JP2006256151A - Image forming device and liquid ejection state determining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which can determine liquid ejection state in a short time, and can adequately correct a driving signal, based on a result of the determination. <P>SOLUTION: An ink-jet printer or the image forming device has a circuit incorporated therein, for determining whether the ejection state is adequate or not, and outputs a detection signal in a time band that falls outside a printing time period but is indispensable for printing, to thereby always monitor fluctuation in pressure mainly caused by bubbles infiltrated into pressure chambers 46 in a recording head 36, and by clogging of nozzles 40. Further by correcting the driving signal, the quality of printed material can be improved without degrading productive ability. Furthermore the ink-jet printer functions to extract only mechanical admittance out of electric admittance and the mechanical admittance of the recording head 36, and by performing spectrum analysis of minute load fluctuation at a high S/N ratio, the load fluctuation is expressed as fluctuation in resonance frequency and sharpness, whereby determination as to whether the ejection state is adequate or not can be quickly and positively carried out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention supplies a drive signal having a predetermined pulse width and amplitude to a piezoelectric element based on image data, generates a vibration wave in the pressure chamber by this drive signal, and discharges the liquid in the pressure chamber from a nozzle. A liquid droplet ejection element of the type, the liquid droplet ejection element is opposed to the recording medium conveyance path, and the liquid droplet ejection element and the recording medium are moved relative to each other, whereby an image is formed on the recording medium. The present invention relates to an image forming apparatus for forming a liquid and a liquid discharge state determination method.

  In the present invention, the braking capacity refers to an electrostatic capacity generated between both electrodes of the drive circuit when driving the piezoelectric element. The mechanical system load is also referred to as a mechanical system load because the piezoelectric element vibrates ultrasonically, and mainly has an electrostatic capacity equivalent to the pressure in the pressure chamber and an electrical resistance equivalent to the fluid resistance of the nozzle (hereinafter simply referred to as “mechanical load”). Called resistance).

  2. Description of the Related Art In recent years, so-called inkjet printers that eject ink from ink ejection ports have been used as many image forming processing engines because of their small size and low cost. Among these ink jet printers, a piezo ink jet method that ejects ink by using deformation of a piezoelectric element is widely used from the viewpoint of high resolution and high speed printability.

  An ink jet printer that uses vibration energy of a piezoelectric element such as a piezoelectric element vibrates a piezoelectric element provided in an ink flow path in accordance with image information, and forms ink droplets by distortion of the piezoelectric element. By controlling the waveform of the voltage applied to the piezoelectric element, it is possible to control the meniscus of the ink ejection port and the re-supply of the ink after ejection. Gradation recording with varying amounts becomes possible.

  In the operation of such an ink jet printer, non-ejection occurs due to air bubbles entering the pressure chamber from the nozzle, ink adhering to the nozzle surface being dried, or viscosity increasing. Usually, in order to prevent this, the nozzle surface is frequently sucked and maintenance such as wiping is performed, which causes a lot of time and waste of ink. In addition, if the maintenance is not complete, dots are lost and the quality of the printed matter is impaired.

  Therefore, it is conceivable to perform printing using a nozzle other than the non-ejection nozzle by detecting the non-ejection nozzle.

  As a non-ejection nozzle detection method, for example, techniques described in Patent Document 1 and Patent Document 2 have been proposed. In the techniques described in Patent Documents 1 and 2, it has been proposed to detect a non-ejection nozzle from a change in the resonance point of a piezoelectric element. Specifically, the resonance point of the piezoelectric element is detected by gradually changing the frequency.

In addition, a technique disclosed in Patent Document 3 has been proposed as a method for detecting a non-ejection nozzle when a piezoelectric element is not used as a drive source for ink ejection.
JP 2000-355100 A JP 2000-318183 A JP 2003-118093 A

  However, the conventional techniques described in Patent Document 1 and Patent Document 2 detect the resonance frequency of the piezoelectric element by gradually changing the frequency, so that it takes time to detect the resonance point. is there.

  In addition, when using a recording head that uses a piezoelectric element as an ink ejection drive source, a piezoelectric device that eliminates the influence of the electrical admittance of the recording head in order to detect changes in the state due to bubble inflow and ink adhesion to the nozzle surface. Although it is necessary to detect the resonance frequency of the mechanical admittance of the recording head composed of the element, the pressure chamber, the ink supply path, and the nozzle, the techniques described in Patent Document 1 and Patent Document 2 use the resonance frequency of the piezoelectric element. Therefore, there is a problem that the detection accuracy of the non-ejection nozzle is lowered.

  In addition, when trying to detect the resonance frequency of the mechanical admittance of the recording head, there is a problem that it is difficult to detect the resonance frequency because the SN ratio is low.

  Furthermore, even if the resonance frequency of the mechanical admittance is detected and the discharge state is determined, it is a capacitive defect caused by bubbles or the like mixed in the pressure chamber, or a resistance caused by clogging of the nozzle or the like. It has not been established whether it is a defect and whether correction based on the determination result is possible.

  In consideration of the above facts, the present invention provides an image forming apparatus and a discharge state determination method that can determine a liquid discharge state in a short time and can appropriately correct a drive signal based on the determination result. Is the purpose.

The first invention supplies a drive signal having a predetermined pulse width and amplitude to the piezoelectric element based on the image data, generates a vibration wave in the pressure chamber by the drive signal, and discharges the liquid in the pressure chamber from the nozzle. A piezoelectric droplet discharge element that is opposed to the recording medium conveyance path, and moves the droplet discharge element and the recording medium relative to each other to move the droplet on the recording medium. An image forming apparatus for forming an image on the basis of a signal output corresponding to a mechanical load of the droplet discharge element when the piezoelectric element is driven based on a predetermined detection signal, Discharge state determination means for determining the discharge state of the droplet discharge element; and control means for changing the pulse width or amplitude of the drive signal according to the determination result of the discharge state determination means;
have.

