Inkjet recording device, method for adjusting inkjet recording device, and method for controlling inkjet recording device

An inkjet recording device includes an inkjet discharge head including a nozzle through which ink is discharged, a pressure chamber that communicates to the nozzle, and a pressure generator that generates a pressure change in ink in the pressure chamber according to application of a drive signal to cause ink to be discharged from the nozzle; a driver that is disposed outside the ink discharge head and that is provided with a drive circuit that outputs the drive signal; and a wire that electrically connects the driver with the ink discharge head and through which the drive signal output from the drive circuit and applied to the pressure generator. The driver includes a resistance element provided in a transmission path of the drive signal between the drive circuit and the wire. A magnitude of a resistance value of the resistance element corresponds to a length of the wire.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a 371 of PCT/JP2019/017993 filed on Apr. 26, 2019, the above application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an inkjet recording device, a method for adjusting an inkjet recording device, and a method for controlling an inkjet recording device

BACKGROUND ART

Conventionally, there have been inkjet recording devices in which ink is discharged from nozzles provided in an ink discharge head and landed at desired positions, thereby recording an image on a recording medium. The ink discharge head is provided with pressure chambers that communicate with nozzles and pressure generators that generate pressure change in ink in the pressure chambers according to application of drive signals. The pressure generators cause pressure change in ink in the pressure chambers, and ink is thereby discharged from the nozzles. A piezoelectric element is used as a pressure generator, and an amount and time of deformation of the pressure chamber is controlled by application of an appropriate voltage to the piezoelectric element. When an image is being recorded, a piezoelectric element(s) to apply a drive signal is selected from the piezoelectric elements respectively corresponding to the nozzles disposed in the inkjet discharge head according to a recorded image, and whether ink is discharged or not from each nozzle is thereby determined.

The piezoelectric elements have a capacitive load, and a drive load is varied according to the number of the piezoelectric elements which share the timing of application of the drive signal (that is, the number of nozzles from which ink is discharged at the same timing (hereinafter referred to as the number of discharge nozzles)). Therefore, an increase in the number of discharge nozzles causes the waveform of drive signal to be unstable, and the speed and volume of ink discharged from the nozzles may fluctuate from desired values, which may lead to a deterioration of the image quality.

Against such a problem, there is a technique to suppress deterioration of the image quality due to the fluctuation of the drive load by adjusting the waveform of the drive signal according to the number of discharge nozzles (ex. Patent Literature 1).

CITATION LIST

Patent Literature

Patent Document 1: JP 2017-061131 A

SUMMARY OF INVENTION

Technical Problem

However, in the case where the drive circuit that outputs drive signals is provided outside the ink discharge head, the transmission path of drive signals is long and the inductance of the transmission path causes the waveform of drive signal to be unstable. Therefore, it is impossible to suppress fluctuation of the speed and volume of ink discharged from the nozzles simply by adjusting the waveform of the drive signal according to the number of discharge nozzles, and it is impossible to effectively suppress deterioration of the image quality.

An object of the present invention is to provide an inkjet recording device, a method for adjusting an inkjet recording device, and a method for controlling an inkjet recording device that can suppress deterioration of the image quality effectively.

Solution to Problem

To achieve the above-mentioned object, one embodiment is the inkjet recording device including according to:an inkjet discharge head including a nozzle through which ink is discharged, a pressure chamber that communicates to the nozzle, and a pressure generating means that generates a pressure change in ink in the pressure chamber according to application of a drive signal to cause ink to be discharged from the nozzle;a driver that is disposed outside the ink discharge head and that is provided with a drive circuit that outputs the drive signal; anda wire that electrically connects the driver with the ink discharge head and through which the drive signal output from the drive circuit and applied to the pressure generating means,in which the driver includes a resistance element provided in a transmission path of the drive signal between the drive circuit and the wire,in which a magnitude of a resistance value of the resistance element corresponds to a length of the wire.

In one embodiment, the resistance element is provided in a state in which the resistance value is changeable.

In one embodiment, the inkjet recording device further includes:a resistance value controlling means that changes the resistance value of the resistance element.

In one embodiment, the ink discharge head includes multiple nozzles, multiple pressure chambers corresponding to the multiple nozzles, and multiple pressure generating means corresponding to the nozzles, and

the resistance value controlling means adjusts the resistance value of the resistance element at each time of application of the drive signal such that the resistance value of the resistance element corresponds to a number of nozzles through which ink is discharged at a same timing among the nozzles.

In one embodiment, the inkjet recording device further includes a temperature detector that detects a temperature corresponding to the temperature in the ink discharge head, and

the resistance value controlling means adjusts the resistance value of the resistance element based on the temperature detected by the temperature detector.

In one embodiment, the ink discharge head includes multiple nozzles, pressure chambers corresponding to the multiple nozzles, and pressure generating means corresponding to the nozzles, and

with C defined as a capacitance of a capacitance load of the multiple pressure generating means and with R as the resistance value of the resistance element, the resistance value of the resistance element is set in a range where a relationship of CR<500 ns is satisfied.

In one embodiment, the ink discharge head includes multiple nozzles, pressure chambers corresponding to the multiple nozzles, and pressure generating means corresponding to the nozzles, and

the resistance value of the resistance element is set such that a change amount of a dropping speed of ink in response to a change in a number of nozzles through which ink is discharged at a same timing among the multiple nozzles satisfies a predetermined change amount suppressing condition.

In one embodiment, the inkjet recording device further includes:multiple ink discharge heads;multiple drivers corresponding to the multiple ink discharge heads; andmultiple wires corresponding to the multiple drivers; anda magnitude of the resistance value of the resistance element included in each of the drivers corresponds to a length of the wire connected to the driver.

