Patent Publication Number: US-2023158797-A1

Title: Ejection apparatus and ejection control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 17/335,766, filed Jun. 1, 2021, which claims priority from Japanese Patent Application No. 2020-103905, filed Jun. 16, 2020, which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to an ejection apparatus and an ejection control method. 
     Description of the Related Art 
     In an inkjet-type recording apparatus, continuous usage may cause a change in ejection velocity of ink droplets due to an individual difference among recording apparatuses or recording heads, characteristics of ink, usage conditions, or environmental influences. For example, when an image is recorded by reciprocating scanning of a recording head, the change in ejection velocity of ink droplets changes a relationship between a landing position of an ink droplet ejected in a forward path direction and a landing position of an ink droplet ejected in a return path direction, which influences image quality. 
     Japanese Patent Application Laid-Open No. 2007-152853 discusses a configuration including an optical detector that measures an ejection velocity of ink, and a registration adjusting method for appropriately setting an ejection timing from a moving velocity of a recording head and the ejection velocity based on a result of the measurement. Japanese Patent Application Laid-Open No. 2007-152853 also discusses, as a measurement method for an ink ejection velocity, a technique of measuring a time from a timing at which ink is ejected until a timing at which the ink reaches a light flux emitted from the optical detector, and calculating the ejection velocity based on a result of the measurement and a distance from the record head to the light flux. 
     According to the technique discussed in Japanese Patent Application Laid-Open No. 2007-152853, however, there is a possibility that increasing the number of measurements so as to decrease a measurement error increases a measurement error instead. Consecutively ejecting ink droplets to increase the number of measurements increases an amount of mist separated from main droplets of ink in the surroundings of a measurement environment as illustrated in  FIG.  7 B . Ejecting ink droplets in a state of an increased amount of mist in the surrounding environment promotes separation of the ink droplets into main and satellite droplets, and thereby the main droplets tend to be small in size. Further, there is a case where consecutive ejection inhibits refilling in time, and the main drops of ejected ink become small in size. There is a possibility that such small main droplets decreases an ejection velocity, and thus causes variations in measurement results. 
     SUMMARY 
     The present disclosure is directed to a technique of increasing accuracy in measuring droplets ejected from an ejection apparatus. 
     According to an aspect of the present disclosure, an ejection apparatus includes an ejection head that includes an ejection port configured to eject a droplet, a droplet detection unit configured to detect that the ejected droplet has reached a predetermined position, an acquisition unit configured to acquire information regarding a velocity of movement of the droplet detected by the droplet detection unit, a control unit configured to control the ejection head to eject the droplet from the ejection port, and a decision unit configured to decide a number of consecutive ejections of a plurality of droplets from the ejection head based on the information acquired by the acquisition unit regarding the velocities of each of the plurality of droplets ejected consecutively by the ejection head and detected by the droplet detection unit, and wherein, in a case where the acquisition unit acquires the information regarding velocities of droplets detected by the droplet detection unit, the control unit controls the ejection head to consecutively eject the droplets from the ejection head based on the decided number of consecutive ejections. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an external view of a recording apparatus according to a first exemplary embodiment. 
         FIG.  2    is a perspective view illustrating an internal configuration of the recording apparatus according to the first exemplary embodiment. 
         FIG.  3 A  is a diagram illustrating an internal configuration of a distance detection sensor according to the first exemplary embodiment.  FIG.  3 B  is a diagram illustrating an example of detection according to the first exemplary embodiment. 
         FIG.  4    is a block diagram illustrating a control configuration of the recording apparatus according to the first exemplary embodiment. 
         FIGS.  5 A and  5 B  are schematic diagrams each illustrating a correlation between an ejection velocity of an ink droplet and a landing position of the ink droplet. 
         FIG.  6    is a diagram for explaining a method of calculating an ejection velocity of an ink droplet according to the first exemplary embodiment. 
         FIGS.  7 A and  7 B  are schematic diagrams each illustrating a state of a measurement environment in the surroundings of a recording head and a droplet detection sensor at the time of measuring a detection time. 
         FIGS.  8 A and  8 B  are graphs each indicating a relationship between a detection time and the number of measurements according to the first exemplary embodiment. 
         FIG.  9    is a flowchart for determining a timing to decide a measurement condition according to the first exemplary embodiment. 
         FIG.  10    is a flowchart of measurement condition decision processing according to the first exemplary embodiment. 
         FIG.  11    is a flowchart of processing of ejection velocity calculation processing according to the first exemplary embodiment. 
         FIGS.  12 A to  12 D  are diagrams each illustrating an internal configuration of a distance detection sensor and an example of detection according to a second exemplary embodiment. 
         FIGS.  13 A to  13 D  are diagrams each illustrating detection times and ejection velocities according to the second exemplary embodiment. 
         FIG.  14    is a graph indicating a relationship between a detection time and the number of measurements according to a third exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     &lt;Overview of Entire Recording Apparatus&gt; 
       FIG.  1    is an external view of an inkjet recording apparatus (hereinafter referred to as a recording apparatus)  100  as one example of a droplet ejection apparatus according to a first exemplary embodiment. 
     The recording apparatus  100  illustrated in  FIG.  1    includes a sheet-discharge guide  101 , a display panel  103 , and an operation button  102 . Output recording media are stacked on the sheet-discharge guide  101 . The display panel  103  is used for displaying, for example, various kinds of recording information, and setting results. The operation button  102  is used for setting, for example, a recording mode, and recording paper. The recording apparatus  100  further includes an ink tank unit  104  that houses an ink tank containing ink in black, cyan, magenta, yellow, or the like, and that supplies ink to a recording head  201  (illustrated in  FIG.  2   ) as one example of a droplet ejection head. The recording apparatus illustrated in  FIG.  1    is capable of performing recording on recording media having a plurality of widths up to a 60 inch-size. Roll paper, cut paper, and the like can be used as the recording medium. In addition, the recording medium is not limited to paper, and may be a cloth or a sheet of vinyl. 
