JP2013212660A - Inkjet head and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet head and an inkjet recording device that can prevent ink in a nozzle from property variation.SOLUTION: An inkjet head includes an ink tank for storing ink, a pressure chamber with ink filled, an ink flow path, a circulator, an actuator, a nozzle, and a controller. The ink flow path feeds ink from the ink tank into the pressure chamber, and returns ink in the pressure chamber to the ink tank. The circulator circulates the ink through the route including the ink tank, the pressure chamber, and the ink flow path. The actuator changes the volume of the pressure chamber. The nozzle discharges the ink in the pressure chamber depending on variation in volume of the pressure chamber. The controller outputs both a first signal changing the volume of the pressure chamber so that the ink may be discharged from the nozzle, and a second signal changing the volume of the pressure chamber so that the meniscus of the ink in the nozzle may be drawn into the pressure chamber without involving any ink discharge, to the actuator.

Description

  Embodiments described herein relate generally to an inkjet head that forms an image on a recording medium by ejecting ink, and an inkjet recording apparatus that includes the head.

  An ink jet head used in an ink jet printer or the like forms an image on a recording medium by ejecting ink from a nozzle provided in a pressure chamber filled with ink.

  If the ink ejection is stopped for a long time, the ink in the nozzles may be dried, and the ink meniscus surface may be highly concentrated (dry thickening). Such a change in ink characteristics such as dry thickening may cause a deterioration in ink ejection performance, which may adversely affect printing results.

JP-A-11-240179

  The problem to be solved by the present invention is to provide an ink jet head and an ink jet recording apparatus capable of preventing a change in ink characteristics in a nozzle.

An inkjet head according to an embodiment includes an ink tank, a pressure chamber, an ink flow path, a circulation device, an actuator, a nozzle, and a controller.
The ink tank contains ink. The pressure chamber is filled with ink. The ink flow path supplies ink from the ink tank to the pressure chamber and returns ink in the pressure chamber to the ink tank. The circulation device circulates ink through a path including the ink tank, the pressure chamber, and the ink flow path. The actuator changes the volume of the pressure chamber according to an input signal. The nozzle discharges ink in the pressure chamber as the volume of the pressure chamber changes. The controller has a first signal for changing the volume of the pressure chamber so that ink is ejected from the nozzle, and a meniscus of ink in the nozzle is drawn into the pressure chamber without ejecting ink from the nozzle. A second signal for changing the volume of the pressure chamber is selectively output to the actuator.

1 is a diagram schematically illustrating a part of the configuration of an inkjet head according to an embodiment. FIG. Sectional drawing of the head unit with which the said head is provided. Sectional drawing which follows the AA line in FIG. FIG. 2 is a block diagram illustrating a circuit configuration of the head and the inkjet recording apparatus. The figure which shows the mode of the nozzle vicinity at the time of volume expansion and contraction of the pressure chamber of the said head. The figure which shows the change of the volume Q in FIG. FIG. 4 is a waveform diagram showing an example of a drive voltage signal output from the head drive voltage signal control circuit. The figure which shows the relationship between the pulse width of the extended pulse which the said drive voltage signal contains, and the discharge speed of an ink droplet. FIG. 4 is a diagram illustrating an example of a table for determining the pulse width of an expansion pulse based on ink temperature. The wave form diagram which shows the drive voltage signal which concerns on a modification.

Hereinafter, an embodiment will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a part of the configuration of an inkjet head 1 according to the present embodiment. The arrows shown in the figure represent the direction of ink flow.
The inkjet head 1 includes a head unit 2, an upstream tank 3, a downstream tank 4, a circulation pump 5 (circulation device), a filtration filter 6, pressure sensors 7 and 8, a negative pressure adjustment tank 9, a negative pressure adjustment pump 10, And ink flow paths 11, 12, 13, 14 and the like.

  The ink flow paths 11 to 14 are made of, for example, a tube made of an elastic material. The ink flow path 11 connects the upstream tank 3 and the head unit 2, the ink flow path 12 connects the head unit 2 and the downstream tank 4, and the ink flow path 13 connects the downstream tank 4 and the upstream tank 3. And connect.