  According to the first invention, when the piezoelectric element is driven, a vibration wave (pressure wave) is generated in the pressure chamber corresponding to the piezoelectric element, and the liquid is drawn into the pressure chamber via the supply path, and from the nozzle. Liquid in the pressure chamber is discharged. By the discharged liquid, printing is performed on a recording medium that is opposed to the liquid discharge element and relatively moves.

  In the image forming apparatus having the above-described configuration, when bubbles are generated in the pressure chamber, liquid discharge failure from the nozzles occurs due to pressure fluctuations or nozzle clogging. For this reason, the nozzle discharge state determination means is controlled to determine the nozzle discharge state.

  In the determination of the nozzle discharge state, a predetermined voltage is output corresponding to a load equivalent to the pressure change in the pressure chamber and the discharge state due to nozzle clogging when the piezoelectric element is driven. The discharge state from the nozzle is determined based on this output signal. The load equivalent to the pressure fluctuation in the pressure chamber corresponds to a mechanical load and can be expressed by a capacitance.

  In this way, it is possible to reliably determine the liquid discharge state, determine whether correction is possible or not based on the determination result, and if the correction is possible, correct the drive signal to realize maintenance-free operation. be able to. This compensates for subtle errors in the load (mechanical load) equivalent to the pressure variation in the pressure chamber when driving the piezoelectric element due to machine head differences, assembly variations, and the ejection state due to nozzle clogging. Can lead to an improvement in the yield for the product. In particular, a great effect can be exhibited for an image forming apparatus that performs high-speed printing using a large number of nozzles.

  The mechanical system load includes an acoustic capacity C, an acoustic resistance R, and an acoustic mass M (inertance). The acoustic capacity C is the elastic compliance or acoustic capacity of the pressure chamber, and specifically indicates the softness of a virtual spring determined by the shape of the pressure chamber and the fluid (ink, bubbles, etc.).

  The acoustic resistance R is a fluid resistance, and specifically is a resistance component that depends on the flow path shape and the viscosity of the fluid. The acoustic mass M is an amount that depends on the nozzle shape and the ink flow rate of the nozzle.

  In the first aspect of the invention, the discharge state determination means includes a first wiring in which the piezoelectric element and a resistor of the droplet discharge element are connected in series, a dummy capacity equivalent to a braking capacity of the piezoelectric element, and the A second wiring in which a dummy resistor equivalent to the resistor is connected in series is connected in parallel, and a predetermined detection signal is applied to both ends of the first wiring, whereby the piezoelectric element and the on-resistance in the first wiring are And a bridge circuit having a potential difference between the dummy capacitor and the dummy resistor in the second wiring as an output voltage.

  Furthermore, in the first invention, a plurality of the droplet discharge elements are provided, and the discharge state determining means connects any one of the piezoelectric elements in the plurality of droplet discharge elements to the bridge circuit. A switch is provided, and the resistor is an on-resistance of the switch.

  In the first invention, the discharge state determination means determines the discharge state based on the resonance frequency of the output signal of the bridge circuit.

  Furthermore, in the first invention, when the resonance frequency is within a preset range, the control means changes a pulse width of the drive signal according to the resonance frequency, and the resonance frequency is set in advance. If it is outside the set range, the amplitude of the drive signal is set to zero.

  In the determination result by the ejection state determination unit, when the error is within a preset correctable range, the control unit corrects the pulse width or amplitude of the drive signal with the reference value that sets the correctable range as a target. . In other words, if it is outside the correctable range, there are too many errors, and adjustment by other means such as maintenance is required.

  In the first invention, the discharge state determining means determines the discharge state based on a Q value of an output signal of the bridge circuit.

  Furthermore, in the first aspect of the present invention, the apparatus further includes suction means for sucking the droplets from the nozzle, and the control means responds to the Q value when the Q value is within a preset range. The correction means is controlled to change the depth section of the drive signal, and when the Q value is outside a preset range, the liquid is sucked from the nozzle of the droplet discharge element. It is a feature.

  In the first aspect of the invention, there is further provided suction means for sucking the liquid from the nozzle, and the discharge state determination means determines the discharge state based on a resonance frequency and a Q value of the output signal of the bridge circuit. The control means changes the pulse width of the drive signal according to the resonance frequency when the resonance frequency is within a preset range, and the resonance frequency is out of the preset range. In this case, the amplitude of the drive signal is set to zero, and when the Q value is within a preset range, the correction means is controlled to change the amplitude of the drive signal according to the Q value, When the Q value is outside a preset range, the suction unit is controlled to suck the liquid from the nozzle of the droplet discharge element.

  The change of the pulse width or amplitude of the drive signal by the control means may be performed for each droplet ejection element, or a group of droplets so that the ejection characteristics of a predetermined group of droplet ejection elements are good on average. It may be changed to the discharge element end.

  Furthermore, in the first invention, there is further provided a discharge state determination execution control unit that executes the determination by the discharge state determination unit and the correction by the correction unit outside the printing period on the recording medium by the droplet discharge element. It is characterized by.

  In the first invention, the detection signal also serves as a viscosity adjustment signal generated for adjusting the viscosity in the pressure chamber.

  For example, in a galvanometer, a load (resistance) is wired in a bridge shape (bridge circuit) in order to detect a minute current. Using this principle, a piezoelectric element and an on-resistance (first resistance) ), A dummy capacitor and a dummy resistor (second wiring) are used to form a bridge circuit.

  As a result, by applying a predetermined detection signal to both ends common to the first wiring and the second wiring, the braking capacity is canceled out, and the potential difference corresponding to the fluctuation of the mechanical system load can be detected. .