       FIG.  2    is a perspective view illustrating an internal configuration of the recording apparatus  100 . A platen  212  is a member that supports a recording medium  203  arranged at a position facing the recording head  201 . The recording medium  203  is conveyed by a sheet-conveying roller  213  in a conveying direction (Y-direction) while being supported by the platen  212 . The recording head  201  includes an ejection port surface  201   a  ( FIGS.  5 A and  5 B ) on which an ejection port is formed. An ejection port array in which a plurality of ejection ports is arrayed in the Y-direction is formed for each ink color on the ejection port surface  201   a . Ejection port arrays are arrayed in an X-direction. The recording head  201  is mounted on a carriage  202 . The recording head  201  includes a distance detection sensor  204  for detecting a distance between the recording medium  203  on the platen  212  and the recording head  201 . The distance detection sensor  204 , which is an optical sensor, includes a light-emitting element ( FIG.  3 A ) that emits light onto the recording medium  203 , and a light-receiving element ( FIG.  3 A ) that receives light reflected from the recording medium  203 . The distance detection sensor  204  measures a distance from the output fluctuation of an amount of light received by the light-receiving element. Details of the measurement will be described with reference to  FIGS.  3 A to  3 B . A droplet detection sensor  205  is a sensor that detects droplets, ink droplets in this case, ejected from the recording head  201 . The droplet detection sensor  205  is an optical sensor that includes a light-emitting element  401  ( FIG.  6   ), a light-receiving element  402  ( FIG.  6   ), and a control circuit substrate  403  ( FIG.  6   ). Details of these elements will be described with reference to  FIG.  6   . A main rail  206  supports the carriage  202 , and the carriage  202  performs reciprocating scanning along the main rail  206  in the X-direction (a direction orthogonal to the conveying direction of the recording medium). The carriage  202  performs scanning by being driven by a carriage motor  208  via a carriage conveying belt  207 . A linear scale  209  is arranged in a scanning direction. An encoder sensor  210  mounted on the carriage  202  reads the linear scale  209  to acquire positional information. The recording apparatus  100  includes a lift cam (not illustrated) and a lift motor  211 . The lift cam makes a height of the main rail  206 , which supports the carriage  202 , variable in a stepwise manner, and the lift motor  211  drives the lift cam. Driving the lift cam with the lift motor  211  allows the lift cam to elevate/lower the recording head  201  and decrease/increase a distance between the recording head  201  and the recording medium  203 . The lift motor  211  can make the height of the main rail  206  variable with predetermined accuracy in a plurality of steps based on a stop position of the lift cam, and drives the lift cam such that a variable amount of the height is relative to a height in a predetermined step. It is thus possible to set a varying distance between steps with high accuracy. Below the platen  212 , a mist fan (not illustrated) is arranged. The mist fan generates air currents for collecting mist that is separated from main ink droplets ejected from the recording head  201  and is floating between the recording head  201  and the platen  212 . The mist fan is driven by a fan motor  214  ( FIG.  4   ). The mist fan is driven at the time of a recording operation for recording an image on a recording medium, and then the mist fan collects mist. An installation position of the mist fan is not limited thereto. The installation position is only required to be a position at which the mist fan is moved to such a location as to prevent mist from influencing recording. 
       FIG.  3 A  is a diagram illustrating an internal configuration of the distance detection sensor  204 .  FIG.  3 B  is a diagram illustrating a change of a light amount (output) in accordance with a distance to an irradiation surface of the recording medium  203  in each of an irradiation region and a light-receiving region. As illustrated in  FIG.  3 A , the distance detection sensor  204  incorporates a control substrate  701 , a light-emitting unit  702 , and light-receiving units  703  and  704 . The control substrate executes processing of turning ON a light source to emit light toward a position to which the recording medium  203  is conveyed and processing of turning OFF the light source. The light-emitting unit  702  emits the light. The light-receiving units  703  and  704  receive the light reflected from the recording medium  203 . In the present exemplary embodiment, a surface of the distance detection sensor  204  facing the recording medium  203  is at an identical position in a Z-direction to that of the ejection port surface  201   a  of the recording head  201 . The distance to the recording medium  203  measured by the distance detection sensor  204  therefore corresponds to a distance between the ejection port surface  201   a  of the recording head  201  and the recording medium  203 . The distance detection sensor  204  also converts intensities of the reflected light acquired in the light-receiving units  703  and  704  to output signals indicating current values or voltage values, executes predetermined computation processing on the output signals, and stores a result of the computation in a memory  303 . For example, the distance detection sensor  204  stores distance information data indicating a relationship between a ratio value between the output signals obtained in the light-receiving units  703  and  704  and the distance from the recording head  201  to the recording medium  203 .  FIG.  3 B  illustrates a relationship between the output signals and the distance information data. As illustrated in  FIG.  3 B , when the distance to the irradiation surface of the recording medium  203  is M1, an amount of reflected light received by the light-receiving unit  704  reaches maximum and an amount of reflected light received by the light-receiving unit  703  reaches minimum. Hence, the ratio value between the output signals from the distance detection sensor  204 , i.e., the distance information data, also indicates a minimum value. When the distance to the irradiation surface of the recording medium  203  is M3, respective amounts of reflected light received by the light-receiving units  703  and  704  become approximately half of the corresponding amounts at the peak. As distribution of output from the distance detection sensor, a signal value of the light-receiving unit  703  and that of the light-receiving unit  704  become equal to each other, and thereby the ratio value between the output signals from the distance detection sensor  204 , i.e., the distance information data also indicates a value of 1. When the distance to the irradiation surface of the recording medium  203  is M5, an amount of reflected light received by the light-receiving unit  704  reaches minimum and an amount of reflected light received by the light-receiving unit  703  reaches maximum. As distribution of output from the distance detection sensor  204 , a signal value of the light-receiving unit  704  indicates a minimum value, and a signal value of the light-receiving unit  703  indicates a maximum value, so that the ratio value between the output signals from the distance detection sensor  204 , i.e., the distance information data also indicates a maximum value. Here, the present exemplary embodiment may preliminarily seek a relationship between the position of the irradiation surface serving as a criterion and a proportional value of an output signal from the distance detection sensor  204 , and store the relationship in the memory  303 . For example, a value detected with respect to a recording medium having a predetermined thickness may be held as a criterion value. Furthermore, the position of the recording head  201  when the distance from the recording head  201  to the recording medium  203  is any of M1 to M5 and the distance from the recording head  201  to the droplet detection sensor  205  at this time can also be stored. 
     &lt;Block Diagram&gt; 
       FIG.  4    is a block diagram illustrating a control configuration of the recording apparatus  100 . The recording apparatus  100  includes a central processing unit (CPU)  301 , a sensor/motor control unit  302 , and the memory  303 . The CPU  301  controls the entire recording apparatus  100 . The sensor/motor control unit  302  controls each sensor and each motor. The memory  303  stores therein various kinds of information, such as an ejection velocity and a thickness of a recording medium. The CPU  301 , the sensor/motor control unit  302 , and the memory  303  are connected to be capable of communicating with one another. The sensor/motor control unit  302  controls the distance detection sensor  204 , the droplet detection sensor  205 , the carriage motor  208  that causes the carriage  202  to perform scanning, and the fan motor  214  for driving the mist fan. The sensor/motor control unit  302  controls a head control circuit  305  based on positional information detected by the encoder sensor  210  to eject ink from the recording head  201 . 
