WO2018186140A1

WO2018186140A1 - Ink jet recording apparatus and driving method

Info

Publication number: WO2018186140A1
Application number: PCT/JP2018/010186
Authority: WO
Inventors: 諒平小林
Original assignee: コニカミノルタ株式会社
Priority date: 2017-04-07
Filing date: 2018-03-15
Publication date: 2018-10-11
Also published as: JP7001090B2; JPWO2018186140A1

Abstract

Provided are an ink jet recording apparatus and a driving method with which ink can be ejected at high speed and stably regardless of a temperature condition. The ink jet recording apparatus is provided with: an ink jet head having a nozzle and a pressure generation element that applies pressure to ink supplied to the nozzle; and a driving control section that controls a voltage applied to the pressure generation element. A driving voltage waveform of the voltage applied to the pressure generation element during a driving operation for causing the ink to be ejected from the nozzle includes a voltage waveform of an ejection pulse related to an ink ejection operation and a voltage waveform of a pulse for stabilizing a fluctuation in the pressure of the ink. Among the voltage waveforms, one is a voltage waveform containing a temporary change from a reference voltage Vref0 to a voltage Vc greater than the reference voltage, and the other is a voltage waveform containing a temporary change from the reference voltage to voltages Va1 and Va2 smaller than the reference voltage. The driving control section changes the reference voltage according to the temperature of the ink to be ejected.

Description

Inkjet recording apparatus and driving method

The present invention relates to an ink jet recording apparatus and a driving method.

Conventionally, there is an ink jet recording apparatus that forms an image or a structure by ejecting ink from a nozzle. Inkjet recording apparatuses are used for a wide range of applications.

In this ink jet recording apparatus, various inks are used depending on applications. Among these inks, there are inks whose characteristics such as viscosity change according to the surrounding environment such as temperature. Due to the change in ink characteristics, there is a problem that even if a certain pressure fluctuation is applied to the ink, the discharge speed and discharge amount of the ink change, so that an image or structure cannot be formed properly.

On the other hand, Patent Document 1 discloses a technique for detecting the temperature using a nozzle plate formed of a thermistor as a material and correcting the amplitude of the drive voltage waveform for ejecting ink according to the temperature change. Has been.

JP 2010-208068 A

However, when the amplitude of the drive voltage is simply changed according to the temperature, there is a problem that the stability of the ink in the nozzle after ink ejection is likely to be lowered, and it is difficult to eject ink stably at high speed.

An object of the present invention is to provide an ink jet recording apparatus and a driving method capable of stably discharging ink at high speed regardless of temperature conditions.

In order to achieve the above object, the invention according to claim 1
An inkjet head having a nozzle that ejects ink, and a pressure generating element that applies a pressure according to the deformation to the ink supplied to the nozzle by being deformed according to an applied voltage;
A drive control unit for controlling a voltage applied to the pressure generating element;
With
The drive voltage waveform of the voltage applied to the pressure generating element during the drive operation of discharging ink from the nozzle includes a discharge drive waveform related to the ink discharge operation and a stable suppression of ink pressure fluctuation caused by the ink discharge operation. Waveform and
One of the ejection drive waveform and the stabilization waveform is a voltage waveform including a temporary change from a reference voltage to a first voltage larger than the reference voltage, and the other is the reference voltage to the reference voltage. A voltage waveform including a temporary change to a smaller second voltage,
The drive control unit is an ink jet recording apparatus that changes the reference voltage according to the temperature of ejected ink.

According to a second aspect of the present invention, in the ink jet recording apparatus of the first aspect,
The drive control unit can change the number of ejection drive waveforms included in the drive voltage waveform.

According to a third aspect of the present invention, in the ink jet recording apparatus according to the second aspect,
The drive control unit discharges one ink droplet from the nozzle by applying a voltage having the drive voltage waveform including a plurality of the discharge drive waveforms to the pressure generating element.

According to a fourth aspect of the present invention, in the ink jet recording apparatus according to the second or third aspect,
The plurality of ejection drive waveforms included in the drive voltage waveform include two or more waveforms having different shapes.

The invention according to claim 5 is the ink jet recording apparatus according to any one of claims 2 to 4,
The drive control unit changes the number of the ejection drive waveforms included in the drive voltage waveform according to the density gradation of the ink on the landing surface of the ink ejected from the nozzle.

The invention according to claim 6 is the ink jet recording apparatus according to any one of claims 1 to 5,
The drive control unit determines the reference voltage according to the type of ink.

The invention according to claim 7 is the ink jet recording apparatus according to claim 6,
A plurality of inkjet heads;
The drive control unit determines the reference voltage according to the type of ink respectively supplied to the plurality of inkjet heads.

The invention according to claim 8 is the ink jet recording apparatus according to any one of claims 1 to 7,
A correspondence storage unit that stores a correspondence relationship between the temperature and the reference voltage is provided.

The invention according to claim 9 is the ink jet recording apparatus according to any one of claims 1 to 8,
The drive control unit causes the pressure generating element to apply a voltage having a non-ejection voltage waveform that causes pressure fluctuation in the ink without ejecting ink from the nozzle,
The non-ejection voltage waveform includes a temporary change in voltage in the same direction as a temporary change in voltage in the ejection drive waveform from the reference voltage, and has the same direction as a temporary change in voltage in the stabilization waveform. Does not include temporary changes in voltage to.

The invention according to claim 10 is the ink jet recording apparatus according to any one of claims 1 to 9,
A temperature measurement unit that measures a temperature corresponding to the temperature of the ejected ink is provided.