  It is preferable to amplify the potential difference with a differential amplifier or the like and remove noise through a filter. Then, resonance is performed by executing a predetermined analysis (spectral analysis by fast Fourier transform, fast wavelet transform, etc.). The frequency is obtained, the pressure fluctuation in the pressure chamber and the clogging of the nozzle are grasped by the displacement of the resonance frequency, and the quality of the discharge state of the nozzle can be determined based on a predetermined threshold value.

  Since the determination and correction are performed outside the printing period on the recording medium by the recording head, there is no trouble in the printing operation, and it is not necessary to provide a separate period for the determination. The ability does not decrease.

  For example, the viscosity in the pressure chamber can be set to an appropriate state along with the determination of the non-ejection state.

  The term “outside of the printing period” varies depending on the printing method of the image forming apparatus (FWA (Full Width Array), PWA (Partial Width Array), etc.). In the case of the PWA method, it becomes acceleration / deceleration timing when the scanning direction is changed. Of course, the page break timing may be used in the PWA method.

  As described above, the determination of the discharge state is performed during a period outside the printing period and indispensable for printing, so that the production capacity is not lowered.

  The second invention supplies a drive signal having a predetermined pulse width and amplitude to the piezoelectric element based on the image data, generates a vibration wave in the pressure chamber by the drive signal, and discharges the liquid in the pressure chamber from the nozzle. A piezoelectric droplet discharge element that is opposed to the recording medium conveyance path, and moves the droplet discharge element and the recording medium relative to each other to move the droplet on the recording medium. A liquid discharge state determination method for determining whether or not a liquid discharge state is good or bad due to volume fluctuation in a pressure chamber and clogging of a nozzle, which is used in an image forming apparatus for forming an image on the piezoelectric element. When the liquid droplet ejection element is driven based on a signal output corresponding to the mechanical load of the liquid droplet ejection element, the ejection state of the liquid droplet ejection element is determined, and a drive signal is determined according to the determination result. Pulse width It is characterized by changing the amplitude.

  According to the second invention, when the piezoelectric element is driven, a vibration wave (pressure wave) is generated in the pressure chamber corresponding to the piezoelectric element, and the liquid is drawn into the pressure chamber via the supply path, and from the nozzle. Liquid in the pressure chamber is discharged. By the discharged liquid, printing is performed on a recording medium that is opposed to the liquid discharge element and relatively moves.

  In the image forming apparatus having the above-described configuration, when bubbles are generated in the pressure chamber, liquid discharge failure from the nozzles occurs due to pressure fluctuations or nozzle clogging. For this reason, the nozzle discharge state determination means is controlled to determine the nozzle discharge state.

  In the determination of the nozzle discharge state, a predetermined voltage is output corresponding to a load equivalent to the pressure change in the pressure chamber and the discharge state due to nozzle clogging when the piezoelectric element is driven. The discharge state from the nozzle is determined based on this output signal. The load equivalent to the pressure fluctuation in the pressure chamber corresponds to a mechanical load and can be expressed by a capacitance.

  For example, the detection signal for determining the ejection state is output outside the printing period based on the image data. This detection signal can use a viscosity adjustment waveform that is still being executed in order to stabilize the viscosity of the liquid in the pressure chamber. This viscosity adjustment waveform vibrates the liquid in the pressure chamber, but there is no ejection force from the nozzle. The single viscosity adjustment waveform is a vibration waveform in which the vibration in the pressure chamber is gradually attenuated.

  When the piezoelectric element is driven based on such a detection signal, vibration is generated in the pressure chamber as described above. The load fluctuation of the mechanical system during this vibration is extracted.

  Next, the liquid discharge state is determined by analyzing at least the resonance frequency of the extracted mechanical system load and the sharpness of the resonance frequency.

  Based on the determination result of the liquid ejection state, when the error is within the correctable range, the pulse width or amplitude of the drive signal is corrected.

  The mechanical system load fluctuation is expressed as, for example, a change in the resonance frequency of vibration, and the liquid discharge state can be determined based on at least the displacement amount of the extracted mechanical system load at the resonance frequency.

  As described above, the present invention has an excellent effect that the liquid discharge state can be determined in a short time and the drive signal can be corrected appropriately based on the determination result.

"Overall configuration of inkjet printer"
FIG. 1 shows a schematic configuration of a PWA inkjet printer 10 as an image forming apparatus according to the present embodiment.

  In the present embodiment, the conveyance direction of the recording paper P as a recording medium is the sub-scanning direction (see arrow S in FIG. 1), and the direction orthogonal to the sub-scanning direction is the main scanning direction (arrow M in FIG. 1). Reference).

  The ink jet printer 10 includes a carriage 14 on which black, yellow, magenta, and cyan ink jet recording units 12 are mounted.

  A pair of brackets 16 protrude from the carriage 14 on the upstream side in the conveyance direction of the recording paper P, and the bracket 16 has a circular opening 16A. A shaft 18 (see FIG. 1) installed in the main scanning direction is inserted through the opening 16A.

  As shown in FIG. 1, a driving pulley 22 and a driven pulley 24 constituting the main scanning mechanism 20 are disposed at both ends in the main scanning direction, respectively. A timing belt 26 is wound around the driving pulley 22 and the driven pulley 24, and the carriage 14 is fixed to a part of the timing belt 26. As a result, the carriage 14 can reciprocate in the main scanning direction.

  The inkjet printer 10 is provided with a sub-scanning mechanism 32 including a conveyance roller 28 and a discharge roller 30. The sub-scanning mechanism 32 sub-records the recording paper P fed one by one from the paper feed tray 34 that stores the recording paper P before printing (printing) in a bundle at a predetermined pitch or continuously at a constant speed. Transport in the scanning direction.

  In addition, a cleaning device 33 as a suction unit is disposed at one end of the shaft 18 so that the lower surface of the carriage 14 is opposed. When the carriage 14 is positioned directly above the cleaning device, the inkjet device Maintenance such as capping and suction is performed on the recording unit 12. For example, it is possible to suck ink from the nozzle 40 shown in FIG.

