JP5029297B2 - Temperature detection device and recording device - Google Patents

Description

  The present invention relates to a temperature detection device that detects the temperature of an object to be detected, and a recording device including the same.

  There is an ink jet printer that prints an image on a recording sheet by ejecting ink droplets onto the recording sheet that is a recording medium. As such an ink jet printer, a recording head having a nozzle that discharges ink droplets and a flow path unit in which a pressure chamber communicating with the nozzle is formed, an actuator that applies discharge energy to ink in the pressure chamber, and an actuator are provided. One having a driver IC that generates a pulse for driving is known. The actuator applies discharge energy to the pressure chamber by changing the volume of the pressure chamber. This actuator is driven when a pulsed drive signal is applied from the driver IC.

  In such an ink jet printer, the speed of printing is increased by increasing the pulse frequency of the drive signal output from the driver IC to shorten the ink droplet ejection cycle. However, when the pulse frequency of the drive signal is increased, the amount of heat generated by the driver IC increases. A technique is known in which when the driver IC becomes a predetermined temperature or higher, the driving of the driver IC is stopped until the driver IC is cooled, and the temperature of the driver IC is prevented from becoming too high (Patent Literature). 1). Thereby, thermal destruction of the driver IC can be prevented. Furthermore, in order to detect the temperature of the driver IC, a diode whose output voltage changes according to the temperature and a comparator that detects that the output voltage from the diode matches the reference voltage (reference voltage) corresponding to the detected temperature are provided. A temperature detection circuit is known (see, for example, Patent Document 2). According to this technique, when the comparator detects that the output voltage from the diode matches the reference voltage, it can detect that the temperature of the driver IC is the detected temperature. In addition, a technique of outputting a reference voltage as a sawtooth wave or a triangular wave and sweeping it has been known. By applying this, the temperature of the driver IC can be detected in a wide range.

Japanese Patent Laying-Open No. 2005-22294 (FIG. 4) JP2003-075264 (FIG. 2)

  According to the above-described technique, the temperature of the driver IC is detected only when the driver IC reaches the detection temperature. Therefore, it is necessary to set the detection temperature low in anticipation of a sudden rise in the temperature of the driver IC. . In this case, the driving efficiency is lowered because the driver IC is driven in a low temperature range. In this case, it is known to use a D / A converter as a circuit for changing the reference voltage, but the cost increases. Therefore, a technique using a circuit that outputs a PWM signal, a smoothing circuit that generates a reference voltage by smoothing the PWM signal, and a circuit that performs pulse width modulation on the PWM signal is known. According to this, the reference voltage can be changed with an inexpensive circuit configuration. However, in order to generate a stable reference voltage with little ripple in order to increase the accuracy of temperature detection, the time constant of the smoothing circuit must be made sufficiently large. As described above, when the time constant of the smoothing circuit is increased, the phase delay of the reference voltage is increased, so that the temperature detection response is lowered.

  An object of the present invention is to provide a temperature detection apparatus and a recording apparatus that have high temperature detection responsiveness while suppressing a decrease in temperature detection accuracy.

  The temperature detection device of the present invention includes a temperature sensor that outputs an output signal whose voltage changes with a change in temperature of the detection object, a reference signal generation circuit that generates a reference signal associated with the temperature of the detection object, A voltage storage circuit that stores a first voltage and a second voltage that define a range in which the voltage of the reference signal changes, and a determination circuit that determines whether the voltage of the reference signal matches the voltage of the output signal And a control circuit that controls the reference signal generation circuit so that the voltage of the reference signal changes from the first voltage stored in the voltage storage circuit to the second voltage. The reference signal generation circuit generates a pulse signal having a predetermined period, and the pulse signal generated within a sampling period composed of a plurality of the predetermined periods is a total time for which the pulse signal is maintained at a high level. A pulse signal generation circuit which is the same in any of the predetermined cycles and has two or more types of patterns of periods maintained at a high level within the predetermined cycle, and the pulse signal generated by the pulse signal generation circuit And a smoothing circuit that performs smoothing and outputs as a reference signal. The control circuit changes the voltage of the reference signal from the first voltage by changing, with the sampling period as a unit, a total time during which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period. When the determination circuit determines that the voltage of the reference signal and the voltage of the output signal match, the detection is performed based on the voltage of the reference signal when the voltages match. Detect the temperature of the object.

  In another aspect, the temperature detection device of the present invention includes a temperature sensor that changes a level of an output signal in accordance with a temperature change of a detection target, a reference signal generation circuit that generates a reference signal whose level can be changed, A level storage unit that rewriteably stores a first signal level and a second signal level that define a range in which the level of the reference signal changes, and the first signal in which the level of the reference signal is stored in the level storage unit A control unit that controls the reference signal generation circuit so as to change from a level to the second signal level; and a comparison circuit that compares the level of the reference signal with the level of the output signal. The reference signal generation circuit generates a pulse signal having a predetermined period, and the pulse signal generated within a sampling period composed of a plurality of the predetermined periods is a total time for which the pulse signal is maintained at a high level. A pulse signal generation unit that is the same in any of the predetermined cycles and has two or more types of patterns of periods that are maintained at a high level within the predetermined cycle, and the pulse signal generated by the pulse signal generation circuit And a smoothing circuit that performs smoothing and outputs as a reference signal. The control unit is configured to change a voltage of the reference signal to the first signal level by changing a total time in which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined cycle in units of the sampling cycle. To the second signal level, and according to the comparison result of the comparison circuit, it is determined that the level of the reference signal has reached the level of the output signal, and the level of the reference signal is the level of the output signal. When the level is reached, a signal corresponding to the level of the reference signal generated by the reference signal generation circuit is generated as a detected temperature signal representing the current temperature of the detection target.

The recording apparatus of the present invention is associated with a recording head that records an image on a recording medium, a temperature sensor that outputs an output signal whose voltage changes with a temperature change of the recording head, and a temperature of the recording head. A reference signal generation circuit for generating a reference signal, a voltage storage circuit for storing a first voltage and a second voltage that define a range in which the voltage of the reference signal changes, a voltage of the reference signal, and a voltage of the output signal And a reference circuit for controlling the reference signal generation circuit so that the voltage of the reference signal changes from the first voltage stored in the voltage storage circuit to the second voltage. And a control circuit. The reference signal generation circuit generates a pulse signal having a predetermined period, and the pulse signal generated within a sampling period composed of a plurality of the predetermined periods is a total time for which the pulse signal is maintained at a high level. A pulse signal generation circuit which is the same in any of the predetermined cycles and has two or more types of patterns of periods maintained at a high level within the predetermined cycle, and the pulse signal generated by the pulse signal generation circuit And a smoothing circuit that performs smoothing and outputs as a reference signal. The control circuit changes the voltage of the reference signal from the first voltage by changing, with the sampling period as a unit, a total time during which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period. When the determination circuit determines that the voltage of the reference signal and the voltage of the output signal match, the recording signal is changed based on the voltage of the reference signal when the voltage matches. Detect the head temperature.

In another aspect, the recording apparatus of the present invention includes a recording head that records an image on a recording medium, a temperature sensor that changes a level of an output signal in accordance with a temperature change of the recording head, and a reference whose level can be changed. A reference signal generation circuit for generating a signal, a level storage unit that rewriteably stores a first signal level and a second signal level that define a range in which the level of the reference signal changes, and a level of the reference signal, A control unit that controls the reference signal generation circuit so as to change from the first signal level stored in the level storage unit to the second signal level, and compares the level of the reference signal and the level of the output signal And a comparison circuit. The reference signal generation circuit generates a pulse signal having a predetermined period, and the pulse signal generated within a sampling period composed of a plurality of the predetermined periods is a total time for which the pulse signal is maintained at a high level. A pulse signal generation unit that is the same in any of the predetermined cycles and has two or more types of patterns of periods that are maintained at a high level within the predetermined cycle, and the pulse signal generated by the pulse signal generation circuit And a smoothing circuit that performs smoothing and outputs as a reference signal. The control unit is configured to change a voltage of the reference signal to the first signal level by changing a total time in which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined cycle in units of the sampling cycle. To the second signal level, and according to the comparison result of the comparison circuit, it is determined that the level of the reference signal has reached the level of the output signal, and the level of the reference signal is the level of the output signal. When the level is reached, a signal corresponding to the level of the reference signal generated by the reference signal generation circuit is generated as a detected temperature signal indicating the current temperature of the recording head .