The invention according to claim 11
An inkjet head driving method comprising: a nozzle that ejects ink; and a pressure generating element that applies a pressure corresponding to the deformation to the ink supplied to the nozzle by being deformed according to an applied voltage. ,
The drive voltage waveform of the voltage applied to the pressure generating element during the drive operation of discharging ink from the nozzle includes a discharge drive waveform related to the ink discharge operation and a stable suppression of ink pressure fluctuation caused by the ink discharge operation. Waveform and
One of the ejection drive waveform and the stabilization waveform is a voltage waveform including a temporary change from a reference voltage to a first voltage larger than the reference voltage, and the other is the reference voltage to the reference voltage. A voltage waveform including a temporary change to a smaller second voltage,
An output adjustment step of changing the reference voltage in accordance with the temperature of the ejected ink.

According to the present invention, there is an effect that ink can be ejected stably at high speed regardless of temperature conditions.

It is a block diagram which shows the function structure of an inkjet recording device. It is a figure which shows the drive voltage signal for the ink discharge in an inkjet recording device. It is a figure which shows the drive voltage signal at the time of the ink non-discharge in an inkjet recording device. FIG. 6 is a diagram illustrating voltage adjustment of an ink ejection drive voltage signal in an inkjet recording apparatus. FIG. 6 is a diagram illustrating voltage adjustment of a drive voltage signal when ink is not ejected in an inkjet recording apparatus. It is a flowchart which shows the control procedure of the drive voltage adjustment control process performed with the inkjet recording device of this embodiment. It is a figure which shows the example of the other waveform of the drive voltage signal which can be output with an inkjet recording device. It is a figure which shows the example of the other waveform of the drive voltage signal which can be output with an inkjet recording device. It is a figure which shows the example of the other waveform of the drive voltage signal which can be output with an inkjet recording device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a functional configuration of an inkjet recording apparatus 1 according to an embodiment of the present invention.

The inkjet recording apparatus 1 includes a main body control unit 41, a movement control unit 42, a movement operation unit 51, a communication unit 52, an operation display unit 53, a notification output unit 54, a temperature measurement unit 55, and head drive control. A unit 20 (drive control unit), an inkjet head 30 and the like are provided, and these are connected via a bus 56 so as to be able to transmit and receive signals.

The main body control unit 41 controls the overall operation of the inkjet recording apparatus 1. The main body control unit 41 includes a CPU 411 (Central Processing Unit), a RAM 412 (Random Access Memory), a storage unit 413, and the like.

The CPU 411 performs various arithmetic processes. The CPU 411 reads out a control program stored in the storage unit 413 and performs various control processes related to image recording and setting thereof.

The RAM 412 provides a working memory space to the CPU 411 and stores temporary data. The storage unit 413 includes a non-volatile memory that stores a control program, setting data, and the like. Further, the storage unit 413 may include a DRAM or the like that temporarily stores settings related to a droplet discharge command (print job) acquired from the outside via the communication unit 52, image data to be recorded, and the like.

The movement operation unit 51 moves a recording medium, which is a target for recording an image, in a predetermined direction to move the recording medium relative to the inkjet head 30, and performs at least operations related to supply and discharge of the recording medium. Examples of the moving operation unit 51 include an outer periphery of a cylindrical drum carrying a recording medium on the surface and a rotary motor that rotates around the surface of an endless belt. The moving operation unit 51 may be configured to move the recording medium and the inkjet head 30 relative to each other, that is, to move the inkjet head 30 relative to the stationary or moving recording medium.
The movement control unit 42 operates the movement operation unit 51 to perform a control operation for moving the carried recording medium at an appropriate timing and speed. The movement control unit 42 may have a common configuration with the main body control unit 41.

The inkjet head 30 is provided with a plurality of nozzles 35 for ejecting ink arranged in a predetermined pattern, and ejects ink droplets from the openings of the plurality of nozzles 35 at an appropriate timing on the recording medium. Record an image. When the ink jet recording apparatus 1 records a color image, a plurality of ink jet heads 30 are provided corresponding to each of a plurality of colors of ink (a plurality of ink types) used for image recording. The arrangement pattern of the nozzles 35 in the inkjet head 30 is not particularly limited, and may be a one-dimensional arrangement or a two-dimensional arrangement. In addition to the plurality of nozzles 35, the inkjet head 30 includes a piezoelectric element 31 as a pressure generating element (electromechanical conversion element) that deforms according to an applied voltage, an ejection selection switching element 32, and the like.

The piezoelectric element 31 is provided for each of the plurality of nozzles 35, deforms according to the applied voltage, and applies a pressure according to the deformation to the liquid (ink) to be ejected, thereby dropping droplets from the nozzles 35. Is an actuator that discharges water. Here, the piezoelectric element 31 is provided along, for example, a pressure chamber that communicates with one of the nozzles 35 and one end that communicates with an ink flow path that supplies ink or an ink chamber. The element 31 vibrates the diaphragm, thereby applying a pressure corresponding to the deformation amount to the ink in the pressure chamber. Thus, the ink is pushed out from the pressure chamber to the nozzle 35 according to the pressure applied to the ink in the pressure chamber, and the ink is pulled back from the nozzle 35 or the like. For example, a deflection mode (bend mode) is used as the deformation mode of the piezoelectric element, but the applied voltage corresponds to the deformation amount of the piezoelectric element, and the pressure applied to the ink changes according to the deformation. It is not particularly limited. Here, when a voltage on the positive side of the reference voltage Vref is applied, the piezoelectric element 31 is deformed in a direction of pressurizing ink (a direction of reducing the pressure chamber), and a voltage on the negative side of the reference voltage Vref. Is applied, the piezoelectric element 31 is deformed in a direction of depressurizing ink (a direction of expanding the pressure chamber).

