Inkjet recording device

Abstract

To provide an inkjet recording device that can generate heater drive voltage with an inexpensive configuration that does not increase costs or negatively affect throughput. [Solution] An inkjet recording apparatus that records an image by applying ink ejected from a recording head to a recording medium, comprising a recording head capable of ejecting ink using thermal energy generated when a drive pulse is applied to an electrothermal conversion element, a temperature acquisition means for acquiring temperature information of the recording head, and a drive control means for generating and stopping the voltage of the drive pulse and controlling the voltage value and pulse width of the drive pulse according to the temperature information, characterized in that the voltage value is set when the drive control means has stopped generating the voltage of the drive pulse. Furthermore, it is characterized in that it is further equipped with a fault detection means for detecting a failure of the recording head, and fault detection by the fault detection means can be performed in parallel with setting the voltage value of the drive pulse.

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus that performs recording on a recording medium by ejecting ink.

Background Art

[0002] As a representative of a recording apparatus for recording a color image, an inkjet recording apparatus can be mentioned. An inkjet recording apparatus includes an inkjet recording head in which an ink ejection port and a recording element including energy generation means for ejecting ink droplets such as a heater or a piezo element are arranged in correspondence, moves the recording head in the main scanning direction, and performs recording scanning for ejecting ink droplets on the recording area, and repeats the conveyance of the recording medium in the sub-scanning direction intersecting the main scanning direction to record an image on the recording medium. An inkjet recording head using a heater applies a voltage to the heater to generate heat, foams the ink in the ink flow path by the heat energy, and ejects the ink from the ink ejection port using the foaming energy.

[0003] In an inkjet recording apparatus using a recording head using a heater, due to the internal temperature of the recording apparatus and the temperature of the recording head, changes occur in the viscosity of the ink, which is a liquid, and the volume during foaming, and there is a possibility that the ink ejection amount changes. For example, when the temperature of the recording head is low, the ink ejection amount decreases and the density of the recorded image becomes thin. Conversely, when the temperature of the recording head is high, the ink ejection amount may increase and the density of the recorded image may become thick. Further, when recording an image using a plurality of recording heads, there is also a possibility that the density of the recorded image partially changes due to the temperature difference between the respective recording heads.

[0004] In response to this, a technique for stabilizing the ink ejection rate is double-pulse drive control. In double-pulse drive control, a predetermined drive voltage (hereinafter referred to as VH) pulse is applied to the heater in two separate pulses. The first pulse is a preheat pulse, which heats the heater to a degree that does not cause ink ejection, thereby adjusting the temperature of the ink in the ink flow path. The second pulse is a main heat pulse, which heats the heater to a degree that causes ink ejection. By adjusting the pulse width of the preheat pulse, the pulse width of the main heat pulse, and the interval between these pulses (interval time), the ink ejection rate can be stabilized. For example, if the temperature of the recording head is low and the ink ejection rate is low, the pulse width of the preheat pulse is adjusted to be relatively long. Conversely, if the temperature of the recording head is high and the ink ejection rate is high, the pulse width of the preheat pulse is adjusted to be relatively short.

[0005] However, if the temperature of the recording head continues to rise due to continuous recording, controlling only the drive pulse width may not be sufficient to suppress the increase in ink ejection, and controlling the ink ejection amount is difficult with double-pulse drive control alone. Therefore, since the energy applied to the heater corresponds to the product of VH and pulse width, by using VH modulation control, which changes VH according to the head temperature, in addition to the double-pulse control described above, it is possible to stabilize the ink ejection amount and record high-quality images.

