CA1329415C - Automated thermal transfer device and control system therefor - Google Patents

Abstract

AN AUTOMATED THERMAL TRANSFER DEVICE
AND CONTROL SYSTEM THEREFOR

ABSTRACT OF THE DISCLOSURE
A control system for a thermal transfer device in which a selected image is transferred from a strip of color carrying ribbon to a strip of image carrying tape and precise alignment between adjacent columns of vertical print is achieved by monitoring and controlling the rotational speed of the drive means for the thermal transfer device and activating the printing of each column of pixel data based upon positional information of the tape and ribbon determined in relation to the rotational speed of the drive means so that each column of pixel data is of a uniform and consistent width.

Description

1 32'~4 1 5 AND CONTRQL SYSTEM THER~FOR
ELATED ~PPLICATIO~S
This application is related to co-pending application entitled TAPE-SUPPLY SYSTEM FOR A THERMAL PRINTING
DEVICE OR THE LIKE, filed in the Canadian Patent Office on January 27, 1989 and identified by Serial No. 589,364, to co-pending application entitled THERMAL PRINTING DEVICE AND TAPE
SUPPLY CARTRIDGE THEREFOR, filed in the Canadian Patent Office on January 27, 1989 and identified by Serial No. 589,359, to co-pending application entitled THERMAL PRINTING DEVICE AND
TAPE SUPPLY CARTRIDGE EMBODYING A TAPE CUT-OFF MECHANISM, filed in the Canadian Patent office on January 27,1989 and identified by Serial No. 589,362, and to co-pending application entitled PIXEL PREHEAT SYSTEM FOR AN AUTOMATED
THERMAL TRANSFER DEICE, filed in the Canadian Patent Office on March 20,1989 and identified by Serial No. 594,220.
TECHNICAL-FIELD
The present invention relates generally to the field of printing apparatus or composing systems, and, more parti~
cularly, to an improved control means for a printing apparatus or composing system of the type involving the use of a thermal ::
process to transfer pixel images of a desired character or design from a color carrying ribbon onto an image carrying ~:
tape as a result of the localized application of heat and pressure at each pixel. This type of printing apparatus or composing system has a particular application in the printing of relative large characters or sequences of characters of 132q415 varying typc sizes and fonts for use in preparing Ie~tering for engineering drawirlg3. nip charts, oYe~head transparencics, poster~, advcrtising brochures, idcntification labels and thc like. The characters printed by this type of printing apparatus or system are generally larger than characters produccd by most typewriters or the likc and inelude a wide variety of typc 5 sizes and fonts for alphanumeric charactcrs, along with arly number of special characters or images such as symbols, logos and trademarks, ~QUND ART
Tape lettering systems cmploying a dry Iettcring printing process that l O mechanically transfer an impression of a charactcr on a rotatable typc disc from a dry film ribbon to an image carrying tapc by mcans of an impact mcans or prcssurc printing forec are well knowa in thc prior art, and arc shown and described in U.S. Pat. Nos. 3,834,S07; 4,243,333; and 4,402,619. An automated tapc lettcring machine employing this proccss is shown and l 5 dcscribed in U.S. Pat. No. 4,462,708. Whilc each of thesc prior art machines is capablc of gcncrating hi8h quality printing and lettcring rcsults, thcrc is a nccd for a high spccd tapc printing apparatus capablc of gcncrating high quality charactcrs without the limitations imposcd by using an impact or prcssure lettering dcviec.
Thermal transfer printing de~iccs also exist in which an image of a desiret charactcr is formed on a strip of image carrying tapc by transferring ink or other color from a color carrying ribbon to the tape as a result of thc localized application of heat and a small amount of pressure. A typical thermal ~ransfer devicc of this type is described in U.S. Pat. No. 4,666,319. Another thcrmal transfer device presently available employs a thermal print head for transferring images from a strip of ribbon to a strip of tape and has a .. . .. . . .

cooperating tape-ribbon cartridge for providing a supply of tape and ribbon to the device. While such devices are use~ul for printing smaller point size characters represented in a dot-matrix array font format, the control systems required by such devices are incapable of handling the precision and accuracy required for the high speed generalion of high quslity characters, 5 particularly characters of larger point sizes.
In some of the thermal transfer devices described above, a platen roller located directly opposite the printhead is used to frictionally engage ~he tape and ribbon and advance the same past the printhead. This arrangement is undesirable in that the pressure necessary to insure that the tape and ribbon 10 will be frictionally advanced by the platen roller is greater than the optimum pressure necessary to achieve a high quality therrnal trar~sfer. In other therrnal transfer devices, a ribbon take-up spool or spindle is used to simply pull the tapo and ribbon past the printhead. This arrangement is also undesirable, however, in that the driving force is applied only to the ribbon and misalignment between the ribbon and tape may occur. Additionally, in all such therrnal transfer devices, any variations in the speed of the platen drive roller or the ribbon take-up spindle negatively impact the quality of prin~ by smearing or smudging the pi~el images at a given vertical segment of the tape Ot by causing a gap between adjacent or corresponding columns of print Though this smearing or smudging of pi%els is desirable in many printers where the transfer ink will melt or smear together to create a consistent and uniform image, it is undesirable in a high quality, high speed tape printing apparatus of ~he type contemplated by the present invention. Because the ribbon used in high quality thermal transfer tape printing apparatus is usually some type of plastic based ribbon, the pixel images transferred from the ribbon to the tape are uniforrnly defined and do not smear or smudge into " . -, , . . . . . . . . . . .
' one another. Therefore. precise alignment between vertical columns of print is nccessary to achieve high quality, high speed lettering results when using a thermal traasfer tape printing apparatus of thè type contemplated by the present in~ention.
Accordingly, allhough the above described prior devices may be S satisfactory for ~arious uses and applications, they are limited in thc sizes and fonts of the characters that can be printed and in the combination of speed and quality of the characters to be printed on lhe tape. Thus, there is a continuing need for improvements in the control systems associated with tape lettering printing apparatus, and, in particutar, with the control systems 10 associated with thermal transfer devices to allow for ~he generalion of high speed, high quality images on a strip of tape.

