JP6816396B2 - Droplet ejection device, image forming device, abnormal ejection detection method for droplet ejection head, and program - Google Patents

Description

The present invention relates to a droplet ejection device, an image forming apparatus, an abnormal ejection detection method for a droplet ejection head, and a program.

An inkjet printer uses a recording medium (paper, metal, wood, etc.) with an inkjet recording head having a nozzle for ejecting ink droplets (droplets), a pressure chamber communicating with the nozzle, and a piezoelectric element for pressurizing ink in the pressure chamber. Form desired characters, figures, etc. on ceramics, etc.).

The recording head of an inkjet printer is provided with a large number of nozzles, but some nozzles are clogged with ink droplets due to drying of the nozzles, thickening of ink in the pressure chamber, and mixing of air bubbles in the pressure chamber. If it cannot be ejected, dot omission occurs in the printed image, which causes deterioration of image quality.

In particular, in a large continuous-type inkjet printer that can continuously apply drive waveforms to the recording head to form images at high speed, image quality deterioration occurs due to nozzle clogging, and if the printed matter does not meet the desired print quality, reprinting is performed. It will be necessary and will have a great impact on productivity.

Residual vibration detection technology is known as a technology that can detect nozzle clogging. The residual vibration detection technique is a technique for detecting the nozzle state by changing the vibration pattern of the counter electromotive force generated by the vibration of the nozzle surface (hereinafter, meniscus) propagating to the piezoelectric element after the ink droplets are ejected.

As an example of using the residual vibration detection technique, a method of detecting a nozzle clogging state using the period of the residual vibration waveform as a parameter is known (see Patent Document 1).

Here, in Patent Document 1, in order to calculate the period of the residual vibration waveform, a dedicated inspection waveform having a waveform length longer than that of the drive waveform is used.

However, as the inspection waveform applied to the recording head becomes longer, the printing speed decreases, so that abnormal ejection is inspected at a predetermined speed or less. Therefore, if a long inspection waveform is applied to detect abnormal discharge during printing, productivity will drop. Furthermore, nozzle clogging could not be detected at a high printing speed such that the drive waveform is continuous.

Therefore, in view of the above circumstances, it is an object of the present invention to provide a droplet ejection device that solves the above problems and detects abnormal ejection while maintaining productivity.

In order to solve the above problems, in one aspect of the present invention, a droplet ejection head including a nozzle, a pressure chamber communicating with the nozzle and accommodating a liquid, and a piezoelectric element arranged so as to face the pressure chamber. A drive waveform generator that drives the piezoelectric element and generates a drive waveform whose potential changes from the reference potential, a potential of a residual vibration waveform generated in the pressure chamber after the piezoelectric element is driven, and the drive waveform. a detector for detecting a magnitude relation between the higher than the reference potential first threshold value, e Bei and a state determination unit determines whether the abnormal state of the nozzle or the pressure chamber on the basis of the detected magnitude relation The state determination unit detects the potential of the residual vibration waveform detected by the detection unit at the detection time after the drive for compressing or expanding the piezoelectric element and after a period of time less than the meniscus natural vibration cycle of the nozzle. Is provided, and a droplet ejection device for determining the state of the nozzle is provided.

According to one aspect, in the droplet ejection device, abnormal ejection can be detected while maintaining productivity.

It is a figure which illustrates the inkjet recording apparatus which concerns on embodiment of this invention. It is a side view which illustrates the droplet ejection device which concerns on embodiment. It is the schematic which shows an example which arranged the recording head which concerns on embodiment in a line head configuration. It is an enlarged bottom view of the recording head of FIG. It is a perspective view which illustrates the inkjet recording head which concerns on embodiment. This is an example of a drive waveform applied to the piezoelectric element. It is an operation conceptual diagram which shows ink ejection and residual vibration in a pressure chamber. It is a figure which illustrates the drive waveform application period and the residual vibration waveform generation period of FIG. FIG. 5 is a block diagram illustrating a droplet ejection device including a recording head and a drive control board according to the first embodiment. It is a circuit diagram explaining one structural example of a detection part. It is a circuit diagram explaining another configuration example of a detection part. It is explanatory drawing about the detection method of the detection part provided in the recording head. It is a judgment figure of the nozzle state used in one Example of this invention. It is a figure explaining the principle that a potential difference is generated for each nozzle state. It is a figure explaining the reason why the nozzle state can be detected without reducing the productivity without using a dedicated waveform. It is a flowchart which showed the whole control of the inkjet recording apparatus in one Example of this invention.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings and tables. In each drawing, the same components may be designated by the same reference numerals and duplicate description may be omitted.

<Inkjet recording device>
FIG. 1 is a schematic configuration diagram showing an example of a line scanning type inkjet recording device in the on-demand method according to the present embodiment. In FIG. 1, the printing system 1000 includes an inkjet recording device 1, a recording medium supply unit 200, and a recording medium collection unit 300.

The inkjet recording device 1 includes a regulation guide 3, an in-feed unit 4, a dancer roller 5, an EPC 6, a meandering amount detector 7, an inkjet recording module 8, a platen 9, a maintenance / recovery module 2, a drying module 10, an out-feed unit 11, and a puller. Has twelve.

The regulation guide 3 positions the recording medium S in the width direction. The in-feed unit 4 includes a drive roller and a driven roller that keep the tension of the recording medium S constant. The dancer roller 5 moves up and down according to the tension of the recording medium S and outputs a position signal. The EPC (Edge Position Controller) 6 controls the position of the end portion of the recording medium S. The platen 9 is provided so as to face the inkjet recording module 8. The outfeed unit 11 includes a drive roller and a driven roller that drive the recording medium S at a set speed. The puller 12 includes a drive roller and a driven roller that discharge the recording medium S out of the apparatus.

