Patent Publication Number: US-9902149-B2

Title: Liquid injection device and inkjet recording device including the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2016-080023 filed on Apr. 13, 2016. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid injection device and an inkjet recording device including the same, and more specifically, to a technology that controls liquid injection using a so-called multi-dot system. 
     2. Description of the Related Art 
     Conventionally, a liquid injection device including a pressure chamber storing a liquid, a vibration plate demarcating a portion of the pressure chamber, a pressure generator coupled with the vibration plate, a nozzle in communication with the pressure chamber to inject an ink drop, and a controller supplying a driving signal to the pressure generator to drive the pressure generator is known. Such a liquid injection device is provided in, for example, an inkjet recording device injecting ink as a liquid. 
     In an inkjet recording device including the above-described liquid injection device, when the controller supplies a pulse signal to the pressure generator, the pressure generator is deformed. In accordance therewith, the vibration plate is deformed. As a result, a capacity of the pressure chamber is increased or decreased, and the pressure of ink in the pressure chamber is changed. In accordance with such a change in the pressure, the ink in the pressure chamber is injected from the nozzle. The injected ink becomes an ink drop and lands on a recording medium supported by a platen. As a result, one dot (corresponding to one pixel) is formed on the recording medium. A great number of such dots are formed on the recording paper sheet, so that an image or the like is formed. 
     It is effective to adjust the size of the dot from the point of view of forming a high-quality image on the recording medium. However, with the inkjet recording device, there is a limit on the amount of ink which can be accurately and reliably injected by one injection pulse. Namely, it is difficult to form a dot of any of various sizes with one injection pulse. In such a situation, the size of the dot is adjusted by a so-called multi-dot system, by which a driving waveform including a plurality of injection pulses is generated in one liquid drop injection period that is preset as a time period for forming one dot. 
     In a liquid injection device as described above, ink has a viscosity thereof changed in accordance the environmental temperature or the like. For example, when the temperature of the ink is increased, the ink has a fluidity thereof increased and thus becomes more easy to be injected. As a result, the injection speed of the ink may be changed, so that the position at which the ink drop lands is shifted, or the size of the dot may be changed. As a result, the darkness of the image may be changed. Conventionally, in order to avoid such an inconvenience, the driving voltage of the injection pulse is changed in accordance with the temperature of the ink, so that a dot of a predetermined size is formed accurately and reliably. 
     For example, Japanese Laid-Open Patent Publication No. 2012-125998 discloses, in FIG. 7, a driving signal Pv includes seven injection pulses in a time-series manner in one liquid drop injection period. In Japanese Laid-Open Patent Publication No. 2012-125998, the driving voltages of all the seven injection pulses included in the driving signal Pv are changed in accordance with the temperature of the ink to generate a driving waveform for temperature correction, and the driving waveform is supplied to the pressure generator (see FIG. 8 of Japanese Laid-Open Patent Publication No. 2012-125998). 
     However, studies performed by the present inventor discovered the following. When, for example, the voltages of all of a plurality of injection pulses are changed in the case where the temperature of the ink is low, the injection stability may be decreased at the time of formation of a large dot. Specifically, the ink is attached to an area in the vicinity of the opening of the nozzle, and thus the distribution of wettability is made non-uniform. When this occurs, the track of an ink drop injected next may be shifted from the proper track, or ink mist may be easily generated. Such problems are not negligible for a large printer for industrial use, which forms a larger dot at higher speed than a home-use printer. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide a liquid injection device capable of injecting a liquid drop accurately and reliably in a wide temperature range. Other preferred embodiments of the present invention provide an inkjet recording device including such a liquid injection device. 
     According to a preferred embodiment of the present invention, a liquid injection device includes a hollow case accommodating a pressure chamber storing a liquid; a vibration plate provided in the case and demarcating a portion of the pressure chamber; a pressure generator coupled with the vibration plate, the pressure generator expanding or contracting the pressure chamber upon receipt of an electric signal; a nozzle provided in the case and in communication with the pressure chamber; a temperature sensor detecting a temperature of the liquid; a driving signal storage circuit storing a reference driving signal including at least four injection pulses, causing the liquid to be injected from the nozzle, in one liquid drop injection period; a correction coefficient calculation circuit calculating a temperature correction coefficient based on the temperature detected by the temperature sensor; a driving signal correction circuit correcting the reference driving signal with the temperature correction coefficient; and a driving signal supply circuit supplying the reference driving signal corrected by the driving signal correction circuit to the pressure generator. The at least four injection pulses included in the reference driving signal include a liquid drop injection speed-controlling injection pulse started at a timing that is about (n+(½))×Tc after start of an immediately previous injection pulse in a time-series manner (n is a natural number, and Tc is a Helmholtz characteristic vibration period of the pressure chamber). The driving signal correction circuit includes a first correction circuit correcting the injection pulses excluding the liquid drop injection speed-controlling injection pulse among the at least four injection pulses when the temperature detected by the temperature sensor is lower than or equal to a predetermined reference temperature, and a second correction circuit correcting all of the at least four injection pulses when the temperature detected by the temperature sensor is higher than the predetermined reference temperature. 
     With the above-described liquid injection device, even when the temperature of the liquid is low, the above-described inconveniences are significantly reduced or eliminated, so that the injection stability is improved. Therefore, the liquid injection device injects a liquid in a preferable manner in a wide temperature range from a low temperature to a high temperature, and forms a dot of a predetermined size with high precision. 
     In another aspect preferred embodiment of the present invention, an inkjet recording device including the above-described liquid injection device is provided. The inkjet recording device forms a dot of a large size accurately and reliably by a multi-dot system. Therefore, for example, the variance in the dot diameter is decreased to improve the image quality. In addition, stains on the recording medium or the device itself caused by ink mist or the like are decreased. 
     A liquid injection device according to a preferred embodiment of the present invention injects a liquid drop of a predetermined size accurately and reliably in a wide temperature range from a low temperature to a high temperature by a multi-dot system. Therefore, the injection stability is improved at the time of formation of a large liquid drop. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an inkjet printer according to a preferred embodiment of the present invention. 
         FIG. 2  is a front view of a portion of the inkjet printer of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a portion of an injection head. 
         FIG. 4  is a block diagram showing a structure of a portion of a controller. 
         FIG. 5  is a waveform diagram of a reference driving signal according to a preferred embodiment of the present invention. 
         FIG. 6A  is a waveform diagram of a post-correction driving signal according to a preferred embodiment of the present invention. 