According to these aspects of the present invention, the pulse signal generation circuit generates a pulse signal having two or more types of patterns of periods that are maintained at a high level within the predetermined period, so that the spectrum of the pulse signal is dispersed in a plurality. At this time, by optimizing the smoothing circuit according to the pulse period corresponding to the spectrum dispersed in a higher frequency band, the time constant of the smoothing circuit can be reduced while suppressing the generation of ripples. Thereby, the phase delay of the reference signal is suppressed, and the responsiveness of the temperature detection can be increased while suppressing the accuracy of the temperature detection from being lowered.
The actually generated pulse signal is a combined wave of a direct current component and an alternating current component. Among these, the AC component has a spectrum composed of its harmonics in addition to the fundamental wave. Here, even if the duty in the two predetermined cycles is the same, there is a difference in spectrum between the case where there is only one high level in the predetermined cycle and the case where there are multiple high levels in the predetermined cycle. In the latter case, the harmonic component tends to increase. Since the smoothing circuit is a kind of low-pass filter, ripples are further suppressed in the signal obtained by smoothing the latter.

  The pulse signal generation circuit may generate a pulse signal in which one pulse is randomly arranged within the predetermined period. According to this, since the spectrum of the pulse signal generated by the pulse signal generation circuit is uniformly distributed in a predetermined range, it is possible to suppress a partial increase in the ripple of the reference signal.

  The pulse signal generation circuit may generate a pulse signal in which a plurality of pulses are randomly arranged within the predetermined period. According to this, the spectrum of the pulse signal generated by the pulse signal generation circuit can be surely shifted to the high frequency band, so that the time constant of the smoothing circuit can be further reduced while suppressing the generation of ripple of the reference signal. it can.

  The pulse signal generation circuit includes a random number generation circuit that generates a random number, and the pulse signal generation circuit determines a position of one or a plurality of pulses within the predetermined period based on an output of the random number generation circuit. May be. According to this, the pulse signal generation circuit can be simplified.

  In the recording apparatus of the present invention, a determination unit that determines that the current temperature of the recording head represented by the detected temperature signal has reached a predetermined upper limit temperature, and the current temperature of the recording head is: When it is determined that a predetermined upper limit temperature has been reached, the recording head may further include a stop unit that stops the recording operation of the recording head after the recording process of one recording medium by the recording head is completed. As a result, paper is not wasted. In addition, printing can be reliably performed without losing image data being printed.

The pulse signal generation unit generates a signal representing a high / low pattern in which a plurality of high level periods corresponding to the high level of the pulse signal are randomly arranged within the predetermined period; and the random number A random number storage unit for temporarily storing the signal generated by the generation unit;
A high-low comparison circuit that compares the code of the last part of the signal stored in the random number storage unit with the code of the head part of the signal newly generated by the random number generation unit; and the code of the last part and the head When the high / low comparison circuit determines that both of the codes of the portions are at a high level, the random number generator may newly generate a signal representing the high / low pattern. As a result, ripples included in the obtained reference signal are further suppressed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a side view of a recording apparatus der Louis inkjet printer comprising a temperature detection device according to an embodiment of the present invention. As shown in FIG. 1, an ink jet printer 101 as a recording apparatus is a color ink jet printer having four ink jet heads 1, that is, recording heads. The inkjet printer 101 has a control device 16 that controls the operation of the entire inkjet printer 101. Further, the ink jet printer 101 includes a paper feeding unit 11 on the left side in the drawing and a paper discharge tray 12 on the right side in the drawing.

  Inside the ink jet printer 101, a paper transport path is formed through which the paper P, which is a recording medium, is transported from the paper supply unit 11 toward the paper discharge tray 12. The paper feed unit 11 includes a paper stocker 11a and a pickup roller 11c. The paper stocker 11a accommodates a large number of papers P therein, and is arranged in a state in which an opening portion opened upward is inclined rightward in the drawing. A support plate 11b urged from the bottom of the paper stocker 11a toward the opening is disposed in the paper stocker 11a, and a number of sheets P are stacked on the support plate 11b. The pickup roller 11c is driven by a placement motor 11d (see FIG. 3) to pick up the stacked paper P one by one from the top and send the picked up paper P downstream. A paper detection sensor 59 is disposed immediately downstream of the paper supply unit 11. The paper detection sensor 59 is for detecting whether or not the paper P sent out by the pickup roller 11c has reached the print standby position A located immediately upstream of the transport belt 8, and the paper in the print standby position A. It is adjusted so that the tip of P can be detected. The paper P sent out from the paper stocker 11 a by the pickup roller 11 c passes the print standby position A and is placed on the outer peripheral surface 8 a of the transport belt 8.

  A transport device 13 is provided at an intermediate portion of the paper transport path. The transport device 13 includes two belt rollers 6 and 7, an endless transport belt 8 wound around the rollers 6 and 7, and a transport motor 19 that rotates the belt roller 6 (see FIG. 3) and the surface of the conveyor belt 8 including the platen 15 disposed in the region surrounded by the conveyor belt 8 is adhesive. The platen 15 supports the conveyance belt 8 so that the conveyance belt 8 does not bend downward at a position facing the inkjet head 1. A nip roller 4 is disposed at a position facing the belt roller 7. The nip roller 4 presses the paper P against the outer peripheral surface 8 a when the paper P is placed on the outer peripheral surface 8 a of the transport belt 8. When the conveyance motor 19 rotates the belt roller 6, the conveyance belt 8 is driven. The conveyor belt 8 has a weakly adhesive silicone resin layer on its surface. As a result, the transport belt 8 transports the paper P toward the paper discharge tray 12 while holding the adhesive P.

  As shown in FIG. 1, a peeling mechanism 14 is provided immediately downstream of the conveyor belt 8. The peeling mechanism 14 is configured to peel the paper P adhered to the outer peripheral surface 8a of the transport belt 8 from the outer peripheral surface 8a and guide the paper P toward the right discharge tray 12 in the drawing.

  The four inkjet heads 1 are arranged and fixed in order along the transport direction of the paper P corresponding to four colors of ink (magenta (M), yellow (Y), cyan (C), and black (K)). Has been. That is, the ink jet printer 101 is a line printer. Each of the four inkjet heads 1 has a head body 2 at the lower end thereof. The head main body 2 has an elongated rectangular parallelepiped shape that is long in a direction orthogonal to the transport direction. Further, the bottom surface of the head body 2 is an ink ejection surface 2 a that faces the outer peripheral surface 8 a of the transport belt 8.

  When the paper P transported by the transport belt 8 sequentially passes immediately below the four head bodies 2, ink droplets of each color are ejected from the ink ejection surface 2a toward the upper surface of the paper P, that is, the printing region. Thereby, a desired color image can be formed in the print area of the paper P. The above-described operations such as paper feeding, image formation, and paper ejection are smoothly performed in synchronization with each other by a control device 16 described later.

  Next, the inkjet head 1 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view taken along the width direction of the inkjet head 1. As shown in FIG. 2, the ink jet head 1 includes a flow path member having a flow path formed therein, an electrical member that discharges ink from the flow path member, and a cover member that protects the electrical member. The flow path member includes a head main body 2 including the flow path unit 9 and the actuator unit 21, and a reservoir unit 71 disposed on the upper surface of the head main body 2. The reservoir unit 71 temporarily stores ink and supplies the stored ink to the head body 2. The electrical component includes a COF (Chip On Film) 50 on which the driver IC 52 is mounted, and a substrate 54 electrically connected to the COF 50. One end of the COF 50 is connected to the actuator unit 21, and a drive signal generated by the driver IC 52 is supplied to the actuator unit 21. The cover member includes a side cover 53 and a head cover 55. The cover member accommodates the electrical component and prevents intrusion of ink mist from the outside.