In one embodiment, the inkjet recording device further includes:a drive controlling means that controls an output operation of the drive signal by the drive circuit, in which the ink discharge head includes multiple nozzles, pressure chambers corresponding to the multiple nozzles, and pressure generating means corresponding to the nozzles,the drive signal includes a pulse signal, andthe drive controlling means adjusts a voltage amplitude of the pulse signal according to a number of nozzles through which ink is discharged at a same timing among the multiple nozzles.

In one embodiment, the drive controlling means adjusts a pulse width of the pulse signal according to the number of the nozzles through which ink is discharged at the same timing.

In one embodiment, the drive controlling means causes the drive circuit to output a sub pulse signal for shaking a liquid surface of ink in the nozzle and the drive signal including the pulse signal applied sequentially after the sub pulse signal.

In one embodiment, the drive controlling means adjusts a waveform of the drive signal such that at least one of a rise time and a fall time of the pulse signal is longer when the number of the nozzles through which ink is discharged at the same timing is smaller.

In one embodiment, the drive controlling means causes the drive circuit to output the drive signal including multiple pulse signals, and

the pressure generating means causes multiple ink droplets that forms a pixel on a recording medium to be discharged from the nozzle according to the multiple pulse signals.

To achieve the above-mentioned object, one embodiment is the method for adjusting the inkjet recording device, the inkjet recording device including an inkjet discharge head including a nozzle through which ink is discharged, a pressure chamber that communicates to the nozzle, and a pressure generating means that generates a pressure change in ink in the pressure chamber according to application of a drive signal to cause ink to be discharged from the nozzle; a driver that is disposed outside the ink discharge head and that is provided with a drive circuit that outputs the drive signal; and a wire that electrically connects the driver with the ink discharge head and through which the drive signal output from the drive circuit and applied to the pressure generating means, in which the driver includes a resistance element provided in a transmission path of the drive signal between the drive circuit and the wire,in which a magnitude of a resistance value of the resistance element is set to a value corresponding to a length of the wire.

To achieve the above-mentioned object, one embodiment is the method for controlling the inkjet recording device, the inkjet recording device including an inkjet discharge head including a nozzle through which ink is discharged, a pressure chamber that communicates to the nozzle, and a pressure generating means that generates a pressure change in ink in the pressure chamber according to application of a drive signal to cause ink to be discharged from the nozzle; a driver that is disposed outside the ink discharge head and that is provided with a drive circuit that outputs the drive signal; and a wire that electrically connects the driver with the ink discharge head and through which the drive signal output from the drive circuit and applied to the pressure generating means, in which the driver includes a resistance element provided in a transmission path of the drive signal between the drive circuit and the wire, in which the ink discharge head includes multiple nozzles, multiple pressure chambers corresponding to the multiple nozzles, and multiple pressure generating means corresponding to the nozzles,in which at each time of application of the drive signal, a resistance value of the resistance element is adjusted such that a magnitude of the resistance value of the resistance element corresponds to a length of the wire and to a number of nozzles through which ink is discharged at a same timing among nozzles.

Advantageous Effects of Invention

According to the present invention, it is possible to effectively suppress deterioration of the image quality.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of an inkjet recording device, a method for adjusting inkjet recording device, and a method for controlling inkjet recording device according to the present invention are described with reference to the drawings.

First Embodiment

FIG.1shows a schematic configuration of the inkjet recording device1in an embodiment of the present invention.

The inkjet recording device1includes a conveyance belt101, conveying rollers102, a head unit103, and the like.

Each of the conveying roller102is rotated around a rotation axis parallel to the X direction inFIG.1, driven by a conveyance motor not shown in the drawings. The conveyance belt101, which is a ring-shaped belt supported by a pair of the conveying rollers102inside, rotationally moves around the pair of the conveying rollers102as the conveyance rollers102rotate. The inkjet recording device1conveys a recording medium M in the moving direction of the conveyance belt101(Y direction inFIG.1) as the conveyance belt101rotationally moves at a speed corresponding to the rotation speed of the conveying roller102with the recording medium M being placed on the conveyance belt101.

The head unit103records an image on the recording medium M by discharging ink from the nozzles N (seeFIG.2) onto the recording medium M conveyed by the conveyance belt101based on the image data. In the inkjet recording device1of the embodiment, four head units103, which correspond respectively to four different color inks of yellow (Y), magenta (M), cyan (C) and black (K), are aligned at predetermined intervals in the order from the upstream in the conveyance direction of the recording medium M. The number of the head units103may be three or less or five or more, according to the number of colors used in the image recording.

FIG.2shows a schematic configuration of the head unit103, which is a plan view of the head unit103viewed from the side facing the conveyance face of the conveyance belt101.

Each of the head units103includes a base103ain a hotplate shape and multiple (seven in this embodiment) ink discharge heads10that are fixed to the base103aby fitting openings that penetrate the base103a.

Each of the ink discharge heads10includes a head chip12provided with multiple nozzles N from which ink is discharged, and the nozzle opening face of the head chip12is exposed from an opening of the base103a. In the head chip12, the nozzles N are one-dimensionally arranged in a direction intersecting the conveyance direction of the recording medium M (the width direction orthogonal to the conveyance direction, namely the X direction, in this embodiment) to form a nozzle row. In the head chip12, there may be multiple nozzle rows in a positional relation such that the positions of the nozzles N are shifted from each other in the X direction.

The ink discharge heads10in each of the head units103are disposed in a staggered pattern such that the arrangement range of the nozzles N in the X direction corners the width in the X direction of the area of the recording medium M on the conveyance belt101where an image is recordable. As the ink discharge heads10are disposed as described above, the inkjet recording device1can record an image on the conveyed recording medium M by discharging ink from the ink discharge heads10at appropriate timings according to the image data with the head unit103being fixed. That is, the inkjet recording device1records images in a single pass method.

