Patent Publication Number: US-2022234345-A1

Title: Liquid ejecting apparatus, inspection method, and storage medium

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-011755, filed Jan. 28, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure relate to a liquid ejecting apparatus, an inspection method, and a non-transitory computer-readable storage medium storing an inspection program. 
     2. Related Art 
     In general, a liquid ejecting apparatus, a typical example of which is an ink-jet printer, is equipped with a liquid ejecting head that ejects a liquid such as ink in the form of droplets. The position where a droplet ejected from a liquid ejecting head lands on to a medium, which is the target of printing, sometimes deviates from a desired position due to a manufacturing error or the like, resulting in a decrease in image quality. In related art, for example, as disclosed in JP-A-2007-021807, a deviation in the landing position, on a reference plane, of a droplet ejected from each nozzle is measured. 
     In the method disclosed in JP-A-2007-021807, a test pattern is printed on the recording surface of a medium that serves as a reference, and, based on the result of printing, the amount of deviation in landing position is calculated. 
     In the method disclosed in JP-A-2007-021807, the deviation in landing position is merely measured for each nozzle and, therefore, it is impossible to tell whether the deviation in landing position is unique to a certain particular nozzle or is common to a plurality of nozzles. For this reason, when the deviation in landing position is common to the plurality of nozzles, complex processing such as controlling ejection from each nozzle individually is performed for the purpose of correcting the deviation in landing position, despite the fact that a simple method of adjusting the mount state of the liquid ejecting head suffices for the correction. Consequently, in related art, the processing load of a system will be heavy, and it is impossible to correct the deviation in landing position accurately. 
     SUMMARY 
     A liquid ejecting apparatus according to a certain aspect of the present disclosure includes: a liquid ejecting head in which a plurality of nozzles for ejecting a liquid as droplets are arranged; a first acquisition unit that acquires position information about positions of droplets ejected from the plurality of nozzles and traveling in air; and a second acquisition unit that acquires, based on the position information, deviation information about a deviation in droplet landing position from a reference position on a reference plane, for droplets ejected from at least two nozzles among the plurality of nozzles; wherein the position information includes first position information about a position, at a first timing, of a droplet ejected from a first nozzle, which is one of the plurality of nozzles, and traveling in air, and second position information about a position, at the first timing, of a droplet ejected from a second nozzle, which is one of the plurality of nozzles N and is different from the first nozzle, and traveling in air. 
     Another aspect of the present disclosure is an inspection method for inspecting a liquid ejecting head in which a plurality of nozzles for ejecting a liquid as droplets are arranged, comprising: a first acquisition step of acquiring, as position information about positions of droplets ejected from the plurality of nozzles and traveling in air, first position information about a position, at a first timing, of a droplet ejected from a first nozzle, which is one of the plurality of nozzles, and traveling in air, and second position information about a position, at the first timing, of a droplet ejected from a second nozzle, which is one of the plurality of nozzles N and is different from the first nozzle, and traveling in air; and a second acquisition step of acquiring, based on the position information, deviation information about a deviation in droplet landing position from a reference position on a reference plane, for droplets ejected from at least two nozzles among the plurality of nozzles. 
     Another aspect of the present disclosure is a non-transitory computer-readable storage medium storing an inspection program for inspecting a liquid ejecting head in which a plurality of nozzles for ejecting a liquid as droplets are arranged, the inspection program causing a computer to execute functions comprising: a first acquisition function of acquiring, as position information about positions of droplets ejected from the plurality of nozzles and traveling in air, first position information about a position, at a first timing, of a droplet ejected from a first nozzle, which is one of the plurality of nozzles, and traveling in air, and second position information about a position, at the first timing, of a droplet ejected from a second nozzle, which is one of the plurality of nozzles N and is different from the first nozzle, and traveling in air; and a second acquisition function of acquiring, based on the position information, deviation information about a deviation in droplet landing position from a reference position on a reference plane, for droplets ejected from at least two nozzles among the plurality of nozzles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of the configuration of a liquid ejecting apparatus according to a first embodiment. 
         FIG. 2  is a block diagram that illustrates the electric configuration of the liquid ejecting apparatus according to the first embodiment. 
         FIG. 3  is a flowchart illustrating the flow of an inspection method according to the first embodiment. 
         FIG. 4  is a schematic diagram for explaining an imaging unit. 
         FIG. 5  is a diagram for explaining position information and deviation information. 
         FIG. 6  is a schematic view of the configuration of a liquid ejecting apparatus according to a second embodiment. 
         FIG. 7  is a diagram for explaining an inspection method according to a third embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     With reference to the accompanying drawings, some preferred embodiments of the present disclosure will now be described. The dimensions and scales of components illustrated in the drawings may be different from actual dimensions and scales, and some components may be schematically illustrated for easier understanding. The scope of the present disclosure shall not be construed to be limited to these specific examples unless and except where the description below contains an explicit mention of limiting the present disclosure. 
     To facilitate the readers&#39; understanding, the description below will be given with reference to X, Y, and Z axes intersecting with one another. In the description below, one direction along the X axis will be referred to as the X1 direction, and the direction that is the opposite of the X1 direction will be referred to as the X2 direction. Similarly, directions that are the opposite of each other along the Y axis will be referred to as the Y1 direction and the Y2 direction. Directions that are the opposite of each other along the Z axis will be referred to as the Z1 direction and the Z2 direction. View in the direction along the Z axis may be referred to as “plan view”. 
     Typically, the Z axis is a vertical axis, and the Z2 direction corresponds to a vertically downward direction. However, the Z axis does not necessarily have to be a vertical axis. The X, Y, and Z axes are typically orthogonal to one another, but are not limited thereto. It is sufficient as long as the X, Y, and Z axes intersect with one another within an angular range of, for example, 80° or greater and 100° or less. 
     1. First Embodiment 
     1-1. Overall Configuration of Liquid Ejecting Apparatus 
       FIG. 1  is a schematic view of the configuration of a liquid ejecting apparatus  100  according to a first embodiment. The liquid ejecting apparatus  100  is an ink-jet-type printing apparatus that ejects droplets of ink, which is an example of a liquid, onto a medium M. A typical example of the medium M is printing paper. The medium M is not limited to printing paper. The medium M may be a print target made of any material such as, for example, a resin film or a cloth. 