[0006] Patent Document 1 proposes a method for stabilizing the ink ejection amount using a VH modulation circuit with a DC / DC converter according to the acquired temperature of the recording head. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-245489 [Overview of the project] [Problems that the invention aims to solve]

[0008] When VH is increased by VH modulation control, an inrush current flows into the capacitor attached to the output of the DC / DC converter. As an example, Figure 2 shows the case where the temperature rise of the recording head is large, that is, when the amount of increase in VH is large. In Figure 2, the horizontal axis is time t, and the vertical axis is VH and VH current. In Figure 2, the temperature of the recording head had risen when the re-scan 1 was completed, so it became necessary to increase VH by ΔVH. Therefore, VH modulation is performed at timing T1 in the figure before the forward scan 2, and at this time a large inrush current flows in the VH current. For this reason, the components of the circuit constituting the DC / DC converter must be able to handle a larger current than when performing normal ink ejection, which increases costs, and in some cases, it may be necessary to use components of a larger size. Also, Figure 3 shows a case in which the voltage increase by ΔVH is performed in multiple steps in order to avoid the occurrence of excessive inrush current. In Figure 3, as in the case of Figure 2, the temperature of the recording head had risen when the re-scan 1 was completed, so it became necessary to increase VH by ΔVH, and VH modulation was performed at timing T2 in the figure before the forward scan 2. However, although this method avoids the occurrence of inrush current, it takes a lot of time to achieve the voltage increase of ΔVH, which negatively affects throughput.

[0009] The objective of this invention is to solve the problems of the prior art and to provide an inkjet recording apparatus that can generate a heater drive voltage with an inexpensive configuration. [Means for solving the problem]

[0010] To achieve the above objective, the present invention provides an inkjet recording apparatus that records an image by applying ink ejected from the recording head to a recording medium, wherein the apparatus includes a recording head capable of ejecting ink using thermal energy generated when a drive pulse is applied to an electrothermal conversion element, a temperature acquisition means for acquiring temperature information of the recording head, and a drive control means for generating and stopping the voltage of the drive pulse, and controlling the voltage value and pulse width of the drive pulse according to the temperature information, and is characterized in that the voltage value is set when the drive control means has stopped generating the voltage of the drive pulse.

[0011] Furthermore, the system is equipped with a fault detection means for detecting a failure of the recording head, and the fault detection by the fault detection means can be performed in parallel with setting the voltage value of the drive pulse. [Effects of the Invention]

[0012] According to the present invention, the heater drive voltage is set at the timing when the heater drive voltage circuit is stopped, preventing inrush current. This makes it possible to construct the circuit with inexpensive components and to reach the target heater drive voltage in a short time. [Brief explanation of the drawing]

[0013] [Figure 1] This diagram shows the configuration of the DC / DC converter that generates VH in an embodiment of the present invention. [Figure 2] This diagram illustrates a case where a large inrush current occurs with conventional technology. [Figure 3] This diagram illustrates a case where it takes time to set a predetermined voltage value using conventional technology. [Figure 4] This is a perspective view showing the schematic configuration of the recording section, mainly, of an image recording device according to an embodiment of the present invention. [Figure 5] This diagram illustrates the printing operation when a precharge voltage is applied to the recording head to perform a leak check. [Figure 6]It is a flowchart when the process shown in FIG. 7 is repeated from the start of printing to the end of printing. [Figure 7] It is a diagram showing the printing operation in the case of performing VH modulation. [Figure 8] It is a flowchart during VH modulation. [Figure 9] It is a diagram explaining the PWM comparator in more detail including its surroundings. [Figure 10] It is a flowchart during discharge.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] FIG. 4 is a perspective view showing a schematic configuration of mainly a recording unit of an image recording apparatus according to an embodiment of the present invention.

[0016] In the figure, reference numeral 401 denotes an ink cartridge, which stores four colors of ink, namely black (Bk), cyan (C), magenta (M), and yellow (Y), separately, and integrally forms respective storage chambers.

[0017] Reference numeral 402 denotes a cartridge of a recording head, and is used in the form of a single unit in which two recording element arrays corresponding to each of the inks stored in the ink cartridge 401 are stored for each color, for a total of eight. That is, in the head cartridge 402, two recording element arrays for discharging each of the inks of Bk, C, M, and Y are provided for each color, and a total of eight recording elements for four colors are stored.