FIG.3is an exploded perspective view showing a configuration of the head chip12. InFIG.3, the number of the nozzles N is simplified to seven, bin the head chip12in this embodiment includes several hundreds or thousands of the nozzles N.

The head chip12includes a channel substrate121on which multiple pressure chambers128(channels) respectively communicating to the nozzles N. A nozzle plate123with the multiple nozzles N is attached to the end face of the channel substrate12L A cover plate122is attached to the upper part of the channel substrate121on the nozzle plate123side.

The channel substrate121has a structure in which two substrates124and125are attached to each other via an attachment portion126. The base substrates124and125are made of a piezoelectric material such as lead zirconate titanate (PZT), and are polarized in opposite directions in the thickness direction. The pressure chambers128are formed at equal intervals on the channel substrate121, and a partition wall1271is formed at each interval between the pressure chambers128. An electrode1272is provided on a side wall of the pressure chamber128(the surface of the partition wall1271), and the partition wall1271is bent (shear deformation) centered around the attachment portion126according to a voltage signal(s) (drive signal(s)) of a drive waveform applied to the electrode1272of the neighboring pressure chambers128. The shear deformation of the partition wall1271according to the drive signal applied to the electrode1272changes the ink pressure in the pressure chamber128, and ink in the pressure chamber128is discharged from the nozzle N accordingly. The partition wall1271with the electrode1272constitutes a piezoelectric element127(pressure generation means, actuator) that causes pressure change in ink in the pressure chamber128.

As described above, the inkjet discharge head10in this embodiment is of a shear mode inkjet discharge head that discharges ink from the nozzles N by the shear stress generated by applying an electric field in a direction orthogonal to the polarization direction of the piezoelectric element.

FIG.4shows a configuration for supplying drive signals to the head chip12of the inkjet discharge head in the inkjet recording device1.

The ink et recording device1includes the ink discharge head10, a driver20that is disposed outside the ink discharge head10, and a wiring cable30(wire) that electrically connects the driver20with the ink discharge head10.

The driver20includes a drive substrate21, a drive controller22(drive controlling means, resistance value controlling means), a DAC23(digital-analog convertor), and drive waveform amplifier circuit24(drive circuit), a resistance element25, a first connector26, and the like. The driver20outputs drive signals that drive the piezoelectric elements127in the ink discharge head10at appropriate timings according to the data of the image to be recorded.

The drive substrate21is a rigid substrate where metal routing wiring is formed on the surface of an insulating base material.

The drive controller22, the DAC23, and the drive waveform amplifier circuit24, which are a group of circuit elements mounted on the drive substrate21, generate the above-described drive signals and output them from the drive waveform amplifier circuit24.

The resistance element25is a terminating resistance connected to an output unit (output terminal) of the drive signals in the drive waveform amplifier circuit24. That is, the resistance element25is provided in the drive signal transmission path between the drive waveform amplifier circuit24and the wiring cable30. The resistance element25may be formed as an independent circuit (ex., leaded package type, chip resistor type), but not limited to this. The resistance element25may be formed in an integrated circuit, for example.

The resistance value of the resistance element25corresponds to the length of the wiring cable30. The method of determining the resistance value of the resistance element25is described later.

The first connector26electrically connects the routing wiring (the signal transmission path connected to the resistance element25) of the drive substrate21with the wiring cable30.

The wiring cable30is connected to the driver20via the first connector26and connected to the ink discharge head10via a second connector14. The drive signals output from the drive waveform amplifier circuit24are transmitted via the wiring cable30and applied to the piezoelectric elements127of the head chip12. The configuration of the wiring cable30is not particularly limited, but a linear conductor such as a copper covered by an insulating member may be used, for example.

The ink discharge head10includes a case11, the head chip12, a head substrate13, the second connector14, a discharge selection switching element15, a third connector16, an FPC17(flexible printed circuit), and the like.

The case11stores the components of the inkjet discharge head10inside and protects them. The head chip12is fixed to the case11with the nozzle opening face being exposed to the outside. The second connector14is provided with a terminal to connect to the wiring cable30being exposed outside.

The head substrate13is a rigid substrate in which metal routing wiring is formed on the surface of an insulating base material. The second connector14, the discharge selection switching element15, and the third connector16are mounted on the head substrate13. The routing wiring of the head substrate13includes an input wire for inputting drive signals from the second connector14to the discharge selection switching element15, and output wires corresponding to the piezoelectric elements127in number for outputting drive signals from the discharge selection switching element15to the piezoelectric elements127respectively corresponding to the nozzles N.

The second connector14electrically connects the wiring cable30with the input wires on the head substrate13.

The discharge selection switching element15changes whether the drive signals input from the input wire on the head substrate13are applied to the piezoelectric elements127respectively corresponding to the nozzles N. That is, the discharge selection switching element15causes the drive signal not to be applied to the piezoelectric element(s)127corresponding to the nozzle(s) from which ink is not to be discharged based on the data of the image to be recorded, thereby switching ink discharge from each nozzle N.

The third connector16electrically connects the output wires on the head substrate13with the connection wires on the FPC17.

The FPC17is provided with connection wires corresponding to the pressure elements127, and is pressure-bonded to the head chip12so that each connection wire can be electrically connected to the routing wiring from the piezoelectric elements127in the head chip12. The drive signals output from discharge selection switching element15to the piezoelectric elements127are applied to the corresponding piezoelectric elements127via the output wires on the head substrate13, the connection wire on the ITC17, and the routing wiring inside the head chip12.

FIG.5is a block diagram showing a functional configuration of the inkjet recording device1.

The inkjet recording device1includes a controller40, a conveyance controller51, a communication unit52, an operation/display interface53, a temperature detector54, and the ink discharge head10, the driver20, the wiring cable30described above, and the like, and these components are connected via a bus55so as to transmit and receive signals.

