JP6051711B2 - Method and apparatus for driving liquid discharge head - Google Patents

Description

  The present invention relates to a method for driving a liquid discharge head, and a discharge apparatus including a liquid discharge head driven by the method for driving a liquid discharge head.

As an ejection device including a recording head composed of a liquid ejection head that ejects liquid recording liquid (hereinafter also referred to as “ink”) droplets (hereinafter also referred to as “ink droplets”), a printer, a facsimile, 2. Description of the Related Art Image forming apparatuses such as copying machines, plotters, and multifunction machines having a plurality of these functions are known. As an image forming apparatus, for example, an ink is used and a medium (hereinafter also referred to as “paper” is not limited to a material, and a recording medium, a recording medium, a transfer material, a recording paper, and the like are also used synonymously. In some cases, image formation (recording, printing, printing, and printing are also used synonymously) is performed by adhering ink to a sheet while conveying.
The “ejection device” is not particularly limited as long as it is a device that ejects liquid from a liquid ejection head. However, an image forming apparatus will be described below as an example.

  “Image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. The term “not only” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium. The “liquid” is not limited to the recording liquid (ink) and is not particularly limited as long as it becomes a fluid when ejected.

  In addition, as an image forming apparatus including a liquid discharge head, a serial type image recording apparatus that performs recording by mounting a recording head on a carriage and moving the recording head in a main scanning direction orthogonal to a sheet feeding direction, and an abbreviation of a recording area. There is a line-type image recording apparatus using a line-type head in which a plurality of discharge ports (nozzles) for discharging droplets over the entire width are arranged.

Liquid ejection heads are roughly classified into several types according to the type of actuator means for ejecting ink droplets.
For example, a part of the wall of the liquid chamber is made into a thin diaphragm, and a piezoelectric element as an electromechanical conversion element is arranged correspondingly, and the diaphragm is deformed by deformation of the piezoelectric element that occurs when voltage is applied. Piezo type that discharges ink droplets by changing the pressure in the pressure chamber. A heating element is placed inside the liquid chamber, bubbles are generated by heating the heating element by energization, and ink droplets are discharged by the pressure of the bubbles. A bubble jet (registered trademark) system is generally well known. In addition, an electrostatic force generated by applying an electric field between the diaphragm and the electrode, including a diaphragm that forms a wall surface of the liquid chamber and an individual electrode outside the liquid chamber that is disposed to face the diaphragm. There has also been proposed an electrostatic type in which an ink droplet is ejected from a nozzle by changing the pressure / volume in the liquid chamber by deforming the diaphragm.

  By the way, since the liquid discharge head performs recording by discharging ink from the discharge port, if the state where ink is not discharged continues, the viscosity of the ink increases as the solvent of the ink in the nozzle evaporates, and the liquid remains as it is. When a droplet discharge operation is performed, the discharge state may be disturbed, and the print quality may be deteriorated due to a discharge impossible state. In addition, since there is no ink flow, the gas dissolved amount of ink in the liquid chamber increases with the standing time, pressure fluctuations are absorbed by bubbles mixed in the ink, and ejection failure may occur.

  In order to solve the above problem, it is already known that an empty discharge operation for discharging thickened ink and bubbles in the flow path is performed by discharging a droplet that does not contribute to recording (image formation) from the nozzle. In addition, a control method for the idle ejection operation has also been proposed (see, for example, Patent Documents 1 to 4).

  Patent Document 1 corrects the time width of the maintenance drive pulse based on the detected environmental temperature for the purpose of providing a liquid ejecting apparatus capable of improving the discharge performance of bubbles existing in the liquid flow path. It is disclosed. In Patent Document 2, the pulse width and the interval between pulses are changed in accordance with the thickened state of the ink in order to make the meniscus formed on the nozzle difficult to be destroyed and improve the recovery efficiency by the idle ejection operation. It is disclosed. In Patent Document 3, for the purpose of providing a liquid ejecting apparatus capable of effectively removing bubbles that cause nozzle ejection failure, the outside air temperature during bubble removal flushing is detected, and the pulse width is determined accordingly. Is disclosed. Patent Document 4 discloses that a waveform is expanded and contracted in the voltage axis direction and the time axis direction in accordance with the environmental temperature for the purpose of favorably discharging a high-viscosity liquid regardless of the environmental temperature. .

However, in the idle ejection operation in a state where the viscosity of the ink is high, such as when the environmental temperature is low, a high voltage is required to obtain a desired droplet velocity. On the other hand, it is known that when ink is ejected at a high voltage, the meniscus pull-in of the nozzle portion increases, and the vibration period (pressure vibration period) of the pressure chamber in which the meniscus resonates is shortened.
Normally, the most efficient pulse width and interval between pulses are set based on the basic characteristics at room temperature, so the same pulse width and interval between pulses at the low temperature environment as described above. When the idle ejection driving waveform is applied, a pulse is applied at a timing deviating from the resonance point, and the voltage required to obtain a desired droplet velocity increases, resulting in a problem that the efficiency of idle ejection deteriorates.

  Patent Document 4 discloses that the waveform is adjusted according to the environmental temperature, and is expanded and contracted at a constant magnification in the time axis direction. However, in this case, both the rise time and fall time constituting the waveform change, and there is a concern that the instantaneous current increases and the amount of heat generation increases when the slope of the waveform becomes steep.