The ejection selection switching element 32 switches whether each piezoelectric element 31 is supplied with a drive voltage signal for ejecting ink or a drive voltage signal for when ink is not ejected from the head drive control unit 20. The ejection selection switching element 32 supplies a drive voltage signal corresponding to the presence or absence of ejection of droplets from each nozzle 35 based on image data to be recorded, and the like, thereby changing the pressure pattern applied to the ink at each nozzle 35. Switch. The drive voltage signal when ink is not ejected is a drive voltage signal having such a small amplitude that ink droplets are not ejected.

The head drive control unit 20 outputs a drive voltage signal for driving the piezoelectric element 31 of the inkjet head 30 at an appropriate timing according to each pixel data of the image to be recorded. The head drive control unit 20 may be formed collectively on a substrate or the like, or may be arranged dispersedly in each part of the inkjet recording apparatus 1. A part or all of the configuration of the head drive control unit 20 may be provided in the inkjet head 30. The head drive control unit 20 includes a head control unit 43, a drive waveform amplification circuit 21, and a DAC 22 (digital / analog converter).

The DAC 22 converts an analog signal obtained by converting the waveform pattern data of each drive waveform (for ink ejection and when ink is not ejected) output from the head controller 43 at a predetermined clock frequency into the drive waveform amplification circuit 21. Output.

The drive waveform amplification circuit 21 outputs a drive voltage signal having a predetermined waveform pattern to each piezoelectric element 31 in accordance with the ejection timing of the ink droplets from the nozzle 35, the non-ejection state type, and the like. In the inkjet recording apparatus 1 of the present embodiment, the drive voltage waveform includes a trapezoidal voltage waveform that changes to the positive side and the negative side with respect to the reference voltage according to the drive voltage signal, although not particularly limited thereto. A voltage is applied to the piezoelectric element 31. An analog signal obtained by the DAC 22 is input to the drive waveform amplifier circuit 21, and the analog signal is power amplified and output.
As will be described later, in the inkjet recording apparatus 1, since the reference voltage Vref changes, the drive waveform amplification circuit 21 amplifies each drive waveform data to a voltage amplitude corresponding to the reference voltage Vref, for example, and then performs an offset. The reference voltage Vref of the value is added and output.

The head control unit 43 controls the operation of the head drive control unit 20 according to the presence or absence of image data to be recorded and the content of the image data. The head control unit 43 includes a CPU 431, a storage unit 432 (corresponding storage unit), and the like. The storage unit 432 preliminarily stores a waveform pattern of a drive voltage signal for ejecting ink from the nozzles 35 and vibrating the liquid level (meniscus) of the ink inside the nozzles 35 as digital discrete value array data (digital data). Hold. The storage unit 432 stores and holds a reference voltage setting table 432a described later. A non-volatile memory such as a ROM or a rewritable flash memory is used for the storage unit 432, and the reference voltage setting table 432a is stored in advance as initial data or according to ink determined at the time of inspection before shipping, etc. Written and stored. Further, the data of the reference voltage setting table 432a can be added or changed according to the addition or improvement of the type of ink to be ejected from the inkjet head 30.

Based on the image data to be recorded stored in the storage unit 432 or the storage unit 413, the CPU 431 uses the head drive control unit 20 to drive a drive voltage having an appropriate waveform pattern according to whether or not to discharge droplets from each nozzle 35. Waveform pattern data for outputting a signal is selected and output at an appropriate timing according to a clock signal (synchronization signal) (not shown).
The head controller 43 may be provided in common with the main body controller 41.

The communication unit 52 communicates with an external device according to a predetermined communication standard, and transmits and receives data. As communication standards to be used, various standards such as LAN (Local Area Network) TCP / IP, near field communication such as wireless LAN, Bluetooth communication (registered trademark: Bluetooth), USB (Universal Serial Bus), etc. It is possible to use direct communication with an external device. The communication unit 52 receives a print job which is a command related to image recording from an external device, and outputs status information of the inkjet recording apparatus 1 to the external device as necessary.

The operation display unit 53 accepts user operations and displays information and menus for the user. As the operation display unit 53, for example, a display unit provided with an LCD (liquid crystal display) as the display unit 532 is used, and various menus and statuses related to image recording are displayed on the display screen of the LCD. In addition, a touch panel serving as the operation detection unit 531 is provided corresponding to the LCD, and the touch operation corresponding to the display on the display screen can be detected by arranging the touch panel on the LCD display screen. Alternatively, the operation display unit 53 may include a push button switch and detect a push operation of the push button switch.

The notification output unit 54 performs a predetermined notification operation when an abnormality occurs in the inkjet recording apparatus 1. Examples of the notification output unit 54 include a sound generation unit that generates a predetermined beep sound using a piezoelectric element or the like, and a light emitting unit that blinks or lights an LED lamp.

The temperature measuring unit 55 measures the temperature according to the temperature of the ink ejected from the nozzle 35 and outputs the measurement result. Instead of directly measuring the temperature of the ink in the nozzle 35, the temperature measuring unit 55 stores, for example, the temperature in the vicinity of the nozzle 35 of the nozzle substrate on which the nozzle 35 is formed, or the ink chamber that stores the ink supplied to the nozzle 35. And the temperature of the ink in the ink channel. These measured values may be directly used as the temperature of the ejected ink, or may be converted into an estimated value of the temperature of the ejected ink by the main body control unit 41 or the head control unit 43 (CPU 431). In the case where a plurality of inkjet heads 30 are provided, the temperature measurement unit 55 may separately measure the temperature of the ink for each, and the configuration, structure, and In the case of the type of ink, the temperature measured for some of the inkjet heads 30 may be used in common.