  The upstream side tank 3 and the downstream side tank 4 store ink supplied from an ink supply source (not shown) such as an ink cartridge. In the present embodiment, it is assumed that the ink supplied from the ink supply source is water-based ink. The upstream tank 3 includes a valve 3a that opens and seals the air layer in the tank 3 to the atmosphere. The downstream tank 4 includes a valve 4a that opens and seals the air layer in the tank 4 to the atmosphere.

  The circulation pump 5 is, for example, a tube pump or a roots pump, and is provided at a predetermined position of the ink flow path 13. The circulation pump 5 sucks the ink in the downstream side tank 4 and sends it out to the upstream side tank 3. When the circulation pump 5 is operated with the valves 3a and 4a closed, the ink circulates including the downstream tank 4, the ink channel 13, the upstream tank 3, the ink channel 11, the head unit 2, and the ink channel 12 in this order. Flows along the path. By increasing or decreasing the rotation speed of the circulation pump 5, the flow rate of the ink flowing through the circulation path can be adjusted.

  The filtration filter 6 is provided in the ink flow path 13 and removes foreign matters and bubbles from the ink flowing through the ink flow path 13.

  The pressure sensor 7 is connected to the ink flow path 11 and measures the pressure of the ink flowing through the ink flow path 11, that is, the pressure of the ink supplied to the head unit 2. The pressure sensor 8 is connected to the ink flow path 12 and measures the pressure of the ink flowing through the ink flow path 12, that is, the pressure of the ink discharged from the head unit 2.

  The ink flow path 14 connects the ink flow path 13 and the negative pressure adjusting tank 9. The negative pressure adjusting tank 9 stores ink supplied from the ink flow path 13 or the ink supply source. The negative pressure adjusting pump 10 is, for example, a tube pump or a roots type pump that can rotate forward and backward, and is provided in the ink flow path 14. By changing the rotation direction and the rotation speed of the negative pressure adjusting pump 10, the pressure in the downstream side tank 4, that is, the negative pressure for sucking ink from the head unit 2 can be adjusted.

Next, the structure of the head unit 2 will be described.
As shown in the cross-sectional view of FIG. 2, the head unit 2 has an ink inlet 20 connected to the ink flow path 11, an ink outlet 21 connected to the ink flow path 12, and ink flowing into the ink inlet 20. Common pressure chamber 22 to be stored, common pressure chamber 23 to store ink flowing out to the ink outlet 21, a plurality of pressure chambers 24 provided between the common pressure chambers 22, 23, each pressure chamber 24 and the common pressure chamber 22 A partition wall 25 partitioning each pressure chamber 24 and the common pressure chamber 23, a plurality of ink ejection nozzles 27 communicating with each pressure chamber 24, and a plurality of walls forming one wall surface of each pressure chamber 24. A diaphragm 28 and a plurality of piezoelectric elements 29 and the like disposed on each diaphragm 28 are provided.

  The head unit 2 further includes a temperature sensor 30 that detects the temperature T of the ink flowing through the ink inlet 20, and a drive voltage signal control circuit 41 that connects the temperature sensor 30 and each piezoelectric element 29. The drive voltage signal control circuit 41 changes the volume of each pressure chamber 24 by outputting a drive voltage signal to each piezoelectric element 29.

  Each diaphragm 28 and each piezoelectric element 29 constitute a plurality of actuators that change the volume of each pressure chamber 24.

  When the ink flows along the circulation path, the ink flows through the ink inlet 20, the common pressure chamber 22, each pressure chamber 24, the common pressure chamber 23, and the ink outlet 21 as shown by arrows in FIG. Flows along the path.

  FIG. 3 shows a cross section taken along the line AA in FIG. 2 in the direction of the arrow. That is, the pressure chambers 24 are adjacent to each other via the partition wall 31.

FIG. 4 is a block diagram illustrating a circuit configuration of the inkjet head 1 and an inkjet recording apparatus 100 including the head 1.
The circuit of the inkjet head 1 connects a drive voltage signal control circuit 41 that connects each piezoelectric element 29 and the temperature sensor 30, a circulation control circuit 42 that connects the circulation pump 5, each pressure sensor 7 and 8, and the negative pressure adjustment pump 10. Negative pressure control circuit 43 and the like.

