JP6171734B2 - Printing apparatus and printing apparatus control method - Google Patents

Description

  The present invention relates to a printing apparatus and a printing apparatus control method.

  2. Description of the Related Art An inkjet printer is known that forms an image on a label on a label sheet while transporting a label sheet having a long sheet-like mount and a label disposed on the mount in a predetermined direction. (For example, patent document 1).

JP 2012-192599 A

Inkjet printers perform printing by driving a discharge unit filled with ink and discharging ink from the discharge unit. If the ink in the ejection part is thickened, it may cause ejection abnormalities. Further, when bubbles are included in the ink in the ejection unit or paper dust adheres in the vicinity of the nozzle of the ejection unit, it may cause ejection abnormalities. When ejection abnormality occurs, the image quality of the printed image decreases. Therefore, it is preferable to inspect the ink discharge state in the discharge portion.
In order to inspect the ink ejection state, it is necessary to detect movement of the ejection unit such as vibration of ink in the ejection unit that occurs when the ejection unit is driven. When the ejection unit is driven, ink may be ejected from the ejection unit even when the ejection unit is driven so as not to eject ink. For this reason, it is common to inspect the ink ejection state in the ejection section after moving the ejection section to a position where ink cannot be ejected onto the label paper from the ejection section.

  However, when printing on a long label sheet, if the ejection unit is moved to a position where ink is not ejected onto the label sheet and the ejection state is inspected, the conveyance of the label sheet is stopped and the printing process is performed. It is necessary to cancel. In this case, when restarting the printing process, it is necessary to align the label paper, and there is a problem that the time required for printing is prolonged.

  The present invention has been made in view of the above-described circumstances, and one of its purposes is to enable inspection of the liquid discharge state in the discharge section without lengthening the time required for printing. Is to provide technology.

  In order to solve the above problems, a printing apparatus according to the present invention is a printing apparatus that discharges liquid onto a recording medium to form an image in a printing area of the recording medium, and is driven based on a drive signal. Thus, the head unit having M (M is an integer of 2 or more) discharge units capable of discharging the liquid, and the discharge unit for driving the discharge unit to discharge or not discharge the liquid. A drive signal generation unit that generates a drive signal based on a print control signal, and vibration of the liquid in the target ejection unit that occurs after the drive signal is supplied to the target ejection unit among the M ejection units. A detection unit that detects a detection signal and generates a detection signal; a determination unit that determines a discharge state of the liquid in the target discharge unit based on the detection signal; and a relative position of the head unit with respect to the recording medium based on a movement control signal Move the position The relative position moving unit and the printing control signal are supplied to the drive signal generating unit to control the driving of the ejection unit, and the movement control signal is supplied to the relative position moving unit to A control unit that controls a relative position of the head unit and selects the target ejection unit from among the M ejection units, and the control unit includes at least a part of the M ejection units. During the first period of the printing operation period in which the relative position of the head unit with respect to the recording medium is controlled so that the ejection unit can eject liquid onto the recording medium, Then, among the ejection units that can eject the liquid to an area other than the printing area of the recording medium, α ejection units (α is an integer that satisfies 1 ≦ α <M) are selected as the target ejection units. , Of the printing operation period, In a second period that starts after the first period has elapsed, a part or all of the ejection units capable of ejecting liquid to the printing region are driven so as to eject the liquid, An image is formed in a print area of a recording medium, and the third discharge period is started from the M period as the target discharge unit in the first period in the third period of the print operation period. Among the ejection units excluding the selected α ejection units, β ejection units (β is 1 ≦ β ≦ M) among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium. −integer satisfying −α) is selected as the target ejection unit, and the liquid can be ejected to the printing region in the fourth period of the printing operation period that starts after the third period has elapsed. Discharge some or all of the discharge parts It is driven so as to discharge the liquid, to form an image on a printing area of the recording medium, characterized in that.