Next, a method for driving the inkjet head 30 in the inkjet recording apparatus 1 of the present embodiment will be described.
FIG. 2A is a diagram illustrating a drive voltage signal for ink ejection in the inkjet recording apparatus 1. FIG. 2B is a diagram illustrating a driving voltage signal driving voltage signal when ink is not ejected in the inkjet recording apparatus 1.

As shown in FIG. 2A, when ink is ejected (during driving operation), the head drive control unit 20 uses the reference voltage Vref, here the initial reference voltage Vref0, as the drive voltage signal (drive voltage waveform). Signals of trapezoidal voltage waveforms W1 and W2 that temporarily change to a negative voltage side (small voltage) than Vref are output, and then a positive voltage side (large voltage) from the reference voltage Vref to the reference voltage Vref. ) Is output as a trapezoidal voltage waveform W3. The peak voltage of the voltage waveform W1 is fixed to the voltage Va1, and the peak voltage of the voltage waveform W2 is fixed to the voltage Va2 (the voltages Va1 and Va2 are the second voltages). The peak voltage of the voltage waveform W3 is fixed at the voltage Vc (first voltage). Although not particularly limited, the reference voltage Vref and the voltages Va1, Va2, and Vc can all be positive voltages here.

The boosted portion Wi1 of the voltage waveform W1 and the boosted portion Wi2 of the voltage waveform W2 are voltage changes related to ink ejection, that is, the voltage waveforms W1 and W2 (one of the three voltage waveforms W1, W2, and W3) are. , Discharge pulses (a plurality of discharge drive waveforms). Here, these intervals are appropriately determined with respect to the resonance frequency of the ink in the ink flow path and the pressure chamber communicating with the nozzle 35 and the nozzle 35 and the phase of the vibration (that is, the same phase), and the liquid level of the ink The vibration is amplified and ink is ejected in accordance with the second boosted portion Wi2. That is, one ink droplet is ejected by the drive voltage waveform including the plurality of ejection pulses. In this case, the amplitude of each ejection pulse, that is, the voltages Va1 and Va2, can be different from each other (ejection drive waveforms having different shapes).

On the other hand, the stepped-down portion Wd3 of the voltage waveform W3 is a voltage change that attenuates and stabilizes the vibration of the ink surface related to ink ejection, that is, the voltage waveform W3 (among the three voltage waveforms W1, W2, and W3). The other is a stabilization pulse (stabilization waveform). Here, the interval between the step-up portion Wi2 and the step-down portion Wd3 is appropriately determined with respect to the resonance frequency of the ink in the ink flow path and the pressure chamber communicating with the nozzle 35 and the nozzle 35 and the phase of the vibration thereof (that is, reverse) Phase), the pressure fluctuation of the ink, that is, the amplitude of vibration of the liquid surface (surface) is effectively suppressed. In this way, even when ink is ejected at high speed (high frequency) by suppressing pressure fluctuation of the ink and stabilizing the liquid level (meniscus) of the ink and then generating pressure fluctuation relating to the next ink ejection again. Pressure fluctuations suitable for ink ejection can be generated in ink in the nozzles stably each time.

On the other hand, as shown in FIG. 2B, when ink is not ejected, the head drive control unit 20 generates a non-ejection voltage waveform with respect to the reference voltage Vref (here, the initial reference voltage Vref0). A signal including only the trapezoidal voltage waveform W4 (non-ejection pulse) that temporarily changes in the same direction as the pulse signal is output. The peak voltage of the voltage waveform W4 is fixed to the voltage Va3 that is larger than the voltages Va1 and Va2 (that is, the potential difference from Vref0 is small). The output time of the voltage waveform W4 is longer than the output time of the voltage waveforms W1 to W3 (in this case, twice). As a result, the ink in the nozzle 35 undergoes a pressure fluctuation within a range where the ink is not ejected from the opening of the nozzle 35, that is, the liquid level vibrates, and this vibration is not suppressed and is maintained at an appropriate cycle. .

The ink to be ejected is not particularly limited, but the viscosity of many inks changes according to the temperature change. For example, when ink is used whose viscosity decreases when the temperature rises and increases when the temperature falls, if ink is ejected with the same drive voltage waveform regardless of the temperature, the ink will vary depending on the difference in viscosity. The discharge speed and discharge amount of droplets can change. Therefore, by adjusting the drive voltage waveform so that the liquid level of the ink in the nozzle 35 is vibrated with a strong force as the viscosity increases, the ink is uniformly ejected regardless of the temperature.

In the inkjet recording apparatus 1 of the present embodiment, the voltage amplitude (voltages Va1 and Va2 at the time of ink ejection is changed by changing the reference voltage Vref according to the temperature measured by the temperature measurement unit 55, that is, according to the temperature of the ink. And the difference between the reference voltage Vref). The reference voltage Vref is preset for each temperature for each ink type (color), and the correspondence between these temperatures and the reference voltage Vref is stored and held in the storage unit 432 as a reference voltage setting table 432a.

FIG. 3A is a diagram for explaining voltage adjustment of an ink ejection drive voltage signal in the inkjet recording apparatus 1. FIG. 3B is a diagram for explaining voltage adjustment of a drive voltage signal when ink is not ejected in the inkjet recording apparatus 1.
As shown in FIG. 3A, the reference voltage Vref is changed from the initial reference voltage Vref0 to a high VrefH or a low VrefL according to a temperature change. The number of change steps is appropriately determined within a range in which the influence of temperature does not affect the image quality. That is, the number of change steps can be changed according to the required image quality.

