JP2007230243A - Method for controlling liquid jet device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling a liquid jet device which prevents increase in viscosity and drying of an ink and can increase drive frequency. <P>SOLUTION: The liquid jet device comprises a pressure generation chamber 32 which communicates with a nozzle opening 33 and has the Helmholtz oscillation frequency with a period of Tc and a pressure generating means 38 which gives pressure to an ink in the pressure generation chamber 32, wherein ink drops are discharged by actuating the pressure generating means 38. In the method for controlling the liquid jet device comprising actuating the pressure generating means 38 to thereby excite fine mechanical vibration in a meniscus to agitate an ink near a nozzle opening 33, the method comprises a fine mechanical vibration actuating step 61 in which the ink in the pressure generation chamber 32 is given pressure without discharging ink drops from the nozzle opening 33 to thereby excite the Helmholtz oscillation with a period of Tc in the meniscus to agitate the ink near the nozzle opening, thereby preventing increase in viscosity and drying of the ink and executing the fine mechanical vibration actuating step in a short time to realize high-speed printing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for controlling a liquid ejection apparatus including a head that applies pressure to ink supplied to a pressure generation chamber communicating with a nozzle opening and ejects ink droplets from the nozzle opening, and more particularly to ink in the pressure generation chamber. The present invention relates to a method for controlling an ink jet recording head in which ink droplets are ejected from nozzle openings by pressurizing the ink through a piezoelectric element or a heating element.

  As the liquid ejecting apparatus, for example, a plurality of pressure generating chambers that generate pressure for ejecting ink droplets by piezoelectric elements or heat generating elements, a common reservoir for supplying ink to each pressure generating chamber, and each pressure generating chamber There is an ink jet recording apparatus including an ink jet recording head having a nozzle opening that communicates with the ink jet recording apparatus. The ink jet recording apparatus applies ejection energy to ink in a pressure generating chamber that communicates with a nozzle corresponding to a print signal. Ink droplets are ejected from the nozzle openings.

  In addition, as described above, the ink jet recording head includes a bubble jet type in which a resistance wire for generating Joule heat is generated in the pressure generating chamber by a drive signal as a pressure generating means, and a part of the pressure generating chamber. The diaphragm is roughly divided into two types of piezoelectric vibration type in which the vibration plate is deformed by a piezoelectric element and ink droplets are ejected from the nozzle openings. Two types are in practical use: one using a longitudinal vibration mode piezoelectric element that extends and contracts in the axial direction of the piezoelectric element, and one using a flexural vibration mode piezoelectric element.

  In these ink jet recording heads, for example, ink is supplied to the pressure generating chamber of the ink jet recording head from an ink cartridge or the like filled with ink through a flow path, and a piezoelectric element is generated by a driving signal from a driving circuit. When the energy for driving at a predetermined timing is applied to the ink, the ink in the pressure generating chamber is pressurized and discharged from the nozzle opening.

  In addition, such an ink jet recording head has a problem in that the ink viscosity increases due to a change in the temperature of the ink accompanying a change in the ambient environmental temperature, and the nozzle opening is clogged. Therefore, in order to maintain the ink at a predetermined viscosity and eject ink droplets reliably, prior to ink ejection, the ink droplets do not eject the free surface of the ink exposed at the nozzle openings. A fine vibration drive for causing a slight vibration is executed (see, for example, Patent Document 1). As a result, the ink in the vicinity of the nozzle opening is agitated, and the ink is maintained at a predetermined viscosity.

  In addition, since the viscosity of the ink is relatively likely to increase, it is desirable that this micro-vibration driving is executed at a predetermined interval even during the ink ejection.

Japanese Patent Application Laid-Open No. 09-201960

  However, the length of such a micro-vibration drive signal is generally longer than the interval of drive signals for continuous ink ejection. For this reason, if micro-vibration driving is executed during ink ejection, the drive frequency of the head must be lowered to increase the drive signal interval, which causes a problem that the ejection speed (throughput) decreases. Such a problem also exists in other liquid ejecting apparatuses.

  In view of such circumstances, it is an object of the present invention to provide a control method for a liquid ejecting apparatus that can prevent thickening and drying of ink and improve the driving frequency.