  In addition to the inkjet head 1, the circuit of the inkjet recording apparatus 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a data memory 104, an input port 105, and an input. An operation panel 106 connected to the port 105, an interface 107, a motor drive circuit 108, a transfer device 109 connected to the motor drive circuit 108, a CPU bus 110, and the like are provided.

  The CPU bus 110 includes an address bus and a data bus, and connects the circuits 41 to 43, the CPU 101, the ROM 102, the RAM 103, the data memory 104, the input port 105, the interface 107, the motor drive circuit 108, and the like.

  The ROM 102 stores computer programs that implement various processes, fixed values used for the processes, and the like. The RAM 103 forms various working storage areas according to the processing scene.

  The CPU 101 executes computer programs stored in the ROM 102 or the RAM 103 and implements various processes related to the control of the inkjet head 1 and the inkjet recording apparatus 100. That is, the CPU 101 functions as a main control unit for the inkjet head 1 and the inkjet recording apparatus 100.

  The data memory 104 is a memory for storing, for example, image data to be printed and development data that is a collection of gradation value data obtained by converting each pixel included in the image data into the number of ink droplet ejections. .

  The operation panel 106 includes various operation buttons, a display with a touch panel, and the like. The operation panel 106 is used for inputting information related to input of a print command, setting of print conditions, and the like, and the operation status of the inkjet recording apparatus 100 is displayed on the display. Notification is made by displaying.

  The interface 107 connects a cable for communicating with an external device such as a host computer, for example, and receives various data and commands from the external device via this cable.

  For example, the transport device 109 picks up a paper that is a recording medium stored in a paper cassette (not shown), picks up the paper picked up by the roller on the outer peripheral surface, and ejects ink by the head unit 2. A suction drum that conveys the paper, a peeling mechanism that peels off the paper on which the image is formed by the head unit 2 from the drum, and a paper discharge roller that discharges the paper peeled off by the peeling mechanism to a paper discharge tray (not shown) Etc. The motor drive circuit 108 drives a motor for operating each unit included in the transport device 109.

  The circulation control circuit 42 controls the rotation speed of the circulation pump 5 in accordance with a command from the CPU 101.

  The negative pressure control circuit 43 controls the rotation speed and rotation direction of the negative pressure adjusting pump 10 according to the pressure measured by the pressure sensors 7 and 8. For example, the negative pressure control circuit 43 can adjust the negative pressure adjusting pump 10 according to the difference between the pressures measured by the pressure sensors 7 and 8 so that the negative pressure applied to the meniscus of each nozzle 27 is constant at a predetermined value. The number of rotations and direction of rotation are controlled.

  The drive voltage signal control circuit 41, the circulation control circuit 42, and the negative pressure control circuit 43 function as a controller for the inkjet head 1.

Next, the drive voltage signal supplied to each piezoelectric element 29 by the drive voltage signal control circuit 41 will be described.
The drive voltage signal control circuit 41 generates an expansion pulse that deforms the piezoelectric element 29 in a direction that expands the volume of the pressure chamber 24 and a contraction pulse that deforms the piezoelectric element 29 in a direction that contracts the volume of the pressure chamber 24. , Has a function of outputting to each piezoelectric element.

  FIG. 5 shows a state in the vicinity of the nozzle 27 when the pressure chamber 24 is expanded and contracted. When the volume of the pressure chamber 24 is expanded by the expansion pulse, the ink meniscus in the nozzle 27 is drawn into the pressure chamber 24 as shown in FIG. On the other hand, when the volume of the pressure chamber 24 is contracted by the contraction pulse, the meniscus of the ink in the nozzle 27 is pushed out from the nozzle 27 as shown in FIG.

  Q in FIG. 5 represents the volume of the region surrounded by the end of the nozzle 27 (broken line position) and the meniscus surface. The volume Q (ie, ink volume) in a state where the ink meniscus protrudes from the end is defined as positive (Q> 0), and the volume Q (ie, air) when the ink meniscus is drawn from the end. Is defined as negative (Q> 0).