  Therefore, in view of the above problems, the present invention applies a driving waveform designed according to conditions under different conditions of the viscosity of the liquid to be discharged, for example, when the ambient temperature is different, and thereby provides efficient emptying. It is an object of the present invention to provide a method for driving a liquid discharge head capable of realizing the discharge operation.

In order to solve the above-mentioned problems, a method of driving a liquid discharge head according to the present invention changes the volume of a pressure chamber containing liquid by a pressure generating means, and discharges droplets from a nozzle communicating with the pressure chamber. In the driving method of the liquid discharge head for performing image formation, the driving waveform applied to the pressure generation unit maintains the state of the nozzle meniscus and the falling element that expands the volume of the pressure chamber and draws the nozzle meniscus. An idle ejection operation in which a droplet group that includes a plurality of drive pulses including an element and a rising element that pushes out the nozzle meniscus by reducing the volume of the pressure chamber and ejects droplets that do not contribute to image formation from the nozzle sometimes, continuous intervals Td between the driving pulse, the to correspond to the pressure chamber of the pressure resonance period Tc, the air discharge operation, the idle discharge of any number of drops The plurality of idle discharge groups are executed a plurality of times, and the plurality of idle discharge groups hold a reference potential for a predetermined time after executing one idle discharge group and execute the next idle discharge group. The driving value of the liquid ejection head is characterized in that the peak value of the voltage of the drive pulse of the idle ejection operation is the largest in the idle ejection group to be executed first and becomes smaller as the number of executions increases. It is.

  According to the driving method of the liquid discharge head of the present invention, even when the viscosity of the discharged liquid is different, for example, when the environmental temperature is different, the drive waveform designed according to the condition is applied, and the efficiency is improved. It is possible to provide a liquid ejection head driving method capable of realizing a good idle ejection operation.

It is sectional drawing along the liquid chamber longitudinal direction of an example of a liquid discharge head. FIG. 6 is a cross-sectional view along the lateral direction of the liquid chamber of an example of a liquid discharge head. It is a block diagram which shows an example of the control means of a discharge apparatus. 3 is a block diagram illustrating an example of a print control unit and a head driver. FIG. It is explanatory drawing which shows the waveform shape of the drive pulse which comprises the idle discharge drive waveform. It is an image figure of the Pw characteristic which plotted the drop speed of the discharge drop. It is a figure explaining the prior art example of the drive waveform for idle discharge. It is a figure explaining the drive waveform for idle discharge which concerns on 1st Embodiment. It is the flowchart which showed an example of the flow which prescribes | regulates the drive waveform for idle discharge. It is a figure explaining the drive waveform for idle discharge which concerns on 3rd Embodiment. It is a figure explaining the drive waveform for idle discharge which concerns on 5th-8th embodiment. 1 is a schematic configuration diagram illustrating an overall configuration of a mechanism unit as an example of an image forming apparatus. It is explanatory drawing of the principal part plane of an example of an image forming apparatus.

  Hereinafter, a liquid ejection head driving method and a droplet ejection apparatus according to the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments of the examples shown below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art. Any aspect is included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

  1 and 2 show an example of a liquid discharge head driven by the liquid discharge head driving method. FIG. 1 is a cross-sectional view along the longitudinal direction of the liquid chamber, and FIG. FIG.

  A liquid discharge head (hereinafter also referred to as an “inkjet head”) includes an ink supply port (not shown) and a frame 10 in which an engraving that becomes a common liquid chamber 12 is formed, an engraving that becomes a fluid resistance portion 21 and a pressure chamber 22. And a flow path plate 20 having a communication port (liquid introduction portion) 23 communicating with the nozzle 31, a nozzle plate forming the nozzle 31, and a diaphragm 60 having a convex portion 61, a diaphragm portion 62, and an ink inlet 63. The pressure generating means (laminated piezoelectric element) 50 joined to the vibration plate 60 via an adhesive layer, and the base 40 that fixes the laminated piezoelectric element 50 are provided.

  The base 40 is made of a barium titanate ceramic, and the laminated piezoelectric elements 50 are arranged in two rows and joined.

The laminated piezoelectric element 50 includes a lead zirconate titanate (PZT) piezoelectric layer 51 having a thickness of 10 to 50 μm / layer, and an internal electrode layer 52 made of silver and palladium (AgPd) having a thickness of several μm / layer. Are stacked alternately. The internal electrode layer 52 is connected to the external electrode 53 at both ends.
The laminated piezoelectric element 50 is divided on comb teeth by half-cut dicing, and is used as a drive unit 55 and a support unit 56 (non-drive unit) one by one. The laminated piezoelectric element 50 includes a lead zirconate titanate (PZT) piezoelectric layer 51 having a thickness of 10 to 50 μm / layer, and an internal electrode layer 52 made of silver / palladium (AgPd) having a thickness of several μm / layer. Are alternately stacked, and the internal electrodes 5-2 are alternately electrically connected to the individual electrodes 53 and the common electrode 54 which are end-face electrodes (external electrodes) on the end faces.

The liquid discharge head of this embodiment is configured to use a laminated piezoelectric element 50 of the d33 method that is displacement in the thickness direction as pressure generating means, and the pressure chamber 22 containing the liquid is contracted by expansion and contraction of the laminated piezoelectric element 50. The volume is changed by inflating.
When the drive signal is applied to the multi-layer piezoelectric element 50 and charging is performed, the multi-layer piezoelectric element 50 expands, and when the charge charged in the multi-layer piezoelectric element 50 is discharged, the multi-layer piezoelectric element 50 contracts in the opposite direction.

