GB2057734A

GB2057734A - Thermal array protection

Info

Publication number: GB2057734A
Application number: GB8028196A
Authority: GB
Original assignee: Gould Inc
Current assignee: Gould Inc
Priority date: 1979-09-04
Filing date: 1980-09-01
Publication date: 1981-04-01
Also published as: CA1178645A; GB2057734B; FR2475986A1; DE3033181A1; NL8005019A; FR2474956A1

Abstract

In a thermal array protection apparatus, data to be printed within a given line of data are compared to data printed within one or more previous lines of data. Whether data will or will not be printed in the given line of data is a function of the previous data printed. Since the apparatus prevents data from being printed for the same position in successive lines of data, the temperature of the individual thermal imaging styli will be kept within acceptable limits. <IMAGE>

Description

SPECIFICATION Thermal array protection method and apparatus FIELD OF THE INVENTION The present invention relates generally to imaging, printing or recording devices and is particularly though not exclusively directed to a protection method and apparatus to prevent overheating of thermal array imaging devices.

BACKGROUND OF THE INVENTION It is known in the art to fabricate thermal recording devices having imaging stylii arranged in a linear array. Such devices typically are comprised of a plurality of stylii which are formed by disposing electrically resistive material on an insulating substrate to form a plurality of individual stylii in a single row. These stylii are electrically connected to driver circuits. Each stylus is selectively energized by the driver circuits to produce Joule heat. When stylii are brought into contact with or suitable proximity to a thermally sensitive imaging medium, each energized stylus makes a mark on the medium. The stylii typically are spaced at a density of 100 stylii per inch and may require as much as one watt of power to raise the temperature of a single stylus to a level suitable for imaging.Energizing the stylii at a high repetition rate can cause overheating or even burn out of the stylii. Overheating of the stylii can also cause smudging or shadows on the recording medium.

To avoid an occurrence of overheating in thermal array stylii, the prior art teaches the use of various types of temperature compensation circuits. One such circuit, disposed in U.S. Patent 3,577,137 to James Brennan, Jr., uses a temperature sensor to sense the temperature of the stylii. The power applied to the stylii then is adjusted in order to reduce the heat. Such circuits require calibration and are therefore expensive to build and maintain and can also be subject to reliability problems.

Another method taught by the prior art to prevent overheating of a thermal array stylii is to control the "on" time of the incoming print command. U.S. Patent 4,070,587 to Takayoshi Hanakata discloses a circuit using a "one shot" control principle, so that the drive current to the thermal stylus is cut off by the "one shot" after a predetermined interval.

Such circuits, however, will not protect against overheating of the thermal stylii caused by rapid repetition of the stylus drive current.

Still another way to prevent overheating is accomplished in the prior art by the use of large metal heat sinks and by air cooling.

Such devices add weight to the device and are not very efficient.

SUMMARY OF THE INVENTION The present invention resides broadly in the concept of logically processing the data content of a data line with that of one or more other data lines in accordance with a predetermined algorithm such that selected stylii, which in accordance with the data in the respective data line are designated to be driven, are elected not to be driven during the time duration of the data line in question.

Thus whereas in accordance with prior art techniques the existence of data in a data position would inevitably result in the correspondingly positioned stylus being driven, in accordance with the invention this is no longer the case and the driving of a stylus is made dependent not only upon the presence of data in a corresponding data position but also upon the data situation for corresponding data locations of one or more preferably but not necessarily immediately preceding data lines. By this means, the thermal loading of the stylii can be considerably reduced without, as will be explained hereinafter, detracting from the quality of data reproduction.

The invention can be performed in many different ways depending upon the particular algorithm selected and, whilst in the following a number of exemplary algorithms will be explained, it is to be appreciated that these are merely illustrative and do not represent the sum total of possibly useful algorithms within the scope of the invention. An exhaustive evaluation of more than an illustrative number of exemplary algorithms clearly is beyond the scope of this document.

In a first illustrative embodiment, the algorithm employed simply compares the data passed to the stylus driver circuits for the preceding data line with the incoming line of data. At start-up, the incoming line of data is received and passed to a thermal array current drive circuit and is simultaneously stored. A new line of data is then received and effectively compared with the first-received line of data. Data in individual datum positions in the newly received line of data is then blocked from passing to the thermal array current drive circuit for those corresponding positions in which the stored first-received line of data had the existence of data. The datum that is passed in the new line of data is then stored in order to be used for the next line of data received. The sequence is then repeated by the method and apparatus of the invention for each next line of data received.Operation of this process can yield a power output reduction up to a maximum of 50%.