  As shown in FIG. 2, each color inkjet recording unit 12 includes a recording head 36 and an ink cartridge 38 that supplies ink to the recording head 36, and is formed on the lower surface of the recording head 36. The plurality of nozzles 40 (see FIG. 3) are mounted on the carriage 14 so as to face the recording paper P.

  Accordingly, the recording head 36 selectively ejects ink droplets from the nozzles 40 on the recording paper P based on the image data while moving in the main scanning direction by the main scanning mechanism 20 (see FIG. 1). An image is formed (printed) on a predetermined band area BE.

  When one movement in the main scanning direction is completed, the recording paper P is conveyed at a predetermined pitch in the sub scanning direction by the sub scanning mechanism 32 (see FIG. 1), and the inkjet recording unit 12 moves again in the main scanning direction. An image is formed (printed) on the next band area. By repeating this, an entire image based on the image data is formed on the recording paper P.

"Recording head configuration"
The recording head 36 includes an ink tank 41, a supply path 44, a pressure chamber 46, a nozzle 40, and a piezoelectric element 42.

  The ink tank 41 stores ink from the above-described ink cartridge 38 (see FIG. 2). The ink tank 41 communicates with the pressure chamber 46 through the supply path 44, and the pressure chamber 46 further connects the nozzle 40. It communicates with the outside through.

  A part of the wall surface (the lower surface in FIG. 3) of the pressure chamber 46 is made of a vibration plate 46A, and the piezoelectric element 42 is attached to the vibration plate 46A. A pressure wave is generated in the ink in the chamber 46. That is, the ink stored in the ink tank 41 is ejected from the nozzle 40 through the supply path 44 and the pressure chamber 46 by the pressure wave generated by the vibration of the piezoelectric element 42.

"Drive circuit"
FIG. 4 shows a drive circuit 100 for the recording head 36 in the inkjet printer 10.

  In addition to the original function of selectively driving the piezoelectric elements 42 of the recording head 36, the driving circuit 100 incorporates a circuit for determining the ink ejection state from the nozzles 40.

  FIG. 4 shows a digital drive circuit 100 according to the present embodiment.

The digital drive circuit 100 is provided with a digital voltage amplifier 102 at a 1: 1 ratio with respect to each piezoelectric element 42.

A dedicated selector 104 is connected to each input terminal of the digital voltage amplifier 102. Each selector 104 is input with a print nozzle selection signal.
Piezoelectric elements are sequentially selected by the print nozzle selection signal.

  A drive power supply unit 105 is connected to the selector 104. The drive power supply unit 105 is provided with a plurality of drive signal data memories 105 (1)... (M) for storing a plurality of drive signal data in advance, and a drive selected by a drive signal selection signal (described later). The drive signal stored in the signal data memory 105 (1)... (M) is output to the selector 104.

  Here, the drive signals stored in the drive signal data memory 105 (1)... (M) are classified into two types: one detection signal and a plurality of print waveform signals having different pulse widths or amplitudes. Can do. The detection signal is such that there is no ink ejection from the nozzles 40 and the vibration is given to the pressure chamber 46, and the print waveform signal is the actual ink ejection. Hereinafter, when only a type is selected without distinguishing a plurality of print waveform signals, they are simply referred to as “detection signal” or “print waveform”. In the present embodiment, the detection signal is stored in the drive signal data memory 105 (m).

  Each digital voltage amplifier 102 is input with either a detection signal selected by the selector 104 or a print waveform.

  A piezoelectric element 42 is connected to the output terminal of the digital voltage amplifier 102 via an on-resistance Rd. Accordingly, the driving power is supplied to the piezoelectric element 42 by either the detection signal or the print waveform, and the piezoelectric element 42 can be driven.

  Here, one end of the determination selection switch 112 is connected between the on-resistance Rd and the piezoelectric element 42. The other end of the determination selection switch 112 is short-circuited by the output signal line 114, and the output signal line 114 is connected to the negative side input end 118 </ b> A of the differential amplifier 118 via the resistor 116.

  On the other hand, one of the digital voltage amplifiers 102 (the lowest stage of the digital voltage amplifiers 102 arranged in FIG. 4) is directly connected to the drive signal data memory 105 (m) from the detection signal generator 106 without passing through the selector 104. And a detection signal is input. The digital voltage amplifier 102 is for energizing the dummy resistor Rdd and the dummy capacitor Cdd for determining the ejection state.

  The output signal line 122 having one end connected between the dummy resistor Rdd and the dummy capacitor Cdd has the other end connected to the plus-side input end 118B of the differential amplifier 118 via the resistor 124.

  The resistor Rdd has the same resistance value as the resistor Rd of the switching element 108 and functions as a dummy resistor for the resistor Rd. The capacitor Cdd is expressed as a braking capacity generated when the recording head 36 is driven. The capacitor Cd has the same capacitance, and functions as a dummy capacitor for the capacitor Cd (details will be described later).

  With the above configuration, during normal printing, the selector 104 selects the print waveform signal, and all the determination selection switches 112 are turned off by the non-ejection detection nozzle selection signal. Based on the image data, the selector 104 Printing is executed by controlling the output.

  The above is the basic circuit system showing the original function of the drive circuit 100. In the present embodiment, the following discharge state detection circuit system is incorporated in the basic circuit system.

  That is, when determining the ejection state, the selector 104 selects a detection signal based on the print nozzle selection signal, and detection signals are output from all the selectors 104.

  Further, the determination selection switch 112 is sequentially turned on by the non-ejection detection nozzle selection signal.

  As a result, voltage fluctuations corresponding to fluctuations in mechanical admittance from the individual piezoelectric elements 42 are output from the differential amplifier 118.

  It should be noted that resistors 126 and 128 for adjusting the voltage that is divided and input to the differential amplifier 118 are interposed between the output signal lines 114 and 122 and the ground, respectively.