~II~M~Y OF THE INvENuoN
In accordance with the present invention, a thennal transfer de~ice, 15 and in particular a control system for such a device, is provided in which anirnage of a desired character is transferred from a strip of color carrying ribbon to a strip of image carryiog tape. Generally, such a device includes an image transfer station defined by a printhead and a cylindrical platen and rotary drive means for advancing the tape and ribbon from a supply cartridge 20 past the image transfer station. It may also include a tape-ribbon cartridge embodying an internal tape-cut mechanism and an input module for entering, editing, storing and lransmitting the selected characters or designs to be printed on the tape.
The control system of the present invention controls the mechanisms 25 for transferring an image of a selected character or design from a ribbon to a tape. In a preferred embodiment of the invention, the control system is comprised of a programmable da~a processing means for receiving print data and control codes representing the desired characters or designs to be printed and for controlling the printing of that informa~ion by the image transfer station. The data processing means is also connected to a detector means for monitoring tho speed and position of the rotary drive mea~. The speed of the 5 rotary drive means as determined by the detector means i5 used by a feedback means to control the speed a~ which the rotary drive means advances ~he tape and ribbon past the image transfer station. The speed of the rotary drive means as determined by the detector means is also utilized to calculate positioninformation of the tape and ribbon relative to the image transfer station. Tbis 10 position information is used by the data processing mean~ to control the time at which print data is output to the printhead to insure that a precise alignment between corresponding venical columns of print data is achieved.
Accordingly, a primary object of the present invention is to provide an improved control system for a thennal transfet tape lettering device for 15 transferring characters of a wide variety of type sizes and fonts from a strip of ribbon to a strip of image carrying tape.
Another object of the present invention is to provide an improved control system for an image transfer station that will monitor and control the speed at which the tape and ribbon are advanced past the image transfer 20 station and output tho data to be printed by the imago transfer station in relation to the position of the tape and sibbon as they are advanced past the . -: . -:' --image transfer station for the purpose of insuring a more accurate alignment between corresponding vertical columns of print data.
Another object of the present invention is to provide an improved 2 control system for a thermal trans~er strip printer which monitors and .
:.

controls the rotational speed of a rotary drive means and controls the posilion at whieh the image is tran5ferred to the tape.
These and other objects of the present invention will become apparent with reference to the drawings, the detailed description of the preferred embodiment and the appended claims.
12]3S~;:RIPTION OF THE DRAW-~GS
FIG. 1 is an e~ploded pietorial view of a tape Ie~tering printing apparatus in accordance with the present invention showi~g a thermal transfer device with associated tape ribbon canridge, and an input module with an umbi1ieal cort attachment to the thermal transfer device.
FIG. 2 is a functional diagram of the control system for the thermal transfer device of the present invention showing various operative components of such system.
FIG. 3 is a bloek diagrarn showing the data flow for processing means of the present invelltion.
FIG. 4 is a simplifiet eireuit diagrarn for the feedbaclc means of the present invention.
FIG. S is a pictorial view of the printheat assembly of the thermal transfer deviee.
2 O FIG. 6 is a functioni~l sehematic diagram of the inpul and output signals used to drive the pnnthead of the transfer device.
FIG. 7 is a timing diagrarn of the input and output signals used to dri~e the printhead of the transfer deviee. -FIG. 8 is a timing diagram of Ihe overall data flow as controlled by the 2 5 processing means of the present invention.

1 32~ 1 5 DESCRIPIION OF TRE PREFE~llEl~ EMBQl~IME~T
Rcferring to FIG. t, an e~plodcd pictorial view of a tapc le~ering or printing apparatu~ 10 i~ accordance with the prescnt invention i~ shown.
Although thc prcferred embodiment i5 a thermal lran~fer device, it is contemplated lhat the fcature~ of the prescnt invcntion arc applicable to othcr 5 similar t8pC lettcring app~ratus and strip printcn a~ well. As illustrated in FIG. I, the operative components of the tape lettering or printing apparatus I Ogenerally include a thermal transfcr devicc 12 embodying, a processing means 14, a pair of font canridges 16 and 18, a rotary drive means 26 and an image transfer station 20 defined by and disposed between a printhead 10 assembly 22 and a cooperating platen assembly 24. Associated with the transfer devicc 12 is a movable canridge scrvice or receiving tray 28 for rcceiving a tape-ribbon cartridgc 30. Thc carttidgc 30 includcs a supply of tape and ribbon for providing a tape 31 and a ribbon 32 to the imagc transfer station 20. The printing apparatus 10 funhcr comprises an input means 40 for 15 cntering, editing, storing, manipulating, and/or transmitting input data to thc processing mcans 14 via an umbilical cord intcrfacc 42. In thc preferred embodimcnt, thc input means 40 comprises a programmablc digital microproccssor 44, a keyboard 46 and a display 48. Thc input means 40 may also, howcvcr, be a digital computer or other device capable of interfacing 20 with the processing means t4 through thc interface 42. In a preferred embodiment, the interface 42 is an RS-232-C communication port.
Although thc eonlrol system has applicability to various lettering apparatus and strip printers, it has particular applicability to a thermal transfer dcvice and associated tape-ribbon cartridge of the type shown and 25 disclosed in co-pending applications entitled TAPE SUPPLY SYSTEM
FC)R A TBRMAL PRINTING DEVICE OR THE LIKE, Serial No. 589,364, TH~5AL