  In the head body 2, as shown in FIG. 2, the actuator unit 21 is fixed to the upper surface of the flow path unit 9. The flow path unit 9 has a laminated structure in which metal plates 122 to 130 are laminated, and an ink ejection surface 2a in which a large number of nozzles that eject ink droplets are opened is formed on the lower surface. Also, inside the flow path unit 9, there are formed a common ink flow path (not shown) to which ink is supplied and a large number of individual ink flow paths from the common ink flow path to the nozzles via the pressure chambers.

  The actuator unit 21 includes a plurality of actuators corresponding to the pressure chambers of the flow path unit 9 and selectively applies ejection energy to the ink in the pressure chamber. In this embodiment, the actuator unit 21 is a piezoelectric actuator that is formed of a ferroelectric lead zirconate titanate (PZT) ceramic material and has a piezoelectric sheet (piezoelectric layer). The piezoelectric sheet is sandwiched between an individual electrode facing the pressure chamber and a common electrode. The common electrode is equally grounded in the region corresponding to all the pressure chambers. On the other hand, the individual electrode is electrically connected to each terminal of the driver IC 52 via the internal wiring of the COF 50, and a drive signal from the driver IC 52 is selectively inputted.

  That is, in the actuator unit 21, the portion sandwiched between the individual electrodes and the pressure chambers functions as individual actuators, and a plurality of actuators corresponding to the number of pressure chambers are built. When a drive signal is input to the individual electrode, a region corresponding to the individual electrode of the actuator unit 21 is displaced convexly toward the inside of the pressure chamber. Thereby, pressure, that is, ejection energy is applied to the ink in the pressure chamber, and a pressure wave is generated in the pressure chamber. Then, the generated pressure wave propagates from the pressure chamber to the nozzle, whereby an ink droplet is ejected from the nozzle.

  The reservoir unit 71 is formed by stacking four metal plates 91 to 94 while being aligned with each other, and an ink channel including an ink reservoir 61 and an ink outflow channel 62 therein. Is formed. Further, the reservoir unit 71 communicates with the ink flow path in the flow path unit 9 on its lower surface. Both units 71 and 9 are joined by an adhesive and are also thermally coupled. The ink reservoir 61 temporarily stores ink supplied from an ink tank (not shown). The ink stored in the ink reservoir 61 is supplied to the common ink channel of the channel unit 9 via the ink outflow channel 62.

  At one end of the COF 50, the internal wiring of the COF 50 is electrically connected to an electrode formed on the upper surface of the actuator unit 21. The COF 50 is drawn upward from the upper surface of the actuator unit 21 so as to pass between the side cover 53 and the reservoir unit 71, and the other end is connected to the substrate 54 via the connector 54a. The board 54 relays a signal from the control device 16 to the COF 50.

  The driver IC 52 outputs a drive signal to the actuator unit 21 via the wiring of the COF 50, and a temperature signal generation circuit 40 (for detecting the temperature of the driver IC 52 (substantially equivalent to the temperature of the inkjet head 1)). 3). Further, the driver IC 52 is urged toward the side cover 53 by a sponge 79 attached to the side surface of the reservoir unit 71. The driver IC 52 is thermally coupled to the side cover 53 by being in close contact with the inner surface of the side cover 53 via the heat dissipation sheet 80.

  The side cover 53 is a metal plate member, and extends upward from the vicinity of both end portions in the width direction on the upper surface of the flow path unit 9. The lower end of the side cover 53 is engaged with a groove formed in the flow path unit 9, and the side cover 53 and the flow path unit 9 are thermally coupled. As described above, the driver IC 52 and the side cover 53 are thermally coupled, and the reservoir unit 71 and the flow path unit 9 are thermally coupled. The unit 9 and the reservoir unit 71 are all thermally coupled. Thereby, the heat from the driver IC 52 is radiated to the outside through the side cover 53, the flow path unit 9 and the reservoir unit 71.

  The head cover 55 is attached above the two side covers 53 so as to seal the space above the reservoir unit 71. Further, both ends of the head cover 55 in the longitudinal direction are bent so as to be disposed between the side covers 53. As described above, the reservoir unit 71, the COF 50, and the substrate 54 are disposed in the space surrounded by the two side covers 53 and the head cover 55. A sealing member 56 made of a silicon resin material or the like is applied to a connection portion between the side cover 53 and the flow path unit 9 and a fitting portion between the side cover 53 and the head cover 55. This more reliably prevents the intrusion of ink mist from the outside.

  Next, the control device 16 will be described in detail with reference to FIG. FIG. 3 is a block diagram of the control device 16. As shown in FIG. 3, the control device 16 includes a print data storage unit 63, a driver IC drive unit 64, a temperature detection circuit 65, a stop unit 66, a restart unit 67, a transport motor control unit 68, And a position control unit 69.

  The print data storage unit 63 stores print data transferred from a host device (not shown) such as a host computer. The print data includes the number of sheets P to be printed continuously and image data relating to images to be printed on each sheet P.

  The temperature detection circuit 65 detects the temperature T of the driver IC 52 based on the temperature detection signal output from the temperature signal generation circuit 40 of each driver IC 52.

  The driver IC drive unit 64 drives the driver IC 52 of each inkjet head 1 based on the print data stored in the print data storage unit 63 so that an image to be printed is formed on the paper P. In the present embodiment, the driver IC drive unit 64 drives the driver IC 52 by using a printing process for forming an image on one sheet of paper P as one drive unit.

  In order to prevent thermal destruction of the driver IC 52, the stop unit 66 relates to one drive unit in the driver IC 52 when the temperature detection circuit 65 detects a temperature T equal to or higher than a predetermined upper limit temperature Toff (for example, 120 ° C.). The driving of the driver IC 52 by the driver IC driving unit 64 is stopped in a state where the driving is completed, that is, in a state where the printing process for the paper P is completed. As a result, the paper P is not wasted, and there is no possibility of losing image data being printed. Here, the upper limit temperature Toff is set to a temperature lower than a temperature at which the thermal destruction of the driver IC 52 occurs.

  The restarting unit 67 is configured such that the temperature T of the driver IC 52 detected by the temperature detection circuit 65 after the stop unit 66 stops driving the driver IC 52 by the driver IC driving unit 64 is a predetermined restart temperature Ton (for example, 80 ° C. ) When it becomes the following, the driving of the driver IC 52 by the driving unit 64 is resumed.

  The transport motor control unit 68 controls the transport motor 19 to cause the transport belt 8 to travel so that the paper P is transported at a speed corresponding to a predetermined printing cycle. Here, the printing cycle is an ejection cycle when ink droplets are ejected from the nozzles. In other words, the paper P is transported by the transport device 13 by a unit distance corresponding to the print resolution of the image printed on the paper P. This is the time required to be transported.

  The placement control unit 69 controls the drive of the pickup roller 11c by controlling the placement motor 11d. The placement control unit 69 determines from the detection result of the paper detection sensor 59 whether or not the leading edge of the paper P sent out by the pickup roller 11c has reached the print standby position A, and the paper P has reached the print standby position A. Then, the driving of the pickup roller 11c is temporarily stopped. At this time, when the driving of the driver IC 52 is stopped by the stop unit 66, the placement control unit 69 waits the sheet P at the print standby position A as it is. The standby of the paper P is continued until the resuming unit 67 determines that the driving of the driver IC 52 can be resumed.

  Next, the temperature signal generation circuit 40 and the temperature detection circuit 65 will be described in detail with reference to FIG. FIG. 4 is a block diagram of the temperature signal generation circuit 40 and the temperature detection circuit 65 constituting the temperature detection device of the present embodiment.

