Device and method for detecting temperature of head driver IC for ink jet printer Number:7,438,376 from the United States Patent and Trademark Office (PTO) owispatent

Title: Device and method for detecting temperature of head driver IC for ink jet printer

Abstract: Each of a plurality of driver ICs, which drives an associated print head, includes an analog voltage provider, which provides an analog voltage which is inversely proportional to a temperature of the driver IC, a reference temperature provider, which provides a digital value corresponding to a reference temperature, a D/A converter, which converts the digital value into a corresponding analog value, and a comparator, which compares the analog voltage with the analog value and outputs a comparison signal indicating whether the analog voltage is higher than the analog value. A temperature detector determines whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal.

Patent Number: 7,438,376 Issued on 10/21/2008 to Tamura,   et al.

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Inventors:	Tamura; Noboru (Nagano, JP), Nishihara; Yuichi (Nagano, JP)
Assignee:	Seiko Epson Corporation (Tokyo, JP)
Appl. No.:	11/561,708
Filed:	November 20, 2006

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	10231461	Aug., 2002

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Foreign Application Priority Data

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Aug 30, 2001 [JP]			P2001-262363
May 29, 2002 [JP]			P2002-156080
May 29, 2002 [JP]			P2002-156081
May 29, 2002 [JP]			P2002-156529

Current U.S. Class:	347/17 ; 347/5; 347/9
Current International Class:	B41J 2/05 (20060101)
Field of Search:	347/5,7,9,17,19,14-15

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References Cited [Referenced By]

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U.S. Patent Documents

5281980	January 1994	Kishida et al.
5576745	November 1996	Matsubara
5736995	April 1998	Bohorquez et al.
5764246	June 1998	Wataya et al.
6068363	May 2000	Saito
6154229	November 2000	Corrigan
6231154	May 2001	Corrigan
6270180	August 2001	Arakawa et al.
6435668	August 2002	Barbour et al.
6464318	October 2002	Kubo
6708279	March 2004	Takenaka

Foreign Patent Documents

	03-247457		Nov., 1991		JP
	04-096267		Mar., 1992		JP
	4-69741		Jun., 1992		JP
	08-244231		Sep., 1996		JP
	09-131879		May., 1997		JP
	11-005324		Jan., 1999		JP
	11-129496		May., 1999		JP
	2000-203061		Jul., 2000		JP
	2001-058406		Mar., 2001		JP

Primary Examiner: Nguyen; Lam S
Attorney, Agent or Firm: Sughrue Mion, PLLC

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Parent Case Text

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CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser. No. 10/231,461 filed Aug. 30, 2002; the entire disclosure of which is incorporated herein by reference.

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Claims

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What is claimed is:

1. A device for detecting a temperature of a head drive based on an output value of a diode which is provided in the head driver, the device comprising: a setting unit, operable to set a reference value corresponding to a reference temperature for temperature detection; a controller, operable to determine a characteristics of temperature changes in the output value of the diode; a comparator, operable to input the reference value into the setting unit based on the characteristics of temperature changes in the output value of the diode, and compares the output value with the reference value; and a detector, operable to detect whether the temperature of the head driver is larger than the reference temperature based on a comparison result of the comparator; wherein the controller the characteristics of temperature changes in the output value of the diode based on a magnitude of change between an output value of the diode at an ambient temperature and an output value of the diode after a drive waveform pulse having a voltage at which no ink is to be ejected is applied to a head a specific number of times.

2. A method for detecting a temperature head driver based on an output value of a diode which is provided in the head driver, the method comprising: setting a reference value corresponding to a reference temperature for temperature detection; determining a characteristic of temperature changes in the output value of the diode; inputting the reference value based on the characteristics of temperature changes in the output value of the diode: comparing the output value with the reference value; and detecting whether the temperature of the head driver is larger than the reference temperature based on a comparison result in the comparing, wherein the characteristics of temperature changes in the output value of the diode is determined based on a magnitude of change between an output value of the diode at an ambient temperature and an output value of the diode after a drive waveform pulse having a voltage at which no ink is to be ejected is applied to a head a specific number of times.

3. A computer-readable recording medium, which causes a computer to execute the temperature detecting method as set forth in claim 2.

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Description

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BACKGROUND OF THE INVENTION

The invention relates to a technique for detecting that head driver ICs of an ink jet printer have reached a predetermined temperature or higher.

FIG. 1 shows the outline of hardware of an ink jet printer constituted by piezoelectric vibrators serving as elements for ejecting ink from nozzles. As shown in this figure, a controller 102 is a control board which is to be implemented in a printer and causes a print engine 103 to perform printing operation complying with data entered by way of an interface 104. A CPU (central processing unit) 123 executes a program stored in a ROM (read-only memory) 121, thereby controlling individual sections provided in the controller 102. A main bus of the controller 102 is connected to a RAM (random access memory) 122 serving as a primary storage device of the CPU 123 and to a PROM 124 (programmable read-only memory) for recording various types of setting items.

An IC chip 126 provided in the controller 102 actually sends various types of signals to the print engine 103 pursuant to a print instruction construed by the CPU 123. The custom IC chip 126 serves as an engine controller which performs a centralized control operation pertaining to printing and driving of the printer.

First, a signal to be sent from the custom IC chip 126 is a drive signal for controlling a motor. The motor drive signal sent by way of a signal line 128 effects feeding of print paper or actuation of a head unit 131 mounted on an unillustrated carriage.

