Patent Publication Number: US-8991957-B2

Title: Liquid ejecting apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a liquid ejecting apparatus such as an ink jet type recording apparatus and a method of controlling the liquid ejecting apparatus, and more particularly, to a liquid ejecting apparatus that generates a fluctuation in pressure of liquid within a pressure chamber by deforming an operation unit constituting a portion of the pressure chamber, which communicates with a nozzle, to thereby eject the liquid from the nozzle. 
     2. Related Art 
     Liquid ejecting apparatuses are apparatuses that include a liquid ejecting head capable of ejecting liquid as droplets from a nozzle and eject various types of liquids from the liquid ejecting head. A typical example of such a liquid ejecting apparatus can include an image recording apparatus such as an ink jet type recording apparatus (printer) which includes an ink jet type recording head (hereinafter, referred to as a recording head) and performs recording by ejecting ink in a liquid state as ink drops from a nozzle of the recording head. Besides, liquid ejecting apparatuses are used to eject various types of liquids such as a coloring material that is used in a color filter of a liquid crystal display or the like, an organic material that is used in an organic electroluminescence (EL) display, or an electrode material that is used to form an electrode. In addition, recording heads for an image recording apparatus eject ink in a liquid state, and coloring material ejecting heads for a display manufacturing apparatus eject a solution of each of red (R), green (G), and blue (B) coloring materials. In addition, electrode material ejecting heads for an electrode forming apparatus eject an electrode material in a liquid state, and biological organic material ejecting heads for a chip manufacturing apparatus eject a solution of a biological organic material. 
     For example, in the above-mentioned printer, when ink is not ejected from a nozzle due to factors such as clogging due to thickening of ink, that is, when so-called dot omission occurs, there is a concern that the quality of an image recorded in a recording medium may be decreased. Therefore, a technique of inspecting whether ink is reliably ejected from all nozzles has been proposed. For example, JP-A-2006-312329 discloses a technique of inspecting ejection abnormality of ink on the basis of a vibration pattern (hereinafter, referred to as residual vibration) of a vibration plate which is generated when an actuator (piezoelectric element) is driven. 
     Incidentally, in the recording head that is mounted to the above-mentioned printer, a plurality of nozzles are disposed in a high density. Thus, a pressure chamber communicating with each nozzle is also formed in a high density. As a result, a partition wall for partitioning the adjacent pressure chambers is formed to be very thin. For this reason, for example, at the time of an ejection abnormality inspection performed on the basis of the above-mentioned residual vibration, when a piezoelectric element corresponding to a nozzle to be inspected is driven independently, the partition wall may be bent toward the adjacent pressure chamber in association with a fluctuation in pressure of ink within the pressure chamber which occurs by the driving of the piezoelectric element. Thus, the amplitude of residual vibration is reduced due to the occurrence of a pressure loss. As a result, there is a problem in that the amplitude of a detection signal which has a sufficient magnitude is not obtained, which leads to a deterioration in detection accuracy. 
     Meanwhile, such a problem exists not only in an ink jet type recording apparatus having a recording head, which ejects ink, mounted thereto but also in other liquid ejecting apparatuses that are configured to detect ejection abnormality on the basis of residual vibration generated by driving a piezoelectric element. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a liquid ejecting apparatus capable of improving detection accuracy in a configuration in which ejection abnormality is detected on the basis of residual vibration generated by driving a piezoelectric element, and a method of controlling the liquid ejecting apparatus. 
     According to an aspect of the invention, there is provided a liquid ejecting apparatus including a nozzle that ejects a liquid, a pressure chamber that communicates with the nozzle, an operation unit that constitutes a portion of the pressure chamber, a liquid ejecting head that has a piezoelectric element for deforming the operation unit and ejects the liquid from the nozzle in association with the driving of the piezoelectric element, a driving waveform generation unit that generates a driving waveform causing a fluctuation in pressure within the pressure chamber by driving the piezoelectric element, a switching unit that switches between an electrical connection state between the piezoelectric element and the driving waveform generation unit and a disconnection state therebetween, and an inspection unit that inspects ejection abnormality on the basis of the vibration of the operation unit which is generated in association with the driving of the piezoelectric element. The inspection unit drives a first piezoelectric element corresponding to a first nozzle to be inspected and a second piezoelectric element corresponding to a second nozzle adjacent to the first nozzle in accordance with the driving waveform in a state where the first piezoelectric element and the second piezoelectric element are switched to a connection state, and then inspects ejection abnormality on the basis of a counter electromotive force of the first piezoelectric element based on the vibration of the operation unit, which is generated by the driving of the first piezoelectric element in a state where the second piezoelectric element is switched to a disconnection state. 