     As illustrated in  FIG. 1 , a liquid container  10  that contains ink is attached to the liquid ejecting apparatus  100 . Some specific examples of the liquid container  10  are: a cartridge that can be detachably attached to the liquid ejecting apparatus  100 , a bag-type ink pack made of a flexible film material, an ink tank which can be refilled with ink, etc. Any type of ink may be contained in the liquid container  10 . 
     The liquid ejecting apparatus  100  includes a control unit  20 , a transport mechanism  30 , a movement mechanism  40 , a liquid ejecting head  50 , an imaging device  60 , which is an example of “an imaging unit”, and a display device  70 , which is an example of “a notification unit”. 
     The control unit  20  is a computer that controls the operation of each component of the liquid ejecting apparatus  100 . The control unit  20  includes a processing circuit, for example, a CPU (central processing unit) or an FPGA (field programmable gate array), and a storage circuit such as a semiconductor memory. The control unit  20  will be described in detail later with reference to  FIG. 2 . 
     The transport mechanism  30  transports the medium M in the Y2 direction under the control of the control unit  20 . The movement mechanism  40  reciprocates the liquid ejecting head  50  in the X1 direction and the X2 direction under the control of the control unit  20 . In the example illustrated in  FIG. 1 , the movement mechanism  40  includes a carriage  41 , which has a shape like a box and houses the liquid ejecting head  50 , and a transportation belt  42 , to which the carriage  41  is fixed. The carriage  41  is an example of “a mounting unit”. In the illustrated example, the number of the liquid ejecting head  50  mounted on the carriage  41  is one, but not limited thereto. Two or more liquid ejecting heads  50  may be mounted. In addition to the liquid ejecting head(s)  50 , the liquid container(s)  10  mentioned above may be mounted on the carriage  41 . 
     Under the control of the control unit  20 , the liquid ejecting head  50  ejects, in the form of droplets from each of a plurality of nozzles N toward the medium M in the Z2 direction, ink supplied from the liquid container  10 . The droplet ejection is performed in parallel with the transportation of the medium M by the transport mechanism  30  and with the reciprocation of the liquid ejecting head  50  by the movement mechanism  40 . As a result of this concurrent execution of the droplet ejection, the medium transportation, and the head reciprocation, an image is formed by ink on the surface of the medium M. 
     In the present embodiment, the nozzles N of the liquid ejecting head  50  are arranged in the direction along the Y axis. In the example illustrated in  FIG. 2 , the plurality of nozzles N is made up of a row La and a row Lb, which are arranged next to each other, with an interval in the direction along the X axis therebetween. Each of the row La and the row Lb is a group of nozzles N arranged linearly in the direction along the Y axis. The number of the nozzles N of the liquid ejecting head  50  is not limited. Either the row La or the row Lb may be omitted. 
     Though not illustrated, the liquid ejecting head  50  includes a plurality of cavities each of which is provided individually for the corresponding one of the plurality of nozzles N, a plurality of piezoelectric elements each of which is provided individually for the corresponding one of the plurality of nozzles N, and a drive circuit configured to supply drive pulses to the plurality of piezoelectric elements. Each of the plurality of cavities contains ink. The plurality of piezoelectric elements mentioned here corresponds to a plurality of piezoelectric elements  51  illustrated in  FIG. 2 , which will be described later. Receiving the drive pulse supplied from the drive circuit, each of the plurality of piezoelectric elements changes the internal pressure of the corresponding cavity, and, as a result of this pressure change, ink is ejected from the nozzle N corresponding to the cavity. The drive circuit mentioned here corresponds to a drive circuit  52  illustrated in  FIG. 2 , which will be described later. 
     The liquid ejecting head  50  having the structure described above can be manufactured by, for example, preparing a plurality of substrates such as silicon substrates that have been treated by etching, etc., and then bonding these substrates together by means of an adhesive. The piezoelectric elements are obtained by, for example, forming an electrode material and a piezoelectric material into films. Instead of the piezoelectric element, a heater that heats ink inside the cavity may be used as a driving element for ejecting ink from the nozzle N. 
     The imaging device  60  is a camera configured to, under the control of the control unit  20 , capture an image of a droplet that has been ejected from the liquid ejecting head  50  and is traveling in air. The imaging device  60  includes, for example, an imaging optical system and an imaging element. The imaging optical system is an optical system that includes at least one imaging lens. The imaging optical system may include various kinds of optical element such as a prism. The imaging optical system may include a zoom lens or a focus lens, etc. The imaging element is, for example, a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary MOS) image sensor, or the like. 
     In the present embodiment, the imaging device  60  is provided at a position on the X2-directional side with respect to the area of movement of the liquid ejecting head  50  by the movement mechanism  40 . In the present embodiment, the imaging device  60  captures, in the X1 direction, an image of a droplet having been ejected from the liquid ejecting head  50  located at the position shown by alternate-long-and-two-short-dashes-line illustration in  FIG. 1 . A more detailed explanation of the capturing of an image of a droplet by the imaging device  60  will be given later. 
     The display device  70  is a device that performs various kinds of display under the control of the control unit  20 . More specifically, the display device  70  displays various kinds of information, for example, information for performing printing by the liquid ejecting apparatus  100 . For example, the display device  70  is a device that includes any of various kinds of display panel such as a liquid crystal display panel, an organic EL (electro-luminescence) display panel, or the like. 
     1-2. Electric Configuration of Liquid Ejecting Apparatus 
       FIG. 2  is a block diagram that illustrates the electric configuration of the liquid ejecting apparatus  100  according to the first embodiment. In  FIG. 2 , among the components of the liquid ejecting apparatus  100  described above, those that relate to its electric configuration are illustrated. 
     As illustrated in  FIG. 2 , the control unit  20  includes a power source circuit  21 , a drive signal generation circuit  22 , a storage circuit  23 , and a processing circuit  24 . The storage circuit  23  is an example of “a storage unit”. 
     The power source circuit  21  receives supply of external power from a commercial power source that is not illustrated, and generates various voltages having predetermined levels. The various voltages generated by the power source circuit  21  are supplied to the components, etc. of the liquid ejecting apparatus  100 . For example, the power source circuit  21  generates a power voltage VHV and an offset voltage VBS. The offset voltage VBS is supplied to the liquid ejecting head  50 , etc. The power voltage VHV is supplied to the drive signal generation circuit  22 , etc. 