An FPC 70 is soldered to the individual electrode 53 of the drive unit.
Further, the common electrode 54 is provided with an electrode layer at the end of the laminated piezoelectric element and is wound around to join the Gnd electrode of the FPC 70. A driver IC (not shown) is mounted on the FPC 70, thereby controlling application of drive voltage to the drive unit 55.

  The diaphragm 60 is joined to a thin film diaphragm 62, an island-shaped convex portion (island portion) 61 that joins the laminated piezoelectric element 50 that is the driving portion 55 formed at the center of the diaphragm portion 62, and a support portion. A thick film portion including a beam and an opening serving as an ink inflow port 63 are formed by stacking two Ni plating films by an electroforming method.

  The flow path plate 20 was formed by using a silicon single crystal substrate, and patterning the engravings to be the fluid resistance portion 21, the pressure chamber 22 and the liquid introduction portion 23, and the through holes to be the communication ports 25 at positions relative to the nozzles 31. The portion left by etching becomes the partition wall 24 of the pressure chamber 22.

  The nozzle plate 30 is formed of a metal material, for example, an Ni plating film formed by an electroforming method, and has a large number of nozzles 31 that are fine discharge ports for flying ink droplets. The internal shape (inner shape) of the nozzle 31 is formed in a horn shape (may be a substantially cylindrical shape or a substantially frustum shape).

  The ink ejection surface (nozzle surface side) of the nozzle plate 30 is provided with a water-repellent treatment layer that has been subjected to a water-repellent surface treatment (not shown). Ink physical properties such as PTFE-Ni eutectoid plating, electrodeposition coating of fluororesin, vapor-deposited fluororesin (for example, fluorinated pitch), baking after solvent application of silicon resin / fluorine resin, etc. A water-repellent treatment film selected according to the above is provided to stabilize the ink droplet shape and flight characteristics so that high-quality image quality can be obtained.

  The frame 1 that forms the engraving that becomes the ink supply port 11 and the common liquid chamber 12 is manufactured by resin molding.

  In the ink jet head configured as described above, a drive waveform (pulse voltage of 10 to 50 V) is applied to the drive unit 56 in accordance with the recording signal, thereby causing a displacement in the stacking direction in the drive unit 56 and the diaphragm 30. The pressure chamber 22 is pressurized via the pressure to increase the pressure, and ink droplets are ejected from the nozzle 31 communicating with the pressure chamber 22.

  Thereafter, the ink pressure in the pressure chamber 22 decreases with the end of ink droplet ejection, and a negative pressure is generated in the pressure chamber 22 due to the inertia of the ink flow and the discharge process of the drive pulse, and the process proceeds to the ink filling process. . At this time, the ink supplied from the ink tank flows into the common liquid chamber 12, passes through the ink inlet 63 from the common liquid chamber 12, passes through the liquid introducing portion 23 and the fluid resistance portion 21, and is filled into the pressure chamber 22. .

  The fluid resistance portion 21 has an effect on the attenuation of the residual pressure vibration after the discharge, but becomes resistant to the maximum filling (refill) due to the surface tension. By appropriately selecting the fluid resistance portion, it is possible to balance the attenuation of the residual pressure and the refill time, and to shorten the time (drive cycle) until the transition to the next ink droplet ejection operation.

Next, the outline of the control means of the ejection device according to the method for driving the liquid ejection head will be described with reference to FIG.
FIG. 3 is a block diagram of a control unit of the image forming apparatus as one embodiment of the ejection device.
The control unit 500 controls the entire apparatus. The CPU 511 also serves as a means for controlling the idle ejection operation according to the present invention, a ROM 502 for storing programs executed by the CPU 511 and other fixed data, and image data. RAM 503 for temporarily storing data, a rewritable nonvolatile memory 504 for holding data even when the power of the apparatus is shut off, image processing for performing various signal processing, rearrangement, etc. on image data and other apparatuses And an ASIC 505 for processing input / output signals for overall control.

  In addition, a print control unit 508 including a data transfer unit for driving and controlling a liquid discharge head (hereinafter also referred to as “recording head”) 234 and a drive signal generating unit, and a recording head 234 provided on the carriage 233 side are driven. Motor driver for driving a head driver (driver IC) 509 for driving, a main scanning motor 254 for moving and scanning the carriage 233, a sub-scanning motor 255 for rotating the conveyor belt 251 and a maintenance and recovery motor 256 of the maintenance and recovery mechanism And an AC bias supply unit 511 that supplies an AC bias to the charging roller 256.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side, an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, and the like. From the host 600 side via the cable or network via the I / F 506.

The CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints the image data. The data is transferred from the unit 508 to the head driver 509.
Note that generation of dot pattern data for image output is performed by the printer driver 601 on the host 600 side.

  The print control unit 508 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 509. Including a D / A converter for D / A converting D / A conversion of drive pulse pattern data stored in the ROM, a voltage signal amplifier, a current amplifier, and the like, and a drive signal or a plurality of drive pulses Is output to the head driver 509.