         FIG. 6B  is a waveform diagram of a supply signal according to a preferred embodiment according of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, liquid injection devices and inkjet recording devices including the same according to preferred embodiments of the present invention will be described with reference to the drawings. The preferred embodiments described herein do not limit the present invention in any way. Components or portions having the same function will bear the same reference signs, and overlapping descriptions will be omitted or simplified. 
     First, an inkjet recording device will be described.  FIG. 1  is a perspective view of a large inkjet printer (hereinafter, referred to as a “printer”)  10  according to a preferred embodiment of the present invention.  FIG. 2  is a front view showing a portion of the printer  10 . The printer  10  is an example of an inkjet recording device. In  FIG. 1  and  FIG. 2 , the letters “L” and “R” respectively refer to left and right. The letters “F” and “Rr” respectively refer to front and rear. It should be noted that these directions are defined merely for the sake of convenience, and do not limit the manner of installation of the inkjet printer  10  in any way. 
     The inkjet printer  10  is to perform printing on a recording paper sheet  5 . The recording paper sheet  5  is an example of a recording medium, and is an example of target to which ink is to be injected. The “recording medium” encompasses recording mediums formed of paper including plain paper and the like, resin materials including polyvinyl chloride (PVC), polyester and the like, and various other materials including aluminum, iron, wood and the like. 
     The printer  10  includes a casing  2 , and a guide rail  3  located in the casing  2 . The guide rail  3  extends in a left-right direction. The guide rail  3  is in engagement with a carriage  1  provided with ink injection heads  15  injecting ink. The carriage  1  moves reciprocally in the left-right direction (scanning direction) along the guide rail  3  by a carriage moving mechanism  8 . The carriage moving mechanism  8  includes pulleys  19   a  and  19   b  provided at a right end and a left end of the guide rail  3 . The pulley  19   a  is coupled with a carriage motor  8   a.  The pulley  19   a  is driven by the carriage motor  8   a.  An endless belt  6  extends along, and between, the pulleys  19   a  and  19   b.  The carriage  1  is secured to the endless belt  6 . When the pulleys  19   a  and  19   b  are rotated and thus the belt  6  runs, the carriage  1  moves in the left-right direction. 
     The printer  10  is a large inkjet printer, and is larger than, for example, a table-top printer for home use. The scanning speed of the carriage  1  may preferably be occasionally set to be relatively high from the point of view of increasing the throughput although the scanning speed is set also in consideration of resolution. For example, the scanning speed may be preferably set to about 600 mm/s to about 900 mm/s when the driving frequency is about 14 kHz. For higher-speed operation, the scanning speed may be set to about 1000 mm/s or greater, for example, about 1100 mm/s to about 1200 mm/s, when the driving frequency is about 20 kHz. In such a case, the interval between injections of ink drops is significantly short. Therefore, the technology disclosed herein is especially effective for the printer  10 . 
     The recording paper sheet  5  is transported in a paper feeding direction by a paper feeding mechanism (not shown). In this example, the paper feeding direction is a front-rear direction (represented by arrow X in  FIG. 1 ). The casing  2  accommodates a platen  4  supporting the recording paper sheet  5 . The platen  4  includes a grid roller (not shown). A pinch roller (not shown) is provided above the grid roller. The grid roller is coupled with a feed motor (not shown). The grid roller is driven to rotate by the feed motor. When the grid roller is rotated in a state where the recording paper sheet  5  is held between the grid roller and the pinch roller, the recording paper sheet  5  is transported in the front-rear direction. 
     The printer  10  includes a plurality of ink cartridges  11 . The plurality of ink cartridges  11  respectively store ink of different colors. In this preferred embodiment, the printer  10  preferably includes five ink cartridges  11  storing cyan ink, magenta ink, yellow ink, black ink and white ink, for example. The ink cartridges  11  are detachably accommodated in the casing  2 . 
     The printer  10  includes ink injection heads  15  respectively provided for the ink cartridges  11  for different colors. The ink injection head  15  and the ink cartridge  11  for each of colors are connected with each other via an ink supply path  12 . The ink supply path  12  is an ink flow path usable to supply the ink from the ink cartridge  11  to the ink injection head  15 . The ink supply path  12  is, for example, a flexible tube. A pump  13  is provided on the ink supply path  12 . The pump  13  is not absolutely necessary, and may be omitted. The ink injection heads  15  are mounted on the carriage  1  and reciprocally move in the left-right direction. By contrast, the ink cartridges  11  are not mounted on the carriage  1  and do not reciprocally move in the left-right direction. A portion of the ink supply path  12  extends in the left-right direction and is covered with a cable protection and guide device  7  so as not to be broken even when the carriage  1  moves in the left-right direction. 
     The ink injection heads  15  each inject the ink toward the recording paper sheet  5  to form a dot of the ink on the recording paper sheet  5 . A great number of such dots are arrayed to form an image or the like. Each ink injection head  15  includes a plurality of nozzles  25  (see  FIG. 3 ) usable to inject the ink. The plurality of nozzles  25  are provided in a surface of the injection head  15  that faces the recording paper sheet  5  (in this preferred embodiment, on a bottom surface of the ink injection head  15 ). The plurality of nozzles  25  are arrayed at a predetermined pitch corresponding to the dot formation density (for example, arrayed at 360 dpi). 
       FIG. 3  is a partial cross-sectional view of one nozzle  25  and the vicinity thereof of the ink injection head  15 . As shown in  FIG. 3 , the ink injection head  15  includes a hollow case  21  provided with an opening  21   a,  and a vibration plate  22  attached to the case  21  so as to cover the opening  21   a.  The vibration plate  22  demarcates a portion of the pressure chamber  23 . The vibration plate  22  defines, together with the case  21 , a portion of a pressure chamber  23  storing the ink. The vibration plate  22  is elastically deformable to the inside and the outside of the pressure chamber  23 . Therein, the term “inside” refers to the upper side with respect to the vibration plate  22  in  FIG. 3 , and the term “outside” refers to the lower side with respect to the vibration plate  22  in  FIG. 3 . The vibration plate  22  is deformable to increase or decrease the capacity of the pressure chamber  23 . The vibration plate  22  is typically a resin film. 