Even greater power output reductions are obtainable by practice of the invention, the limiting factor being the need to preserve the integrity of the resultant display, that is the need to ensure that the number of stylii selected not to be driven does not detract from the display quality to any significant extent. Thus in accordance with a further embodiment the line of data is passed by a first passing means to a second passing means and is simultaneously stored in a first storing means. The second passing means passes the line of data to a drive circuit which in turn current drives the thermal array stylii.

A next line of data is received and is compared to the previous line of data in the first storing means to determine if data exist in corresponding positions. The data of the next line of data are blocked from passing through the first passing means for those positions. All other data are passed. A first storing means stores the data passed in the next line of data.

A second storing means stores data for those corresponding positions between the two lines of data. The next line of data is then passed to the drive circuit by the second passing means. Another line of data is received and is compared to the line of data just passed to determine again if data exist in corresponding positions. Only the data that does not have data in a corresponding position will be passed to the second passing means by the first passing means. The second passing means is arranged so as to pass only that data in positions for which the second storing means has stored data in corresponding positions or for positions which are a coincidence function of one-fourth the word length frequency and one-half the datum position frequency. The sequence is then repeated for each subsequent line of data received.

The principal advantages afforded by the invention are in effecting a reduction of the heating problems associated with prior art thermal imaging arrays by means of simple and affordable circuits. A secondary advantage of the reduction of the heating problem is the resultant ability of thermal imaging arrays to accommodate higher data rates than before.

The usefulness of the invention is not limited to linear thermal array devices but can be used in any display device that receives successive lines of data wherein the lines of data comprise a plurality of individual datum separated into a number of datum positions. In its broadest aspect the invention thus provides a method of display imaging in which, in each of a series of addressing operations, a plurality of display component imagers are selectively addressed in accordance with display data so as each to generate an image component according to whether or not data exists in a datum location of said display data corresponding to the respective imager, and wherein an incoming line of data adapted for addressing the imagers is logically processed, in a predetermined manner, with data representative of the addressing of the imagers during one or more previous operations of the series in order to derive a depleted data line wherein data in some of the datum locations of the data line are selected to be redundant for generating an acceptable display image corresponding to the display data, the said depleted data line being used for addressing the plurality of display component imagers.

The invention together with its features and advantages will best be made clear by reference to the following descriptions of a number' of exemplary embodiments which are illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing a first generalized embodiment of the present invention.

Figure 2 is a block diagram showing a second generalized embodiment of the present invention.

Figure 3 is a circuit diagram showing the embodiment of Fig. 1 in more detail.

Figure 4 is a circuit diagram showing the embodiment of Fig. 2 in more detail.

Figure 5 is a truth table for a portion of the embodiment shown in Fig. 4.

Figure 6 is a print out representation for illustrating the operation of the embodiment shown in Figs. 1 and 2.

Figure 7 is a signal waveform representation for illustrating the operation of the embodiment shown in Fig. 4.

Figure 8 is a dot pattern representation for illustrating the overlap phenomena that occur in thermal printers.

Figure 9 is a block diagram showing a third generalized embodiment of the present invention.

Figure 10 is a circuit diagram showing the embodiment of Fig. 9 in more detail.

Figure ii is a signal waveform representation for illustrating the operation of the embodiment shown in Fig. 10.

Figure 12 is a print out representation for illustrating the operation of the embodiment shown in Fig. 10.

Figure 13 is a circuit diagram showing yet another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODI MENTS A description of the method and apparatus according to the invention follows, referring to the drawings in which like reference numerals denote like elements of structure in each of the several Figures.

In the following, the word HIGH is used, as is known in the art, to represent a digital voltage level. A digital HIGH in this application will also be designated by the numeral "1" and will be referred to as a logic state 1.

The word LOW is used, as is known in the art, to represent a different, lower digital voltage level. A digital LOW in this application will also be designated by the numeral "0" and will be referred to as a logic state 0. The voltage levels that define a digital HIGH or a digital LOW will depend on the type of digital devices used. For example, if Transistor-Transistor Logic (TTL) is used, a digital LOW will typically be from 0.0 to 0.8 volts d.c. and a digital HIGH will be from 2.0 to 5.5 volts d.c.