The head driver 509 selectively selects droplets of the recording head 7 as drive pulses constituting a drive signal given from the print control unit 508 based on image data corresponding to one line of the recording head 34 inputted serially. The recording head 7 is driven by applying it to a driving element (for example, a piezoelectric element) that generates energy to be discharged.
At this time, by selecting a driving pulse constituting the driving signal, for example, dots having different sizes such as a large droplet, a medium droplet, and a small droplet can be sorted.

The I / O unit 513 acquires information from various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, and print control unit 508, motor control unit 510, AC bias supply unit Used to control 511.
The sensor group 515 includes an optical sensor for detecting the position of the paper, a thermistor for monitoring the temperature in the machine, a sensor for monitoring the voltage of the charging belt, an interlock switch for detecting opening and closing of the cover, and the like. The I / O unit 513 can process various sensor information.

Next, an example of the print control unit 508 and the head driver 509 will be described with reference to FIG.
As described above, the print control unit 508 generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle at the time of image formation. A drive waveform generation unit 701 that generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within the idle ejection cycle, and 2-bit image data (gradation) corresponding to the print image And a data transfer unit 702 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The drop control signal is a 2-bit signal that instructs each drop to open and close an analog switch 715, which will be described later, of the head driver 509. The drop control signal is a waveform to be selected in accordance with the print cycle of the common drive waveform. The state transitions to the level (ON), and when not selected, the state transitions to the L level (OFF).

  The head driver 509 receives a transfer clock (shift clock) from the data transfer unit 702 and serial image data (gradation data: 2 bits / 1 channel (1 nozzle)), and register values of the shift register 711. Is latched by a latch signal, a decoder 713 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 713 is a level at which the analog switch 715 can operate. A level shifter 714 that performs level conversion to an analog switch, and an analog switch 715 that is turned on / off (opened / closed) by an output of a decoder 713 provided via the level shifter 714.

  The analog switch 715 is connected to the selection electrode (individual electrode) 53 of each piezoelectric element 50, and the common drive waveform from the drive waveform generation unit 701 is input thereto. Accordingly, when the analog switch 715 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 713, a required drive signal constituting the common drive waveform is obtained. Passed through (selected) and applied to the piezoelectric element 50.

Next, an example of the idle ejection driving waveform applied during the conventional idle ejection operation will be described with reference to FIGS. 5, 6, and 7.
FIG. 5 shows the waveform shape of a drive pulse (single pulse) constituting the idle ejection drive waveform, and FIG. 6 shows Pw obtained by plotting the droplet velocity of the ejected droplet by varying the pulse width Pw of the element included in the drive pulse. FIG. 7 is an illustration of characteristics, and FIG. 7 is a diagram for explaining an example of an idle ejection drive waveform (a pulse group including a plurality of drive pulses) when environmental temperatures are different.

The idle ejection driving waveform applied to the piezoelectric element 50 as the pressure generating means during the idle ejection operation is a falling element that expands the volume of the pressure chamber 22 in which the liquid to be ejected is accommodated and draws the nozzle meniscus. , And a drive pulse (single pulse) including an element that maintains the state of the nozzle meniscus and a rising element that reduces the volume of the pressure chamber 22 and pushes out the nozzle meniscus.
That is, as shown in FIG. 5, the waveform of the drive pulse is contracted by the waveform element (fall time) Tf in which the potential of the drive pulse falls from the reference potential Ve, and the volume of the pressure chamber 22 is reduced. Expands. Next, the hold state in which the state of the nozzle meniscus after the falling does not change (is held) is represented by the pulse width Pw. Further, the laminated piezoelectric element 50 expands and the pressure chamber 22 contracts due to the waveform element (rise time) Tr rising from the hold state.

  FIG. 6 shows the Pw characteristic at normal temperature (for example, 23 to 25 ° C.), and the pulse width Pw of the driving pulse constituting the conventional idle ejection driving waveform is set by the value of Pw_1. Pw_1 is the first peak value of pressure resonance. The peak is caused by resonance of the vibration system including the opening of the nozzle 31 and the size of the pressure chamber 22. For example, when the droplet speed of the ejected droplet is measured while changing the pulse width Pw, the peak is the most. The drop velocity peak that appears first is called the first peak. As the pulse width Pw increases, a plurality of peaks such as a second peak Pw_2 and a third peak PW_3 (not shown) are generated. The period of pressure resonance (hereinafter also referred to as “natural period”) Tc is calculated from the difference between the first peak and the second peak.

FIG. 7 shows an example of a drive waveform for idle ejection when the environmental temperature is high, normal, and low. The high temperature is indicated by a broken line 7a, the normal temperature is indicated by a solid line 7b, and the low temperature is indicated by a dashed line 7c. . Here, high temperature means a temperature that is about 5 ° C. higher than normal temperature, and low temperature means a temperature that is about 5 ° C. lower than normal temperature.
FIG. 7 shows an example in which the idle ejection drive waveform is composed of a pulse group including five drive pulses (single pulse). However, the number of included pulses is not limited and is appropriately selected according to the purpose. can do.

  In the conventional example shown in FIG. 7, the interval Td between drive pulses is set so that the length from the end of the pulse width Pw of the drive pulse to the end of Pw of the next drive pulse is twice the natural period Tc. doing. It should be noted that the lengths of Td present in four places in FIG. 7 are all the same.