     A side wall of the case  21  (left wall in  FIG. 3 ) is provided with an ink inlet  24 . The ink inlet  24  allows the ink to flow into the case  21 . The ink inlet  24  merely needs to be in communication with the pressure chamber  23 , and there is no limitation on the position of the ink inlet  24 . The ink inlet  24  is in communication with the ink cartridge  11 . The pressure chamber  23  is supplied with the ink from the ink cartridge  11  via the ink inlet  24 , and stores the ink. The viscosity of the ink in the pressure chamber  23  may preferably be about 1 mPa·s to about 50 mPa·s, for example, about 5 mPa·s to about 10 mPa·s in a temperature range of, for example, about 20° C. to about 40° C. from the point of view of improving the injection stability and thus realizing high-quality printing. The nozzles  25  each inject an ink drop toward the recording paper sheet  5 . The nozzles  25  are preferably located in a bottom surface  21   b  of the case  21 . The nozzles  25  each have a diameter of, for example, about 25 μm (tolerance: about +1.5 μm/−1.0 μm). A liquid surface (free surface) of the ink in each of the nozzles  25  forms a meniscus  25   a.    
     A thermistor  28  is provided on an inner wall of the case  21  (right wall in  FIG. 3 ). The thermistor  28  is an example of temperature sensor detecting the temperature of the ink injection head  15 . In this example, the thermistor  28  detects the temperature of the inner surface of the case  21  and approximates the temperature of the inner surface to the temperature of the ink. The thermistor  28  is, for example, a diode sensor, a metal thin film sensor or the like. The thermistor  28  may be provided, for example, on an outer wall of the case  21 , in the ink supply path  12  or the like. The temperature sensor may be a thermocouple capable of directly detecting the temperature of the ink. The temperature sensor may be provided in the carriage  1  or the casing  2  to detect the temperature of the environment in which the printer  10  is provided. In this case, the temperature of the ink may be extrapolated from the detected temperature of the environment. 
     The pressure chamber  23  has the Helmholtz characteristic vibration period Tc. The Helmholtz characteristic vibration period Tc is uniquely specified by the material, size, shape or location of each of components defining the pressure chamber  23 , for example, the case  21  and the vibration plate  22 , the opening area size of the nozzle  25 , properties (e.g., viscosity) of the ink, and the like. The Helmholtz characteristic vibration period Tc is a vibration period characteristic to the ink injection head  15  at the time of ink injection. The Helmholtz characteristic vibration period Tc is, for example, a vibration period of several microseconds to several ten microseconds. After an ink drop is injected, the pressure chamber  23  has a residual vibration having such a vibration period. 
     A piezoelectric element  26  is in contact with a surface of the vibration plate  22  opposite to the pressure chamber  23 . An end of the piezoelectric element  26  is secured to a secured member  29 . The piezoelectric element  26  is an example of a pressure generator. The piezoelectric element  26  is connected with the controller  18  via a flexible cable  27 . The piezoelectric element  26  is supplied with an electric signal (driving signal) via the flexible cable  27 . In this preferred embodiment, the piezoelectric element  26  is a stacked body including a piezoelectric material layer and a conductive layer stacked alternately. The piezoelectric element  26  is extended or contracted upon receipt of the driving signal supplied thereto by the controller  18  to act to elastically deform the vibration plate  22  to the inside or to the outside of the pressure chamber  23 . In this example, the piezoelectric element  26  is a piezoelectric transducer (PZT) of a longitudinal vibration mode. The PZT of the longitudinal vibration mode is extendable in the stacking direction, and, for example, is contracted when being discharged and is extended when being charged. There is no specific limitation on the type of the piezoelectric element  26 . The pressure actuator is not limited to the piezoelectric element  26 . 
     In the ink injection head  15  having the above-described structure, the piezoelectric element  26  is contracted by, for example, a decrease in the potential thereof from an intermediate potential. When this occurs, the vibration plate  22  follows this contraction to be elastically deformed to the outside of the pressure chamber  23  from an initial position, and thus the pressure chamber  23  is expanded. The expression that the “pressure chamber  23  is expanded” refers to that the capacity of the pressure chamber  23  is increased by the deformation of the vibration plate  22 . Next, the potential of the piezoelectric element  26  is increased to extend the piezoelectric element  26  in the stacking direction. As a result, the vibration plate  22  is elastically deformed to the inside of the pressure chamber  23 , and thus the pressure chamber  23  is contracted. The expression that the “pressure chamber  23  is contracted” refers to the capacity of the pressure chamber  23  being decreased by the deformation of the vibration plate  22 . Such expansion/contraction of the pressure chamber  23  changes the pressure inside the pressure chamber  23 . Such a change in the pressure inside the pressure chamber  23  pressurizes the ink in the pressure chamber  23 , and the ink is injected from the nozzle  25 . Then, the potential of the piezoelectric element  26  is returned to the intermediate potential, so that the vibration plate  22  returns to the initial position and the pressure chamber  23  is expanded. At this point, the ink flows into the pressure chamber  23  via the ink inlet  24 . 
     The controller  18  is communicably connected with the carriage motor  8   a  of the carriage moving mechanism  8 , the feed motor of the paper feeding mechanism, the pump  13 , and the ink injection head  15 . The controller  18  is configured or programmed to control operations of these components. The controller  18  is typically a computer, for example. The controller  18  includes, for example, an interface (I/F) receiving printing data or the like from an external device such as a host computer or the like, a central processing unit (CPU) executing a command of a control program or programs, a ROM storing the program(s) to be executed by the CPU, a RAM usable as a working area in which the program is developed, and a storage device (storage medium) such as a memory or the like storing the above-described program and various other types of data. 
       FIG. 4  is a block diagram showing a structure of a portion of the controller  18 . As shown in  FIG. 4 , the controller  18  includes a driving signal storage circuit  30  storing a reference driving signal S, a correction coefficient calculation circuit  40  calculating a temperature correction coefficient from the temperature of the ink detected by the thermistor  28 , a driving signal correction circuit  50  correcting the reference driving signal S, stored by the driving signal storage circuit  30 , with the temperature correction coefficient calculated by the correction coefficient calculation circuit  40  and generating a post-correction driving signal Ss, and a driving signal supply circuit  60  supplying a portion of, or the entirety of, the post-correction driving signal Ss, generated by the correction performed by the driving signal correction circuit  50 , to the piezoelectric element  26  of the ink injection head  15 . In the following description, an electric signal supplied from the driving signal supply circuit  60  to the piezoelectric element  26  may be referred to as a “supply signal”. 
     The driving signal storage circuit  30  is mutually communicable with the driving signal correction circuit  50 . The driving signal storage circuit  30  stores the reference driving signal S including at least four injection pulses in one liquid drop injection period Pa. The injection pulses are each a driving pulse causing an ink drop to be injected from the nozzle  25  in the ink injection head  15 . The details of the reference driving signal S will be described below. There is no limitation on the hardware configuration of the driving signal storage circuit  30 . The hardware configuration may be the same as a conventional configuration. 
