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MXPA96005850A - Detecting the temperature of a head depression in a printer by jeting it - Google Patents

Detecting the temperature of a head depression in a printer by jeting it

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Publication number
MXPA96005850A
MXPA96005850A MXPA/A/1996/005850A MX9605850A MXPA96005850A MX PA96005850 A MXPA96005850 A MX PA96005850A MX 9605850 A MX9605850 A MX 9605850A MX PA96005850 A MXPA96005850 A MX PA96005850A
Authority
MX
Mexico
Prior art keywords
print head
temperature
signals
oscillator
printer
Prior art date
Application number
MXPA/A/1996/005850A
Other languages
Spanish (es)
Other versions
MX9605850A (en
Inventor
J Becerra Juan
A Tellier Thomas
R Morton Christopher
Original Assignee
Xerox Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/570,024 external-priority patent/US5745130A/en
Application filed by Xerox Corporation filed Critical Xerox Corporation
Publication of MXPA96005850A publication Critical patent/MXPA96005850A/en
Publication of MX9605850A publication Critical patent/MX9605850A/en

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Abstract

The present invention relates to a thermal inkjet printer, characterized in that it comprises: a print head having a plurality of ink droplet ejectors, each ejector having a heater resistor activated in response to electrical signals selectively applied from a source of input signal, a controlled temperature oscillator formed on the print head, a controller to control the operations of the print head and to apply as an activation signal to the oscillator which causes the oscillator to produce binary output pulses whose frequency varies with the temperature variations of the print head, a counter for counting the output pulse signals during a predetermined period of time defined by the start and stop signals from the controller applied through a synchronization circuit on the which synchronizes the writing or typing operation, means for converting an account at the end of the predetermined time period into a digital multi-bit signal representative of the temperature of the print head, and a first means that responds to the multiple-bit signals for adjusting the electrical signals applied to the heater recorder so that it measures the size of the ink droplets and the volume changes caused by variations in temperature

Description

DETECTING THE TEMPERATURE OF A PRINTING HEAD IN A PRINTER BY INK CHIP BACKGROUND AND EXPOSURE OF THE RELEVANT DESCRIPTION The present invention relates to an ink jet printer and, more particularly, to a system and method for detecting the operating temperature of a print head and representing the temperature by means of a digital signal generated within the circuits of detection. Ink jet printers eject the ink on a printing medium such as a paper in. controlled configurations of closely spaced points. To form color images, multiple ink jet print heads are used, with each head being supplied or supplied with ink of a different color from an associated ink container. Thermal ink jet printing systems use thermal energy produced selectively by resistors located in channels or ink filled chambers near the nozzles of the channel termination. The on or off signals are applied to the resistors through the associated impulse or excitation circuits to momentarily vaporize the ink and form bubbles when requested. Each temporary bur-ejects a droplet of ink and propels it towards a recording medium. The printing system can be REF: 23161 incorporated in either a cart type printer or a page width type printer. A car-type printer, such as the one described, for example, in U.S. Pat. Nos. 4,571,599 and Re. 32,572, generally includes a relatively small printhead containing ink channels and nozzles. The contents of these patents are incorporated herein for reference. The print head is usually fixed in a sealing manner to an ink supply container and the combined print head and container form a cartridge assembly which is reciprocated to print a row or row of information at a time on a recording medium maintained stationary, such as paper. After the row or row is printed, the paper is graded or staggered at a distance equal to the height of the printed row or row, so that the next printed row or row will be contiguous with it. The procedure is repeated until the entire page is printed. The printer on the width page has a stationary print head that has a length equal to or greater than the width of the paper. The paper is moved continuously once the print head of the width of the page has been passed in a direction normal to the length of the print head at a constant speed during the printing process.