Signals used directly for printing operation are a digital signal and an analog signal for driving a switcher 135. A digital signal, representing whether ink is ejected from each nozzle, is delivered without modification via a signal line 132 to a switcher 135. A signal to be used for determining the size of ink droplets is temporarily sent to a digital/analog converter 133 in the form of a set of digital vector data through via a signal line 134. The digital signal is converted into an analog trapezoidal waveform, an example of which is shown in FIG. 2, and then delivered to the switcher 135.

In an ink jet printer which causes nozzles to eject ink, by utilization of expanding action of a piezoelectric vibrator 137 shown in FIG. 1, the switcher 135 assumes a configuration such as that shown in FIG. 3.

In FIG. 3, each of the switchers 135 (135-1 through 135-n) has two input ports; that is, a digital input port and an analog input port. An analog drive signal complying with these inputs is output to piezoelectric vibrators 137 (137-1 through 137-n) by way of signal lines 136 (136-1 through 136-n). The digital signal line 132 is connected to an input terminal of the custom IC chip 126 (FIG. 1). Data which have been serially input by way of the custom IC chip 126 are serially transferred to each of shift registers 141 (141-1 through 141-n) in accordance with a clock signal CLK, and latched in each of latches 142 (142-1 through 142-n) at a predetermined timing defined by a latch signal LAT. The thus-latched data are output to the switcher 135.

The switcher 135 outputs to the piezoelectric vibrator 137 an amplitude represented by the analog waveform signal (FIG. 2) at a timing defined by the digital signal. By means of provision of such a switcher for each nozzle, ink droplets of arbitrary size can be ejected at an arbitrary timing. Such switchers equal in number to nozzles are integrated, thereby constituting a single switching semiconductor element.

In a standard assembly process for an ink jet printer, one head is constructed of a total of eight groups of nozzles; that is, a group of black ink nozzles, a group of yellow ink nozzles, a group of cyan ink nozzles, a group of magenta ink nozzles, a group of light cyan ink nozzles, a group of light magenta ink nozzles, and a group of dark yellow ink nozzles. A switching semiconductor element is provided for each of the nozzle groups.

The thus-integrated switcher has a heat resisting temperature at which normal operation of the switcher is guaranteed. Similarly, a heat-resisting temperature is determined also for a conductive adhesive or the like to be used for assembling constituent components of the head. Hence, in order to prevent a hindrance to normal operation of individual constituent components or thermal breakdown of the components, which would otherwise be caused by idle ejecting operation stemming from depletion of ink, a diode which is to serve as a semiconductor element for detecting a temperature is incorporated in each of the ink nozzle drive switching elements. An internal temperature of the semiconductor element is measured by a voltage output from the diode.

FIG. 4 shows a configuration for measuring a temperature, by potential differences among four diodes connected between a constant current source CS and ground. The diodes have physical properties whose output voltages are determined in accordance with a temperature environment when constant power is supplied from the constant current source CS.

An output from the temperature detecting semiconductor element (diode) having such a configuration is returned to the previously-described custom IC chip 26 from the carriage having the printer head unit 131 mounted thereon, by way of a signal line of a flexible flat cable (i.e., the signal line 127 shown in FIG. 1). By utilization of a value of the output, the custom IC chip 26 performs various types of print control operations, such as suspension of a printing operation in the event of generation of, e.g., overheat.

In actual assembly processes relating to manufacture of a printer, a temperature detecting diode has already been incorporated into an ink nozzle drive switching semiconductor element supplied as a component. When the ink nozzle drive switching semiconductor element is produced by way of a single manufacturing process, errors resulting from variations in quality may arise. However, the ink nozzle drive switching semiconductor elements do not vary from each other in terms of principal characteristics; that is, the quantity of heat stemming from switching actions or a characteristic of a voltage changing in accordance with the temperature of a diode.

From the viewpoint of the quantity of supplied parts and costs incurred in material procurement, in many cases parts produced through different manufacturing processes are used in a single printer at a site for controlling manufacturing processes. Even in the case of an ink nozzle drive switching semiconductor element, semiconductor elements produced through different manufacturing processes are employed. In such a case, semiconductor elements supplied from certain manufacturing processes often differ from those supplied from other manufacturing processes in terms of characteristics of diodes built in the semiconductor elements.

FIG. 5 is a graph representing the relationship between characteristics of diodes. In the graph, the vertical axis represents a voltage of an anode output 50 shown in FIG. 4. In other words, the vertical axis corresponds to a total potential difference between the anodes and cathodes of four diodes connected in series with each other. The horizontal axis represents temperatures of locations where a temperature detecting circuit, such as that shown in FIG. 4, is disposed.

The graph shows a physical property of a diode built in a switcher produced through production processes A and that of a diode built in a switcher produced through production processes B, wherein output voltages of the diodes are determined in accordance with a temperature environment. Specifically, a diode produced through manufacturing processes A produces an anode output of 2.4 V in a temperature environment of 25.degree. C., whilst a diode produced through manufacturing processes B produces an anode output of 2.0 V in a temperature environment of 25.degree. C.

Further, the graph also shows a characteristic of a rate at which an output voltage is changed in accordance with changes in a temperature environment; that is, different gradients of respective line segments of the graph.

Variations exist in respective diodes produced through the manufacturing processes A and in those produced through the manufacturing processes B, the variations being attributable to individual differences. In the graph, standard values of products are denoted by solid lines, and the range of variation is denoted by dashed lines.