[0018] Reference numeral 403 is a carriage for detachably mounting the above-described ink cartridge 401 and the head cartridge 402 in which the recording element arrays are stored. The carriage 403 can move along the guide shaft 210 by slidably engaging with the guide shaft 210.

[0019] 404 is an encoder scale provided on the surface facing the carriage 403, with slits spaced at 150 lpi intervals. The encoder sensor (not shown) emits light, which is shone onto this encoder scale 404, and A-phase and B-phase signals are output based on the transmitted light, corresponding to the scanning position of the carriage 403. The B-phase signal is 90 degrees behind the A-phase signal.

[0020] 405 is a paper feed roller, and together with the auxiliary roller 406, it grips the recording paper 409 and rotates in the direction of the arrow in the figure, thereby transporting the recording paper 409 in the y direction in the figure. Also, 407 and 408 represent a pair of paper feed rollers, which grip the recording paper 409 and feed it. [Examples]

[0021] Figure 1 is a block diagram showing the configuration of the DC / DC converter that generates VH in this embodiment. The DC / DC converter input voltage VHin supplied from the power supply unit (not shown) is input to the switching element Q1, converted via the switching element Q1, diode D1, inductor L1, and capacitor C2, and output as a DC output VH. Capacitor C1 is connected to the input side of the switching element Q1, and capacitor C2 is connected to the output side via inductor L1. This inductor L1 and capacitor C2 form a smoothing circuit that outputs VH. The Vcc_ENB signal output from the CPU 101 is a signal that turns the reference voltage (Vcc) circuit 104 on and off. By setting the Vcc_ENB signal to a high level, the reference voltage circuit 104 is turned on and outputs the reference voltage Vcc, supplying the reference voltage to the DC / DC control circuit (DC / DC control IC) via the D / A converter 211 and resistors R4 and R5. On the other hand, by setting the Vcc_ENB signal to a low level, the reference voltage circuit 104 is turned off and the output of Vcc is stopped. Furthermore, when the Vcc_ENB signal is used to switch the reference voltage Vcc of the DC / DC converter on or off, the VH_ENB signal is used to control the on / off state of the DC / DC converter for VH modulation.

[0022] In the DC / DC converter of this embodiment, the output Vdac of the D / A converter 103 is connected via R3 to the voltage divider point, which is created by R1 and R2 to modulate VH. As a result, the current I3 corresponding to the output Vdac of the D / A converter 103 is added to the voltage divider point of resistors R1 and R2 through R3. For example, if the control signal Din is an 8-bit digital signal, the output of the D / A converter 103 can be adjusted in 256 steps. In this case, if the input voltage of the D / A converter 103 is Vcc and the value of the 8-bit control signal Din is Xbit, the output voltage Vdac of the D / A converter 103 is expressed by the following formula.

[0023]

number

[0024] The current I3 corresponding to this output voltage Vdac is added to the voltage divider point of resistors R1 and R2, and the output voltage VH is changed as described below.

[0025] The voltage input to the non-inverting terminal of the error amplifier 105 is controlled to eliminate the error between it and the reference voltage Vref input to the inverting terminal. Therefore, the currents I1, I2, and I3 flowing through resistors R1, R2, and R3 are expressed by the following equations.

[0026]

number

[0027] From Kirchhoff's law of currents

[0028]

number

[0029]

number

[0030] Therefore, VH is expressed by the following equation.

[0031]

number

[0032] In this way, the output voltage VH can be changed by changing the value of the output voltage Vdac of the D / A converter 103. Vref and the feedbacked output voltage signal VH are input to the error amplifier 105. The output signal of the error amplifier 105, along with the triangular wave output from the oscillator 108, is input to the PWM comparator 106, and the PWM comparator 106 outputs a square wave as a result of comparing the two signals mentioned above. This square wave is converted to a predetermined voltage through the MOS driver 107 and PWM controls the switching element Q1 to maintain a constant voltage. The upper limit voltage level of the triangular wave is set lower than the operating voltage of the logic section of the DC / DC converter control IC. Figure 9 shows a more detailed explanation of the PWM comparator 106, including its surroundings.