     In this case, the first piezoelectric element corresponding to the first nozzle to be inspected and the second piezoelectric element corresponding to the second nozzle adjacent to the first nozzle are driven in accordance with the driving waveform in a state where the first piezoelectric element and the second piezoelectric element are switched to a connection state, and then ejection abnormality is inspected on the basis of the counter electromotive force of the first piezoelectric element based on the vibration of the operation unit, which is generated by the driving of the first piezoelectric element, in a state where the second piezoelectric element is switched to a disconnection state. In a step of causing a fluctuation in pressure within the pressure chamber, the first piezoelectric element and the second piezoelectric element are simultaneously driven. Accordingly, when a fluctuation in pressure occurs within the pressure chamber corresponding to a nozzle to be inspected, a fluctuation in pressure also occurs within the adjacent pressure chamber. Thus, a partition wall for partitioning the pressure chamber of the nozzle to be inspected is prevented from being bent in association with the fluctuation in pressure, thereby reducing a pressure loss in the pressure chamber corresponding to the nozzle to be inspected. Thus, it is possible to obtain a detection signal having an amplitude with a sufficient magnitude for the detection of ejection abnormality. In addition, in a step of detecting a counter electromotive force signal of the first piezoelectric element based on the vibration of the operation unit, the second piezoelectric element is switched to a disconnection state, and thus it is possible to prevent a leak current from flowing from the second piezoelectric element side. As a result, it is possible to improve the detection accuracy of ejection abnormality. 
     According to another aspect of the invention, there is provided a method of controlling a liquid ejecting apparatus including a nozzle that ejects a liquid, a pressure chamber that communicates with the nozzle, an operation unit that constitutes a portion of the pressure chamber, a liquid ejecting head that has a piezoelectric element for deforming the operation unit and ejects the liquid from the nozzle in association with the driving of the piezoelectric element, a driving waveform generation unit that generates a driving waveform causing a fluctuation in pressure within the pressure chamber by driving the piezoelectric element, a switching unit that switches between a connection state and a disconnection state of the driving waveform with respect to the piezoelectric element, and an inspection unit that inspects ejection abnormality on the basis of the vibration of the operation unit which is generated in association with the driving of the piezoelectric element, the method including a first process of switching a first piezoelectric element corresponding to a first nozzle to be inspected and a second piezoelectric element corresponding to a second nozzle adjacent to the first nozzle to a connection state, a second process of driving the first piezoelectric element and the second piezoelectric element at approximately the same time in accordance with the driving waveform, a third process of switching the second piezoelectric element to a disconnection state, and a fourth process of inspecting ejection abnormality on the basis of a counter electromotive force of the first piezoelectric element based on the vibration of the operation unit which is generated in association with the driving of the first piezoelectric element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective view illustrating a configuration of a printer. 
         FIG. 2  is a perspective view illustrating a configuration of a recording head. 
         FIG. 3  is a partial cross-sectional view of the recording head. 
         FIG. 4  is a block diagram illustrating an electrical configuration of a printer. 
         FIG. 5  is a waveform diagram illustrating a configuration of a driving signal and a correspondence table of waveform selection data. 
         FIGS. 6A and 6B  are diagrams illustrating a circuit configuration for detecting a counter electromotive force signal of a piezoelectric element. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments for implementing the invention will be described with reference to the accompanying drawings. Meanwhile, various limits are made for preferred specific examples of the invention in the embodiments described below. However, the scope of the invention is not limited to those embodiments as long as there is particularly no disclosure to limit the invention in the following description. In addition, hereinafter, an ink jet type recording apparatus (hereinafter, a printer) will be described as an example of a liquid ejecting apparatus of the invention. 
       FIG. 1  is a perspective view illustrating a configuration of a printer  1 . The printer  1  schematically includes a carriage  4  that has a recording head  2 , which is a kind of liquid ejecting head, mounted thereto and an ink cartridge  3 , which is a kind of liquid supply source, detachably mounted thereto, a platen  5  that is disposed below the recording head  2  at the time of a recording operation, a carriage moving mechanism  7  that reciprocates the carriage  4  in a width direction of a recording paper  6  (a kind of recording medium and landing object), that is, in a main scanning direction, and a paper feeding mechanism  8  that transports the recording paper  6  in a sub-scanning direction perpendicular to the main scanning direction. 
     The carriage  4  is axially supported by and mounted to a guide rod  9  that is laid in the main scanning direction, and is configured to move in the main scanning direction along the guide rod  9  in accordance with the operation of the carriage moving mechanism  7 . The position of the carriage  4  in the main scanning direction is detected by a linear encoder  10 , and a detection signal thereof, that is, an encoder pulse (a kind of positional information), is transmitted to a control unit  37  (see  FIG. 4 ) of a printer controller  31 . The linear encoder  10  is a kind of positional information output unit, and outputs the encoder pulse according to a scanning position of the recording head  2  as positional information in the main scanning direction. For this reason, the control unit  37  can recognize the scanning position of the recording head  2  which is mounted to the carriage  4 , on the basis of the received encoder pulse. That is, for example, it is possible to recognize the position of the carriage  4  by counting the received encoder pulses. Thus, the control unit  37  can control a recording operation through the recording head  2  while recognizing the scanning position of the carriage  4  (the recording head  2 ) on the basis of the encoder pulse that is output from the linear encoder  10 . 