For instance, in a case where the guaranteed heat-proof temperature of the switcher is 120.degree. C., the switcher is determined to be overheated when the anode output voltage has dropped to 1.3 V (i.e., the maximum value of the individual differences) in light of the temperature-voltage characteristic of the diode produced through the manufacturing processes B. In a case where the temperature of the printer is controlled on the assumption of a characteristic of a rate at which the output voltage of the diode changes, the anode output voltage is considered to have dropped to 2.1 V (i.e., the maximum value of the individual differences) when the ink nozzle driver switching semiconductor element produced through the manufacturing processes A is used for a product. Accordingly, overheat of the switcher cannot be detected.

As mentioned previously, a related-art head driver IC temperature detector of an ink jet printer measures anode voltages of diodes provided in a head driver IC, and the temperatures of junctions of transistors provided in the IC are detected by temperature characteristics of the anode voltages.

However, since diodes have great variations in characteristics thereof, a result of mere measurement of junction temperatures performed by the temperature detecting diodes provided in the head driver IC also includes a great variation.

In short, the above-described temperature detecting method encounters difficulty in detecting temperatures accurately, because of individual differences in anode voltage at a certain temperature or individual differences in temperature coefficient of an anode voltage.

By the way, the head driver ICs generate heat when they are driven, and the heat is dissipated by the ejected ink droplets. However, as a result of uninterrupted operation under extremely high load, heat dissipation capacity may become insufficient. Moreover, in a state in which ink is not properly squirted for reasons of depletion of ink or clogging of nozzles, sufficient heat dissipation is not achieved. If printing operation is continued in such a state, the temperatures of respective head driver ICs rise further, potentially resulting in thermal destruction of the respective head driver ICs.

Therefore, in a related-art ink jet printer, attention is paid to the anode voltage of a diode provided in each of the head driver ICs changing in accordance with the ambient temperature. As shown in FIG. 6, the anode voltages of the diodes provided in four head driver ICs 1a, 1b, 1c, and 1d are output to a controller 4 which is provided in a printer main unit 3 and is constituted of, e.g., an ASIC, by way of respective signal lines 2a, 2b, 2c, and 2d provided in a flexible flat cable (FFC).

In the controller 4, the anode voltages are converted into digital values by an analog-to-digital converter 5, thereby detecting anode voltages of diodes of the respective head driver ICs. In accordance with the anode voltages, the temperatures of the respective head driver ICs 1a, 1b, 1c, and 1d are detected. When any one of the head driver ICs 1a, 1b, 1c, and 1d has reached a predetermined temperature or more, the controller 4 temporarily stops a printing operation, thereby lowering the temperatures of the head driver ICs 1a, 1b, 1c, and 1d.

However, according to such a method of detecting the temperatures of the head driver ICs 1a, 1b, 1c, and 1d, analog signals pass through the signal lines 2a, 2b, 2c, and 2d provided in the comparatively long FFC 7 extending from the printer head 6 to the printer main unit 3. The analog signals are susceptible to the influence of noise, thereby deteriorating the accuracy of detection.

The anode voltages of the respective head drivers ICs 1a, 1b, 1c, and 1d are converted into digital signals by the analog-to-digital converter 5 within the controller 4, thereby prolonging a detection time and requiring provision of the analog-to-digital converter 5 within the controller 4. Accordingly, the controller 4 constituted of, e.g., an ASIC, becomes bulky.

Moreover, the lines 2a, 2b, 2c, and 2d must be provided in the FFC 7 in equal number with the head drier ICs. Further, the number of input pins of the controller 4 increases, thereby resulting in a cost hike.

In a case where a rupture has arisen in any one of the signal lines, a rise in the temperature of a corresponding head driver IC cannot be detected. Hence, the rise in the temperature of that head driver IC may be left undetected. Accordingly, damage may be inflicted on the printer head.

In this way, when a temperature detecting circuit has become broken as a result of occurrence of a rupture in a signal line or a short-circuit in any one of circuits for detecting temperatures, the configuration shown in FIG. 6 encounters difficulty in immediately detecting the failure and taking a countermeasure, such as suspension of operation of a printer.

SUMMARY OF THE INVENTION

It is therefore a first object of the invention to provide a device for detecting the temperatures of head driver ICs of an ink jet printer in which a configuration is simplified without involvement of the influence of noise.

It is a second object of the invention to provide a device and a method for detecting the temperatures of a plurality of head driver ICs in an ink jet printer, wherein a determination can be made as to which one of the head driver ICs has reached an increased temperature.

It is a third object of the invention to provide a device and a method which enable immediate detection of failures in a circuit for detecting the temperatures of a plurality of head driver ICs in an ink jet printer.

It is a fourth object of the invention to provide a device and a method for detecting temperatures of head driver ICs of an ink jet printer, which enable accurate detection of junction temperatures by highly-accurate correction of variations in the characteristics of diodes to be used for detecting temperatures of head driver ICs.

In order to achieve the above objects, according to the present invention, there is provided an ink jet printer, comprising:

a plurality of driver ICs, each of which drives an associated print head, each driver IC including:

an analog voltage provider, which provides an analog voltage which is inversely proportional to a temperature of the driver IC;

a reference temperature provider, which provides a digital value corresponding to a reference temperature;

a D/A converter, which converts the digital value into a corresponding analog value; and

a comparator, which compares the analog voltage with the analog value and outputs a comparison signal indicating whether the analog voltage is higher than the analog value; and

a temperature detector, which determines whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal.