A first aspect of the present invention that solves the above-described problem includes a pressure generation chamber that communicates with a nozzle opening and has a Helmholtz oscillation frequency of a period Tc, and a pressure generation unit that applies pressure to ink in the pressure generation chamber. In a control method of a liquid ejecting apparatus that excites vibrations in a meniscus by driving the pressure generating means of a liquid ejecting apparatus that ejects ink droplets by driving the pressure generating means and agitates ink in the vicinity of the nozzle opening. A micro-vibration driving step of stirring the ink in the vicinity of the nozzle opening by exciting the Helmholtz oscillation of the period Tc to the meniscus by applying pressure to the ink in the pressure generating chamber without discharging an ink droplet from the nozzle opening. A control method of the liquid ejecting apparatus.
In the first aspect, by exciting the Helmholtz vibration in the meniscus, the ink in the vicinity of the nozzle opening can be reliably stirred with a short period of slight vibration. The “meniscus” means the free surface of the ink exposed at the nozzle opening.

According to a second aspect of the present invention, in the first aspect, in the fine vibration driving step, each of the time for increasing the pressure of the ink in the pressure generating chamber and the time for decreasing the pressure of the ink is a Helmholtz vibration period Tc. There is a control method of a liquid ejecting apparatus characterized by being shorter than the above.
In the second aspect, Helmholtz vibration is reliably excited in the meniscus.

According to a third aspect of the present invention, in the second aspect, in the fine vibration driving step, each of the time for increasing the pressure of the ink in the pressure generating chamber and the time for decreasing the pressure of the ink is the Helmholtz vibration period Tc. The control method of the liquid ejecting apparatus is characterized by being shorter than 1/2 of the above.
In the third aspect, Helmholtz vibration is reliably excited in the meniscus, and discharge of minute ink droplets (ink mist) due to this vibration is prevented.

According to a fourth aspect of the present invention, in any one of the first to third aspects, in the fine vibration driving step, the total time t during which the pressure in the pressure generating chamber is changed by increasing or decreasing the pressure is n. In the control method of the liquid ejecting apparatus, xTc <t <n * Tc + Tc / 2 (n is an integer).
In the fourth aspect, Helmholtz vibration is reliably excited in the meniscus, and ink mist discharge due to this vibration is more reliably prevented.

According to a fifth aspect of the present invention, in the fourth aspect, in the fine vibration driving step, the total time t during which the pressure in the pressure generating chamber is changed by increasing or decreasing the pressure is 1 in the Helmholtz vibration period Tc. The present invention resides in a control method for a liquid ejecting apparatus, which is shorter than / 2.
In the fifth aspect, the fine vibration driving process can be executed without reducing the frequency of the ejection waveform.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the driving voltage applied to the pressure generating unit in the micro-vibration driving step is a discharge step of discharging an ink droplet from the nozzle opening. The control method of the liquid ejecting apparatus is characterized in that it is 1/5 or less of the driving voltage applied to the pressure generating means.
In the sixth aspect, the ink mist is reliably prevented from being ejected by the fine vibration drive.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the drive voltage applied to the pressure generating unit in the fine vibration driving step is the discharge step of discharging an ink droplet from the nozzle opening. The control method of the liquid ejecting apparatus is characterized by being 1/20 or more of the driving voltage applied to the pressure generating means.
In the seventh aspect, the ink in the vicinity of the nozzle opening can be reliably agitated by executing the fine vibration driving process with a drive voltage of 1/20 or more.

An eighth aspect of the present invention is the liquid ejecting apparatus according to any one of the first to seventh aspects, wherein the driving voltage applied to the pressure generating means in the fine vibration driving step is changed according to an environmental temperature. Is in the control method.
In the eighth aspect, it is possible to execute the optimum micro vibration driving process according to the change in the environmental temperature.

According to a ninth aspect of the present invention, in any one of the first to eighth aspects, the fine vibration driving step is performed during the discharge step.
In the ninth aspect, it is possible to maintain good ink ejection characteristics and realize high-speed printing.

According to a tenth aspect of the present invention, in any one of the first to ninth aspects, the fine vibration driving step is performed during a discharge step of discharging an ink droplet from the nozzle opening. It is in the control method of the apparatus.
In the tenth aspect, by performing fine vibration driving on the nozzles that are not ejected during the printing operation, the ink in the vicinity of the nozzle openings is surely agitated, and good ink ejection characteristics are maintained and high speed is achieved. Printing can be realized.

According to an eleventh aspect of the present invention, in any one of the first to tenth aspects, the pressure generating means is a piezoelectric element disposed on a diaphragm provided on one surface of the pressure generating chamber. A control method of the liquid ejecting apparatus.
In the eleventh aspect, the Helmholtz vibration is excited in the meniscus by driving the piezoelectric element.