The inkjet recording module 8 has a line head in which nozzles 16 (print nozzles, ejection ports) (see FIG. 4) are arranged over the entire print width. Color printing is performed by black, cyan, magenta, and yellow line heads. At the time of printing, the nozzle surface of each line head is supported on the platen 9 with a predetermined gap. The inkjet recording module 8 ejects ink according to the transport speed of the recording medium S to form a color image on the recording medium S.

The maintenance / recovery module (maintenance / recovery means) 2 performs an appropriate maintenance / recovery operation on the inkjet recording module 8 mounted on the inkjet recording device (image forming device) 1 to recover the ejection performance of the inkjet recording head.

An operation panel 91 that functions as a user interface (operation unit) that allows the user to input and output information is installed in the housing of the inkjet recording device 1.

By using the line scanning type as the inkjet recording device 1, high-speed image formation becomes possible.

<Overview of Inkjet Recording Module>
FIG. 2 is a side view showing the configuration of the inkjet recording module 8. As shown in FIG. 2, the inkjet recording module 8 mainly includes a drive control substrate 18, an inkjet recording head 15, and a connection portion 50.

The drive control board 18 is equipped with a control unit 81, a drive waveform generation unit 82, and a storage means 83 shown in FIG.

In the connection portion 50, the cable 51 is attached with the drive control board side connector 52 and the head side connector 53, and is an analog signal and a digital signal between the drive control board 18 and the head board 60 mounted on the recording head 15. Take charge of communication.

The recording head (also referred to as an inkjet recording head unit or a piezoelectric droplet ejection head) 15 includes a head substrate 60, a state detection substrate 40, and a piezoelectric element support substrate (head drive IC substrate) 32 as control drive units. Further, as shown in FIG. 5, a plurality of plates are laminated on the recording head 15 so as to eject ink.

The recording head 15 is provided with a rigid plate 28 for accommodating the piezoelectric element 31 and a flow path plate 36 in which a nozzle 16 and a pressure chamber (individual pressure chamber, liquid chamber) 20 (see FIG. 5) are formed. .. Further, the ink tank 70 containing the ink is provided in the recording head 15 in the vicinity of the piezoelectric element support substrate 32.

In the line scanning type inkjet recording device 1, the recording head 15 has a line head configuration in which the recording heads 15 are arranged in the depth direction (or the front direction) of FIG. 2, which is the direction perpendicular to the transport direction of the recording medium S. is there.

However, the present invention is not limited to the line scanning type configuration. While moving one or more recording heads 15 in the depth direction (or the front direction) of the paper surface, which is the direction perpendicular to the transport direction of the recording medium S, the recording medium S is transported in the transport direction to form an image. A serial scanning printer, another droplet ejection device, or the like may be used.

<Inkjet recording head>
FIG. 3 is a schematic view in which the recording head 15 is arranged in a line head configuration. The recording head 15 shown in FIG. 3 is composed of an aggregate of four head arrays 14K, 14C, 14M, and 14Y. The black head array 14K ejects black ink droplets, the cyan head array 14C ejects cyan ink droplets, the magenta head array 14M ejects magenta ink droplets, and the yellow head array 14Y ejects yellow ink droplets. Ink droplets are ejected.

The head arrays 14K, 14C, 14M, and 14Y extend in a direction orthogonal to the transport direction (arrow direction) of the recording medium S such as paper. By arranging the heads in this way, a wide print area width is secured.

FIG. 4 is an enlarged view of the bottom surface of the recording head 15 of FIG. A large number of nozzles 16 are arranged in a staggered pattern on the nozzle surface (bottom surface) 17 of the recording head 15, and in this embodiment, 64 nozzles 16 are arranged in a staggered pattern in two rows. By arranging a large number of nozzles 16 in a staggered manner in this way, high resolution can be supported.

FIG. 5 is a configuration perspective view of the recording head 15. The recording head 15 mainly includes a nozzle plate 19, a pressure chamber plate 21, a restrictor plate 23, a diaphragm plate 26, a rigid plate 28, and a piezoelectric element group 35.

The flow path plate 36 is formed by sequentially stacking, positioning and joining the nozzle plate 19, the pressure chamber plate 21, the restrictor plate 23, and the diaphragm plate 26.

A large number of nozzles 16 are arranged and formed in a staggered pattern on the nozzle plate 19. A pressure chamber 20 corresponding to each nozzle 16 is formed in the pressure chamber plate 21. The restrictor plate 23 is formed with a restrictor 22 that communicates the common ink flow path 27 with the (individual) pressure chamber 20 to control the ink flow rate to the pressure chamber 20. The diaphragm plate 26 is provided with a diaphragm 24 and a filter 25.

The flow path plate 36 is joined to the rigid plate 28 so that the filter 25 faces the opening of the common ink flow path 27. The upper opening end of the ink introduction pipe 30 is connected to the common ink flow path 27 of the rigid plate 28, and the lower opening end of the ink introduction pipe 30 is connected to the ink tank 70 (see FIG. 2) filled with ink. ..

The piezoelectric element support substrate 32 is mounted with a piezoelectric element drive IC (head drive IC) 33 and supports the piezoelectric element 31. An electrode pad (piezoelectric pad) 34 is connected to the piezoelectric element drive IC 33, and the drive waveform generated by the piezoelectric element drive IC 33 is applied to the piezoelectric element 31 via the electrode pad 34 (see FIG. 7).