An example of a page width printer is found in U.S. Pat. No. 5,221,397, the content of which is incorporated herein for reference. A known problem with thermal ink jet printers is the degradation in the output print quality due to the increased volume of ink ejected from the nozzles of the print head, which results from fluctuations in the temperatures of the print head. print head. These temperatures produce variations in the size of the ejected droplets which lead to degraded print quality. The size of the drops ejected varies with the temperature of the print head because the two properties that control the size of the droplets vary with the temperature of the print head: the viscosity of the ink and the amount of the ink vaporized by an activation or ignition resistor when driven or excited by a printing pulse. Temperature fluctuations of the print head commonly occur during the printer startup, during changes in the ambient temperature, and when the output of the printer varies. When the text is printed in black and white, the dark of the print varies with the temperature of the print head because the darkening depends on the size of the drops ejected. When printing grayscale images, the contrast of the image also varies with the temperature of the print head because the contrast depends on the size of the droplets ejected. When printing color images, the printed color varies with the temperature of the. print head because the printed color depends on the size of all the primary color droplets that create the printed color. If the temperature of the print head varies from one primary color nozzle to another, the size of the droplets ejected from a primary color nozzle will differ from the size of the droplets ejected from another primary color nozzle. The resulting printed color will differ from the proposed color. When all of the nozzles of the print head have the same temperature, but the temperature of the print head increases or decreases when the page is printed, the colors at the top of the page will differ from the colors in the part bottom of the page. To print text, graphics, or images at the highest quality, the temperature of the print head must remain constant. Various systems and methods for controlling the temperature of the print head in the prior art are already known to detect the temperature of the print head and use the detected temperature signals to compensate for fluctuations or increases in temperature. The U.S. Patent No. 4,910,528 discloses an analog temperature detection system wherein a resistor of the thin film temperature is co-deposited on a substrate with the resistors which are heated to eject the droplets of ink from the nozzles of the print head . The outputs of the voltage reduction or drop across the temperature resistor are sent to a temperature prediction circuit which controls the strategy of the print to maintain the temperature of the print head within a predetermined operating range . The U.S. Patent No. 5,075,690 discloses an analog temperature sensor for an ink jet printhead which achieves a more accurate response by the formation of the thermistor on the substrate of the printed head and the same polysilicon material as the resistors which are heated to eject the droplets from the nozzles of the print head. The U.S. Patent No. 5,220,345 discloses a temperature control system of the print head which places a plurality of temperature sensors in different positions and verifies temperature differences to control the ink supplied to the associated ink channels.
The U.S. Patent No. 5,315,316 discloses a temperature control circuit of the print head which includes a temperature sensor formed on the substrate of the print head. The analog signals of the sensor are delayed and analyzed by a data processor. A summing operation of the temperature is performed during a printing operation, the sum is compared with a previously stored value to determine whether the ink flow through the print head is sufficient for continuous printing. The U.S. Patent No. 5,172,142 detects changes in a temperature sensor to change the excitation or impulse frequency of the print head. The analog signals of the sensor are converted into digital signals which are sent to a controller of the sequence that controls the operation of an actuator of the drive motor. The U.S. Patent No. 5,168,284 describes a closed circuit system which produces non-printing pulses in response to a difference between a reference temperature signal and the temperature signals of the print head produced by a temperature sensor located on the head of impression. The U.S. Patent No. 5,223,853 to Wysocki et al., Discloses a method for controlling dot sizes printed by a thermal ink jet printer. The temperature of the ink in the print head is detected and a combination of the power level and time duration of the electrical input signal to the heating elements is selected by entering the detected temperature of the ink in a predetermined function which relates the energy of the input signal to the corresponding resulting size of the point on the sheet for copying. These prior art descriptions that form the temperature sensor on the print head typically require circuit and high-voltage switches and are prone to erroneous temperature correction feedback signals because of the signal-to-noise ratio low. If the temperature detection signals are generated during a row or row of printing, the excessive noise affects the ratio. In some applications, the print carriage is stopped at the end of a row or row to generate the analog output temperature signals, to avoid the noise generated during scanning or scanning. A system such as this, however, leads to diminished performance or production. In addition, the conversion of the temperature signal from an analog output to a digital one requires extra logic circuits that will be located in the printer. In addition, the initial calibration requires additional electrical components such as compensation resistors.