  Here, when the recording head 36 is driven, a braking capacity and a mechanical load are generated by the drive signal from the drive signal generation unit 104. The braking capacity is a capacitance (C component) generated in the electric circuit when a drive signal is output. Further, the mechanical system load is a resistance, reactance, capacitance component (RLC component) included in the piezoelectric element 42 itself, a supply path 44 of the recording head 36, a pressure chamber 46, and a discharge state (RLC component) generated in the nozzle 40. is there.

  That is, when a drive signal is supplied to the recording head 36, it can be represented by an equivalent circuit as shown in FIG.

  This equivalent circuit can be divided into an electrical admittance Ye (capacitor Cd) and a mechanical admittance Ya (piezoelectric element 42, supply path 44, pressure chamber 46, nozzle 40).

  The piezoelectric element 42 is represented by L0, R0, C0 connected in series, the supply path 44 is represented by L1, R1 connected in series, the nozzle 40 is represented by L2, R2 connected in series, and the pressure chamber 46 Is represented by C1.

  When the angular frequency is ω and the imaginary unit is j, the electrical admittance Ye and the mechanical admittance Ya are | Ye (jω) | >> | Ya (jω) | (actually, the electrical admittance Ye and mechanical admittance Ya are about 1:30). Further, Rd << | Za (jω) |.

  Here, the equivalent circuit can be regarded as a parallel circuit of the electrical admittance Ye (that is, Cd) and the mechanical admittance Ya shown in FIG.

FIG. 6 shows only the discharge state detection circuit system incorporated in the drive circuit 100 (see FIG. 4) based on the admittance equivalent circuit of FIG. 5B.
`` Discharge status judgment circuit ''
As shown in FIG. 6, the first wiring 130 in which the parallel circuit of the electrical admittance Ye and the mechanical admittance Ya of each recording head 36 and the resistance Rd of the switching element 108 (see FIG. 4) are connected in series, A bridge circuit is constituted by a dummy capacitor Cdd having a load (capacitance) equivalent to that of the electric admittance Ye and a second wiring 132 in which a dummy resistor Rdd having a resistance value equivalent to that of the resistor Rd is connected in series. ing.

  One end of the bridge circuit, that is, one end where the first wiring 130 and the second wiring 132 are short-circuited is connected to the output terminal of the drive signal generation unit 104. The other end of the first wiring 130 and the second wiring 132 that are short-circuited is grounded.

  A single detection signal is output from the drive power supply unit 105 (drive signal data memory 105 (m)) (see FIG. 7). This detection signal is the same waveform as the viscosity adjustment waveform that is still applied. The viscosity adjustment waveform is a signal output outside the printing period in order to adjust the viscosity of the ink in the pressure chamber 46 of the recording head 36. In this embodiment, the viscosity adjustment waveform is applied as a detection signal. ing. The viscosity adjustment waveform applies a vibration to the pressure chamber 46, but has a voltage that does not cause ink to be ejected from the nozzle 40.

  In such a circuit configuration, the potential between the resistors Rd is input to the negative input end 118A of the differential amplifier 118 (input voltage V1), and the potential between the dummy resistors Rdd is input to the positive input end 118B of the differential amplifier 118. If wiring is performed so as to input (input voltage V2), the output voltage V0 of the differential amplifier 118 can be expressed by V1-V2. Since this potential difference V0 corresponds to the current I11 applied to the mechanical admittance, it is almost equal to Ya × Rd × Vs.

  In other words, the influence of the electric admittance is canceled out by the dummy capacitor Cdd, and the voltage fluctuates in proportion to the mechanical admittance (fluctuation of the pressure chamber 46), which becomes the output voltage of the differential amplifier 118.

  As shown in FIG. 7, when a detection signal (trapezoidal wave) is output from the drive signal generation unit 104, a vibration waveform that gradually attenuates is output from the differential amplifier 118. In the design value, when the pressure chamber 46 is appropriate (bubbles or the like do not exist), the resonance frequency is 70 KHz. In FIG. 7, when the pressure chamber 46 is used as a reference, outputs of resonance frequencies of + 10% and + 20% are obtained. The waveforms are also shown.

  In the pressure chamber 46, if bubbles are mixed, the capacitor C1 in FIG. 5A tends to increase and the resonance frequency tends to decrease. When + 20%, ink is not ejected from the nozzle 40 (non-ejection). I know that I will fall into. In other words, it can be said that the limit of the allowable range is 20%. In the present embodiment, if the allowable range is within this allowable range, one of the drive signals having different preset pulse widths is selected and applied. (See FIGS. 4 and 8).

  Further, if there is a change in the fluidity of the nozzle 40, the resistance R1 in FIG. 5A increases and the sharpness Q at the resonance frequency varies. That is, when the Q value is small (when the amplitude is small), it can be determined that the nozzle 40 is clogged, and when the Q value is large (when the amplitude is large), it can be determined that the clogging of the nozzle 40 has been eliminated. Is given a predetermined allowable range, and the voltage value of the drive signal is adjusted. The adjustment of the voltage of the drive signal is executed by the voltage setting unit 109 shown in FIG.

  That is, a drive power supply is input to the voltage setting unit 109 and a set voltage value signal based on the Q value is input, and the voltage value of the drive power supply is set based on the set voltage signal.

  FIG. 8 is a control block diagram for analyzing the fluctuation of the resonance frequency as described above.

"Discharge status judgment control system"
As shown in FIG. 8, when the recording head 36 is driven using the drive circuit 100 by the input of the detection signal, an output voltage is output from the differential amplifier 118.

  This output voltage is input to the admittance extraction means 134.

  This output voltage is inputted to the controller 133 after noise is removed by the filter 136, A / D converted by the A / D converter 138.

  The controller 133 is programmed with a CPU 140 and spectrum analysis means (software) 139 so as to derive a resonance frequency by a predetermined spectrum analysis.