  As described above, in the present invention, the ink in the vicinity of the nozzle opening is formed by applying pressure to the ink in the pressure generating chamber without causing the ink to be ejected from the nozzle opening and exciting the Helmholtz vibration in the meniscus to slightly vibrate the ink. Was stirred. As a result, it is possible to reliably stir the ink in the vicinity of the nozzle opening in a short time, prevent thickening and drying of the ink in the vicinity of the nozzle opening, and increase the driving frequency of the head to realize high-speed printing. .

Hereinafter, the present invention will be described in detail based on embodiments.
(Embodiment 1)
FIG. 1 is a diagram illustrating a schematic configuration of the liquid ejecting apparatus according to the first embodiment. The liquid ejecting apparatus according to the present embodiment is, for example, an ink jet recording apparatus, and schematically includes a printer controller 11 and a print engine 12 as shown in FIG.

  The printer controller 11 includes an external interface 13 (hereinafter referred to as an external I / F 13), a RAM 14 that temporarily stores various data, a ROM 15 that stores a control program, a control unit 16 that includes a CPU, and the like. An oscillation circuit 17 that generates a clock signal, a drive signal generation circuit 19 that generates a drive signal to be supplied to the ink jet recording head 18, and dot pattern data (bitmap) developed based on the drive signal and print data An internal interface 20 (hereinafter referred to as an internal I / F 20) that transmits data) to the print engine 12.

  The external I / F 13 receives print data including, for example, a character code, a graphic function, image data, and the like from a host computer (not shown). Further, a busy signal (BUSY) and an acknowledge signal (ACK) are output to the host computer or the like through the external I / F 13.

  The RAM 14 functions as a reception buffer 21, an intermediate buffer 22, an output buffer 23, and a work memory (not shown). The reception buffer 21 temporarily stores the print data received by the external I / F 13, the intermediate buffer 22 stores the intermediate code data converted by the control unit 16, and the output buffer 23 stores the dot pattern data. . This dot pattern data is constituted by print data obtained by decoding (translating) gradation data.

  The ROM 15 stores font data, graphic functions, etc. in addition to a control program (control routine) for performing various data processing.

  The control unit 16 reads the print data in the reception buffer 21 and stores the intermediate code data obtained by converting the print data in the intermediate buffer 22. Further, the intermediate code data read from the intermediate buffer 22 is analyzed, and the intermediate code data is developed into dot pattern data by referring to the font data and graphic functions stored in the ROM 15. Then, the control unit 16 stores the developed dot pattern data in the output buffer 23 after performing necessary decoration processing.

  If dot pattern data corresponding to one line of the ink jet recording head 18 is obtained, the dot pattern data for one line is output to the ink jet recording head 18 through the internal I / F 20. When dot pattern data for one line is output from the output buffer 23, the developed intermediate code data is erased from the intermediate buffer 22, and the development process for the next intermediate code data is performed.

  The print engine 12 includes an ink jet recording head 18, a paper feed mechanism 24, and a carriage mechanism 25.

  The paper feed mechanism 24 includes a paper feed motor and a paper feed roller, and sequentially feeds a print storage medium such as a recording paper in conjunction with the recording operation of the ink jet recording head 18. That is, the paper feeding mechanism 24 relatively moves the print storage medium in the sub-scanning direction.

  The carriage mechanism 25 includes a carriage on which the ink jet recording head 18 can be mounted and a carriage driving unit that causes the carriage to travel along the main scanning direction. The ink jet recording head 18 is moved by moving the carriage. Move in the main scanning direction. Note that the carriage driving unit may take any configuration as long as it is a mechanism that can move the carriage, such as one using a timing belt.

  The ink jet recording head 18 has a large number of nozzle openings along the sub-scanning direction, and ejects ink droplets from the nozzle openings at a timing defined by dot pattern data or the like.

  Next, the ink jet recording head 18 will be described in detail. 2 is a diagram showing a mechanical configuration of the ink jet recording head, and FIG. 3 is a diagram showing an electrical configuration thereof.

  The ink jet recording head 18 of the present embodiment is a so-called longitudinal vibration type ink jet recording head. As shown in FIG. 2, a pressure generating chamber 32 is formed in the spacer 31. It is sealed by a nozzle plate 34 having an opening 33 and a vibration plate 35. The spacer 31 is formed with a reservoir 37 communicating with the pressure generating chamber 32 via the ink supply port 36, and an ink tank (not shown) is connected to the reservoir 37.