  As shown in FIG. 4, the temperature signal generation circuit 40 includes a temperature sensor 44, a comparator 45 that is a determination circuit and a comparison circuit, and an amplification circuit 46. The temperature sensor 44 will be described with reference to FIG. FIG. 5 is a graph showing the temperature characteristics of the voltage output from the temperature sensor 44. The temperature sensor 44 is provided in a part of the semiconductor constituting the driver IC 52. The energy gap or energy barrier of a semiconductor varies with temperature and decreases with increasing temperature. The temperature sensor 44 utilizes such semiconductor characteristics and outputs a voltage corresponding to an energy gap or an energy barrier. As shown in FIG. 5, the temperature characteristic of the temperature sensor 44 exhibits good linearity in a relatively wide range. The voltage Voff is output for the upper limit temperature Toff, and the voltage Von is output for the restart temperature Ton.

  The comparator 45 compares the output voltage from the temperature sensor 44 with the reference voltage, which is a reference signal from the temperature detection circuit 65, and when they match, that is, the reference voltage level becomes the output voltage level. When it reaches, it outputs a temperature detection signal. The temperature detection signal is a signal having temperature information of the driver IC 52 and the ink jet head 1, more specifically, a signal indicating the detection timing of the temperature. The amplifier circuit 46 amplifies the temperature detection signal output from the comparator 45. The temperature detection signal amplified by the amplifier circuit 46 is output to the PWM controller 42 of the temperature detection circuit 65. As will be described later, the reference voltage is swept so as to increase stepwise in the range from the lowest reference voltage V1 corresponding to the highest temperature Tmax of the detected temperature range to the highest reference voltage V2 corresponding to the lowest temperature Tmin. The The reference voltage is swept repeatedly with a variable sweep cycle (see FIG. 9). The temperature detection signal is a signal indicating the timing at which the temperature of the driver IC 52 is detected within this sweep cycle, and is a pulse signal that switches from a low level to a high level at this timing. FIG. 9 shows an example in which the duty of a reference voltage obtained by smoothing a PWM signal described later is stepped up every 10% in order to make it easy to understand the change in the reference voltage within the sweep cycle. The temperature range to be swept includes the upper limit temperature Toff and the restart temperature Ton.

Next, the temperature detection circuit 65 will be described with reference to FIGS. The temperature detection circuit 65 generates a reference voltage and outputs it to the temperature signal generation circuit 40, detects the temperature T of the driver IC 52 when the temperature detection signal is output from the temperature signal generation circuit 40, and outputs the detection result. Output as detected temperature signal. As shown in FIG. 4, the temperature detection circuit 65, a pulse signal Ru generator or pulse signal generator der a P WM signal generating circuit 41, a PWM controller 42, and a smoothing circuit 43.

  The PWM signal generation circuit 41 generates a PWM (Pulse Width Modulation) signal having only one pulse within a predetermined PWM period. FIG. 6 is a diagram showing the relationship between the PWM signal output from the PWM signal generation circuit 41 and the reference voltage (Vref) obtained by smoothing the PWM signal. FIG. 6 shows an example in which the pulse width, that is, the duty is 100%, 50%, 25%, and 10%. The PWM signal generation circuit 41 generates a PWM signal whose pulse high level position is random within each PWM period. As a result, the PWM signal generated by the PWM signal generation circuit 41 becomes a signal having a plurality of types of patterns of periods maintained at a high level within the PWM cycle. If the duty is the same, the pulse width of each pulse, that is, the period during which the high level is maintained is the same. The PWM signal generated by the PWM signal generation circuit 41 is output to the smoothing circuit 43.

  The PWM controller 42 performs pulse width modulation of the PWM signal generated by the PWM signal generation circuit 41 and detects the temperature T of the driver IC 52. The temperature of the driver IC 52 is determined based on the pulse width of the PWM signal at the timing when the temperature detection signal from the temperature signal generation circuit 40 switches from the low level to the high level. The detected temperature T is output as a detected temperature signal (see FIG. 7).

  The smoothing circuit 43 is a CR integration circuit composed of a resistor R1 and a capacitor C1, and smoothes the PWM signal generated by the PWM signal generation circuit 41. The values of the resistor R1 and the capacitor C1, that is, the time constant (CR) of the smoothing circuit 43 are smoothed so that the ripple after smoothing becomes smaller than a predetermined allowable conversion error in a range sufficiently shorter than the PWM cycle. Is determined to be smaller than a predetermined allowable response delay allowed in the system. The signal smoothed by the smoothing circuit 43 is output to the comparator 45 of the temperature signal generation circuit 40 as a reference voltage. In other words, the PWM signal generation circuit and the smoothing circuit 43 constitute a reference signal generation circuit.

  When the PWM controller 42 performs pulse width modulation of the PWM signal, the reference voltage changes as shown in FIG. The PWM signal is a pulse train including a plurality of pulses having the same pulse width. The subsequent period of a plurality of pulses having the same pulse width corresponds to the duration of one step in the reference voltage shown in FIG. 9, that is, the sampling period. In the present embodiment, the number of pulses is the same in any sampling period. There are a plurality of types of pulse intervals within the sampling period. Each time one sampling period ends, the pulse width of the pulses sequentially output from the PWM signal generation circuit 41 is changed, that is, gradually increased or decreased. As a result, the reference voltage changes stepwise within a predetermined voltage range. When the reference voltage finishes changing from the upper limit to the lower limit or from the lower limit to the upper limit of the voltage range corresponding to the detected temperature range, one sweep operation (the time required for this is referred to as “one sweep cycle”) is completed.

  Next, the PWM signal generation circuit 41 and the PWM controller 42 will be described with further reference to FIGS. FIG. 7 is a block diagram of the PWM signal generation circuit 41 and the PWM controller 42. FIG. 8 is a diagram for explaining a PWM signal generated by the PWM signal generation circuit 41. FIG. 9 is a diagram showing the relationship between the reference voltage from the temperature detection circuit 65 and the output voltage from the temperature sensor 44.

  As shown in FIG. 7, the PWM signal generation circuit 41 includes a PWM clock generation circuit 81 and a PWM counter 82. The PWM clock generation circuit 81 is a circuit that generates a reference clock of the PWM signal generated by the PWM signal generation circuit 41, that is, a PWM clock. The reference clock generated by the PWM clock generation circuit 81 is output to the PWM counter 82 and the repeat counter 84 of the PWM controller 42. In this embodiment, the PWM clock generation circuit 81 generates a maximum of 4096 reference clocks every PWM cycle.

  The PWM counter 82 generates one pulse that is High (high level) for a time corresponding to the number of control clocks to be described later output from the sweep counter 83 in each PWM cycle.

  The PWM counter 82 has a random pattern storage unit 82a. The random pattern storage unit 82a includes a random number generation circuit 182 and a storage circuit 183 that is a random number storage unit that temporarily stores the output thereof. Furthermore, the random pattern storage unit 82 a also includes a high / low comparison circuit 184 that compares information stored in the storage circuit 183 with the output of the random number generation circuit 182. The random number generation circuit 182 generates a high-low (HL) pattern for one pulse of the PWM signal corresponding to the number of control clocks (corresponding to the duty of the PWM signal) output from the sweep counter 83. The storage circuit 183 stores the HL pattern generated by the random number generation circuit 182 just before 1 PWM period.

  As shown in FIG. 8, the PWM signal is a signal in which periods of high level are randomly arranged in each PWM cycle. The random pattern is composed of pulses for a plurality of PWM periods that form one sampling period. In the drawing, a code indicating a high level period is represented by “H”, and a code indicating a low level period is represented by “L”. In each random pattern, each pulse included in the PWM signal is continuously at a high level by the number of control clocks. FIG. 8 shows a part of the random pattern of the PWM signal when the duty is 20%. FIG. 8 shows a random pattern in which one PWM cycle is composed of 10 reference blocks and two consecutive reference blocks are at a high level. In this embodiment, the period of one reference block corresponds to about 409 control pulses (duty 10%).

  The random number generation circuit 453a of the random pattern storage unit 453 generates an HL pattern signal in which high-level periods are randomly arranged corresponding to the number of control clocks. The HL pattern signal is generated every PWM cycle, and the PWM counter 452 generates a PWM signal having a plurality of pulse intervals.