A piezoelectric element group 35 formed by arranging a large number of piezoelectric elements 31 is mounted on the rigidity plate 28. The recording head 15 is configured by inserting the piezoelectric element group 35 into the opening 29 of the rigid plate 28 and adhesively fixing the free ends of the piezoelectric elements 31 to the diaphragm 24.

In FIG. 5, for simplification of the drawing, the nozzle 16, the pressure chamber 20, the restrictor 22, the piezoelectric element 31, and the like are shown in a smaller number than the actual number.

<Detection of residual vibration>
FIG. 6 is a drive waveform diagram applied to the piezoelectric element. The drive waveforms include a first reference potential holding waveform that holds a predetermined reference potential Vs, a PULL waveform that contracts the piezoelectric element, a HOLD waveform that holds the contracted state, a PUSH waveform that extends the piezoelectric element, and a second. Consists of the reference potential holding waveform of.

FIG. 7 is an operation conceptual diagram showing ink ejection and residual vibration in the pressure chamber. FIG. 7A shows the pressure chamber expanding (E in FIG. 6), FIG. 7B shows the pressure chamber contracting (C in FIG. 6), and FIG. 7C holds the second reference voltage (potential). It shows the pressure change generated in the pressure chamber 20 after the period R2 and after the ink is ejected.

At the time of ink ejection shown in FIGS. 7 (a) and 7 (b), the analog SW (switch) 37 in the piezoelectric element drive IC 33 is turned ON / OFF according to the image data transmitted from the drive control board 18. , The drive waveform of FIG. 6 is applied to the electrode pad 34.

The expansion and contraction force of the piezoelectric element 31 based on the drive waveform expands and contracts the volume of the pressure chamber 20 via the vibrating plate 24 forming the elastic wall of the pressure chamber 20, and changes the pressure in the pressure chamber 20. , A pressure is generated (pressurized) in the direction of the nozzle 16 to eject the ink (liquid L).

Specifically, the PULL waveform of FIG. 6 is a falling waveform element that lowers the voltage from the reference voltage Vs, and the piezoelectric element 31 is as shown in FIG. 7A during the period in which the falling waveform element is applied to the piezoelectric element 31. The pressure chamber 20 is expanded and depressurized through the vibrating plate 24, which is the pressure chamber expansion period E.

The HOLD waveform of FIG. 6 is a holding waveform element that holds a falling potential, and ink flows from the supply path (ink introduction pipe) 30 into the pressure chamber 20 while the holding waveform element is applied to the piezoelectric element 31. Be supplied.

The PUSH waveform of FIG. 6 is a rising waveform that raises the voltage from the held voltage to the reference potential Vs, and during the period in which the rising waveform element is applied to the piezoelectric element 31, the piezoelectric element 31 is moved as shown in FIG. 7B. The pressure chamber contraction period C is set in which the pressure chamber 20 is expanded and contracted through the vibrating plate 24 to pressurize.

When the first reference potential holding waveform and the second reference potential holding waveform that hold a predetermined reference potential (holding waveform element) Vs are applied to the piezoelectric element 31 (FIG. 6), the reference voltage holding periods R1 and R2 , A reference potential is applied from the electrode pad 34 to the piezoelectric element 31, and the vibrating plate 24 is in a substantially horizontal state.

After the ink is ejected in FIG. 7C, after the reference voltage holding period R2 in FIG. 6, the analog SW37 that applies the drive waveform to the piezoelectric element 31 is turned off as described later, so that the piezoelectric element 31 and the diaphragm 24 are turned off. Is no longer controlled by the drive waveform. Therefore, after ejecting the ink, the residual vibration of the ink meniscus (surface) propagates in the pressure chamber 20 as a wave and is transmitted to the piezoelectric element 31 via the diaphragm 24, so that the residual vibration voltage is induced in the electrode pad 34. Will be done.

In this way, the nozzle state (the state of the ink in the nozzle) can be grasped by detecting the residual vibration voltage change (that is, the potential at a predetermined detection time) induced in the electrode pad 34.

FIG. 8 is a diagram illustrating a drive waveform application period and a residual vibration waveform generation period of FIG. 7.

During the drive waveform application period of FIG. 8, the piezoelectric element 31 is contracted by the PULL waveform (falling waveform element) of the drive waveform as shown in FIG. 7 (a), and then the PUSH waveform (PUSH waveform) as shown in FIG. 7 (b). By extending by the rising waveform element), it corresponds to the operation of ejecting ink droplets.

The residual vibration waveform generation period of FIG. 8 corresponds to the operation of FIG. 7 (c). The residual vibration waveform is a damped vibration waveform that is generated at the time when the analog SW37 (see FIG. 10) is turned off, and the residual pressure wave propagates to the piezoelectric element 31 via the diaphragm 24.

<Configuration of inkjet recording module>
FIG. 9 is a block diagram illustrating a drive system of a droplet ejection device (injection recording module 8) including a recording head 15 and a drive control substrate 18 according to the first embodiment.

The drive control board 18 includes a control unit (drive control unit) 81, a drive waveform generation unit 82, and a storage means 83. The storage means 83 stores image data transmitted from the main control unit 90 that controls the entire device. The control unit 81 generates a timing control signal and drive waveform data based on the image data. The drive waveform generation unit 82 D / A-converts the generated drive waveform data, amplifies the voltage, and amplifies the current to generate a drive waveform.