     Image data transmitted from a host apparatus  1  is converted to an ejection signal by the CPU  301 , and ink is ejected from the recording head  201  in accordance with the ejection signal. Print on the recording medium  203  is thus performed. The CPU  301  includes a driver unit  306 , a sequence control unit  307 , an image processing unit  308 , a timing control unit  309 , and a head control unit  310 . The sequence control unit  307  performs the overall control of recording. Specifically, the sequence control unit  307 , for example, starts and stops the image processing unit  308 , the timing control unit  309 , the head control unit  310 , each serving as a functional block, controls conveyance of a recording medium, and controls scanning by the carriage  202 . Control of each functional block is implemented by the sequence control unit  307  reading out various kinds of programs from the memory  303  and executing the programs. The driver unit  306  generates control signals for, for example, the sensor/motor control unit  302 , the memory  303 , and the head control circuit  305  based on a command from the sequence control unit  307 , and transmits input signals from each block to the sequence control unit  307 . 
     The image processing unit  308  executes image processing of subjecting image data input from the host apparatus  1  to color separation and conversion, and converting the input image data to recording data that can be recorded by the recording head  201 . The timing control unit  309  transfers the recording data converted and generated by the image processing unit  308  to the head control unit  310  in conjunction with the position of the carriage  202 . In addition, the timing control unit  309  also performs timing control of ejecting the recording data. The timing control unit  309  performs timing control in accordance with an ejection timing decided based on an ejection velocity calculated in ejection velocity calculation processing described below. The head control unit  310  functions as an ejection signal generating unit, and converts the recording data input from the timing control unit  309  to an ejection signal to output the ejection signal. The head control unit  310  also outputs a control signal at such a level as not to eject ink based on a command from the sequence control unit  307  to perform temperature control of the recording head  201 . The head control circuit  305  functions as a driving pulse generating unit, generates a driving pulse in accordance with the ejection signal input from the head control unit  310 , and applies the driving pulse to the recording head  201 . 
     &lt;Ejection Timing Adjustment&gt; 
     A description will now be given of an ejection timing with reference to  FIGS.  5 A and  5 B .  FIG.  5 A  illustrates a relationship between an ejection velocity of an ink droplet and a landing position of the ink droplet. Assume that a distance H is a distance between the ejection port surface  201   a  of the recording head  201  and the recording medium  203  in the Z-direction. The recording head  201  ejects ink while performing reciprocating scanning at a velocity Vcr in the X-direction to record an image in the recording medium  203 . Assume that an ejection velocity Va is a velocity of ejecting an ink droplet from the recording head  201 . Since a scanning direction is different between scanning in the forward path direction and scanning in the return path direction, a landing position of an ink droplet with respect to an ejection position of the ink droplet is different between the scanning in the forward path direction and the scanning in the return path direction as illustrated in  FIG.  5 A . Ejection timings of ink droplets are adjusted to align the landing positions of the ink droplets ejected from the recording head  201 . First, a distance Xa from the ejection position of an ink droplet to the landing position of the ink droplet on the recording medium  203  in the scanning in the forward path direction is calculated by the following formula. 
         Xa =( H/Va )× Vcr  
 
     Furthermore, a distance Xb from the ejection position of an ink droplet to the landing position of the ink droplet on the recording medium  203  in the scanning in the return path direction is calculated by the following formula. 
         Xb =( H/Va )×(− Vcr )=− Xa  
 
     With these formulas, an appropriate ejection timing with respect to the position of the recording head  201  detected by the encoder sensor  210  can be sought based on the distance from the recording head  201  to the recording medium  203  and the ejection velocity of an ink droplet detected by the droplet detection sensor  205 . In the present exemplary embodiment, a default ejection velocity and an ejection timing with respect to the default ejection velocity are predetermined and stored in the memory  303 . An adjustment value is adjusted to be a value from −4 to +4 in accordance with an ejection velocity with an adjustment value of the ejection timing with respect to this default ejection velocity being 0. The adjustment is performed in units of 1200 dots per inch (dpi). A table, in which this ejection velocity and the adjustment value of the ejection timing are brought into correspondence with each other, is preliminarily stored in the memory  303 . The present exemplary embodiment acquires the adjustment value of the ejection timing in accordance with the ejection velocity acquired by the ejection velocity calculation processing, which will be described below with reference to  FIG.  11   , and adjusts the ejection timing. 
       FIG.  5 B  illustrates a case where the ejection velocity of an ink droplet detected by the droplet detection sensor  205  decreases from the ejection velocity of an ink droplet illustrated in  FIG.  5 A . At this time, a distance Xa′ from the ejection position of an ink droplet in the scanning in the forward path direction to the landing position of the ink droplet on the recording medium  203  is calculated by the following formula. 
         Xa ′=( H/Va ′)× Vcr  
 
     If the ejection velocity of the ink droplet ejected from the recording head  201  and landing on the recording medium  203  is attenuated by 10%, a distance from the ejection position to the landing position can be sought by the following formula. 
         Xa ′=( H/Va ′)× Vcr =( H /( Va× 0.9))× Vcr= 1.11× Xa  
 
     In this manner, the landing position is shifted in the scanning direction of the recording head  201  when the ejection velocity becomes lower. When the distance from the ejection position to the landing position is obtained, an appropriate adjustment value of the ejection timing can be sought based on the ejection velocity similarly to  FIG.  5 A . The first exemplary embodiment is on the assumption that the recording medium  203  is sufficiently thin, and the distance between the ejection port surface  201   a  of the recording head  201  and the recording medium  203  can be equated with a distance between the ejection port surface  201   a  and the platen  212 . 
     &lt;Ejection Velocity Calculation&gt; 
     A description will be given of a method of calculating an ejection velocity of an ink droplet ejected from the recording head  201  according to the present exemplary embodiment with reference to  FIG.  6   .  FIG.  6    is a schematic diagram illustrating the recording head  201  and the droplet detection sensor  205  when the recording apparatus  100  is cut along a Y-Z cross section.  FIG.  6    also illustrates a timing chart of an ejection signal for applying a driving pulse to the recording head  201  and a detection signal when the droplet detection sensor  205  detects passage of an ink droplet. 