At any environmental temperature, the droplet speed is controlled to be the same by the idle ejection operation. In the high temperature environment (7a), the viscosity of the ink is lower than that in the normal temperature environment (7b). The peak value of the voltage required to obtain the same drop velocity (Vj) is low. On the other hand, since the ink viscosity is higher in the low temperature environment (7c) than in the normal temperature environment (7b), the peak value of the voltage is large.
That is, in the conventional example shown in FIG. 7, only the voltage peak value is changed according to the environmental temperature, and the same value is used for the pulse width Pw and the interval Td between pulses.

In the conventional idle ejection operation, thickened ink is discharged by changing the peak value of the pulse voltage without changing the pulse width and interval between pulses constituting the idle ejection drive waveform at all environmental temperatures. It was. Usually, the most efficient pulse width Pw and interval Td between pulses are set at the resonance timing based on the basic characteristics at room temperature. However, it has been found that when the voltage of the drive waveform for idle ejection, such as in a low temperature environment, increases, the meniscus pull-in of the nozzle portion increases and the natural period decreases. In such a state, since the pulse is applied at a timing deviating from the pressure resonance point, the voltage required to produce a desired droplet velocity increases, which is not efficient.
On the other hand, in the drive waveform during the idle ejection operation of the liquid ejection head driving method described below, the interval Td between pulses of the idle ejection drive waveform is adjusted and applied at the timing of pressure resonance depending on the environmental temperature. Thus, the idle ejection operation can be efficiently executed regardless of the change in the ink viscosity, that is, at any environmental temperature.

<Driving method of liquid ejection head>
[First Embodiment]
A first embodiment of the liquid ejection head driving method will be described with reference to FIG.
8A and 8B are diagrams showing idle ejection drive waveforms, in which FIG. 8A is an idle ejection drive waveform in a high temperature environment, FIG. 8B is an idle ejection drive waveform in a room temperature environment, and FIG. (C) is a drive waveform for idle discharge in a low temperature environment. The high temperature environment means about 30 ° C. or more, the low temperature environment means about 18 ° C. or less, and the normal temperature environment means a temperature range between them, particularly about 23 to 25 ° C.

  In the method of driving the liquid discharge head, the volume of the pressure chamber 22 containing the liquid is changed by a pressure generating means (piezoelectric element) 50, and liquid is discharged from a nozzle communicating with the pressure chamber 22 to form an image. In the ejection head driving method, the drive waveform applied to the pressure generating means 50 includes a falling element that expands the volume of the pressure chamber 22 to draw the nozzle meniscus, an element that maintains the state of the nozzle meniscus, and a pressure chamber In the idling operation in which droplets that do not contribute to image formation are ejected from the nozzles 31, the drive pulse interval is composed of a pulse group including a plurality of drive pulses composed of rising elements that reduce the volume of the nozzle 22 and push out the nozzle meniscus. This interval Td is made to correspond to the pressure resonance period Tc in the pressure chamber 22.

In the present embodiment, unlike the conventional example shown in FIG. 7, the interval Td between drive pulses constituting the idle ejection drive waveform is controlled at each environmental temperature in accordance with the environmental temperature.
Specifically, the interval (Td−H) between the drive pulses of the idle ejection drive waveform in the high temperature environment shown in FIG. 8A is the interval between the drive pulses in the room temperature environment shown in FIG. It is set longer than (Td−M). Further, the interval (Td−L) between the drive pulses of the idle ejection drive waveform in the low temperature environment shown in FIG. 8C is set shorter than Td−M. This is based on the fact that the pressure resonance period (hereinafter also referred to as “natural period”) Tc changes as the environmental temperature changes.

  In the case of the low temperature environment shown in FIG. 8C, since the ink viscosity is higher in the low temperature environment than in the normal temperature environment, the voltage required to obtain a desired droplet velocity is higher. Experiments have shown that when ink is ejected at a high voltage, the meniscus pull-in of the nozzle portion is large, and the natural period Tc is shorter than when ink is ejected at a low voltage. Therefore, since Tc-L is shortened in a low temperature environment, Td-L is also shortened accordingly.

  Similarly, in the case of the high temperature environment of FIG. 8A, the natural period Tc-H becomes longer due to low voltage driving, and the pulse interval Td-H is also longer than Td-M in accordance with it. .

  At any environmental temperature, only the conventional voltage is controlled by setting the interval Td between pulses so that the idle ejection operation is performed in accordance with the timing of resonance, that is, at a timing Tc or an integer multiple of Tc. The idle discharge operation can be executed more efficiently than the method, and the same idle discharge effect can be obtained at any environmental temperature.

  Note that, as in the conventional driving method described above, the voltage is a voltage at which the drop velocity of the empty discharge droplet during the empty discharge operation becomes a constant value at an arbitrary environmental temperature.

[Second Embodiment]
A second embodiment of the liquid ejection head driving method will be described.
In the second embodiment, the interval Td between the drive pulses is set so that the idle ejection operation is performed corresponding to the pressure resonance period Tc shown in the first embodiment, and the nozzles included in the drive pulse When the element that maintains the meniscus state is the pulse width Pw, the pulse width Pw of the drive waveform during the idle ejection operation is the pulse width of the first peak of the pressure resonance period Tc.