     The drive signal generation circuit  22  is a circuit that generates a drive signal Com for driving each piezoelectric element  51  of the liquid ejecting head  50 . Specifically, the drive signal generation circuit  22  includes, for example, a DA conversion circuit and an amplification circuit. In the drive signal generation circuit  22 , the DA conversion circuit converts the format of a waveform specifying signal dCom supplied from the processing circuit  24  from a digital signal format into an analog signal format, and the amplification circuit generates the drive signal Com by amplifying the analog signal by using the power voltage VHV supplied from the power source circuit  21 . The waveform specifying signal dCom will be described later. A signal having, of the waveform included in the drive signal Com, a waveform supplied actually to the piezoelectric element  51  serves as a drive pulse PD. 
     The storage circuit  23  stores various programs that are to be run by the processing circuit  24  and various kinds of data such as print data that are to be processed by the processing circuit  24 . The storage circuit  23  includes, for example, one semiconductor memory that is either one of a volatile memory and a nonvolatile memory, or semiconductor memories constituted by both thereof. The volatile memory is, for example, a random-access memory (RAM), and the nonvolatile memory is, for example, a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), or a programmable ROM (PROM). The storage circuit  23  may be configured as a part of the processing circuit  24 . 
     An inspection program PG, position information DP, and deviation information DE are stored in the storage circuit  23 . The inspection program PG is a program that causes the control unit  20  to execute an inspection method that will be described later. 
     The position information DP is information about the positions of droplets ejected from a plurality of nozzles N of the liquid ejecting head  50  and traveling in air. Specifically, the position information DP includes first position information DP 1 , second position information DP 2 , and third position information DP 3 . 
     The first position information DP 1  is information about the position, at a first timing, of a droplet ejected from a first nozzle, which is one of the plurality of nozzles N, and traveling in air. The second position information DP 2  is information about the position, at the first timing, of a droplet ejected from a second nozzle, which is one of the plurality of nozzles N and is different from the first nozzle, and traveling in air. The third position information DP 3  is information about the position, at a second timing later than the first timing, of the droplet ejected from the first nozzle and traveling in air. 
     In the position information DP described above, for example, as illustrated in  FIG. 5 , which will be described later, the position of each droplet is expressed either using the coordinate value of a real-space coordinate system or using the coordinate value of a camera coordinate system associated with the real-space coordinate system on the imaging device  60 . These coordinate systems are set based on a reference plane, which will be described later, or a plane corresponding to the reference plane. The data format of the position information DP is not specifically limited. Namely, the position information DP may have any data format. The position information DP may include information about the position, at any other timing different from the first timing and different from the second timing, of the droplet traveling in air and/or information about the position of a droplet ejected from any other nozzle different from the first nozzle and different from the second nozzle and traveling in air, in addition to the first position information DP 1 , the second position information DP 2 , and the third position information DP 3  described above. 
     The deviation information DE is information about a deviation in droplet landing position from a reference position on the reference plane, for droplets ejected from at least two nozzles among the plurality of nozzles of the liquid ejecting head  50 . The reference plane is a plane set along the surface of the medium M or set along an extensional plane of it. For example, the reference plane is a plane B illustrated in  FIG. 5 , which will be described later. The reference plane may be the surface of the medium M, may be the surface of another object, which is not the medium M, or may be a virtual plane set in a space. The reference position is an ideal landing position of a droplet ejected from each nozzle N onto the reference plane. For example, the reference position is a position P 0 _ a  or a position P 0 _ b  illustrated in  FIG. 5 , which will be described later. The landing position is a position where a droplet ejected from each nozzle N actually lands onto the reference plane, or an estimated position of it. For example, the landing position is a position P 1 _ a  or a position P 1 _ b  illustrated in  FIG. 5 , which will be described later. In the description below, the reference position P 0 _ a  and the reference position P 0 _ b  may be referred to as “reference position P 0 ” without making a distinction therebetween. Similarly, the landing position P 1 _ a  and the landing position P 1 _ b  may be referred to as “landing position P 1 ” without making a distinction therebetween. 
     In the present embodiment, the deviation information DE includes common error information DE 1 , individual error information DE 2 , and identifying information DE 3 . 
     The common error information DE 1  is information about an error that is common to any two nozzles N among the plurality of nozzles N such as an angle of inclination θ 2 , which will be described later. The two nozzles N mentioned here are, for example, a first nozzle N_a and a second nozzle N_b, which will be described later. An example of this error is a mount error of the liquid ejecting head  50  mounted on the carriage  41 . The data format of the common error information DE 1  may be any format as long as it is possible to show a relationship between the two nozzles and the error. 
     The individual error information DE 2  is information about an error that is not common to the two nozzles N such as an angle of inclination θ 1 , which will be described later. An example of this error is each individual manufacturing error of the two nozzles N. The data format of the individual error information DE 2  may be any format as long as it is possible to show a relationship between each of the two nozzles and the error. 
     The identifying information DE 3  is information for identifying one nozzle N whose error indicated by the individual error information DE 2  is greater than the other of the two nozzles N. The data format of the identifying information DE 3  may be any format as long as it is possible to identify the nozzle N whose error is not less than a predetermined value. 
     In the deviation information DE described above, for example, as illustrated in  FIG. 5 , which will be described later, each error described above and the landing positions are expressed as amounts in the real-space coordinate system or amounts in the camera coordinate system associated with the real-space coordinate system on the imaging device  60 . 
     The processing circuit  24  has a function of controlling the operation of each component of the liquid ejecting apparatus  100  and a function of processing various kinds of data. The processing circuit  24  includes one or more processors such as, for example, such as CPU (Central Processing Unit). Instead of the CPU or in addition to the CPU, the processing circuit  24  may include a programmable logic device such as FPGA (field-programmable gate array). 
     The processing circuit  24  controls the operation of each component of the liquid ejecting apparatus  100  by running a program stored in the storage circuit  23 . As signals for controlling the operation of the components of the liquid ejecting apparatus  100 , the processing circuit  24  generates control signals Sk 1 , Sk 2 , and SI and a waveform specifying signal dCom, etc. 
     The control signal Sk 1  is a signal for controlling the driving of the transport mechanism  30 . The control signal Sk 2  is a signal for controlling the driving of the movement mechanism  40 . The control signal SI is a signal for controlling the driving of the drive circuit  52 . Specifically, for each predetermined unit period, the control signal SI specifies whether or not the drive circuit  52  should supply, as the drive pulse PD to the liquid ejecting head  50 , the drive signal Com received from the drive signal generation circuit  22 . By this means, for example, the amount of ink that is to be ejected from the liquid ejecting head  50  is specified. The waveform specifying signal dCom is a digital signal for specifying the waveform of the drive signal Com that is generated by the drive signal generation circuit  22 . 