     A home position serving as a base point of the scanning of the carriage is set in an end region that is located further outside than a recording region within a movement range of the carriage  4 . The home position in this embodiment is provided with a capping member  11  that seals a nozzle forming surface (a nozzle plate  29 , see  FIG. 3 ) of the recording head  2  and a wiper member  12  for wiping the nozzle forming surface. The printer  1  is configured to be capable of so-called bidirectional recording for recording characters or images on the recording paper  6  bidirectionally, both in a forward motion when the carriage  4  moves toward an end on the opposite side from the home position and in a backward motion when the carriage  4  returns to the home position side from the end on the opposite side. 
     As illustrated in  FIG. 2  and  FIG. 3 , the recording head  2  includes a pressure generation unit  15  and a flow channel unit  16 , and is integrally formed in a state where the pressure generation unit and the flow channel unit are superimposed on each other. The pressure generation unit  15  is configured in such a manner that a pressure chamber plate  18  for partitioning a pressure chamber  17 , a communication port plate  19  having a communication port  22  on the supply side and a first communication port  24   a  being opened therein, and a vibration plate  21  having a piezoelectric element  20  mounted thereon are stacked on each other and integrated through baking. In addition, the flow channel unit  16  is configured in such a manner that plate members, which are constituted by a supply port plate  25  having a supply port  23  and a second communication port  24   b  formed therein, a reservoir plate  27  having a reservoir  26  and a third communication port  24   c  formed therein, and a nozzle plate  29  having a nozzle  28  formed therein, are attached to each other in a stacking state. The nozzle plate  29  includes a nozzle array in which a plurality of the nozzles  28  (for example, 360 nozzles) are arranged. For example, the nozzle array is provided for each color of ink. 
     The piezoelectric element  20  is disposed on the outer surface of the vibration plate  21  which is the opposite side of the pressure chamber  17  so as to correspond to each pressure chamber  17 . The exemplified piezoelectric element  20  is a piezoelectric element in a so-called flexural vibration mode, and includes a driving electrode  20   a , a common electrode  20   b , and a piezoelectric layer  20   c  interposed between the driving electrode and the common electrode. When a driving signal (driving pulse) is applied to a driving electrode of the piezoelectric element  20 , an electric field is generated between the driving electrode  20   a  and the common electrode  20   b  due to a potential difference. The electric field is applied to the piezoelectric layer  20   c , which is deformed in accordance with the strength of the electric field applied to the piezoelectric layer  20   c . That is, as a potential of the driving electrode  20   a  increases, a central portion of the piezoelectric layer  20   c  in a width direction (a direction of the nozzle array) bends toward the inside of the pressure chamber  17  (the side coming close to the nozzle plate  29 ), thereby deforming the vibration plate  21  so as to reduce the volume of the pressure chamber  17 . On the other hand, as the potential of the driving electrode  20   a  decreases (as the potential thereof comes close to 0), a central portion of the piezoelectric layer  20   c  in a shorter direction bends toward the outside of the pressure chamber  17  (the side away from the nozzle plate  29 ), thereby deforming the vibration plate  21  so as to increase the volume of the pressure chamber  17 . Here, in the vibration plate  21 , a portion that seals an opening of the pressure chamber  17  functions as an operation unit in the invention. An area of the operation unit is slightly larger than an area of the opening of the pressure chamber  17  which is sealed by the operation unit. Thus, the operation unit can be easily bent further inside or outside than an opening surface of the pressure chamber  17 . Meanwhile, in the exemplified configuration, it is also possible to employ a configuration in which the driving electrode  20   a  and the common electrode  20   b  are reversed. 
       FIG. 4  is a block diagram illustrating an electrical configuration of the printer  1 . The printer  1  of this embodiment schematically includes a printer controller  31  and a print engine  32 . The printer controller  31  includes an external interface (external I/F)  33  to which printing data or the like is input from an external device such as a host computer, a RAM  34  that stores various pieces of data or the like, a ROM  35  that stores a control program or the like for various types of control operations, the control unit  37  that generally controls units in accordance with the control program that is stored in the ROM  35 , an oscillation circuit  38  that generates a clock signal, a driving signal generation circuit  39  (a kind of driving waveform generation unit) which generates a driving signal to be supplied to the recording head  2 , and an internal interface (internal I/F)  40  for outputting dot pattern data, which is obtained by developing printing data for each dot, or the driving signal to the recording head  2 . In addition, the print engine  32  includes the recording head  2 , the carriage moving mechanism  7 , the paper feeding mechanism  8 , and the linear encoder  10 . 