The controller40centrally controls the overall operation of the inkjet recording device1. The controller40includes a CPU41(central processing unit), a RAM42(random access memory), a storage43, and the like.

The CPU41reads out control programs stored in the storage43and performs various kinds of control processing concerning the image recording, its setting, and the like.

The RAM42provides a working memory space for the CPU41and stores temporal data. The storage43includes a non-volatile memory that stores the control programs, setting data, and the like. The storage43may include a DRAM that temporarily stores setting concerning image recording commands (print jobs) externally obtained via the communication unit52, image data of images to be recorded, and the like.

The drive controller51causes a motor to rotate the conveying roller102to rotate the conveying roller102at an appropriate speed and timing. The conveyance controller51may be configured in the same way as the controller40.

The communication unit52transmits and receives data to and from an external device(s) by a predetermined communication standard. The communication unit.52includes a connection terminal concerning the communication standard used, a hardware (network card), and the like of a driver concerning and communication connection.

The operation/display interface53displays status information, a menu, and the like related to image recording, and receives operation input by a user. The operation/display interface53includes, for example, a display screen of a liquid crystal panel, a driver for the liquid crystal panel, a touch panel piled on the liquid crystal screen, and the like, and outputs an operation detection signal corresponding to a position of touch operation by a user and a kind of operation to the controller40.

The temperature detector54, which is attached to the ink discharge head10or disposed near the ink discharge head10, detects the temperature corresponding to the temperature of the ink discharge head10and outputs the detection result to the controller40.

The drive controller22of the driver20controls the operations of the components of the driver20according to the content of the image data of the images to be recorded. The drive controller22includes a CPU221, a storage222, and the like. The storage222retains waveform patterns222aof drive signals for discharging ink from the nozzles N as digital discrete value array data. The CPU221selects waveform pattern data (digital waveform data) corresponding to a waveform pattern for applying a drive voltage of an appropriate waveform pattern to the piezoelectric element127according to whether ink is discharged from each nozzle N based on the image data of the image to be recorded stored in the storage222or the storage43and outputs the data to the DAC23at an appropriate timing according to a clock signal not shown in the drawings.

The DAC23converts the waveform pattern data of the drive waveform input from the drive controller22into analog, and outputs the obtained analog signal (drive signal) to the drive waveform amplifier circuit24.

The drive waveform amplifier circuit24amplifies the drive signal input from the DAC23(voltage amplification, and then current amplification) and outputs the amplified drive signal. The drive signal output from the drive waveform amplifier circuit24is transmitted to the ink discharge head10via the transmission path with the resistance element25and the wiring cable30.

Next, a method for driving the ink discharge head10and a method for determining the resistance value of the resistance element25in the inkjet recording device1are described.

In the inkjet recording device1in this embodiment, multiple ink droplets sequentially discharged from the nozzle are joined and landed on a recording medium M, thereby forming a pixel of the recorded image. The density (gradation) of the pixel can be adjusted by changing the number of droplets to be joined. The multiple ink droplets before being joined may be connected by a columnar ink (ink liquid column), or may be separate from each other.

FIG.6shows an example of a drive signal used m this embodiment.

The drive signal inFIG.6includes three first pulse signals Pa, and a second pulse signal Pb applied after the first pulse signals. Hereinafter, any one of the first pulse signals Pa and the second pulse signal Pb is referred to as a “pulse signal P.”

The pulse signal P is a voltage signal of a trapezoidal wave. As a raised part of the trapezoidal wave of the pulse signal P is applied to the piezoelectric element127, the piezoelectric element127(the partition wall1271) is shear-deformed in a direction of the pressure chamber128expanding (the direction of increase in the volume), and as a lowered part of the trapezoidal wave is applied to the piezoelectric element127(the partition wall1271) is shear-deformed in a direction of the pressure chamber128shrinking (the direction of reduction in the volume). As described above, as the pressure chamber128expands and then shrinks, the ink pressure inside the pressure chamber128increases and an ink droplet is discharged from the nozzle N. That is, as each pulse signal P is applied, an ink droplet is discharged from the nozzle N. Therefore, four ink droplets to form one pixel are sequentially discharged from the nozzle N according to the drive signal inFIG.6including the four pulse signals P.

The voltage amplitude of the first pulse signal Pa is Va, and the time from the trapezoidal wave starts to rise until it starts to fall (pulse width) is 1.3 AL. The AL (acoustic length) is ½ of the acoustic resonance period of the pressure wave in the pressure chamber128, and is approximately 3.5 μs in this embodiment. A rise time T1and a fall time T2of the trapezoidal wave of the first pulse signal Pa are 1 μs. The three first pike signals Pa are applied with a pulse period of 2 AL.

The voltage amplitude of the second pulse signal Pb is Vb, and be pulse width is AL.

The voltage amplitude VU of the first pulse signal Pa is adjusted to a smaller value than the voltage amplitude \/b of the second pulse signal Pb. This is for suppressing a difference in the ink speed when the numbers of ink droplets sequentially discharged from different nozzles N are different from each other. That is, while the ink speed when two or more ink droplets by the first pulse signals Pa added to the second pulse signal Pb are sequentially discharged and joined together tends to be higher than the ink speed of a single ink droplet by the second pulse signal Pb only, the voltage amplitude Va. of the first pulse signal Pa, is smaller than the voltage amplitude Vb and the dropping speed of ink discharged by the first pulse signal Pa is decreased. It is thereby possible to suppress the dropping speed of ink when two or more ink droplets are sequentially discharged and reduce the difference in speed described above.

As described above, the drive signal applied to each piezoelectric element127is adjusted so that ink droplets are discharged from the nozzle N at a desired speed and in a desired volume (ink amount).