In this configuration, a digital reference value is set by the reference temperature provider after the ink jet printer is activated. As a result, the D/A converter in each of the head driver ICs converts the digital reference value into an analog reference value, and the analog reference value is input to one of input terminals of the comparator.

In this state, the comparator compares the analog voltage with the analog reference value output from the D/A converter. When the analog voltage is higher than the analog reference value, the comparator renders the digital signal inactive. When the analog voltage has become lower than the analog reference value, the comparator renders the digital signal active.

During the course of a printing operation, the temperature detector can detect that the head driver ICs have become higher than a predetermined temperature, by monitoring digital signals output from comparators provided in the respective head driver ICs. Further, as mentioned previously, when the head driver ICs have been detected as having reached a temperature higher than a predetermined temperature, the temperature detector temporarily suspends printing operation or, in some cases, forcefully terminates printing operation, thereby preventing thermal destruction of the head driver ICs, which would otherwise be caused by a temperature increase.

Accordingly, signals which are output from the respective head driver ICs to the temperature detector are digital signals. Hence, even when a cable linking a head driver IC to the controller is long, the signal carried thereby is less susceptible to the influence of noise, whereby the accuracy of detection is improved. Since the temperature detector does not need an A/D converter, only a short period of detecting time is required. Even during a short period of time, such as a period of printing operation, temperatures of the head driver ICs can be detected surely.

Preferably, the comparison signal from each of the driver ICs is inputted to the temperature detector independently from another.

In this configuration, digital signals output from comparators of respective head driver ICs are independently output to the controller of the printer main unit. Even when a fault, such as a rupture, has arisen in a portion of cables which link the respective head driver ICs to the temperature detector, a temperature of only the head driver IC using the cable in which the fault has arisen fails to be detected, and temperatures of the head driver ICs using the remaining cables can be detected.

Preferably, the driver IC includes an FET in which the comparison signal is inputted to a gate and a drain is left open.

In this configuration, the FETs are turned on or off, by the digital signals output from the respective comparators, and outputs from the open drains are input into the temperature detector.

Here, it is preferable that a digital output signal from the FET in each of the driver ICs is inputted to the temperature detector independently from another.

In this configuration, digital signals output from the FETs of the respective head driver ICs are independently output to the temperature detector. Hence, even when a fault, such as a rupture, has arisen in a portion of the cable which links the respective driver ICs to the printer main unit, a temperature of only the head driver IC using a cable in which the fault has arisen fails to be detected, and temperatures of the head driver ICs using the remaining cables can be detected.

Alternatively, it is preferable that an output terminal of the FET in each of the driver ICs is wired-AND connected with another output terminals so that a digital output signal from each FET is transmitted to the temperature detector via a single line.

In this configuration, digital signals output from the FETs of the respective head driver ICs are output by open drains. Hence, even when outputs of open drains of the respective FETs are connected together in the form of a wired-AND configuration, digital signals output from the respective FETs are output to the temperature detector by way of a single cable without involvement of occurrence of interference.

Accordingly, only a single cable is required for detecting the temperatures of a plurality of head driver ICs. Hence, costs are curtailed, and only a few input pins of the temperature detector are required. Hence, the invention can contribute to a reduction in the number of pins of an ASIC constituting the temperature detector (controller).

Preferably, the driver IC includes a bipolar transistor in which the comparison signal is inputted to a base and a collector is left open.

In this configuration, the bipolar transistors are turned on or off by digital signals output from the respective comparators, and outputs of open collectors are input to the temperature detector.

Here, it is preferable that a digital output signal from the bipolar transistor in each of the driver ICs is inputted to the temperature detector independently from another.

In this configuration, digital signals output from the bipolar transistors of the respective head driver ICs are independently output to the temperature detector. Hence, even when a fault, such as a rupture, has arisen in a portion of the cable which links the respective driver ICs to the temperature detector, a temperature of only the head driver IC using a cable in which the fault has arisen fails to be detected, and temperatures of the head driver ICs using the remaining cables can be detected.

Alternatively, it is preferable that an output terminal of the bipolar transistor in each of the driver ICs is wired-AND connected with another output terminals so that a digital output signal from each bipolar transistor is transmitted to the temperature detector via a single line.

In this configuration, digital signals output from the bipolar transistors of the respective head driver ICs are output by open collectors. Hence, even when outputs of open collectors of the respective bipolar transistors are connected together in the form of a wired-AND configuration, digital signals output from the respective bipolar transistors are output to the temperature detector by way of a single cable without involvement of occurrence of interference.

Accordingly, only one cable is required for detecting the temperatures of a plurality of head driver ICs. Hence, costs are curtailed, and only a few input pins of the controller of the temperature detector are required. Hence, the invention can contribute to a reduction in the number of pins of an ASIC constituting the temperature detector (controller).

Preferably, the reference temperature is determined for each driver IC in accordance with a placement condition of the driver IC.

In this configuration, the digital reference values of the reference temperature providers of the respective head driver ICs can be set in accordance with individual conditions of the respective head driver ICs and variations in the characteristics of diodes provided in the head driver ICs.

Preferably, a digital data storage composed of a predetermined number of bit which defines an adjustable range of the digital value.

In this configuration, a printer designer can freely set the digital reference value within the range of bits by reference to individual conditions ascertained through preliminary measurement of each head driver IC.

Preferably, the temperature detector determines that a fatal error occurs in the printer when a number of determination that the temperature of the print head is higher than the reference temperature exceeds a predetermined number.