  On the other hand, the tip of the piezoelectric element 38 abuts on the opposite side of the diaphragm 35 from the pressure generation chamber 32. The piezoelectric element 38 is configured to have a laminated structure in which the piezoelectric material 39 and the electrode forming materials 40 and 41 are alternately sandwiched, and an inactive region that does not contribute to vibration is fixed to the fixed substrate 42. . The fixed substrate 42, the diaphragm 35, the spacer 31, and the nozzle plate 34 are integrally fixed via a base 43.

  The piezoelectric element 38 of the ink jet recording head 18 is supplied with an electrical signal, for example, a drive signal (COM) or print data (SI) described later via a flexible cable (not shown).

  In the ink jet recording head 18 configured as described above, when a voltage is applied to the electrode forming materials 40 and 41 of the piezoelectric element 38, the piezoelectric element 38 contracts and the vibration plate 35 is displaced, and the pressure generating chamber 32 is formed. Inflate. When the application of voltage is canceled from this state, the pressure generating chamber 32 contracts and ink droplets can be ejected from the nozzle openings 33.

  Further, in such an ink jet recording head, fine vibration that excites vibration in the ink in the vicinity of the nozzle opening 33 by applying pressure to the ink in the pressure generating chamber 32 at a predetermined timing to such an extent that ink droplets are not ejected. Running drive. As a result, the ink in the vicinity of the nozzle opening 33 is agitated to prevent thickening and drying of the ink in the vicinity of the nozzle opening 33.

  In the present embodiment, as described above, pressure is applied to the ink in the pressure generation chamber 32 by driving the piezoelectric element 18. That is, by charging the piezoelectric element 18 with a voltage, the pressure generating chamber 32 is expanded to reduce the pressure of the ink inside. Thereafter, by discharging the voltage charged in the piezoelectric element 18, the pressure generating chamber 32 is contracted to increase the pressure of the ink inside and return to the original state. Therefore, the time for decreasing the pressure of the ink in the pressure generating chamber 32 is the time for charging the voltage in the piezoelectric element 18, and the time for increasing the pressure of the ink in the pressure generating chamber 32 is charging for the piezoelectric element 18. It is time to discharge the voltage.

  Although this fine vibration drive will be described in detail later, in this embodiment, the ink in the vicinity of the nozzle opening 33 is agitated by exciting the meniscus with the Helmholtz vibration period Tc.

  Next, the electrical configuration of the ink jet recording head 18 will be described.

  As shown in FIG. 1, the ink jet recording head 18 includes a shift register 51, a latch circuit 52, a level shifter 53, a switch 54, a piezoelectric element 38, and the like. Further, as shown in FIG. 3, the shift register 51, the latch circuit 52, the level shifter 53, the switch 54, and the piezoelectric element 38 are respectively provided with a shift register element 51 </ b> A provided for each nozzle opening 33 of the ink jet recording head 18. ˜51N, latch elements 52A to 52N, level shifter elements 53A to 53N, switch elements 54A to 54N, and piezoelectric elements 38A to 38N. The shift register 51, latch circuit 52, level shifter 53, switch 54, and piezoelectric element 38 They are electrically connected in order.

  Note that the shift register 51, the latch circuit 52, the level shifter 53, and the switch 54 generate drive pulses from the ejection drive signal and the micro-vibration drive signal generated by the drive signal generation circuit 19. Here, the drive pulse is an applied pulse that is actually applied to the piezoelectric element 38.

  Next, control of the ink jet recording head 18 having such an electrical configuration will be described. First, a procedure for applying a drive pulse to the piezoelectric element 38 will be described.

  Here, in the present embodiment, the fine vibration drive is executed during printing, but this fine vibration drive is executed in correspondence with, for example, the nozzle openings 33 that do not eject ink droplets.

  The application procedure of the drive pulse at the time of micro-vibration driving and the application procedure of the drive pulse at the time of ink ejection are applied to the piezoelectric element 38 as a drive pulse at the time of ink agitation and the ejection drive signal at the time of ink ejection. Although the difference is that the drive pulse generated based on is applied to the piezoelectric element 38, the procedure is basically the same. For this reason, in the following description, the procedure at the time of ink discharge is given as an example.