BRIEF DESCRIPTION OF THE INVENTION Therefore, it is an object of the invention to provide a system for detecting the temperature of the head, of printing which has a high immunity against noise. It is an additional object to provide the detector circuits of the print head, which generate digital signals representative of the temperature of the print head. It is still an additional object to form circuits to generate digital signals representative of the temperature of the print head on a single microcircuit located on the print head. These and other objects are made by providing circuits and enabling or making possible programming elements capable of directly producing a digital signal representative of the real-time temperature of the print head as measured during a row or row of printing and feeding this signal back to the circuits that control the electrical input signals to the print head. In a described embodiment, a print head is conventionally mounted on a carriage of printing adapted to record images during a row or row of printing. An oscillator controlled by means of temperature is formed on the printhead. The oscillator is triggered or put into operation and generates digital output signals that have a frequency which varies in proportion to the temperature of the print head. These digital output signals from the oscillator are synchronized in a counter. The counter accumulates the number of pulses that occur or occur over a predetermined sampling period. The value of the counter, which is a direct binary representation of the temperature of the printhead, is sampled at the end of the time period. A digital signal, representing the temperature of the print head, is fed back to a controller of the system where it is converted into an adjusted electrical signal which is applied to the impulse or drive circuits of the print head. The adjusted signal adjusts the pulse width and / or the power of the drive signals for the resistors of the print head heater, to maintain the required spot diameter of the droplets ejected to the recording medium. The correction for an increased temperature in general is the shortening of the width of the pulse to reduce the diameter and consequently the volume of the ink spots or spots ejected. In a typical application, when the printing operation advances, the temperature of the print head rises, causing the size of the ejected ink point to increase. Computer signals are generated to reduce the pulse width of the activation or drive signal, to reduce the size of the point. In a preferred embodiment, an operation of the oscillator is enabled by the application of a relatively large trigger signal (3v-5v) instead of the conventional 10 mv-100 mv signal of the prior art. The noise is considerably reduced on analogue schemes. The result is a higher signal-to-noise ratio and an immunity against relative noise. In addition, pulse counting acts as a noise filter which reduces measurement error due to noise commutation. More particularly, the present invention relates to a thermal ink jet printer, comprising: a print head for ejecting droplets of ink in response to selectively applied electrical input signals, means for detecting the temperature of the ink head, printing, the detection means include: circuits for generating binary output pulse signals whose frequency varies with variations in the temperature of the print head, a counter for counting the signals of the output pulse over a predetermined period of time and means to convert the contact at the end of the predetermined period into a digital, multi-bit signal, representative of the temperature of the print head.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an electrical block diagram showing the circuits for detecting changes in the temperature of the print head, including a counter for counting the output signals from an oscillator controlled by means of temperature. Figure 2 is a timing diagram or synchronization of the temperature sensor signals. Figure 3 is a graph of the clock or period against temperature signals. Figure 4 is a schematic view of a mode of the oscillator controlled by means of temperature, of Figure 1. Figure 5 is an operational flow diagram for the generation of a digital signal proportional to the temperature of the head of the Print. Figure 6 is a partial schematic view of a page width printer. Figure 7 shows a modular portion of the page width printer of Figure 6 with a micro-circuit for controlling the temperature formed on the module. Figure 8 shows an alternative embodiment of Figure 1 where all of the temperature sensing circuits are formed on a single microcirculation on the printhead.