However, the waveform of the drive signal is distorted by the capacitance of the piezoelectric element127, the inductance and resistance of the transmission path of the drive signal, and the like. When the waveform of the drive signal is distorted, the dropping speed and volume of ink discharged from the nozzle N deviate from the desired values, and the landing position on the recording medium M and the landing liquid amount are fluctuated, leading to deterioration of the image quality.

In particular, in the inkjet recording device1in this embodiment, as the drive waveform amplifier circuit24that outputs drive signals is provided outside the ink discharge head10, the transmission path of drive signals (mainly the wiring cable30) is longer and the inductance and resistance are increased. Therefore, it is impossible to disregard the fluctuation of the ink dropping speed and volume due to the inductance and resistance of the transmission path of drive signal, or the wiring cable30in particular. Specifically, an increase lathe inductance of the wiring cable30causes overshoot and undershoot in the drive signal, leading to larger distortion from the desired waveform. The dropping speed and volume of ink thereby deviate from the desired values. The ink speed among those is usually decreased by a distortion of the waveform, but may be higher than the desired value depending on the distortion of the waveform. The inductance of the wiring cable30may change the change amount of the dropping speed of ink when he number of the piezoelectric elements127which share the period of application of the drive signal, that is, the number of the nozzles N through which ink is discharged at the same timing (number of discharge nozzles), is changed. As the change amount of the dropping speed of ink with respect to the number of discharge nozzles is larger, the deterioration of the image quality of recorded images is significant.

Thus, in this embodiment, with the resistance element25provided in the output unit of the drive waveform amplifier circuit24, occurrence of overshoot and undershoot due to the inductance of the wiring cable30is suppressed and also distortion of the waveform of the drive signal is suppressed. The resistance value R of the resistance element25is set to a magnitude corresponding to the length of the wiring cable30. Hereinafter, the method for setting the resistance value R of the resistance element25is described.

The resistance value R of the resistance element25is set so that the change amount (range) of the dropping speed of ink when the number of discharge nozzles is changed satisfies a predetermined condition of suppressing the change amount. Here, the condition of suppressing the change amount can be that the change amount of the dropping speed of ink when the number of discharge nozzles is changed is the smallest.

FIGS.7A to7Cshows an ink dropping speed change rate with respect to the number of discharge nozzles when the resistance value R is changed.

Specifically, the graphs show the ink dropping rate change rates plotted thereon for the resistance values R 0.75Ω, 1.0Ω, and 1.5Ω of the resistance element25when ink is discharged from the nozzles N each using the same drive signals and the number of discharge nozzles is changed stepwise to 1024. The reference value of the ink dropping speed change rate may be, for example, an ink dropping speed when ink is discharged from a single nozzle N by a drive signal not distorted.

The options of the resistance value R is preferably selected in a range which satisfies the relationship CR<500 μs, where the capacitance of the capacitive load of the multiple piezoelectric elements127of the ink discharge head10is defined as C.

FIG.7Ashows an ink dropping speed change rate when the length of the wiring cable30(hereinafter, referred to as a “wiring length L”) is 1000 mm. In the graph ofFIG.7A, the range of the ink dropping speed change rate (the change amount of the dropping speed) is the smallest when the resistance value R of the resistance element25is 1.0Ω. Thus, when the wiring length L is 1000 nan, the resistance value R is set to 1.0Ω.

FIG.7Bshows an ink dropping speed change rate when the wiring length L of the wiring cable30is 700 min. in the graph ofFIG.7B, the range of the ink dropping speed change rate is the smallest when the resistance value R of the resistance element25is 0.75Ω. Thus, when the wiring length L is 700 mm the resistance value R is set to 0.75Ω.

FIG.7Cshows an ink dropping speed change rate when the wiring length L of the wiring cable30is 500 mm. In the graph ofFIG.7C, the range of the ink dropping speed change rate is the smallest when the resistance value R of the resistance element25is 0.75Ω. Thus, when the wiring length L is 500 mm, the resistance value R is set to 0.75Ω.

FIG.8shows an setting example of the resistance values R of the resistance elements25in the multiple ink discharge heads10.

InFIG.8, the wiring lengths L of the wiring cables30connected to the ink discharge heads10of No. 1 to No. 7 and the resistance values R of the resistance elements25set according to the wiring lengths L. In the example ofFIG.8, the wiring length L of the wiring cables30connected to the inkjet discharge heads10of No. 1 and No. 7 are 1000 mm, and the resistance value R of the ink discharge heads10of No. 1 and No. 7 is set to 1.0Ω corresponding to that cable length L. The wiring length L of the wiring cables30connected to the ink discharge heads10of No. 2 and No. 6 is 700 mm, and the wiring length L of the wiring cables30connected to the ink discharge heads10of No. 3 to No. 5 is 500 min. The resistance value R of the ink discharge heads10of No. 2 to No. 6 is set to 0.75 n corresponding to those cable lengths L.

FIG.8is an example of the setting of the resistance values R corresponding to the wiring lengths L of the wiring cables30, and the present invention is not limited to this example. For example, the resistance values R of the resistance elements25in all the ink discharge heads10may be different from each other or may be the same depending on the wiring lengths L of the wiring cables30connected to the ink discharge heads10.

The method for setting the resistance value R of the resistance element25is not limited to those shown inFIGS.7A to7C, and the resistance value R may be set so that the range of the ink dropping speed change rate in the most frequent range of the number of discharge nozzles in the image recording (ex, the range of the number of discharge nozzles inFIGS.7A to7C, 128 to 1024) is the smallest. That is, the above-described condition of suppressing the change amount may be that the change amount of the dropping speed of ink in a predetermined number of discharge nozzles is the smallest. For example, in the examples ofFIGS.7A to7C, in a case where the resistance value R is set so that the range of the dropping speed change rate for the number of discharge nozzles of 128 to 1024 is the smallest, the resistance value R is persistently set to 1.5Ω for the wiring lengths L of 1000 mm, 700 mm, and 500 mm.