  In the ink jet recording head 18 having the electrical configuration as described above, as shown in FIG. 4, first, print data (SI) constituting dot pattern data is synchronized with the clock signal (CK) from the oscillation circuit 17. ) Are serially transmitted from the output buffer 23 to the shift register 51 and sequentially set. In this case, first, the most significant bit data in the print data of all the nozzle openings 33 is serially transmitted, and when the most significant bit data serial transmission is completed, the second most significant bit data is serially transmitted. . Similarly, the lower bit data is serially transmitted sequentially.

  When the print data of the bit is set in the shift register elements 51A to 51N for all the nozzles, the control unit 16 causes the latch circuit 52 to output a latch signal (LAT) at a predetermined timing. In response to this latch signal, the latch circuit 52 latches the print data set in the shift register 51. The print data (LATout) latched by the latch circuit 52 is applied to a level shifter 53 that is a voltage amplifier. The level shifter 53 boosts the print data up to a voltage value at which the switch 54 can be driven, for example, several tens of volts when the print data is “1”, for example. The boosted print data is applied to the switch elements 54A to 54N, and the switch elements 54A to 54N are connected by the print data.

  The ejection drive signals (COM) generated by the drive signal generation circuit 19 are also applied to the switch elements 54A to 54N. When the switch elements 54A to 54N are connected, the switch elements 54A to 54N are connected to the switch elements 54A to 54N. An ejection drive signal is applied to the piezoelectric elements 38A to 38N thus formed.

  As described above, in the illustrated ink jet recording head 18, it is possible to control whether or not the ejection drive signal is applied to the piezoelectric element 38 based on the print data. For example, since the switch 54 is connected by the latch signal (LAT) during the period when the print data is “1”, the drive signal (COMout) can be supplied to the piezoelectric element 38, and the supplied drive signal ( The piezoelectric element 38 is displaced (deformed) by COMout). Further, since the switch 54 is not connected during the period when the print data is “0”, the supply of the drive signal to the piezoelectric element 38 is cut off. Note that, during the period in which the print data is “0”, each piezoelectric element 38 holds the previous charge, so the previous displacement state is maintained.

  Therefore, when the ejection drive signal is composed of a plurality of pulses, print data is set for each pulse, and by selecting “1” or “0” of the print data, a plurality of types of drive pulses are generated. Ink droplets of different sizes can be ejected by this drive pulse.

  Although not shown in FIG. 4, the basic drive signal (COM) is composed of an ejection drive signal and a fine vibration drive signal, and the ejection drive or the fine vibration drive is selectively executed according to print data. . That is, when the print data of the ejection drive signal portion is “1”, the ink droplet is ejected from the nozzle opening as described above, and when the print data of the ejection drive signal portion is “0”, the slight vibration is generated. “1” is set in the print data of the drive portion. This fine vibration drive signal is applied as a drive pulse to the piezoelectric element, and the piezoelectric element 38 is deformed to vibrate the meniscus.

  Hereinafter, such a drive signal, in particular, a fine vibration drive signal for stirring ink will be described in detail. 5A is a diagram showing the waveform shape of the drive signal according to one embodiment of the present embodiment, FIG. 5B is an enlarged view of the waveform shape of the micro-vibration drive signal, and FIG. These are figures which show the waveform showing the position of the meniscus with respect to the nozzle opening surface by Helmholtz vibration.

  As shown in FIG. 5A, the drive signal according to the present embodiment includes an ejection drive process 61 that is an ejection drive signal for ejecting ink droplets, and a minute vibration for agitating ink in the vicinity of the nozzle opening 33. In this embodiment, the driving signal is configured by combining one ejection driving process with respect to the three ejection driving processes. Of course, a fine vibration driving process may be provided for each ejection driving process.

  Here, as shown in FIG. 5B, the time t of the fine vibration driving process 62 is shorter than ½ of the Helmholtz vibration period Tc, so that the fine vibration driving process 62 is substantially one ejection drive. It will be executed during step 61. Therefore, even if the fine vibration driving is executed during printing, the printing speed is not reduced. Note that the time of the micro-vibration driving step 62 here means the total time during which the pressure of the ink in the pressure generating chamber 32 is increased or decreased by driving the piezoelectric element 38.

  The micro-vibration driving process 62 includes an expansion process a for expanding the pressure generating chamber 32 by charging a voltage to the piezoelectric element 38, a holding process b for holding the voltage charged to the piezoelectric element 38, and the piezoelectric element 38. And a contraction step c for contracting the pressure generating chamber 32 by discharging the charged voltage, and is set so that Helmholtz vibration can be excited in the meniscus. That is, the time t1 of the expansion process a and the time t2 of the contraction process c are set to be shorter than the Helmholtz oscillation period Tc. Further, at least the time t1 of the expansion step a is preferably shorter than ½ of the Helmholtz oscillation period Tc. In the present embodiment, the time t of the fine vibration driving process 62 is set to be shorter than ½ of the Helmholtz vibration period Tc, and the time t1 of the expansion process a and the time t2 of the contraction process c are respectively The Helmholtz oscillation period Tc is set to be shorter.