     The correction coefficient calculation circuit  40  is mutually communicable with the driving signal correction circuit  50 . The correction coefficient calculation circuit  40  includes, for example, a temperature detection circuit  41  and a main calculation circuit  42 . The temperature detection circuit  41  drives the thermistor  28  to detect the temperature of the ink. The main calculation circuit  42  calculates a temperature correction coefficient in consideration of the viscosity and the fluidity of the ink based on the temperature of the ink detected by the temperature detection circuit  41 . 
     The driving signal correction circuit  50  is mutually communicable with each of the driving signal storage circuit  30 , the correction coefficient calculation circuit  40  and the driving signal supply circuit  60 . The driving signal correction circuit  50  includes, for example, a determination circuit  51 , a first correction circuit  52  and a second correction circuit  53 . The determination circuit  51  determines whether the temperature of the ink detected by the temperature detection circuit  41  is no higher than a predefined reference temperature. In the case where the temperature of the ink is determined by the temperature detection circuit  41  as being lower than, or equal to, the predetermined reference temperature, the first correction circuit  52  corrects only a portion of the injection pulses included in the reference driving signal S with the temperature correction coefficient. In the case where the temperature of the ink is determined by the temperature detection circuit  41  as being higher than the reference temperature, the second correction circuit  53  corrects all the injection pulses included in the reference driving signal S with the temperature correction coefficient. 
     The driving signal supply circuit  60  is mutually communicable with the driving signal correction circuit  50 . The driving signal supply circuit  60  selects a portion of, or all of, the injection pulses included in a post-correction driving signal Ss, generated by the driving signal correction circuit  50 , in accordance with the size of the dot. Then, the driving signal supply circuit  60  generates a supply signal. The driving signal supply circuit  60  supplies the generated supply signal to the piezoelectric element  26  of the ink injection head  15 . There is no limitation on the hardware configuration of the driving signal supply circuit  60 . The hardware configuration may be the same as a conventional configuration. 
     Now, the reference driving signal S generated by the driving signal storage circuit  30  will be described. The reference driving signal S includes at least four driving pulses (injection pulses), typically four to 10 driving pulses, for example, four to six driving pulses, each causing an ink drop to be injected from the nozzle  25  during a unit period (one liquid drop injection period), which is a time period for forming one dot. An injection pulse is a waveform typically including a waveform component by which the potential is decreased to expand the pressure chamber  23 , a waveform component by which the decreased potential is maintained at the decreased level to keep the pressure chamber  23  expanded, and a waveform component by which the maintained potential is increased to contract the pressure chamber  23 . The reference driving signal S may include, before or after each injection pulse in a time-series manner, a driving pulse causing the pressure chamber  23  in the ink injection head  15  to expand or contract to such a degree that an ink drop is not injected from the nozzle  25  (namely, the reference driving signal S may include a non-injection driving pulse). 
     In one preferred embodiment of the present invention, the reference driving signal S includes an even-number of injection pulses of four or more during one liquid drop injection period. More specifically, where N is a natural number, the reference driving signal S includes at least a (2N−1)th pulse, a (2N) th pulse, a (2N+1)th pulse, and a (2N+2)th pulse in a time-series manner. With such an arrangement, a large dot is formed more accurately and reliably. Preferably, a (2X+1)th pulse (X is a natural number) included in the reference driving signal S in a time-series manner is an injection pulse to control the liquid drop speed (hereinafter, referred to as a “liquid drop speed-controlling injection pulse”). The liquid drop speed control injection pulse is a driving pulse started at a timing that is (n+(½))×Tc after the start of an immediately previous injection pulse in a time-series manner (n is a natural number, and Tc is the Helmholtz characteristic vibration period of the pressure chamber  23 ). One, or two or more, liquid drop speed control injection pulses may be included in one liquid drop injection period. With such an arrangement, for example, each two ink drops may be merged together before landing on the recording paper sheet  5 , so that one large dot is formed more accurately and reliably. 
       FIG. 5  is a waveform diagram of a reference driving signal S according to a preferred embodiment of the present invention. The reference driving signal S shown in  FIG. 5  is an example of reference driving signal including four injection pulses P 1 , P 2 , P 4  and P 6  in a time-series manner in one liquid drop injection period, with N being 1. The reference driving signal S in this preferred embodiment generates the four injection pulses P 1 , P 2 , P 4  and P 6  sequentially and causes first through four ink drops to be continuously injected from the nozzle  25 . As a result, one large dot is formed on the recording paper sheet  5 . 
     The first driving pulse P 1  is a trapezoidal waveform including a discharge waveform component T 11  by which the potential is decreased from reference potential V 0  to first minimum potential V 1  at a constant gradient, a discharge maintaining waveform component T 12  by which the potential is maintained at the decreased potential (first minimum potential V 1 ) for a predetermined time period, and a charge waveform component T 13  by which the potential is increased to the reference potential V 0  at a constant gradient. The first injection pulse P 1  causes a first ink drop to be injected from the nozzle  25  at a predetermined injection speed S 1 . 
     The second driving pulse P 2  is a trapezoidal waveform including a discharge waveform component T 21  by which the potential is decreased from the reference potential V 0  to second minimum potential V 2  at a constant gradient, a discharge maintaining waveform component T 22  by which the potential is maintained at the decreased potential (second minimum potential V 2 ) for a predetermined time period, and a charge waveform component T 23  by which the potential is increased to potential V 12  at a constant gradient. The second injection pulse P 2  causes a second ink drop to be injected from the nozzle  25  at a predetermined injection speed S 2 . 
     The reference driving signal S includes, after the second injection pulse P 2  in a time-series manner, a non-injection vibration-controlling pulse P 3 . The vibration-controlling pulse P 3  is a trapezoidal waveform including a charge waveform component T 31  by which the potential is increased from the potential V 12  to a third maximum potential V 3  at a constant gradient, a charge maintaining waveform component T 32  by which the potential is maintained at the increased potential (third maximum potential V 3 ) for a predetermined time period, and a discharge waveform component T 33  by which the potential is decreased to the reference potential V 0  at a constant gradient. The vibration-controlling pulse P 3  provides the pressure chamber  23  with an expansion/contraction vibration of a phase opposite to that of the injection pulse P 2 . Such an expansion/contraction vibration decreases the kinetic energy of the meniscus  25   a  to stabilize the pressure chamber  23 . 