Fig. 1 is a block diagram showing a generic embodiment of the apparatus according to the present invention. Print data is generated by a suitable source 2 and transmitted to a receiving means 4. The print data coming from source 2 is a series of digital lines of data which may be representative of an analog waveform. Each line of data comprises individual datum points located in individual datum positions. The number of datum positions in each line corresponds to the number of stylii in the thermal print head or array. For example, if the print head has 51 2 stylii, there will be 512 datum positions in each line of data received. If a digital HIGH or a logic state 1 is present in a particular datum position, that will be interpreted as data existing in that position. The line of data received is passed by passing means 6 to a current drive circuit 8.The current drive circuit 8 powers each individual stylus within the thermal array 10. For example, if data exist in datum positions 21 through 50 and 1 76 through 200 and are passed by passing means 6, the current drive circuit 8 will power stylii 21 through 50 and 1 76 through 200. A clocking means 1 2 is operatively connected to the passing means 6 in order to synchronize and position the line of data passing to the individual stylus to be driven. If there are 512 stylii in the print head, there will be 512 clock pulses per line of data; each clock pulse corresponding to a separate stylus to be driven.

The line of data passed by passing means 6 is also stored in storing means 14. The next line of data is then received by receiving means 4. As each individual datum position is received by receiving means 4, the storing means 1 4 passes its stored data to blocking means 1 8 such that the datum positions being received by the receiving means 4 correspond to the datum positions being passed to blocking means 1 8 by storing means 1 4. The blocking means 1 8 will prevent the passing of data for all positions for which data exist in the corresponding stored line of data. In the previous example, the first line of data had data in datum positions 21 through 50 and 1 76 through 200.If the next line of data has data in datum positions 1 6 through 25 and 1 90 through 250, the blocking means 1 8 prevents passing of data from positions 201 through 25 and 190 through 200. The storing means 14 then stores the passing of data for datum positions 16 through 20 and 201 through 250 and the same stylii positions are powered by the current drive circuit 8. The result is to prevent the passing of data from occurring in the same datum positions in two successive lines of data received. As will be discussed infra, this has no adverse effect on the resultant print out but can yield a reduction of power output up to a maximum of 50%. An effective reduction of power supplied to the thermal array stylii means a reduction in heat build up and the prevention of a possible stylii burn out.

Fig. 2 is a block diagram showing another embodiment of the apparatus according to the present invention. A comparing means 1 6 is provided and is operatively connected to receiving means 4 and storing means 1 4. Comparing means 1 6 is then operatively connected to blocking means 1 8. Each datum position in the new line of data received is compared to the corresponding datum position in the line of data stored in storing means 14 by use of the comparing means 1 6.If the comparing means 1 6 determines that data exist in corresponding datum positions, comparing means 1 6 sends a signal to blocking means 1 8 such that blocking means 1 8 will block data for the corresponding position or positions from passing through passing means 6.

Fig. 3 illustrates a specific embodiment of the invention according to the embodiment shown in Fig. 1. The print data from source 2 is a series of lines of data comprising individual datum positions as described above. The line of data is received by AND gate 20 through one of its inputs 22. The line of data passes from the output 24 of AND gate 20 to the input 26 of FLIP-FLOP 28. Clocking means 1 2 is connected to the clock input 30 of FLIP-FLOP 28. The FLIP-FLOP 28 positions and synchronizes the line of data received to the stylii to be driven. The output 32 of FLIP FLOP 28 is connected to the drive circuit 8.

The drive circuit 8 is connected to the thermal array 10 and provides the power to each individual stylus in the stylii. The stylii are driven in accordance with the same mode of operation as described above. The output 31 of FLIP-FLOP 28 is connected to input 34 of shift register 36. The clocking means 1 2 is connected also to the clock input 38 of shift register 36. The shift register 36 is of the type selected to correspond to the number of datum positions within a line of data. As in the previous examples, if a line of data has 512 positions, shift register 36 will have 512 positions. The effect of shift register 36, as will be apparent to those skilled in the art, is to invert and delay the line of data passed by one line of data. Thus, the first datum position clocked through the output 40 of shift register 36 will be synchronized with and correspond to the first datum position of the next line of data received.

Output 40 of shift register 36 is connected to input 50 of AND gate 20. It will be apparent to those skilled in the art that AND gate 20 acts as a blocking means to allow incoming data to be passed only when data does not exist in the corresponding datum position in the stored line of data. AND gate 20 also acts as a receiving means. The effect of this circuit embodiment is to prevent the passing of data to the driving means if data exist in corresponding datum positions within two successive lines of data received. Moreover, if a particular stylus is powered in one line of data, it will not be powered in the next line of data even if data exist in that position.

Fig. 4 illustrates another specific embodiment of the invention. The general mode of operation of this circuit is the same as that of the generalized embodiment shown in Fig. 2.