  The memory circuit 453b stores the previous HL pattern signal. The high / low comparison circuit 453c compares the code of the last block of the previous PWM cycle with the code of the first block of the current PWM cycle with respect to the HL pattern signal. If it is determined that both are high, the random number generation circuit generates the HL pattern again. This regeneration of the HL pattern is repeated until the high / low comparison circuit 453c determines that the codes do not match. As a result, the PWM counter 452 generates a PWM signal in which the high levels of adjacent PWM periods do not continue, so that the ripple of the reference voltage is suppressed. In each random pattern, except for the case where the duty is 100%, “H” does not continue between two adjacent PWM periods.

  The PWM controller 42 includes a sweep counter 83 which is a part of the control circuit or control unit, a repeat counter 84 which is a part of the control circuit or control unit and is a pulse number storage circuit, and a voltage storage circuit or level storage unit. Two temperature PWM duty conversion circuits 85 and 86, a comparator 87, a latch circuit 88 that is part of the control circuit or control unit, and a PWM duty temperature conversion circuit 89 that is part of the control circuit or control unit, It has a voltage rewriting circuit 90 which is a level rewriting unit. In the PWM controller 42, the external maximum temperature signal Smax is input to the temperature PWM duty conversion circuit 85, the minimum temperature signal Smin is input to the temperature PWM duty conversion circuit 86, and the repeat count signal Repeat is input to the repeat counter 84. Entered. Further, the temperature detection signal from the temperature signal generation circuit 40 is input to the latch circuit 88. Here, the maximum temperature signal Smax indicates the maximum temperature Tmax in the detection temperature range, and the minimum temperature signal Smin indicates the minimum temperature Tmin in the detection temperature range. The repeat number signal Repeat indicates the number of repetitions of the PWM period in one sampling period. That is, the upper limit and the lower limit of the detected temperature range are determined by the maximum temperature signal Smax and the minimum temperature signal Smin. By changing these, the sweep range of the reference voltage that is the detected temperature range can be arbitrarily changed. Further, the sampling period is determined by the repeat number signal Repeat, and the sweep time of the reference voltage, that is, the sweep period can be changed by changing the sampling period.

  The repeat counter 84 outputs an increment signal to the sweep counter 83 so that the reference voltage changes stepwise from the minimum reference voltage to the maximum reference voltage. This increment signal is output every sampling period. The sampling period is a time in which the PWM period is repeated by the number of repeats indicated by the input repeat number signal Repeat.

  Specifically, the repeat counter 84 stores the total number of PWM clocks output in each sampling period. The repeat counter 84 counts the number of PWM clocks generated by the PWM clock generation circuit 81. Here, when the stored total number of PWM clocks matches the count value, the repeat counter 84 outputs an increment signal to the sweep counter 83. That is, this increment signal is output at every sampling period based on the number of pulses from the PWM clock generation circuit 81.

  For example, when one sampling period is five times the PWM period, the PWM clock generation circuit 81 outputs 20480 (= 4096 × 5) PWM clocks to the repeat counter 84 every sampling period. . The repeat counter 84 outputs an increment signal when the total count of PWM clocks reaches 20480. The counter function of the repeat counter 84 is realized by a preset type down counter. Then, the borrow of the down counter, that is, the carry-down signal that is output when the count value becomes 0 is used as the increment signal.

  When the borrow signal is output, the number of repeats in the next sampling period is loaded into the repeat counter 84 from a storage unit (not shown) such as a ROM by a CPU (not shown) that is a part of the control circuit or control unit. In the present embodiment, the number of repeats is fixed. However, the number of repeats to be loaded may be changeable by the CPU. As a result, the length of the sampling period can be changed. The number of repeats may be changed according to the rate of change of the detected temperature. For example, when the rate of change is high, that is, when the temperature shows a sudden change, the number of repeats is reduced to shorten the sampling period. The rate of change is calculated by the CPU.

  The temperature PWM duty conversion circuits 85 and 86 determine the pulse width of the PWM signal corresponding to the temperature indicated by the temperature signal from the input temperature signals (Smax, Smin), and convert the pulse width into the number of the corresponding PWM clocks. Then, the obtained clock number is stored in a rewritable manner. Therefore, the temperature PWM duty conversion circuit 85 converts the input maximum temperature signal Smax into the minimum clock number (the value of the first voltage or the first signal level) indicating the pulse width of the PWM signal corresponding to the maximum temperature Tmax in the detected temperature range. Equivalent to) and store. Information on the minimum number of clocks stored in the temperature PWM duty conversion circuit 85 is output to the sweep counter 83. On the other hand, the temperature PWM duty conversion circuit 86 converts the input minimum temperature signal Smin into the maximum number of clocks (second voltage or second signal level value) indicating the pulse width of the PWM signal corresponding to the minimum temperature Tmin in the detected temperature range. Equivalent to) and store. Then, the information on the maximum number of clocks stored in the temperature PWM duty conversion circuit 86 is output to the comparator 87.

  Note that a rewrite signal from the voltage rewriting circuit 90 is input to the temperature PWM duty conversion circuits 85 and 86. The rewrite signal is a temperature signal indicating temperature, and when the rewrite signal is input, the temperature PWM duty conversion circuits 85 and 86 perform the same operation as when the temperature signal (Smax, Smin) is input.

  Here, a configuration in which the temperature PWM duty conversion circuits 85 and 86 convert the temperature signal into the pulse width of the PWM signal will be briefly described. From the linear temperature-voltage characteristic of the temperature sensor 44, the relationship between the detected temperature T and the output voltage V can be expressed as V = a−bT. “a” and “b” are constants, and when the maximum temperature Tmax is detected, the output voltage becomes V = 0 [v], and when the minimum temperature Tmin is detected, the output voltage becomes V = 3.3 [v]. For example, a = 1.341 and b = 0.422. V = 3.3 [v] is the output voltage of the logic element used in the PWM signal generation circuit 41 of the temperature detection circuit 65. The PWM signal having this voltage value is smoothed as a reference voltage, the output voltage V = 0 [v] corresponds to 0% duty of the PWM signal, and the output voltage V = 3.3 [v] becomes 100% duty. Equivalent to. In the present embodiment, an arbitrary voltage v between 0 and 3.3 [v] is expressed as 3.3 × D (duty) and depends on the duty. Furthermore, when the number of PWM clocks corresponding to the voltage v is n, there is a relationship of D = n / 4096, so 3.3 × n / 4096 = a−bT. By arranging this, a relationship of n = c−dT (where c and d are constants) is obtained.

  Each of the temperature PWM duty conversion circuits 85 and 86 includes a pulse number calculation circuit 200 including an addition circuit 202, a subtraction circuit 204, and a multiplication circuit 206 as shown in FIG. The multiplication circuit 206 receives a T value (actually, a temperature signal S corresponding to the T value) and a d value. The output from the multiplication circuit 206 is inverted in sign by the subtraction circuit 204 and input to the addition circuit 202. The adder circuit 202 receives the c value and obtains an n value, that is, the number of clocks indicating the pulse width of the PWM signal. The number of clocks is temporarily stored in storage means (for example, a latch circuit) (not shown) of the temperature PWM duty conversion circuits 85 and 86. The obtained clock number is stored as the aforementioned minimum clock number in the temperature PWM duty conversion circuit 85 to which the maximum temperature signal Smax is inputted, and is stored as the maximum clock number in the temperature PWM duty conversion circuit 86.

  In the present embodiment, every time one sampling period elapses, the PWM controller 42 increases the pulse width of the PWM signal by a certain width, and the PWM signal generation circuit 41 and the smoothing circuit 43 sequentially increase the reference voltage correspondingly. .

  The sweep counter 83 derives the number of control clocks to be generated in accordance with the change rate of the reference voltage. The control clock is used to control the pulse width of the PWM signal output from the PWM signal generation circuit 41. The control clock is output from the sweep counter 83 to the comparator 76, the comparator 87, and the latch circuit 88 of the PWM signal generation circuit 41, respectively. In the sweep counter 83, the minimum number of clocks output from the temperature PWM duty conversion circuit 85 is set as the number of control clocks when the inkjet printer 101 is started and each time a load signal described later is output from the comparator 87, that is, every sweep cycle. Is loaded (LD) as an initial value. Thereafter, every time an increment signal is output from the repeat counter 84, the sweep counter 83 increments the number of control clocks according to the change rate of the reference voltage.