f ~
~ ' 1 329~ 1 5 PRINTING DEVlCE AND TAPE SUPP~Y CARl~DlGE THEREFOR, Serial No. 589,359 and TliER~ML PRINTING DEVICE AND TAPE SUPP~Y 'ARTRDIGE EMBODYING A
TAPE CUT-OF~: MECHANISM, Serial No. 589,362.
As illustrated best i~ FIG, 2, the operative components of the ther~al 5 transfer device utilizing the control system of ~he pre~ent invention include a printhead assembly 22, a platen assembly 24 and a tape-ribbon drive means 26.
In the preferred embodiment, the drive means 26 is a rotary drive means comprised of a drive motor S4 and an associated pair of drive rollers 60 and 34 located downstream from the printhcad and platen assemblies 22 and 24. Tho drive rollers 22 and 24 function to advance the tape 31 and ribbon 32 pas~ the transfer station 20 defined by and positioned between the printhead and platen assemblies. The drive roller 60 is rotatably mounted within a drive roller hous;n~ 61 with top end of the drive roller shaft journaled in a ponion of the housing 6l. Adjacent to the lower end of the drive roller 60 is a drive gear 62 that is designed for meshing engagement with a corresponding drive gear 33 associated with the drive roller 34. The drive roller 34 is rotatably journaled in a housing portion 3S. Although it is eontemplated that both rollers 60 and 34 could be rotstably mounted in a eommon housing, the roller 60 of the preferred embodiment is mounted in a portioo of the machine housing 6 l, whiie the roller 34 is mounted in a portion of a tape-ribbon canridge housing 3S. Such a structure is illustrated in each of the related applicalions filed February l, 1988 and rcferred to above. In the preferrcd structure, the drive roller 34 is biased into engagement with the driver roller 60 by a pair of spring members (not shown) in the cartridge 30 (Fig. l).
A drive roller shaft 63 extends downwardly from the drive roller 60 and is connec~ed at its lower end with a toothed gear 64. The toothed gear 64 is 1 32 q '''~ 1 5 connectcd via an appropriate gcar asse-mbly 65 and a motor shaft 66 to thc drive motor 54. In the preferred embodiment, the gear assembly 65 can comprise either a single gear as shown in the drawings or multiple gears.
With this structure, rotation of the drive motor S4 causcs rotation of the gear 64 of the drive roller 60. Rotation of the drive roller 60 causcs corresponding 5 rotation of the drive roller 34 as a result of the engagement between the gears 62 and 33. When the tape 31 and ribbon 32 are disposcd betwcen the drive rollers 60 and 34, this rotation advances the tape 31 and ribbon 32 past the transfer station 20. In a preferred embodiment of the invention, ~hc drivc motor S4 is a DC-servo motor, Model EN35-lSlNlB, available from Canon 10 Precision of Tokyo, Japan. The motor 54 is a pulse driven motor or a serv-o-motor driven with a pulse-width-modulated voltage pulse for high efficiency.
Mounted on the shaft 66 and positioned between thc motor 54 and the gear 65 is an optical detection means or rotational optical encoder 70 for detecting the rotational speed of the shaft 66 so that the speed of the tape 31 1 5 and ribbon 32 and the position of the tape 31 and ribbon 32 relative to Ihe printhead 22 can be determined. In a preferrcd embodiment of the invention, the detection means 70 is implcmented using a conventional rotational optical encoder or choppcr wheel photo-detector having an optical interrupter 74 mounted on the motor shaft 66 and positioned between the mo~or 54 and the 20 gear assembly 65. The optica~ interrupter is a plastic disc having a pluralily of vanes 75. The interrupter 74 is coupled to the motor shaft 66 and is disposed between 3 light source and a photo-detector located in the dctector housing 7~
By de~ecting ~he presence or absence of light within the photo-detector 72, the detection means 70 translates the rotational speed of the shaft 66 into a digital 25 pulse train or Processed Encoded Tick (Vpet) 76 having a frequency corresponding to the rotational speed of shaft 66.