An EXCLUSIVE-OR gate 42 is provided as a comparing means. The output of shift register 36 is connected to input 44 of EXCLUSIVE OR gate 42. The incoming print data from source 2 is connected to the other input 46 of EXCLUSIVE-OR gate 42. This means that the input 46 of EXCLUSIVE-OR gate 42 is connected to input 22 of AND gate 20. The output 48 of EXCLUSIVE-OR gate 42 is connected to the other input 50 of AND gate 20.

Fig. 5 shows the truth table for the operation of the EXCLUSIVE-OR gate 42 in conjunction with AND gate 20. There are two inputs in the truth table. The first input is designated as 22/46 which represents input 22 of AND gate 20 and input 46 of EXCLU SIVE-OR gate 42. The second input is designated 44 which is the second input of EXCLU SIVE-OR gate 42. The column designated 50/48 in the truth table of Fig. 5 represents output 48 of EXCLUSIVE-OR gate 42 which is also the input 50 of AND gate 20. It can be seen from this truth table that a logic state 1 will occur at the output 24 of AND gate 20 when there is a logic state 1 at 22/46 and a logic state 0 at 44.It will, therefore, be apparent to those skilled in the art that AND gate 20 acts as a blocking means to allow the incoming data to be passed only when data exist in a datum position of the new line of data received and there was no data in the corresponding datum position of the previous line of data.

The circuits of Figs. 3 and 4 are not limited to construction with discrete or individual components. These protection circuits may be formed into hybrid integrated circuits which may, in turn, lead to a reduction in the number of components.

An individual stylus can use one watt of power to generate a sufficient amount of Joule heat to make a mark on thermally sensitive paper. If there are 512 stylii in an array and a line of incoming data has data in all 512 positions, the stylii would use 512 watts of power. If every successive line also contains datum in all positions, this invention would yield an effective reduced power output of 50% since only every other line of data after the first line of data would be printed.

Fig. 6 shows a print out pattern generated by the present invention for a thermal array containing 1 6 stylii. An "x" represents datum received within a line of data and the represents the mark that would be made on the thermally sensitive paper by the stylii.

Fig. 7 shows the digital waveform pattern for a line of data received by the circuits shown in Figs. 3 and 4. Lines of data received are lines 5 and 6 of Fig. 6, line 5 being the previous line of data received and line 6 being the new line of data received. The output data passed to the drive circuit 8 is shown in Fig.

7 and the print pattern is shown in Fig. 6, line 6.

Fig. 6 is only a diagrammatical representation of what the typical print out would look like in actual practice of this invention. A typical thermal linear array may contain 512 stylii at a spacing of 100 stylii per inch. New lines of data can typically be receives at a rate of 200 lines per second. An individual energized stylus will make a mark on a thermal sensitive paper approximately 0.25 mm in diameter, assuming a stylus of approximately that size. A maximum paper speed in a thermal recording device in an orthogonal direction from the linear array can typically be 50 mm per second. Fig. 8 shows a dot pattern produced by one stylus pulsed at a rate of 200 hertz with the paper moving at 50 mm per second. It can be seen that there is an overlapping of data for successive positions.

At even moderate paper speed, there can be an overlapping of data by as much as eightfold or more, i.e. there can be as many as eight or more pieces of data printed at least partially on top of each other. Thus, it will be apparent to those skilled in the art that there will be no loss of resolution and no appreciable effect in the print out by the use of the present invention. But, it will also be apparent that there will be a reduction in the heat produced by the thermal array when the stylii are pulsed at a high repetition rate.

Fig. 9 is a block diagram showing a third, more complex embodiment of the apparatus according to the present invention. As in the previously described embodiments print data is generated by a suitable source 2 and is transmitted to a receiving means 4. The print data coming from source 2 is a series of digital lines of data which may be representative of an analog waveform. Each line of data comprises individual datum points located in individual datum positions. The number of datum positions in each line corresponds to the number of stylii in the thermal array. For example, if the thermal array has 512 stylii, there will be 512 datum positions in each line of data received. If a digital HIGH or a 1 is present in a particular datum position, this will be interpreted as data existing in that position.

The embodiment of Fig. 9 differs from the previous embodiments in that the line of data received is passed by a first passing means 6 to a second passing means which, as explained hereafter, determines the passing of data to a current drive circuit 10 which powers the individual stylii within the thermal array 1 2. For example, if data exist in datum positions 21 through 50 and 176 through 200 and is passed by first passing means 6 and second passing means 8, the drive circuit 10 will power the stylii 21 through 50 and 1 76 through 200 in thermal array 1 2. A clocking means 14 is operatively connected to the passing means 6 in order to synchronize and position the line of data passing to the individual stylus to be driven.If there are 51 2 stylii in thermal array 12, there will be 512 clock pulses from clocking means 14 per line of data received; each clock pulse corresponding to a separate stylus to be driven.