  As a means for spectrum analysis, fast Fourier change using a window function, fast wavelet transform, or the like can be applied. The CPU 140 can perform high-speed arithmetic processing by using a digital signal processor (DSP) having an architecture specialized for digital signal processing.

  The controller 133 outputs a drive signal selection signal for selecting an optimum drive signal based on the result of the spectrum analysis to the drive power supply unit 105 (see FIG. 4).

  By selecting the driving signal, driving signals having different pulse widths are selected (pressure fluctuation correction).

  Further, the CPU 140 sends a set voltage value signal to the voltage varying means 141 (nozzle clogging correction).

  The voltage variable means 141 is connected to the digital voltage amplifier 102 shown in FIG. 4 (shown as a single voltage amplifying means 143 in FIG. 8), and a reference drive power supply voltage is applied. In this voltage variable means 141, the amplitude of the drive signal is changed based on the input voltage setting information and is input to the digital voltage amplifier 102 (nozzle clogging correction).

  FIG. 9 is a diagram showing frequency-phase characteristics of the admittance of the electro-mechanical coupling system in the recording head 36, and FIG. 10 is a diagram showing frequency-phase characteristics of the mechanical system in the recording head 36.

  The frequency-phase characteristic of the admittance of the recording head 36 is greatly affected by the electrical admittance (Cd) as shown by the arrow A in FIG. The ejection failure was detected indirectly from the fluctuation of the resonance point of the piezoelectric element 42 shown in FIG.

  In this embodiment, as described above, a signal having a high SN ratio can be obtained by using the output voltage V0 of the differential amplifier 118. That is, as shown in FIG. 10, the mechanical admittance of the recording head 36 can be detected with a high S / N ratio. Accordingly, it is possible to detect a non-ejection nozzle from the fluctuations in the normal ejection frequency and the non-ejection frequency shown in FIG.

  In other words, the frequency characteristics shown in FIGS. 11A and 11B can be obtained by extracting the output as shown in FIG. 10 by the discharge state detection circuit system and performing the spectrum analysis.

  FIG. 11A shows a boundary between pass / fail judgment and correctability in the case where the resonance frequency (peak point) is shifted due to bubbles or the like mixed in the pressure chamber 46, and is relative to the reference value. A displacement of + 10% is defective but can be corrected, and a displacement of + 20% is defective and cannot be corrected.

  On the other hand, FIG. 11 (B) shows a boundary between whether the resonance frequency sharpness (Q) fluctuates due to resistance fluctuation due to clogging of the nozzle 40 and whether or not correction is possible. A displacement of + 10% is defective but can be corrected, and a displacement of + 20% is defective and cannot be corrected.

  When correction is possible in FIG. 11A or 11B, the controller 133 shown in FIG. 8 selects a drive signal in consideration of the error amount (see FIG. 4).

  The operation of this embodiment will be described below.

"Printing procedure"
When printing is instructed, the recording paper P fed one by one from the paper feed tray 34 is conveyed in the sub-scanning direction at a predetermined pitch or continuously at a constant speed.

  When the recording sheet P is positioned at a predetermined position, the recording head 36 is selectively moved from the nozzle 40 to the recording sheet P based on the image data while moving in the main scanning direction by the main scanning mechanism 20. Discharge drops. As a result, an image is formed (printed) on the predetermined band area BE.

  When one movement in the main scanning direction is completed, the recording paper P is conveyed by a predetermined pitch in the sub scanning direction by the sub scanning mechanism 32. In the present embodiment, the intermittent transport is performed at predetermined pitches, but the sub-scan may always be performed at a constant speed even during the one main scan.

  After transporting the predetermined pitch, the inkjet recording unit 12 forms (prints) an image on the next band area while moving in the main scanning direction again.

  By repeating this, the entire image based on the image data can be formed on the recording paper P.

  In the repeated main scanning movement, the carriage 12 always decelerates, stops, and accelerates. This is outside the printing period and is also an indispensable time.

  The recording paper P on which the image is formed is discharged by the discharge roller 30 and one printing is completed. In addition, when printing a plurality of pages continuously, the next recording paper P is fed from the paper feed tray 34 at the same time as or after the discharge of the recording paper P by the discharge roller 30.

(Printing (ink ejection))
At the time of printing, in the drive circuit 100, a drive signal as shown in FIG. This drive signal is a combination of a plurality of trapezoidal waves, and is output with a period of about 50 μsec.

  The image data is converted into a print nozzle selection signal, and on / off of the switching element 108 is controlled by the print nozzle selection signal.

  When the switching element 108 is turned on, a voltage is applied to the piezoelectric element 42 and vibration is started.

  This vibration is transmitted to the vibration plate 46A of the pressure chamber 46, and the vibration plate 46A vibrates to generate a pressure wave in the ink in the pressure chamber 46. By this pressure wave, the ink stored in the ink tank 41 is ejected from the nozzle 40 through the supply path 44 and the pressure chamber 46.

`` Discharge status judgment ''
In the present embodiment, whether or not the ink is discharged from the nozzles 40 during the main scanning direction switching interval (deceleration, stop, acceleration) when printing on a plurality of recording papers P is performed. (See FIG. 13). In particular, it is an object to detect ink ejection failure (worst is non-ejection) due to air bubbles entering the pressure chamber 46 and clogging of the nozzle 40.

  In order to determine the quality of the discharge state, a discharge state detection circuit system is incorporated in the drive circuit 100 with respect to the basic circuit system.

  FIG. 14 is a timing chart for determining the ejection state during the main scanning direction reversal period during printing on a plurality of recording sheets P. When the main scanning direction is reversed, the viscosity adjustment / non-ejection detection trigger signal is generated. The detection signal is output based on the trigger signal.

  As a result, the determination selection switch 112 provided in the drive circuit 100 is sequentially turned on based on the non-ejection detection nozzle selection signal. At this time, all the switch portions 108A of the switching element 108 are turned on, so that the non-ejection detection and the viscosity adjustment in the pressure chamber 46 can be performed.