* Trade Mark :

With continuing reference to Fig. 2, ~hc platen a~sembly 24 includes a rotatable, cyliDdrically shaped plalen 2S which is movable into an image transfer position relative to the printhead assembly 22. Movement of thc platen 2S into such posi~ion i~ caused by the linear acluator 2~ lO creatc the dcsired printing pressure between the platen 2S and thc printhcad a~scmbly 5 22.
The structure illustrated in Fig. 2 also includes an electronic tapc-ribbon sensor 230 positioncd upstrcam from the printhead assembly 22 and a tape cut-off mechanism 220 positioned dow~stream from the tape-ribbon drive mcans 26. The detailcd structure of thesc components as well as the printhcad 10 asscmbly 22, the platen asscmbly 24, the drive assembly 26 and other components are disclosed in thc above identif~led related applications filed January 27, 1989.
Reference is nc~t made to FIG. S showing thc printhead assembly 22.
The printhead assembly 22 comprises a printhead 90 and an associated heat l 5 sink 91 mountcd to a frame (oot shown) for operative alignment with the platcn assembly 24 (Fig. 2). The printhead assembly 22 i8 electrically connected to the processing means 14 (Fig. I) via an appropriate clectrical conncctor. In thc prefcrred embotiment, the printhead 90 is a single column 300 dpi (dots per inch) thin fil~D thermal printhead with associatcd integrated 20 circuit drivers and which is identified as Modcl KFT-22-12MPEI-PA a~/ailable from Kyocera International of Framingham, Massachusetts. The printhead 90 consis~s of a single column of squafe hcating elements 94, each hea~ing element 94 reprcsenting a unique pixel and being electrically connectcd to a driver circuit 95. The driver circuit 9S electronically controls the head 2 5 tcmpcrature of all of the heating elements 94. The printhcad 90 of thc preferred embodimcnt includes 256 hea~ing elements 94 serially drivcn by f,~ :

` 1 32q4 1 5 four sixty~four bit driver chips illustrated by reference numerals 96, 97, 98 and 99. As will be described further below, the driver circuit 95 receives data from the four driver chips (HIGH to print and LOW to not print) and applies a printing voltage ~o each of thc heating elements 94 to therrnally transfer the square area corresponding to that heating clement from the ~hermal ribbon .
32 to the image carrying tape 31. A therrnal transfer ribbon 32 suitable for use with the preferred embodiment of this invention is Therrnal Transfer Ribbon, ~odel TRX-6-5-4 available from Fuji Kagakusi of Kogyo, Japan. The image carrying tape 31 may be any type of plastic or polymer based film that is capable of receiving a thermal transfer of an image without distorting the 10 substrate or carrier material.
R~ferring now to FlGs. 2 and 3, the operation of a preferred embodiment of the control system of the present invcntion will be explained. In general the control system of the present invention includes a processing means (generally illustrated in Fig. 1 by the reference numcral 14 and more specifically illustrated in Figs. 2 and 3 by thc reference numerals 50 and 52) for receiving various input data and proccssing the same to generate data and control signals to drive thc printhead asscmbly 22. More specifically, the processor 52 receives Input Data 100 represen~ing selccted charactcrs or dcsigns to be printed and Font Data 110 generally representing a set of character outlirles. The processor 52 then processes the In?ut Data 100 and Font Data 110 to generate Outpul Data 130 and Control Signals 140, through a FIFO Buffer 134, to be provided to the output processor 50 in response to an Interrupt Signal 160. The output processor 50 receives the Output Data 130 and Control Signals 140 and provides the printhead assembly 22 with Print Data 150 in the form of a single columnar set of pixel data representing the selected characters to be printed. The processor 50 also supplies Control Signals 140 to ;~.
.

~," ; ~ ",~ ~"~

the printhead asscmbly 22 to print the characters rcpresented by Output Data 130.
The combination of features that make up the processing means 50, 52 of the present invention is preferably controlled by a stored sofiware program that operat~s on the data in the manner describcd in conncction with FIG. 3, 5 although those skilled in the art will recognize that softwarc functions can be accomplished by equivalent hardware. While a pair of microproc~ssors 50 and 52 are shown as a preferred embodiment of processing means 14, it should also be recognized that the invention could also be achieved through the use of a single microcomputer and associated circuitry, or multiple microcomputers 10 and associated circuitry, or any combination thercof. In the preferred embodiment of the invention, both processors 50 and 52 arc programmable digital microprocessors with the output processor 50 being an 8051 microprocessor available from Intel Corporation of Santa Clara, California, and the processor 52 being an 80186 rasterization microprocessor, also available l 5 from Intel Corporation.
Though in thc preferred embodiment of the invention both Control Signals 140 and PriDt Data 150 are generated by a real-time rasterization system based on Input l)ata 100 representing the desired characters to be printed and Font Data l lO representing the outlines for such characters, it will 20 be apparent to those skilled in the art that Control Signals 140 and Print Data 150 may be supplied by any number of methods or in any number of formats without departin~ from the spirit of the prese~t invention. For example, Print Data 150 might be generated from a dot-matrix representation of the selected characters to be printed, instead of being based on an outlinc representalion 25 of ~he characters; or Print Data 150 might be simultaneously transmi[ted as multiple columns of pixel data, instead of sequentially transmitted as single s"",~ ,,".,. ;,"~.,",~ "'~

r ~~ . .
1 32q4 1 5 columns of pixel tata. Similarly, Control Signals 140 might be separate control lincs connected to thc output processor S0, or they might bc incorporated as special control codes cootained within Prins Daul IS0.
Bccause the pi~el images created by the thcrmal transfer of the ribbon 32 onto thc tape 31 are of a consistent and uniform width and do not smear or 5 smudge into a pixel element in the adjacent vertical column, precise alignmcnt betweeo vertical columns of pixels is necessary to avoid creating any white space between vertical columns of pi~els and/or overlapping vcnical columns of print. The present invention overcomcs the inadequacies of the prior an by both controlling thc spccd at which the tape 31 and ribbon 10 32 are transported past thc image transfcr station 20 and by controlling and monitoring thc position of the tapc 31 and ribbon 32 so that cach column of pi%els is printed at thc appropriatc and prcdcfincd position on thc tape. This is accomplishcd by thc combination of a dctcction means ~0 and a fccdback means 80 that are connected to the drive motor 54 and the output proccssor 50.