The line of data passed by passing means 6 is also stored in first storing means 1 6. A next line of data is then received by receiving means 4. Each datum position in this next line of data received is compared to the corresponding datum positions in the passed line of data stored in first storing means 16. This comparison is done in first comparing means 1 8. If the comparing means 1 8 determines that data exist in corresponding datum positions, a first blocking means 20 is provided to block the passing through the first passing means 6 of data for those positions containing corresponding data in this next line of data. In the prior example, the first line of data had data in positions 21 through 50 and 176 through 200.If the next line of data has data in positions 1 6 through 25 and 1 90 through 250, the first blocking means 20 will prevent the passing of data for positions 21 through 25 and 1 90 through 200. The first storing means 1 6 will then be updated to store the datum for positions 16 through 20 and 201 through 250. This will be the data passed to second passing means 8. The effect of first storing means 1 6 is to delay the line of data passed by first passing means 6 by one line of data, i.e., 512 clock pulses.

A second comparing means 22 is provided which is operatively connected to both the receiving means 4 and first storing means 1 6.

Second comparing means 22 compares the corresponding datum positions between the line of data in first storing means 1 6 and the next line of data received by receiving means 4. The second comparing means 22 will generate a digital signal, typically a digital HIGH when data is detected in corresponding datum positions. This signal generated by second comparing means 22 is stored in second storing means 24.

A word enable means 26 is provided that preferably generates a digital HIGH signal for a duration equal to a line of data received. For example, if a line of data is 51 2 clock pulses long, the word enable means 26 would preferably generate a digital HIGH signal for a time equivalent to 51 2 clock pulses.

A first division means 28 is operatively connected to word enable means 26 to divide the frequency of the word enable output by four. A second division means 30 is operatively connected to the clocking means 14 to divide the clocking frequency by two. A coincidence means 32 is operatively connected to both the first division means 28 and the second division means 30 to produce an EXCLUSIVE-OR output signal of the two divided frequencies. An enabling means 34 is operatively connected to coincidence means 32 and second storing means 24 to provide an enabling signal when the coincidence means 32 produces a signal or when the second storing means 24 has datum in the line of data position presently being clocked by the clocking means 14.Second blocking means 36 is operatively connected to enabling means 34 and to second passing means 8 to block the passing of datum from first passing means 6 to the current drive circuit 10 for those positions which the enablingmeans 34 produced a signal. The result of this invention is to reduce the effective power output and thus reduce the heat generated by the thermal array by as much as 75%. As will be discussed infra, this has no adverse effect on the resultant print out on the thermal sensitive media caused by using this apparatus.

Fig. 10 illustrates a specific embodiment of the invention. The general mode of operation of this circuit is the same as that of the generic embodiment shown in Fig. 9. The print data from source 2 is a series of lines of data comprising individual datum positions as described above. The line of data is received by AND gate 38 through one of its inputs 40.

The line of data passes from the output 42 of AND gate 38 to the input 44 of FLIP-FLOP 46. Clock means 14 is connected to the clock input 48 of FLIP-FLOP 46. The FLIP-FLOP 46 positions and synchronizes the line of data received to the stylii to be driven. The output 50, of FLIP-FLOP 46 is connected to one of the inputs 52 of AND gate 54 and is also connected to input 56 of shift register 58.

Clocking means 1 4 is also connected to the clock input 60 of shift register 58. The shift register 58 is of a type selected to correspond to the number of datum positions within a line of data. As in the previous examples, if a line of data has 51 2 datum positions, shift register 58 will have 51 2 positions. The effect of shift register 58, as will be apparent to those skilled in the art, is to delay the line of data passed by one line of data. Thus, the first datum position passed by the output 62 of shift register 58 will be synchronized with and correspond to the first datum positions of the next line of data received. An EXCLUSIVE-OR gate 64 is provided as a comparing means.

The output 62 of shift register 58 is connected to the input 66 of EXCLUSIVE-OR gate 64. The incoming print data from source 2 is connected to the other input 68 of EXCLU SIVE-OR gate 64. This means that the input 68 of EXCLUSIVE-OR gate 64 is connected to the input 40 of AND gate 38. The output 70 of EXCLUSIVE-OR gate 64 is connected to the other input 72 of AND gate 38. It will be apparent to those skilled in the art that AND gate 38 acts as a first blocking means to allow incoming data to be passed only when data exist in a datum position of the new line of data received and there was no data in the corresponding datum positions of the previously passed line of data. AND gate 38 in comination with FLIP-FLOP 46 acts as the first blocking means and the first passing means.