     As illustrated in  FIG.  6   , the recording head  201  includes the ejection port surface  201   a . The droplet detection sensor  205  is composed of, for example, the light-emitting element  401 , the light-receiving element  402 , and the control circuit substrate  403 . The light-emitting element  401  emits light  404 , and the light-receiving element  402  receives the light  404  emitted from the light-emitting element  401 . The control circuit substrate  403  detects an amount of light received by the light-receiving element  402 . Since an amount of received light decreases when an ink droplet passes the light  404 , the control circuit substrate  403  can detect the passage of the ink droplet. The droplet detection sensor  205  is installed at a position where the optical axis of the light  404  is at an identical position in the Z-direction to the position of a surface of the platen  212  on which the recording medium  203  is supported. A slit, which is arranged in proximity to each of the light-emitting element  401  and the light-receiving element  402 , focuses the light  404  incident thereon and increases a signal-to-noise (S/N) ratio. Assume that a positional relationship in the X-direction between the droplet detection sensor  205  and the recording head  201  is a positional relationship for detection. In the droplet detection sensor  205 , an ink droplet ejected from the recording head  201  passes through the light  404  emitted from the droplet detection sensor  205 . When the droplet detection sensor  205  detects an ink droplet to calculate an ejection velocity of the ink droplet, the sequence control unit  307  causes the sensor/motor control unit  302  to control the carriage motor  208 , and the recording head  201  moves to a detectable position. According to the present exemplary embodiment, a cross-section area of a light flux of the light  404  is approximately 1 mm 2 . An area of parallel light projection of an ink droplet when the ink droplet passes through the light  404  is approximately 2 −3  mm 2 . 
       FIG.  6    illustrates a state when a distance between the ejection port surface  201   a  of the recording head  201  and the light  404  emitted from the light-emitting element  401  in a height direction (Z-direction) is a distance H1. In a case where the distance between the ejection port surface  201   a  and the light  404  is not the distance H1, the sensor/motor control unit  302  drives the lift motor  211  to cause the lift cam to change the height of the recording head  201 . In the state illustrated in  FIG.  6   , the head control unit  310  in the CPU  301  transmits the ejection signal to the head control circuit  305  via the driver unit  306 . The driver unit  306  transmits a transmission timing of the ejection signal to the sequence control unit  307 . The head control circuit  305  generates a driving pulse in accordance with the ejection signal, and applies the driving pulse to the recording head  201  to eject ink from the ejection port. When an amount of received light received by the light-receiving element  402  is changed by the passage of an ink droplet through the light  404  emitted from the light-emitting element  401 , the control circuit substrate  403  outputs a timing at which the amount of received light is changed as a detection signal. The output detection signal is transmitted to the sequence control unit  307  via the sensor/motor control unit  302 . The sequence control unit  307  then detects a detection time T1 from the transmission of the ejection signal until the output of the detection signal, assuming that a timing of the transmission of the ejection signal from the driver unit  306  to the head control circuit  305  is an ejection start timing. As described above, the sequence control unit  307  functions as a time detection unit that detects a time from the start of ejection of an ink droplet until the detection of the ejected ink droplet, and detects a detection time for calculating an ejection velocity. In the present exemplary embodiment, the timing of the transmission of the ejection signal to the head control circuit  305  is assumed to be the ejection start timing. However, there may be a case where it takes long from input of the ejection signal to the head control circuit  305  until actual ejection of an ink droplet depending on a structure or the like of the recording head  201 . In such a configuration, a time from a point of time when a predetermined time has elapsed from the timing of transmission of the ejection signal until a point of time when the detection signal is output can be assumed as the detection time. 
     When detecting the detection time T1, the sequence control unit  307  calculates an ejection velocity V from the detection time T1 and the distance H1 by the following formula. 
         V=H 1/ T 1 
     In this manner, the ejection velocity can be calculated. 
     &lt;Decision of Measurement Condition&gt; 
     A description will now be given of decision of a measurement condition for a detection time. To calculate an ejection velocity, the present exemplary embodiment measures a detection time a plurality of times, a total of 1000 times in this case, and calculates an ejection velocity based on the measured detection times. When measuring the detection times, the present exemplary embodiment does not drive the mist fan to prevent ejected ink droplets from being influenced by air currents. 
       FIGS.  7 A and  7 B  are schematic diagrams each illustrating a state of a measurement environment in the surroundings of the recording head  201  and the droplet detection sensor  205  at the time of measuring the detection times.  FIG.  7 A  illustrates a case where there is only a small amount of mist suspended in the air in the measurement environment.  FIG.  7 B  illustrates a state where there is a large amount of mist suspended in the air in the measurement environment. Immediately after the start of ejection of ink droplets for measurement, there is a small amount of mist suspended in the air as illustrated in  FIG.  7 A . However, with the increased number of ejections, the measurement environment becomes a state where there is a large amount of mist suspended in the air as illustrated in  FIG.  7 B . When ink is ejected in such an environment in which a large amount of mist is generated, ink droplets are easily separated into main and satellite droplets and an ejection velocity decreases, which elongates detection times. Even in the state where there is a small amount of mist suspended in the air, in a case where consecutive ejection inhibits refilling in time, ink droplets become small in size, which elongates detection times. 
       FIGS.  8 A and  8 B  are graphs each indicating a relationship between a detection time and the number of measurements.  FIG.  8 A  indicates detection times in a case of performing 1000 times consecutive ejections of ink. As illustrated in  FIG.  8 A , detection times become longer with the increased number of measurements. An increasing tendency of detection times is different depending on a composition of ink and characteristics of a recording head due to manufacturing irregularities. 
     To address this issue, the present exemplary embodiment decides such a measurement condition as to enable stable detection of detection times. In this processing, the present exemplary embodiment decides the number of consecutive ejections of ink from an identical ejection port. In a period of measuring detection times with respect to a predetermined ejection port, the present exemplary embodiment does not measure detection times with respect to another ejection port.  FIG.  9    illustrates a flowchart for determining a timing to decide a measurement condition. This processing is executed when the recording head  201  is mounted on the recording apparatus  100 , and is executed by the sequence control unit  307  in the CPU  301  in accordance with a program stored in, for example, the memory  303 . 
     In step S 501 , the sequence control unit  307  determines whether the mounted recording head  201  is mounted on the recording apparatus  100  for the first time. The sequence control unit  307  makes the determination by reading out data stored in a memory in the recording head  201 . If the sequence control unit  307  determines that the recording head  201  is mounted on the recording apparatus  100  for the first time (YES in step S 501 ), the processing proceeds to step S 502 . In step S 502 , the sequence control unit  307  executes measurement condition decision processing. In this processing, the sequence control unit  307  decides the number of consecutive ejections to be performed in the measurement of detection times. Details of the measurement condition decision processing will be described below with reference to  FIG.  10   . If the sequence control unit  307  determines that the recording head  201  is not mounted on the recording apparatus  100  for the first time (NO in step S 501 ), the processing proceeds to step S 503 . In step S 503 , the sequence control unit  307  selects a measurement condition stored in the memory  303 . 
