a pin from a mounting 
structure is present within the cassette projecting therein through one of 
the holes in the side of the cassette discussed above, and the brake 
frictionally engages the reel when the pin is not in the hole. 
The brake comprises an arm pivotably mounted in the housing having a free 
end which frictionally engages the reel in a first position of the arm and 
does not engage the reel in a second position of the arm, means urging the 
arm into its first position, and means positioned in alignment with the 
hole so as to be contacted by the pin of the mounting means for pivoting 
the arm towards the second position in response to the pin projecting in 
the hole. Removal of the pin from the hole allows the arm to pivot to its 
first position with the free end of the arm in frictional engagement with 
the one reel. Preferably, the arm is configured and positioned so that 
when the arm is in frictional engagement with the reel, the arm applies a 
harder braking force to the reel when the reel is urged to rotate or does 
rotate in a direction to unwind ribbon therefrom. In the preferred 
embodiment, a brake is provided for each of the reels. 
A see-through window is preferably provided in a major side of the housing 
adjacent at least one of the reels positioned a given distance radially 
from the axis of the reel such that ribbon wound on the reel may be gauged 
by the naked eye from the exterior of the cassette. In the preferred 
embodiment, the window is an opening on a major side and is positioned 
adjacent the supply reel. 
A bar code is preferably positioned on a major side of the cassette. 
Preferably the bar code is a linear bar code positioned adjacent the 
peripheral side and has a longitudinal axis, and the bar code is oriented 
such that the longitudinal axis is at approximately 90.degree. to a line 
passing through the axes of the reels. 
A plurality of cassettes are stored on a storage element in an adjacent 
relationship extending about a circle with the major side of each of the 
cassettes having the bar code thereon facing away from the storage 
element. Means are provided for machine reading the bars codes comprising 
means for rotating the storage element, and a bar code reader positioned 
adjacent the storage element spaced therefrom sufficiently to permit the 
cassettes to pass by the bar code reader. The linear bar code is 
positioned on each of the cassettes and the cassettes are positioned on 
the storage element such that the linear bar code on each cassette passes 
the bar code reader when the storage element is rotated. The linear bar 
code is preferably mounted on the major side of the cassette at 
substantially the greatest radius from the axis of rotation of the storage 
element. 
The cassette housing is preferably made of plastic and includes a 
conductive additive, and the housing is in contact with the ribbon as the 
ribbon is moved for conducting static charge on the ribbon from the ribbon 
to the housing. Also, the ribbon preferably has a conductive coating for 
conducting static charge. 
The cassette preferably includes means for removably attaching one of the 
major sides to the housing such that it may be removed to gain access to 
the interior of the housing to remove and replace ribbon therein. However, 
both sides may be non-removably attached to the housing, if desired.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Ribbon cassette 10 (FIG. 1) according to the invention is especially suited 
for carrying a thermal donor medium for use in a thermal printer. A 
cassette 10 according to the invention has particular application to the 
strip mode thermal printer described in the cited applications. However, 
the invention is not limited to a cassette for carrying a thermal donor 
medium, and is applicable to cassettes for carrying other types of strip 
material, tape or ribbon, and is not limited to use in thermal transfer 
printers, and is applicable to other printers and to applications other 
than printing or plotting. 
Cassette 10 shown in FIGS. 1-3 carries a thermal donor material in the form 
of a ribbon 12 which is employed in the thermal printing process described 
in the cited applications and carried out by the thermal printer 14 shown 
in FIGS. 4 and 5 and also described in the cited applications. Referring 
to FIGS. 4, 5 and 12, thermal printer 14 includes a print carriage 16 on 
which is mounted a cassette drive 18 (FIG. 5) and a cassette holder 20. 
Thermal printer 14 prints an image on receptor sheet medium 22 (FIG. 12) 
in the strip printing mode described in detail in the cited applications 
employing a thermal print head 24 (FIGS. 4 and 12) and a thermal donor 
material or ribbon 12 carried in cassette 10. The receptor sheet medium 22 
may be paper, plastic, mylar, etc.; the thermal transfer ribbon 12 may be 
a conventional film having a heat activated pigment, wax, resin, ink, etc. 
("ink") layer thereon; and the thermal print head 28 may be conventional 
in so far as the construction and operation of the thermal elements are 
concerned. However, as mentioned above and explained in detail in the 
cited applications, the X-axis length of thermal print head 28 is 
approximately two inches, and thermal printer 14 prints in strips about 
two inches wide. The width of ribbon 12 must therefore be at least two 
inches wide, and in the preferred embodiment is about 2.25 inches wide. To 
accommodate such a wide ribbon, to mount the ribbon reels in the cassette, 
and to allow for other functions such as driving and braking of the ribbon 
reel, cassette 10 is about three inches wide. 
As discussed herein and in the cited applications, mounting, guiding and 
printing in strip mode presents certain problems which the inventions 
disclosed herein and in the cited applications overcome. 
Referring to FIGS. 4, 5 and 12, print carriage 16 carries thermal print 
head 24 above a platen 26 which cooperates with thermal print head 24 and 
ribbon 12 to transfer ink from ribbon 12 to the sheet medium 22. The 
thermal printer 14 also includes a Y-axis drive system (not shown) for 
moving print carriage 16 back and forth over platen 26 parallel to the 
Y-axis (left-right in FIG. 4), and an X-axis drive system 28 for moving 
the sheet medium 22 back and forth over platen 26 parallel to the X-axis. 