     Based on the control signal SI, for each of the plurality of piezoelectric elements  51 , the drive circuit  52  switches whether or not to supply at least a part of the waveform included in the drive signal Com as the drive pulse PD. 
     The processing circuit  24  reads the inspection program PG out of the storage circuit  23  and runs the read program. By running this program, the processing circuit  24  behaves as a first acquisition unit  24   a , a second acquisition unit  24   b , a first control unit  24   c , a second control unit  24   d , a third control unit  24   e , a fourth control unit  24   f , and a fifth control unit  24   g.    
     The first acquisition unit  24   a  has “a first acquisition function” of acquiring the position information DP. Specifically, the first acquisition unit  24   a  acquires the position information DP by using an image recognition technique, etc. based on the result of image capturing by the imaging device  60 . The acquisition of the position information DP will be described in detail later with reference to  FIG. 5 . 
     The second acquisition unit  24   b  has “a second acquisition function” of acquiring, based on the position information DP, the deviation information DE. More specifically, based on the first position information DP 1  and the second position information DP 2 , the second acquisition unit  24   b  acquires the common error information DE 1 . In addition, based on the first position information DP 1  and the third position information DP 3 , the second acquisition unit  24   b  acquires the individual error information DE 2 . The acquisition of the deviation information DE will be described in detail later with reference to  FIG. 5 . 
     Based on the common error information DE 1 , the first control unit  24   c  causes the display device  70  to notify the user of information for reducing the error indicated by the common error information DE 1 . More specifically, for example, the first control unit  24   c  determines whether the error indicated by the common error information DE 1  is not less than a predetermined value or not, and, if this error is not less than the predetermined value, the first control unit  24   c  causes the display device  70  to display a message, etc. saying that the mount state of the liquid ejecting head  50  mounted on the carriage  41  needs to be adjusted or corrected. In the present embodiment, this notification is performed by performing display by the display device  70 . However, the method of the notification is not limited to display. For example, voice notification may be used. 
     Based on the common error information DE 1 , the second control unit  24   d  limits the use of the liquid ejecting head  50 . More specifically, for example, the second control unit  24   d  determines whether the error indicated by the common error information DE 1  is not less than a predetermined value or not, and, if this error is not less than the predetermined value, the second control unit  24   d  causes the liquid ejecting head  50  to stop. The phrase “limits the use of the liquid ejecting head  50 ” is a concept that includes narrowing the available range of operation of the liquid ejecting head  50 , not limited to causing the liquid ejecting head  50  to stop. The use of the liquid ejecting head  50  may be permitted or prohibited depending on the type of an image that is to be printed or the required quality of an image, etc.; for example, the use of the liquid ejecting head  50  may be limited such that the printing of a high-definition image such as a photo is prohibited although the printing of a simple solid-color image is permitted. 
     Based on the individual error information DE 2 , the third control unit  24   e  causes the liquid ejecting head  50  to perform complementary droplet ejection by using another nozzle N, which is selected from among the plurality of nozzles N, in place of the nozzle N whose error indicated by the individual error information DE 2  is not less than a predetermined value among the plurality of nozzles N of the liquid ejecting head  50 . More specifically, the third control unit  24   e  determines for a predetermined nozzle N among the plurality of nozzles N whether or not its error indicated by the individual error information DE 2  is not less than a predetermined value, and performs this determination for each of the plurality of nozzles N; then, if there exists any nozzle N whose error is not less than the predetermined value, the third control unit  24   e  causes the liquid ejecting head  50  to perform complementary droplet ejection by using another nozzle N, which is selected from among the plurality of nozzles N, instead without using this error nozzle N. In the complementary droplet ejection, the timing, etc. of ejection from said another nozzle N is adjusted such that the droplet ejected from said another nozzle N will land onto the position where the droplet from the error nozzle N that is not used were supposed to land. 
     Based on the individual error information DE 2 , the fourth control unit  24   f  causes the storage circuit  23  to store the identifying information DE 3  for identifying the nozzle N whose error indicated by the individual error information DE 2  is not less than a predetermined value among the plurality of nozzles N of the liquid ejecting head  50 . More specifically, based on the individual error information DE 2 , the fourth control unit  24   f  determines for a predetermined nozzle N among the plurality of nozzles N whether or not its error indicated by the individual error information DE 2  is not less than a predetermined value, performs this determination for each of the plurality of nozzles N, and causes the storage circuit  23  to store the result of this determination as the identifying information DE 3 . 
     Based on the individual error information DE 2 , the fifth control unit  24   g  changes the waveform of the drive pulse PD. More specifically, based on the individual error information DE 2 , the fifth control unit  24   g  determines for a predetermined nozzle N among the plurality of nozzles N whether or not its error indicated by the individual error information DE 2  is not less than a predetermined value, and performs this determination for each of the plurality of nozzles N; then, if there exists any nozzle N whose error is not less than the predetermined value, the fifth control unit  24   g  changes the waveform of the drive pulse PD corresponding to this error nozzle N such that the error will be reduced. 
     1-3. Inspection Method 
       FIG. 3  is a flowchart illustrating the flow of an inspection method according to the first embodiment. The inspection method is executed using the liquid ejecting apparatus  100  described above. As illustrated in  FIG. 3 , the liquid ejecting apparatus  100  executes a first acquisition step S 1 , a second acquisition step S 2 , and a post-processing step S 3  in this order. 
     In the first acquisition step S 1 , the position information DP is acquired. This acquisition is performed by the first acquisition unit  24   a  described above. 
     In the second acquisition step S 2 , the deviation information DE is acquired based on the position information DP. This acquisition is performed by the second acquisition unit  24   b  described above. 
     In the post-processing step S 3 , various processing based on the deviation information DE is performed. This step is executed by at least one of the first control unit  24   c , the second control unit  24   d , the third control unit  24   e , the fourth control unit  24   f , and the fifth control unit  24   g  described above. That is, in the post-processing step S 3 , at least one of the following kinds of processing is executed: notification by the first control unit  24   c , use limitation by the second control unit  24   d , complementary droplet ejection by the third control unit  24   e , storing the identifying information DE 3  by the fourth control unit  24   f , and changing the drive pulse PD by the fifth control unit  24   g . It suffices to execute the post-processing step S 3  if needed. The post-processing step S 3  may be omitted. 