     In step S 504 , the sequence control unit  307  executes the ejection velocity calculation processing. The sequence control unit  307  detects detection times used for calculating an ejection velocity based on the measurement condition decided in step S 502  or step S 503 . Details of the ejection velocity calculation processing will be described with reference to  FIG.  11   . 
       FIG.  10    illustrates a flowchart of the measurement condition decision processing. 
     In step S 601 , the sequence control unit  307  measures detection times in a case of performing 1000 times consecutive ejections of ink droplets as a first measurement condition. The first to fourth measurement conditions to be used for this processing are preliminarily stored in the memory  303 . 
     In step S 602 , the sequence control unit  307  determines whether the detection times measured in step S 601  are stable. Determination whether the measured detection times are stable depends on variations in the measured detection times. For example, the sequence control unit  307  obtains a variance from measurement values, and determines that the measured detection times are stable if the obtained variance is equal or less than a predetermined value. Alternatively, the sequence control unit  307  may determine that the measured detection times are stable if a ratio of detection times that fall within ±5% from an average value of the measurement values is higher than or equal to 80%. Still alternatively, the sequence control unit  307  may derive an expression of approximate curve of time-series data of the measured detection times, and determine that the detection times are stable if a coefficient of the expression is less than or equal to a predetermined value. In addition, the present exemplary embodiment employ fixed values, instead of the ratio, to set a range. If the sequence control unit  307  determines that the detection times are stable (YES in step S 602 ), the processing proceeds to step S 603 . If the sequence control unit  307  determines that the detection times are not stable (NO in step S 602 ), the processing proceeds to step S 604 . 
     In a case where the processing proceeds to step S 603 , the sequence control unit  307  decides on a condition of measuring detection times by performing 1000 times consecutive ejections of ink droplets in the measurement. In step S 611 , the sequence control unit  307  then stores the measurement condition decided in step S 603  in the memory  303 . 
     After completion of the processing in step S 611 , the processing proceeds to step S 612 . In step S 612 , the sequence control unit  307  determines whether measurement conditions have been decided with respect to all of ink colors. If the sequence control unit  307  determines that the measurement conditions have been decided with respect to all of the ink colors (YES in step S 612 ), the processing ends. If the sequence control unit  307  determines that the measurement conditions have not been decided with respect to all of the ink colors (NO in step S 612 ), the processing returns to step S 601 . The sequence control unit  307  then executes the processing with respect to an ink color for which a measurement condition has not been decided. 
     In a case where the processing proceeds to step S 604 , the sequence control unit  307  repeats an operation of performing 100 times consecutive ejections and thereafter performing a wait operation ten times, which is a second measurement condition, and measures detection times in a case of performing 1000 times ejections. 
     In step S 605 , the sequence control unit  307  determines whether the detection times measured in step S 604  are stable. Determination whether the measured detection times are stable depends on variations in the measured detection times in the case of performing 1000 times ejections. The variations can be calculated in a similar manner to step S 602 . A calculation method and a determination criterion are preferably identical to those used in step S 602  in terms of evaluating whether improvement is seen in detection by changing the number of consecutive ejections, but may be changed as appropriate. If the sequence control unit  307  determines that the detection times are stable (YES in step S 605 ), the processing proceeds to step S 606 . In step S 606 , the sequence control unit  307  decides on a measurement condition of measuring detection times by repeatedly performing 100 times consecutive ejections ten times. In step S 611 , the sequence control unit  307  stores the measurement condition decided in step S 606  in the memory  303 . 
     If the sequence control unit  307  determines that the detection times are not stable (NO in step S 605 ), the processing proceeds to step S 607 . In step S 607 , the sequence control unit  307  repeats an operation of performing ten times consecutive ejections and thereafter performing a wait operation 100 times, which is a third measurement condition, and measures detection times in a case of performing 1000 times ejections. 
     In step S 608 , the sequence control unit  307  determines whether the detection times measured in step S 607  are stable. Determination whether the measured detection times are stable depends on variations in the detection times in the 1000 times consecutive ejections, which is measured in step S 607 . The variations can be calculated in a similar manner to step S 602 . A calculation method and a determination criterion are preferably identical to those used in steps S 602  and S 604  in terms of evaluating whether improvement is seen in detection by changing the number of consecutive ejections, but may be changed as appropriate. The determination method is similar to that used in step S 602 . If the sequence control unit  307  determines that the detection times are stable (YES in step S 608 ), the processing proceeds to step S 609 . In step S 609 , the sequence control unit  307  decides on a measurement condition of measuring detection times by repeatedly performing ten times consecutive ejections 100 times. In step S 611 , the sequence control unit  307  stores the measurement condition decided in step S 609  in the memory  303 . 
     If the sequence control unit  307  determines that the detection times are not stable (NO in step S 608 ), the processing proceeds to step S 610 . In step S 610 , the sequence control unit  307  decides to measure detection times by inserting a wait operation every ejection and performing 1000 times ejections, which is a fourth measurement condition. In step S 611 , the sequence control unit  307  stores the measurement condition decided in step S 610  in the memory  303 . 
     As described above, the sequence control unit  307  decides on a measurement condition for detection times with respect to each of the ink colors. In a case where an identical condition can be set with respect to each of the ink colors, the sequence control unit  307  may decide on a measurement condition with respect to one ink color by executing the processing in  FIG.  10   , and decide on the measurement condition decided with respect to the one ink color also as a measurement condition with respect to the other ink colors. While the present exemplary embodiment sets a condition that enables measurement of detection times in a total of 1000 times ejections as each of the measurement conditions that can be decided, the second to fourth measurement conditions require insertion of a wait time, and thus it takes long to measure detection times. To reduce a measurement time, the present exemplary embodiment may set such a measurement condition as to decrease a total number of detections. 
     The present exemplary embodiment determines stability of detection times in  FIG.  10   , but may alternatively seek a measurement condition by also calculating an ejection velocity and determining stability of the ejection velocity. 
     In a period of measuring detection times with respect to the predetermined ejection port, the present exemplary embodiment does not measure detection times with respect to another ejection port. However, detection times with respect to the predetermined ejection port and another ejection port in an identical period may be measured. In a case where two ejection ports are arranged at such positions as being influenced by mist, the present exemplary embodiment may set a measurement condition in consideration of ejections from the two ejection ports. 