  As a result, data from the piezoelectric element 42 corresponding to the determination selection switch 112 being turned on (the output voltage V0 from the differential amplifier 118) can be collected.

  At the time of data collection from the next piezoelectric element 42, data processing (spectrum analysis) of data collected last time is executed by the CPU 140 (see FIG. 8), and the quality of the ejection state is determined.

  In this way, by performing the sequential processing on the plurality of piezoelectric elements 42, the quality determination of the ejection state of all the piezoelectric elements 42 is executed during the main scanning direction reversal period.

  As shown in FIG. 15, the detection signal is not limited to a trapezoidal wave but may be a rectangular wave.

  In the present embodiment, the PWA type ink jet printer 10 has been described as an example, but the same effect can be obtained even with an FWA type ink jet printer.

  FIG. 16 is a control flowchart showing a control routine for correcting the drive signal given to the piezoelectric element 42 in the controller 133.

  In step 200, it is determined whether or not data (voltage V0 from the differential amplifier 118 of the bridge circuit) has been input. If an affirmative determination is made, the process proceeds to step 202, where the resonance frequency and the resonance frequency are determined. Compare with the reference value of sharpness (Q).

  In the next step 204, it is determined whether or not the resonance frequency deviation is within a correctable range. If an affirmative determination is made, the process proceeds to step 206 to select a drive signal. In step 208, the drive power supply unit 105 is driven. A drive signal selection signal for specifying the type of signal is output, and the process proceeds to step 210.

  In Step 210, it is determined whether or not the sharpness (Q) of the resonance frequency is within the correctable range. If an affirmative determination is made, the process proceeds to Step 212 to set the voltage value of the drive signal. A set voltage value signal is output to the voltage varying means 141, and this routine ends.

  If a negative determination is made in step 204 (resonance frequency deviation is outside the correctable range), or a negative determination is made in step 210 (sharpness deviation is outside the correctable range), the process proceeds to step 216 and error processing ( For example, a message for instructing the maintenance of the recording head 36 is displayed, and this routine ends.

  In addition, when it is out of the correctable range, the following measures can be considered.

  (1) The drive signal amplitude is set to zero so that ink is not ejected.

  In order to prevent the missing dots (white streaks, etc.) from becoming conspicuous, it is preferable to use a known image processing that increases the dot size for the dots around the missing dots.

  (2) Conduct maintenance.

  If the discharge failure is not resolved even after maintenance is performed, take action (1).

"Modification of inkjet printer"
FIG. 17 shows a schematic configuration diagram of an FWA type ink jet printer 150, and the recording head 150 has piezoelectric elements arranged in the entire main scanning direction (not shown in FIG. 17).

In this FWA type ink jet printer 150, for example, by changing the position in the sub-scanning direction, it can be made to face a cleaning device (not shown) as a suction means, and directly above this cleaning device. When the carriage 14 is positioned, it is possible to suck ink from the nozzles 40.
The recording heads 150 are arranged in a plurality of rows (two rows in FIG. 17) in the sub-scanning direction, and ink is ejected from the nozzles while the recording paper P is being transported at a constant pitch or at a constant speed by the transport belt 152. Discharge and print. For this reason, since there is no non-printing period in the period for printing all of the recording paper P, the next recording paper P is positioned at a predetermined position by the transport of the transport belt 152 (detected by the paper detection sensor 154). Until a predetermined time) (during the page break period in FIG. 18), a detection signal is output to each nozzle, and the quality of the discharge state of each nozzle is determined.

  As described above, in the present embodiment, a circuit for determining whether or not the ejection state is good is incorporated in the inkjet printer 10, and a detection signal is output in a time zone that is outside the printing period and is indispensable for printing. Thus, the pressure fluctuation mainly caused by the bubbles mixed in the pressure chamber 46 of the recording head 36 and the fluctuation of the fluid resistance caused by the clogging of the nozzle 40 are monitored at any time. Further, by correcting the drive signal, it is possible to improve the quality of the printed matter without reducing the production capacity.

  Further, by extracting only the mechanical admittance out of the electrical admittance and the mechanical admittance of the recording head 36, a slight load fluctuation is analyzed with a high S / N ratio, which is expressed as a fluctuation in resonance frequency and sharpness. Therefore, the quality of the discharge state can be determined quickly and reliably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an external appearance of a PWA type ink jet printer according to an embodiment. FIG. 4 is a perspective view of a carriage provided in the inkjet printer according to the present embodiment. FIG. 6 is a cross-sectional view showing the internal structure of the recording head according to the present embodiment. It is a drive circuit diagram (digital) for driving a piezoelectric element according to the present embodiment. FIG. 4 is an equivalent circuit diagram of a load generated when driving a piezoelectric element according to the present embodiment. FIG. 4 is a discharge state determination circuit diagram included in a drive circuit according to the present embodiment. FIG. 6 is a vibration wave characteristic diagram when a detection signal (viscosity adjustment waveform) is used as an input source according to the present embodiment. It is a control block diagram for discharge state determination control according to the present embodiment. FIG. 6 is a frequency-phase characteristic diagram of an electro-mechanical coupling system admittance according to the present embodiment. FIG. 6 is a frequency-phase characteristic diagram of mechanical admittance according to the present embodiment. FIG. 4 is a frequency-amplitude characteristic diagram showing a spectrum analysis result based on an output voltage from a differential amplifier according to the present embodiment, where (A) shows pressure fluctuation in the pressure chamber, and (B) shows discharge resistance due to nozzle clogging. Show. FIG. 6 is a vibration wave characteristic diagram when a print waveform when printing is performed by driving a piezoelectric element according to the present embodiment is used as an input source. 6 is a timing chart of carriage operation and drive signal output in a PWA inkjet printer according to the present embodiment. 5 is a timing chart of the printing operation of the inkjet printer, data extraction for determining the ejection state, and data analysis according to the present embodiment. 10 is a timing chart of the printing operation of the inkjet printer, data extraction for determining the ejection state, and data analysis according to a modification of the present embodiment. 4 is a control flowchart showing a control routine for correcting a drive signal given to a piezoelectric element 42 in a controller 133. FIG. 10 is a schematic configuration diagram of an FWA inkjet printer according to a modification of the present embodiment. 10 is a timing chart of carriage operation and drive signal output in an FWA inkjet printer according to a modification of the present embodiment.