According to this invention, in the printing operation period in which at least some of the M ejection units can eject liquid onto the recording medium, the liquid ejection state in the target ejection unit is determined. For this reason, compared with the case where the determination is made after moving the head unit to a position where the discharge unit cannot discharge the liquid onto the recording medium, the printing speed is reduced by determining the liquid discharge state. Can be kept small.
In addition, according to the present invention, the determination of the liquid discharge state is performed for a discharge unit that can discharge liquid to a region other than the print region, that is, a discharge unit that cannot discharge liquid to the print region. Therefore, when the determination is executed, it is possible to prevent the liquid from being discharged from the discharge unit to be determined to the print area. For this reason, it is possible to prevent the image quality from being deteriorated due to the determination of the discharge state of the liquid.

The printing apparatus according to the present invention is a printing apparatus that discharges liquid onto a recording medium to form an image in a printing area of the recording medium, and includes a piezoelectric element that is displaced according to a drive signal, and the inside A pressure chamber in which liquid is filled and the internal pressure is increased or decreased by the displacement of the piezoelectric element based on the drive signal; and the pressure chamber communicates with the pressure chamber to increase or decrease the pressure inside the pressure chamber. A head unit having M ejection units (M is a natural number of 2 or more) having a nozzle that ejects the filled liquid; and a drive signal generation unit that generates the drive signal based on a print control signal; The piezoelectric element included in the target discharge unit is generated based on a change in the pressure inside the pressure chamber of the target discharge unit that occurs after the drive signal is supplied to the target discharge unit among the M discharge units. Detect and detect changes in power A detection unit that generates a signal, a determination unit that determines a liquid discharge state in the target discharge unit based on the detection signal, and a relative that moves the relative position of the head unit with respect to the recording medium based on a movement control signal A head for the recording medium by controlling the driving of the ejection unit by supplying a position moving unit and the print control signal to the drive signal generating unit and supplying the movement control signal to the relative position moving unit; A control unit that controls the relative positions of the units and selects the target discharge unit from among the M discharge units, wherein the control unit discharges at least a part of the M discharge units. In the first period of the printing operation period in which the relative position of the head unit with respect to the recording medium is controlled so that the unit can discharge liquid onto the recording medium, the M discharges Among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium, α ejection units (α is an integer satisfying 1 ≦ α <M) are used as the target ejection unit. In the second period that starts after the first period of the printing operation period, a part or all of the ejection units that can eject liquid to the printing region are The M ejection units are driven so as to eject liquid to form an image in a printing area of the recording medium, and the M ejection units in a third period that starts after the second period of the printing operation period. Among the ejection units excluding the α ejection units selected as the target ejection unit in the first period from among the ejection units capable of ejecting the liquid to an area other than the print area of the recording medium, β discharge units (β is an integer satisfying 1 ≦ β ≦ M−α) Is selected as the target discharge portion,
Of the printing operation period, in a fourth period started after the third period has elapsed, a part or all of the ejection units capable of ejecting the liquid to the printing region are caused to eject the liquid. And driving to form an image in the print area of the recording medium.

  Further, in the above-described printing apparatus, the control unit performs a first printing mode in which printing is performed at a first printing speed, and a second printing mode in which printing is performed at a second printing speed higher than the first printing speed. When the printing is executed in the first printing mode, the number of target ejection units selected by the control unit in the first period is the number in the case where the printing is executed in the second printing mode. It is preferable that the number of target ejection units selected by the control unit in the first period is larger than the number of target ejection units.

When printing is performed in the second printing mode, which is faster than the first printing mode, the moving speed related to the relative position of the head unit with respect to the recording medium may be increased. Therefore, the time length of the first period when the second print mode is executed may be shorter than the time length of the first period when the first print mode is executed.
According to this aspect, the number of target ejection units selected in the first period when the second printing mode is executed is the number of target ejection units selected in the first period when the first printing mode is executed. Less than the number of As a result, when the second printing mode is executed, the printing speed is increased, and as a result, the time for supplying the drive signal to one target ejection unit even when the time length of the first period is shortened. Alternatively, it is possible to prevent the time for detecting the operation in the one target ejection unit from being shortened. As a result, even when printing is performed in the second printing mode, the degree of accuracy of detection of the liquid ejection state in the ejection unit is suppressed from being reduced as compared with the case of the first printing mode. be able to.