  The characteristics of the pulse width Pw will be described with reference to FIG. When a high voltage is applied, the first peak Pw_1 of the pulse width characteristic shifts in the direction in which the pulse width becomes longer, and the second peak Pw_2 shifts in the direction in which the pulse width becomes shorter. For this reason, the pulse width Pw-L of the idle ejection drive waveform in the low temperature environment shown in FIG. 8C is made to coincide with the first peak Pw_1 of the pressure resonance period Tc at the ambient temperature by increasing the pulse width. Set to

In a low temperature environment, the interval Td between pulses is short, the pulse width Pw is long, and the peak value of the voltage is high. As the environmental temperature rises, the pulse interval Td becomes longer, the pulse width Pw becomes shorter, and the voltage peak value becomes lower.
For this reason, in the idle ejection driving waveform, the interval Td between the pulses is shortened as the environmental temperature is low, the peak value of the voltage of the driving pulse is increased as the environmental temperature is low, and the pulse width Pw is increased as the environmental temperature is low. To do.

In this way, the interval Td between pulses, the pulse width Pw, and the change in the peak value of the voltage due to the change in the environmental temperature all have a certain direction, for example, when the change in the value is shown in a graph Is not a curve with an inflection point. Therefore, a predictive curve having continuity can be obtained from the pulse interval Td, pulse width Pw, and voltage values under a plurality of arbitrarily selected temperature conditions, and the drive waveform can be designed based on the predictive curve.
If the idle ejection driving waveform under the temperature condition to be selected is designed, the temperature waveform between two adjacent points can be predicted and complemented. The more the temperature conditions to be selected are set, the higher the accuracy of the complemented drive waveform.

[Control flow]
A specific flow for defining the idle ejection drive waveform will be described with reference to the flowchart of FIG.
First, the temperature of the liquid ejection head is detected (S01), and the optimum pulse interval Td and pulse width Pw are determined based on the obtained temperature (S02). Next, by determining the peak value of the optimum voltage of the idle ejection drive waveform (S03), the idle ejection drive waveform under the temperature condition is determined (S04). By applying the determined empty discharge driving waveform to the pressure generating means 50, the empty discharge driving is performed (S05), and the empty discharge operation is executed.
“Determining” includes obtaining an optimum value from the prediction curve or the like and designing a waveform based on the obtained value.
By performing the idle discharge operation according to this flow, an equivalent idle discharge effect can be obtained at any environmental temperature.

[Third Embodiment]
A third embodiment of the liquid ejection head driving method will be described with reference to FIG.
10A shows a driving waveform for idle ejection in a high temperature environment, FIG. 10B shows a driving waveform for idle ejection in a room temperature environment, and FIG. 10C shows a driving waveform for idle ejection in a low temperature environment.
The present embodiment is a method of setting the interval Td between drive pulses so that the idle ejection operation is performed corresponding to the pressure resonance period Tc, as in the first embodiment. Whereas Td is set at a resonance timing that is twice the pressure resonance period Tc, in the present embodiment, Td is set at the resonance timing of Tc.

According to the method of the present embodiment, the ejection efficiency of subsequent drive pulses is improved, so that the voltage necessary to obtain a desired droplet velocity can be reduced. Furthermore, since the pulse interval Pw is shortened, the entire length of the idle ejection drive waveform can be shortened.
By shortening the idle ejection driving waveform, the pressure generating means 50 can be driven at a high frequency, and the time required for the idle ejection operation can be shortened.

[Fourth Embodiment]
A fourth embodiment of the liquid ejection head driving method will be described.
In the fourth embodiment, as shown in the third embodiment, the interval Td between the drive pulses is made to correspond to the pressure resonance period Tc, and the pulse width Pw is set to the first of the pressure resonance period Tc corresponding to the environmental temperature. The peak pulse width.

As described above, when a high voltage is applied, the first peak Pw_1 of the pulse width characteristic shifts in the direction in which the pulse width becomes longer, and the second peak Pw_2 shifts in the direction in which the pulse width becomes shorter. For this reason, the pulse width Pw-L of the idle ejection drive waveform in the low temperature environment shown in FIG. 10C is made long so as to match the first peak Pw_1 of the pressure resonance period Tc at the ambient temperature. To.
According to the present embodiment, the efficiency of the idle ejection operation can be further improved as compared with the method of the third embodiment.

[Fifth Embodiment]
A fifth embodiment of the liquid ejection head driving method will be described with reference to FIG.
As shown in FIG. 11 (a), the idle ejection driving waveform has an idle ejection operation in which an idle ejection group (Pa1, Pa2,. Is performed by intermittently executing the unit of the idle ejection group.

  FIG. 11B shows a drive waveform for idle discharge constituting the idle discharge group, 11a is a waveform constituting the idle discharge group of Pa1 in FIG. 11A, and 11b is FIG. ) Of Pa2 idle discharge group. As shown in FIG. 11 (b), the peak value of the voltage of 11a executed first is larger than 11b executed later. This is because the ink having a high viscosity is discharged by increasing the voltage of the drive waveform constituting the idle ejection group executed earlier, and the voltage of the drive waveform constituting the idle ejection group executed next is set higher than the previous one. This control is intended to adjust the meniscus state by reducing the size.