     &lt;Ejection Velocity Calculation Processing&gt; 
       FIG.  11    is a flowchart of the ejection velocity calculation processing, which corresponds to the method of calculating an ejection velocity described with reference to  FIG.  6    and the processing in step S 504  illustrated in  FIG.  9   . 
     The ejection velocity calculation processing illustrated in  FIG.  11    is processing executed when a user of the recording apparatus  100  performs an operation for initial installation to operate the recording apparatus  100  for the first time or when the recording head  201  is replaced with a new one and the new recording head  201  is mounted. Further, the ejection velocity calculation processing may be periodically executed as maintenance, or may be executed in accordance with the user&#39;s instruction. The processing in  FIG.  11    is processing executed by the sequence control unit  307  in the CPU  301  in accordance with a program stored in, for example, the memory  303 . 
     In step S 701 , the sequence control unit  307  first drives the lift motor  211 , and separates the recording head  201  and the droplet detection sensor  205  from each other by a predetermined distance. The distance for separation is preliminarily set in the memory  303 , and is distance H (H1) described with reference to  FIGS.  5 A and  5 B  in the present exemplary embodiment. 
     In step S 702 , the sequence control unit  307  executes preprocessing for detecting an ejection velocity. Specifically, examples of the preprocessing include preliminary setting of appropriate ejection control for detecting an ejection velocity, a preliminary ejection operation for stably ejecting ink droplets, and a mist fan stop operation for stabilizing control of air currents in the recording apparatus  100 . 
     In step S 703 , the sequence control unit  307  executes an ejection operation of ejecting ink droplets for detection from the recording head  201  to the light  404  emitted from the light-emitting element  401  of the droplet detection sensor  205 , in accordance with the condition decided in the measurement condition decision processing in  FIG.  10   . Specifically, the sequence control unit  307  detects, at the distance H1 for separation performed in step S 701 , a detection time from the start of ejection of an ink droplet from a predetermined nozzle of the recording head  201  until the passage of the ink droplet through the light  404  detected by the light-receiving element  402  of the droplet detection sensor  205 . At this time, the sequence control unit  307  detects a plurality of detection times using a plurality of nozzles of the recording head  201 . As the nozzles to be used for measuring the detection times, a wide range of nozzles including both ends and the center of the recording head  201  is preferably selected to accurately detect an ejection velocity. 
     In step S 704 , the sequence control unit  307  executes data processing on the detection times acquired in step S 703 , and calculates a detection time with respect to the distance for separation performed in step S 701 . Specifically, the sequence control unit  307  executes data processing including averaging processing based on the number of acquisition samples used for stabilizing measurement of detection times, and deletion of data outside an upper/lower error range to eliminate an abnormal value of data. 
     In step S 705 , the sequence control unit  307  executes calculation of an ejection velocity. Specifically, the sequence control unit  307  calculates the ejection velocity based on the detection time measured at the distance H1, as described with reference to  FIG.  6   . When the ejection velocity is calculated, the processing proceeds to step S 706 . In step S 706 , the sequence control unit  307  stores information of the ejection velocity calculated in step S 705  in the memory  303 . The ejection velocity information stored herein is used for data processing and drive-control of the recording head  201  as the need arises in processing. 
     In step S 707 , the sequence control unit  307  performs end processing. Specifically, since the calculation of the ejection velocity has been completed, the sequence control unit  307 , for example, retracts the recording head  201  to a predetermined position, makes a transition to a standby state for executing the next recording operation processing, or furthermore, starts to execute cleaning processing of the recording head  201  based on the acquired ejection velocity information. Thereafter, the present processing ends. 
     When completing the ejection velocity calculation processing in  FIG.  11   , the sequence control unit  307  acquires a table preliminarily stored in the memory  303  in which an ejection velocity and an adjustment value of an ejection timing are in correspondence with each other, and acquires an adjustment value of an ejection timing from the table based on the ejection velocity acquired by the processing in  FIG.  11   . The ejection timing is then adjusted based on the acquired adjustment value. When performing print of an image, the timing control unit  309  performs control of the ejection timing of ink in accordance with recording data. 
     As described above, the present exemplary embodiment decides a measurement condition for measuring detection times for calculating an ejection velocity, and can thereby stably measure the detection times while suppressing the influence by a composition of ink and characteristics of a recording head due to manufacturing irregularities. This configuration can improve accuracy of calculating an ejection velocity. Further, if consecutive ejection is possible, the present exemplary embodiment performs measurement by consecutively ejecting ink, and can thereby perform measurement while preventing an increase in measurement time. 
     The present exemplary embodiment stops the mist fan while measuring detection times. However, the mist fan may be driven to collect mist during a wait operation under the measurement condition of inserting the wait operation during the measurement. 
     In a case where the detection times are stable at the time of 1000 times consecutive ejections as the first measurement condition, the present exemplary embodiment described above uses the first measurement condition as the measurement condition. Alternatively, the present exemplary embodiment may measure the detection times under all the measurement conditions and select a condition under which the detection times are the most stable. 
     While the present exemplary embodiment uses the optical sensor as a sensor that detects ink droplets, any sensor other than the optical sensor can also be used as long as the sensor is capable of detecting that an ink droplet reaches a predetermined position. 
     The first exemplary embodiment calculates an ejection velocity from detection times in the case where the distance from the ejection port surface of the recording head  201  to the droplet detection sensor  205  is the distance H1. A second exemplary embodiment measures detection times at a plurality of distances and calculates ejection velocities. A description of a part similar to that of the first exemplary embodiment will be omitted. 
     &lt;Calculation of Ejection Velocity&gt; 
     A description will be given of an ejection velocity of an ink droplet ejected from the recording head  201  according to the present exemplary embodiment with reference to  FIGS.  12 A to  12 D .  FIGS.  12 A to  12 D  are schematic diagrams each illustrating the recording head  201  and the droplet detection sensor  205  when the recording apparatus  100  is cut along a Y-Z cross section.  FIGS.  12 A to  12 D  each illustrate a timing chart of an ejection signal for applying a driving pulse to the recording head  201  and a detection signal when the droplet detection sensor  205  detects the passage of an ink droplet. 