  The sweep counter 83 includes an increment calculation circuit that calculates the increment of the control clock number corresponding to the change rate of the reference voltage, that is, the new control clock number when the increment signal is input, based on the repeat number signal Repeat. Contains. At the time of start-up, a predetermined repeat number signal Repeat corresponding to a preset maximum temperature range is input.

  The comparator 87 determines the sweep cycle. Specifically, the comparator 87 outputs a load (LD) signal to the sweep counter 83 when the maximum number of clocks output from the temperature PWM duty conversion circuit 86 matches the number of control clocks output from the sweep counter 83. Is output. That is, the comparator 87 outputs a load signal when the number of control clocks output from the sweep counter 83 is incremented to the maximum number of clocks corresponding to the lowest temperature Tmin in the detected temperature range. At this time, one sweep is completed.

  Subsequently, in the sweep counter 83, the minimum number of clocks output from the temperature PWM duty conversion circuit 85 is loaded again into the sweep counter 83. As a result, the number of control clocks output from the sweep counter 83 is reset to the minimum number of clocks. Thereafter, the sweep counter 83 again increments the number of control clocks based on the increment signal from the repeat counter 84. For example, in the example of FIG. 9 in which the pulse width is increased by 10%, the number of control clocks is increased by about 409 (≈4096 × 0.1) for each increment operation.

  As a result, as shown in FIG. 9, the reference voltage output from the temperature detection circuit 65 is swept stepwise from the lowest voltage 0V to the highest voltage 3.3V. In other words, the reference voltage is swept within the range corresponding to the minimum temperature signal Smin from the maximum temperature signal Smax. In this way, by sweeping the reference voltage from a voltage corresponding to a high temperature, the temperature T can be quickly detected when the driver IC 52 is at a high temperature.

  The latch circuit 88 latches information on the number of control clocks output from the sweep counter 83 when a temperature detection signal is output from the temperature signal generation circuit 40 of the driver IC 52. Information on the number of latched control clocks is output to the PWM duty temperature conversion circuit 89. The PWM duty temperature conversion circuit 89 uses the information on the number of control clocks output from the latch circuit 88 as the temperature corresponding to the reference voltage generated by the PWM signal having the pulse width of the number of control clocks, that is, the temperature of the driver IC 52. Convert to T.

  A specific configuration of this conversion will be described based on the linearity of the temperature sensor 44 as in the case of the above-described case where the temperature signal is converted into the pulse width of the PWM signal. As described above, there is a relationship of n = c−dT between the number of PWM clocks n representing the pulse width of the PWM signal and the detected temperature T. From this, the relationship T = e−fn (where e and f are constants) is obtained. The PWM duty temperature conversion circuit 89 has a temperature calculation circuit having the same structure as the temperature PWM duty conversion circuits 85 and 86. The structure of this temperature calculation circuit is shown in FIG. As illustrated in FIG. 13, the temperature calculation circuit 300 includes an addition circuit 302, a subtraction circuit 304, and a multiplication circuit 306. The multiplication circuit 306 receives an n value (in this case, the number of output control clocks) and an f value. The output from the multiplication circuit 306 is inverted in sign by the subtraction circuit 304 and input to the addition circuit 302. When the e value is also input to the adder circuit 302, the T value, that is, the temperature of the driver IC 52 is obtained.

  The temperature T detected by the PWM duty temperature conversion circuit 89 is output to the voltage rewriting circuit 90 as a detected temperature signal. The detected temperature signal is output every time the temperature detection signal is output from the temperature signal generation circuit 40 of the driver IC 52. For example, in the example of FIG. 9, detected temperature signals indicating the detected temperatures 1 to 3 are sequentially output. The detected temperature signal is output to the stop unit 66 and the restart unit 67 in addition to the voltage rewriting circuit 90.

  The voltage rewriting circuit 90 that has received the detected temperature signal outputs a rewriting signal for changing the minimum clock number and the maximum clock number stored in at least one of the temperature PWM duty conversion circuits 85 and 86. To do. The rewrite signal is a signal obtained based on the detected temperature signal as described below.

  A storage means (for example, RAM) (not shown) stores a detected temperature that goes back a predetermined number of sweeps from the current time. The voltage rewriting circuit 90 predicts the temperature detected in the next sweep by linear approximation (for example, based on the moving average) using the detected temperatures for the predetermined number of sweeps. The voltage rewriting circuit 90 generates a rewriting signal based on the predicted temperature.

  For example, as shown in FIG. 9, when the detected temperature rises with time, the minimum temperature of the rewrite signal is sequentially changed to a higher temperature in accordance with this rise. The newly set minimum temperature Tmin may be set to a temperature that is 20-30% lower than the previously measured detected temperature. If the increment of the number of control clocks for each increment is not changed, the number of samplings during one sweep cycle is reduced. As a result, the time required for one sweep is shortened, and the detection speed of the head temperature, that is, the temperature of the driver IC 52 is improved. At this time, since the change rate of the reference voltage does not change, the resolution with respect to the detected temperature does not change.

  If the number of repeats is increased, the resolution at the time of sweeping is improved, but if the number of samplings is the same, the sweep time becomes longer. On the other hand, if the number of repeats is reduced, the resolution at the time of sweeping is lowered, but the sweep time is shortened even if the number of samplings is the same. Here, since the number of times of sampling is reduced, the sweep time does not become longer than necessary even if the resolution is emphasized with an increased number of repeats. If the detection time-oriented configuration with a reduced number of repeats, the detection time can be further shortened. This embodiment can be said to have a balanced configuration in which the resolution is maintained and the detection time is shortened.

  The voltage rewriting circuit 90 predicts the detected temperature in the next sweep period from one or a plurality of detected temperature signals traced back from the present, and sets the range where the predicted value is included with a margin as the minimum temperature and the maximum temperature of the next sweep. To do. As a result, the swept temperature range is narrowed. Then, a rewrite signal indicating a temperature at which at least one of the lowest temperature and the highest temperature is changed is generated.

  Thus, by grasping the detected temperature in time series, the temperature T detected in the next sweep can be predicted, and the corresponding detected temperature range can be narrowed down. That is, based on the detected temperature T, the new maximum temperature (corresponding to the minimum number of clocks stored in the temperature PWM duty conversion circuit 85) and the minimum temperature (maximum number of clocks stored in the temperature PWM duty conversion circuit 86). Is determined in accordance with the predicted value of the temperature T, the range in which the reference voltage is next swept can be narrowed.

  As described above, the voltage rewriting circuit 90 changes the temperature detection range based on the detection result of the head temperature by the temperature sensor 44. If the detection result shows an increasing tendency of the temperature, the minimum temperature that determines the detection range is sequentially changed to a higher value to narrow the detection range. As a result, the sweep cycle is shortened and the temperature detection time is also shortened. Thereby, the thermal damage of the driver IC 52 can be prevented in advance. On the other hand, the present invention can also be applied to a case where the detection result shows a downward trend in temperature. If the detection result is a decrease after the temperature has once increased, the minimum temperature may be changed to a lower value sequentially. If the temperature decreases from the time of start-up, the maximum temperature that determines the detection range is sequentially changed to a lower value. Generally, when the temperature is lowered, the viscosity of the ink is increased and the ejection characteristics are deteriorated. It can be detected that the head temperature reaches this Tlow in a short time when the lower limit temperature is Tlow in the temperature range showing the proper ejection characteristics. When this is detected, the CPU may issue a warning command to the user using a display means (not shown) and stop driving the driver IC 52.