During operation of the preferred thcrmal transfer device, the tape 31 and ribbon 32 arc advanccd past the image transfcr statioo 20 by the drive rollers 60 and 34 at a constant rate (1 inch per second) and thc vertical columns of pixel data are printcd at a width of 300 pixcls pcr inch. Since the dctector 70 is uscd for sensing both thc proper location of the 300 pi~tels per 20 inch and the proper drive spced, it must providc an integer multiple of 300 eounts per inch, which also means 300 counts per second. Because of the operational characteristics of the drive mo~or 54, and ~o enablc realization of thc control circuitry dcscribed below, thc desired detcctor 70 count ratc was set at 1200 Hz. It is contemplatcd that software modification can bc made to 25 provide for different pi~el width and frequency. It will be seen that various olher types of de~ection means 70 would work equally well wi~b lhe presen~

;-` 1 329~

inven~ion. For e~ample, any rotational detector means which produces position and speed information and which is mounted on the drive motor shaft 66 would achieve the same results as the rotational encoder 70. It is also seen that the placement of detection means 70 on the drive motor shaft 66 is optional, and that the detection means 70 could also be mounted on the drive 5 roller shaft 63 and utilize a different detector count rate. Even though the objective is to monitor the speed and location of the drive roller 60, and thus the tape 31 and ribbon 32. Iocating the detection means 70 on the drive motor shaft 66 accomplishes this objective because the rotary drive means 26 is only operated in a forward direction and the gear ratio of gear assembly 65 is fixed l O and known.
It is also contemplated that detection means other than rotational speed detection means could be utilized. For example, detection means to detect the linear speed or movement of the tape 31 or ribbon 32 could be used as long as the means is capable of generating the tape-ribbon position and speed data 15 needed for use in the processors 50 and 52.
Reference is next made to FIG. 4 illustrating the feedback means 80 used to monitor and control the speed of the motor 54. Essentially, the feedback means 80 cooperates with the rotary drive means 26 to operate in a fashion similar to a conventional Phase Locked Loop (PLL). During operation, the 20 rotational frequency sensed by the detector 70 is compared to a reference frequency (Vref 78) in a phase comparator 82. The output of this comparison is then used to modify the speed of the motor 54. The mechanical inertia and electrical inductance of the motor operate as a filter for the PLL and the mo~oroperates as the voltage controlled oscillator since, as the voltage to the motor is 2 5 changed, the speed of the motor changes and so does lhe frequency of the signal frorn the detector. As shown in FIG. 4, the motor rotntional frcquency ,.... . . . . - , . :