  By executing such a fine vibration process, Helmholtz vibration is reliably excited in the meniscus without the entire meniscus moving within the nozzle. Further, the ink in the vicinity of the nozzle opening 33 is agitated by Helmholtz vibration excited by the meniscus by the micro-vibration driving process 62 which is a signal having a relatively short period, whereby the ink is efficiently agitated and thickened and dried. Can be prevented.

  In addition, in the driving of the piezoelectric element 38 in the fine vibration driving process 62, a minute ink droplet (ink mist) is not ejected from the nozzle opening 33. As described above, in the present embodiment, since the time t of the fine vibration driving process 62 is shorter than ½ of the Helmholtz vibration period Tc, the entire meniscus does not move within the nozzle, and FIG. As shown by the waveform A, Helmholtz oscillation is excited in the meniscus.

  In the present embodiment, since the time t of the fine vibration driving process 62 is shorter than ½ of the Helmholtz vibration cycle Tc, naturally, the time of the expansion process a and the holding process b of the fine vibration driving process 62 (t1 + t3). Is shorter than ½ of the Helmholtz oscillation period Tc. Therefore, while the meniscus is moved to the pressure generation chamber side of the nozzle opening (opposite to the ink discharge direction) by driving the piezoelectric element 38 in the expansion step a, that is, the meniscus has a peak P1 on the pressure generation chamber side. Before reaching, the contraction step c is performed. For this reason, a part of the force acting in the ink ejection direction by driving the piezoelectric element 38 in the contraction step c is canceled by the force acting in the direction opposite to the ink ejection direction in the expansion step a. Accordingly, the force acting in the ink discharge direction is weakened, and the inclination is gentler than the waveform A, as shown by the waveform B in FIG. 5C, and the peak P2 on the nozzle opening side of the meniscus is the nozzle opening surface. Never exceed. Therefore, no ink droplet is ejected from the nozzle opening 33.

  On the other hand, when the time t of the fine vibration driving process 62 is longer than ½ of the Helmholtz vibration period Tc, for example, as shown in FIG. When the time (t1 + t3) of b is longer than ½ of the Helmholtz oscillation period Tc, the meniscus starts to move in the ink discharge direction by driving the piezoelectric element 38 in the expansion step a, that is, the meniscus generates pressure. The shrinking step c is performed after the chamber-side peak P3 is passed and the ink starts to move in the ink ejection direction. In this case, the force by which the meniscus moves in the ink ejection direction is amplified, and the inclination thereof is steeper than the waveform A as shown by the waveform C in FIG. Peak P4 exceeds the nozzle opening surface. For this reason, ink mist may be ejected from the nozzle opening 33.

  Actually, if the time t1 of the expansion step a is shorter than ½ of the Helmholtz vibration period Tc, the time t of the fine vibration driving step 62 is n × Tc <t <n × Tc + Tc / 2 (n The ink mist can be prevented from being ejected if the length satisfies the relationship of (integer), but it is preferable that the time t of the micro-vibration driving process 62 is shorter in consideration of speeding up of the head. That is, it is desirable to make the signal short enough to be executed during one ejection driving process 61 without increasing the interval between the ejection driving processes 61. Therefore, it is preferable that the time t of the fine vibration driving process 62 is shorter than ½ of the Helmholtz vibration period Tc.

  Further, the voltage (microvibration driving voltage) applied to the piezoelectric element in the micro-vibration driving process 62 is set to 1/5 or less (20% or less) of the voltage (ejection driving voltage) applied to the piezoelectric element in the ejection driving process 61. In this embodiment, the fine vibration driving voltage is set to about 10% of the ejection driving voltage. Thereby, it is possible to prevent the ink mist from being discharged by the fine vibration driving process 62. Furthermore, while the conventional micro-vibration driving voltage is about 40% of the ejection driving voltage, in the present embodiment, it can be greatly reduced to 20% or less, thereby reducing the cost. it can. In order to obtain an effect as fine vibration that prevents thickening and drying of the meniscus, it is preferable to drive at a voltage of 1/20 or more (5% or more) of the discharge voltage.