     The control unit  37  functions as a timing pulse generation unit that generates a timing pulse PTS (see  FIG. 5 ) from the encoder pulse that is output from the linear encoder  10 . The timing pulse PTS is a signal for determining a generation starting timing of the driving signal that is generated by the driving signal generation circuit  39 . That is, the driving signal generation circuit  39  outputs a driving signal COM whenever receiving the timing pulse PTS. In other words, the driving signal generation circuit  39  repeatedly generates the driving signal COM with a period (hereinafter, referred to as a unit period T) based on the above-mentioned timing pulse PTS. In addition, the control unit  37  outputs a latch signal LAT for specifying a latch timing of printing data and a change signal CH for specifying a selection timing of each ejection driving pulse included in the driving signal. Meanwhile, the latch signal LAT of this embodiment generates a first LAT 1  by receiving the timing pulse PTS and then generates a second LAT 2  on condition that a specified time has elapsed. 
     The driving signal generation circuit  39  is constituted by a driving voltage supply source and a constant voltage supply source (both are not shown in the drawing). The driving signal generation circuit outputs the above-mentioned driving signal COM from the driving voltage supply source and outputs a direct current voltage VBS from the constant voltage supply source. The driving voltage supply source is electrically connected to the driving electrode  20   a  of the piezoelectric element  20  through a first switch  48  (a kind of switching unit in the invention) which is provided for each piezoelectric element  20  (see  FIGS. 6A and 6B ). In addition, the constant voltage supply source is electrically connected to the common electrode  20   b  of the piezoelectric element  20  through a second switch  49 , which is commonly provided with respect to the piezoelectric elements  20  belonging to the same nozzle array, and a detection resistor  50  that is connected in parallel to the second switch  49  (see  FIGS. 6A and 6B ). 
       FIG. 5  is a waveform diagram illustrating an example of a configuration of the driving signal COM and a correspondence table of waveform selection data according to this embodiment. Meanwhile, in  FIG. 5 , a horizontal axis represents time, and a vertical axis represents a potential. The driving signal COM of this embodiment can be divided into a first half portion and a second half portion based on the latch signal. In this embodiment, a portion corresponding to a first half (period T 1 ) is a unit signal for recording, and a portion corresponding to a second half (period T 2 ) is a unit signal for inspection. In this embodiment, it is possible to perform an ejection abnormality inspection of the nozzle  28  by using the unit signal for inspection of the second half during a recording operation (during a printing operation of an image or the like) which is performed on a recording medium such as the recording paper  6 . The ejection abnormality inspection will be described later in detail. 
     The unit signal for recording in this embodiment is a series of signals having four ejection driving pulses P 1  to P 4  within the period T 1 . In this embodiment, the period T 1  of the first half portion is divided into four periods (pulse generation periods) t 1  to t 4 . The first ejection driving pulse P 1  is generated in the period t 1 , the second ejection driving pulse P 2  is generated in the period t 2 , the third ejection driving pulse P 3  is generated in the period t 3 , and the fourth ejection driving pulse P 4  is generated in the period t 4 . The ejection driving pulses P 1  to P 4  become waveforms having a potential changing to a reverse trapezoidal shape between a reference potential VB and an ejection potential VL that is lower than the reference potential. A driving voltage Vh 1  (a potential difference between the reference potential VB and the ejection potential VL) of each of the ejection driving pulses P 1  to P 4  is adjusted so that a predetermined amount of ink is ejected from the nozzle  28 . In this embodiment, a total of four gray-scales including non-recording in which no dot is formed can be expressed with respect to a forming region of one pixel (a constituent unit of an image or the like). 
     More specifically, whenever each of the first ejection driving pulse P 1  to the fourth ejection driving pulse P 4  is applied to the piezoelectric element  20 , a specified amount of ink is ejected from the nozzle  28 . In addition, it is possible to differentiate sizes of dots, which are recorded in one pixel region (a virtual pixel forming region of the recording paper  6 ), from each other by changing the number of ejection driving pulses to be applied to the piezoelectric element  20  within the period T 1 . The ejection driving pulses are selected within the period T 1  in accordance with 2 bits of selection data that is generated on the basis of the printing data, as illustrated in a left-hand column (LAT 1 ) in the correspondence table of  FIG. 5 . 