     The third driving pulse P 4  is a trapezoidal waveform including a discharge waveform component T 41  by which the potential is decreased from the reference potential V 0  to a fourth minimum potential V 4  at a constant gradient, a discharge maintaining waveform component T 42  by which the potential is maintained at the decreased potential (fourth minimum potential V 4 ) for a predetermined time period, and a charge waveform component T 43  by which the potential is increased to the reference potential V 0  at a constant gradient. The fourth injection pulse P 4  causes a third ink drop to be injected from the nozzle  25  at a predetermined injection speed S 3 . 
     The reference driving signal S includes, after the third injection pulse P 4  in a time-series manner, a non-injection microvibration pulse P 5 . The microvibration pulse P 5  is a trapezoidal waveform including a discharge waveform component T 51  by which the potential is decreased from the reference potential V 0  to fifth minimum potential V 5  at a constant gradient, a discharge maintaining waveform component T 52  by which the potential is maintained at the decreased potential (fifth minimum potential V 5 ) for a predetermined time period, and a charge waveform component T 53  by which the potential is increased to the reference potential V 0  at a constant gradient. While, for example, the ink is not injected, the microvibration pulse P 5  may micro-vibrate the meniscus  25   a  to stir the ink in the pressure chamber  23 . This significantly reduces or prevents an inconvenience that, for example, the nozzle  25  is clogged. 
     The fourth driving pulse P 6  is a trapezoidal waveform including a discharge waveform component T 61  by which the potential is decreased from the reference potential V 0  to sixth minimum potential V 6  at a constant gradient, a discharge maintaining waveform component T 62  by which the potential is maintained at the decreased potential (sixth minimum potential V 6 ) for a predetermined time period, and a charge waveform component T 63  by which the potential is increased to sixth maximum potential Vh 6  at a constant gradient. The sixth injection pulse P 6  causes a fourth ink drop to be injected from the nozzle  25  at a predetermined injection speed S 4 . 
     The reference driving signal S includes, after the fourth injection pulse P 6  in a time-series manner, a non-injection vibration-controlling pulse P 7 . The vibration-controlling pulse P 7  is a trapezoidal waveform including a charge waveform component T 71  by which the potential is increased from the sixth maximum potential Vh 6  to seventh maximum potential V 7  at a constant gradient, a charge maintaining waveform component T 72  by which the potential is maintained at the increased potential (seventh maximum potential V 7 ) for a predetermined time period, and a discharge waveform component T 73  by which the potential is decreased to the reference potential V 0  at a constant gradient. The vibration-controlling pulse P 7  provides the pressure chamber  23  with an expansion/contraction vibration of a phase opposite to that of the injection pulse P 6 . Such an expansion/contraction vibration decreases the kinetic energy of the meniscus  25   a  to stabilize the pressure chamber  23 . 
     The timing to start each of the first through fourth injection pulses P 1 , P 2 , P 4  and P 6  shown in  FIG. 5  is set as follows. The second injection pulse P 2  is started at timing ΔT 1 , which is m×Tc after the start of the first injection pulse P 1  (m is a natural number). ΔT 1  is synchronized to the Helmholtz characteristic vibration period Tc of the pressure chamber  23 , so that the ink injection is stabilized. The value of m is preferably m≦2, for example, m=1. In this specification, “m×Tc” is a value in the range represented by, for example, m×Tc−(⅙)×Tc to m×Tc+(⅙)×Tc. 
     The third injection pulse P 4  is started at timing ΔT 2 , which is (n+(½))×Tc after the start of the second injection pulse P 2  (n is a natural number). Namely, in this preferred embodiment, the third injection pulse P 4  in a time-series manner is a liquid drop speed control injection pulse. ΔT 2  is set to (n+(½))×Tc, so that the expansion/contraction vibration of the pressure chamber  23  is controlled. As a result, the injection speed S 3  of the third ink drop is reduced and thus the third ink drop is injected while being separated from the first and second ink drops. Therefore, the ink drop is prevented from being excessively large and thus is prevented from being attached to an area in the vicinity of the opening of the nozzle  25 . In addition, the meniscus  25   a  is stabilized to prevent an inconvenient that the track of the ink drop is shifted from the proper track. Therefore, the injection stability is improved in a preferable manner. The value of n is preferably n≦5, and is more preferably n≦3, for example, n=2. In this specification, “n×Tc” is a value in the range represented by, for example, n×Tc−(⅙)×Tc to n×Tc+(⅙)×Tc. 
     The fourth injection pulse P 6  is started at timing ΔT 3 , which is p×Tc after the start of the third injection pulse P 4  (p is a natural number of 2 or greater). With such an arrangement, the fourth ink drop is injected in a state where the meniscus  25   a  is recovered toward the opening of the nozzle  25  at least by a predetermined degree. Therefore, the liquid amount of the fourth ink drop is increased. The value of p is preferably p≦3, for example, p=2. In this specification, “p×Tc” is a value in the range represented by, for example, p×Tc−(⅛)×Tc to p×Tc+(⅛)×Tc, preferably p×Tc−( 1/10)×Tc to p×Tc+( 1/10)×Tc. 
     The driving voltage of each of the first through fourth injection pulses P 1 , P 2 , P 4  and P 6  shown in  FIG. 5 , namely, the change amount of the potential between the reference portion V 0  to each of the minimum potentials (potential difference), is set as follows. Driving voltage ΔV 2  of the second injection pulse P 2  is greater than, or equal to, driving voltage ΔV 1  of the first injection pulse P 1 . In other words, ΔV 1  and ΔV 2  have the relationship of ΔV 1 ≦ΔV 2 . From the point of view of reducing the vibration of the meniscus  25   a  to be small, ΔV 1  and ΔV 2  may have the relationship of ΔV 1 ≦ΔV 2 ≦3×ΔV 1 , for example, ΔV 1 ≦ΔV 2 ≦2×ΔV 1 . 
     Driving voltage ΔV 4  of the fourth injection pulse P 6  is greater than, or equal to, driving voltage ΔV 3  of the third injection pulse P 4 . In other words, ΔV 3  and ΔV 4  have the relationship of ΔV 3  ΔV 4 . From the point of view of suppressing the vibration of the meniscus  25   a  small, ΔV 3  and ΔV 4  may have the relationship of ΔV 3 ≦ΔV 4 ≦3×ΔV 3 , for example, ΔV 3 ≦ΔV 4 ≦2×ΔV 3 . The driving voltage ΔV 3  of the third driving pulse P 4  may be greater than the driving voltage ΔV 1  of the first driving pulse P 1  and may be approximately 1.3 times of V 1  or less. Namely, ΔV 1  and ΔV 3  may satisfy the relationship of ΔV 1 &lt;ΔV 3 ≦1.3×ΔV 1 . 