1 32q4 1 5 signal Vpet 76 i8 one of two signals fed into Ihe phase comparator 82 for generaling tho output voltage (VOUt) 77 used to control the motor 54; the other is the reference frequency Vref 78. In the preferred embodiment, phase comparator 82 is comprised of a portion of a conventional PLL integrated circuit, i~ this ease a 14046 Phase Loclced Loop available from Motorola, Ine., of 5 Austin, Texas. Also utilized in the feedback means 8D is an assoeiated pull upcircuitry 83 and a power driver 84 for presenting Vout 77 to the motor S4. The comparator 82 eompares the frequency of Vpet 76 at pin 3 with a reference frequency Vref 78 at pin 14. Vref 78 is seleeted to he e~actly equal to the desired operating frequency for VOUt 77, na nely, 1200 Hz. This establishes V ref 78 as the center frequency of the loclc ran8e of tho feedback means 80.
In one embodiment of the invention, Vref 78 is generated by the rasterization processor 52 based upon the master cloclc signal used to operate the 80t86 microprocessor. As supplied to the drive motor 54, VOut 77 is comprised of two outputs of the power driver 84, Vm 85 and GNDm 86, that are co~necsed to the 1 5 input terminals of the motor 54. It should be understood that the motor S4 is operated in a pulse-width-modulated fashion whereby the frequency of Vout 77 controls the speed at which the motor S4 turns by determining how often the motor S4 is on. Vout 87 is alsio gated with MOTOR ON 88 to prevent applying a voltage to the motor S4 when motor operation is not desired.
V pet 76 is also connected to the output processor 50 for detennining when to print the next column of Print Data 150. In the preferred embodiment of the present invenlion, the output processor 50 uses Vpe t 76 as a position indicator to identify the current position of the tape 31 and ribbon 32 disFosedbetween the printhead assembly 22 and the platen assembly 24. The output processor 50 uses the digital pulses of Vpet 76 ~o directly detelmine when to print the pixel data as a function of counting a specified number of pulses on ~:- ; . : . ` : : ` . - . :, - . . . , .: . ; , 1 32q~ 1 5 V pct 76. Whcn thc tape 31 and ribbon 32 arc advanced past ~he transfcr station at a ratc of 1 inch per second and each column of Print Data IS0 is to be printed at 300 pi%els pcr inch, thc tape 31 will move one pi~el width past thc ~ransfcr station 20 evcry 3.3 milliscconds (ms). Accordingly, by using thc leading edgc of every fourth pu19e on Vpet 76 (at 1200 Hz), a refcrence position for the bcginning of each column of pixcl data is established. The rcference position ties the outpuning of the Print Data 150 directly to the advancement of the tape31 and ribbon 32 past thc transfer station 20 to insurc that each succceding column of Print Data IS0 will bc properly aligned.
Wi~h specific refercnce to the schematic diagrarn shown in FIG. 6 and the timing diagram shown in FIG. 7, the outputting of Print Data 150 to the printhead 90 will bc described. Print Data IS~ i~ cloclccd into thc driver chips96, 97, 98 and 99 by scrially placing Print Data 150 on DATA IN 200, waiting until CLOCK 206 has cloclccd all of the pi~cl data that comprises one column of Print Data 150 and then enabling LATCH 202 to latch Print Data 150 into the rcspective drivcr chips. Pixel data bits 1-64 of Print Data IS0 are latched into driver chip 99, pi~el data bits 6S-128 are latched into driver chip 98, pixel data bit~ 129-192 are latchcd into drivcr chip 97, and pixcl data bits 193-2S6 arc latchcd into drivcr chip 96. Thc driver chips allow thc next column of pi~el data to be transfcrred and latched into one of thc driver chips 96-99 of the printhcad 90 while the current column of pixcl data is being printed. Whcn Print Data IS0 has been transferred and latched into the respcctive driver chips, the output processor 50 enables STROBE 210 and STROBE 212 for a specific time pcriod to apply the heating voltages to thc sclected heating elemcnts 94.
In thc preferred embodiment of thc present invention, the printhcad 90 is equippcd with two scparate STROBE lines, STROBE I (2103 and STROBE 2 (212) to allow for the more efficient driving of thc driver chips. STROBE 210 and ~ 7 1 329~
STROBE 212 are tied togethcr aDd do~not opera~e indepentently of onc ~nother.
STROBE~ 210 and STROBE 212 ~ctivate the driver circuit 9S to apply a spocific hcatirlg voltagc to each of thc hcating elemcnts 94 in the printhead 90 for a predcterrnincd timc pcriod. For thei particul~r printhead and tapc of the preferred embodiment. STROBE 210 is activated for a fi~ed dme poriod of 1.4 DIS
to achicve the optimurn print quality.
As Print Data 150 is being strobed into the driver chips 96, 97, 98, and 99.
thc output processor 50 also signals the rasterization processor 52 by means of Interrupt Signal 160 (shown in FIG. 3) that another column of Print r)ata 1S0 may be loaded into FIFO Buffer 134. In the prsferred embodiment, Print Data IS0 is storcd in FIFO Buffer 134 as a series of 33 bytes representing 1 bytc of control informa~ion or Control Signals 140 and 32 bytes of pixel data 130 organized to be printed as a singlc vcrtical column.
As described in more dctail in co-pending application cntitled PIXEL
PREH~AT SYSTEM FOR AN AUTOMATED THERMAL TRANSFER DEVICE, filed Marc~ 20, 1989 and identifed by Serial No. 594,220, each of the heating elements 94 is preheated ~ith a unique pi~cl preheat data value. The pixel prehcat valuc for the ncxt pixel to be printed is determined by the value of thc next pixel to be printed and thc valucof thc current pixel to be printed. Because the preferred embodiment of thc driver circuit 95 is provided with Data Out 214, thc output proccssor 50 can makc use of the current pixcl values as they are being shifted ou~ of the drivercircuil 9S ~o calcula~e the pixcl preheat values for the next column of pixel data.
Having described the operation of the elemen~s of ~he output processor 2 5 S0 and the printhead assembly 22 the overall timing and data flow can best be understood by reference to FIG. 8. The timing sequence and data flow is shown '~ ' , ' ' .
~
.

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- 132q~15 - ~ ' for the trans~er of a single column of Print Data lS0 from the rasterization processor S2 to the output processor S0, to the printhead 90 to be printed, aDd then finally back to the output processor S0 to be used in calculate the pixel preheat valuos for tho rle~t column of Priut Data IS0. Thi~ entire process is completed once every 3.3 ms. This results in an effective prin~ing rate of 1 inch per second. Vpet 76 defines the duratioh of each cycle, with the leading edge of every fourth pulse indicating the start of a new column to be prin~ed.
At AA of Fig. 8, the output processor S2 raises Interrupt Signal 160 lo tell therasterization processor S2 to, load FIFO Buffer 134 with a new column of Print Data 150 which occurs at BB. At CC, the oulput processor S0 unloads Print Data ISO from FIFO Buffer 134 and examines the control bytç for a control code as explained below. If the data in FIFO Buffer 134 is pixel data to be pri~ted, theoutput processor S0 sets up Print Data IS0 to be combined with the pixel data currently in the prinlhead 90 and shiftçd out beginning at DD to generate the pixel preheat values. At EE, the pixel preheat values for Print Data IS0 are strobed into the driver chips 96, 97, 98, and 99 and subsequently latehed at FF.At GG, the actual pixel values for Print Data IS0 are strobed into the driver chips 96, 97, 98, and 99 and will remain ready to be latched into the printhead elements 94 at the bçginning of the next pAnt cycle. From GG to HH, the prinlhead elernen~s 94 are on the cool-down phase of their heating cycle from the previous print cycle and by HH all of the heating elements 94 should have ~;
returned to a temperature just below the threshold transfer temperature of the thermal ribbon 32. At HH, STROBE 210 and STROBE 212 are activa~ed for 1.4 ms and the printing voltage is applied to the pixel values for each of the heating elements 94, which at HH will be the pixel preheat values that were latched at 2 5 F~:. As will be seen at II, the pixel preheat voltages are applied for .2 ms, after which LATCH 206 is enabled and the ac~ual pixel values for Print Data 150 are lg ; .