Preferably, the ink jet printer further comprises a selector, which selectably varies the digital value of at least one reference temperature provider. Here, the selector varies the digital value of each reference temperature provider in accordance with a predetermined order, when the comparison signal indicates that the temperature of at least one print head is higher than the reference temperature. The temperature detector determines that the temperature of one drive IC is higher than the reference temperature when the comparison signal changes in accordance with the variation of the digital signal of the one drive IC.

More specifically, the digital reference values of respective head driver ICs are varied one after another. For instance, the selector minimizes the digital value. The head driver IC whose comparison signal has been changed is specified as a head driver IC whose temperature has increased above or decreased below the reference temperature.

Alternatively, in an ink jet printer having, e.g., eight head driver ICs, digital reference values (threshold values) of four head driver ICs are preferably switched simultaneously; then digital reference values (threshold values) of two head driver ICs are preferably switched simultaneously; and then a digital reference value (threshold value) of one head driver IC is preferably switched, so as to avoiding switching of digital reference value (threshold value) eight times. In this way, a head driver IC whose temperature has increased above or decreased below the reference value can be specified by only three switching operations.

Preferably, the ink jet printer further comprises:

a thermistor, provided on each print head to detect an ambient temperature of the print head; and

a corrector, which corrects the temperature of each print head detected based on the analog voltage, by using the ambient temperature detected by the thermistor.

Here, it is preferable that the ink jet printer further comprises:

a first calculator, which calculates a theoretical temperature dependency of the analog voltage when the print head is driven in a predetermined manner; and

a second calculator, which calculates an actual temperature dependency of the analog voltage when the print head is driven in the predetermined manner.

The corrector corrects the detected temperature of each print head based on a difference between the theoretical temperature dependency and the actual temperature dependency.

Further, it is preferable that the thermistor detects a first ambient temperature at an initial condition and a second ambient temperature when the print head is driven such an extent that no ink drop is ejected from the nozzle array. The actual temperature dependency of the analog voltage is determined by measuring a difference between a first analog voltage at the first ambient temperature and a second analog voltage at the second ambient temperature.

According to the present invention, there is also provided an ink jet printer, comprising:

a plurality of driver ICs, each of which drives an associated print head, each driver IC including a diode, which provides an anode voltage which is inversely proportional to a temperature of the driver IC;

a thermistor, provided on each print head to detect an ambient temperature of the print head; and

a corrector, which corrects the temperature of each print head detected based on the anode voltage, by using the ambient temperature detected by the thermistor.

Namely, the invention can also be applied to an ink jet printer in which an analog signal corresponding to an anode voltage of the diode is outputted via a signal line, and converting the analog signal into a digital signal through use of the controller of the printer main unit.

Here, it is preferable that the ink jet printer further comprises:

a first calculator, which calculates a theoretical temperature dependency of the anode voltage when the print head is driven in a predetermined manner; and

a second calculator, which calculates an actual temperature dependency of the anode voltage when the print head is driven in the predetermined manner.

The corrector corrects the detected temperature of each print head based on a difference between the theoretical temperature dependency and the actual temperature dependency.

Further, it is preferable that the thermistor detects a first ambient temperature at an initial condition and a second ambient temperature when the print head is driven such an extent that no ink drop is ejected from the nozzle array. The actual temperature dependency of the anode voltage is determined by measuring a difference between a first anode voltage at the first ambient temperature and a second anode voltage at the second ambient temperature.

These correction are performed preferably at the time of assembly of an ink jet printer, at the time of first activation of the printer after a user has purchased the printer, or every time the printer is activated.

The anode voltage is subjected to the A/D conversion, and a junction temperature is determined by use of the temperature dependency of the anode voltage determined above. The upper limit anode voltage of the junction temperature is determined from the thus-determined dependency. A protection measure, such as interruption of printing operation, is taken when the anode voltage has achieved the value.

As mentioned above, the anode voltage is corrected by matching the result of temperature detected by the thermistor provided on the print head with the temperature corresponding to the anode voltage. Hence, the junction temperatures of the head driver ICs can be detected accurately.

According to the present invention, there is also provided an ink jet printer, comprising:

a plurality of driver ICs, each of which drives an associated print head, each driver IC including:

an analog voltage provider, which provides an analog voltage which is inversely proportional to a temperature of the driver IC;

a reference temperature provider, which provides a digital value corresponding to a reference temperature;

a D/A converter, which converts the digital value into a corresponding analog value; and

a comparator, which compares the analog voltage with the analog value and outputs a comparison signal indicating whether the analog voltage is higher than the analog value;

a digital data storage, composed of a predetermined number of bit which defines an adjustable range of the digital value;

a selector, which selectably changes the digital value of each reference temperature provider; and

a failure detector, which determines that whether at least one of the driver ICs is in a failure, wherein:

the selector selectively varies the digital value of each reference temperature provider in accordance with a predetermined order at a predetermined timing; and

the failure detector determines that one drive IC is in a failure when the comparison signal changes in accordance with the variation of the digital signal of the one drive IC.

Preferably, the selector maximizes the digital value.

Preferably, the selector varies the digital value periodically.

For instance, the predetermined timing is at least one of when the printer is activated, when a printing operation is sustained, when a page break is performed.

If the comparison signals are not changed, occurrence of a rupture in the FFC is suspected. The failure detector determines that there is a failure common to the respective driver ICs when it is determined that all the driver ICs are in a failure.

Preferably, the ink jet printer further comprises a temperature detector, which determines whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal. The selector minimizes the digital values of all the driver ICs collectively, when the comparison signal indicates that the temperature of at least one print head is higher than the reference temperature. The failure detector determines that at least one of the driver ICs is in a failure when the comparison signal changes in accordance with the minimization.