In the printing apparatus described above, in the second period, the control unit may be configured such that, out of the α target ejection units selected by the control unit in the first period, the determination unit is based on the drive signal. It is preferable that an image is formed on the print area of the recording medium from the target ejection unit that has been determined to be in a state where it is not possible to eject the liquid, without ejecting the liquid.
According to this aspect, since the discharge unit that is determined to have the above-described liquid discharge state is not used for printing, even when a discharge abnormality occurs in the discharge unit, the degree of deterioration in image quality can be kept small. it can.

In the above-described printing apparatus, the target ejection unit selected by the control unit in the printing operation period is a part or all of the M ejection units. preferable.
In this aspect, for example, only the ejection portion that contributes to the image formation in the second period or the fourth period may be a target for determining the liquid ejection state. In this case, it is possible to determine the liquid discharge state only for the discharge portions directly related to the image formation.

  Moreover, it is preferable that the printing apparatus described above is a line printer.

  Further, the control method of the printing apparatus according to the present invention includes M ejection units (M is an integer of 2 or more) capable of ejecting liquid based on a drive signal, and ejects liquid onto a recording medium. A control method of a printing apparatus for forming an image in a printing area of the recording medium, wherein a printing operation period in which at least some of the M ejection units can eject liquid onto the recording medium is provided. Among the M ejection units, α (α is an integer satisfying 1 ≦ α <M) among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium. A first operation for determining whether or not the liquid can be ejected based on the drive signal, and after the first operation is completed, of the ejection units capable of ejecting the liquid to the print region The liquid is ejected to a part or all of the ejection units, and the recording medium A discharge unit that executes a second operation for forming an image in the printing region and, after the second operation is finished, excludes the α number of discharge units that are targets of determination in the first operation from the M discharge units. Among these, among the ejection units that can eject the liquid to an area other than the printing area of the recording medium, the determination is performed on β (β is an integer that satisfies 1 ≦ β ≦ M−α) ejection units. The third operation is performed, and after completion of the third operation, the liquid is ejected to a part or all of the ejection units capable of ejecting the liquid to the print region, and the print region of the recording medium A fourth operation for forming an image is executed.