DESCRIPTION OF THE INVENTION Referring now to Figure 1, there is shown a simplified block diagram of a portion of a thermal ink jet printer employing the temperature detection techniques of the invention. The invention can be used in a printer of the type described in U.S. Pat. Nos. 4,980,702 and Re. 32,572, modified in accordance with the principles of the invention as described below. These Patents are incorporated herein for reference. A controller 10 receives data signals from the input image from an image data source such as a computer (not shown). The controller processes the print data in a data conversion circuit to provide print control information to a print head 12. The controller 10 conventionally comprises a CPU, a ROM 14 for storing programs and a RAM. The controller, in addition to performing the temperature detection and correction functions described below, also controls the operation of the print carriage on which the print head 12 is mounted, the movement of the recording medium as well as the timing functions. or system synchronization. The controller 10 sends heater resistor drive pulses and power level signals to the driver circuits or drivers 16 which can be formed on the substrate of the print head 12 as shown or can alternatively be in the controller . The driver circuits or drivers 16 comprise a plurality of driver transistors or drivers for applying the pulse signals to the heaters 18 of the associated resistor. The driver or driver circuits 16 also include a plurality of power transistors for controlling the power level of the drive or drive signals applied to the resistor heaters. It is understood that the excitation and power level signals could be applied directly from the controller 10 by means of flexible electrical cables as is conventional in the art. When a printing operation is started, the scanning or scanning carriage carrying the print head 12 is moved from back to front in a scanning path with the ink being ejected through the print head nozzles. when the heaters of the associated resistor are driven or activated by signals from the driver circuits or activators 16. When the printing operation continues, the temperature of the print head 12 may begin to rise affecting the volume of the ink that is ejected from the nozzles and leading to an increased dot size of the ink ejected on the record sheet. According to a first embodiment of the invention, an oscillator 20 controlled by means of temperature, is located on the substrate of the print head 12 in a location which experiences the temperature variations of the print head. The oscillator 20 is enabled or enabled by a function clear signal (FCLR) from the controller 10 and begins to generate an output pulse train whose frequency is temperature dependent. Referring to Figure 1 and the timing diagram or timing of the signal of Figure 2, the oscillator 20 produces a series of digital, rectangular output pulses during the time that the FCLR is held high. These output pulses, of a relatively high amplitude of 3-5v, are sent to a counter 22. The counter is enabled or enabled by a start signal from a sequencer (state machine) in the controller 10 when applied to through a synchronizing circuit 24. The function of the synchronizing circuit is to synchronize the timing operation and prevent the counter metastabilization. During the start and stop periods shown in Figure 2, the counter 22 accumulates (counts) the number of pulses that occur during the predetermined period initiated by the start signal and are terminated by a stop or stop signal. The contents of the counter 22 are synchronized or taken as clock signals, such as N (T) in a logic control circuit 26 for reading. The digital output of the control / reading circuit is a direct binary representation of the temperature of the print head as shown by the graph in Figure 3. Figure 3 shows a clock period f (T) in nseg plotted against the I count about the temperature. A sampling duration of 153 microseconds was used to collect approximately 260 counts at 25 ° C. As can be seen, a clock period (solid line) increases with temperature, causing the total count (dotted line) to decrease. Continuing with the description of Figure 1, the digital temperature signal, a word or digital byte, representing the temperature of the print head, is sent to ROM 14. ROM 14 is loaded with corresponding look-up tables to the temperature sensitive characteristics for heater 18 by resistance. The processor 10 reads the digital word representative of the temperature of the detected printhead and "observes" the appropriate combination of pulse duration and the power level to be applied to the pulse circuits or drivers 16 to compensate the effects of the change in temperature. Additional details of the loading of ROM 14 are found in U.S. Pat. No. 5,223,853, referred supra. To summarize this first aspect of the invention, the temperature of the print head is detected by enabling an oscillator, whose output frequency is temperature dependent, for a selected period of operation of the printer. The output of the oscillator is a digital pulse train set to a selected, relatively high voltage amplitude, reducing the signal to noise ratio. The oscillator output pulses