The X- and Y- axes are referenced in FIG. 3 in accordance with convention, 
where the Y-axis is parallel to the line direction or scan direction of 
printers and plotters (parallel to platen 26), and the X-axis is parallel 
to the sheet medium feed direction which is perpendicular to the Y-axis. 
Sheet medium 22 (FIG. 12) is fed from a roll 30 mounted to the frame of 
printer 14, past print head 24 and platen 26, as shown in FIG. 11, and to 
X-axis drive system 28, which is not fully illustrated in the drawings. 
Referring to FIG. 5, print carriage 16 supports cassette 10 for moving 
ribbon 12 from a supply reel 36 (FIGS. 1 and 12) in cassette 10 past print 
head 24 to a take-up reel 37 in cassette 10, and also supports the 
cassette holder 20 for retaining a cassette on carriage 16. Cassette drive 
system 18 is described in detail in the cited applications. Briefly, 
cassette drive system 18 includes a supply spindle 32 (FIG. 5) and a 
take-up spindle 31 which project from wall 19 on print carriage 16 behind 
which parts of cassette drive 18 are housed. Mounted to take-up spindle 31 
and to supply spindle 32 are drive hubs 33. Movement of ribbon 12 from 
supply reel 36 to take-up reel 37 is described below. Guide pins 54 and 55 
on print carriage 16 and guide pins 170 and 171 on turret 34 help support 
cassette 10 when it is mounted to the print carriage or turret, 
respectively, and assist during transfer of a cassette between print 
carriage 16 and turret 34. Cassette 10 is removably mounted to print 
carriage 16 as described below and in the cited applications. 
Printer 14 may print in monochrome or color. For color printing, a number 
of ribbons of desired final colors are provided or an color system is 
provided, e.g., a four color system comprising yellow, magenta, cyan and 
black, or both. Loading and unloading of cassettes 10 to and from print 
carriage 16 for color printing, or simply for loading a fresh cassette on 
print carriage 16, is automated. Referring to FIGS. 4 and 6, a number of 
cassettes 10 may be stored on a turret 34 located in the Y-axis path of 
travel of print carriage 16 at the left end thereof (but may be located at 
either the right or the left end). As discussed above, in the presently 
preferred embodiment, the four color (yellow, magenta, cyan and black) 
system is used. Both a primary and a redundant four color system are 
provided, so that a total of eight cassettes are mounted to turret 34. As 
also discussed above, the number of cassettes to be mounted on turret 34 
impacts on the size, configuration and mounting of the cassettes on turret 
34 and the size of turret 34. Turret 34 is indexed by a controller in 
printer 14 to position a desired cassette (or unoccupied cassette holder) 
on turret 34 into a cassette transfer position aligned with the cassette 
holder 20 mounted on print carriage 16. 
A passive cassette transfer system is used (e.g. retention arms 87 and lugs 
150), i.e., the devices actively involved with a cassette transfer are not 
in a servo system and are not controlled by a controller. Rather, these 
devices simply passively react to movement of the print carriage 16 during 
a cassette transfer operation. Specifically, the cassette holders 20 and 
20A on print carriage 16 and turret 34 are structured to permit automatic 
and passive transfer of a cassette from an occupied cassette holder on 
carriage 16 or turret 34 to an unoccupied cassette holder on turret 34 or 
carriage 16, respectively, simply by moving aligned cassette holders on 
the print carriage and turret into and out of engagement with each other. 
Sequences for transferring a cassette between turret 34 and print carriage 
16 are described in the cited applications and below. Referring now to 
FIG. 1, ribbon cassette 10 comprises a cassette housing 35, the thermal 
donor ribbon 12, the ribbon supply reel 36 and the ribbon take-up reel 37. 
Cassette housing 35 comprises major side 39 (right or carriage side) and 
opposed major side 40 (left or turret side), and a peripheral side or edge 
42. Since in cassette use side 39 faces carriage 16 and side 40 faces 
turret 34, side 39 is referred to as the carriage side (or right side with 
respect to the printer 14 shown in FIG. 4), and side 40 is referred to as 
the turret side (or left side of the cassette). Side 39 and side 42 are 
integrally joined and form a one piece receptacle or enclosure open at one 
major side. Cassette housing 12 is made of plastic, and sides 39 and 42 
are integrally molded as one piece as presently preferred, or can be 
ultrasonically or heat welded together. Side 40 closes the receptacle or 
enclosure defined by sides 39 and 42, and may be removably attached to 
peripheral side 42 or non-removably attached to peripheral side 42 as by 
ultrasonic or heat welding. 
In an embodiment of cassette 10 in which side 40 is removable, cassette 10 
is provided with a snap arrangement for removably attaching side 40 to 
peripheral side 42, comprising flexible tabs 43 having a barbed or hooked 
end (not shown) projecting from side 40, and recesses 44 in peripheral 
side 42 terminating in an opening 45 (FIG. 3) in an edge of which the barb 
on tab 43 is engaged. Pressing a tab 43 inwardly disengages it from 
peripheral side 42 so that side 39 may be removed from the cassette. Sides 
39, 40 and 42 are configured to define a cassette body 46 and arms 47 and 
48 projecting from cassette body 46. Supply and take-up reels 36 and 37 
are rotatably mounted within cassette body 46, and ribbon 12 is guided 
from supply reel 36 to take-up reel 37 by internal guides described below 
and arms 47 and 48. 