     In the inspection method described above, based on the result of image capturing by the imaging device  60 , the first acquisition unit  24   a  acquires the position information DP in the first acquisition step S 1 . 
       FIG. 4  is a schematic diagram for explaining the imaging device  60 . As illustrated in  FIG. 4 , the imaging device  60  captures an image of a droplet DR of ink ejected from the nozzle N of the liquid ejecting head  50  and traveling in air, in an image-capturing direction that is orthogonal to or intersects with the direction in which the droplet DR is ejected. In the present embodiment, the imaging device  60  captures the image in a direction intersecting with the Y1 direction or the Y2 direction, in which the nozzles N described earlier are arranged. In the example illustrated in  FIG. 4 , the image-capturing direction is the X1 direction. 
     In the example illustrated in  FIG. 4 , the liquid ejecting head  50  includes a nozzle substrate  53 . The nozzle N is a through hole going from one surface to the opposite surface of the nozzle substrate  53 . In ordinary installation, a nozzle surface  53   a , which is one of these two surfaces of the nozzle substrate  53  and faces in the Z2 direction, is parallel to the print target surface of the medium M described earlier. 
     The droplet DR is a main droplet ejected from the nozzle N. Actually, in addition to the droplet DR, a sub droplet(s) called as a satellite, which is generated secondarily to follow the droplet DR as caused by the generation of the droplet DR, is ejected from the nozzle N. The satellite droplet is smaller in diameter than the main droplet DR. Whether the satellite droplet is generated or not, the number of droplets, the size thereof, and the like, differ depending on the type of ink, the waveform of the drive pulse PD, and the like. 
     The imaging device  60  captures an image of the droplet DR traveling in air either continuously or at very short capturing time intervals intermittently. Based on the result of image capturing, it is possible to measure the position of the droplet DR each at predetermined timing and to measure the ejection direction, the ejection speed, or the landing position of the droplet DR based on the positions at the plurality of timing. 
     However, capturing an image of a droplet DR ejected from only one nozzle N by the imaging device  60  is not enough to determine whether the measured landing position, etc. is influenced by a tilt in the mount orientation of the liquid ejecting head  50  or not when the liquid ejecting head  50 , which is not supposed to be tilted, is mounted in a tilted state due to a mount error, etc. 
     For a solution, the liquid ejecting apparatus  100  operates as follows. The imaging device  60  image-captures droplets DR ejected from a plurality of nozzles N at predetermined capturing timing. Based on the result of image capturing, the position information DP is acquired. Then, based on the position information DP, the deviation information DE is acquired as information that makes it possible to determine whether the measured landing position, etc. is influenced by a tilt in the mount orientation of the liquid ejecting head  50  or not. 
       FIG. 5  is a diagram for explaining the position information DP and the deviation information DE. 
     Illustrated in  FIG. 5  is the state, at each timing, of the droplets DR ejected toward the reference plane B from the first nozzle N_a and the second nozzle N_b that are any two of the plurality of nozzles N of the liquid ejecting head  50 . In  FIG. 5 , it is assumed that the ejection direction of the droplet DR ejected from the first nozzle N_a is normal, whereas the ejection direction of the droplet DR ejected from the second nozzle N_b is deviated from the normal direction. In the example illustrated in  FIG. 5 , the reference plane B is a plane that is perpendicular to the Z axis. In  FIG. 5 , for easier illustration, the first nozzle N_a and the second nozzle N_b are located next to each other. However, one or more nozzles N may exist between the first nozzle N_a and the second nozzle N_b. 
     Each of a droplet DR_a 1 , a droplet DR_a 2 , and a droplet DR a 3  illustrated in  FIG. 5  depicts the droplet DR ejected from the first nozzle N_a. The droplet DR_a 1  is the droplet DR traveling in air at a first timing after having been ejected from the first nozzle N_a. The droplet DR_a 2  is the droplet DR traveling in air at a second timing later than the first timing after having been ejected from the first nozzle N_a. The droplet DR a 3  is the droplet DR traveling in air at a third timing later than the second timing after having been ejected from the first nozzle N_a. The droplet DR_a 1 , the droplet DR_a 2 , and the droplet DR a 3  may be an identical droplet DR with different timing from one another, or may be droplets DR with different points in time of ejection from one another. 
     The “first timing” is a timing that is within a period from the start of applying the drive pulse PD to the piezoelectric element  51  corresponding to the nozzle N of interest to the landing of the droplet DR ejected from the nozzle N of interest onto the reference plane B, and is a timing of the lapse of predetermined time since the start of applying the drive pulse PD. In the example illustrated in  FIG. 5 , the “first timing” is a timing that is immediately after the ejection of the droplet DR from the nozzle N. The phrase “immediately after” mentioned here means that the time that has elapsed since the start of applying the drive pulse PD is 0.1 μs or less. 
     The “second timing” is a timing that is within a period from the start of applying the drive pulse PD to the piezoelectric element  51  corresponding to the nozzle N of interest to the landing of the droplet DR ejected from the nozzle N of interest onto the reference plane B, and is a timing later than the first timing of the lapse of predetermined time since the start of applying the drive pulse PD. The time interval between the first timing and the second timing is, for example, a few μs or so. 
     The “third timing” is a timing that is within a period from the start of applying the drive pulse PD to the piezoelectric element  51  corresponding to the nozzle N of interest to the landing of the droplet DR ejected from the nozzle N of interest onto the reference plane B, and is a timing later than the second timing of the lapse of predetermined time since the start of applying the drive pulse PD. The time interval between the second timing and the third timing is, for example, a few μs or so. 
     Similarly, each of a droplet DR_b 1 , a droplet DR_b 2 , and a droplet DR_b 3  illustrated in  FIG. 5  depicts the droplet DR ejected from the second nozzle N_b. The droplet DR_b 1  is the droplet DR traveling in air at a first timing after having been ejected from the second nozzle N_b. The droplet DR_b 2  is the droplet DR traveling in air at a second timing later than the first timing after having been ejected from the second nozzle N_b. The droplet DR_b 3  is the droplet DR traveling in air at a third timing later than the second timing after having been ejected from the second nozzle N_b. 