     From the above-described relationships between the driving voltages, in this preferred embodiment, the injection speed S 2  of the second ink drop is greater than the injection speed S 1  of the first ink drop, and the injection speed S 4  of the fourth ink drop is greater than the injection speed S 3  of the third ink drop. Namely, S 1 &lt;S 2 , and S 3 &lt;S 4 . The injection speed S 4  of the fourth ink drop is greater than the injection speed S 2  of the second ink drop. Namely, S 2 &lt;S 4 . Therefore, in this preferred embodiment, the second ink drop is merged with the first ink drop, and the fourth ink drop is merged with the third ink drop. First, the merged ink drop of the first ink drop and the second ink drop lands on the recording paper sheet  5 , and then the merged ink drop of the third ink drop and the fourth ink drop lands on the recording paper sheet  5 , at the same position as the merged ink drop, already landed, of the first ink drop and the second ink drop. As a result, a large dot is formed on the recording paper sheet  5 . 
     The discharge time period, namely, the sum of the time period in which the piezoelectric element  26  is discharged and the time period in which the potential thereof is maintained at the decreased potential, of each of the first through fourth injection pulses P 1 , P 2 , P 4  and P 6  shown in  FIG. 5  is set as follows. The discharge time period (i.e., the sum of the time period in which the piezoelectric element  26  is discharged and the time period in which the potential thereof is maintained at the decreased potential) t 1  of the first injection pulse P 1 , the discharge time period t 2  of the second injection pulse P 2 , the discharge time period t 3  of the third injection pulse P 4 , and the discharge time period t 4  of the fourth injection pulse P 6  are each about ½ of the Helmholtz characteristic vibration period Tc of the ink injection head  15 . Such an arrangement increases the amplitude of the Helmholtz characteristic vibration of the pressure chamber  23 . As a result, the injection stability is improved, and a large ink drop is injected efficiently by a small driving voltage. In this preferred embodiment, the discharge waveform components T 11 , T 21 , T 41  and T 61  of the first through fourth injection pulses have an equal or substantially equal time period in which the potential is discharged. The discharge maintaining waveform components T 12 , T 22 , T 42  and T 62  of the first through fourth injection pulses have an equal or substantially equal time period in which the potential is maintained at the decreased potential. 
     Now, generation of a supply signal will be described. The driving signal storage circuit  30  has, for example, the reference driving signal S shown in  FIG. 5  stored thereon. The timings to start the injection pulses, and the driving voltages, the discharge time periods and the like of the injection pulses shown in  FIG. 5  are examples. The reference driving signal S shown in  FIG. 5  includes the non-injection vibration-controlling pulses P 3  and P 7  for the purpose of stabilizing the meniscus  25   a  in the ink injection head  15 . The reference driving signal S does not need to include, for example, the vibration-controlling pulse P 3 . The reference driving signal S shown in  FIG. 5  includes the non-injection microvibration pulse P 5  for the purpose of micro-vibrating the meniscus  25   a  while an ink drop is not injected. The reference driving signal S does not need to include the non-injection microvibration pulse P 5 . 
     The temperature detection circuit  41  of the correction coefficient calculation circuit  40  controls the thermistor  28  to detect the temperature of the ink. The temperature of the ink detected by the temperature detection circuit  41  is input to the main calculation circuit  42 . The main calculation circuit  42  calculates a temperature correction coefficient based on the temperature of the ink, such that the size of the dot formed on the recording paper sheet  5  is not influenced by a change in the temperature of the ink. Namely, the temperature correction coefficient is calculated such that the liquid amount (volume) of the ink contained in the ink is constant in a wide temperature range. The temperature correction coefficient may be calculated by a well-known calculation method, which will not be described herein. In general, when the temperature of the ink is low, the ink has a high viscosity and a low fluidity. Therefore, the temperature correction coefficient is a value with which the potential difference of a waveform of an injection pulse (driving voltage) of the reference driving signal S is increased to increase the expansion/contraction of the pressure chamber  23 . By contrast, when the temperature of the ink is high, the ink has a low viscosity and a high fluidity. Therefore, the temperature correction coefficient is a value with which the potential difference of a waveform of an injection pulse (driving voltage) of the reference driving signal S is decreased to decrease the expansion/contraction of the pressure chamber  23 . The temperature correction coefficient is may be common in all the ink cartridges  11 , or may be different by, for example, color. 
     The reference driving signal S stored on the driving signal storage circuit  30  is input to the driving signal correction circuit  50 . The temperature of the ink detected by the temperature detection circuit  41  of the correction coefficient calculation circuit  40 , and the temperature correction coefficient calculated by the main calculation circuit  42 , are input to the driving signal correction circuit  50 . The determination circuit  51  of the driving signal correction circuit  50  determines whether the temperature of the ink detected by the temperature detection circuit  41  is no higher than the reference temperature. The reference temperature is predefined based on, for example, the temperature of the environment in which the printer  10  is installed, the position of the thermistor  28 , the viscosity of the ink contained in the ink cartridge  11  or the like. The reference temperature is, for example, about 20° C. to about 30° C., more specifically, about 28° C., for example. 
     In the case where the determination circuit  41  determines that the temperature of the ink is lower than, or equal to, the reference temperature, the first correction circuit  52  of the driving signal correction circuit  50  corrects a portion of the injection pulses included in the reference driving signal S with the temperature correction coefficient. Specifically, a portion of the injection pulses included in the reference driving signal S is corrected such that the potential difference is increased. By contrast, the potential difference of the liquid drop speed control injection pulse is not corrected and is kept as it is in the reference driving signal S. As a result, the meniscus  25   a  is stabilized, and the injection stability is increased at the time of formation of a large dot. The maximum potential (or minimum potential) of a non-injection driving pulse (e.g., vibration-controlling pulse or microvibration pulse) may be corrected with the temperature correction coefficient or may not be corrected. 
     The first correction circuit  51  does not correct the liquid drop speed control injection pulse. Therefore, in order to maintain the liquid amount of the ink contained in one dot even in a low-temperature environment (e.g., 15° C. or higher and 28° C. or less), typically, the driving voltage of an injection pulse to be corrected needs to be made higher than the value obtained as a result of the correction performed with the temperature correction coefficient. The reference driving signal obtained as a result of the correction is output as the post-correction driving signal Ss to the driving signal supply circuit  60 . 