In accordance with the invention, side 40 is made removable so that the 
used ribbon in cassette 10 may be removed, replaced with new ribbon and 
the cassette reused. In that embodiment, cassette 10 need not be 
disposable. If ribbon replacement is carried out at the factory, the used 
ribbon can be properly disposed of. Also, the cassette housings may be 
re-used, and therefore need not be disposed of. However, as indicated 
above, side 40 can be non-removably attached to cassette housing 35 if it 
is desired to make cassette 10 fully disposable. Cassette housing 35 may 
also be made so that sides 39 and 40 may be removed to remove the ribbon 
and reels in the cassette, but may not be easily reattached. In short, 
cassette housing 35 may be made so that the entire cassette is disposed of 
without any recycling, or so that a side may be removed but not replaced 
and the cassette housing and ribbon are separated for separate disposal or 
recycling, or without the cassette be used again, or so that a side may be 
removed and easily replaced so that the ribbon can be recycled or disposed 
of and replaced in cassette, and the cassette reused. 
Referring to FIGS. 1 and 2, cassette body 46 has four holes 49-52 used in 
mounting cassette 10 to print carriage 16 or turret 34, and in 
transferring a cassette 10 between them. Holes 49 and 50 open on carriage 
side 39 and are guide holes used in mounting cassette 10 to print carriage 
16. Holes 51 and 52 open on turret side 40 and are guide holes for 
mounting cassette 10 to cassette storage turret 34. Guide pins 54 and 55 
on print carriage 16 (FIG. 5) enter holes 49 and 50 on carriage side 39, 
and guide pins 170 and 171 on turret 34 (FIG. 7) enter holes 51 and 52 on 
turret side 40. Guide pin 54 on print carriage 16 when fully received in 
guide hole 50 deactivates a brake mechanism 120 in cassette 10 which 
prevents reels 36 and 37 from rotating when cassette 10 is not mounted on 
print carriage 16, as discussed below. In the preferred embodiment, hole 
50 is a blind hole because part of the brake mechanism 120 is mounted to 
the inside of side 40 in alignment with hole 50. Hole 49 is also a blind 
hole, but need not be. Holes 51 and 52 are through holes, but need only 
open on turret side 40 of the cassette. Other functions of guide holes 
49-52 are discussed below. 
An important consideration for proper strip mode thermal printing is the 
geometry of cassette 10 for the delivery and take-up of ribbon 12. Ribbon 
12 must not be allowed to wrinkle prior to or during delivery to thermal 
print head 24. Additionally, the delivery path must prevent contact of 
unused ribbon by other parts of the thermal printer 14. Also, the 
departure angle of ribbon 12 from sheet medium 22 (FIG. 12) must be 
controlled and maintained not only because of geometric packaging 
considerations relating to the cassette and the thermal printer parts, but 
also because of peel angle and print head pressure considerations of the 
thermal printing process. The configuration and geometry of arms 58 and 59 
and guides 60-65 is in response to those considerations. 
Referring to FIG. 3 in which the turret side 40 of the cassette is not 
shown, ribbon 12 from supply reel 36 is guided to arm 47 by a single guide 
60 and exits arm 47 passing a single guide 61. Ribbon 12 then extends 
outside of cassette 10 spaced from body 46, and re-enters cassette 10 
through arm 48, in which three guides 62-64 guide ribbon 12 towards 
take-up reel 37. A single guide 65 guides ribbon 12 from arm 48 to take-up 
reel 37. In the thermal strip mode printer described in the cited 
applications, accurate tension control of the just printed ribbon is 
required for proper operation. Therefore, cassette 10 provides a low 
friction internal ribbon path in which there is minimal contact between 
the ribbon and the cassette, i.e., the number of ribbon guides are held to 
a minimum. Cassette 10 has only enough guide surfaces to ensure integrity 
of the ribbon path, and the guides are located so as to introduce gentle 
direction changes, which minimizes the frictional force as ribbon 12 
passes over the guides. Referring to FIG. 12, in the preferred embodiment 
when cassette 10 is in use, each guide 60- 65 introduces an oblique angle 
change in the path of ribbon movement, and there are no sharp (acute) 
angle changes in the path of ribbon movement. When cassette 10 is not in 
use (FIG. 2), there is only one sharp angle change introduced by guides 
60-65, i.e., guide 62 introduces an angle change of approximately 
90.degree.. 
Referring to FIGS. 1, 3, 7-9, the supply and take-up reels 36 and 37 are 
mounted in cassette 10 spring biased towards side 39 to ensure that stop 
surfaces 70 (FIGS. 7 and 8) on reels 36 and 37 are properly seated against 
stop surfaces 71 on the supply and take-up reel spindles 31, 32 of the 
cassette drive 18 when the cassette is mounted on the print carriage 16. 
To provide for spring-biasing while maintaining low frictional drag on 
reels 36, 37, each reel 36, 37 is provided with a pointed nipple 74 (FIGS. 