are counted during a sampling period by a counter. At the end of the sampling period, the value of the counter is converted into a byte representative of the temperature of the print head. The output byte is sent to the query tables in a ROM and is converted into excitation and power signals adjusted to the temperature change; for example, the size of the drop set to reduce the size of the dot on the recording medium to compensate for the rise in temperature. According to a feature of the invention, the detection period can be any time during the printing operation, even during a row or row printing, and is not limited to the generation of temperature control signals only at the end of printing a row or row. Further elaboration of the block diagram of Figure 1 is provided below in conjunction with the descriptions of a form of a temperature controlled oscillator shown as an electrical schematic diagram in Figure 4. Referring to Figure 4, the oscillator 20 comprises two circuit segments, a timer circuit 30, and an inverter circuit 32. The circuit 30 consists of the resistor 34, the capacitor or capacitor 36, the trigger circuit of Schmitt 38 and the Mosfet 40. V,, is the supply voltage of power. The trigger circuit 38 is a fast acting on / off switch, which generates the rectangular pulses shown in Figure 2. The output frequency of the trigger circuit 38 is determined by the RC circuit but is variable in proportion to the voltage a through the resistor 34 whose resistance, in turn, varies with the temperature of the print. The inverter circuit 32 contains the inverters 1-K which grade the signals to a desired output level. The output of the inverter circuits 32 are rectangular pulses at the desired amplitude and are referred to herein or later as a clock signal of the temperature f (T). The period of the clock signal of the temperature f (T) is defined as P = -R0 [1 + (T - To) TCR] C ln (1 - Vsw / V d) +? Tpd + tdML Rn is the resistance in the timer circuit 30 at a reference temperature T ". TCR is the temperature coefficient of the resistance of the resistor 34 = R "[1 + (T - Tn) TCR]. C is the capacitance in the timer circuit, including the value of the capacitor or capacitor 36 and the input capacitance of the Schmitt trigger circuit 38. Vs is the switching threshold of the Schmitt trigger circuit. Vdd is the voltage in the power supply. The sum of the propagation delays, t ,, pd of the K inverters must be added to the oscillation period. The time td "is required for the Mosfet 40 for the unloading node 1. The value of R, C and V is adjusted in such a way that: -Ro [1 + (T-To) TCR] Cln (1-Vsw / Vdd). > > ? tpd + td? - (Eq. l) therefore, p -R0 [1 + (T - T0) TCR] C ln (1 - V5w / Vdd). (Eq. 2) and »3P / 3T - - 0CTCR Ip (1 - Vsw / Vdd). (E c "3 It is important to note that even when T t, + td ", - * - pd MI is negligible with respect to the clock period, this value must be sufficiently large such that the width of the minimum pulse of f (T ) is found for the counter circuit. The temperature-dependent clock frequency, f (T), or a derivative of f (T) is used to excite or activate the counter circuit 22. The nominal frequency will be about 590 ns + _ 3 ns at 25 ° C. The configuration of Figure 4 is only exemplary; modifications consistent with the purposes of the invention can be made. For example, two timer circuits can be used to minimize the effects of noise on the firing point of the pointer, making possible a shorter RC time constant.
OPERATIONAL SEQUENCE Referring to Figures 1-4, and to the flow chart of Figure 5, a counter reset signal is sent from the controller to the counter 22. The counter 22, in a preferred embodiment, is a 9-bit counter plus a bit of overflow. The counter by 9 can therefore register 2 = 512 pulses. The oscillator is enabled by an FCLR signal which has an elevated time of 4.25 microseconds X 34 enabling cycles for a total time of 144.5 microseconds. The clock signal of the temperature f (T) excites the counter 22 during a sampling period defined by the start and stop signals from the sequencer circuits of the controller by means of the synchronizer circuit 24. The synchronizer delay from the Starting until the stop, shown in the timing of the counter of Figure 2, depends on the relative timing in the clock synchronization. A minor error is introduced by the delay from the instant in which the sequencer activates the start / stop sequence until the instant in which the counter actually responds. This introduces some minor errors in the count which are compensated by providing a delay between the stop signal and the counter reading as shown in the timing of the counter of Figure 2. In a measurement, a sensitivity of the The ra of f (T) of 1.9ns / ° C was recorded. The use of the synchronizer circuit 24 induces an error of at least 2 significant bits. In the worst case condition of the junction temperature of 125 ° C, the least significant bit of a 9-bit counter corresponds to 1.61 ° C. At 25 ° C the error improves to 0.53 ° C per bit less significant. This means that a measurement error of 6.44 ° C can be expected at 125 ° C. At 25 ° C, a measurement error of 2.12 ° C can be expected. The measurement error due to fluctuations in the FCLR pulse