     In the example illustrated in  FIG. 5 , the position of each droplet DR described above is expressed in terms of a coordinate value in an orthogonal coordinate system defined by the Y axis and the Z axis. The position of the droplet DR_a 1  is expressed as a coordinate (Y_a 1 , Z_a 1 ). The position of the droplet DR_a 2  is expressed as a coordinate (Y_a 2 , Z_a 2 ). The position of the droplet DR a 3  is expressed as a coordinate (Y_a 3 , Z_a 3 ). The position of the droplet DR_b 1  is expressed as a coordinate (Y_b 1 , Z_b 1 ). The position of the droplet DR_b 2  is expressed as a coordinate (Y_b 2 , Z_b 2 ). The position of the droplet DR_b 3  is expressed as a coordinate (Y_b 3 , Z_b 3 ). 
     The angle of inclination θ 2  of the nozzle surface  53   a  with respect to the reference plane B is calculated based on the positions at the same timing of droplets DR ejected from two nozzles different from one another. For example, the angle of inclination θ 2  is calculated using the following relational expression (1): 
       tan θ2=(Δ Zα/ΔY α)  (1),
 
     where ΔZα is |Z_b 1 −Z_a 1 |, and ΔYα is |Y_b 1 −Y_a 1 |. 
     The angle of inclination θ 1  of the actual ejection direction of the droplet DR with respect to the ideal ejection direction thereof, namely, the angle formed by a normal line LN that is normal to the nozzle surface  53   a  and a straight line going in the actual ejection direction, is calculated based on the positions at two different timing of the droplet DR ejected from the identical nozzle N. For example, the angle of inclination θ 1  is calculated using the following relational expression (2): 
       tan(θ1+θ2)=(Δ Zβ/ΔY β)  (2),
 
     where, for the first nozzle N_a, ΔZβ is |Z_a 2 −Z_a 1 |, and ΔYβ is |Y_a 2 −Y_a 1 |, and, for the second nozzle N_b, ΔZβ is |Z_b 2 −Z_b 1 |, and ΔYβ is |Y_b 2 −Y_b 1 |. In  FIG. 5 , ΔZβ and ΔYβ for the first nozzle N_a are illustrated. It should be noted that ΔYβ and ΔZβ are not limited to a difference between the position at the first timing and the position at the second timing. For example, ΔYβ and ΔZβ may be a difference between the position at the first timing and the position at the third timing or a difference between the position at the second timing and the position at the third timing. 
     The amount of deviation in the landing position P 1  of the droplet DR from the reference position P 0  on the reference plane B can be expressed as VT sin(θ 1 +θ 2 ). In this expression, V denotes the initial velocity of the droplet DR having been ejected. In this expression, T denotes the length of time from the ejection of the droplet DR from the nozzle N to the landing of the droplet DR onto the reference plane B. To be exact, due to a tilt, there is a difference between the distance to the reference plane B in the Z direction for the first nozzle N_a and the distance to the reference plane B in the Z direction for the second nozzle N_b and, therefore, there is a difference between the length of time T taken for the first nozzle N_a and the length of time T taken for the second nozzle N_b. However, the difference between the length of time T taken for the first nozzle N_a and the length of time T taken for the second nozzle N_b is negligible because, actually, the distance between the liquid ejecting head  50  and the medium M in the Z direction is set to be very short. Since gravitational acceleration does not act on the droplet DR in the horizontal direction, for the first nozzle N_a, the ejection direction of the droplet DR is normal and, accordingly, the amount of deviation in the landing position P 1 _ a  from the reference position P 0 _ a  can be calculated by VT sin θ 2 , which is a product of V sin θ 2  and the length of time T, wherein V sin θ 2  is the Y-directional component of the initial velocity of the ejection from the first nozzle N_a. By contrast, for the second nozzle N_b, the ejection direction of the droplet DR is deviated from the normal direction and, therefore, the amount of deviation in the landing position P 1 _ b  from the reference position P 0 _ b  can be calculated by VT sin(θ 1 +θ 2 ), which is a product of V sin(θ 1 +θ 2 ) and the length of time T, wherein V sin(θ 1 +θ 2 ) is the Y-directional component of the initial velocity of the ejection from the second nozzle N_b. 
     As will be understood from the above description, in the first acquisition step S 1 , information about the positions of the droplets DR needed for calculating the angle of inclination θ 1  and the angle of inclination θ 2  described above is acquired as the position information DP. In the second acquisition step S 2 , based on the position information DP, the angle of inclination θ 1  and the angle of inclination θ 2  are calculated, and the deviation information DE is acquired using the calculation results. 
     As explained above, the liquid ejecting apparatus  100  includes the liquid ejecting head  50 , the first acquisition unit  24   a , and the second acquisition unit  24   b . In the liquid ejecting head  50 , the plural nozzles N from which ink, as an example of “a liquid”, is ejected in the form of droplets DR are arranged. The first acquisition unit  24   a  acquires the position information DP about the positions of the droplets DR ejected from the plurality of nozzles N and traveling in air. Based on the position information DP, the second acquisition unit  24   b  acquires, for droplets DR ejected from at least two nozzles among the plurality of nozzles N, the deviation information DE about a deviation in the landing position P 1  of the droplet DR from the reference position P 0  on the reference plane B. 
     The position information DP includes the first position information DP 1  and the second position information DP 2 . The first position information DP 1  is information about the position, at the first timing, of the droplet DR ejected from the first nozzle N_a, which is one of the plurality of nozzles N, and traveling in air. The second position information DP 2  is information about the position, at the first timing, of the droplet DR ejected from the second nozzle N_b, which is one of the plurality of nozzles N and is different from the first nozzle N_a, and traveling in air. 
     In the liquid ejecting apparatus  100  described above, the position information DP includes the first position information DP 1  and the second position information DP 2  as information about the positions at the same timing of droplets DR ejected from two nozzles different from one another. Therefore, based on the first position information DP 1  and the second position information DP 2 , it is possible to measure a state such as the angle of inclination θ 2  caused by an error such as a mount error of the liquid ejecting head  50 . This kind of error is common to the plurality of nozzles N. Therefore, by using the measurement result based on the first position information DP 1  and the second position information DP 2 , it is possible to tell whether the deviation in the landing position P 1  of the droplet DR is unique to the particular nozzle N or is common to the plurality of nozzles N. Consequently, suitably for the cause of the deviation in the landing position P 1  of the droplet DR, it is possible to perform processing for improving the quality of an image. For the reason explained above, as compared with related art, it is possible to make the burden of processing performed by the system of the liquid ejecting apparatus  100  lighter, and it is possible to correct the deviation in the landing position P 1  more accurately. 