AND gate 38 also acts as the receiving means. Output 62 of shift register 58 is connected to input 74 of AND gate 76. The other input 78 of AND gate 76 is connected to the print data source 2. Output 80 of AND gate 76 is connected to input 82 of shift register 84. Clocking means 1 4 is connected to clock input 86 of shift register 84. AND gate 76 acts as a second comparing means to compare the data being clocked out of shift register 58 to the next line of data received from print data source 2. AND gate 76 will produce the digital HIGH out of output 80 whenever data is detected in corresponding positions for the next line of data received and the line of data stored in shift register 58.

Shift register 84 acts as a second storing means to store the signals produced by AND gate 76. Output 88 of shift register 84 is connected to the input 90 of INVERTER 92.

The output 94 of INVERTER 92 is connected to the input 96 of OR gate 98. The output 100 of OR gate 98 is connected to input 102 of AND gate 54.

Word enable means 26 is connected to the input 104 of FLIP-FLOP 106. The output 108 of FLIP-FLOP 106 is connected to the input 110 of FLIP-FLOP 112. The output 114 of FLIP-FLOP 112 is connected to input 11 6 of EXCLUSIVE-OR gate 118.

An individual stylus can use one watt of power to generate a sufficient amount of Joule heat to make a mark on thermal sensitive paper. If there are 512 stylii in an array and a line of incoming data has data in all 512 positions, the stylii would use 512 watts of power. If every successive line also contains data in all positions, this embodiment of the invention would yield an effective reduced power output of 75%.

Fig. 1 2 shows a print out pattern generated by the Fig. 9 embodiment for a thermal array containing 1 6 stylii. An "x" represents data received within a line of data and the represents the mark that would be made on the thermal sensitive paper by the stylii using the present invention. Fig. 1 2 is only a diagrammatic representation of what the typical print out would look like in actual practice of this embodiment of the invention.

Fig. 1 3 illustrates another embodiment of this invention. The embodiment illustrated in Fig. 1 3 is more particularly useful for displaying graphical data. Since character generation requires a high degree of resolution, a modifi- - cation has been made to the Fig. 10 embodiment. Referring now to Fig. 13, the portion of the circuit designated B is essentially the same circuit as shown and described with reference to Fig. 10. Print data A generated by an appropriate source 2A is graphic data, i.e. sine waves, square waves, etc. Print data B generated by an appropriate source 2B is character data. The portion of the circuit designated A' operates identically as described above for the portion of the circuit designated A and the embodiment of Fig. 4 described earlier.Output 1 32 of AND gate 54 is connected to input 1 38 of OR gate 1 36. Print data B from an appropriate source 2B is connected to input 1 34 of OR gate 1 36.

Output 140 of OR gate 136 is connected to the input of the circuit A'. The output of circuit A' is connected to current drive circuit 10 which is connected to thermal array 1 2.

Clock 14 is also connected to circuit A' but because of inherent timing delays in digital circuitry, may be required to pass through a delay means or skewing means, not shown, prior to the connection with circuit A'. The result of this modification is to allow graphic data to be printed out in the manner described above and to allow character data to be printed out for all datum positions that were not printed in the prior line of data. This gives the needed higher resolution for character data. The effective power reductions are 75% for graphic data and 50% for character data printed.

This invention has been described with reference to preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding of this specification. The intention is to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

The circuits hereinbefore described are not limited to construction with discrete or individual components, but can be constructed as hybrid integrated circuits leading to a reduction in the number of components.

Claims

1. A method of display imaging in which, in each of a series of addressing operations, a plurality of display component imagers are selectively addressed in accordance with display data so as each to generate an image component according to whether or not data exists in a datum location of said display data corresponding to the respective imager, and wherein an incoming line of data adapted for addressing the imagers is logically processed, in a predetermined manner, with data representative of the addressing of the imagers during one or more previous operations of the series in order to derive a depleted data line wherein data in some of the datum locations of the data line are selected to be redundant for generating an acceptable display image corresponding to the display data, the said depleted data line being used for addressing the plurality of display component imagers.

2. A method of thermal display imaging by selectively addressing a plurality of heat generating display elements each adapted when addressed to make a mark upon a thermally sensitive display medium, and wherein the display elements are addressed successively in accordance with successive data packets each comprising a plurality of datum locations corresponding to respective ones of the display elements, the method comprising logically processing the data content of an incoming data packet with stored data representative of previous addressings of the plurality of display elements in accordance with a predetermined algorithm so as to derive a depleted data packet for addressing the display elements wherein selected datum locations, designated in the incoming data packet for energizing the corresponding display element, are inhibited.