Digital signals such as timing control signals generated by the control unit 81 of the drive control board 18 are transmitted to the recording head 15 by serial communication, deserialized by the head control unit 61 (timing control signal) on the head board 60, and deserialized. It is input to the piezoelectric element drive IC 33.

The drive waveform generated by the drive waveform generation unit 82 is input to the piezoelectric element 31 based on ON / OFF of the analog SW37 (see FIG. 10) in the piezoelectric element drive IC 33.

The state detection substrate 40 is equipped with a detection unit 41 that detects the potential of the residual vibration waveform generated according to the nozzle state and compares it with the threshold value.

In the example of FIG. 9, the state determination unit 63 is mounted on the head control unit 61 of the head substrate 60 on the inkjet recording head 15 side, but the state determination unit 63 is mounted on the drive control board 18 side. May be good.

The state determination unit 63 mounted on the head control unit 61 or the control unit 81 determines the state (whether or not it is an abnormal state) of the nozzle and the pressure chamber from the detection result (detected magnitude relationship) of the detection unit 41, and prints. Decide whether to continue or stop printing and move to recovery measures.

Specifically, the abnormal state of the nozzle or the pressure chamber includes a dry / thickening state (a dry state of the nozzle or a thickening state of the ink in the pressure chamber) and a state in which air bubbles are mixed in the pressure chamber.

The dry / thickened state means that the surface of the ink in the pressure chamber is in contact with the outside air through the opening of the nozzle during continuous printing, so that the ink surface of the nozzle is partially thickened. The solvent evaporates in the pressure chamber due to the effects of self-heating due to changes in the ambient temperature and humidity due to the dry condition (including the partially solidified state) and continuous driving, and the viscosity of the ink in the pressure chamber increases overall. Including thickened state.

Further, in the ejection operation, when the meniscus of the ink is pulled back into the nozzle, air bubbles are entrained, so that the air bubbles are mixed into the pressure chamber.

When an abnormal state occurs, the ink ejection speed fluctuates for each nozzle, causing abnormal images such as uneven density, streaks, and color changes. Furthermore, as the thickening of the ink progresses, the thickened ink clogs the nozzles (missing failure). ), There is a possibility that missing dots (pixel loss) may occur in the image forming region. Therefore, the state determination unit 63 determines the state of the nozzle and the pressure chamber, and in the case of an abnormal state, determines to perform an appropriate maintenance / recovery operation on the nozzle and the pressure chamber.

A main control unit 90, which is a higher-level device for control, is connected to the drive control board 18, and an operation panel 91 and maintenance / recovery means 2 are connected to the main control unit 90.

Information such as printing continuation or printing stop, execution of recovery processing, etc. determined by the state determination unit 63 is sent to the main control unit 90 via the control unit 81. The main control unit 90 executes printing continuation or printing stop, and a recovery operation by the maintenance / recovery means 2 is executed according to an instruction from the main control unit 90.

Alternatively, the state of the nozzle or the state of the pressure chamber determined by the state determination unit 63 (normal state, dry / thickened state (dry state of the nozzle or thickened state of ink in the pressure chamber), air bubble mixed state in the pressure chamber), etc. After the information is sent to the main control unit 90 via the control unit 81, it may be displayed on the operation panel 91 and reported to the user. In this case, the user can select to continue printing or stop printing and set whether or not to execute the recovery process.

By inquiring to the user, it is possible to reflect the user's intention to allow the abnormal image and continue printing or stop printing without allowing it. The medium for reflecting the user's intention is not limited to the operation panel 91, and information may be input by an external computer or the like connected to the main control unit 90 or the main control unit 90.

(Configuration example 1 of detection unit)
FIG. 10 is a circuit diagram illustrating a configuration example of one of the detection units. The detection unit 41 includes one comparison detection unit 42 and a switching unit 45.

The comparison detection unit 42 uses the first comparison means 43 having a first threshold value Vth1 having a potential higher than the reference potential Vs as the comparison potential and the second threshold value Vth2 having a potential lower than the reference potential Vs as the comparison potential. It is provided with a second comparison means 44. The switching unit 45 switches each piezoelectric element 31 to be detected (inspected).

For example, the comparison means 43 and 44 are composed of a comparator, and the switching unit 45 is composed of a multiplexer.

When two comparison means are provided in the detection unit as shown in FIGS. 10 and 11, the detected voltage Vrs can be compared with the first threshold value Vth1 and the detected voltage Vrs can be compared with the second threshold value Vth2. , The abnormal state of the nozzle or pressure chamber can be separated into a dry / thickened state and a bubble mixed state.

Here, immediately after turning off the analog SW37 and immediately after switching the input destination of the switching unit 45 that functions as a changeover switch, switching noise is superimposed on the residual vibration waveform, and the correlation between the nozzle state and the potential difference affects the noise. Easy to receive. Therefore, in order to prevent false detection due to noise and to compare voltage values more accurately, it is preferable to exclude a predetermined time from the detection target.

In order to exclude the predetermined period from the inspection target, the timing is controlled by the timing control unit (control unit) 62 of the head control unit 61 in the state determination unit 63 in the subsequent stage of the detection unit 41, and the read timing of the detected comparison result is read. By controlling, the voltage is masked for a predetermined period.

Alternatively, the switching unit 45 may mask the voltage by not connecting the comparison detection unit 42 to the piezoelectric element 31 to be detected for a predetermined period from the time when the analog SW 37 is turned off until the detection time.

Further, the detection unit 41 may be configured to convert the potential by using an AD converter instead of the comparison means 43 and 44.