     As described earlier, the deviation information DE includes the common error information DE 1 , which is information about an error that is common to the first nozzle N_a and the second nozzle N_b. Therefore, based on the common error information DE 1 , it is possible to determine whether an error that is common to the plurality of nozzles N has occurred or not. 
     As described earlier, the liquid ejecting apparatus  100  further includes the carriage  41 , which is an example of “a mounting unit” on which the liquid ejecting head  50  is mounted. The common error information DE 1  includes information about a mount error of the liquid ejecting head  50  mounted on the carriage  41 . Therefore, based on the common error information DE 1 , it is possible to determine whether there is a mount error of the liquid ejecting head  50  mounted on the carriage  41  or not, or, if there is such a mount error, it is possible to determine the degree of the mount error. 
     As described earlier, based on the difference ΔZα and the difference ΔYα, the second acquisition unit  24   b  acquires the common error information DE 1 . In the present embodiment, the difference ΔZα is the difference between the position Z_a 1  indicated by the first position information DP 1  and the position Z_b 1  indicated by the second position information DP 2  in the Z1 direction or the Z2 direction, which is orthogonal to the reference plane B. The difference ΔYα is the difference between the position Y_a 1  indicated by the first position information DP 1  and the position Y_b 1  indicated by the second position information DP 2  in the Y1 direction or the Y2 direction, which is parallel to the reference plane B. It is possible to calculate the angle of inclination θ 2  of the liquid ejecting head  50  by using a trigonometric function based on these differences. 
     The common error information DE 1  described above is used for various kinds of processing in the liquid ejecting apparatus  100  when needed. In the present embodiment, as described earlier, the liquid ejecting apparatus  100  further includes the display device  70 , which is an example of “a notification unit”, and the first control unit  24   c . Based on the common error information DE 1 , the first control unit  24   c  causes the display device  70  to notify the user of information about a mount state of the liquid ejecting head  50 . Therefore, it is possible to prompt the user to adjust or correct the mount state of the liquid ejecting head  50  as the need dictates. Some examples of the information notified by the display device  70  are: information that shows the mount error of the liquid ejecting head  50  quantitatively or qualitatively, information for informing the user that the mount state of the liquid ejecting head  50  needs to be adjusted or corrected, information for informing the user that printing is canceled/aborted or restricted due to the mount error of the liquid ejecting head  50 , and the like. 
     As described earlier, the liquid ejecting apparatus  100  further includes the second control unit  24   d . Based on the common error information DE 1 , the second control unit  24   d  limits the use of the liquid ejecting head  50 . Therefore, it is possible to reduce wasteful ink ejection. 
     As described earlier, the position information DP includes the third position information DP 3 , which is information about the position, at the second timing later than the first timing, of the droplet DR ejected from the first nozzle N_a and traveling in air. Therefore, by using the first position information DP 1  and the third position information DP 3 , it is possible to calculate the deviation in the landing position P 1  of the droplet DR ejected from the first nozzle N_a. Therefore, it is possible to acquire the deviation information DE that includes information about the deviation by the second acquisition unit  24   b.    
     As described earlier, the deviation information DE includes the individual error information DE 2 , which is information about an error that is not common to the first nozzle N_a and the second nozzle N_b. Based on the first position information DP 1  and the third position information DP 3 , the second acquisition unit  24   b  acquires the individual error information DE 2 . 
     As described earlier, the individual error information DE 2  is information about a manufacturing error of the first nozzle N_a or the second nozzle N_b. Therefore, based on the individual error information DE 2 , it is possible to determine whether there is a manufacturing error of the first nozzle N_a or not, there is a manufacturing error of the second nozzle N_b or not, or, if there is such a manufacturing error, it is possible to determine the degree of the manufacturing error. 
     As described earlier, based on the difference ΔZβ and the difference ΔYβ, the second acquisition unit  24   b  acquires the individual error information DE 2 . The difference ΔZβ is the difference between the position Z_a 1  indicated by the first position information DP 1  and the position Z_a 2  indicated by the third position information DP 3  in the Z1 direction or the Z2 direction, which is orthogonal to the reference plane B. The difference ΔYβ is the difference between the position Y_a 1  indicated by the first position information DP 1  and the position Y_a 2  indicated by the third position information DP 3  in the Y1 direction or the Y2 direction, which is parallel to the reference plane B. It is possible to calculate the angle of inclination θ 1  of the ejection direction of the droplet DR ejected from the first nozzle N_a by using a trigonometric function based on these differences. The angle of inclination θ 1  is an angle formed by the normal line LN, which is normal to the nozzle surface  53   a , and the ejection direction of the droplet DR ejected from the liquid ejecting head  50 . 
     In the present embodiment, as described earlier, the first timing is a timing that is immediately after the ejection of the droplet DR from the first nozzle N_a or the second nozzle N_b. Therefore, the droplet DR ejected from the first nozzle N_a or the second nozzle N_b is not susceptible to the influence of an airflow, etc. till reaching the first timing, and, moreover, the angle of inclination θ 2  will have almost no influence on the position of the droplet DR. Advantageously, this makes it easier to increase the precision of the deviation information DE. 
     The individual error information DE 2  described above is used for various kinds of processing in the liquid ejecting apparatus  100  when needed. In the present embodiment, as described earlier, the liquid ejecting apparatus  100  further includes the third control unit  24   e . Based on the individual error information DE 2 , the third control unit  24   e  causes the liquid ejecting head  50  to eject a droplet DR that serves as a complement by using another nozzle N, which is selected from among the plurality of nozzles N, in place of either one of the first nozzle N_a and the second nozzle N_b whose error indicated by the individual error information DE 2  is greater than the other. Therefore, it is possible to suppress a decrease in image quality ascribable uniquely to the nozzle N for which the deviation in the landing position P 1  occurs. 
     As described earlier, the liquid ejecting apparatus  100  further includes the storage circuit  23 , which is an example of “a storage unit”, and the fourth control unit  24   f . Based on the individual error information DE 2 , the fourth control unit  24   f  causes the storage circuit  23  to store the identifying information DE 3  for identifying either one of the first nozzle N_a and the second nozzle N_b whose error indicated by the individual error information DE 2  is greater than the other. Therefore, based on the identifying information DE 3  stored in the storage circuit  23 , it is possible to identify the unique nozzle N for which the deviation in the landing position P 1  occurs. 