width may be negligible since the fluctuations are maintained at a lower value than the Period f (T) / 2. At any speed, the 2 least significant bits may be negligible due to the synchronizer error. Thus, the reading / control 26 will assemble a byte of information related to the temperature; 7 bits for the temperature value, and 1 bit indicating the counter overflow. The measurements show that f (T) is insensitive to the variation of the power supply from 4.5 to 5.5V. The digital output of the reading / control 26 is reported to ROM 14 in the controller for conversion into appropriate impulse or excitation signals of the heater. A representation of digital temperature can be reported to other temperature control mechanisms. For example, circuits for providing cooling to the print head or for delaying printing provide gradual cooling of the print head. Further modifications of the modalities described so far are possible consistently with the present invention. For example, although only one oscillator was described in conjunction with the embodiment of Figure 1, two or more oscillators can be formed on the substrate of the print head at strategic locations. The oscillators can be connected in series with the clock signal of the summed output temperature to obtain an averaged f (T). This would lead to even more exact temperature compensation. In particular, for a printer using one or more full-width array printing bars, temperature-controlled, distributed oscillators may be desirable. Figure 6 shows an inkjet printing system of the page width type (full width), which is supplied with ink from an ink tank 70. A black, full-width print head 80 is placed for writing on a recording medium 82 which is indexed and moved in the direction of arrow 84. The print head 80 has been assembled from a plurality of modules 80A which have been spliced together to form an array of 30.48 cm (12") according to the techniques described in US Patent No. 5,221,397, the content of which is incorporated herein by reference.The printhead 80, in this embodiment, provides 7,200 nozzles or dispensers.As described in the ' 397, the print head module 80A, is formed by embedding together an array of channels containing recess arrays that are used as sets of associated ink channels and reservoirs and a plate Heater contact that contains heating elements and steering circuits. The attached contact plates are cut to form the print head leading to the formation of jets, each nozzle or jet associated with a channel with a heater therein. The heater is selectively energized to heat the ink and eject a droplet of ink from the associated dispenser. The ink channels are combined in a common ink manifold 86, mounted on the side of the print head 80 in sealed communication with the ink inlets of the channel arrangements through the aligned openings. The manifold 86 is supplied with the appropriate ink, black for this mode, from an ink cartridge 70 by means of the flexible tubing 88. Because of the length of the print head 80, uneven heating may occur throughout of its length. According to another aspect of the invention, two or more microcircuits 75 for controlling the temperature can be formed on the modules 80A. A module 80A is shown in an enlarged view in Figure 7 with a microcircuit 75 for temperature control, formed on the substrate of the print head. The microcircuit 75 includes an oscillator 90 controlled by means of the temperature, a counter 92 and a synchronizer 94. The inputs to the microcircuit 75 are as described in the embodiments of FIGS. 1 and 6, and the operation sequences as shown in FIG. described above. Each microcircuit 75 will detect temperature changes of the associated module 80A, and the signals compensated by the temperature, observed by the controller, will be applied to the heaters of the resistor for this module. When a line registration operation is performed, each resistor associated with a jet in the print head 80 is selectively energized or activated in accordance with corrected image data signals for temperature variations, so that the ink droplets of the optimum diameter are ejected from the associated jets forming a registration line on the surface of the recording medium 82. Although the embodiments described herein are preferred, it will be appreciated from this teaching that various modifications, variations or alternative improvements can be made in it, by those skilled in the art. For example, the embodiments of the invention shown in Figures 1-5 describe the printhead 12 containing the circuits used to implement the temperature sensing function (the oscillator 20, the counter 22, the read / control 26 and the synchronizer 24) formed on the substrate of the print head. The observation and adjustment of the pulse generation are performed using circuits in the controller 20. Figure 8 shows a print head 12 modified so that all of the functions described above are formed on a single microcircuit, on the head of Print; for example, the microcircuit 90 contains the data conversion 92, the oscillator 20, the counter 12, the synchronizer 24, the reading / control 26 and the ROM 14. The total integration of the function of the detection of the temperature is enabled by consequent.