Therefore, since the detection unit of the present invention requires only the comparison unit, a waveform shaping unit composed of a high-pass filter or low-pass filter that removes noise components, a negative feedback amplifier that adjusts amplitude, a voltage follower, or a counter is provided. It becomes unnecessary.

Therefore, it is possible to suppress the circuit cost and the substrate area in the detection unit that detects the residual vibration.

In this configuration example, residual vibration is detected by using a common detection unit while switching the detection target by the switching means for the piezoelectric elements corresponding to the plurality of nozzles. Therefore, the number of circuits can be reduced in the droplet ejection device.

(Configuration example 2 of detection unit)
FIG. 11 is a circuit diagram illustrating another configuration example of the detection unit.

In FIG. 10 described above, a configuration example in which the detection unit 41 includes the switching unit 45 has been described, but the switching unit may not be included in the detection unit, and as shown in FIG. 11, the piezoelectric elements 31a to 31x A comparative detection unit 42a to 42x may be provided for each of them.

In this configuration example, in order to prevent erroneous detection due to switching noise of analog SW37a to 37x, the state determination unit 63 whose timing is controlled by the timing control unit 62 masks the voltage of the comparison result detected by the detection unit 41A for a predetermined period. Then, the predetermined period is excluded from the inspection target.

In this configuration example, the same number of detection units are provided so as to correspond to each of the plurality of piezoelectric elements. Therefore, the residual vibrations of the plurality of piezoelectric elements can be detected at the same time, and can be detected at a higher speed.

As described above, it is preferable that the detection unit appropriately selects the configuration (configuration example 1, configuration example 2) according to the circuit scale and application.

<Detection method for abnormal discharge>
FIG. 12 is an explanatory diagram relating to a detection method of a detection unit provided in the recording head. According to the measurement results shown in FIG. 12, the drive waveform is applied, the analog SW37 is turned off, and then the detection timing is appropriately set to allow the nozzle and pressure chamber to be in a normal discharge state and a dry / thickened state (nozzle surface). The potential difference shown in FIG. 12 occurs in the three states of drying or thickening of the liquid in the pressure chamber) and in the state of air bubbles in the pressure chamber communicating with the nozzle.

Here, the frequency of the residual vibration in the normal discharge state is substantially equal to the natural vibration frequency fc of the pressure chamber 20. The meniscus natural vibration cycle is uniquely determined for each nozzle by the nozzle diameter, pressure chamber volume, pressure chamber constituent members, and the like.

In FIG. 12, Vs indicates a reference potential, Vth1 indicates a first threshold value which is a voltage larger than the reference potential Vs, and Vth2 indicates a second threshold value which is a voltage smaller than the reference potential Vs.

FIG. 13 shows a determination diagram of the nozzle state. The detection unit 41 uses the potential difference shown in FIG. 12 to determine the nozzle state.

As an example, a first threshold value Vth1 having a potential higher than the reference potential Vs and a second threshold value Vth2 having a potential lower than the reference potential Vs are set. From the combination of the magnitude relationship between the detected residual vibration waveform potential Vrs and the first threshold value Vth1 and the second threshold value Vth2 at the detection time after masking a predetermined period from the time when the analog SW37 is turned off, Detects (determines) the nozzle state.

Immediately after the analog SW37 is turned off, switching noise is superimposed on the residual vibration waveform, and the potential difference indicating the state of the nozzle is easily affected by the noise. Therefore, in order to prevent erroneous detection due to noise and to compare voltage values more accurately, a predetermined time is excluded (masked) from the detection target.

The masking period may be less than the meniscus natural vibration cycle Tc of the nozzle. The relationship between the masking period and continuous driving will be described later with reference to FIG.

Here, the nozzle state is determined by comparing the potential Vrs of the residual vibration waveform at the detection time of FIG. 12, the detection voltage Vrs of the residual vibration, and Vth1 and Vth2.

That is, when the detected voltage Vrs is larger than the first threshold value Vth (Vth1 <Vrs), the nozzle and the pressure chamber are in the normal discharge state. When the detection voltage Vrs is larger than the second threshold value Vth2 and equal to or less than the first threshold value Vth1 (Vth2 <Vrs ≦ Vth1), the nozzle surface is dry (the surface of the liquid). Is partially thickened or solidified), or the liquid in the pressure chamber is totally thickened. When the detected voltage Vrs is equal to or less than the second threshold value Vth2 (Vrs ≦ Vth2), the pressure chamber communicating with the nozzle is in a state of air bubbles.

It should be noted that, including (or more or less) or not including (greater than or equal to or less than) the threshold value in the predetermined range described here is an example, and the presence or absence of the threshold value in each range is appropriate. You may change it.

When the determination is made using the two thresholds of the first threshold value Vth1 and the second threshold value Vth2 as described above, the abnormal state is determined as a dry / thickening state (nozzle drying or thickening state of pressure chamber ink) and a pressure chamber. There is an advantage that it is possible to separate from the air bubble mixed state and the type of recovery operation can be appropriately selected.

On the other hand, when the dry / thickened state and the bubble mixed state are recognized as some abnormal state, the threshold value to be compared is set to only the first threshold value Vth1, and the nozzle is compared by comparing the detected voltage Vrs and the first threshold value Vth1. And a determination method for separating the normal discharge state and the abnormal state of the pressure chamber may be used.

In this case, only one comparison unit may be provided in the detection unit provided in FIGS. 10 and 11 of the above-mentioned detection unit, or a switching unit is not required, so that further increase in circuit cost and increase in substrate area can be suppressed. effective.

Therefore, it is preferable that the detection unit appropriately selects the number of threshold values to be set according to the circuit scale and the application.