In this embodiment, the resistance value R of the resistance element25is set as shown above, and in addition, the drive signal is adjusted (corrected) according to the number of discharge nozzles. When the number of discharge nozzles is varied, the number of the piezoelectric elements127which apply drive signals, that is, the drive load of the capacitance, is increased or decreased, and thus the distortion of the drive signal (e.x., the way the waveform rises or falls gets slow) is changed and the dropping speed and volume of discharged ink. On contrary, by adjusting the drive signal according to the number of discharge nozzles, it is possible to suppress change in the distortion of the drive signal and stabilize the dropping speed and volume of ink regardless of the number of discharge nozzles.

Specifically, the voltage amplitude of the pulse signal of the drive waveform is adjusted according to the number of discharge nozzles. The dropping speed of discharged ink can be increased by increasing the voltage amplitude of the pulse signal.

The pulse width of the pulse signal of the drive waveform described above may be adjusted according to the number of discharge nozzles.

As shown inFIG.9, a sub pulse signal Pc for shaking the ink liquid surface in the nozzles N may be added for adjustment before the first pulse signals Pa and the second pulse signal Pb. The sub pulse signal Pc has a voltage amplitude Vc smaller than the voltage amplitude Va of the first pulse signal Pa. The dropping speed and volume of ink may be adjusted according to the relationship between the phase of the shaking of the liquid surface according to the sub pulse signal Pc and the phase of the pressure change by the pulse signal P. The voltage amplitude and pulse width of the sub pulse signal Pc may be further adjusted according to the number of discharge nozzles.

The adjusted rise time T1of the pulse signal P may be longer as the number of discharge nozzles is smaller, and the adjusted fall time T2of the pulse signal P may be longer as the number of discharge nozzles is smaller. The adjusted rise time T1and fail time T2may be longer as the number of discharge nozzles is smaller. The adjustment range of the rise time T1and fall time T2may be, for example, about 0 μs to 2 μs.

The drive signals are adjusted by the drive controller22. That is, the drive controller22specifies the number of discharge nozzles of the ink discharge head10based on line data of the image data, input from the controller40and outputs the waveform pattern data adjusted according to the specified result to the DAC23. Here, the adjusted waveform pattern data corresponding to the number of discharge nozzles is registered in advance in the waveform patterns222ain the storage222, and the waveform pattern data corresponding to the number of discharge nozzles can be selected and output to the DAC23by the drive controller22. Otherwise, the voltage amplitude, the pulse width, the adjustment amount of the rise time T1and the fall time T2, and the setting of presence/absence of the sub pulse signal Pc corresponding to the number of discharge nozzles are registered in the storage222or the storage43, and the adjusted waveform may be generated each time based on the number of discharge nozzles and the settings described above by the drive controller22.

Modification Example 1

Next, Modification Example 1 of the above-described embodiment is described. In the above-described embodiment, the example in which the resistance value P. of the resistance element25is fixed is described, but the resistance value R may be changeable.

FIG.10shows a configuration of part of the inkjet discharge head10according to Modification Example 1. InFIG.10, a potentiometer is used as the resistance element25. The configuration of the potentiometer is not particularly limited, but may be one that can adjust the resistance value R by changing the position of the connecting point according to the rotation of the adjustment axis. The potentiometer is not limited to one that can continuously adjust the resistance value R, and may be one that can change the resistance value IR stepwise.

Modification Example 2

Next, Modification Example 2 of the above-described embodiment is described. This Modification Example is different from the above-described embodiment in that the drive controller22can change the resistance value R of the resistance value25. Hereinafter, differences from the above-described embodiment are described,

FIG.11shows a configuration of a part of the ink discharge head10according to Modification Example 2.

The resistance element25in this Modification Example includes the first resistance element251having the resistance value R1, the second resistance element252having the resistance value R2, and the third resistance element253having the resistance value113, and those resistance elements are disposed in series and connected to the first connector26. A switching element27that electrically connects the waveform amplifier circuit24with any one of the first resistance element251, the second resistance element252, and the third resistance element253. The connection state by the switching element27is changeable under the control of the drive controller22. That is, the drive controller22can change the resistance value R of the resistance element25among the three different resistance values R1, R2, and R3. The drive controller22of this Modification Example constitutes a resistance value controlling means.

The resistance value R of the resistance element25may be selected from two, four or more different values.

In this Modification Example, the drive controller22changes the resistance value R of the resistance element25for adjustment every time the drive signal is applied so that the resistance value R of the resistance element25corresponds to the number of discharge nozzles. That is, the drive controller22specifies the number of discharge nozzles of the ink discharge head10based online data of the image data input from the controller40and changes the resistance value IR of the resistance element25according to the specified result. For example, the resistance value R of the resistance element25corresponding to the number of discharge nozzles is registered in advance in the storage222or the storage43, and the drive controller22switches the connection state of the switching element27so that the resistance value R corresponds to the number of discharge nozzles.

The drive controller22may adjust the resistance value R of the resistance value25according to the result of detection of the temperature by the temperature detector54in addition to the number of discharge nozzles. Since the capacitance of the piezoelectric element127and the resistance of the wiring cable30are varied according to the temperature, changes in those capacitance and resistance lead to distortion of the drive signal depending on the change amount of the temperature. Thus, it is possible to suppress distortion of the drive signal to stabilize the speed and volume of ink more effectively by adjusting the resistance value R according to the result of detection of the temperature. For example, as the temperature rises, the capacitance C of the piezoelectric element127increases. Thus, as the resistance R of the resistance25is reduced accordingly, it is possible to effectively suppress distortion of the drive signal.

FIG.12is a flowchart showing control steps of the drive control process by the drive controller22according to Modification Example 2.