  As described above, in the present embodiment, the time of the micro-vibration driving process 62 is made shorter than 1/2 of the Helmholtz vibration Tc to excite the Helmholtz vibration in the meniscus, and the ink near the nozzle opening is agitated by this Helmholtz vibration. I tried to do it. Accordingly, it is possible to reliably prevent the ink in the vicinity of the nozzle opening 33 from being thickened and dry, and to stir the ink in the vicinity of the nozzle opening 33 in a short time. Therefore, since the micro-vibration driving process 62 can be substantially executed during one ejection driving process 61 without increasing the interval of the ejection driving process 61 for ejecting ink droplets, the head driving frequency is reduced. Can be raised.

  In addition, the micro-vibration driving voltage can be suppressed lower than that of the conventional one, and the same stirring effect can be obtained, so that the cost can be reduced.

  In contrast to the fine vibration driving process according to the present embodiment, the conventional fine vibration driving process 162 includes an expansion process a1 at time t4 and a contraction process c1 at time t5, as shown in FIG. The meniscus surface has a length substantially the same as the Helmholtz vibration period Tc, and the meniscus surface moves up and down in the nozzle by this fine vibration driving step 162. Since such a micro-vibration driving process 162 has a relatively long time for each process, it is difficult to execute the micro-vibration driving process 162 without substantially changing the ejection timing in the ejection driving process 161. The drive frequency must be lowered.

  Here, when a head having a Helmholtz oscillation period Tc = 7.5 μs is used, specifically, the time t1 of the expansion step a is 1 μs, the time t3 of the hold step b is 1.5 μs, and the time t2 of the contraction step c. And 1 μs, and the time t of the entire fine vibration driving process is set to about 3.5 μs, it is possible to execute good fine vibration driving. On the other hand, in the conventional micro-vibration driving process, the time t4 of the expansion process a1 requires 8 μs, the time t6 of the hold process b1 needs about 2 μs, and the time t5 of the contraction process c1 needs about 8 μs. The time t7 requires about 18 μs. That is, in the fine vibration driving process of the present embodiment, the time can be shortened to about 1/5 compared with the conventional fine vibration driving process, so that the driving frequency can be increased.

(Other embodiments)
In the ink jet recording head described above, the pressure generating chamber is expanded by applying a voltage to the piezoelectric element. However, the present invention is not limited to this, and the pressure generating chamber can be formed by applying a voltage to the piezoelectric element. The control method of the present invention can also be applied to an ink jet recording head that contracts.

  An example of an ink jet recording head having such a structure is shown in FIG. The ink jet recording head shown in FIG. 8 has a similar structure except that it has a piezoelectric element 138 instead of the piezoelectric element 38 of FIG. The piezoelectric element 138 is configured to have a laminated structure in which the piezoelectric material 139 and the electrode forming materials 140 and 141 are alternately sandwiched on the opposite side of the diaphragm from the pressure generating chamber 32 and does not contribute to vibration. The inactive region is fixed to the fixed substrate 32. Therefore, when a voltage is applied to the electrode forming materials 140 and 141 of the piezoelectric element 138, the piezoelectric element 38 expands toward the nozzle plate 34, so that the vibration plate 35 is displaced and the volume of the pressure generating chamber 32 is compressed. . For example, the voltage can be removed from a state in which a voltage of 30 V is applied in advance, and the piezoelectric element 138 can be contracted so that ink flows from the reservoir 37 into the pressure generating chamber 32 via the ink supply port 36. Thereafter, by applying a voltage, the piezoelectric element 38 expands and the vibration plate 35 deforms, whereby the pressure generating chamber 32 contracts and ink droplets are ejected from the nozzle openings 33. Therefore, the same control method can be implemented by reversely charging and discharging the voltage during the expansion and contraction of the control method described above.

  In this embodiment, in the expansion process, the piezoelectric element 138 is charged with a voltage to increase the pressure of the ink in the pressure generating chamber 132, and in the contraction process, the voltage charged in the piezoelectric element 138 is discharged. Thus, the pressure of the ink in the pressure generation chamber 132 is decreased.

  Further, for example, in the fine vibration driving process of the above-described embodiment, the driving voltage applied to the piezoelectric element may be appropriately adjusted according to the environmental temperature. Specifically, in a high temperature environment where the ink viscosity is relatively low, a relatively weak vibration is sufficient, so the drive voltage is adjusted to be low. On the other hand, in a low temperature environment where the ink viscosity is relatively high, a relatively strong vibration is required. Therefore, it is possible to always obtain the optimum micro-vibration effect by adjusting the drive voltage to be increased.