Next, the principle of generating a potential difference for each nozzle state will be described with reference to FIG. 14 (a) is a schematic diagram of a normal discharge state, FIG. 14 (b) is a dry / thickened state, and FIG. 14 (c) is a schematic diagram of a bubble mixed state.

In the normal ejection state shown in FIG. 14A, the residual vibration of the meniscus is large because the ink droplets (droplets) have been ejected. Further, since the volume of the pressure chamber 20 is smaller by the amount of the droplets ejected than before the ejection, the piezoelectric element 31 is in a state of extending in the nozzle 16 direction.

That is, a residual vibration waveform having a large amplitude is observed on the electrode pad 34 with a potential higher than the reference potential Vs of the drive waveform as the vibration center.

After the ink is ejected, the ink is supplied to the pressure chamber 20, but since it is supplied over a time sufficiently longer than the residual vibration cycle, the amount of ink in the pressure chamber 20 is still small at the detection time. The vibration center of the residual vibration waveform holds a potential higher than the reference potential Vs.

As shown in FIG. 14B, the surface of the nozzle 16 is dry (the surface of the ink is partially thickened or solidified), or the ink in the pressure chamber 20 is totally increased. If it is sticky, the residual vibration of the meniscus is small. At this time, since the ink is not discharged, the volume of the pressure chamber 20 does not change. That is, in the dry / thickened state, a residual vibration waveform having a small amplitude centered on the reference potential Vs is observed on the electrode pad 34.

In FIG. 14C, since air bubbles are mixed in the pressure chamber 20, the volume in the pressure chamber 20 increases by the volume integral, and the piezoelectric element 31 contracts in the direction opposite to the nozzle 16. .. That is, in the bubble mixed state, the residual vibration waveform centered on the potential lower than the reference potential Vs is observed on the electrode pad 34.

When it is determined that the state is abnormal as shown in FIGS. 14 (b) and 14 (c), for example, a flushing operation, a suction operation, or the like is performed as the maintenance / recovery operation.

For example, in the flushing operation (empty discharge operation), a drive waveform (recovery waveform) larger than the normal drive waveform is applied to the piezoelectric element of the inkjet recording module 8 without using the maintenance / recovery means 2. By this operation, the dried (increased viscosity) ink can be discharged from the nozzle 16 as shown in FIG. 14 (b). This recovery operation can be performed immediately even during printing.

In the suction operation, the ink in the pressure chamber 20 is sucked through the nozzle cap by using the nozzle cap, tube, tube pump, drain ink cartridge and the like provided in the maintenance recovery means (suction recovery means) 2. This is an operation of discharging the ink to the discharge ink cartridge via the tube. By this operation, bubbles (gas) mixed in the pressure chamber 20 are discharged as shown in FIG. 14 (c), and ink having increased viscosity (thickening) is discharged from the nozzle 16 as shown in FIG. 14 (b). Can be made to. The recovery by the suction operation is performed by suspending the printing operation.

Here, in the present invention, the reason why the nozzle state can be detected while maintaining high productivity without using a dedicated waveform will be described. FIG. 15 is a diagram illustrating the reason why the state of the nozzle and the pressure chamber can be detected without reducing the productivity without using the dedicated waveform.

The application unit of the drive waveform is composed of the first reference potential holding waveform, the PULL waveform, the HOLD waveform, the PUSH waveform, and the second reference potential holding waveform shown in FIG.

Further, in general, the times R1 and R2 of the first and second reference potential holding waveforms are set longer than one cycle of the meniscus natural vibration cycle, respectively.

In the present invention, for example, when the continuous drive waveforms are the first drive waveform and the second drive waveform, respectively, the time for detecting the state of the nozzle and the pressure chamber is after the mask. The mask period is less than one cycle of the meniscus natural vibration cycle from the time when the analog SW37 is turned off while the second reference potential holding waveform of the first drive waveform is applied.

Here, since the meniscus natural vibration cycle is uniquely determined for each nozzle, it is assumed that the meniscus natural vibration cycle is the shortest among a plurality of nozzles in the head, and the mask period is set shorter than the shortest cycle.

Further, the detection of the residual vibration for determining the state of the nozzle and the pressure chamber can be carried out instantly by comparing the potentials at the above detection times. For example, the detection of the present invention makes it unnecessary to detect a continuous change in the residual vibration voltage for a predetermined period used for calculating a period of residual vibration or a damping ratio from a plurality of amplitudes. Therefore, it is possible to immediately shift to the application of the next drive waveform to the same nozzle after the potential is detected at the detection time.

Therefore, after the mask period (after the end), by instantly completing the detection of the residual vibration by measuring the potential, it can be detected earlier than the ON time of the analog SW37 of the second drive waveform, so that the first drive waveform can be detected. The detection of residual vibration after application does not affect the application of the second drive waveform.

From the above, it is possible to instantly detect the state of the nozzle and the pressure chamber at a printing speed in which the drive waveform is continuous without using the dedicated waveform. That is, abnormal discharge can be detected with high production without reducing productivity.

<Overall control>
FIG. 16 is a flowchart showing overall control (printing control, abnormality ejection detection method) of the inkjet recording apparatus according to the embodiment of the present invention. Such a print flow may be stored in a program such as the main control unit 90 or another computer and executed.

First, as a print start flow, after START (S201), initialization (S202) is performed, and printing is started by setting print settings (S203) for setting an image, resolution, transport speed, other correction values, and the like (S204). ..

During printing, the drive waveform generation unit 82 applies a drive waveform (drive pulse for discharge) to determine the state of the nozzle and the pressure chamber (S205).