       FIG. 6A  shows an example of the post-correction driving signal Ss output from the first correction circuit  52 . As shown in  FIG. 6A , in the post-correction driving signal Ss, the third injection pulse P 4 , which is a liquid drop speed control injection pulse, has the same waveform as that in the reference driving signal S. By contrast, the injection pulses other than the third injection pulse P 4 , namely, the first, second and fourth injection pulses P 1 , P 2  and P 6 , have been corrected with the temperature correction coefficient. As a result, driving voltages ΔV 1   s,  ΔV 2   s  and ΔV 6   s  included in the post-correction driving signal Ss are respectively higher than the driving voltages ΔV 1 , ΔV 2  and ΔV 6  included in the reference driving signal S. Herein, the term “high” indicates that the absolute value of the difference from reference potential Δ 0  is large. This is also applicable to the following description. 
     The above-described correction is preferably performed such that the driving voltages of the first through fourth injection pulses included in the post-correction driving signal Ss, namely, the driving voltage ΔV 1   s  of the first injection pulse P 1 , the driving voltage ΔV 2   s  of the second injection pulse P 2 , driving voltage ΔV 3   s  of the third injection pulse P 4 , and the driving voltage ΔV 4   s  of the fourth injection pulse P 6  satisfy the relationships of ΔV 1   s ≦ΔV 2   s  and ΔV 1   s ≦ΔV 3   s ≦ΔV 4   s≦ 1.5×ΔV 1   s.  With such a correction, the third ink drop and the fourth ink drop land on the recording paper sheet  5 , at the same position as the merged ink drop of the first ink drop and the second ink drop with high precision, while being separated from the merged ink drop of the first ink drop and the second ink drop. In addition, although the amount of the third ink drop is decreased because the temperature of the liquid drop speed control injection pulse P 4  is not corrected, such decrease is compensated for in a preferable manner. Therefore, a dot of a predetermined size is formed accurately and reliably in a wide temperature range. 
     In the case where the determination circuit  51  determines that the temperature of the ink is higher than the reference temperature, the second correction circuit  53  of the driving signal correction circuit  50  corrects all the injection pulses included in the reference driving signal S with the temperature correction coefficient. Specifically, all the injection pulses included in the reference driving signal S are corrected such that the driving voltages thereof are decreased. As a result, a dot of a predetermined size is formed accurately and reliably even in a high-temperature environment (e.g., about 28° C. or higher and about 40° C. or less). The maximum potential (or minimum potential) of a non-injection driving pulse (e.g., vibration-controlling pulse or microvibration pulse) may be corrected with the temperature correction coefficient or may not be corrected. The corrected reference driving signal is output as the post-correction driving signal Ss to the driving signal supply circuit  60 . 
       FIG. 6B  shows an example of the post-correction driving signal Ss output from the second correction circuit  53 . As shown in  FIG. 6B , the first through fourth injection pulses P 1 , P 2 , P 4  and P 6  in the post-correction driving signal Ss have been corrected with the temperature correction coefficient. As a result, the driving voltages ΔV 1   s,  ΔV 2   s,  ΔV 4   s  and ΔV 6   s  included in the post-correction driving signal Ss are respectively lower than the driving voltages ΔV 1 , ΔV 2 , ΔV 4  and ΔV 6  included in the reference driving signal S. In this preferred embodiment, maximum potentials V 3   s,  V 7   s  and V 5   s  of the non-injection vibration-controlling pulses P 3  and P 7  and the microvibration pulse P 5  are respectively lower than V 3 , V 7  and V 5  included in the reference driving signal S. 
     The above-described correction is preferably performed such that the driving voltages of the first through fourth injection pulses included in the post-correction driving signal Ss, namely, the driving voltage ΔV 1   s  of the first injection pulse P 1 , the driving voltage ΔV 2   s  of the second injection pulse P 2 , the driving voltage ΔV 3   s  of the third injection pulse P 4 , and the driving voltage ΔV 4   s  of the fourth injection pulse P 6  satisfy the relationships of ΔV 1   s ≦ΔV 2   s  and ΔV 1   s &lt;ΔV 3   s ≦ΔV 4   s≦ 1.3×ΔV 1   s.  With such a correction, the third ink drop and the fourth ink drop land on the recording paper sheet  5 , at the same position as the merged ink drop of the first ink drop and the second ink drop with high precision, while being separated from the merged ink drop of the first ink drop and the second ink drop. 
     The post-correction driving signal Ss is input to the driving signal supply circuit  60  from the driving signal correction circuit  50 . Printing data is input from the storage medium in the controller  18  to the driving signal supply circuit  60 . The driving signal supply circuit  60  determines whether or not to form a dot based on the printing data, and when determining that a dot is to be formed, determines the size of the dot. The driving signal supply circuit  60  then selects a portion of the driving pulses from the post-correction driving signal Ss to generate a supply signal. For example, in the case where no dot is to be formed, the driving signal supply circuit  60  selects only the non-injection microvibration pulse P 5  to generate a supply signal. By contrast, in the case where a dot is to be formed, the driving signal supply circuit  60  selects a portion of, or all of, the injection pulses P 1 , P 2 , P 4  and P 6  and the non-injection vibration-controlling pulses P 3  and P 7  to generate a supply signal. Appropriate driving pulses are selected, so that a supply signal to form a dot of any of various sizes, for example, a large dot, a medium dot or a small dot is generated. 
     Now, an operation of the printer  10  will be described. When the printer  10  is started by a user, the controller  18  performs a preparation to start printing. Specifically, printing data and various types of data representing the characteristics of the ink injection head  15  (e.g., the Helmholtz characteristic vibration period Tc) are read from the controller  18 . The controller  18  also decreases the potential of the piezoelectric element  26  to the reference potential V 0  to expand the pressure chamber  23  microscopically. The ink injection head  15  waits in this state until a driving signal is transmitted thereto from the controller  18 . 