  Next, the operation of the control device 16 will be described with reference to FIG. FIG. 10 is a flowchart showing the operation of the control device 16. As shown in FIG. 10, when printing is started, the process proceeds to step S <b> 101 (hereinafter referred to as S <b> 101, the same applies to other steps), and the placement control unit so that the paper P is arranged at the print standby position A. 69 drives the pickup roller 11c to prepare for printing. Thereafter, the process proceeds to S102, where the temperature detection circuit 65 detects the temperature T of the driver IC 52 of the inkjet head 1.

  Then, the process proceeds to S103, and when the temperature detection circuit 65 does not detect the temperature T equal to or higher than the upper limit temperature Toff (S103: NO), the process proceeds to S106. On the other hand, when the temperature detection circuit 65 detects the temperature T equal to or higher than the upper limit temperature Toff (S103: YES), the process proceeds to S104, where the stop unit 66 stops the driving of the driver IC 52 by the driving unit 64, and the conveyance motor is controlled. The unit 68 stops the conveyor belt 8. Then, the process proceeds to S105, and when the temperature detection circuit 65 does not detect the temperature T equal to or lower than the restart temperature Ton (S105: NO), the process waits until the temperature T equal to or lower than the restart temperature Ton is detected. When the driver IC 52 is naturally cooled and the temperature detection circuit 65 detects the temperature T equal to or lower than the restart temperature Ton (S105: YES), the process proceeds to S106.

  In S106, the printing process for the next sheet P is performed. At this time, when the driving of the driver IC 52 is stopped by the stopping unit 66, the resuming unit 67 restarts the driving of the driver IC 52. When performing the printing process, the placement control unit 69 drives the pickup roller 11c so that the paper P waiting at the print standby position A is placed on the outer peripheral surface 8a of the transport belt 8 at a predetermined timing. . When the printing process is completed, the process proceeds to S107, and it is determined whether or not all printing is completed. When the printing is not completed (S107: NO), the process proceeds to S101, and the above-described processing regarding the printing processing for the next paper P is repeated. When printing is completed (S107: YES), the processing of the flowchart shown in FIG. 10 is completed.

  As described above, according to the present embodiment described above, the PWM counter 82 of the PWM signal generation circuit 41 generates a PWM signal having a plurality of types of patterns of periods maintained at a high level within the PWM cycle. Is dispersed. By optimizing the smoothing circuit 43 according to the pulse period corresponding to the spectrum dispersed in a higher frequency band, the time constant of the smoothing circuit 43 can be reduced while suppressing the generation of ripples. Thereby, the phase lag of the reference voltage is suppressed, and the responsiveness of the temperature detection can be increased while suppressing the accuracy of the temperature detection from being lowered.

  In addition, since the PWM counter 82 generates a PWM signal with reference to the HL pattern generated by the random number generation circuit 182 of the random pattern storage unit 82a, the PWM counter 82 can have a simple configuration.

  In addition, except for the case where the duty is 100%, “H” does not continue between two adjacent PWM periods. As a result, the load on the power supply circuit is reduced and the influence of ripple is also reduced.

  Furthermore, since the PWM counter 82 generates a pulse in which one high level is randomly arranged for each PWM period, the spectrum of the PWM signal composed of this pulse is uniformly dispersed. Thereby, it is possible to suppress the ripple of the reference voltage from partially increasing.

  In the present embodiment, the PWM counter 82 is configured to generate a PWM signal in which one pulse is randomly arranged in each PWM cycle. However, as shown in FIG. A pulse in which two pulses are randomly arranged in a cycle may be generated. Further, the PWM counter 82 may store a pulse pattern (random pattern) that generates a pulse in which three or more pulses are randomly arranged in each PWM cycle in the random pattern storage unit 82a. In any case, it is preferable that the respective high levels do not continue between adjacent PWM periods as in the above-described embodiment. According to this, since the spectrum of the PWM signal generated by the PWM signal generation circuit can be reliably shifted to the high frequency side, the time constant of the smoothing circuit can be further reduced while suppressing the ripple of the reference voltage. Thereby, the responsiveness of temperature detection can be further increased.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. For example, in the above-described embodiment, the PWM counter 82 is configured to generate a PWM signal in which one pulse is randomly arranged in each PWM cycle, but the total time maintained at the high level is any PWM cycle. The PWM signal in which an arbitrary number of pulses are arranged in a range having at least two types of high-level period patterns in each PWM cycle may be used. Further, the temperature detection device of the present invention does not need to include a voltage rewriting circuit.

  Further, in the above-described embodiment, the PWM counter 82 is configured to generate a PWM signal with reference to the HL pattern generated by the random number generation circuit. However, the random counter storage unit 82a or a separately stored random number table is referred to. However, the PWM signal may be generated with another configuration such as a configuration in which the PWM signal is generated according to a pattern determined in real time.

  In the above-described embodiment, the reference voltage change rate is changed by changing the repeat count signal Repeat input to the repeat counter 84. However, even if the reference voltage change rate is fixed. Good.

  In addition, in the embodiment described above, the actuator unit 21 is a unimorph type actuator using a piezoelectric sheet, but may be another actuator that applies discharge energy to the pressure chamber.

  In the above-described embodiment, the present invention is applied to the ink jet printer 101, and the temperature detection circuit 65 is configured to detect the temperature T of the driver IC 52 of the ink jet head. However, for any other device that requires temperature detection, Therefore, the present invention is applicable.

1 is a side view of an inkjet printer according to an embodiment of the present invention. It is sectional drawing along the width direction of the inkjet head shown in FIG. It is a block diagram of the control apparatus shown in FIG. FIG. 4 is a block diagram of a temperature signal generation circuit and a temperature detection circuit shown in FIG. 3. It is a graph which shows the temperature characteristic of the voltage which the temperature sensor shown in FIG. 4 outputs. FIG. 5 is a diagram showing a relationship between a PWM signal output from the PWM signal generation circuit shown in FIG. 4 and a reference voltage. FIG. 5 is a block diagram of a PWM signal generation circuit and a PWM controller shown in FIG. 4. It is a figure for demonstrating the PWM signal which the PWM signal generation circuit shown in FIG. 3 produces | generates. It is the figure which showed the relationship between the reference voltage in the temperature signal generation circuit shown in FIG. 3, and the output voltage from a temperature sensor. It is a flowchart which shows operation | movement of the control apparatus shown in FIG. It is a figure for demonstrating the PWM signal which the modification of the PWM signal generation circuit shown in FIG. 3 produces | generates. FIG. 8 is a block diagram of a pulse number calculation circuit included in the temperature PWM duty conversion circuit shown in FIG. 7. FIG. 8 is a block diagram of a temperature calculation circuit included in the PWM duty temperature conversion circuit shown in FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 2 Head main body 16 Control apparatus 40 Temperature signal generation circuit 41 PWM signal generation circuit 42 PWM controller 43 Smoothing circuit 44 Temperature sensor 45 Comparator 46 Amplification circuit 63 Print data storage part 64 Driver IC drive part 65 Temperature detection circuit 66 Stop part 67 Restart unit 81 PWM clock generation circuit 82 PWM counter 82a Random pattern storage unit 83 Sweep counter 84 Repeat counters 85, 86 Temperature PWM duty conversion circuit 87 Comparator 88 Latch circuit 89 PWM duty temperature conversion circuit 101 Inkjet printer 52 Driver IC
C1 capacitor R1 resistance

Claims (15)