     For example, when the selection data is (00), no ejection driving pulse is applied to the piezoelectric element  20 . For this reason, ink is not ejected from the nozzle  28  in the period T 1 . That is, when the selection data is (00), non-recording (non-ejection) in which no dot is formed occurs. In addition, when the selection data is (01) in the period T 1 , only the second ejection driving pulse P 2  in the period t 2  within the period T 1  is applied to the piezoelectric element  20 , and thus ink is ejected only once from the nozzle  28  in the period T 1 . Thus, one dot (hereinafter, referred to as a unit dot) is formed on the recording paper  6 , and this becomes a small dot. Furthermore, when the selection data is (10), the first ejection driving pulse P 1  in the period t 1  and the third ejection driving pulse P 3  in the period t 3  within the period T 1  are selected and sequentially applied to the piezoelectric element  20 . Thus, an ejection operation of ink is performed twice in a row within the period T 1 . When these pieces of ink are landed on the recording paper  6 , two unit dots are formed on the recording paper  6 , and a medium dot is constituted by the two unit dots. When the selection data is (11), the four ejection driving pulses P 1  to P 4  within the period T 1  are selected and sequentially applied to the piezoelectric element  20 , and thus an ejection operation of ink is performed four times in a row within the period T 1 . Thus, each piece of ink is landed on the recording paper  6  to thereby form four unit dots, thereby constituting a large dot by these unit dots. 
     On the other hand, the unit signal for inspection in this embodiment is a series of signals having one inspection driving pulse Pd (a kind of driving waveform) within the period T 2 . In this embodiment, the period T 2 , which is a second half portion, is further divided into two periods, i.e., a period t 5  and a period t 6 . The inspection driving pulse Pd is generated in the period t 5 , and a potential is constant at the reference potential VB in the period t 6 . Meanwhile, when an ejection abnormality inspection is performed in the period T 2  (hereinafter, appropriately referred to as an ejection abnormality inspection mode), a counter electromotive force signal of the piezoelectric element  20  corresponding to a nozzle to be inspected is detected in the period t 6  after the piezoelectric element  20  is driven by the inspection driving pulse Pd in the period t 5 . Hereinafter, the period t 5  and the period t 6  are also referred to as a pressure vibration generation period (or pressure vibration generation step) and a detection period (or detection step), respectively. The inspection driving pulse Pd becomes a waveform having a potential changing to a reverse trapezoidal shape between the reference potential VB and an inspection potential Vd that is lower than the reference potential. That is, the inspection driving pulse Pd is a waveform causing the piezoelectric element  20  to perform a series of operations including bending toward the outside of the pressure chamber  17  from a reference state corresponding to the reference potential VB to thereby expand the volume of the pressure chamber  17  and then bending toward the inside of the pressure chamber  17  to thereby contract the volume of the pressure chamber  17  up to a reference volume corresponding to the reference potential VB. 
     A driving voltage Vh 2  (a potential difference between the reference potential VB and the ejection potential Vd) of the inspection driving pulse Pd is set to be lower than the driving voltage Vh 1  of the ejection driving pulse. The inspection driving pulse Pd is a pulse intended to generate pressure vibration in ink within the pressure chamber  17  by driving the piezoelectric element  20 . For this reason, ink may be or may not be ejected from the nozzle  28  when the piezoelectric element  20  is driven by the application of the inspection driving pulse Pd. However, in this embodiment, since an ejection abnormality inspection of the nozzle  28  is performed during a recording operation, the driving voltage Vhd is set to such a driving voltage Vh 2  that ink is not ejected from the nozzle  28  even though the inspection driving pulse Pd is applied to the piezoelectric element  20 . 
     The selection of the inspection driving pulse Pd in an ejection abnormality inspection mode (period T 2 ) is performed on the basis of 2 bits of selection data, similar to the selection of the ejection driving pulse of the period T 1 . In this embodiment, for example, when the detection of ejection abnormality is not performed (non-detection), selection data (00) is allocated. That is, when the selection data is (00), the inspection driving pulse Pd is not applied to the piezoelectric element  20  in the period T 2 . In addition, as described below, when an adjacent nozzle (corresponding to a second nozzle in the invention) which is next to the nozzle to be inspected (corresponding to a first nozzle in the invention) is driven, selection data (01) is allocated. In this case, the inspection driving pulse Pd is applied to the piezoelectric element  20  (a kind of a second piezoelectric element in the invention) which corresponds to the adjacent nozzle in the period t 5  of the period T 2 . When the nozzle to be inspected is driven, selection data (11) is allocated. In this case, the inspection driving pulse Pd is applied to the piezoelectric element  20  (a kind of a first piezoelectric element in the invention) which corresponds to the nozzle to be inspected in the period t 5  of the period T 2 . Meanwhile, in the ejection abnormality inspection mode of this embodiment, selection data (10) is not used. A driving difference between the nozzle to be inspected and the adjacent nozzle at the time of inspection will be described below. 