As described above, when the reference voltage Vref is changed, the amplitude dV1 of the voltage waveforms W1 and W2 and the amplitude dV3 of the voltage waveform W3 at the time of ink ejection change according to the fluctuation of the reference voltage Vref. When the highest upper reference voltage VrefH is set, the voltage waveform of the drive voltage signal has a shape indicated by a thick dotted line. The amplitude of the voltage waveform W1 at this time changes to a first upper limit interval dV1H wider than the first reference interval dV1m, and the amplitude of the voltage waveform W3 changes to a third lower limit interval dV3H narrower than the third reference interval dV3m. In addition, when the lowest lower limit reference voltage VrefL is set, the voltage waveform of the drive voltage signal has a shape indicated by a thick solid line. The amplitude of the voltage waveform W1 at this time changes to a first lower limit interval dV1L narrower than the first reference interval dV1m, and the amplitude of the voltage waveform W3 changes to a third upper limit interval dV3L wider than the third reference interval dV3m.

When the ink viscosity is low, the attenuation rate of the ink vibration in the nozzle 35 is small, so the vibration is attenuated with a strong force and stabilized. On the contrary, when the viscosity of the ink is high, the attenuation rate of the vibration of the ink in the nozzle 35 is increased, and the vibration of the ink is sufficiently reduced in a short time without being stabilized by a strong force. Accordingly, the magnitude relationship between the necessary forces is opposite to that during ejection of the ink droplets, that is, the magnitudes of the amplitudes necessary for ejection and stability are complementary. In the ink jet recording apparatus 1, the magnitude of such an amplitude is determined by changing only the reference voltage Vref while fixing the discharge voltages Va1 and Va2 and the stabilization voltage Vc.

That is, when the ink temperature rises and the viscosity of the ink decreases, the discharge energy applied to the ink in the discharge pulse is reduced by decreasing the reference voltage Vref from the initial reference voltage Vref0 to the lower limit reference voltage VrefL. And increase the stabilization energy applied to the ink in the stabilization pulse. On the other hand, when the ink temperature decreases and the ink viscosity increases, the discharge voltage is increased and the stabilization energy is decreased by increasing the reference voltage Vref from the initial reference voltage Vref0 to the upper limit reference voltage VrefH. Let

In this case, when the temperature rises and the reference voltage Vref (positive value as described above) decreases, the absolute value of the applied voltage decreases, so the deformation amount of the piezoelectric element 31 decreases. Since the substrate member of the ink jet head 30 may be slightly distorted due to an increase in temperature, the amount of deformation of the piezoelectric element 31 in the normal state is reduced in such a case, so that the piezoelectric element 31 continues in the normal state. Therefore, it is possible to reduce the load.

Here, regardless of the value of the reference voltage Vref, the voltage change start timing and the change end timing in the voltage waveforms W1, W2 (ejection pulse) and the voltage waveform W3 (stabilization pulse) are fixed, depending on the amplitude. Although the inclination is changed, either the change start timing or the change end timing and the inclination may be fixed, and the other of the change start timing or the change end timing may be changed. In addition, when the change in the value of the reference voltage Vref is large compared to the amplitude, and the slope when the drive voltage rises and falls greatly changes, affecting the discharge characteristics, the slope is maintained and changed. You may switch between both, such as shifting start timing.

Similarly, as shown in FIG. 3B, the reference voltage Vref changes according to the temperature for the drive voltage signal when ink is not ejected. That is, the reference voltage Vref is used in common for the drive voltage signal for ink ejection and the drive voltage signal when ink is not ejected. In this case, the difference from the voltage Va3, that is, the amplitude increases as the reference voltage Vref increases. When the viscosity increases due to a decrease in temperature or the like, the amplitude of the voltage waveform W4 of the non-ejection pulse increases in the same manner as the voltage waveforms W1 and W2 of the ejection pulse. It is possible to cause the ink inside the nozzle 35 to vibrate and agitate to effectively prevent the influence of the ink density change due to the ink evaporation on the ink surface.

FIG. 4 is a flowchart showing a control procedure by the head controller 43 of the drive voltage adjustment control process executed in the ink jet recording apparatus 1 of the present embodiment.
This process constitutes the output adjustment step of the embodiment of the present invention, and is regularly performed at a predetermined interval and based on a predetermined input operation to the operation detection unit 531 by a user or an administrator of the inkjet recording apparatus 1. Will start.

When the drive voltage adjustment control process is started, the head control unit 43 (CPU 431) acquires temperature data measured from the temperature measurement unit 55 (step S11). The head controller 43 calculates an estimated value of the temperature of the ink in the nozzles 35 based on the temperature data acquired as necessary. The head controller 43 refers to the reference voltage setting table 432a and acquires the reference voltage Vref of each ink corresponding to the temperature of the ink (step S12).

The head control unit 43 sets the acquired Vref value for each drive waveform amplification circuit 21 that outputs a drive voltage signal for each inkjet head 30 according to the type of ink ejected by each inkjet head 30. (Step S13). Then, the head controller 43 ends the drive voltage adjustment control process.

In addition, although it was set as control by the head control part 43 here, the main body control part 41 may control this operation | movement. In this case, the reference voltage setting table 432a may be stored in the storage unit 413.

FIGS. 5A to 5C are diagrams showing examples of other waveforms of the drive voltage signal that can be output by the inkjet recording apparatus 1. FIG.

As shown in FIGS. 5A and 5B, the number of ejection pulses in the drive voltage waveform is not limited to two and can be changed. In FIG. 5A, a signal having a drive voltage waveform in which one ejection pulse (voltage waveform W11) and one stabilization pulse (voltage waveform W13) are combined is output. On the other hand, as shown in FIG. 5B, the number of ejection pulses can be three (voltage waveforms W21 to W23), and then one stabilization pulse (voltage waveform W24) can be output.