3. A method of thermal display imaging by use of an apparatus having a linear array of heat-generating resistive elements adapted when energized to place marks on thermal sensitive recording media during printing operations, said method comprising the steps of: a) receiving an incoming digital first line of data from an appropriate source, said first line of data comprising a plurality of individual datum; b) passing said received digital first line of data to a driving means for current driving thermal array stylii; c) clocking the passing first line of data to position and synchronize the individual datum within said first line of data to the individual stylus to be driven; d) storing said passing first line of data; e) receiving an incoming digital second line of data from said appropriate source, said second line of data comprising a plurality of individual datum; and f) blocking the passing to said driven means of the individual datum within the second line of data for those positions in which data exists in corresponding positions of the stored first line of data.

4. The method claimed in Claim 3 further comprising the steps of: g) passing the datum not blocked from said second line of data to said driving means; h) clocking the passing of the unblocked datum of said second line of data to position and synchronize said unblocked datum of said second line of data to the individual stylus to be driven; i) storing said unblocked datum of said second line of data; j) receiving an incoming digital next line of data from said appropriate source, said next line of data comprising a plurality of individual datum; and k) blocking the passing to said driving means of the individual datum within said next line of data for those positions in which data exist in corresponding positions of the stored unblocked datum of said second line of data.

5. The method claims in Claim 4 wherein the steps of passing, clocking, storing, receiving and blocking are repeated for each new line of data received.

6. A method as claimed in Claim 3 or 4 or 5 wherein the blocking step (f) is effected by comparing each datum position within the stored first line of data to the second line of data to determine if datum exists in corresponding positions, and blocking the passing to said driver means of the individual datum within the second line of data if datum exists in the corresponding positions of the previous line of data passed as determined in the comparing step.

7. A display apparatus comprising:- a plurality of display component imagers each energizable for generating a display component; means for addressing said display component imagers for selectively energizing the same in accordance with data packets including a plurality of datum locations corresponding to respective ones of said display component imagers; means for receiving incoming data packets assembled for addressing said plurality of display component imagers; means for assembling data pertaining to a historical record of the energization of the display component imagers in consequence of the receipt of one or more previous data packets; and logic means for processing an incoming data packet with said historical data according to a predetermined algorithm so as to obtain a depleted data packet for application to said addressing means for selectively energizing the display component imagers according to the data in the depeleted data packet, the depleted data packet having certain datum locations thereof, selected in accordance with said algorithm and said historical data, inhibited from energizing a display component imager.

8. A thermal array protection apparatus for use in thermal imaging apparatuses of the type in which a linear array of heat-generating resistive elements is used to place marks on thermal sensitive recording media during printing operations, said protection apparatus comprising: receiving means to receive an incoming digital line of data from an appropriate source, said line of data comprising a plurality of individual datum; passing means operatively connected to said receiving means to pass the digital line of data received to a driving mans for current driving the thermal array stylii; clocking means operatively connected to said passing means to position and synchronize the individual datum within said digital line of data received to the individual stylus to be driven;; storing means operatively connected to the output of said passing means for storing the datum passed through said passing means; and blocking means operatively connected to said storing means and said passing means to block the passing of the individual datum from said next line of data received for those positions which said storing means has stored datum.

9. Apparatus as claimed in Claim 8 wherein a comparing means is operatively connected to the receiving means and the storing means to compare the datum positions of the stored data in said storing means to the datum positions of the next line of data received by said receiving means and determine when datum exists in corresponding positions, and said blocking means is operatively connected to said comparing means and said passing means to block the passing of the individual datum from said next line of data received for those positions which said comparing means determined the existence of corresponding datum.

10. Apparatus as claimed in Claim 8 or 9 wherein said storing means is updated each time datum is passed by said passing means.