It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.
Having described the invention as above, property is claimed as contained in the following

Claims (21)

R E I V I N D I C A C I O N S
1. A thermal ink jet printer, characterized in that it comprises: a print head for ejecting droplets of ink in response to selectively applied electrical input signals, means for detecting the temperature of the print head, the detection means include: for generating binary output pulse signals, the frequency of which varies with variations in the temperature of the print head, a counter for counting the output pulse signals over a predetermined period of time and means for converting the count to the end of the predetermined period in a digital multi-bit signal, representative of the temperature of the print head.
2. The printer according to claim 1, characterized in that the print head has a plurality of drop ejectors, each ejector has a heater resistor activated in response to the electrical signals and also includes circuit means for adjusting the electrical signals to compensate for volume changes in the size of the drop caused by the correction of the temperature.
3. The printer according to claim 1, characterized in that the means for detecting the temperature of the print head include at least one oscillator controlled by means of temperature.
4. The printer according to claim 3, characterized in that the oscillator and the counter are formed on a microcircuit located on the print head.
5. The printer according to claim 3, characterized in that it also includes synchronization means for synchronizing the start and stop of the predetermined time period with the operation of the oscillator and the other timing functions of the printer.
6. The printer according to claim 3, characterized in that a plurality of oscillators are formed on the printhead with its outputs connected in series to form averaged input for the counter.
7. A system for detecting the temperature of the print head in an ink jet recording apparatus having a driver or impeller of the printer carriage, a printer carriage moved by the driver of the printer carriage through a row or row of printing and having a thermal ink jet print head mounted on the carriage and a controller for controlling the movement of the carriage and for applying electric excitation or impulse signals to the print head, the detection system is characterized in that it comprises: temperature detection circuits formed on the print head, the circuits include means for generating binary output signals whose frequency varies with variations in the temperature of the print head, an electrical counter connected to the output signals generated by the temperature detection circuits, means to start and stop the For a predetermined period of time, so as to count the binary output signals during the period of time, the accumulated count is a function of the temperature of the print head and logical read / control means to convert the accumulated count in binary signals of multiple bits representative of the temperature of the print head during the counting period.
8. The system according to claim 7, characterized in that it also includes modification means for modifying the electrical excitation or impulse signals to the print head in response to the generation of the multiple bit binary signals.
9. The system according to claim 7, characterized in that the means for generating the binary output signals include at least one oscillator controlled by means of the temperature whose operation is controlled by the controller.
10. The system according to claim 9, characterized in that it also includes synchronization circuits for synchronizing the start and stop of the predetermined time period with the operation of the oscillator and the other timing functions of the printer controlled by the controller.
11. The system according to claim 9, characterized in that the oscillator, the counter, and the synchronization circuits, the reading / control circuits, and the circuits for modifying the electrical signals for the print head are formed on a microcircuit. only which is located on the printhead.
12. The system according to claim 11, characterized in that a plurality of the micro-circuits is formed.
13. The system according to claim 8, characterized in that the electrical impulse or excitation signals are applied to the heater resistors in the print head, each resistor associated with a nozzle for ejecting the ink on a recording medium in response to the electrical signals, ejected ink creates dots on the recording medium and wherein the modification means include logic means to select a combination of power level and time duration of the electrical input signal for the heating element, to drive at a desired size of the mark on the sheet for copying, selecting, in response to the signal from the read / output logic means, a duration of the electric input signal for the heating element consistent with a desired size of the mark on the sheet for copying, and select a power level consistent with the selected duration of the signal At the electrical input to produce or achieve ejection of the ink, the controlling means activates the heater resistors according to the selected combination of the power level and the duration of time.