The drive control process is started with the start of the recording operation by the inkjet recording device1.

At the start of the drive control process, the drive controller22specifies the number of nozzles used for recording lines to be recorded in the image based on the image data input from the controller40and the number of discharge nozzles (Step S101).

The drive controller22can switch the resistance value R of the resistance element25according to the specified number of discharge nozzles (Step S102). That is, the drive controller22outputs the control signal to the switching element27so that the resistance value R of the resistance element25corresponds to the specified number of discharge nozzles, and switches the resistance element to be connected to the drive waveform amplifier circuit24by the switching element27.

The drive controller22outputs the drive signal adjusted according to the specified number of discharge nozzles from the drive waveform amplifier circuit24and causes ink to be discharged from each of the nozzles N (Step S103).

If the recording of all the lines of the image to be recorded is not completed (“NO” at Step S104), the drive controller22returns the process to Step S101, and if the recording of all the lines of the image to be recorded is completed (“YES” at Step S104), the drive controller22ends the drive control process.

As described hereinbefore, the inkjet recording device1in the embodiment of the present invention includes the ink discharge head10that includes the nozzles N through which ink is discharged, the pressure climbers128communicating to the nozzles N, the piezoelectric elements127generating pressure change in ink in the pressure chambers128to cause ink to be discharged from the nozzles N according to application of the drive signals, the driver20that is disposed outside the ink discharge head10and that includes the drive waveform amplifier circuit24as the drive circuit outputting the drive signals, and the wiring cable30that electrically connects the driver20with the ink discharge head10and through which the drive signals output from the drive waveform amplifier circuit24and applied to the piezoelectric elements127are transmitted. The driver20includes the resistance element25provided in the transmission path of the drive signals between the drive waveform amplifier circuit24and the wiring cable30, and the magnitude of the resistance value R of the resistance element25corresponds to the wiring length L of the wiring cable30.

In the configuration in which the drive waveform amplifier circuit24as this is disposed outside the ink discharge head10, the drive signal is distorted by the inductance of the wiring cable30and the dropping speed and volume of ink deviate from the desired values. However, it is possible to appropriately suppress overshoot and undershoot of the drive signal due to the inductance of the wiring cable30to suppress distortion of the waveform of the drive signal by providing the resistance element25and setting the resistance value R of the resistance element25to a value corresponding to the wiring length L of the wring cable30. This makes it possible to suppress variation in the dropping speed and volume of ink due to the inductance of the wiring cable30. The change amount of the dropping speed of ink when changing the number of discharge nozzles is different according to a combination of the wiring length L of the wiring cable30and the resistance value R of the resistance element25. Thus, it is possible to suppress the change amount of the dropping speed of ink with respect to the number of discharge nozzles by setting the resistance value R appropriately according to the wiring length of the wiring cable30. As a result of these, it is possible to effectively suppress deterioration of the image quality.

The resistance element25in Modification Example 2 and Modification Example 3 is provided in a state where the resistance value R can be changed. This makes it possible to easily adjust the resistance value R in the case where the wiring length L of the wiring cable30is varied or in the case where the ink discharge head10is replaced.

The inkjet recording device1in Modification Example 2 includes the drive controller22as a resistance value controlling means that changes the resistance value R of the resistance element25. This makes it possible to change the resistance value R of the resistance element25inside the inkjet recording device. The user can then change the resistance value R without replacing the resistance element25or directly adjusting the resistance value R, and the user convenience can be thereby improved.

In the inkjet recording device1in Modification Example 2, the ink discharge head10includes the nozzles N, the pressure chambers128corresponding to the pressure chambers128, and the piezoelectric elements127corresponding to the nozzles N. The drive controller22adjusts the resistance value R of the resistance element25every time a drive signal is applied so that the magnitude of the resistance value R of the resistance element25corresponds to the number of discharge nozzles (the number of the nozzles N from which ink is discharged at the same tinting among all the nozzles N). This makes it possible to suppress variation of the dropping speed and volume of ink according to the number of discharge nozzles by also adjustment of the resistance value R of the resistance element25. Thus, it is possible to more effectively suppress deterioration of the image quality.

The inkjet recording device1in Modification Example 2 includes the temperature detector54that detects the temperature corresponding to the temperature of the ink discharge head10, and the drive controller22adjusts the resistance value R of the resistance element25based on the temperature detected by the temperature detector54. This makes it possible to suppress distortion of the drive waveform caused by variation in the resistance value of the piezoelectric element127by the temperature and variation of the resistance of the wiring cable30or the like.

When the capacitance of the capacitive load of the piezoelectric elements127is defined as C and the resistance value of the resistance element25is defined as R, the resistance value R is set in a range where a relationship of CR<500 ns. It is thereby possible to suppress variation in the dropping speed and volume of ink due to slowing of a rise and fall of the waveform of the drive signal and suppress distortion o the drive signal caused by the inductance of the wiring cable30as well.

As the resistance value R of the resistance element25is set such that the change amount of the dropping speed of ink when changing the number of discharge nozzles satisfies the predetermined change amount suppressing condition, it is possible to keep the change amount of the dropping speed of ink with respect to the number of discharge nozzles small and effectively suppress deterioration of the image quality.

The inkjet recording device1includes the inkjet discharge heads10, the drivers20corresponding to the ink discharge heads10, and the wiring cables30corresponding to the ink discharge heads10, and the magnitude of the resistance value R of the resistance element25of each of the drivers20corresponds to the wiring length L of the wiring cable30connected to the concerning driver20. This makes it possible to effectively suppress deterioration of the image quality of each part of the image to be recorded by each of the ink discharge heads10in the configuration in which the ink discharge heads10and the drivers20are connected with each other using the wiring cables30of different wiring lengths L.