7-12), which bears against a leaf spring 75 held in place adjacent 
cassette side 40 by dimples 76, 77 on side 40 snap-fitted into holes 78 in 
spring 75 (FIG. 10). The central part 79 of spring 75 is interleaved 
between dimple 76 on one side and dimples 77 on the other side. Center 
dimple 76 projects from cassette side 40 towards cassette side 39 and 
holds spring 75 off side 40, and the outer dimples 77 project from flanged 
portions 80 (FIGS. 2 and 12), which are attached to and spaced from side 
40, towards side 40. Nipples 74 make essentially point contacts with leaf 
spring 75, which makes the resulting frictional drag imparted to the 
rotating reels 36, 37 from the stationary spring 75 very small. The ends 
85 of reels 36, 37 (FIG. 1) opposite the pointed nipple ends are loosely 
fitted into holes 83 in the carriage side 39 of cassette 10 and are not 
rotatably connected to cassette housing 35. Holes 83 and respective 
generally semi-circular walls (not shown) coaxial with the axes of reels 
36 and 37 on the inside of cassette side 39 loosely locate and guide reels 
36 and 37. It is not necessary for cassette housing 35 to positively 
engage reel ends 85 since they are engaged by spindles 31 and 32 of the 
cassette drive 18 when cassette 10 is mounted to the print carriage 16. 
This further reduces the frictional drag on reels 36, 37 imparted by 
cassette 10. 
To further ensure smooth and low friction movement of ribbon 12, cassette 
10 incorporates an anti-static feature. As ribbon 12 tracks through and 
out of cassette 10, through the printing process, then back into cassette 
10, a static charge is built up on the surface of ribbon 12. If not 
contained and/or dissipated in a controlled fashion, this charge could 
build to a level substantial enough to adversely affect the printing 
process. For example, the charged ribbon 12 may tend to cling to the 
receptor sheet medium 22, the printhead 24, or its support mechanism, or 
other parts of the printer 14. To control such static build-up, the 
plastic cassette housing material is formulated with an anti-static agent, 
e.g., AKZO Armostat 555, or equivalent. Ribbon 12 is provided with a 
similar conductive agent in its backcoating, so that static charge on 
ribbon 12 tends to be conducted away from ribbon 12 onto the cassette 
housing 35 which is, in turn, firmly in contact with (grounded to) the 
printer 14. Ribbons with such conductive backcoatings are conventional and 
are commercially available. 
As with any paper handling machine such as a printer, there is the 
potential for paper and office dust to be present within the confines of 
the machine. Should these contaminants be allowed to accumulate on the 
ribbon 12, it could affect print or plot quality by preventing complete 
transfer of the ink from ribbon 12 onto the receptor sheet medium 22 
(paper) in localized areas. Hence, cassette housing 35 serves to shield 
the unused ribbon from potential contaminants until just prior to use in 
the printing process. The ribbon is exposed to potential contamination for 
only its last 2.5 inches of travel immediately prior to use in the 
printing process. At a slow print speed of 1 inch per second, that 
corresponds to only a 2.5 second exposure window. 
Referring to FIGS. 4 and 5, a cassette 10 is mounted to the cassette drive 
18 (part of which is shown in FIG. 5) on print carriage 16 with print head 
24 positioned between cassette body 46 and ribbon 12. Cassette holder 20, 
which includes retention arms 87 and guide pins 54 and 55, holds a 
cassette 10 on print carriage 16 with the cassette drive 18 engaged with 
the cassette reels 36 and 37, as described below. Referring to FIG. 5, 
cassette drive 18 includes the supply reel spindle 31, the take-up reel 
spindle 32 and a drive motor (not shown) which rotates the take-up reel 
spindle 32. A brake (not shown) engages take-up reel spindle 32 to 
introduce drag on ribbon being unwound from supply reel 36 so that the 
ribbon may be tensioned. The supply reel spindle 31 and the take-up reel 
spindle 32 both include a drive hub 33 mounted to rotate with the 
respective spindle. Drive hub 33 has axially extending, radially 
projecting ribs or teeth 91 and the stop surface 70 discussed above. The 
supply reel 36 and the take-up reel 37 both include a drive sprocket 94 
(FIG. 7) mounted to rotate with the respective reel. Drive sprockets 94 
have axially extending, radially projecting ribs or teeth 95 and the stop 
surface 70. 
As illustrated in FIGS. 8 and 9, when a respective spindle is seated in a 
respective reel with the stop surfaces 70 and 71 in contact, ribs 91 on 
the spindle drive hub 33 mesh with ribs 95 on the reel drive sprocket 94. 
When a cassette 10 is mounted to the cassette drive 18, it is possible 
that the ribs 91, 95 on a drive hub 33 and drive sprocket 94 are aligned 
and therefore interfere with meshing of the ribs. To permit meshing in 
such a case without rotating either the supply reel 36 or the take-up reel 
37, the drive hubs 33 are mounted axially displaceable on respective 
spindles 31, 32, and the ribs 91, 95 have tapered portions 97, 98 facing 
each other. In an interference situation, a drive hub 33 is simply 
displaced axially (not shown), thereby allowing the cassette 10 to be 
mounted and engaged to the cassette drive 18. Then, when the take-up 
spindle 32 is rotated, the corresponding drive sprocket 94 on take-up reel 
37 remains stationary while the tapered portions 97, 98 slide relative to 
each other a short distance until the respective ribs mesh. The take-up 
reel 37 is then rotated by the drive hub 33 of the take-up spindle 32, 
which rotates the supply reel 36, and causes the ribs 91, 95 on the drive 
hub 33 for the supply spindle 31 and the drive sprocket 94 for the supply 
reel 36 to also mesh if they have not already done so when the cassette 10 
was mounted to the cassette drive 18. 