  For reference, how the volume Q changes when the expansion pulse is input to the piezoelectric element 29 three times in succession, and how the volume Q changes when the contraction pulse is input to the piezoelectric element 29 three times in succession. Is shown in the graph of FIG. The horizontal axis is time (μs), and the vertical axis is the displacement of volume Q (arbitrary unit). When an expansion pulse is input to the piezoelectric element 29, the volume Q decreases rapidly. After the expansion pulse is input, the volume Q temporarily turns positive. On the other hand, when a contraction pulse is input to the piezoelectric element 29, the volume Q increases rapidly. After the input of the contraction pulse, the volume Q temporarily turns negative. When the pulse width (period) of the expansion pulse and the contraction pulse is changed, the displacement amplitude of the volume Q increases or decreases.

  When printing an image, the drive voltage signal control circuit 41 outputs a drive voltage signal obtained by combining an expansion pulse and a contraction pulse having the above-described properties to each piezoelectric element 29.

  FIG. 7 is a waveform diagram showing an example of the drive voltage signal. The ejection waveform (first signal) for ejecting one ink droplet from the nozzle 27 is constituted by the expansion pulse P1, the ground potential (pulse pause) R1, and the contraction pulse P2 shown in the second half of the time axis (right side) in FIG. Is done.

  The expansion pulse P1 deforms the piezoelectric element 29 in the direction in which the volume of the pressure chamber 24 expands. The ground potential R1 returns the piezoelectric element 29 deformed by the expansion pulse P1 to a steady state. The contraction pulse P2 deforms the piezoelectric element 29 returned to the steady state by the ground potential R1 in a direction in which the volume of the pressure chamber 24 contracts. In the process of changing the volume of the pressure chamber 24, one ink droplet is ejected from the nozzle 27.

  The expansion pulse P1 is a positive rectangular pulse, and the contraction pulse P2 is a negative rectangular pulse. However, the piezoelectric element 29 is deformed in the direction in which the volume of the pressure chamber 24 is expanded by the negative expansion pulse P1, and the piezoelectric element 29 is deformed in the direction in which the volume of the pressure chamber 24 is contracted by the positive contraction pulse P2. It may be.

  In the period of the expansion pulse P1, the ground potential R1, and the contraction pulse P2, ink droplets can be efficiently ejected from the nozzles 27 in consideration of the resonance period of the ink in the pressure chamber 24 and the pressure chamber 24, and the like. What is necessary is just to set to the period when the vibration of the ink in the pressure chamber 24 is easy to be suppressed after discharge. The resonance period is determined by the structure of the pressure chamber 24, ink characteristics, and the like, and is referred to as a Helmholtz resonance period.

  In the present embodiment, the multi-drop method is adopted, and the ejection waveform including the expansion pulse P1, the ground potential R1, and the contraction pulse P2 is repeated up to three times in one pixel period that is a period for forming one pixel. By outputting to the same piezoelectric element 29, one pixel is formed on the paper. As a result, it is possible to form an image with four gradations (0 drop, 1 drop, 2 drop, 3 drop) with one head unit 2. FIG. 7 shows a case where the discharge waveform is output three times (1 to 3 drops) repeatedly.

  In one pixel cycle for a pixel that does not involve ink ejection (0 drop), the drive voltage signal control circuit 41 corresponds to the expansion pulse P3 (second signal) shown in the first half (left side) of the time axis in FIG. Output to the piezoelectric element 29.

  The expansion pulse P3 is a positive rectangular pulse, and deforms the piezoelectric element 29 in the direction in which the volume of the pressure chamber 24 expands. However, the piezoelectric element 29 may be deformed in the direction in which the volume of the pressure chamber 24 is expanded by the negative expansion pulse P3. The pulse width (period) D of the expansion pulse P3 is set to a value that is equal to or less than the half value (= AL) of the Helmholtz resonance period and that ink is not ejected from the nozzles 27.

  When the volume of the pressure chamber 24 is expanded by the expansion pulse P3, the ink meniscus in the nozzle 27 provided in the pressure chamber 24 is drawn into the pressure chamber 24 as shown in FIG. The drawn ink in the vicinity of the meniscus is agitated on the circulation flow described with reference to FIGS.