11. A thermal array protection apparatus for use in thermal imaging apparatuses of the type in which a linear array of heat-generating resistive elements is used to place marks on thermal sensitive recording media during imaging operations, said apparatus comprising: receiving means to receive an incoming digital line of data comprising a plurality of individual datum positions; first passing means operatively connected to said receiving means to pass the digital line of data received; clocking means operatively connected to said first passing means to position and synchronize the individual data within said digital line of data received to the individual stylus to be driven; first storing means operatively connected to said first passing means and said clocking means to store the data passed through said first passing means;; first comparing means operatively connected to said receiving means and said first storing means to compare the datum positions of the stored data in said first storing means to the datum positions of the next line of data received by said receiving means and determine when data exists in corresponding positions; first blocking means operative connected to said first comparing means to block the passing by said first passing means of the individual data from said next line of data received for those positions which said first comparing means determined the existence of said corresponding data; second passing means operatively connected to said first passing means to pass the digital line of data passed by said first passing means to a driving means for current driving the thermal array stylii;; second comparing means operatively connected to said first storing means and said receiving means to compare the datum position in said first storing means to the datum positions of another line of data received by said receiving means and determine when data exist in corresponding positions; second storing means operatively connected to said second comparing means and said clocking means to store data for those positions which said second comparing means determined the existence of corresponding data; word enable means to generate digital HIGH signal of a duration corresponding to the length of a digital line of data received; first division means operatively connected to said word enable means to divide the word enable means frequency by four; second division means operatively connected to said clocking means to divide the clock frequency by two;; coincidence means operatively connected to both first and second division means to produce an EXCLUSIVE-OR signal of the two divided frequencies; enabling means operatively connected to said second storing means and said coincidence means to provide an enabling signal when the coincidence signal produces a signal or when the second storing means has data in the position presently being clocked by said clocking means; and second blocking means operatively connected to said enabling means and second second passing means to block the passing by said second passing means of the individual data from the following lines of data received for those positions which said enabling means produces a signal.

1 2. The thermal array protection apparatus of Claim 11 wherein said first and second storing means are updated each time a a new line of data is received by said receiv- ing means.

1 3. A thermal array protection apparatus for use in thermal imaging apparatuses of the type in which a linear array of heat-generating resistive elements is used to place marks on thermal sensitive recording media during imaging operations, said apparatus comprising:: first receiving means to receive an incoming digital line of graphic data, said line of graphic data comprising a plurality of individual datum; first passing means operatively connected to said first receiving means to pass the digital line of graphic data received; clocking means operatively connected to said first passing means to position and synchronize the individual datum within said digital line of graphic data received to the individual stylus to be driven; first storing means operatively connected to said first passing means and said clocking means to store the data passed through said first passing means;; first comparing means operatively connected to said first receiving means and said first storing means to compare the datum positions of the stored data in said first storing means to the datum positions of the next line of graphic data received by said first receiving means and determine when data exist in corresponding positions; first blocking means operatively connected to said first comparing means to block the passing by said first passing means of the individual data from said next line of graphic data received for those positions which said first comparing means determined the existence of said corresponding data; second passing means operatively connected to said first passing means to pass the digital line of graphic data passed by said first passing means to a driving means for current driving the thermal array stylii;; second comparing means operatively connected to said first storing means and said first receiving means to compare the datum position in said first storing means to the datum positions of another line of graphic data received by said first receiving means and determine when data exist in corresponding positions; second storing means operatively connected to said second comparing means and said clocking means to store data for those positions which said second comparing means determined the existence of corresponding data; word enable means to generate a digital signal of a duration corresponding to the length of a digital line of graphic data received; first dividion means operatively connected to said word enable means to divide the word enable means frequency by four; second division means operatively connected to said clocking means to divide the clock frequency by two;; coincidence means operatively connected to both first and second division means to produce an EXCLUSIVE-OR signal of the two divided frequencies; enabling means operatively connected to said second storing means and aid coincidence means to provide an enabling signal when the coincidence signal produces a signal or when the second storing means has data in the position presently being clocked by said clocking means; second blocking means operatively connected to said enabling means and said second passing means to block the passing by said second passing means of the individual data from the following lines of graphic data received for those positions which said enabling means produces a signal; second receiving means to receive an incoming digital line of character data, said line of character data comprising a plurality of individual data;; third passing means operatively connected to said second receiving means to pass the digital line of character data received to said driving means for current driving the thermal array stylii wherein said clocking means is operatively connected to said third passing means to position and synchronize the individual data within said line of character data received in the individual stylus to be driven; third storing means operatively connected to said third passing means and said clocking means to store the data passed through said third passing means; third comparing means operatively connected to said second receiving means and said third storing means to compare datum positions of the stored data in said third storing means to the datum positions of the next line of character data received by said second receiving means and determine when data exist in corresponding positions; and third blocking means operatively connected to said third comparing means to block the passing by said third passing means of the individual data from said next line of character data received for those positions which said third comparing means determined the existence of said corresponding data.

1 4. The thermal array protection apparatus of Claim 1 3 wherein said first and second storing means are updated each time a new line of graphic data is received by said first receiving means and said third storing means is updated each time a new line of character data is received by said second receiving means.

1 5. A thermal array protection apparatus substantially as herein described with referpence to any of Figs. 1 to 4, 9, 10 and 13 of the accompanying drawings.

16. Information processing and display methods substantially as hereinbefore described with reference to any of the accompanying drawings.