The arrangement described above, and the brake mechanism 120 for supply 
reel 36 and take-up reel 37, described below, ensure that there is no 
movement of ribbon 12 between the time a cassette 10 is removed from 
cassette drive 18 on print carriage 16 and re-mounted at a later time. 
This prevents the exposed ribbon from developing a slack loop during 
storage and exchange. If the span of ribbon outside cassette 10 were 
allowed to go slack, the resulting form of the span would be unpredictable 
and could interfere and become entangled with nearby machine structure and 
mechanisms during the cassette exchange process or could twist or crinkle 
making that part of the ribbon unusable. Also, if ribbon 12 were allowed 
to move when a cassette 10 was removed from the cassette drive 18, then an 
unused part of the ribbon may have moved into position for the next 
printing operation. In other words, the ribbon could have moved so that a 
used part of the ribbon is in position to be used again, which could 
affect the quality of the print or produce a print with a skip in it. 
Also, if the ribbon moved in the opposite direction so that an unused part 
of the ribbon moved past the printing location, such ribbon part would not 
be used and would be wasted. Where a cassette is mounted and demounted a 
number of times, the risk of the problems described above occurring is 
considerable. 
Referring to FIGS. 3 and 12, cassette 10 includes a brake mechanism 120 
which frictionally engages supply reel 36 and take-up reel 37 when 
cassette 10 is not mounted to cassette drive 18 on print carriage 16. 
Brake mechanism 120 includes two brake pawls 122, 123 each carrying a 
brake pad 125, and drums 127, 128 respectively axially extending from the 
inner rims of the supply reel 36 and the take-up reel 37. Brake pads 125 
are made of a relatively high friction material and when engaged with 
respective drums 127, 128, as shown in FIG. 3, hold the respective reels 
in place and prevent them from rotating when cassette 10 is not mounted to 
cassette drive 18. 
Brake pawls 122, 123 (FIGS. 3 and 10-12) are L-shaped members having an arm 
130, a leg 131 and a tubular hole 132 at the point where the arm 130 and 
leg 131 are connected. Respective brake pads 125 are connected to the free 
ends of respective brake pawl arms 130. Pins 133 project from the inner 
surface of cassette end 39 adjacent the peripheral side 42 of cassette 10, 
and a respective tubular hole 132 is placed on a respective pin 133 to 
pivotally mount each brake pawl 122, 123 to cassette side 40. A leaf 
spring 135 is mounted between legs 131 of brake pawls 122, 123 and the 
peripheral side 42 of cassette 10 with each free end 136, 137 of spring 
135 bearing against a respective brake pawl leg 131. Pins 138, 139 and 140 
projecting from cassette side 40 adjacent leaf spring 35 hold leaf spring 
135 in place. Leaf spring 135 is positioned under stress between pins 138 
and 139 on one side, and pin 140 on the other side. 
Each leg 131 of a respective brake pawl 122,123 includes at the free end 
thereof a beveled projection (or cam) 141 (FIGS. 10-11) functioning as a 
cam extending perpendicular to the longitudinal extent of the leg, i.e., 
towards side 39 of cassette 10. The cams 141 taper in thickness, becoming 
thicker in the direction of cassette Side 40. Brake pawls 122 and 123 are 
positioned so that cams 141 are aligned with hole in cassette side 39 so 
that they are contacted by guide pin 54 of cassette holder 20 on print 
carriage 16 when cassette 10 is mounted to cassette drive 18 on the print 
carriage. When cassette 10 is mounted to print carriage 16 as shown in 
FIG. 12, guide pin 54 cams brake pawls 122,123 against leaf spring 135 
causing respective brake pawls to pivot away from respective reels 36, 37 
so that respective brake pads 125 do not frictionally engage respective 
drums 127, 128. 
When cassette 10 is not mounted to cassette holder 20 on print carriage 16, 
as for example when it is mounted to turret 34 or is off printer 14 
altogether, as shown in FIG. 3, leaf spring 135 urges respective arms 130 
of brake pawls 122, 123 towards respective reels 36, 37 to frictionally 
engage respective brake pads 125 with respective drums 127,128. The 
sequence for pivoting brake pawls 122, 123 out of engagement with 
respective drums 127 is illustrated in FIGS. 7-11, which is described 
below in connection with the transfer of a cassette 10 from turret 34 to 
print carriage 16. 
For the reasons discussed above, brake pads 125 engage the outer surface of 
drums 127, 128 in a continuous manner, i.e., the contact surfaces of brake 
pads 125 and drums 127, 128 are continuous, as opposed to toothed in a 
pawl and ratchet arrangement. This allows brake pawl arms 130 to engage 
respective drums 127, 128 in any angular position thereof, i.e., in an 
infinite number of angular positions as opposed to a discrete number of 
angular positions in a pawl and ratchet arrangement. As mentioned above, 
brake pads 125 directly engage drums 127, 128 attached to the respective 
reels 36, 37, as opposed to contacting ribbon 12 so as not to stress 
ribbon 12 or damage the ink on ribbon 12 or to otherwise damage ribbon 12. 
Also, brake pawls 122,123, brake pawl arms 130 and brake pads 125 are 
configured and/or arranged to apply a greater breaking force to the 
respective drum 127, 128 when torque is applied to the respective reel 36, 
37 to unwind ribbon from the respective reel. This feature minimizes the 
force which spring 135 must supply to pivot the respective brake pawl arms 
towards the respective drums 127, 128. 