A temperature sensor that outputs an output signal whose voltage changes in accordance with the temperature change of the detection object;
A reference signal generation circuit for generating a reference signal associated with the temperature of the detection object;
A voltage storage circuit for storing a first voltage and a second voltage defining a range in which the voltage of the reference signal changes;
A determination circuit for determining whether or not the voltage of the reference signal and the voltage of the output signal match;
A control circuit that controls the reference signal generation circuit so that the voltage of the reference signal changes from the first voltage stored in the voltage storage circuit to the second voltage;
The reference signal generation circuit includes:
A pulse signal having a predetermined cycle is generated, and a pulse signal generated within a sampling cycle composed of a plurality of the predetermined cycles has the same total time maintained at a high level in any of the predetermined cycles. And a pulse signal generation circuit having two or more patterns in a period maintained at a high level within the predetermined period;
A smoothing circuit that smoothes the pulse signal generated by the pulse signal generation circuit and outputs it as a reference signal;
The control circuit includes:
The voltage of the reference signal is changed from the first voltage to the second voltage by changing the total time in which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period in units of the sampling period. And when the determination circuit determines that the voltage of the reference signal matches the voltage of the output signal, the temperature of the detection object is set based on the voltage of the reference signal when the voltage matches. A temperature detecting device characterized by detecting.   The temperature detection apparatus according to claim 1, wherein the pulse signal generation circuit generates a pulse signal in which one pulse is randomly arranged within the predetermined period.   The temperature detection device according to claim 1, wherein the pulse signal generation circuit generates a pulse signal in which a plurality of pulses are randomly arranged within the predetermined period. The pulse signal generation circuit includes a random number generation circuit for generating a random number;
The temperature detection device according to claim 2, wherein the pulse signal generation circuit determines a position of one or a plurality of pulses within the predetermined period based on an output of the random number generation circuit.   5. The temperature according to claim 1, further comprising a voltage rewriting circuit that rewrites at least one of the first voltage and the second voltage stored in the voltage storage circuit. Detection device. A temperature sensor in which the level of the output signal changes as the temperature of the object to be detected changes,
A reference signal generation circuit for generating a reference signal whose level can be changed;
A level storage unit that rewriteably stores a first signal level and a second signal level that define a range in which the level of the reference signal changes;
A control unit that controls the reference signal generation circuit so that the level of the reference signal changes from the first signal level stored in the level storage unit to the second signal level;
A comparison circuit for comparing the level of the reference signal and the level of the output signal;
The reference signal generation circuit includes:
A pulse signal having a predetermined cycle is generated, and a pulse signal generated within a sampling cycle composed of a plurality of the predetermined cycles has the same total time maintained at a high level in any of the predetermined cycles. And a pulse signal generator having two or more types of patterns in a period maintained at a high level within the predetermined period;
A smoothing circuit that smoothes the pulse signal generated by the pulse signal generation circuit and outputs it as a reference signal;
The control unit is
The voltage of the reference signal is changed from the first signal level to the second signal by changing the total time that the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period in units of the sampling period. When the level of the reference signal reaches the level of the output signal, it is determined that the level of the reference signal has reached the level of the output signal according to the comparison result of the comparison circuit. A temperature detection device that generates a signal corresponding to the level of the reference signal generated by the reference signal generation circuit as a detection temperature signal that represents a current temperature of the detection target. The control unit is
A sweep counter that counts the signal of the predetermined period;
A latch circuit that stores and holds the count content of the sweep counter when the level of the reference signal reaches the level of the output signal;
The sweep counter is loaded with the first signal level as an initial value, and when the counted content reaches the second signal level, the first signal level is loaded again as an initial value.
The temperature detection apparatus according to claim 6, wherein the control unit generates a signal corresponding to the stored contents of the latch circuit as the detected temperature signal. The temperature detection range from the first signal level to the second signal level is composed of a plurality of the sampling periods, and each sampling period is composed of a plurality of pulse width modulation periods each including a plurality of the predetermined periods,
The temperature detection device according to claim 7, wherein the sweep counter counts the signal of the predetermined period generated within the sampling period. The control unit includes a repeat counter that counts a clock having a constant repetition period shorter than the pulse width modulation period,
The repeat counter can store the number of the pulse width modulation periods constituting each sampling period, and the repeat counter can set a period corresponding to the stored number of the pulse width modulation periods according to the clock. 9. The temperature detecting device according to claim 8 , wherein when the count is counted, an increment signal is supplied to the sweep counter. The pulse signal generator is
A random number generator for generating a signal representing a high / low pattern in which a plurality of high level periods corresponding to the high level of the pulse signal are randomly arranged within the predetermined period;
A random number storage unit for temporarily storing the signal generated by the random number generation unit;
A high-low comparison circuit that compares the code of the last part of the signal stored in the random number storage unit with the code of the head part of the signal newly generated by the random number generation unit;
When the high / low comparison circuit determines that both the code of the final part and the code of the head part are at a high level, the random number generation unit further generates a signal representing the high / low pattern. The temperature detection apparatus in any one of Claims 6-9.   The temperature detection according to any one of claims 6 to 10, further comprising a level rewriting unit that rewrites at least one of the first signal level and the second signal level stored in the level storage unit. apparatus. A recording head for recording an image on a recording medium;
A temperature sensor that outputs an output signal whose voltage changes with a change in temperature of the recording head;
A reference signal generation circuit for generating a reference signal associated with the temperature of the recording head ;
A voltage storage circuit for storing a first voltage and a second voltage defining a range in which the voltage of the reference signal changes;
A determination circuit for determining whether or not the voltage of the reference signal and the voltage of the output signal match;
A control circuit that controls the reference signal generation circuit so that the voltage of the reference signal changes from the first voltage stored in the voltage storage circuit to the second voltage;
The reference signal generation circuit includes:
A pulse signal having a predetermined cycle is generated, and a pulse signal generated within a sampling cycle composed of a plurality of the predetermined cycles has the same total time maintained at a high level in any of the predetermined cycles. And a pulse signal generation circuit having two or more patterns in a period maintained at a high level within the predetermined period;
A smoothing circuit that smoothes the pulse signal generated by the pulse signal generation circuit and outputs it as a reference signal;
The control circuit includes:
The voltage of the reference signal is changed from the first voltage to the second voltage by changing the total time in which the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period in units of the sampling period. And when the determination circuit determines that the voltage of the reference signal and the voltage of the output signal match, the temperature of the recording head is detected based on the voltage of the reference signal when the voltage matches. A recording apparatus. A recording head for recording an image on a recording medium;
A temperature sensor in which the level of an output signal changes with a change in temperature of the recording head;
A reference signal generation circuit for generating a reference signal whose level can be changed;
A level storage unit that rewriteably stores a first signal level and a second signal level that define a range in which the level of the reference signal changes;
A control unit that controls the reference signal generation circuit so that the level of the reference signal changes from the first signal level stored in the level storage unit to the second signal level;
A comparison circuit for comparing the level of the reference signal and the level of the output signal;
The reference signal generation circuit includes:
A pulse signal having a predetermined cycle is generated, and a pulse signal generated within a sampling cycle composed of a plurality of the predetermined cycles has the same total time maintained at a high level in any of the predetermined cycles. And a pulse signal generator having two or more types of patterns in a period maintained at a high level within the predetermined period;
A smoothing circuit that smoothes the pulse signal generated by the pulse signal generation circuit and outputs it as a reference signal;
The control unit is
The voltage of the reference signal is changed from the first signal level to the second signal by changing the total time that the pulse signal generated by the pulse signal generation circuit is maintained at a high level in each predetermined period in units of the sampling period. When the level of the reference signal reaches the level of the output signal, it is determined that the level of the reference signal has reached the level of the output signal according to the comparison result of the comparison circuit. And generating a signal corresponding to the level of the reference signal generated by the reference signal generation circuit as a detected temperature signal representing the current temperature of the recording head . A determination unit that determines that the current temperature of the recording head represented by the detected temperature signal has reached a predetermined upper limit temperature;
When it is determined that the current temperature of the recording head has reached a predetermined upper limit temperature, the recording head stops the recording operation after the recording processing of one recording medium by the recording head is completed. The recording apparatus according to claim 13, further comprising: a recording unit. The pulse signal generator is
A random number generator for generating a signal representing a high / low pattern in which a plurality of high level periods corresponding to the high level of the pulse signal are randomly arranged within the predetermined period;
A random number storage unit for temporarily storing the signal generated by the random number generation unit;
A high-low comparison circuit that compares the code of the last part of the signal stored in the random number storage unit with the code of the head part of the signal newly generated by the random number generation unit;
When the high / low comparison circuit determines that both the code of the final part and the code of the head part are at a high level, the random number generation unit further generates a signal representing the high / low pattern. The recording apparatus according to claim 13 or 14.

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