The inkjet recording device1includes the drive controller22as a drive controlling means that controls output operations of drive signals by the drive waveform amplifier circuit24. The drive signals include a pulse signal P, and the drive controller22adjusts the voltage amplitude of the pulse signal according to the number of discharge nozzles. This makes it possible to suppress distortion of the drive signal (e.x., the way the waveform rises or falls gets slow) due to an increase and decrease in the drive load of the capacitance by a change in the number of the piezoelectric elements127which share the period of application of the drive signal. Thus, it is possible to stabilize the dripping speed and volume of discharged ink regardless of the number of discharge nozzles.

The drive controller22adjusts the pulse width of the pulse signal P according to the number of discharge nozzles. Adjustment of the pulse width makes it possible to subtly adjust the dropping speed and volume of discharged ink. Thus, it is possible to stabilize the dripping speed and volume of discharged ink more when the number of discharge nozzles is changed.

The drive controller22causes the drive waveform amplifier circuit24to output the drive signal including the sub pulse signal Pc for shaking the ink liquid surface in the nozzle N, the pulse signal P applied after the sub pulse signal Pc. This makes it possible to adjust the dropping speed and volume of ink according to the relationship between the phase of the shaking of the liquid surface according to the sub pulse signal Pc and the phase of the pressure change by the pulse signal O. Thus, it is possible to stabilize the dropping speed and volume of discharged ink more when the number of discharge nozzles is changed.

The drive controller22adjusts the waveform of the drive signal such that at least one of the rise time T1and the fall time T2of the pulse signal P is longer as the number of discharge nozzles is smaller. As the number of discharge nozzles is smaller, that is, as the drive load of the capacitance of the piezoelectric element127is smaller overshoot and undershoot due to an effect of the inductance of the wiring cable30tend to increase. Thus, it is possible to suppress overshoot and undershoot to stabilize the dropping speed and volume of discharged ink by adjusting at least one of the rise time T1and the fall time T2as described above.

The drive controller22causes the drive waveform amplifier circuit24to output the drive signal including multiple pulse signals P, and the piezoelectric element127causes ink droplets that forms one pixel on the recording medium M to be discharged from the nozzle N. This makes it possible to record an image in the multi-drop method in which the density of a pixel can be adjusted by the number of ink droplets. As it is also possible to stabilize the dropping speed and volume of ink by adjusting the resistance value R of the resistance element25, it is possible to join multiple ink droplets appropriately to land them at a desired position on the recording medium M.

In the method for adjusting the ink discharge head10in this embodiment in which the magnitude of the resistance value R of the resistance element25corresponds to the wiring length L of the wiring cable30, it is possible to suppress a variation in the dropping speed and volume of ink caused by the inductance of the wiring cable30and effectively suppress deterioration of the image quality.

In the method for controlling the ink discharge head10according to Modification Example 2 of the present invention, the resistance value R and the resistance element25is adjusted every time a drive signal is applied so that the magnitude of the resistance value R of the resistance element25corresponds to the wiring length L of the wiring cable30and the number of the nozzles N through which ink is discharged according to the number of discharge nozzles. This makes it possible to suppress a variation of the dropping speed and volume of ink according to the number of discharge nozzles by adjustment of the resistance value R of the resistance element25. Thus, it is possible to suppress deterioration of the image quality more effectively.

The present invention is not limited to the above-described embodiment, and a variety of changes can be made.

For example, in the above-described embodiment, the wiring cable30is an example of the wire, but the wiring cable30is not limited to this, and may be any other wiring such as an FPC.

At least part of the functions of the drive controller22may be realized by the controller40. In that case, the drive controller22and the controller40constitute the drive controlling means and the resistance value controlling means.

“The number of the piezoelectric elements127which share the period of application of the drive signal” in the above-described embodiment is not necessarily the number of the piezoelectric elements127which share the start timing of application of the drive signal, and may be the number of the piezoelectric elements127which share the period of application of the drive signal at least partially. That is, “the number of the nozzles N through which ink is discharged at the same timing (the number of discharge nozzles)” is not limited to the number of the nozzles N through which ink is discharged simultaneously, but may be the number of the nozzles N corresponding to the piezoelectric elements127which share the period of application of the drive signal at least partially.

In the above-described embodiment, a multi-drop method is described in which multiple droplets are discharged to form one pixel as an example, but the present invention is not limited to this, and the present invention may be applied to an inkjet recording device in which a single droplet is discharged to form one pixel.

Adjustment of the drive signals according to the number of discharge nozzles may be omitted in a case where adjustment of the resistance value R of the resistance element25can suppress a variation of the dropping speed and volume of ink sufficiently.

In the above-described embodiment, a shear-mode ink discharge head10is described as an example, but the present invention is not limited to this example. For example, the present invention may be applied to a vent-mode ink discharge head which ink is discharged by pressure change in ink in the pressure chambers by deformation of the piezoelectric elements (pressure generating means) fixed on the wall surfaces of the pressure chambers.

In addition to this, any other pressure generating means that can cause pressure change in ink in the pressure chambers by exchanging heat and electromagnetism into space deformation may be used.

In the above-described embodiment, an example in which the recording medium M is conveyed by the conveyance belt101is described, but instead of this, the recording medium M may be held on the outer peripheral surface of the rotating conveying drum and conveyed.

The above-described embodiment illustrates the single-path inkjet recording device1as an example. However, the present invention may be applied to an inkjet recording device that records an image by scanning the ink discharge head10.

While the present invention is described with some embodiments, the scope of the present invention is not limited to the above-described embodiment but encompasses the scope of the invention recited in the claims and the equivalent thereof.

INDUSTRIAL APPLICABILITY

The present invention can be used in an inkjet recording device, a method for adjusting an inkjet recording device, and a method for controlling an inkjet recording method.

REFERENCE SIGNS LIST