1 is a block diagram illustrating a configuration of an inkjet printer 1 according to a first embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of an inkjet printer 1. 5 is an explanatory diagram for explaining a shape of a label paper P. FIG. 2 is a schematic cross-sectional view of a head unit 30 according to the first embodiment. FIG. 3 is an exploded perspective view showing a configuration of a head unit 30. FIG. FIG. 6 is an explanatory diagram for explaining a change in the cross-sectional shape of the head unit 30 when a drive signal Vin is supplied. 4 is a circuit diagram showing a model of simple vibration representing residual vibration in the discharge section 35. FIG. It is a graph which shows the relationship between the experimental value of residual vibration in case the discharge state in the discharge part 35 is normal, and a calculated value. FIG. 6 is an explanatory diagram illustrating a state of the discharge unit when air bubbles are mixed into the cavity. 6 is a graph showing experimental values and calculated values of residual vibration in a state where ink cannot be ejected due to bubbles mixed into the cavity 141; It is explanatory drawing which shows the state of the discharge part 35 when the ink of the vicinity of a nozzle adheres. It is a graph which shows the experimental value and calculated value of a residual vibration in the state which cannot discharge ink by adhesion of the ink vicinity of a nozzle. It is explanatory drawing which shows the state of the discharge part 35 when paper dust adheres to the exit vicinity of a nozzle. It is a graph which shows the experimental value and calculated value of a residual vibration in the state which became unable to discharge ink by adhesion of the paper dust to the exit vicinity of a nozzle. 3 is a block diagram illustrating a configuration of a drive signal generation unit 51. FIG. It is explanatory drawing which shows the decoding content of decoder DC. 6 is a timing chart illustrating an operation of the drive signal generation unit 51 in a unit printing operation period Tp. It is a timing chart showing the waveform of the drive signal Vin in the unit printing operation period Tp. It is a timing chart which shows operation | movement of the drive signal generation part 51 in the unit detection operation period Tt. It is a timing chart showing the waveform of the drive signal Vin in the unit detection operation period Tt. 3 is a block diagram illustrating a configuration of a switching unit 53. FIG. It is a block diagram which shows the structure of the discharge abnormality detection circuit DT. It is a timing chart which shows operation | movement of the discharge abnormality detection circuit DT. It is explanatory drawing explaining the production | generation of the determination result signal Rs in the determination part 56. FIG. 3 is a timing chart showing the operation of the inkjet printer 1. It is a timing chart which shows operation | movement of the inkjet printer which concerns on contrast. It is explanatory drawing explaining the relationship between position Xp on a label, and unit operation period Tu. It is explanatory drawing for demonstrating a printing process and an abnormal discharge detection process. It is explanatory drawing for demonstrating a printing process and an abnormal discharge detection process. It is explanatory drawing for demonstrating a printing process and an abnormal discharge detection process. It is explanatory drawing for demonstrating the printing process and discharge abnormality detection process of the inkjet printer which concerns on 2nd Embodiment. 10 is a timing chart showing the operation of the ink jet printer according to Modification 1. FIG. 10 is an explanatory diagram for explaining a printing process and an ejection abnormality detection process of an ink jet printer according to Modification 3. FIG. 10 is an explanatory diagram for explaining a printing process and an ejection abnormality detection process of an inkjet printer according to Modification Example 4.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each figure, the size and scale of each part are appropriately changed from the actual ones. Further, since the embodiments described below are preferable specific examples of the present invention, various technically preferable limitations are attached thereto. However, the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these forms.

<A. First Embodiment>
In this embodiment, as a printing apparatus, an ink jet line printer that ejects ink (an example of “liquid”) and forms an image in an area where a label Lb of label paper P (an example of “recording medium”) is disposed. An example will be described.
FIG. 1 is a functional block diagram showing the configuration of the ink jet printer 1 according to this embodiment. As shown in this figure, the ink jet printer 1 drives a head unit 30 having M ejection units 35 (M is a natural number of 2 or more) that can eject ink filled therein, and the head unit 30. When a discharge abnormality is detected in the head driver 50, the paper feed position moving unit 4 (an example of a “relative position moving unit”) for moving the relative position of the head unit 30 to the label paper P, and the discharge unit 35. And a recovery mechanism 70 that executes a recovery process for recovering the discharge state of the discharge unit 35 normally.
The ink jet printer 1 controls the operations of the paper feed position moving unit 4, the head driver 50, and the recovery mechanism 70 based on the image data Img supplied from the host computer 9 such as a personal computer or a digital camera. Thus, it controls the execution of various processes such as a printing process for forming an image on the label paper P, an ejection abnormality detection process for detecting an ejection abnormality of the ejection unit 35, and a recovery process for recovering the ejection state of the ejection unit 35 normally And a control unit 6 that performs.

The control unit 6 includes a CPU 61 and a storage unit 62.
The storage unit 62 includes an EEPROM (Electrically Erasable Programmable Read-Only Memory) that is a type of nonvolatile semiconductor memory that stores image data Img supplied from the host computer 9 via an interface unit (not shown) in a data storage area. . Further, the storage unit 62 temporarily stores data necessary for executing printing processing such as information on the shape of the label paper P and ejection abnormality detection result data representing a result obtained by the ejection abnormality detection processing. A RAM (Random Access Memory) that temporarily stores a control program for storing or executing various processes such as a printing process is provided. The storage unit 62 includes a PROM which is a kind of nonvolatile semiconductor memory that stores a control program for controlling each unit of the inkjet printer 1.