It is detected whether or not the detection voltage Vrs of the residual vibration generated after applying the drive waveform in S205 is larger than the first threshold value Vth (Vth1 <Vrs). More specifically, the detection unit 41 detects the magnitude relationship by comparing the voltages.

When the detection voltage Vrs is larger than the first threshold value Vth (S206, Yes), the state determination unit 63 determines that the nozzle and the pressure chamber are in the normal discharge state (S207).

The control unit 81 determines whether or not the printing is completed (S208), and if "No", the printing is continued, so the process returns to S205, and the drive waveform is transmitted from the drive waveform generation unit 82 to the piezoelectric element 31 again. Apply (S205).

Then, again, the detection unit 41 detects whether the detection voltage Vrs of the residual vibration generated after applying the drive waveform in S205 is larger than the first threshold value Vth (Vth1 <Vrs) (S206), and the nozzle or Determine if the pressure chamber is in an abnormal state.

In this way, when the normal ejection state (Yes in S206) continues, S205 to S208 are repeated while changing the inspection target of the nozzle for inspecting abnormal ejection during printing, and the printing ends (S208, Yes). END, S209).

In S206, if the detected voltage Vrs is equal to or less than the first threshold value Vth (Vth1 ≧ Vrs) (No), the process proceeds to step S210.

In step S210, the detection unit 41 detects whether the detection voltage Vrs is larger than the second threshold value Vth2 and equal to or less than the first threshold value Vth1 (Vth2 <Vrs ≦ Vth1).

When the detection voltage Vrs is larger than the second threshold value Vth2 and equal to or less than the first threshold value Vth1 (Vth2 <Vrs ≦ Vth1) (Yes in S210), the state determination unit 63 dries the nozzle 16 or the pressure chamber 20. It is determined that the thickening state is present (S211).

When the ink is in a dry / thickened state, a recovery waveform is applied at the timing between pages, which is a non-printing area, to perform empty ejection as one recovery operation, and dry ink (locally thickened (solidified) ink). ), Or the nozzle 16 is refreshed by ejecting the thickened ink that is thickened as a whole (S212).

Here, the recovery waveform is a waveform having a voltage amplitude difference larger than that of the drive waveform, and by giving a sudden pressure change in the pressure chamber 20, the viscosity of a part or the whole increases in the nozzle or the pressure chamber. As a result, it has the effect of ejecting (empty ejection) dry ink or thickening ink that is difficult to move and eject.

Since the recovery (S212) by such an empty discharge operation can be performed immediately even during printing, the next drive waveform is applied (returns to S205) after the empty discharge operation is performed.

On the other hand, when it is not determined in S210 that Vth2 <Vrs ≦ Vth1 (No), the detection voltage Vrs is smaller than the second threshold value Vth2 (Vrs <Vth2), and the state determination unit 63 communicates with the nozzle 16. It is determined that the chamber 20 is in a state where air bubbles are mixed (S213).

At this time, printing is stopped (S214), and a suction recovery operation (S215) for sucking ink from each nozzle is performed as one recovery operation. The suction recovery operation has a function of attaching a suction device to the nozzle surface 17 and sucking out dry ink, thickening ink, or air bubbles in the pressure chamber 20.

Since the recovery by such a suction operation (S215) is performed by pausing the printing operation, the process returns to the print setting (S203) after the suction operation is performed.

Further, when detecting only two states, that is, the nozzle and the pressure chamber are in a normal discharge state or an abnormal state, S210 may be omitted, and if S206 is "No", some recovery processing may be performed.

Further, when an abnormal state is detected, an inquiry may be made so that the user can select the recovery process (whether or not to recover, the type of recovery process, etc.).

Further, S214 and S215 are omitted, and the nozzle 16 communicating with the pressure chamber 20 in which air bubbles are mixed is reported to the user in S203 in a state where printing is not stopped even after the bubble mixing state is detected and the printing operation is continued. The user may select to continue printing or stop printing, and it may be possible to set whether or not to execute the recovery process.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and is within the scope of the gist of the embodiment of the present invention described in the claims. Various modifications and changes are possible.

1 Inkjet recording device (image forming device)
8 Inkjet recording module (droplet ejection device)
15 Recording head (invertical recording head, droplet ejection head)
16 nozzles (print nozzle, discharge port)
18 Drive control board 20 Pressure chamber (individual pressure generation chamber, individual liquid chamber)
31 Piezoelectric element 32 Piezoelectric element support substrate 33 Piezoelectric element drive IC (head drive IC)
34 Electrode pad 40 State detection board 41, 41A Detection unit 42, 42a to 42x Comparison detection unit 43 First comparison means 44 Second comparison means 45 Switching means 50 Connection unit 60 Head board 61 Head control unit 62 Timing control unit ( Control unit)
63 Status determination unit 81 Control unit 82 Drive waveform generation unit 83 Storage means S Recording medium L Ink (liquid)
E Pressure chamber expansion period (falling waveform, PULL)
C Pressure chamber contraction period (rising waveform, PUSH)
H Fall voltage retention period (HOLD)
R1 First reference voltage holding period R2 Second reference voltage holding period Vs Reference potential Vth1 First threshold value Vth2 Second threshold value

JP-A-2015-47803

Claims (16)