  A plurality of expansion pulses P3 can be included in one pixel period. The number of outputs K of the expansion pulse P3 in one pixel cycle is set to a value equal to or less than the maximum multi-drop ejection number N (K ≦ N), for example. FIG. 7 illustrates a case where K = 3 (= N), and three extended pulses P3 are output at the ground potential (pulse pause) R2 interval.

The drive voltage signal control circuit 41 dynamically sets the pulse width D according to the ink temperature T detected by the temperature sensor 30. Hereinafter, a method for setting the pulse width D will be described.
A graph showing the result of measuring the velocity (m / s) of an ink droplet ejected from the nozzle 27 while changing the pulse width D (μs) of the expansion pulse P3 input to the piezoelectric element 29 at a certain ink temperature T. It is shown in FIG. In addition, the plot of the measurement result in which the ink droplet was not ejected is set to 0.0 m / s.

  In the range where the pulse width D is 1.7 μs or less, the discharge speed is 0.0 m / s. That is, ink droplets are not ejected.

  As can be seen from the measurement results regarding the expansion pulse shown in FIG. 6, the ink meniscus protrudes from the end of the nozzle 27 after the expansion of the volume of the pressure chamber 24 by the expansion pulse. When the pulse width D is increased, the protruding portion is separated to form an ink droplet. In the example of FIG. 8, this separation occurs from around the pulse width D = 1.7 μs.

  When the pulse width D is further increased from 1.7 μs, the ejection speed of the ink droplets increases, and eventually reaches a peak near the pulse width D = 2.3 μs and starts to decrease, and reaches 0 when the pulse width D = 2.9 μs. 0.0 m / s. The peak pulse width D is half the Helmholtz resonance period, that is, AL.

  The pulse width D needs to be determined within a range where ink droplets are not ejected. That is, in the example of FIG. 8, the lower limit of the range of the pulse width D in which the ink droplet is ejected is 1.7 μs or less (D ≦ 1.7 μs), or the range of the pulse width D in which the ink droplet is ejected. The pulse width D must be determined within the upper limit of 2.9 μs or more (D ≧ 2.9 μs).

  Even within this range, if the pulse width D is too small, the ink meniscus in the nozzle 27 is not sufficiently drawn into the pressure chamber 24. If the pulse width D is too large, the power consumption increases. End up. Therefore, it is preferable to determine the pulse width D in the range of about 0.1 AL to about 0.7 AL (≈1.7 μs). In particular, in the present embodiment, the lower limit value is set to the pulse width D. However, the pulse width D may be a value obtained by subtracting a predetermined margin from the lower limit value in order to reliably prevent ink droplets from being ejected by the expansion pulse P3.

  The relationship between the pulse width D exemplified in FIG. 8 and the ejection speed differs for each ink temperature T. In this embodiment, the relationship between the pulse width D and the ejection speed as shown in FIG. 8 is obtained in advance for each ink temperature T experimentally or theoretically, and the pulse width D for ejecting ink at each ink temperature T is obtained. Find the lower limit of the range. This result is stored in the memory or ROM 102 provided in the drive voltage signal control circuit 41 in the form of a table, for example.

  An example of the table is shown in FIG. In this table, the pulse width D (D1, D2, D3,...) That is the lower limit value is assigned to each ink temperature T (T1, T2, T3,...).

  The drive voltage signal control circuit 41 refers to such a table, acquires the pulse width D assigned to the current ink temperature T, and outputs an extended pulse P3 having the pulse width D to each piezoelectric element 29.

  Here, a series of operations when the ink jet head 1 to the ink jet recording apparatus 100 execute one print job and an operation by introducing the expansion pulse P3 will be described.

  When the ink jet recording apparatus 100 is powered on, the circulation control circuit 42 starts driving the circulation pump, and the negative pressure control circuit 43 monitors the pressure measured by the pressure sensors 7 and 8 and responds to the difference between these pressures. Then, control of the rotation speed and rotation direction of the negative pressure adjusting pump 10 is started. Thereby, the ink of the ink jet head 1 circulates in the circulation path described above, and the negative pressure applied to the meniscus of each nozzle 27 becomes constant at a specified value. The specified value is set to a value such that the meniscus of each nozzle 27 stops at a position suitable for ink ejection.