     Next, an electrical configuration of the recording head  2  will be described. As illustrated in  FIG. 4 , the recording head  2  includes a shift register (SR) circuit constituted by a first shift register  41  and a second shift register  42 , a latch circuit constituted by a first latch circuit  43  and a second latch circuit  44 , a decoder  45 , a control logic  46 , a level shifter  47 , a switch  48  (first switch), the piezoelectric element  20 , the switch  49  (second switch), and an ejection abnormality detection circuit  51 . In addition, numbers of shift registers  41  and  42 , latch circuits  43  and  44 , level shifter  47 , first switch  48 , and piezoelectric element  20  which correspond to the number of nozzles  28  are provided. Meanwhile,  FIG. 4  illustrates only a configuration corresponding to one nozzle, and configurations corresponding to other numbers of nozzles are not illustrated. 
     The recording head  2  controls the ejection of ink (a kind of liquid) on the basis of selection data (gray-scale data) SI that is transmitted from the printer controller  31 . In this embodiment, the selection data is transmitted in synchronization with a clock signal CLK to the recording head  2  in the order of a higher-order bit group of the selection data constituted by 2 bits and a lower-order bit group of the selection data, and thus the higher-order bit group of the selection data is first set to the second shift register  42 . When the higher-order bit group of the selection data is set to the second shift register  42  with respect to all the nozzles  28 , the higher-order bit group is subsequently shifted to the first shift register  41 . At the same time, the lower-order bit group of the selection data is set to the second shift register  42 . 
     The first latch circuit  43  is electrically connected downstream of the first shift register  41 , and the second latch circuit  44  is electrically connected downstream of the second shift register  42 . In addition, when a latch pulse is input to each of the latch circuits  43  and  44  from the printer controller  31  side, the first latch circuit  43  latches a higher-order bit group of recording data, and the second latch circuit  44  latches a lower-order bit group of the recording data. The pieces of recording data (the higher-order bit group and the lower-order bit group) which are respectively latched by the latch circuits  43  and  44  are output to the decoder  45 . The decoder  45  generates pulse selection data for selecting each driving pulse included in the driving signal COM, on the basis of the higher-order bit group and the lower-order bit group of the recording data. 
     The driving signal COM is supplied to the input side of the first switch  48  from the driving signal generation circuit  39 . In addition, the driving electrode  20   a  of the piezoelectric element  20  is connected to the output side of the first switch  48  (see  FIGS. 6A and 6B ). The first switch  48  selectively supplies a driving pulse included in each driving signal to the piezoelectric element  20 , on the basis of the above-mentioned selection data. The first switch  48 , which performs such an operation, functions as a kind of selection supply unit. In addition, when the ejection abnormality inspection is performed in the period T 2 , the first switch  48  also functions as a kind of switching unit that switches between a connection state and a disconnection state of the piezoelectric element  20  with respect to the driving signal generation circuit  39 . Operations of the first switch  48  in the ejection abnormality inspection mode will be described below. 
     On the other hand, the ejection abnormality detection circuit  51  is connected to the common electrode  20   b  side of the piezoelectric element  20  through the second switch  49 . The second switch  49  is switching-controlled in response to a switching signal that is output from the control logic  46 . The ejection abnormality detection circuit  51  is configured to output a counter electromotive force signal of the piezoelectric element  20  based on residual vibration when the piezoelectric element  20  is driven by the inspection driving pulse Pd, as a detection signal, to the printer controller  31  side. The printer controller  31  (the control unit  37 ) inspects for the presence or absence of ejection abnormality of a nozzle to be inspected, on the basis of the counter electromotive force signal that is output from the ejection abnormality detection circuit  51 . Therefore, the ejection abnormality detection circuit  51  and the printer controller  31  function as an inspection unit in the invention. 
       FIGS. 6A and 6B  are diagrams illustrating a circuit configuration for detecting a counter electromotive force signal Sc of the piezoelectric element  20 . Meanwhile,  FIG. 6A  illustrates an ejection abnormality inspection mode, that is, a state in the period t 5  (pressure vibration generation period) within the period T 2 , and similarly,  FIG. 6B  illustrates a state in the period t 6  (inspection period) within the period T 2 . In addition,  FIGS. 6A and 6B  illustrate a configuration corresponding to three nozzles, and for convenience of description, configurations corresponding to other numbers of nozzles  28  are not illustrated. However, numbers of piezoelectric elements  20  and first switches  48  which correspond to the number of nozzles  28  constituting the same nozzle array are provided. In addition, in  FIGS. 6A and 6B , the central piezoelectric element  20  is the piezoelectric element  20  (first piezoelectric element) which corresponds to a nozzle to be inspected (first nozzle), and the piezoelectric elements  20  (second piezoelectric elements) of both sides thereof correspond to nozzles (second nozzles) which are adjacent to the nozzle to be inspected. As described above, a driving voltage supply source of the driving signal generation circuit  39  is connected to the driving electrode  20   a  of the piezoelectric element  20  through the first switch  48  for each piezoelectric element  20 , and a constant voltage supply source is electrically connected to the common electrode  20   b  of the piezoelectric element  20  through the second switch  49  and the detection resistor  50  that is connected in parallel to the second switch  49 . The second switch  49  is constituted by, for example, a MOS-FET, and is switched to an on-state during a recording operation in the period T 1  or during application (a pressure vibration generation period) of the inspection driving pulse Pd in the period t 5  of the period T 2  ( FIG. 6A ). In this case, a current Id flows through the second switch  49  side. On the other hand, the second switch is switched to an off-state in a detection period in the period t 6  of the period T 2  ( FIG. 6B ). In this case, the current Id flows through the detection resistor  50  side. 