Basically, in a range where ink droplets are not separated or leaked from the opening of the nozzle 35, the ink level in the nozzle 35 is increased according to the increase in the number of ejection pulses. The amplitude increases and the ink discharge amount increases. Therefore, on the basis of the case of one ejection pulse, a drive voltage waveform in which the number (number) of ejection pulses according to the density gradation (ink on the ink landing surface) of the recording image and one stabilization pulse are combined. This signal can be output.

Further, as shown in FIGS. 5A and 5C, the boosted portion in the last ejection pulse (voltage waveforms W11, W32) and the boosted portion in the stabilization pulse (voltage waveforms W13, W33) do not have to be continuous. Even in this case, since the interval between the boosted portion of the ejection pulse and the stepped-down portion of the stabilization pulse is the timing at which the phase is reversed at the resonance frequency of the ink in the nozzle 35, the ink flow path, and the pressure chamber, the vibration of the ink is caused. It is suppressed.

As described above, the ink jet recording apparatus 1 according to the present embodiment has a nozzle 35 that ejects ink and a pressure corresponding to the deformation applied to the ink supplied to the nozzle 35 by being deformed according to the applied voltage. An ink-jet head 30 having a piezoelectric element 31 for applying pressure, and a head drive control unit 20 that controls a voltage applied to the piezoelectric element 31, and is applied to the piezoelectric element 31 during a driving operation of ejecting ink from the nozzle 35. The voltage drive voltage waveform includes an ejection pulse related to the ink ejection operation and a stabilization pulse that suppresses ink pressure fluctuation caused by the ink ejection operation. One of the ejection pulse and the stabilization pulse is a reference voltage. A voltage waveform including a temporary change from Vref to a voltage Vc larger than the reference voltage Vref, and the other is a reference voltage Vre From a voltage waveform including a temporary change to the reference voltage is smaller than Vref voltage Va1, Va2, the head drive control unit 20 changes the reference voltage Vref according to the temperature of ink ejected.
As described above, when increasing or decreasing the pressurization (energy to be applied) to the ink at the time of ink ejection according to the viscosity that changes depending on the temperature, the voltages Va1, Va2, and Vc are not individually changed, but only the reference voltage Vref. By changing (single parameter), it is possible to easily make the size appropriate for the ink ejection operation. In particular, the increase or decrease in energy required for uniform ink discharge (excitation of pressure fluctuation) according to the viscosity is complementary to the increase or decrease in energy required to suppress pressure fluctuation in the ink after ink discharge. Since these are collectively adjusted by changing the reference voltage Vref, effective adjustment can be easily performed. In this way, ink pressure fluctuation and liquid level vibration are appropriately excited and suppressed within the cycle of the drive voltage waveform in this way, so that the influence of the previous pressure fluctuation and liquid level vibration can be reduced during the next ink ejection. Appropriate pressure fluctuations can be excited again without leaving them. Accordingly, it is possible to stably eject ink at high speed (high frequency) regardless of temperature conditions without depending on attenuation of pressure fluctuation due to the viscosity of ink in the nozzle 35. In particular, even when the temperature rises due to continuous operation for a long time, the adjustment can be easily performed in the middle, and stable high-speed ink ejection operation, that is, high-speed image recording can be performed.

In the range of the above embodiment, it is possible to easily adjust the driving voltage waveform according to the temperature while the voltages Va1, Va2, and Vc are fixed values. Due to variations in the characteristics of the piezoelectric element 31, initial adjustment of the voltages Va 1, Va 2, and Vc and adjustment accompanying aging can be performed. However, instead of adjusting the voltages Va1, Va2, Vc, the voltage Va1, Va2, Vc, etc. can be adjusted by changing the width (pressurization frequency) of the ejection pulse or the stabilization pulse to adjust the correspondence with the resonance frequency. It is good also as a structure which does not require adjustment.

Further, the head drive control unit 20 can change the number of ejection pulses included in the drive voltage waveform. Thereby, it is possible to stably record an image having a plurality of density gradations. In addition, when the pressure fluctuation of the ink is amplified by a plurality of ejection pulses as described above, or the ink is ejected individually, the pressure of the ink when the voltage of each ejection pulse is appropriately applied depending on the temperature. Since the amplitude of fluctuation (surface vibration) can be controlled, it is possible to prevent ink ejection failure and unintended satellite (sub-droplet) ejection, and to maintain an effective and stable high-speed ink ejection operation. . In addition, the ink surface (meniscus) is finely oscillated as compared with the discharge of droplets in this way, so that the ink is dried due to contact with the air through the opening in the nozzle and the viscosity associated therewith. It is possible to reduce the influence of changes and maintain a proper ink ejection operation more stably.

Further, the head drive control unit 20 causes a single ink droplet to be ejected from the nozzle 35 by applying a voltage having a drive voltage waveform including a plurality of ejection pulses to the piezoelectric element 31. In this way, when a plurality of ejection pulses are combined into a single ink droplet, if the error in the pressure fluctuation range (vibration width of the liquid surface) in each ejection pulse overlaps, a large deviation in ejection amount is likely to occur. According to the present invention, a more effective and stable ink ejection operation can be performed.

In addition, the plurality of ejection pulses included in the drive voltage waveform includes two or more waveforms having different shapes. That is, in the ink jet recording apparatus 1 of the present embodiment, the ink ejection operation is performed by combining ejection pulses that shift from the reference voltage Vref to different voltages Va1 and Va2. Even in such a case, if the change is within a normal change range of the reference voltage Vref, that is, a change sufficiently smaller than the amplitude dV1 or the like, the ink pressure fluctuation or the liquid in the nozzle related to each ejection pulse is changed. The vibration of the surface can be controlled to an appropriate magnitude.