Explanation of symbols

P Recording paper 10 Inkjet printer (PWA)
12 Inkjet recording unit 14 Carriage 20 Main scanning mechanism 32 Sub scanning mechanism 33 Cleaning device (suction means)
34 Paper Tray 36 Recording Head 40 Nozzle 41 Ink Tank 42 Piezoelectric Element 44 Supply Path 46 Pressure Chamber 46A Diaphragm 100 Drive Circuit (Discharge State Detection Means)
DESCRIPTION OF SYMBOLS 102 Digital voltage amplifier 104 Selector 106 Detection signal generation part 108 Print waveform generation part 112 Determination selection switch 118 Differential amplifier 134 Admittance extraction means (nozzle discharge state determination means)
136 Filter 138 A / D converter 139 Spectrum analysis means (nozzle discharge state determination means)
140 CPU (correction means)
Rd resistance Cd capacitor (detection circuit)
Rdd dummy resistor (detection circuit)
Cdd dummy capacitor (detection circuit)
Ye Electric admittance (detection circuit)
Ya Mechanical admittance (detection circuit)

Claims (11)

A piezoelectric droplet that supplies a drive signal having a predetermined pulse width and amplitude to the piezoelectric element based on the image data, generates a vibration wave in the pressure chamber by this drive signal, and discharges the liquid in the pressure chamber from the nozzle. An image that includes an ejection element, faces the droplet ejection element with respect to the recording medium conveyance path, and moves the droplet ejection element and the recording medium relatively to form an image on the recording medium. A forming device,
Discharge for determining the discharge state of the droplet discharge element based on a signal output corresponding to the mechanical load of the droplet discharge element when the piezoelectric element is driven based on a predetermined detection signal State determination means;
Control means for changing the pulse width or amplitude of the drive signal according to the determination result of the ejection state determination means;
An image forming apparatus.   The discharge state determining means includes a first wiring in which the piezoelectric element and a resistor of the droplet discharge element are connected in series, a dummy capacitor equivalent to a braking capacitor of the piezoelectric element, and a dummy resistor equivalent to the resistor. The second wirings connected in series are connected in parallel, and a predetermined detection signal is applied to both ends of the second wiring, so that between the piezoelectric element and the on-resistance in the first wiring, the second wiring The image forming apparatus according to claim 1, further comprising a bridge circuit that uses a potential difference between the dummy capacitor and the dummy resistor as an output voltage. A plurality of the droplet discharge elements,
The ejection state determination means includes a switch for connecting any one piezoelectric element of the plurality of droplet ejection elements to the bridge circuit,
The image forming apparatus according to claim 2, wherein the resistance is an on-resistance of the switch.   The image forming apparatus according to claim 1, wherein the discharge state determination unit determines the discharge state based on a resonance frequency of an output signal of the bridge circuit.   When the resonance frequency is within a preset range, the control unit changes a pulse width of the drive signal according to the resonance frequency, and the resonance frequency is outside the preset range. The image forming apparatus according to claim 4, wherein an amplitude of the drive signal is set to zero.   The image forming apparatus according to claim 1, wherein the discharge state determination unit determines a discharge state based on a Q value of an output signal of the bridge circuit. A suction means for sucking the droplet from the nozzle;
When the Q value is within a preset range, the control means controls the correction means to change the depth section of the drive signal according to the Q value, and the Q value is preset. The image forming apparatus according to claim 5, wherein the liquid is sucked from the nozzle of the liquid droplet ejection element when the liquid is out of the range. A suction means for sucking the liquid from the nozzle;
The discharge state determination means determines the discharge state based on the resonance frequency and Q value of the output signal of the bridge circuit,
When the resonance frequency is within a preset range, the control unit changes a pulse width of the drive signal according to the resonance frequency, and the resonance frequency is outside the preset range. The correction means is controlled so as to change the amplitude of the drive signal according to the Q value when the amplitude of the drive signal is zero, and the Q value is within a preset range. 6. The image forming apparatus according to claim 5, wherein when the value is out of a preset range, the old unit is controlled to suck the liquid from the nozzle of the droplet discharge element.   2. The apparatus according to claim 1, further comprising: a discharge state determination execution control unit that executes determination by the discharge state determination unit and change by the control unit outside a printing period on the recording medium by the droplet discharge element. The image forming apparatus according to claim 8.   The image forming apparatus according to claim 1, wherein the detection signal also serves as a viscosity adjustment signal generated for adjusting the viscosity in the pressure chamber. A piezoelectric droplet that supplies a drive signal having a predetermined pulse width and amplitude to the piezoelectric element based on the image data, generates a vibration wave in the pressure chamber by this drive signal, and discharges the liquid in the pressure chamber from the nozzle. An image that includes an ejection element, faces the droplet ejection element with respect to the recording medium conveyance path, and moves the droplet ejection element and the recording medium relatively to form an image on the recording medium. A liquid discharge state determination method that is used in a forming apparatus and determines the quality of a liquid discharge state caused by volume fluctuation in a pressure chamber and clogging of a nozzle,
When the piezoelectric element is driven based on a predetermined detection signal, a discharge state of the droplet discharge element is determined based on a signal output corresponding to a mechanical load of the droplet discharge element;
A liquid discharge state determination method, wherein the pulse width or amplitude of a drive signal is changed according to the determination result.

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