  In FIGS. 11A and 11B, two examples of the idle ejection groups are shown, but the number of idle ejection groups is not limited to this. When the number of idle ejection groups is 2 or more, the peak value of the voltage of the drive pulse of the idle ejection operation is controlled to be the largest in the idle ejection group that is executed first, and decreases as the number of executions increases. The

  In the present embodiment, as the waveform of 11a in FIG. 11B, the interval Td between the drive pulses is set so that the idle ejection operation is performed at the resonance timing (2Tc) that is twice the pressure resonance period Tc. The idle ejection driving waveform of the first embodiment is used.

  The idle ejection operation controlled by the method of the present embodiment can reduce the ink consumption more than the idle ejection operation that is continuously executed, and can adjust the meniscus state before image formation.

[Sixth Embodiment]
A sixth embodiment of the liquid ejection head driving method will be described.
In the sixth embodiment, as the waveform of 11a in FIG. 11B in the fifth embodiment, the pulse width Pw becomes the pulse width of the first peak of the pressure resonance period Tc according to the environmental temperature. The set idle discharge driving waveform of the second embodiment is used.
The idle ejection operation controlled by the method of the present embodiment can realize an idle ejection operation with higher efficiency than that of the fifth embodiment.

[Seventh Embodiment]
A seventh embodiment of the liquid ejection head driving method will be described.
In the seventh embodiment, as the waveform of 11a in FIG. 11B in the fifth embodiment, the idle discharge of the third embodiment in which the interval Td between drive pulses is set at the resonance timing of the pressure resonance period Tc. Use drive waveforms.
The idle ejection operation controlled by the method of the present embodiment can realize an idle ejection operation with further improved efficiency compared to the fifth and sixth embodiments.

[Eighth Embodiment]
An eighth embodiment of the liquid ejection head driving method will be described.
In the eighth embodiment, as the waveform of 11a in FIG. 11B in the fifth embodiment, the interval Td between drive pulses is set at the resonance timing of the pressure resonance period Tc, and the pulse width Pw is set to the ambient temperature. The idle ejection drive waveform of the fourth embodiment, which is set to have the pulse width of the first peak of the pressure resonance period Tc according to the above, is used.
The idle ejection operation controlled by the method of the present embodiment can realize an idle ejection operation with further improved efficiency compared to the seventh embodiment.

<Discharge device>
An image forming apparatus as an embodiment of a discharge apparatus including a liquid discharge head driven by the driving method will be described with reference to FIGS.
FIG. 12 is a schematic configuration diagram illustrating the overall configuration of the mechanism unit of the image forming apparatus, and FIG. 13 is a plan view illustrating a main part of the mechanism unit. The image forming apparatus according to the present embodiment is a serial type image forming apparatus, and is a guide component horizontally mounted on the left and right side plates 201A and 201B.

The carriage 233 is slidably held in the main scanning direction by the main and slave guide rods 231 and 232, and is moved and scanned in the direction indicated by an arrow (carriage main scanning direction) via a timing belt by a main scanning motor (not shown).
The carriage 233 is provided with liquid discharge heads 234a and 234b comprising the liquid discharge head according to the present invention for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). (When not distinguished, it is referred to as “liquid ejection head 234”.) Nozzle rows comprising a plurality of nozzles are arranged in the sub-scanning direction orthogonal to the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.

Each of the liquid discharge heads 234 has two nozzle rows, and one nozzle row of the liquid discharge head 234a discharges black (K) droplets and the other nozzle row discharges cyan (C) droplets. One nozzle row of the head 234b discharges magenta (M) droplets, and the other nozzle row discharges yellow (Y) droplets.
The carriage 233 is equipped with head tanks 235a and 235b (referred to as “head tank 235” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the liquid ejection head 234. The sub tank 235 is supplementarily supplied with ink of each color from the ink cartridge 210 of each color via the supply tube 36 of each color.

  On the other hand, as a paper feeding unit for feeding the paper 242 stacked on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feeding) that separates and feeds the paper 242 one by one from the paper stacking unit 241. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  In order to feed the sheet 242 fed from the sheet feeding unit to the lower side of the liquid discharge head 234, a guide component 245 for guiding the sheet 242, a counter roller 246, a conveyance guide component 247, and a tip pressurization. A pressing member 248 having a roller 249 is provided, and a conveying belt 251 is provided as a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the liquid ejection head 234.

  The transport belt 251 is an endless belt, and is configured to wrap around the transport roller 252 and the tension roller 253 so as to circulate in the belt transport direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the liquid discharge head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. And a paper discharge tray 203 below the paper discharge roller 262.

A duplex unit 271 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.
Further, a maintenance / recovery mechanism that is a head maintenance / recovery device according to the present invention includes a recovery means for maintaining and recovering the state of the nozzles of the liquid ejection head 234 in the non-printing region on one side in the scanning direction of the carriage 233. 281 is arranged.

  The maintenance and recovery mechanism 281 includes cap parts (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the liquid ejection head 234, and nozzles. A wiper blade 283 which is a blade part for wiping the surface, and an idle discharge receptacle 284 for receiving droplets when performing idle discharge for discharging droplets that do not contribute to recording in order to discharge the thickened recording liquid. I have.