Further, the head drive control unit 20 changes the number of ejection pulses included in the drive voltage waveform according to the density gradation of the ink on the landing surface of the ink ejected from the nozzle 35. That is, the density gradation can be appropriately expressed with easy control according to the density gradation. In this case, the density gradation can be appropriately maintained regardless of the temperature condition, which leads to the maintenance and improvement of stable image quality.

Also, the head drive control unit 20 determines the reference voltage Vref according to the type of ink. Since the viscosity characteristics of the inks differ depending on the dyes and pigments of each color, by separately setting the reference voltage Vref, the ink of each color can be ejected at a proper amount and speed without any defect regardless of temperature conditions. Thus, an image using a plurality of types of ink, in particular, a color image can be stably generated.

In addition, a plurality of inkjet heads 30 are provided, and the head drive control unit 20 determines a reference voltage Vref according to the type of ink supplied to each of the plurality of inkjet heads 30. That is, when a plurality of types of ink are ejected on the same landing surface (recording medium) such as a color image and an output image is obtained by combining them, the landing amount (density) of these types of ink ) Can be appropriately maintained, and a recorded image with stable image quality can be obtained at high speed.

Further, a storage unit 432 is provided for storing a reference voltage setting table 432a indicating a correspondence relationship between the temperature and the reference voltage Vref. In the ink jet recording apparatus 1, it is only necessary to obtain the temperature measurement value and obtain the reference voltage Vref corresponding to the ink temperature from the reference voltage setting table 432 a, so that the reference voltage Vref can be easily adjusted. In particular, when a plurality of types of ink are used, the trouble of obtaining an appropriate reference voltage Vref does not become excessive, so that the process related to adjustment becomes easy.

Further, the head drive control unit 20 causes the piezoelectric element 31 to apply a voltage of a non-ejection voltage waveform that causes pressure fluctuation (liquid level vibration) in the ink without ejecting the ink from the nozzle 35. This non-ejection voltage waveform includes a non-ejection pulse that is a temporary change in voltage in the same direction (a direction in which the voltage value is small) as a temporary change in voltage in the ejection pulse from the reference voltage Vref. It does not include a temporary change in voltage in the same direction (a direction in which the voltage value is large) as a temporary change in voltage.
By using such a non-ejection voltage waveform, the reference voltage Vref is changed in conjunction with it, and ink pressure fluctuations and ink liquid surface (surface) vibrations are maintained at appropriate magnitudes regardless of temperature conditions. Thus, it is possible to suppress changes in the viscosity (concentration) of the ink due to effective stirring or the like without discharging the ink.

Further, the inkjet recording apparatus 1 includes a temperature measuring unit 55 that measures a temperature corresponding to the temperature of the ejected ink. That is, the ink jet recording apparatus 1 itself can appropriately measure the temperature corresponding to the ink temperature. Therefore, the reference voltage Vref can be easily adjusted.

Further, in the driving method of the ink jet head 30 of the present embodiment, the driving voltage waveform applied to the piezoelectric element 31 during the driving operation for discharging ink from the nozzles 35 includes an ejection pulse related to the ink ejection operation and an ink ejection. A stabilization pulse that suppresses ink pressure fluctuation caused by the operation, and one of the ejection pulse and the stabilization pulse includes a temporary change from the reference voltage Vref to a voltage Vc larger than the reference voltage Vref. The other is a voltage waveform including a temporary change from the reference voltage Vref to voltages Va1 and Va2 smaller than the reference voltage Vref. The reference voltage Vref is changed according to the temperature of the ejected ink. Including an output adjustment step.
As described above, when the drive voltage waveform that outputs the ejection pulse and the stabilization pulse with a temporary voltage change on the positive side and the negative side with respect to the reference voltage Vref is used, the reference voltage Vref is changed according to the temperature. By doing so, it is possible to maintain the ink pressure fluctuation and the level of the liquid level vibration appropriately according to the temperature for each period of the drive voltage waveform with easy control, and to suppress it after ink ejection. Accordingly, it is possible to maintain a stable and high-speed ink discharge operation regardless of temperature conditions.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above embodiment, the ink discharge operation is performed at a voltage lower than the reference voltage, and the pressure fluctuation (liquid level vibration) of the ink is stabilized at a voltage higher than the reference voltage. The ink discharge operation can be performed at a voltage higher than the reference voltage by reversing the polarity of the connection.

In the above embodiment, one droplet is ejected by a plurality of ejection pulses in the drive voltage waveform. However, each ink pulse may be ejected by each ejection pulse. When each ink droplet lands on the nearest position, the landed area as a whole changes on the landing surface, and the density gradation can be changed.

In the above embodiment, a trapezoidal driving waveform is used. However, a rectangular shape or a waveform having a finer shape may be used. Further, the waveform may be different between when the voltage rises and when it falls.

In the above embodiment, the stabilization pulse is output immediately after ink ejection in the driving voltage waveform related to one ink ejection. However, after the ink ejection, the stabilization is performed at the head of the next driving voltage waveform. The ink ejection operation may be performed after the pulse is output.

In the above-described embodiment, the portion that returns to the reference voltage Vref from the voltages Va1 and Va2 in the ejection pulse is the portion that excites the ink pressure fluctuation, and the portion that returns to the reference voltage Vref in the stabilization pulse is the ink pressure fluctuation. Although it is generated at the phase timing to suppress, the rising part of the stabilization pulse (the part rising from the reference voltage Vref to the voltage Vc) is used for both ink ejection and suppression of pressure fluctuation according to the phase timing. Can do.

In the above embodiment, it is possible to eject ink with a plurality of gradations. However, a single gradation of ink is ejected for each pixel, and a multi-gradation image is obtained only by halftone processing. May be used.