In this configuration, occurrence of a failure can be detected immediately.

According to the present invention, there is also provided a temperature detecting method for an ink jet printer provided with a plurality of driver ICs, each of which drives an associated print head, the method comprising the steps of:

a) providing a digital value corresponding to a reference temperature;

b) converting the digital value into a corresponding analog value;

c) comparing an analog voltage, which is inversely proportional to a temperature of the driver IC, with the analog value;

d) generating a comparison signal indicating whether the analog voltage is higher than the analog value; and

e) determining whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal, wherein the steps a) to d) are performed in each driver IC.

Preferably, the reference temperature is determined for each driver IC in accordance with a placement condition of the driver IC.

Preferably, the temperature detecting method further comprises the step of determining that a fatal error occurs in the printer when a number of determination that the temperature of the print head is higher than the reference temperature exceeds a predetermined number.

Preferably, the temperature detecting method further comprises the steps of:

varying selectively the digital value of at least one driver IC in accordance with a predetermined order, when the comparison signal indicates that the temperature of at least one print head is higher than the reference temperature; and

determining that the temperature of one drive IC is higher than the reference temperature when the comparison signal changes in accordance with the variation of the digital signal of the one drive IC.

Here, it is preferable that the digital data is minimized in an adjustable range thereof.

Preferably, the temperature detecting method further comprises the steps of:

minimizing collectively the digital values of all the driver ICs in adjustable ranges thereof, when the comparison signal indicates that the temperature of at least one print head is higher than the reference temperature; and

determining that at least one of the driver ICs is in a failure when the comparison signal changes in accordance with the minimization.

Preferably, the temperature detecting method further comprises the steps of:

detecting an ambient temperature of the print head; and

correcting the temperature of each print head detected based on the analog voltage, by using the detected ambient temperature.

Here, it is preferable that the temperature detecting method further comprises the steps of:

calculating a theoretical temperature dependency of the analog voltage when the print head is driven in a predetermined manner; and

calculating an actual temperature dependency of the analog voltage when the print head is driven in the predetermined manner.

The detected temperature of each print head is corrected based on a difference between the theoretical temperature dependency and the actual temperature dependency.

Further, it is preferable that the ambient temperature detecting step including: detecting a first ambient temperature at an initial condition; and detecting a second ambient temperature when the print head is driven such an extent that no ink drop is ejected from the nozzle array. The actual temperature dependency of the analog voltage is determined by measuring a difference between a first analog voltage at the first ambient temperature and a second analog voltage at the second ambient temperature.

According to the present invention, there is also provided a temperature detecting method for an ink jet printer provided with a plurality of driver ICs, each of which drives an associated print head, the method comprising the steps of:

detecting an ambient temperature of each print head; and

correcting the temperature of each print head detected based on an anode voltage of a diode provided in each of the driver ICs, by using the detected ambient temperature.

Here, it is preferable that the temperature detecting method further comprises the steps of:

calculating a theoretical temperature dependency of the anode voltage when the print head is driven in a predetermined manner; and

calculating an actual temperature dependency of the anode voltage when the print head is driven in the predetermined manner.

The detected temperature of each print head is corrected based on a difference between the theoretical temperature dependency and the actual temperature dependency.

Further, it is preferable that the ambient temperature detecting step including: detecting a first ambient temperature at an initial condition; and detecting a second ambient temperature when the print head is driven such an extent that no ink drop is ejected from the nozzle array. The actual temperature dependency of the anode voltage is determined by measuring a difference between a first anode voltage at the first ambient temperature and a second anode voltage at the second ambient temperature.

According to the present invention, there is also provided a failure detecting method for an ink jet printer provided with a plurality of driver ICs, each of which drives an associated print head, the method comprising the steps of:

providing a digital value corresponding to a reference temperature;

converting the digital value into a corresponding analog value;

comparing an analog voltage, which is inversely proportional to a temperature of the driver IC, with the analog value;

generating a comparison signal indicating whether the analog voltage is higher than the analog value;

determining whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal;

varying selectively the digital value of at least one driver IC in accordance with a predetermined order at a predetermined timing; and

determining that one drive IC is in a failure when the comparison signal changes in accordance with the variation of the digital signal of the one drive IC.

Preferably, the digital value is maximized in an adjustable range thereof.

Preferably, the predetermined timing is at least one of when the printer is activated, when a printing operation is sustained, when a page break is performed.

Preferably, the selector varies the digital value periodically.

Preferably, the failure detector determines that there is a failure common to the respective driver ICs when it is determined that all the driver ICs are in a failure.

Preferably, the failure detection method further comprises the steps of:

determining whether the temperature of at least one of print heads is higher than the reference temperature in accordance with the comparison signal;

minimizing the digital values of all the driver ICs collectively, when the comparison signal indicates that the temperature of at least one print head is higher than the reference temperature; and

determining that at least one of the driver ICs is in a failure when the comparison signal changes in accordance with the minimization.

According to the present invention, there is also provided a computer-readable recording medium, which causes a computer to execute the above temperature detecting methods and the failure detecting methods.