  In addition, in the non-printing area on the other side in the scanning direction of the carriage 233, the liquid that receives liquid droplets when performing idle ejection that ejects liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An ink recovery unit (empty discharge receiver) 288 that is a recovery container is disposed, and the ink recovery unit 288 includes an opening 289 along the nozzle row direction of the liquid discharge head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feeding tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and transported. Further, the leading end is guided by the transporting guide 237 and pressed against the transporting belt 251 by the leading end pressing roller 249, and the transporting direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated with respect to the charging roller 256, that is, a charging voltage pattern in which an alternating voltage is applied and the conveying belt 251 alternates, that is, in a sub-scanning direction that is a circumferential direction. The plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the liquid ejection head 234 in accordance with the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and the paper 242 is conveyed by a predetermined amount. Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

  Since this image forming apparatus is equipped with the liquid discharge head driven by the above-described driving method, it is possible to execute efficient empty discharge regardless of the environmental temperature, and a stable empty discharge effect can be obtained.

  In the above embodiment, the image forming apparatus, which is an ink jet recording apparatus, is described as an ejection apparatus. However, the present invention is not limited to this. For example, the image forming apparatus is not limited to a copier, and may be a printer or a facsimile. Alternatively, it may be a multifunction machine having a plurality of functions. Further, the present invention can be similarly applied to a line type liquid discharge head and a line type image forming apparatus. Furthermore, the present invention can also be applied to a liquid discharge head or a liquid discharge apparatus that discharges a DNA sample, a resist, a pattern material, or the like.

DESCRIPTION OF SYMBOLS 10 Frame 12 Common liquid chamber 20 Flow path plate 21 Fluid resistance part 22 Pressure chamber 23 Liquid introduction part 24 Partition 25 Communication port 30 Nozzle plate 31 Nozzle 40 Base 50 Pressure generating means (piezoelectric element)
51 Piezoelectric layer 52 Internal electrode layer 52 Individual electrode 54 Common electrode 60 Diaphragm 70 FPC
234 Liquid discharge head

JP 2011-104916 A JP 2011-056729 A JP 2009-220505 A JP 2006-264287 A

Claims (8)

In a method of driving a liquid ejection head that forms an image by changing the volume of a pressure chamber containing liquid by a pressure generating unit and ejecting liquid droplets from a nozzle communicating with the pressure chamber.
The drive waveform applied to the pressure generating means includes a rising element that expands the volume of the pressure chamber to draw the nozzle meniscus, an element that maintains the state of the nozzle meniscus, and a volume of the pressure chamber that decreases. It is composed of a pulse group including a plurality of drive pulses composed of a rising element that pushes out the nozzle meniscus,
In the idle ejection operation for ejecting droplets that do not contribute to image formation from the nozzle, the interval Td between the drive pulses is made to correspond to the pressure resonance period Tc in the pressure chamber ,
The idle discharge operation is performed by performing an idle discharge group that continuously performs an idle discharge of an arbitrary number of drops a plurality of times,
The plurality of idle discharge groups is to hold a reference potential for a predetermined time after executing one idle discharge group, and to execute the next idle discharge group,
The liquid ejection head drive method according to claim 1, wherein a peak value of the voltage of the drive pulse in the idle ejection operation is the largest in the idle ejection group to be executed first and becomes smaller as the number of executions increases . When the element that holds the state of the nozzle meniscus included in the drive pulse is a pulse width Pw, the pulse width Pw of the drive waveform during the idle ejection operation is set to the first peak value of pressure resonance according to the environmental temperature. The method of driving a liquid ejection head according to claim 1, wherein the pulse width corresponds to the above.   The method of driving a liquid ejection head according to claim 1, wherein the interval Td between the drive pulses is shortened as the environmental temperature is lower.   4. The method of driving a liquid ejection head according to claim 1, wherein the peak value of the voltage of the drive pulse is increased as the environmental temperature is lower. 5. The method of driving a liquid ejection head according to claim 2 , wherein the pulse width Pw is increased as the environmental temperature is lower.   6. The method of driving a liquid ejection head according to claim 1, wherein the voltage at which the droplet ejection speed during the idle ejection operation is a constant value at an arbitrary environmental temperature is set to a constant value. When an element that maintains the state of the nozzle meniscus included in the drive pulse is a pulse width Pw, the pulse width Pw of the drive waveform during the idle ejection operation , and a plurality of pulse intervals T d set at different environmental temperatures. obtains a prediction curve from the value of 及 beauty voltage have continuity, the driving method of a liquid discharge head according to any of claims 1 to 6, characterized by designing the driving waveforms on the basis of the prediction curve. A liquid discharge head for forming an image by changing the volume of the pressure chamber containing the liquid by a pressure generating unit and discharging droplets from a nozzle communicating with the pressure chamber;
The drive waveform applied to the pressure generating means includes a rising element that expands the volume of the pressure chamber to draw the nozzle meniscus, an element that maintains the state of the nozzle meniscus, and a volume of the pressure chamber that decreases. An interval Td between the drive pulses is formed in a pulse group including a plurality of drive pulses including a rising element that pushes out the nozzle meniscus, and discharges droplets that do not contribute to image formation from the nozzle. And control means corresponding to the pressure resonance period Tc in the pressure chamber.
The idle discharge operation is performed by performing an idle discharge group that continuously performs an idle discharge of an arbitrary number of drops a plurality of times,
The plurality of idle discharge groups is to hold a reference potential for a predetermined time after executing one idle discharge group, and to execute the next idle discharge group,
2. A discharge apparatus according to claim 1, wherein a peak value of the voltage of the drive pulse in the idle ejection operation is the largest in the idle ejection group to be executed first, and becomes smaller as the number of executions increases .