[0033] The error amplifier 105 receives the VH_ENB signal along with the outputs from the oscillator 108 and the error amplifier 105 via a circuit consisting of R10, R11, and C3. The PMW comparator circuit 106 outputs a high level when the voltage of all other input signals is lower than the voltage of the triangular wave output from the oscillator 108, and turns on Q1 via the MOS driver 107. The voltage at the point where R10 and R11 are connected is at the same voltage level as the VH_ENB signal immediately after the VH_ENB signal reaches a high level due to the influence of C3, but thereafter it converges toward the value obtained by dividing the voltage of the VH_ENB signal by R10 and R11. Therefore, immediately after the VH_ENB signal reaches a high level, the DC / DC converter has just started operating, so the output voltage from the error amplifier 105 is lower than the triangular wave, but the input from the VH_ENB signal is higher than the triangular wave, so the output of the PMW comparator circuit 106 is at a low level and Q1 is turned off. Subsequently, as the voltage across the point where R10 and R11 are connected converges, the time that Q1 is on increases, and VH also converges to the value shown in [Equation 5]. By using a configuration with such a soft-start function, the rise in the voltage value of VH is prevented from becoming too steep, and excessive inrush current flows into VH.

[0034] The rise time of VH is adjusted by adjusting the constant of C3. The voltage divider values ​​of R10 and R11 may be set to values ​​below the lower limit of the triangular wave, or they may be set to values ​​midway between the upper and lower limits of the triangular wave so that Q1 is always off for a predetermined time. Furthermore, although not shown, a phase compensation circuit is configured to adjust the stability and responsiveness of the output voltage by connecting resistors and capacitors to the inverting terminal and output terminal of the error amplifier 105. The discharge circuit, consisting of R9 which limits the discharge current and the MOS-FET Q2 which is a switching element, discharges the charge of capacitor C2 when the DC / DC converter is turned off. The discharge circuit also discharges the charge of capacitor C2 when modulating the VH output voltage. The discharge signal is the on / off signal of the discharge circuit 301 and is connected to the gate of the switching element Q2. If the discharge signal is at a high level, Q2 is turned on, and if the discharge signal is at a low level, Q2 is turned off.

[0035] If a short circuit occurs in the recording head due to a malfunction or other reason, and VH is supplied to the recording head from the DC / DC converter, there is a possibility of fire or smoke because VH is usually a high voltage. To avoid this, before supplying VH to the recording head from the DC / DC converter, a voltage (hereinafter referred to as precharge voltage) is supplied to the recording head from a separate constant voltage source with low current supply capacity. Since the precharge voltage source has low current supply capacity, a voltage drop occurs when a short circuit occurs in the recording head and current flows. By monitoring this voltage drop with the CPU 101, a failure of the recording head can be detected. Hereinafter, the operation of applying this precharge voltage to check for the presence or absence of a failure in the recording head will be referred to as a leak check. The above precharge voltage supply system consists of a precharge voltage generation circuit 102, R6, and diode D2.

[0036] The precharge voltage generation circuit 102 consists of constant voltage circuits such as a linear regulator and a DC / DC converter. When the Vp_ENB signal of the CPU 101 reaches a high level, the precharge voltage generation circuit 102 is turned on and outputs a precharge voltage. R6 limits the current supply capability of the precharge voltage. Diode D2 prevents VH from being applied to the precharge voltage generation circuit 102 when VH is supplied from the DC / DC converter. The precharge voltage is divided by R7 and R8 to a level that can be input to the port of the CPU 101 and input. On the other hand, when the Vp_ENB signal is at a low level, the precharge voltage is turned off. If the precharge voltage is to continue to be supplied while the DC / DC converter is operating, the precharge voltage can be set lower than the voltage range that VH can take during printing, thereby preventing the precharge voltage from flowing into VH while the DC / DC converter is operating.