       FIG.  12 A  illustrates a state assuming that the distance in the height direction (Z-direction) between the ejection port surface  201   a  of the recording head  201  and the light  404  emitted from the light-emitting element  401  of the droplet detection sensor  205  is the distance H1. A detection time is detected in a method similar to that according to the first exemplary embodiment. In a case where the distance between the ejection port surface  201   a  and the light  404  is not the distance H1, the sensor/motor control unit  302  drives the lift motor  211  to cause the lift cam to change the height of the recording head  201 . In the state illustrated in  FIG.  12 A , the head control unit  310  in the CPU  301  transmits an ejection signal to the head control circuit  305  via the driver unit  306 . The driver unit  306  transmits a transmission timing of the ejection signal to the sequence control unit  307 . The head control circuit  305  generates a driving pulse in accordance with the ejection signal, and applies the driving pulse to the recording head  201  to eject ink from the ejection port. When an amount of received light received by the light-receiving element  402  is changed by the passage of an ink droplet through the light  404  emitted from the light-emitting element  401 , the control circuit substrate  403  outputs a timing at which the amount of received light is changed as a detection signal. The output detection signal is transmitted to the sequence control unit  307  via the sensor/motor control unit  302 . The sequence control unit  307  then detects the detection time T1 from the transmission of the ejection signal until the output of the detection signal. 
       FIG.  12 B  illustrates a state at the time of driving the lift motor  211  after the ejection of an ink droplet as illustrated in  FIG.  12 A , and assuming that the distance in the height direction (Z-direction) between the ejection port surface  201   a  and the light  404  emitted from the light-emitting element  401  is a distance H2. Similarly to  FIG.  12 A , a timing at which an amount of light received by the light-receiving element  402  is changed when an ink droplet passes through the light  404  emitted from the droplet detection sensor  205  is output as a detection signal. The sequence control unit  307  then detects a detection time T2 from the transmission of the ejection signal for causing the recording head  201  to eject an ink droplet until the output of the detection signal. 
     In the present exemplary embodiment, when detecting the detection times T1 and T2 in the states illustrated in  FIGS.  12 A and  12 B , respectively, the sequence control unit  307  calculates an ejection velocity V1 of an ink droplet, which passes between the ejection start point of the distance H2 and the ejection start point of the distance H1, based on a time difference between the detection time T1 and the detection time T2 and a distance difference between the distance H1 and the distance H2, by the following formula. 
         V 1=( H 2− H 1)/( T 2− T 1)
 
     After calculating the ejection velocity V1, the sequence control unit  307  drives the lift motor  211  to change the distance in the height direction between the ejection port surface  201   a  and the light  404  to the distance H3, which is longer than the distance H2.  FIG.  12 C  illustrates this state. Similarly to  FIGS.  12 A and  12 B , the control circuit substrate  403  detects a timing at which an amount of light is changed when an ink droplet, which has been emitted from the ejection port of the recording head  201 , passes through the light  404  emitted from the droplet detection sensor  205  as a timing detection signal. The sequence control unit  307  then detects a detection time T3 from the transmission of the ejection signal for causing the recording head  201  to eject an ink droplet until the output of the detection signal. Similarly to the cases described with reference to  FIGS.  12 A and  12 B , the sequence control unit  307  calculates an ejection velocity V2 of an ink droplet, which passes between the ejection start point of the distance H3 and the ejection start point of the distance H2, based on a time difference between the detection time T2 and the detection time T3 and a distance difference between the distance H2 and the distance H3, by the following formula. 
         V 2=( H 3− H 2)/( T 3− T 2)
 
     After calculating the ejection velocity V2, the sequence control unit  307  further drives the lift motor  211  to change the distance in the height direction between the ejection port surface  201   a  and the light  404  to the distance H4, which is longer than the distance H3.  FIG.  12 D  illustrates this state. Similarly to  FIGS.  12 A to  12 C , the sequence control unit  307  causes the ejection port of the recording head  201  to eject an ink droplet. The control circuit substrate  403  then detects a timing at which an amount of light is changed when the ejected ink droplet passes through the light  404  emitted from the droplet detection sensor  205 , and outputs a detection signal. The sequence control unit  307  then detects a detection time T4 from the transmission of the ejection signal for causing the recording head  201  to eject an ink droplet until the output of the detection signal. Similarly to the cases described with reference to  FIGS.  12 A to  12 C , the sequence control unit  307  calculates an ejection velocity V3 of an ink droplet, which passes between the ejection start point of the distance H4 and the ejection start point of the distance H3, based on a time difference between the detection time T3 and the detection time T4 and a distance difference between the distance H3 and the distance H4, by the following formula. 
         V 3=( H 4− H 3)/( T 4− T 3)
 
     As described above, the present exemplary embodiment calculates an ejection velocity V of an ink droplet by changing a distance between the recording head  201  and the droplet detection sensor  205 , and detecting a detection time at each of distances. While the present exemplary embodiment sequentially detects detection times at corresponding distances in ascending order, the detection order is not limited thereto. For example, the present exemplary embodiment may detect detection times at corresponding distances in descending order. In the present exemplary embodiment, the distance H for separation is a distance of 1.2 mm to 2.2 mm. 
     The present exemplary embodiment may also calculate ejection velocities by measuring detection times at a larger number of distances between the recording head  201  and the droplet detection sensor  205 . Since the present exemplary embodiment can calculate ejection velocities corresponding to a large number of distances, and can thereby acquire detailed data of influence by attenuation of an ejection velocity (whether the ejection velocity is constant or changed depending on a distance). As a result, the present exemplary embodiment can acquire the ejection velocity of ink droplets and the influence by attenuation with high accuracy. 
       FIGS.  13 A and  13 C  are graph charts each illustrating the distance between the ejection port surface  201   a  and the light  404  emitted from the droplet detection sensor  205 , and an output result of a detection time at each distance, which is described with reference to  FIGS.  12 A to  12 D .  FIG.  13 B  is a graph chart illustrating a relationship between an ejection velocity, which is calculated from the distance and detection time illustrated in  FIG.  13 A , and a difference between corresponding distances.  FIG.  13 D  is a graph chart illustrating a relationship between an ejection velocity, which is calculated from the distance and detection time illustrated in  FIG.  13 C , and a difference between corresponding distances. 
     In a graph illustrated in  FIG.  13 A , the vertical axis indicates a detection time detected by the sequence control unit  307 , and the horizontal axis indicates a distance between the ejection port surface  201   a  of the recording head  201  and the light  404  emitted from the droplet detection sensor  205 . A portion indicated by a hatched circle illustrated in  FIG.  13 A  is a measured portion. In this case, the detection is performed when a distance is each of the distances H1 to H5. The distance H5 is longer than the distance H4. 