... .. . . . .. . . . . . . .. . . . . . . .

~-" 1 32q4 1 5 provided to the hcating elements 94. During this SO microsccond la~ch time, the hçating ~voltage will still be applicd to the heating elements 94 and the pixcl value will bc transicnt, but will not be sufficiently heated or coolcd to affect the tempcrature of each heating elemcnt 94. Conscqucntly, the tempcrature of each heating element 94 will bc deterrnined by thç pi~cl value 5 of Print Data ISO DOW shifted into each of the heating clernents 94. The printing voltage is applied or not applicd dcpending on the pi~el data value for thc duration of the 1.4 ms period until KK, when thc applied printing voltage is removed. The temperature of those hesting elements to which priDting voltagc was applied arc then allowed to return to just below the threshold 10 temperature.
In the preferred embodiment, the application of thc printing voltages to thc hcating clemcnts 94 is control1cd by thc drivcr circuit 9S. The printhead 90 is supplied by two voltagc ~upple~, a logic voltage Icvel (+SV) and a printing voltage level (+16V). The printhead 90 is providcd with a gross 15 feedback mechanism in thc form of a thcrmistor 214 to reguluc thc overall tcmperature of thc printhead 90 and associatcd hcat sinl~ 91. The output of ~he thcrrnistor 214 is used by the dnvcr citcuit 95 to adjust thc a nplitudc of thc printing voltagc uscd to drivc the hcating clemcnts 94 based on the measured temperature of the hcat sinlc 91. An alternativc embodimeot of the present 20 invention allows the output proccssor 5û to monitor the overall temperature of thc printhead 90 and associated hcat sink 91, and adjust the powcr Icvcl of the printing voltages by adjus~ing the duration of STROBE 210 and STROBE 212 to compensatc for changes in ambient temperaturc, whcthcr thosc temperature changes are external or internal to trans~cr devicc 12. In either case, it is 2 5 advantageous to be able to adjust the power level of the printing voltagcs so as to prolong the life of thc heating elcments 94 and to prevent over-heating or 132')~15 over-liquefying of the transfer ribbon 32 which may result in running or smeariog of the cbaracters on the tape 31.
In addition to controlling the printing of Print Data 150 by the printhead assembly 22, the output processor S0 may also perfonn various o~her control fuoctions inherent in controlling a thern~al transfer device 10 of the 5 type contemplated by the present invention. The output processor S0 e~amines the control byte in FIFO Buffer 134 to determine whether the ne~t set of Print Data 150 is pixel da~a to be output to printhead 90 or whether the control byte of Print Data 150 is one of several control functions that may be requested of the output processor S0. These functions include: Stop Print, Start10 Print, Advance Tape, Cut Tape, and Tape Inquiry.

Stop Prin~ instructs the system ~o immediately cease printing of data and causes output processor S0 to stop drive motor S4. The Stop Priot instruction also causes the platen assembly 24 to disengage from the printhead assembly 22 via a control signal 216.
Start Print instructs the system to begin printing and eauses the output processor 50 to engage the platen assembly 24 and then stan drive motor S4.
To insure that the drive motor S4 is up to the proper speed, the output processor S0 monitors Vpet 76 for a specifiet time period to detennine if the e~pected number of signals are received. The output processor 50 will not begin printing any pixel data until it deterrnines that VpCt 76 is within a specified range of the expected rotational speed for the drive motor 54. If the drive motor 54 does not come up lo speed within a second specified time penod, the output processor 50 would report an error condition and no printing would be performed.
Advance Tape instructs the system to adYance the tape 31 and ribbon 32 a specified number of print columns past the transfer station 20. The output . .

.

1 329~ 1 5 processor so disengages the platen assembly 24 and then monitors Vpet 76 t o count the number of print columns that are advanced past the transfer station 20. WheD the desired number of print columns is reached, the drive motor 54 is stopped and the output processor S0 waits until either a Start Print or Cut Tape control command is received.
Tape Cut instructs the system to activate a tape-cut meehanism 220 by causing the output processor to activate an actuator 222 via an appropriate control signal 224 causing forward movement of a blade to eut the tape 31 and ribbon 32. Wben Ihe blade is advanced to its fanhest point of travel, the outpul processor 50 deaetivates the tape-eut meehanism 220 eausing the return of the blade to its relracted positioo.
The output proeessor S0 also monitors the tape indieator 230 to check whelher the tape 31 and ribbon 32 are being presented to the trar~sfer station 20. In a preferred embodiment, the tape indicator 230 uses a light source and a photo-detector localed in a photo-detector housing 232 to sense the presence or l 5 absence of the tape 31 and ribbon 32 and reports this information to the output processor 50 via the control signal 234. In an out of lape eondition, ~he outputproeessor 50 will e~secute a Stop Print command and send a control message to the input module 40, for e~ample, indieating that an out of tape message should be displayed to the operator.
While each of the control commands for the output proeessor 50 has been described individually, it is contemplated that the control commands may be used in conjunction to cause the output processor 50 to perform a series of operations. For example, a sequence of control commands of Stop Print, Advanee Tape, Cut Tape, Advance Tape, and lhen Stan Print might be used to eause the transfer device 10 to end a first strip of tape and begin a second strip of tape. It is also apparent that multiple eontrol eommands could be combined ; ' ' ' `: ~' ' ' ' ~ .