  In this state, when the interface 107 receives image data to be printed and a print command transmitted from the external device, the interface 107 writes the image data in the data memory 104 and notifies the CPU 101 of reception of the print command. Upon receiving this notification, the CPU 101 generates the expanded data based on the image data to be printed written in the data memory 104 and writes it in the data memory 104.

  Further, the CPU 101 instructs the drive voltage signal control circuit 41 and the motor drive circuit 108 to start operation. Upon receiving this command, the motor drive circuit 108 drives a motor provided in the transport device 109 to start transporting the paper stored in the paper cassette.

  On the other hand, the drive voltage signal control circuit 41 receiving the operation start command acquires the pulse width D assigned to the ink temperature T detected by the temperature sensor 30 from the table shown in FIG. The pulse width D of the extended pulse P3 used in the print job is set.

  Thereafter, after the paper transported by the transport device 109 reaches the ink ejection position by the head unit 2, the drive voltage signal control circuit 41 is written in the data memory 104 in synchronization with the transport of the paper by the transport device 109. A drive voltage signal based on the development data is output to each piezoelectric element 29. That is, the drive voltage signal control circuit 41 supplies a drive voltage signal including one ejection waveform including the expansion pulse P1, the ground potential R1, and the contraction pulse P2 to the pixel at the formation timing of the pixel corresponding to the one-drop gradation value data. A drive voltage signal including two ejection waveforms is output to the piezoelectric element 29 corresponding to the pixel, and output to the piezoelectric element 29 corresponding to the 2-drop gradation value data. A drive voltage signal including three ejection waveforms is output to the piezoelectric element 29 corresponding to the pixel at the formation timing of the pixel corresponding to the gradation value data. From the nozzles 27 corresponding to the piezoelectric elements 29 to which the ejection waveform is input, ink droplets are ejected by the number of the input ejection waveforms, and these ink droplets land on the paper to form pixels.

  Further, the drive voltage signal control circuit 41 outputs a drive voltage signal including three expansion pulses P3 to the piezoelectric element 29 corresponding to the pixel at the formation timing of the pixel corresponding to the gradation value data of 0 drop. In the nozzle 27 corresponding to the piezoelectric element 29 to which the expansion pulse P3 is input, the ink meniscus is drawn into the pressure chamber 24 in accordance with the change in the volume of the pressure chamber 24 due to the expansion pulse P3. The drawn ink in the vicinity of the meniscus is agitated on the circulation flow described with reference to FIGS. Thereby, the dry image viscosity of the ink meniscus in the nozzle 27 corresponding to the pixel is prevented at the formation timing of the pixel without ink ejection.

  When all the pixels are formed on the paper, the drive voltage signal control circuit 41 stops operating. The paper on which the pixels are formed is discharged to a paper discharge tray by the transport device 109. This completes a series of print jobs.

  As described above, the ink jet head 1 to the ink jet recording apparatus 100 according to the present embodiment circulates the ink along the circulation path and outputs the expansion pulse P3 to each piezoelectric element 29, whereby the meniscus of the ink in the nozzle 27 is obtained. This prevents changes in properties such as the viscosity of dried images. By doing in this way, the ink discharge performance of each nozzle 27 is kept favorable.

As a method of drawing the ink meniscus in the nozzle 27 into the pressure chamber 24, it is conceivable to always increase the negative pressure applied to the meniscus by the negative pressure adjusting pump 10 or the like. However, in such a case, there is a possibility that the smooth ejection of ink may be hindered. In addition, after the completion of a print job by a certain print command, the negative pressure is increased only during execution of the print job by the next print command, the meniscus is drawn into the pressure chamber 24, and the negative pressure is relaxed during execution of the print job. Conceivable. However, in such a case, it takes time to return the meniscus to a position suitable for printing when a print job is executed. On the other hand, according to the method of the present embodiment, the meniscus in each nozzle 27 can be always located at a position suitable for ink ejection, so these problems do not occur.
In addition, various suitable effects can be obtained from the configuration disclosed in the present embodiment.

  The configuration disclosed in the above embodiment can be embodied by appropriately modifying each component in the implementation stage.