Cassette holders 20 and 20A on print carriage 16 and turret 34, 
respectively, each include two retention arms 87 (see FIGS. 4-6) which 
engage respective lugs 150 on the peripheral side 42 of cassette 10 as 
described in detail in the '116 Application. Briefly, the end of each 
retention arm 87 is structured so as to engage a lug 150 on the peripheral 
side 42 of cassette 10 and thereby retain a cassette. Also the end of each 
retention arm 87 is structured to permit a retention arm of an unoccupied 
cassette holder to cam a retention arm of an occupied holder out of 
engagement with the lug on the retained cassette that the later holds, and 
into engagement with the retention arm of the unoccupied holder, thereby 
effecting a passive, automatic and direct transfer of a cassette from one 
holder to the other simply by moving aligned cassette holders into and out 
of engagement with each other. 
With reference to FIG. 7, the end of each retention arm 87 resembles in 
cross section the tip of a fish hook, and is structured as follows. On one 
side of the end of each retention 87 extends a sloping camming surface 151 
which begins with a right angle detent surface 152. The other side 153 of 
the end of retention arm 87 opposite camming surface 157 is straight. Lugs 
150 are positioned on the peripheral side 42 of cassette 10 to contact and 
engage respective right angle detent surfaces 152 of respective retention 
arms 87 to thereby mount cassette 10 to print carriage 16 or turret 34. 
Two locating guide pins 54 and 55 which are pre-loaded with spring-loaded 
plungers 56 on print carriage 16, and two locating guide pins 170, 171 
which are preloaded with spring-loaded plungers 173 on turret 34 properly 
locate cassette relative to print carriage 16 and turret 34, respectively, 
during a transfer between turret 34 and carriage 16. However, to properly 
seat and load cassette 10 on turret 34 an additional spring-loaded offset 
plunger 174 (without a guide pin) is provided to prevent a cassette being 
transferred to turret 34 from pivoting or cocking under the action of 
retention arms 87 engaging lugs 150. Guide holes 51 and 52 on turret side 
40 of cassette 10 (FIG. 1) are not symmetrically located relative to the 
supply and take-up reels 36 and which account for most of the weight of 
cassette 10, and are not symmetrically located relative to the center of 
gravity of cassette 10 the center of the lug/retention arm forces. Offset 
plunger 174 on turret 34 frictionally engages side 40 of cassette 10 and 
effectively prevents the cassette from rotating when it is being 
transferred to turret 34. Holes 49 and 50, which are used to mount 
cassette 10 to carriage 16, are generally centrally located in cassette 
10, and a line joining the centers of holes 49 and 50 passes through the 
central region of cassette 10. Holes 49 and 50 on carriage side 39 of 
cassette 10, are symmetrically located relative to the supply and take-up 
reels 36 and 37 and straddle the center of gravity of cassette 10 and the 
center of the lug/retention arm forces. Therefore, there is less tendency 
for the cassette to cock when it is being transferred to carriage 16 as 
retention arms 87 on print carriage 16 engage lugs 150 on cassette 10. 
Therefore, an off-set plunger is not needed on carriage 16. 
Referring to FIG. 7, each retention arm 87 is pivotally mounted at one end 
thereof to an ear 156 by a pivot joint 157. Retention arm 87 at the end 
thereof pivoted to ear 156 has an extension 160 extending therefrom at a 
right angle to the main part 161. A compression spring 163 is mounted in 
engagement with the end of arm extension 160 and wall 19 to urge main part 
161 of retention arm 87 to pivot towards cassette 10 to cause the right 
angle detent surface 152 of a respective arm 87 to engage a respective lug 
150 on cassette 10. A stop to limit pivoting of retention arm 87 toward 
cassette 10 comprises another extension 165 extending from retention arm 
87 in the opposite direction to extension 160, and a projection 166 on 
wall 19 extending up to extension 165. With no cassette held between 
retention arms 87, pivoting of retention arm 87 is stopped by engagement 
of extension 165 with projection 166. Cassette holders 20, 20A function to 
retain a cassette between retention arms 87 as also described in the '116 
Application. 
Referring to FIGS. 5-7, the automatic exchange system for transferring 
cassettes 10 between turret 34 and print carriage 16 depends on the set of 
two guide pins 170 and 171 and offset plunger 174 located on turret 34 and 
the set of two guide pins 54 and 55 located on print carriage 16. During 
the exchange the process, the guide pins serve to maintain cassette 
location and orientation ensuring that the retention arms 87 engage the 
lugs 150 properly. The size of the holes 49-52 in cassette 10 is 
determined by the maximum expected tolerance stackup between the 
cassette/turret and cassette/carriage interfaces. In short, the guide pin 
holes 49-52 in the cassette 10 must be large enough to accept the most 
misaligned guide pin. The cassette's guide pin holes 49-52 are located 
according to several criteria. The carriage-side holes 49 and 50 are the 
most favorably located because they are responsible for locating and 
maintaining the cassette position during the actual printing operation. As 
discussed above, holes 49 and 50 are symmetrically located relative to the 
supply and take-up reels 36 and 37 and straddle the center of gravity of 
cassette 10 and the center of the lug/retention arm forces. The 
turret-side holes 51 and 52 are less favorably located since they only 
serve to locate and maintain the cassette during storage on turret 34. 