     When the user instructs the printer  10  to perform a printing operation, the controller  18  drives the feed motor of the paper feeding mechanism. As a result, the recording paper sheet  5  is transported to be located at a predetermined printing position. The controller  18  drives the carriage motor  8   a  of the carriage moving mechanism  8 . The controller  18  drives the ink injection head  15  while moving the carriage  1  in the scanning direction (left-right direction in  FIG. 1 ). In more detail, the controller  18  supplies a portion of, or all of, the driving pulses included in the post-correction driving signal Ss as an electric signal to the piezoelectric element  26  of the ink injection head  15 . This causes the piezoelectric element  26  to be extended or contracted in accordance with the post-correction driving pulse Ss, which changes the pressure in the pressure chamber  23 . As a result, an ink drop having a predetermined mass is injected from the nozzle  25  at a predetermined speed. The injected ink drop lands on the recording paper sheet  5  to form one dot. For example, when printing is performed at a driving frequency of about 21.0 kH and a scanning speed of the carriage  1  of about 1185 mm/s, a large dot of about 20 ng/dot is obtained. When one row of printing is performed as a result of such an operation being repeated, the feed motor of the paper feeding mechanism is driven and the recording paper sheet  5  is located at the next printing position. The printer  10  repeats such an operation to perform predetermined printing. When there is no input of an electric signal to the piezoelectric element  26  anymore, the controller  18  sets the potential of the piezoelectric element  26  to zero. 
     As described above, the printer  10  in this preferred embodiment includes the first correction circuit  52  and the second correction circuit  53 . In the case where the temperature of the ink detected by the temperature detection circuit  41  is lower than, or equal to, the reference temperature, the first correction circuit  52  corrects the injection pulses other than the liquid drop speed control injection pulse P 4 , namely, the three injection pulses P 1 , P 2  and P 6 . In the case where the temperature of the ink is higher than the reference temperature, the second correction circuit  53  corrects all the four injection pulses P 1 , P 2 , P 4  and P 6 . With such an arrangement, even when the temperature of the ink is low, the injection stability is improved, and thus a dot of a predetermined size is formed with high precision in a wide temperature range from a low temperature to a high temperature. 
     In this preferred embodiment, the reference driving signal S includes four injection pulses, more specifically, first through fourth injection pulses P 1 , P 2 , P 4  and P 6 , and the third injection pulse P 4  in a time-series manner is a liquid drop speed control injection pulse. With such an arrangement, the injection speed S 3  of the third ink drop is reduced, so that the third ink drop is injected while being separated from the first and second ink drops. This further improves the injection stability. 
     In this preferred embodiment, the second ink drop is injected at a higher speed than that of the first ink drop, and the fourth ink drop is injected at a higher speed than that of the third ink drop. With such an arrangement, the second ink drop is merged with the first ink drop to form a merged drop, and the fourth ink drop is merged with the third ink drop to form a merged drop. These two merged drops form one large dot on the recording paper sheet  5  accurately and reliably. 
     In this preferred embodiment, the reference driving signal S is formed such that the driving voltage ΔV 1  of the first injection pulse P 1 , the driving voltage ΔV 2  of the second injection pulse P 2 , the driving voltage ΔV 3  of the third injection pulse P 4 , and the driving voltage ΔV 4  of the fourth injection pulse P 6  satisfy the relationships of ΔV 1 ≦ΔV 2  and ΔV 1 &lt;ΔV 3 ≦ΔV 4 ≦1.3×ΔV 1 . This further improves the injection stability. 
     In this preferred embodiment, the first correction circuit  52  corrects the injection pulses such that the driving voltages of the first through fourth injection pulses to be supplied to the piezoelectric element  26 , more specifically, the driving voltage ΔV 1   s  of the first injection pulse P 1 , the driving voltage ΔV 2   s  of the second injection pulse P 2 , the driving voltage ΔV 3   s  of the third injection pulse P 4 , and the driving voltage ΔV 4   s  of the fourth injection pulse P 6  satisfy the relationships of ΔV 1   s ≦ΔV 2   s  and ΔV 1   s ≦ΔV 3   s ≦ΔV 4   s ≦1.5×ΔV 1   s.  This further improves the injection stability. 
     In this preferred embodiment, the second correction circuit  53  corrects the injection pulses such that the driving voltages of the first through fourth injection pulses to be supplied to the piezoelectric element  26 , more specifically, the driving voltage ΔV 1   s  of the first injection pulse P 1 , the driving voltage ΔV 2   s  of the second injection pulse P 2 , the driving voltage ΔV 3   s  of the third injection pulse P 4 , and the driving voltage ΔV 4   s  of the fourth injection pulse P 6  satisfy the relationships of relationships of ΔV 1   s ≦ΔV 2   s  and ΔV 1   s &lt;ΔV 3   s ≦ΔV 4   s≦ 1.3×ΔV 1   s.  This further improves the injection stability, and allows a large dot to be formed accurately and reliably. 
     Preferred embodiments of the present invention have been described. The above preferred embodiments are merely examples, and the present invention may be carried out in any of various other forms. 
     In the above-described preferred embodiments, the pressure generator preferably includes the piezoelectric element  26  operative in a longitudinal vibration mode. The pressure generator is not limited to this, and may be a piezoelectric element of a transverse vibration mode. The pressure generator is not limited to a piezoelectric element and may be, for example, a magnetostrictive element or the like. 
     In the above-described preferred embodiments, any of the ink injection heads  15  does not include a temperature adjusting function. Alternatively, the ink injection heads  15  may each include a temperature adjuster such as, for example, a heater or the like in order to keep the temperature or the viscosity of the ink in a predetermined range. 
     In the above-described preferred embodiments, the liquid is ink. The liquid injected by the liquid injection device is not limited to ink, and may be, for example, a resin material, any of various liquid compositions containing a solute and a solvent (e.g., washing liquid, etc.), or the like. 
     In the above-described preferred embodiments, the injection head of the liquid is the ink injection head  15  mounted on the inkjet recording device. The injection head of the liquid is not limited to this, and may be mounted on, for example, any of various production devices and measuring devices such as a micropipette and the like using an inkjet system and may be usable for any of various applications. 
     The terms and expressions used herein are for description only and are not to be interpreted in a limited sense. These terms and expressions should be recognized as not excluding any equivalents to the elements shown and described herein and as allowing any modification encompassed in the scope of the claims. The present invention may be embodied in many various forms. This disclosure should be regarded as providing preferred embodiments of the principles of the present invention. These preferred embodiments are provided with the understanding that they are not intended to limit the present invention to the preferred embodiments described in the specification and/or shown in the drawings. The present invention encompasses any of preferred embodiments including equivalent elements, modifications, deletions, combinations, improvements and/or alterations. The elements of each claim should be interpreted broadly based on the terms used in the claim, and should not be limited to any of the preferred embodiments described in this specification or referred to during the prosecution of the present application. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.