A droplet ejection head comprising a nozzle, a pressure chamber communicating with the nozzle and accommodating a liquid, and a piezoelectric element arranged so as to face the pressure chamber.
A drive waveform generator that drives the piezoelectric element and generates a drive waveform whose potential changes from the reference potential,
A detection unit that detects the magnitude relationship between the potential of the residual vibration waveform generated in the pressure chamber after driving the piezoelectric element and the first threshold value higher than the reference potential of the driving waveform.
E Bei and a state determination unit determines whether the abnormal state of the nozzle or the pressure chamber on the basis of the detected magnitude relation,
The state determination unit determines the potential of the residual vibration waveform detected by the detection unit at the detection time after the drive for compressing or expanding the piezoelectric element and after a period of time less than the meniscus natural vibration cycle of the nozzle. A droplet ejection device that reads and determines the state of the nozzle . The drive waveform includes at least a falling waveform element that lowers the voltage from the reference potential so as to compress the piezoelectric element and expand the pressure chamber, a holding waveform element that holds the falling voltage, and extends the piezoelectric element. A rising waveform element that raises a voltage from the held potential to the reference potential so as to cause the pressure chamber to contract.
The droplet ejection device according to claim 1. The state determination unit from after the rising waveform element of the drive waveform has risen to the reference potential, and a predetermined period mask below the meniscus natural vibration period of the nozzle, to the detection time of the post-mask period, the detector Reads the potential of the residual vibration waveform detected by
The state determination unit determines the state of the nozzle at the detection time after the mask period.
The droplet ejection device according to claim 2. The droplet ejection device is provided with a plurality of nozzles.
The mask period set by the state determination unit is less than the shortest period of the meniscus natural vibration cycle of the plurality of nozzles provided in the droplet ejection head.
The droplet ejection device according to claim 3. When the potential of the residual vibration waveform detected by the detection unit is higher than the first threshold value, the state determination unit determines that the nozzle or the pressure chamber is in a normal state, and the potential of the residual vibration waveform becomes When it is equal to or less than the first threshold value, it is determined that the nozzle or the pressure chamber is in an abnormal state.
The droplet ejection device according to any one of claims 1 to 4. The detection unit includes a first comparison means for comparing the potential of the residual vibration waveform generated in the pressure chamber after driving the piezoelectric element with the first threshold value.
The droplet ejection device according to any one of claims 1 to 5. The droplet ejection device is provided with a plurality of nozzles, a plurality of pressure chambers communicating with each of the plurality of nozzles to store a liquid, and a plurality of piezoelectric elements arranged so as to face the pressure chambers.
The detection unit includes a switching unit that can select each piezoelectric element to be detected.
The droplet ejection device according to any one of claims 1 to 6. The droplet ejection device is provided with a plurality of nozzles, a plurality of pressure chambers communicating with each of the plurality of nozzles to store a liquid, and a plurality of piezoelectric elements arranged so as to face the pressure chambers.
The same number of detection units are provided so as to correspond to the plurality of piezoelectric elements.
The droplet ejection device according to any one of claims 1 to 6. The detection unit detects the magnitude relationship between the first threshold value and the detected potential, and the magnitude relationship between the second threshold value, which is a potential lower than the reference potential, and the detected potential.
When the potential of the residual vibration waveform detected by the detection unit is higher than the first threshold value, the state determination unit determines that the nozzle is in a normal state, and the potential of the residual vibration waveform is the first. When it is equal to or lower than the threshold value of and higher than the second threshold value, it is determined that the nozzle is dry or the liquid in the pressure chamber is thickened, and the residual vibration waveform is determined. When the potential of the pressure chamber is equal to or less than the second threshold value, it is determined that the pressure chamber is in a bubble-mixed state.
The droplet ejection device according to any one of claims 1 to 4, 6 to 8. The detection unit includes a second comparison means for comparing the potential of the residual vibration waveform generated in the pressure chamber after driving the piezoelectric element with the second threshold value.
The droplet ejection device according to claim 9. An image forming apparatus including the droplet ejection device according to any one of claims 1 to 10.
A recovery process is executed to recover the state of the liquid in the nozzle or the pressure chamber according to the state of the nozzle determined by the state determination unit.
Image forming device. In the recovery process, during printing, a recovery waveform having a larger amplitude than the drive waveform is applied to the piezoelectric element, and thickened droplets are discharged from the nozzle to change the state of the liquid in the nozzle or the pressure chamber. It is an action to recover,
The image forming apparatus according to claim 11. The image forming apparatus is provided with suction recovery means.
The recovery process is an operation in which the suction recovery means recovers the state of the nozzle or the pressure chamber by stopping printing and executing a suction recovery operation.
The image forming apparatus according to claim 11. The operation of the recovery process can be selected.
The image forming apparatus according to any one of claims 11 to 13. A method for detecting abnormal discharge of a droplet discharge head, comprising a nozzle, a pressure chamber communicating with the nozzle and accommodating a liquid, and a piezoelectric element arranged so as to face the pressure chamber.
A drive waveform generation step for generating a drive waveform in which the potential changes from the reference potential, which drives the piezoelectric element,
A detection step for detecting the magnitude relationship between the potential of the residual vibration waveform generated in the pressure chamber after driving the piezoelectric element and the threshold value higher than the reference potential of the driving waveform.
Have a, a state determination step determines whether the abnormal state of the nozzle or the pressure chamber on the basis of the detected magnitude relation,
In the state determination step, the potential of the residual vibration waveform detected in the detection step is set at the detection time after the drive for compressing or expanding the piezoelectric element and after a period less than the meniscus natural vibration cycle of the nozzle. A method for detecting abnormal discharge of a droplet discharge head that reads and determines the state of the nozzle . A computer is made to execute the abnormal discharge detection method according to claim 15.
program.

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