Also, all of the guide pin holes are located such that they do not 
interfere with the internal ribbon path. Finally, the guide pin holes are 
located in such a way as to provide the maximum stance in holding the 
cassette both on turret 34 and on print carriage 16. 
Referring to FIGS. 7-9, like the guide pin holes 49-52, the lugs 150 on 
cassette 10 are configured and located in such a way as to provide the 
most reliable passive exchange system possible. The width of lug 150 is 
largely arbitrary and the depth of lug 150 is set to provide adequate 
structural integrity of the lug. However, the height of lug 150 is closely 
tied to the kinematics of the passive retention arms 87. Specifically, the 
height of lug 150 is set such that, during exchange, the approaching 
retention arm 87 will always be able to "get under" the engaged retention 
arm 87. The interaction between the cassette lugs 150 and the passive 
retention arms 87 is fundamental to the operation of the exchange system. 
Four guide holes are provided in cassette 10 and two guide pins on both 
turret 34 and print carriage 16 to ensure that a cassette is always 
adequately supported during a transfer operation. With four guide holes, 
two on each major side 39, 40 of cassette 10, four pins will support 
cassette 10 as the cassette is transferred from one set of retention arms 
87 on the print carriage or turret to the other set on the turret or print 
carriage, respectively. If only one set of two holes opening in both sides 
39 and 40 of cassette 10 were used, then guide pins on turret 34 and print 
carriage 16 would have to share the same guide holes during a transfer 
operation, so that the respective guide pins would have to be only half 
the thickness of cassette 10 and the cassette would not be supported as 
stably during a transfer and when mounted. 
Referring to FIGS. 7-9, the spring loaded plungers 173 on guide pins 170, 
171 on turret 34, and the spring-loaded plungers 56 on guide pins 54 and 
55 on carriage 16 assist in seating a cassette 10 and in transferring a 
cassette 10 during a cassette transfer as follows. While at rest, the 
respective set of spring-loaded plungers acts to force the cassette lugs 
150 against the right angle detent surfaces 157 of the ends of the 
respective retention arms 87. This ensures accurate, repeatable axial 
location of the cassette. During a cassette transfer, the set of the 
spring-loaded plungers 173 or 56 on guide pins 170, 171 and 54, 55, 
respectively, act to counter the force imparted by the retention arms 87 
of the approaching cassette holder 20 or 20A mounted to print carriage 16 
or turret 34. By providing a force for the unoccupied retention arms 87 of 
the print carriage or turret to act against, the unoccupied retention arms 
87 can perform their camming motions against the occupied retention arms 
87 and on the cassette lugs 150 on the cassette to be transferred. The 
resilient mounting of cassette 10 also guards against jamming, bending, 
and breakage while always ensuring that the cassette is returned to a 
known position, i.e., engagement of the lugs 150 on the cassette against 
the right angle detent surface 152 of the retention arms 87. 
FIGS. 7-9 show the sequence for mounting a cassette 10 to cassette drive 18 
on print carriage 16. First, turret 34 is rotated by turret drive 175 
(FIG. 6) to position the desired cassette holder 20A in a cassette 
exchange position under control of the printer controller. The turret 
drive 195 and indexing of turret 34 are described in the '116 Application. 
Referring to FIG. 7, cassette 10 is shown mounted to turret 34. Retention 
arms 87 engage lugs 150, and guide pins 170, 171 on turret 34 (FIG. 6) are 
received in holes 51 and 52 (FIG. 1) in side 40 of cassette 10. As 
indicated above, each guide pin 170, 171 (FIG. 6) has mounted thereto a 
spring loaded, axially movable plunger 173. When cassette 10 is mounted to 
turret 34, spring loaded plungers 173 urge the cassette lugs 150 into 
engagement with the retaining surface 152 of retention arms 87, as shown 
in FIG. 7. In FIG. 7, print carriage 16 and the cassette drive 18 are 
moving towards but are still spaced from cassette 10 on turret 34. As 
movement of print carriage 16 towards turret 34 continues, the ends of 
retention arms 87 of cassette holder 20 mounted to print carriage 16 
contact the ends of retention arms 87 of cassette holder 20A on turret 34, 
as shown in broken lines in FIG. 7. The unoccupied set of retention arms 
87 are pivoted inwardly towards each other, is shown in FIG. 7, which 
causes the outer surface 153 of the ends of the unoccupied retention arms 
87 on the carriage cassette holder 20 to contact the inner camming 
surfaces 151 of the occupied retention arms 87 of the turret cassette 
holder 20A. 
Referring to FIG. 8, as movement of print carriage 16 towards turret 34 
continues, the unoccupied retention arms 87 of carriage cassette holder 20 
disengage the occupied retention arms 87 of turret cassette holder 20A 
from lugs 150, and the formerly occupied retention arms 87 on turret 34 
pivot outwardly. Movement of print carriage 16 towards turret 34 continues 
until stopped by the printer controller in response to an encoder (not 
shown) which tracks movement of the print carriage. At that point in the 
sequence, which is shown in FIG. 8, retention arms 87 of carriage cassette 
holder 20 engage lugs 150 on cassette 10, plungers 56 of guide pins 54 and 
55 engage cassette 10, drive hubs 33 of supply spindle 31 and take-up 
spindle 32 are fully or partially seated in drive sprockets 94 of supply 
and take-up reels 36 and 37, and guide pin 54 is contacting camming 
surfaces 140 of brake pawls 122, 123 to pivot brake pawl arms 130 away 
from reel drums 127, 128. Drive hubs 33 may be partially or fully seated, 
depending upon whether respective ribs 97, 98 mesh or not, as described 
above. To complete the sequence, print carriage 16 is moved in the 
opposite direction, as shown in FIG. 9, taking with it cassette 10. During 
a transfer operation, cassette 10 is supported by all four guide pins 54, 
55 and 170, 171. Transfer of a cassette 10 on carriage 16 to turret 34 
proceeds in essentially the same way, but with the unoccupied and 
unengaged retention arms 87 of holder 20A on turret 34 and the occupied 
and engaged retention arms 87 of holder 20 on print carriage 16 being 
reversed from the positions shown in FIGS. 6-9. 