     Here, after the piezoelectric element  20  is driven by the inspection driving pulse Pd, the vibration plate  21  which is an operation unit of the pressure chamber  17  vibrates in accordance with the pressure vibration generated in ink within the pressure chamber  17 . Consequently, damping vibration (residual vibration) is also generated in the piezoelectric element  20 , and a counter electromotive force based on the residual vibration is generated. The ejection abnormality detection circuit  51  obtains the counter electromotive force signal Sc (detection signal) of the piezoelectric element  20  by amplifying and binarizing a potential difference between both ends of the above-mentioned detection resistor  50 . It can be seen that, at the time of abnormality such as a case of a so-called dot omission in which ink is not ejected from the nozzle  28  or a case where an amount or flying speed of ink is extremely decreased as compared with a normal nozzle  28  even though ink is ejected from the nozzle  28 , phase components based on a period component, an amplitude component, and a latch signal (LAT 2 ) of the above-mentioned detection signal are different from those at the time of normality. For this reason, the determination of ejection abnormality based on the counter electromotive force signal Sc is performed by specifying in advance a normal range of each of the above-mentioned components and determining whether each component of the detection signal is in the specified range. Meanwhile, since a determination method is well known, a detailed description thereof will be omitted. 
     Incidentally, in the related art, at the time of an ejection abnormality inspection performed on the basis of the above-mentioned residual vibration, when a piezoelectric element corresponding to a nozzle to be inspected is driven independently, a partition wall for partitioning the adjacent pressure chambers may be bent in association with a fluctuation in pressure of ink within the pressure chamber. Thus, the amplitude of residual vibration is reduced due to the occurrence of a pressure loss. That is, crosstalk occurs between the adjacent nozzles. As a result, there is a problem in that the amplitude of a detection signal which has a sufficient magnitude is not obtained in performing the above-mentioned determination, which leads to a deterioration in detection accuracy. On the other hand, the printer  1  according to the invention has a feature that the crosstalk is suppressed by simultaneously driving the piezoelectric element  20  corresponding to a nozzle to be inspected and the piezoelectric element  20  corresponding to the adjacent nozzle which is next to the nozzle to be inspected, at the time of an ejection abnormality inspection. 
     The above-mentioned points will be described below with reference to  FIGS. 6A and 6B . 
     The ejection abnormality inspection is sequentially performed on each of the nozzles  28  constituting the nozzle array. As described above, in the printer  1  according to the invention, crosstalk is suppressed by simultaneously driving both the nozzle to be inspected and nozzles adjacent to the nozzle to be inspected. Meanwhile, when the nozzles  28  located at both ends of the nozzle array are objects to be inspected, an adjacent nozzle is present on only one side. Accordingly, in this case, the inspection is performed by driving the piezoelectric elements  20  corresponding to two of the nozzles. When other nozzles  28  are inspected, the inspection is performed by driving a total of three piezoelectric elements  20  including the piezoelectric element  20  corresponding to a nozzle to be inspected and the piezoelectric elements  20  corresponding to adjacent nozzles located on the both sides of the nozzle to be inspected. Hereinafter, an example of the latter case will be described. 
     As described above, in  FIGS. 6A and 6B , the central piezoelectric element  20  is the piezoelectric element  20  corresponding to a nozzle to be inspected, and the piezoelectric elements  20  of both sides thereof correspond to nozzles which are adjacent to the nozzle to be inspected. In the ejection abnormality inspection mode in the period T 2 , first, the second switch  49  is turned on in response to a switching signal, and the first switch  48  of the piezoelectric element  20  corresponding to the nozzle to be inspected and the first switches  48  of the piezoelectric elements  20  corresponding to the adjacent nozzles located on the both sides thereof are turned on (first process,  FIG. 6A ). Meanwhile, the first switches  48  of other piezoelectric elements  20  are turned off. This is to prevent a leak current from other piezoelectric elements  20  from going around to the detection resistor  50  side when the counter electromotive force signal Sc of the piezoelectric element  20  of the nozzle to be inspected is detected. 