According to the present invention, there is also provided a computer program, which causes a computer to execute the above temperature detecting methods and the failure detecting methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram showing a hardware configuration of a printer;

FIG. 2 is a view showing an example of analog waveform data utilized in the printer;

FIG. 3 is a schematic diagram showing a configuration for activating a piezoelectric vibrator using a switcher;

FIG. 4 is a schematic diagram showing an example configuration of a related-art temperature detecting circuit;

FIG. 5 is a graph representing the characteristics of the related-art temperature detecting circuit;

FIG. 6 is a block diagram showing a related-art temperature detector for a head driver IC;

FIG. 7 is a block diagram showing the configuration of a head driver IC temperature detector according to a first embodiment of the invention;

FIG. 8 is a block diagram showing the principal section of each of the head driver ICs in the head driver IC temperature detector shown in FIG. 7;

FIG. 9 is a view showing a specific example configuration of the principal section of each of the head driver ICs shown in FIG. 8;

FIG. 10 is a graph showing procedures for setting analog reference values of the head driver IC temperature detector shown in FIG. 7;

FIG. 11 is a flowchart showing example control of the controller in the head drive IC temperature detector shown in FIG. 7;

FIG. 12 is a block diagram showing the configuration of a head driver IC temperature detector according to a second embodiment of the invention;

FIG. 13 is a block diagram showing the principal section of each of head drier ICs in a head driver IC temperature detector according to a third embodiment of the invention;

FIG. 14 is a flowchart showing an example control of temperature detecting operation of the head driver IC temperature detector according to a fifth embodiment of the invention;

FIG. 15 is a view showing variations in the waveform of a drive waveform for a single path of a print head;

FIG. 16 is a flowchart showing an example control of temperature detecting operation of a head driver IC temperature detector according to a sixth embodiment of the invention;

FIG. 17 is a flowchart showing a failure detecting operation performed in a head driver IC temperature detector according to a seventh embodiment;

FIG. 18 is a flowchart showing a failure detecting operation performed in a head driver IC temperature detector according to an eighth embodiment;

FIG. 19 is a block diagram showing the configuration of a head driver IC temperature detector according to a ninth embodiment of the invention;

FIG. 20 is a flowchart showing a temperature detecting operation performed in the head driver IC temperature detector shown in FIG. 19; and

FIG. 21 is a graph showing a method of correcting individual differences in the anode voltages of diodes through use of the thermistor provided on a head board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a head driver IC equipped with a device for detecting temperatures of head driver ICs (hereinafter often simply called a "head driver IC temperature detector") according to the invention will now be described with reference to the accompanying drawings. The embodiments to be described below are specific, preferable examples of the invention. Hence, various technically-preferable limitations are imposed on the specific examples. However, unless otherwise specified, the scope of the invention is not limited to the embodiments.

FIG. 7 shows the configuration of a head driver IC temperature detector according to a first embodiment of the invention. An ink jet printer having the head driver IC temperature detector of the embodiment is a seven-color printer comprising: cyan (C), magenta (M), yellow (Y), black (K), light cyan (LC), light magenta (LM), and dark yellow (DY). The printer has a printer head comprising a total of eight rows of nozzles; namely, a row of cyan nozzles, a row of magenta nozzles, a row of yellow nozzles, two rows of black nozzles, a row of light-cyan nozzles, a row of light-magenta nozzles, and a row of dark-yellow nozzles.

The head driver IC temperature detector according to the embodiment is configured in a printer head 15 of the ink jet printer such that anode voltages of diodes provided in a plurality of head driver ICs 11a, 11b, 11c, 11d, 11e, 11f, 11g, and 11h (eight driver ICs) disposed for respective rows of nozzles are compared with the reference voltage. A result of comparison is digitized, and the thus-digitized result is output to a controller 14 provided in a printer main unit 13.

Here, the head driver ICs 11a through 11h are of the same configuration, and are ICs (integrated circuits) each constituting a transmission gate for activating or deactivating a switching circuit which controls ejection of ink from a plurality of rows of nozzles provided in a total of eight rows of nozzles.

FIG. 8 is a block diagram showing the configuration of a portion related to detecting of temperatures of the head driver ICs 11a through 11h. Each of the head driver ICs 11a through 11h includes a reference temperature provider 21, a digital-to-analog converter 22, a diode 23, a comparator 24, and an FET 25.

The reference temperature provider 21 is constituted of, e.g., a register or the like, and sets a digital reference value Vd corresponding to a reference temperature Tref for detecting a temperature. The digital-to-analog converter 22 converts the digital reference value Vd output from the reference temperature provider 21 into an analog reference value Va. The diode 23 is provided in the head driver IC 11a, and the anode of the diode 23 is connected to a constant voltage source Vdd1 via a resistor R1. Further, the cathode of the diode 23 is connected to ground.

In the illustrated case, the diode 23 is constructed by serial connection of a plurality of diodes (e.g., four diodes). Here, as will be described later, the anode voltage of the diode 23 has the characteristic of dropping as the temperature of the head driver IC rises.

An anode voltage V of the diode 23 is input to an inverted input terminal of the comparator 24, and an analog reference value Va output from the digital-to-analog converter 22 is input into a non-inverted input terminal of the same. Then, the comparator 24 compares the anode voltage V is compared with the analog reference value Va. When the anode value V of the diode 23 is higher than the analog reference value Va, the comparator 24 outputs a low-level digital signal. When the anode voltage V of the diode 23 has become lower than the analog reference value Va, the comparator 24 outputs a high-level digital signal.