A sensor 180 mounted to wall 39 on print carriage 16 senses the presence of 
a fully seated cassette 10 on print carriage 16. Sensor 180 comprises a 
blade member 181 fixed to plunger 56 on spindle 54 which enters and trips 
an optical switch 182 when cassette 10 is fully seated. (When cassette 10 
is fully seated, it drives plunger 56 back far enough to cause blade 
member 181 to interrupt a beam of infrared light in optical switch 182 to 
trip the switch.) The optical switch 182 is coupled to the printer 
controller. 
FIGS. 10 and 11 depict the sequence for pivoting brake pawls 122, 123 to 
move pawl arms 130 away from and out of engagement with reel brake drums 
127,128. FIG. 9 shows guide pin 38 approaching the camming surfaces 141 of 
brake pawls 122, 123. At this point, brake pawl arms 130 are urged into 
engagement with reel drums 127, 128 by leaf spring 135. Referring to FIG. 
10, when the end of guide pin 38 contacts camming surfaces 141, it causes 
brake pawl 122 to pivot counterclockwise and brake pawl 133 to pivot 
clockwise against the action of leaf spring 135, which moves brake pawl 
130 arms away from the respective drums. When cassette 10 is removed from 
print carriage 16, guide pin 54 is withdrawn, which allows leaf spring 135 
to pivot brake pawl 122 clockwise (FIG. 10) and brake pawl 123 
counterclockwise, which causes the brake pads 125 on brake pawl arms 130 
to engage respective drums. 
Referring to FIG. 1, a machine readable bar code 180 is affixed to (or 
imprinted on) side 39 of cassette 10. Bar code 180 identifies the ribbon 
type, color, supplier, etc. Cassettes 10 are mounted to turret 34 with 
major sides 40 parallel to a plane in which the active side of turret 34 
lies (see FIG. 6), and with major side 40 facing turret 34 and major side 
39 facing away from turret 34 with the bar code 180 exposed. Referring to 
FIG. 4, a bar code reader 181 is mounted to the frame of thermal printer 
14 adjacent turret 34, spaced therefrom by slightly more than the 
thickness of a cassette 10. The bar code 180 on each cassette 10 which is 
mounted to turret 34 is read by bar code reader 181 whenever a cassette is 
loaded onto turret 34. The printer controller thereby "knows" the identity 
of each cassette 10 on turret 34 so a cassette 10 designated by the print 
data of the print being executed by printer 14 may be located and moved 
into the cassette exchange position for transfer from turret 34 to print 
carriage 16. 
The bar codes 180 on cassettes 10 are read "on the fly", i.e., as turret 34 
is rotated. Because a linear bar code is employed and because each bar 
code moves in a circular path, care must be taken to ensure that the 
entire linear bar code is read as it moves in a curved path past the 
stationary bar code reader 181. 
Bar code 180 (FIGS. 1 and 4) is located on cassette 10 so that it will be 
at the greatest possible radius from the center axis of turret 34 when 
cassette 10 is mounted thereto. Bar code 180 is a linear bar code, and its 
location at the greatest possible radius from the center of turret 34 
minimizes temporal distortion when it is rotated past the stationary bar 
code reader 181. Using a linear bar code rather than one in which the bar 
code elements extend about the arc of a circle simplifies design of the 
bar code. 
The bar code elements (FIG. 1) have equal heights and are aligned 
(linearly) along a longitudinal axis which extends approximately 
perpendicular (89.degree.) to a line intersecting the axes of supply reel 
36 and take-up reel 37. Since the bar code elements are aligned in a 
straight line, and each cassette 10 on turret 34 is rotated along a curved 
path past bar code reader 181 (FIG. 4), each point on the straight line 
does not pass the same point on bar code reader 181. Therefore, there is a 
relationship between the position, height and length of the linear bar 
code 180 and its elements, and the position and field of view of the bar 
code reader 181 such that a substantial portion of each bar code element 
passes the bar code reader 181. 
In order to permit visual determination of the amount of unused ribbon in 
each cassette 10, as shown in FIG. 1, a window 185 is provided in cassette 
side 39 near supply reel. Window 185 may simply be an opening in cassette 
end 39, or may be a transparent insert seated in the opening, or a 
transparent part of cassette 10, etc. 
While the invention has been described and illustrated in connection with 
preferred embodiments, many variations and modifications as will be 
evident to those skilled in this art may be made without departing from 
the spirit and scope of the invention. The invention as set forth in the 
appended claims is thus not to be limited to the precise details of 
construction set forth above as such variations and modifications are 
intended to be included within the spirit and scope of the invention as 
defined in the appended claims.