     In addition, as illustrated in  FIG. 6A , in a pressure vibration generation period of the period t 5 , the inspection driving pulse Pd is applied to the piezoelectric element  20  corresponding to the nozzle to be inspected, on the basis of selection data (11). At the same time, the inspection driving pulse Pd is also applied to the piezoelectric elements  20  corresponding to the adjacent nozzles, on the basis of selection data (01). Thus, the piezoelectric elements  20  are simultaneously driven (second process), and a fluctuation in pressure occurs in both the pressure chamber  17  corresponding to the nozzle to be inspected and the pressure chambers  17  corresponding to the adjacent nozzles at the same timing. Thus, the bending of a partition wall that partitions the pressure chamber is suppressed even though the internal pressure of the pressure chamber  17  of the nozzle to be inspected increases. Thus, it is possible to reduce a pressure loss occurring in the pressure chamber  17  of the nozzle to be inspected. As a result, it is possible to generate pressure vibration that is sufficient for the inspection. The vibration plate  21  and the piezoelectric element  20 , which are operation units of the pressure chamber  17 , also vibrate in association with damping vibration (residual vibration) of the pressure vibration, and a counter electromotive force is generated in the piezoelectric element  20  due to the vibration. 
     Subsequently, in the period t 6  which is an inspection period, the second switch  49  is switched to an off-state in response to a switching signal, and the first switches  48  of the piezoelectric elements  20  corresponding to the adjacent nozzles are switched to an off-state (third process,  FIG. 6B ). Thus, only the current Id based on the counter electromotive force of the piezoelectric element  20  corresponding to the nozzle to be inspected flows to the detection resistor  50 . That is, a current based on the counter electromotive force of the piezoelectric elements  20  corresponding to the adjacent nozzles does not flow to the detection resistor  50 . In addition, since the piezoelectric elements  20  corresponding to the adjacent nozzles are prevented from being deformed in a reference state corresponding to a reference potential VBS, the stiffness of the vibration plate  21  in the adjacent nozzle increases. Thus, residual vibration is prevented from being lost at the side of the nozzle to be inspected, and the amplitude of the counter electromotive force signal of the piezoelectric element  20  based on the residual vibration is prevented from being reduced. The ejection abnormality detection circuit  51  obtains the counter electromotive force signal Sc of the piezoelectric element  20  from a potential difference between both ends of the above-mentioned detection resistor  50 . The presence or absence of abnormality of the nozzle  28  is determined on the basis of the counter electromotive force signal Sc (fourth process). 
     In this manner, in the printer  1  according to the invention, the piezoelectric elements  20  of the nozzle to be inspected and the adjacent nozzles are simultaneously driven in a step (pressure vibration generation period) of causing a fluctuation in pressure within the pressure chamber  17  in the ejection abnormality inspection mode, and thus when a fluctuation in pressure occurs within the pressure chamber  17  corresponding to the nozzle to be inspected, a fluctuation in pressure also occurs within the pressure chamber  17  that is adjacent thereto. Thus, the partition wall for partitioning the pressure chamber  17  of the nozzle to be inspected is prevented from being bent in association with the fluctuation in pressure, thereby reducing a pressure loss in the pressure chamber  17  corresponding to the nozzle to be inspected. Thus, it is possible to obtain a detection signal having an amplitude with a sufficient magnitude for the detection of ejection abnormality. In addition, in a step (detection period) of detecting a counter electromotive force signal based on residual vibration, the piezoelectric elements  20  of the adjacent nozzles are switched to a disconnection state, and thus it is possible to prevent a leak current from flowing from the piezoelectric element  20  side of the adjacent nozzle. As a result, it is possible to improve the detection accuracy of ejection abnormality. 
     Meanwhile, in the above-mentioned embodiment, an example has been described in which one adjacent nozzle located next to a nozzle to be inspected is disposed for each side (one nozzle on one side when the nozzle to be inspected is a nozzle located at the end of a nozzle array, and a total of two nozzles located on both sides when other nozzles are nozzles to be inspected). However, the invention is not limited thereto, and it is also possible to employ a configuration in which two or more adjacent nozzles are provided on one side. 
     In addition, in the above-mentioned embodiment, a configuration has been exemplified in which an ejection abnormality inspection can be performed during a recording operation, but the invention is not limited thereto. For example, it is also possible to employ a configuration in which an ejection abnormality inspection is not performed during a recording operation and is performed independently from the recording operation. 
     In addition, the invention is not limited to a printer as long as it is a liquid ejecting apparatus having a configuration in which ejection abnormality is detected on the basis of residual vibration generated by driving a piezoelectric element, and the invention can also be applied to various types of ink jet type recording apparatuses such as a plotter, a facsimile apparatus, or a copy machine, a liquid ejecting apparatus other than a recording apparatus, for example, a display manufacturing apparatus, an electrode manufacturing apparatus, or a chip manufacturing apparatus, and the like. 
     The entire disclosure of Japanese Patent Application No. 2012-244230, filed Nov. 6, 2012 is expressly incorporated by reference herein.