into a single control command, fot e~cample Stop Print, Ad~ance Tape, and Cut Tape might be received by the output processor S0 as an End of Line Cut Command.
Although the description of the preferred embodiment has been presented, it is contemplated that various changes coult be made without 5 deviating from the spirit of the present inventio~. Accordingly, it is intended that the scope of lhe present invention be dictated by the appended clairns rather than by the descripLion of the preferred embodiment.
We claim:
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Claims (15)

1. A control system for an automated thermal transfer device having an image transfer station defined by a printhead for transferring a selected image comprised of a set of columns of pixel data from a ribbon to a tape and having a tape-ribbon drive means for advancing said ribbon and tape past said image transfer station, comprising:
detector means for detecting the speed and position of said tape and ribbon past said image transfer station;
feedback means operably connected to said detector means and said drive means for controlling the speed of said tape and ribbon past said image transfer station; and processing means operably connected to said detector means and said printhead for transferring said columns of pixel data to said printhead in response to a position of said tape and ribbon.

2. The control system of claim 1 wherein the position of said tape and ribbon is determined in relation to the speed of the tape and ribbon such that the width of each of said columns of pixel data is uniform.

3. The control system of claim 2 wherein said tape-ribbon drive means is a rotary drive means.

4. The control system of claim 3 wherein said detector means detects the speed of said tape and ribbon by detecting the rotational speed of said drive means.

5. The control system of claim 4 wherein said detector means is an optical interrupter disposed between a light source and a photo detector.

6. The control system of claim 1 wherein said feedback means is a phase comparator for comparing the frequency of a signal produced by said detection means and a reference frequency and generating an output signal for controlling the speed of said drive means..

7. A thermal transfer tape lettering apparatus for transferring a selected image from a ribbon to a tape comprising:
an image transfer station;
means for supplying ribbon and tape at said image transfer station;
means for generating print data comprised of a set of columnar pixel data representing said selected image;
printhead means for transferring said image from said ribbon to said tape comprised of a column of thermal heating elements, each of said healing elements being responsive to a unique bit of data in said print data to be selectively heated for a duration of time;
cylindrical platen means for operably engaging said ribbon and tape with said printhead means;
rotary drive means for advancing said ribbon and tape past said printhead means, said drive means located downstream from said platen means;
detector means operably connected to said drive means for detecting the rotational speed of said drive means and generating a speed signal;
control means operably connected to said rotary drive means and said detector means for receiving said speed signal and generating a drive control signal to selectively alter the rotational speed of said drive means to maintain said speed signal within a predefined rotational speed range; and processing means operably connected to said printhead means and said control means for receiving said print data and transmitting said print data to said printhead means in a predefined relationship with said speed signal such that each successive set of said columnar pixel data is printed on said tape in proper alignment with the previous set of said columnar pixel data.

8. The image transfer station of claim 7 wherein said printhead means comprises:
a printhead having a single column of thermal heating elements; and control circuitry having a memory location corresponding to each said heating elements such that said set of columnar pixel data may be latched into said memory locations;
whereby each of said heating elements is simultaneously responsive to a data bit in said memory locations.

9. The image transfer station of claim 8 wherein said heating elements are responsive to the amplitude and duration of a voltage applied to each of said elements.

10. The image transfer station of claim 7 wherein each of said thermal heating elements comprises a square resistive element abuttably adjoining the adjacent heating elements.

11. The image transfer station of claim 7 wherein said rotary drive means comprises a pair of rotatable drive rollers having said ribbon and tape disposed therebetween, one of said driver rollers operably connected to a pulse driven motor.

12. The image transfer station of claim 7 wherein said detector means is comprised of a rotational optical encoder having an optical interrupter operably connected to said drive means and disposed between a light source and a photo-detector to generate said speed signal.

13. The image transfer station of claim 7 wherein said control means is a reference signal and a phase comparator for comparing said speed signal to said reference frequency.

14. A method for controlling a thermal tape lettering apparatus having an image forming station for forming a selected image on a tape, said selected image comprised of a successive sets of pixel data, comprising the steps of:
monitoring the rotational speed of a drive means for advancing said tape past said image forming station;
controlling the rotational speed of said drive means by maintaining the rotational speed within a specified frequency lock range; and printing each of said successive sets of columnar pixel data in response to the rotational speed such that the width of each of said successive sets of columnar pixel data is uniform.

15. A control system for an automated thermal transfer device for transferring a selected image represented by successive sets of columns of pixel data from a ribbon to a tape, said transfer device comprising a printhead having a single column of square resistive heating elements abuttably adjoining the adjacent heating elements, each of said heating elements being responsive to the amplitude and duration of a voltage applied to each of said elements by a control circuit having a memory location corresponding to each of said heating elements that said pixel data is latched into, said thermal transfer device also including a cylindrical platen for engaging said ribbon and tape between said platen and said printhead, and a pair of rotatable drive rollers located downstream from said printhead and having said ribbon and tape disposed therebetween, one of said drive rollers operably connected to a pulse-driven motor, comprising:
a rotational speed detector operably connected to said motor and generating a digital pulse train having a frequency in a specified relation to the rotational speed of said motor;
a phase comparator operably connected to said rotational speed detector, a predefined reference frequency and said motor to control the rotational speed of said motor within a predefined frequency lock range; and a microprocessor operably connected to said rotational speed detector and said control circuit of said printhead for transferring said successive sets of columns of pixel data to said printhead in response to said digital pulse train such that the width of each of said columns of pixel data is uniform.