  Furthermore, the structure of the ink jet recording head that can realize the driving method of the present invention is not limited to the longitudinal vibration type ink jet recording head, and for example, a flexural vibration type ink jet recording head or a bubble jet ink jet recording method. The present invention can also be applied to liquid ejecting apparatuses having various structures such as a head.

1 is a block diagram showing a schematic configuration of an ink jet recording apparatus according to Embodiment 1 of the present invention. 1 is a cross-sectional view of an ink jet recording head according to Embodiment 1 of the present invention. FIG. 2 is a circuit diagram illustrating a circuit configuration of the ink jet recording head according to the first embodiment of the invention. It is a figure which shows an example of the waveform of the drive signal which concerns on Embodiment 1 of this invention. It is the schematic explaining an example of the drive signal and micro vibration drive signal which concern on Embodiment 1 of this invention. It is the schematic explaining the fine vibration drive signal compared with the fine vibration drive signal which concerns on Embodiment 1 of this invention. It is the schematic explaining the conventional drive signal and a micro vibration drive signal. It is sectional drawing which shows the example of the inkjet recording head which concerns on other embodiment of this invention.

Explanation of symbols

  31 spacer, 32 pressure generating chamber, 34 nozzle plate, 35 diaphragm, 38 piezoelectric element

Claims (11)

An ink droplet is ejected by driving a pressure generating chamber that communicates with the nozzle opening and has a pressure generating chamber having a Helmholtz oscillation frequency with a period Tc and applies pressure to the ink in the pressure generating chamber. In a control method of a liquid ejecting apparatus that agitates ink in the vicinity of the nozzle opening by exciting vibration in a meniscus by driving the pressure generating unit of the liquid ejecting apparatus.
A fine vibration driving step of stirring the ink in the vicinity of the nozzle opening by exciting the Helmholtz vibration of the period Tc in the meniscus by applying pressure to the ink in the pressure generating chamber without discharging ink droplets from the nozzle opening. A control method for a liquid ejecting apparatus comprising:   2. The liquid ejection according to claim 1, wherein in the fine vibration driving step, each of a time for increasing the pressure of the ink in the pressure generating chamber and a time for decreasing the pressure of the ink are shorter than the Helmholtz vibration period Tc. Device control method.   3. The fine vibration driving step according to claim 2, wherein each of the time for increasing the pressure of the ink in the pressure generating chamber and the time for decreasing the pressure of the ink are shorter than ½ of the Helmholtz vibration period Tc. A control method of the liquid ejecting apparatus.   4. The micro vibration driving step according to claim 1, wherein the total time t during which the pressure in the pressure generating chamber is changed by increasing or decreasing the pressure is n × Tc <t <n × Tc + Tc / 2. (N is an integer) A control method for a liquid ejecting apparatus.   5. The micro vibration driving step according to claim 4, wherein the total time t during which the pressure in the pressure generating chamber is changed by increasing or decreasing the pressure is shorter than ½ of the Helmholtz vibration period Tc. Control method of liquid ejecting apparatus.   6. The driving voltage applied to the pressure generating unit in the fine vibration driving step according to claim 1, wherein the driving voltage applied to the pressure generating unit in the ejection step of ejecting ink droplets from the nozzle openings is one. / 5 or less, A method for controlling a liquid ejecting apparatus.   7. The driving voltage applied to the pressure generating unit in the fine vibration driving step according to claim 1, wherein the driving voltage applied to the pressure generating unit in the ejection step of ejecting ink droplets from the nozzle openings is one. / 20 or more, Control method of liquid ejecting apparatus.   8. The method for controlling a liquid ejecting apparatus according to claim 1, wherein a driving voltage applied to the pressure generating unit in the fine vibration driving step is changed according to an environmental temperature.   9. The method for controlling a liquid ejecting apparatus according to claim 1, wherein the micro-vibration driving step is executed during an ejection step of ejecting ink droplets from the nozzle openings.   10. The micro vibration driving process according to claim 1, wherein the micro-vibration driving process is executed only for a nozzle opening where ink droplets are not ejected in the ejection process of ejecting ink droplets from the nozzle openings. Control method of liquid ejecting apparatus.   11. The method of controlling a liquid ejecting apparatus according to claim 1, wherein the pressure generating means is a piezoelectric element disposed on a vibration plate provided on one surface of the pressure generating chamber. .