[0037] Figure 5 shows the printing operation when a precharge voltage is applied to the recording head and a leak check is performed. At timing T3 in the figure, the VH voltage is 0V, which is the timing before printing starts. When a print job is sent from the host PC, the CPU 101 sets the Vp_ENB signal to H level and turns on the precharge voltage generation circuit 102. When the precharge voltage generation circuit 102 is turned on, the precharge voltage is supplied to the recording head via R6 and D2, and VH gradually rises to the precharge voltage. The time it takes to rise to the precharge voltage is roughly determined by the constants of R6 and C2, so it is estimated in advance, and a leak check is performed after a predetermined time has elapsed (T4 in the figure). At T4, the leak check is performed and the CPU 101 monitors whether the precharge voltage is being maintained.

[0038] After the leak check is complete, the Vcc_ENB and VH_ENB signals are set to H level to start the DC / DC converter operation and raise VH to the level indicated as the printed voltage in the diagram. After printing in forward scan 1 in the diagram, the Vcc_ENB and VH_ENB signals are set to L level to stop the DC / DC converter operation. At this time, the Discharge signal is also set to H level to turn on Q2 and discharge the charge accumulated in C2. Then, during T4 between scans, another leak check is performed. In the subsequent reverse scan 1, VH is supplied from the DC / DC converter as in forward scan 1, and then a series of printing operations, DC / DC converter shutdown, and discharge are performed. A leak check is also performed during T4 between scans after reverse scan 1. The back-and-forth scan is repeated thereafter until printing is complete.

[0039] Next, Figure 7 shows the printing operation when VH modulation is performed. The operation of raising VH to the precharge voltage before forward scan 1, the discharge after each scan, and the leak check between scans are the same as in the operation in Figure 5, so they are omitted here, and only the operation when VH modulation is performed and the parts that differ from the operation in Figure 5 will be explained. In forward scan 1 and reverse scan 1, VH is set to print voltage 1 and the printing operation continues. After reverse scan 1, the temperature of the recording head has risen, so the CPU 101 sends Din to the D / A converter 103 in order to raise VH from print voltage 1 to print voltage 2 by ΔVH. This timing is T5 in the figure. At T6, the Vcc_ENB signal and VH_ENB signal are set to H level and the DC / DC converter starts operating. At T6, VH has risen from the precharge voltage to print voltage 2, but as explained in Figure 9, the voltage value of VH rises slowly due to the soft start function, so the inrush current is suppressed.

[0040] In Figure 7, the timing T5 for inputting Din to the D / A converter 103 overlaps with the timing T4 for performing the leak check in Figure 5. However, the order of T4 and T5 does not matter during scans. This is because, during scans, the VH_ENB signal is at a low level, and no VH voltage is supplied from the DC / DC converter. Therefore, the VH voltage is the precharge voltage, and the input of Din to the D / A converter 103 does not affect the VH voltage.

[0041] Figure 6 is a flowchart showing the process described in Figure 7 repeated from the start to the end of printing.

[0042] (S601) The CPU 101 sets the Vcc_ENB signal to a high level and turns on the power supply of the reference voltage (Vcc) generation circuit 104. This supplies Vcc to the DC / DC converter, turns on the power supply of the D / A converter 103, and also supplies Vref to the inverting terminal of the error amplifier 105.

[0043] (S602) Set the Discharge signal to L level to turn off the discharge circuit (this is a precautionary control as the discharge circuit is already turned off at this stage).

[0044] (S603) The temperature of the recording head is obtained, and the obtained temperature is set as the base temperature T0.

[0045] (S604) The CPU101 sets the Vp_ENB signal to high level, turning on the power supply to the precharge voltage generation circuit. This supplies the precharge voltage to VH.

[0046] (S605) Perform a leak check and use CPU101 to verify whether the precharge voltage is being maintained.

[0047] (S606) Perform VH modulation control. Detailed control of VH modulation is shown in the flowchart in Figure 8 and will be described later.