  For example, in the above embodiment, the pulse width D is set using a table as shown in FIG. 9, but the pulse width D may be set by calculation based on a calculation formula or the like. Further, the relationship between the pulse width D and the ejection speed as illustrated in FIG. 8 varies depending on the type of ink. In view of this, a table as shown in FIG. 9 or the above calculation formula is determined for each ink type, and the pulse width D is determined based on the above table or calculation formula corresponding to the type of ink used in the inkjet head 1. You may do it. In this case, the type of ink used for setting the pulse width D may be specified by the user operating the operation panel 106, for example.

  Further, instead of changing the pulse width D of the extension pulse P3 according to the ink temperature T, the voltage value of the extension pulse P3 may be changed according to the ink temperature T to draw the meniscus appropriately.

  Further, FIG. 7 illustrates the case where the number K of output of the expansion pulse P3 in one pixel cycle is 3, but the output number K may be other values.

  Further, the expansion pulse P3 and the ejection waveform may be mixed during one pixel period related to the pixels that are accompanied by ink ejection. An example in which the expansion pulse P3 and the ejection waveform are mixed in one pixel period is shown in FIG. In FIG. 10, one pixel cycle shown in the first half (left side) of the time axis includes a discharge waveform for one drop, and one pixel cycle shown in the second half (right side) of the time axis includes a discharge waveform for two drops. In one pixel period shown in the first half of the time axis, two expansion pulses P3 are arranged following the ejection waveform. In addition, in one pixel period shown in the second half of the time axis, one extended pulse P3 is arranged following the second ejection waveform. That is, in this example, the number of outputs of the expansion pulse P3 in one pixel period is K = N− (the number of ejection waveforms in the pixel period). Therefore, the pixel period of 0 drop includes three expansion pulses P3, and the pixel period of 3 drops does not include the expansion pulse P3. The number K of output of the expansion pulse P3 does not necessarily need to be N or less, but if the expansion pulse P3 is excessively mixed, the shape of the ink meniscus becomes unstable, so that the number of outputs K does not exceed N Is preferred.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  P1, R1, P2 ... expansion pulse, ground potential, contraction pulse (first signal), P3 ... expansion pulse (second signal), 1 ... inkjet head, 3, 4 ... upstream tank, downstream tank (ink tank) DESCRIPTION OF SYMBOLS 5 ... Circulation pump (circulation apparatus), 9 ... Negative pressure adjustment tank, 10 ... Negative pressure adjustment pump, 11-14 ... Ink flow path, 24 ... Pressure chamber, 27 ... Nozzle, 28, 29 ... Diaphragm, Piezoelectric Element (actuator), 30... Temperature sensor, 41... Drive voltage signal control circuit (controller), 100.

Claims (5)

An ink tank for containing ink;
A pressure chamber filled with ink;
An ink flow path for supplying ink from the ink tank to the pressure chamber and returning the ink in the pressure chamber to the ink tank;
A circulation device for circulating ink in a path including the ink tank, the pressure chamber, and the ink flow path;
An actuator for changing the volume of the pressure chamber according to an input signal;
A nozzle that ejects ink in the pressure chamber in accordance with a change in the volume of the pressure chamber;
A first signal that changes the volume of the pressure chamber so that ink is ejected from the nozzle, and a meniscus of ink in the nozzle is drawn into the pressure chamber without ink ejection from the nozzle. A controller that selectively outputs a second signal for changing the volume of the pressure chamber to the actuator;
An ink jet head comprising:   The inkjet head according to claim 1, wherein the second signal is an expansion pulse that expands a volume of the pressure chamber.   3. The ink jet head according to claim 1, wherein a pulse width of the extension pulse is set to a value smaller than a half value AL of a Helmholtz resonance period of the pressure chamber and ink. A temperature sensor for detecting the temperature of the ink;
4. The inkjet head according to claim 1, wherein the controller changes a pulse width of the extended pulse according to a temperature detected by the temperature sensor. 5. An inkjet head according to any one of claims 1 to 4,
A transport device for transporting a recording medium for forming an image to a position where ink is ejected from the nozzle;
An ink jet recording apparatus comprising:

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