     In a graph chart illustrated in  FIG.  13 B , the vertical axis indicates an ejection velocity, and the horizontal axis indicates a difference between corresponding distances for separation. At this time, there may be a case where obtained data of the calculated ejection velocities indicates a non-linearly transition due to various kinds of influence. Hence, the present exemplary embodiment derives a quadratic or higher order polynomial of approximate curve from the acquired data of ejection velocities to calculate more accurate data of an ejection velocity at each difference between corresponding distances, and uses the polynomial of approximate curve as an expression of an ejection velocity. Three or more ejection velocities are used to perform approximate curve. To calculate three or more ejection velocities, detection times at four or more distances need to be detected. The method of seeking an ejection velocity is as described above. 
     It has been found from experiment by the inventors that there is also a possibility that data indicating a linear transition is obtained depending on an individual difference among recording heads, a difference in physical properties of ink colors, and furthermore, usage conditions and environmental influence.  FIG.  13 C  illustrates data indicating such a linear transition. In this case, the present exemplary embodiment can also calculate an ejection velocity from a detection time at each distance and a difference between corresponding distances from the ejection port surface  201   a  and the light  404 .  FIG.  13 D  is a diagram illustrating a relationship between a calculated ejection velocity and a difference between corresponding distances. As illustrated in  FIG.  13 D , a calculated ejection velocity at each difference between corresponding distances indicates a constant ejection velocity. In a case where it is found that data indicating a linear transition can be obtained, the obtained ejection velocities indicate a constant value regardless of distances, and thus one ejection velocity is only required to be obtained. To calculate one ejection velocity, detection times at two distances are required to be detected. 
     Even if the ejection velocities make a non-linear transition, the present exemplary embodiment does not necessarily perform approximate curve when performing recording only in a case where the distance between the ejection port surface  201   a  and the recording medium  203  is a constant distance. In this case, the present exemplary embodiment is only required to detect detection times at two distances including a distance at which the recording is performed between the two distances. 
     The present exemplary embodiment executes the processing of calculating an ejection velocity, i.e., the processing of the first exemplary embodiment in steps S 701  to S 703  illustrated in  FIG.  11   , at the distances H1 to H4, and executes the processing in step S 705  to calculate the ejection velocity as described above. 
     The present exemplary embodiment adjusts an ejection timing in a method similar to that according to the first exemplary embodiment. 
     &lt;Decision of Measurement Condition&gt; 
     The present exemplary embodiment executes processing of deciding a timing of setting a measurement condition similarly to the processing according to the first exemplary embodiment described with reference to  FIG.  9   . 
     The present exemplary embodiment performs measurement condition decision processing in step S 502  similarly to that according to the first exemplary embodiment illustrated in  FIG.  10    to decide a measurement condition. A distance between the ejection port surface  201   a  and the light  404  emitted from the light-emitting element  401 , the distance being used for measuring detection times, is predetermined and stored in the memory  303 , and is any of the distances H1 to H4. Alternatively, the present exemplary embodiment may measure detection times at a plurality of distances, determine stability of detection times at respective distances, and decide a measurement condition that enables the least number of consecutive ejections among the distances. 
     As described above, the present exemplary embodiment changes a distance between the recording head  201  and the droplet detection sensor  205 , and detects a detection time from the ejection of an ink droplet until the detection of the ink droplet at each of a plurality of distances. The present exemplary embodiment then calculates an ejection velocity based on a difference between corresponding distances and a difference between detection times. The present exemplary embodiment can thereby accurately calculate an ejection velocity of an ink droplet even if the distance detection sensor  204  is not in a state of being assembled with high accuracy. The present exemplary embodiment detects detection times at four or more distances, and can thereby acquire accurate data regarding an individual difference among recording apparatuses and recording heads, a difference in physical properties of ink colors, influence by usage conditions or circumstances, and influence by attenuation of an ejection velocity at each separated distance. 
     In the processing described above, the present exemplary embodiment has the configuration of changing a distance by moving the recording head  201  with respect to the droplet detection sensor  205 . However, the present exemplary embodiment is only required to have a configuration of relatively changing the distance in the Z-direction between the droplet detection sensor  205  and the recording head  201 . Hence, the present exemplary embodiment may alternatively have a configuration of changing the distance by moving the droplet detection sensor  205  in the Z-direction. 
     In a case where the recording head  201  is in a state of not having ejected ink for a while, moisture of ink evaporates from a portion exposed to the air via an ejection port, and the viscosity of ink around the ejection port increases. Ejecting ink in such a state may influence an amount of ejection and an ejection velocity. A third exemplary embodiment calculates an ejection velocity in consideration of such influence. A description of a part having similar to that of the exemplary embodiments described above will be omitted. 
     The following description can be applied to the measurement condition decision processing in step S 502  illustrated in  FIG.  9   , and the ejection velocity calculation processing illustrated in  FIG.  11   . 
       FIG.  14    is a graph illustrating a relationship between a detection time and the number of measurements when the recording head  201  starts measuring detection times in a state of not having ejected ink for a while. The measurement of the detection times at this time is performed under such a measurement condition as to decrease the influence by mist. As illustrated in  FIG.  14   , variations in data of detection times from the first measurement to the tenth measurement are large, and the detection times are not stable. Thus, the present exemplary embodiment excludes a predetermined number of pieces of data until detection times can be measured in a stable ejection state from data to be used for calculating an ejection velocity. The number of pieces of data to be excluded is a number predetermined by a person skilled in the art from experiment or the like. The number of pieces of data to be excluded may also be changed depending on an elapsed time from the previous ejection. The ejection velocity is calculated by the method of the exemplary embodiments described above. 
     The larger the number of ejections is, the higher a temperature of the recording head  201  becomes, and thus the lower the viscosity of ink becomes. Hence, even in a case where a constant amount of driving energy is applied to the recording head  201 , an amount of ejected ink droplets changes depending on a temperature of the recording head  201  and a temperature of ink, and thus an ejection velocity changes. To further increase stability of detection times to be used for an ejection velocity calculation, the present exemplary embodiment may perform a simple moving averaging method per predetermined number of measurements based on measured time-series data. In this case, the present exemplary embodiment calculates an ejection velocity using data of a section determined to be stable among detection times sought by the simple moving averaging method. 
     Further, a configuration of assigning weights in consideration of characteristics of an ink color serving as a measurement target and influence by a surrounding circumferential change, and using a weighted moving averaging method can be applied to the present exemplary embodiment. 
     Further, even an apparatus that is less susceptible to mist and does not require switching of a measurement condition as described with reference to  FIG.  10    may be configured to exclude data of the first several times measurements from data to be used for calculating an ejection velocity. 
     According to the exemplary embodiments described above, deciding the number of consecutive ejections based on a measurement result can increase accuracy of measurement. 
     OTHER EMBODIMENTS 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.