14. The system according to claim 10, characterized in that the synchronization circuits introduce a predetermined delay between the instant in which the counter is stopped and the instant in which the accumulated count is converted into the binary multiple bit signal.
15. The system according to claim 9, characterized in that the oscillator includes a timer circuit which includes an RC circuit connected to the input of a Schmitt trigger circuit, the Schmitt trigger circuit provides generally rectangular output pulses whose frequency changes as A function of the resistance of R, the resistance of R varies as a function of the temperature of the print head.
16. The system according to claim 15, characterized in that the oscillator also includes an inverter circuit which contains a series of inverters 1-K, the output of the inverter K is a clock signal of the temperature f (T) which is a entry for the electric meter.
17. The system according to claim 16, characterized in that the counter is a 9-bit counter.
18. A thermal ink jet printer, which includes a print head for ejecting droplets of ink through the nozzles onto a recording medium in response to selectively applied electrical signals, applied to the resistors associated with the nozzles. , and a controller for controlling the application of the electrical signals to the resistors, the printer is characterized in that it also includes: a first temperature detection circuit for detecting the temperature of the print head, the circuits include an oscillator controlled by means of the temperature, whose output frequency varies with the temperature of the print head, an electrical counter for counting the outputs from the oscillator for a predetermined period of time and logical means for converting the output of the next counter to the period default in a multi-bit signal representing the temperature of the head of impression detected during the sampled time interval, a second temperature detection circuit to detect the temperature of the print head, the circuit includes a thermistor located on the print head whose resistance varies with the temperature of the print head and an A / D converter to convert the Analog output voltage of the resistor to a digital signal representative of the temperature of the print head and switching means controlled by the controller to selectively enable either the first or the second temperature sensing circuit.
19. A thermal ink jet printer, which includes at least one print head of the page width type having a plurality of droplet emitting jets, the jets confronts a path through which a recording medium is moved to further defining a printing area having a width of at least one page width, the printer is characterized in that it also includes: a plurality of temperature sensing circuits located at discrete locations along the width of the print head , each circuit generates a digital signal representative of the temperature of the print head in the discrete location.
20. The printer according to claim 19, characterized in that the print head comprises the plurality of modules embedded together, the circuits formed on a plurality of the modules.
21. A method for detecting the temperature of an inkjet print head in an ink jet printer, characterized in that it comprises the steps of: generating digital output pulses having a frequency which varies with the temperature of the print head , count the pulses for a period of time and convert the accumulated count of the pulses into a digital byte representative of the temperature of the print head. SUMMARY OF THE INVENTION The invention discloses a temperature sensing system which provides a digital signal representative of the temperature of a print head by ink jet for a predetermined period of time. In one embodiment, a temperature controlled oscillator is formed on the print head, the oscillator includes a resistor whose resistance varies proportionally with the temperature variations of the print head. An analog signal from the resistor, representative of the temperature of the print head, is converted by the oscillator into a digital output signal whose frequency varies with the variations in the resistor and, therefore, with the temperature of the print head . The outputs of the oscillator are counted in an electric meter during a sampling period. The accumulated count is converted into a digital code that represents the temperature of the print head. This byte is available for comparison with the predetermined values stored in a look-up table and is converted into electrical image signals sent to the print head, which are adjusted and compensate for changes in the volume of the ink ejected by the nozzles of the print head. In a preferred embodiment, the oscillator counter and synchronization circuits are formed on a microcircuit located on the print head. The print head can be either a single-part, partial-width printhead located on a carriage which is moved through a print area or a print head of the full-width type. The temperature detection circuit has a high signal to noise ratio, which leads to a more accurate temperature measurement. Because of the immunity against noise, detection can be carried out during a printing operation.
MX9605850A 1995-12-11 1996-11-26 Sensing the temperature of a printhead in an ink jet printer. MX9605850A (en)

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US08/570,024 US5745130A (en) 1995-12-11 1995-12-11 System for sensing the temperature of a printhead in an ink jet printer
US08570024 1995-12-11

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