[0048] (S607) The CPU101 sets the VH_ENB signal to a high level and turns on the power to the DC / DC converter control IC. This supplies the voltage necessary for printing to VH from the DC / DC converter.

[0049] (S608) Scan and print the outbound path.

[0050] (S609) When scanning and printing on the forward path are completed, the CPU 101 sets the VH_ENB signal to L level and turns off the power to the DC / DC converter control IC.

[0051] (S610) Perform the discharge operation. Detailed control of the discharge operation is shown in the flowchart in Figure 10 and will be described later.

[0052] (S611) After the discharge operation, the VH voltage is at the precharge voltage. In this state, a leak check is performed as in S605, and CPU101 checks whether the precharge voltage is maintained.

[0053] (S612) Perform VH modulation control (detailed control is shown in the flowchart in Figure 8).

[0054] (S613) The CPU101 sets the VH_ENB signal to a high level and turns on the power to the DC / DC converter control IC. This supplies the voltage necessary for printing to VH from the DC / DC converter.

[0055] (S614) Scan and print the return leg.

[0056] (S615) When scanning and printing on the forward path are completed, the CPU 101 sets the VH_ENB signal to L level and turns off the power to the DC / DC converter control IC.

[0057] (S616) Perform a discharge operation (detailed control is shown in the flowchart in Figure 10).

[0058] (S617) Determine whether all scanning necessary for printing has been completed. If not, return to S605. If all scanning is completed, proceed to S618.

[0059] (S618) The CPU101 lowers the Vp_ENB signal to a low level, turning off the power to the precharge voltage generation circuit. This causes VH to drop to GND level, and the printing operation ends.

[0060] Figure 8 shows the flowchart for VH modulation as described in S606 and S612 of Figure 6.

[0061] (S801) Get the current temperature T.

[0062] (S802) Determine whether the value obtained by subtracting the base temperature T0 obtained in S603 from the temperature T obtained in S801 is greater than 5°C. If yes, proceed to S804; otherwise, proceed to S803.

[0063] (S803) Next, determine whether the value obtained by subtracting the base temperature T0 from the temperature T is less than -5°C. If yes, proceed to S804; otherwise, terminate the process.

[0064] (S804) Substitute T for the base temperature T0.

[0065] (S805) Input Din from CPU 101 to D / A converter 103 and change the output value Vdac of D / A converter 103. Then terminate the process.

[0066] Figure 10 shows the flowchart for the discharge process described in S610 and S616 of Figure 6.

[0067] (S1001) CPU101 sets the Discharge signal to high level, turning on Q2.

[0068] (S1002) Wait 120ms for the charge to be released from C2.

[0069] (S1003) CPU101 sets the Discharge signal to L level, turning off Q2. [Explanation of Symbols]

[0070] 101 CPU 102 Precharge Voltage Generation Circuit 103 D / A Converter 104 Reference voltage (Vcc) generation circuit 105 Error Amplifier 106 PWM comparator 107 MOS Drivers 108 Oscillators 401 Ink Cartridge 402 Recording head cartridge 403 Carriage 404 IOS scale 405 Paper feed roller 406 Auxiliary roller 407 Paper feed roller 408 Paper feed roller 409 Recording paper 410 Guide axis

Claims

1. An inkjet recording apparatus that records an image by applying ink ejected from the recording head to a recording medium, comprising: a recording head capable of ejecting ink using thermal energy generated when a drive pulse is applied to an electrothermal conversion element; a temperature acquisition means for acquiring temperature information of the recording head; and a drive control means for generating and stopping a drive pulse voltage and controlling the voltage value and pulse width of the drive pulse according to the temperature information, characterized in that the voltage value is set when the drive control means has stopped generating the drive pulse voltage.

2. The inkjet recording apparatus according to claim 1, further comprising fault detection means for detecting a failure of the recording head when the drive control means has stopped generating the voltage of the drive pulse, and the fault detection by the fault detection means can be performed in parallel with setting the voltage value of the drive pulse.

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