     As described earlier, the liquid ejecting apparatus  100  further includes the fifth control unit  24   g . Based on the individual error information DE 2 , the fifth control unit  24   g  changes the waveform of the drive pulse PD for driving the liquid ejecting head  50 . Therefore, it is possible to suppress a decrease in image quality ascribable uniquely to the nozzle N for which the deviation in the landing position P 1  occurs. 
     As described earlier, the liquid ejecting apparatus  100  further includes the imaging device  60 , which is an example of “an imaging unit”. The imaging device  60  captures an image of the droplet DR ejected from the liquid ejecting head  50  and traveling in air, in an image-capturing direction that is parallel to the reference plane B and is orthogonal to the direction in which the plurality of nozzles N are arranged. The image-capturing direction in the present embodiment is orthogonal to the direction in which the medium M is transported. Based on the result of image capturing by the imaging device  60 , the first acquisition unit  24   a  acquires the position information DP. Therefore, it is possible to acquire the position information DP in a suitable manner. 
     2. Second Embodiment 
     A second embodiment of the present disclosure will now be explained. In the exemplary embodiment described below, the same reference numerals as those used in the description of the first embodiment are assigned to elements that are the same in operation or function as those in the first embodiment, and a detailed explanation of them is omitted. 
       FIG. 6  is a schematic view of the configuration of a liquid ejecting apparatus  100 A according to a second embodiment. Except for a difference in the position and orientation of the imaging device  60 , the liquid ejecting apparatus  100 A is the same as the liquid ejecting apparatus  100  according to the first embodiment described earlier. 
     In the present embodiment, the imaging device  60  performs image capturing in a direction that is along the array of the plurality of nozzles N described earlier. In the example illustrated in  FIG. 6 , the image-capturing direction is the Y1 direction. In this image capturing performed by the imaging device  60 , a nozzle N in one of the rows La and Lb corresponds to the first nozzle, and a nozzle N in the other of the rows La and Lb corresponds to the second nozzle. 
     Even if configured as disclosed in the second embodiment above, similarly to the first embodiment described earlier, as compared with related art, the present disclosure makes it possible to make the burden of processing performed by the system of the liquid ejecting apparatus  100  lighter, and it is possible to correct the deviation in the landing position P 1  more accurately. 
     3. Third Embodiment 
     A third embodiment of the present disclosure will now be explained. In the exemplary embodiment described below, the same reference numerals as those used in the description of the first embodiment are assigned to elements that are the same in operation or function as those in the first embodiment, and a detailed explanation of them is omitted. 
       FIG. 7  is a diagram for explaining an inspection method according to a third embodiment. The present embodiment is the same as the first embodiment described earlier, except that a reference device SC is provided behind droplets DR the images of which are to be captured. 
     The reference device SC has scales set based on the nozzle surface  53   a . In the example illustrated in  FIG. 7 , the reference device SC has a plurality of ruler lines perpendicular to the nozzle surface  53   a  and a plurality of ruler lines parallel to the nozzle surface  53   a . These ruler lines constitute a pattern made up of a plurality of squares like a grid sheet. By using the reference device SC described here, it is possible to know the angle of inclination θ 1  based on the result of image capturing by the imaging device  60 , without any need for computing the mount orientation of the liquid ejecting head  50 . 
     Even if configured as disclosed in the third embodiment above, similarly to the first embodiment described earlier, as compared with related art, the present disclosure makes it possible to make the burden of processing performed by the system of the liquid ejecting apparatus  100  lighter, and it is possible to correct the deviation in the landing position P 1  more accurately. The form, pattern, etc. of the reference device SC is not limited to the example illustrated in  FIG. 7 . For example, the reference device SC may be like an L-shaped ruler or a protractor. 
     4. Modification Example 
     The embodiments described as examples above can be modified in various ways. Some specific examples of modification that can be applied to the embodiments described above are described below. Any two or more modification examples selected from the description below may be combined as long as they are not contradictory to each other or one another. 
     4-1. First Modification Example 
     In the foregoing embodiments, each of a first driving element and a second driving element is disclosed as a piezoelectric element. However, the structure of the present disclosure is not limited to such an example. Each of the first driving element and the second driving element may be a heater. That is, the liquid ejecting head is not limited to a piezoelectric-type head, and may be a thermal-type head. 
     4-2. Second Modification Example 
     In the foregoing embodiments, the liquid ejecting apparatus  100  that is a so-called serial-type liquid ejecting apparatus configured to reciprocate the carriage  41  on which the liquid ejecting head  50  is mounted has been described as examples. However, the present disclosure may be applied to a so-called line-type liquid ejecting apparatus in which the plural nozzles N are arranged throughout the entire width of the medium M. 
     4-3. Third Modification Example 
     The liquid ejecting apparatus  100  disclosed as examples in the foregoing embodiments can be applied to not only print-only machines but also various kinds of equipment such as facsimiles and copiers, etc. The scope of application and use of the liquid ejecting apparatus according to the present disclosure is not limited to printing. For example, a liquid ejecting apparatus that ejects a colorant solution can be used as an apparatus for manufacturing a color filter of a liquid crystal display device. A liquid ejecting apparatus that ejects a solution of a conductive material can be used as a manufacturing apparatus for forming wiring lines and electrodes of a wiring substrate. Moreover, the liquid ejecting apparatus of the present disclosure can be used as a 3D printer, used for compounding small amounts of chemical or medical agents, used for cell culturing, used for vaccine production, and so forth. 
     In the foregoing embodiments, no distinction is made between the drive pulse PD that is applied when a liquid is ejected for executing the inspection method illustrated in  FIG. 3  and the drive pulse PD that is applied when a liquid is ejected for printing a real image. However, the drive pulse PD applied for inspection may be configured to be a unique pulse suited for inspection. For example, when an inspection is conducted, the drive pulse PD that applies pressure to a liquid to an extent that a meniscus will not be in contact with the exit of an orifice of the nozzle surface may be used. In other words, this drive pulse PD is a drive pulse for ejecting a very small amount of a liquid, smaller than that of real image printing, having a diameter smaller than the internal diameter of a nozzle. If the drive pulse PD described here is used, it is possible to eject a liquid without being influenced by the wettability (critical surface tension) of the nozzle surface. Therefore, it is possible to inspect a deviation in landing position regardless of a difference in wettability.