The gate of the FET 25 is connected to an output terminal of the comparator 24, and the source of the same is connected to ground. The drain of the FET 25 is connected to a constant voltage source Vdd2 via a resistor R2. A digital signal is output from a drain, which is an open drain. As a result, when the signal output from the comparator 24 is at a low level, the FET 25 remains inactive. The drain of the FET is held at the voltage of the constant voltage source Vdd2 (i.e., a high level). When the signal output from the comparator 24 has become high, the FET 25 becomes active, and the drain thereof is dropped to the ground potential (i.e., a low level).

Respective temperature detecting sections of the head driver ICs 11a through 11h constituted in the manner set forth are connected to the output terminal 28 shared among outputs from the open drains of the respective FETs 25, in the form of a wired-AND configuration. Accordingly, when temperature detecting outputs from all the head driver ICs 11a through 11h are held at the voltage of the constant voltage supply Vdd2 (i.e., a high level), a temperature detecting signal XHOT output from the output terminal 28 remains at a high level. In contrast, when any one of temperature detecting outputs from the head driver ICs 11a through 11h has dropped to a ground potential (a low level), the temperature detecting signal XHOT output from the output terminal 28 becomes low. Alternatively, the output terminals of the open drains of the respective FETs 25 may be connected to the common output terminal 28 in the form of a wired-OR configuration such that, when any one of the temperature detecting outputs from the head driver ICs 11a through 11h has dropped to the ground potential (a low level), the temperature detecting signal XHOT output from the output terminal 28 becomes low.

FIG. 9 shows a specific example configuration of the head driver IC 11a. The head driver IC 11a is identical in configuration with that shown in FIG. 8. In place of the reference temperature provider 21 and the digital-to-analog converter 22, the head driver IC 11a comprises a plurality of flip-flop circuits 26 and a group of resistors 27.

In the case shown in the illustration, the flip-flop circuit 26 is constituted of eight flip-flop circuits 26a. A latch signal is input to a clock terminal CLK of each of the flip-flop circuits 26a, and a setting signal is input to a terminal D of each flip-flop circuit 26a. A reference voltage Vref is input to a Vref terminal of the flip-flop circuit 26a.

When flip-flops are set to a high level, they output a reference voltage Vref. When the flip-flops are set to a low level, they output a ground potential GND. Data to be used for selecting a nozzle (data to be used for activating or deactivating a switching circuit for controlling the ejection of ink from a plurality of nozzles provided in respective nozzle rows) are serially sent to the head driver IC. However, the data are preferably used as inputs D0 through D7 to be delivered to terminals D. In this case, serial data are input to the shift register. For instance, the finally-sent data are taken as DO through D7, and a latch signal LAT to be used specifically with a temperature detection circuit is used, whereby data are stored in the flip-flop.

The group of resistors 27 comprises seven resistors 1R and one resistor 2R, which are serially connected between a non-inverted input terminal and ground of the comparator 24, and eight resistor 2R connected between the anodes of the respective resistors 1R and output terminals Q of the respective flip-flop circuits 26a.

As a result, the analog reference value Va to be input to the non-inverted input terminal of the comparator 24 is set in 256 steps from a voltage of 0 to a voltage slightly lower than the reference voltage Vref, by combination of the setting signals to be input to the terminals D of the respective flip-flop circuits 26a.

The analog reference value Va to be input to the non-inverted input terminal of the comparator 24 is set for respective head driver ICs 11a through 11d prior to shipment, in consideration of variations in the characteristics of the diodes 23 to be incorporated into the head drivers ICs 11a through 11d such that the analog reference value Va corresponds to an upper limit temperature T2 set so as to become slightly lower than the guaranteed temperature T1 of each of the head drivers ICs 11a through 11d.

The temperature detector 10 of the embodiment is operated in the following manner. First, setting of the analog reference value Va will be described.

As shown in FIG. 10, the diodes 23 to be incorporated into the respective head drivers ICs 11a through 11d each have a temperature-voltage characteristic falling within the range defined between straight lines P and Q. Variations in characteristics include inclination variations and offset variations, of which the inclination variations impose greater adverse influence on the diodes. The offset variations can be corrected by measuring voltages at a certain temperature at the time of shipment from a factory.

First, consideration is given of a case where initial measurement is not performed. Each of the diodes 23 has a characteristic falling within the range defined between the straight lines P and Q. A voltage Vb defines a point of intersection A between the straight line P showing the upper limit characteristic and an upper limit temperature T2 which is slightly lower than the guaranteed temperature T1 of the head driver IC by a predetermined margin. While the voltage Vb is taken as a threshold value for the anode voltage of the diode when the diode is not subjected to initial measurement, a point of intersection B between the voltage Vb and the straight line Q of the threshold value is determined (i.e., a temperature T3 and the voltage Vb are determined).

In this way, when the diode 23 is not subjected to initial measurement, the threshold value Vb of the anode voltage set in consideration of variations in the characteristic of each diode 23 falls within a temperature range defined between the points A and B; namely, a temperature range of T2 to T3.

For this reason, depending on variations in the characteristic of the diode 23, a rise in the temperature of the head driver IC is detected even at a temperature T3 which is considerably lower than the upper limit temperature T2.

In contrast, when the anode voltage of the diode 23 is actually measured at room temperature T0, the thus-measured anode voltage is taken as a measured voltage V0. As shown in FIG. 10, a point C is plotted on a temperature-voltage graph. A straight line R is drawn from the point C so as to become parallel with the straight line P (having a negative gradient) which represents upper limits imposed on inclination variations and has a gentle gradient, thereby determining a point of intersection D (a temperature T2, a voltage Vc) between the straight line R and the upper limit temperature T2.

At this tim