In the above embodiment, the correspondence relationship between the reference voltage Vref and the temperature is determined according to each of the inks of a plurality of colors. However, the reference voltage is similarly applied to inks having the same color but different in viscosity. Correspondence between Vref and temperature can be determined and held.

In the above embodiment, the reference voltage Vref corresponding to the ink temperature is determined with reference to the reference voltage setting table 432a. However, a conversion formula for converting the ink temperature to the reference voltage Vref is held in the control program. The reference voltage Vref may be calculated.

In the above embodiment, the drive voltage signal and the reference voltage Vref of the signal at the time of non-ejection operation are changed in common, but the reference voltage Vref at the time of non-ejection operation may be controlled separately.

In the above embodiment, the reference voltage Vref is determined in advance for each ink type and each temperature. However, the initial reference voltage Vref0 at a predetermined temperature corresponding to each ink type and the temperature from the predetermined temperature are used. A common voltage correction amount corresponding to the difference may be determined, and the reference voltage Vref may be calculated from each initial reference voltage Vref0 and the voltage correction amount.

In the above embodiment, when the drive voltage waveform includes two or more ejection pulses, the first ejection pulse amplitude (voltage Va1) is different from the second and subsequent ejection pulse amplitudes (voltage Va2). However, it is not limited to this. Any combination of amplitudes capable of obtaining an appropriate ink discharge amount and ink discharge speed can be used.

In the above embodiment, the temperature measurement unit 55 measures the ink temperature. However, the ink temperature data is acquired from the external temperature sensor, for example, a non-contact temperature sensor, via the communication unit 52. Also good.
In addition, specific details such as the configuration, control contents, and procedures shown in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 20 Head drive control part 21 Drive waveform amplification circuit 22 DAC
30 Inkjet head 31 Piezoelectric element 32 Discharge selection switching element 35 Nozzle 41 Main body control unit 411 CPU
412 RAM
413 Storage unit 42 Movement control unit 43 Head control unit 431 CPU
432 Storage unit 432a Reference voltage setting table 51 Moving operation unit 52 Communication unit 53 Operation display unit 531 Operation detection unit 532 Display unit 54 Notification output unit 55 Temperature measurement unit 56 Bus Vref Reference voltage

Claims

An inkjet head having a nozzle that ejects ink, and a pressure generating element that applies a pressure according to the deformation to the ink supplied to the nozzle by being deformed according to an applied voltage;
A drive control unit for controlling a voltage applied to the pressure generating element;
With
The drive voltage waveform of the voltage applied to the pressure generating element during the drive operation of discharging ink from the nozzle includes a discharge drive waveform related to the ink discharge operation and a stable suppression of ink pressure fluctuation caused by the ink discharge operation. Waveform and
One of the ejection drive waveform and the stabilization waveform is a voltage waveform including a temporary change from a reference voltage to a first voltage larger than the reference voltage, and the other is the reference voltage to the reference voltage. A voltage waveform including a temporary change to a smaller second voltage,
The said drive control part changes the said reference voltage according to the temperature of the discharged ink. Inkjet recording device.
2. The ink jet recording apparatus according to claim 1, wherein the drive control unit can change the number of the ejection drive waveforms included in the drive voltage waveform.
3. The inkjet recording according to claim 2, wherein the drive control unit discharges one ink droplet from the nozzle by applying a voltage of the drive voltage waveform including a plurality of the discharge drive waveforms to the pressure generating element. apparatus.
4. The ink jet recording apparatus according to claim 2, wherein the plurality of ejection driving waveforms included in the driving voltage waveform include two or more waveforms having different shapes.
The drive control unit changes the number of the ejection drive waveforms included in the drive voltage waveform according to the density gradation of the ink on the landing surface of the ink ejected from the nozzle. The inkjet recording apparatus according to Item.
The ink jet recording apparatus according to any one of claims 1 to 5, wherein the drive control unit determines the reference voltage according to a type of ink.
A plurality of inkjet heads;
The inkjet recording apparatus according to claim 6, wherein the drive control unit determines the reference voltage according to a type of ink respectively supplied to the plurality of inkjet heads.
The inkjet recording apparatus according to any one of claims 1 to 7, further comprising a correspondence storage unit that stores a correspondence relationship between the temperature and the reference voltage.
The drive control unit causes the pressure generating element to apply a voltage having a non-ejection voltage waveform that causes pressure fluctuation in the ink without ejecting ink from the nozzle,
The non-ejection voltage waveform includes a temporary change in voltage in the same direction as a temporary change in voltage in the ejection drive waveform from the reference voltage, and has the same direction as a temporary change in voltage in the stabilization waveform. The ink jet recording apparatus according to any one of Claims 1 to 8, which does not include a temporary change in voltage.
The ink jet recording apparatus according to any one of claims 1 to 9, further comprising a temperature measuring unit that measures a temperature corresponding to a temperature of the ejected ink.
An inkjet head driving method comprising: a nozzle that ejects ink; and a pressure generating element that applies a pressure corresponding to the deformation to the ink supplied to the nozzle by being deformed according to an applied voltage. ,
The drive voltage waveform of the voltage applied to the pressure generating element during the drive operation of discharging ink from the nozzle includes a discharge drive waveform related to the ink discharge operation and a stable suppression of ink pressure fluctuation caused by the ink discharge operation. Waveform and
One of the ejection drive waveform and the stabilization waveform is a voltage waveform including a temporary change from a reference voltage to a first voltage larger than the reference voltage, and the other is the reference voltage to the reference voltage. A voltage waveform including a temporary change to a smaller second voltage,
A driving method including an output adjustment step of changing the reference voltage according to the temperature of the ejected ink.