  The CPU 61 controls execution of various processing such as printing processing, ejection abnormality detection processing, and recovery processing. More specifically, the CPU 61 stores the image data Img supplied from the host computer 9 in the storage unit 62. The CPU 61 also controls driver control signals Ctr1 and Ctr2 for controlling the driving of the paper feed position moving unit 4 based on various data stored in the storage unit 62 such as the image data Img, and the head driver 50. Various signals such as a print signal SI for controlling driving, a switching control signal Sw, and a driving waveform signal Com, and various control signals for controlling driving of the recovery mechanism 70 are generated, and these signals are ink-jetted. Supplied to each part of the printer 1. Thus, the CPU 61 controls the operations of the paper feed position moving unit 4, the head driver 50, and the recovery mechanism 70, and controls the execution of various processes such as a printing process, an ejection abnormality detection process, and a recovery process. Each component of the control unit 6 is electrically connected via a bus (not shown).

The head driver 50 includes a drive signal generation unit 51, an ejection abnormality detection unit 52, and a switching unit 53.
The drive signal generation unit 51 generates a drive signal Vin for driving the ejection unit 35 included in the head unit 30 based on the print signal SI and the drive waveform signal Com supplied from the control unit 6. Although details will be described later, in the present embodiment, the drive waveform signal Com includes two signals of the drive waveform signal Com-A and the drive waveform signal Com-B.
The print signal SI and the drive waveform signal Com are collectively referred to as “print control signal”. That is, the drive signal generation unit 51 generates the drive signal Vin based on the print control signal.
The ejection abnormality detection unit 52 detects, as the residual vibration signal Vout, a change in the pressure inside the ejection unit 35 caused by the vibration of the ink inside the ejection unit 35 that occurs after the ejection unit 35 is driven by the drive signal Vin. At the same time, based on the residual vibration signal Vout, whether or not there is a discharge abnormality in the discharge unit 35 and the ink discharge state in the discharge unit 35 are determined, and the determination result is output as a determination result signal Rs.
The switching unit 53 connects each ejection unit 35 to either the drive signal generation unit 51 or the ejection abnormality detection unit 52 based on the switching control signal Sw supplied from the control unit 6.

  The paper feed position moving unit 4 includes a carriage motor 41 for moving the head unit 30 (more precisely, for moving a carriage 32 on which the head unit 30 is mounted), and a carriage for driving the carriage motor 41. A motor driver 401, a paper feed motor 42 for transporting the label paper P, and a paper feed motor driver 402 for driving the paper feed motor 42 are provided. The carriage motor driver 401 and the paper feed motor driver 402 may be collectively referred to as the motor driver 40.

FIG. 2 is a schematic diagram illustrating the configuration of the ink jet printer 1. As shown in this figure, the inkjet printer 1 includes a roll paper storage unit 43 for storing a roll paper having a configuration in which the label paper P is wound up in a roll shape, and the roll paper storage unit 43 stores the roll paper. The label paper P is fed out from. The label paper P is defined by a guide roller 441, a driven paper feed roller pair 442, a drive paper feed roller pair 443, a platen 444, and the like by a drive side paper feed roller pair 443 driven to rotate by the paper feed motor 42. The paper is transported along the transport path 44 in the X-axis direction and is transported from the paper discharge port 46.
The label paper P includes a long sheet-like mount PR and a plurality of labels Lb arranged on the surface of the mount PR.

  The carriage 32 on which the head unit 30 is mounted is disposed on the opposite side of the platen 444 across the conveyance path 44 of the label paper P, that is, in the (+ Z) direction when viewed from the platen 444. The carriage 32 is linearly moved within a predetermined range along the X-axis direction by a head portion moving mechanism including a carriage guide shaft 321 made of, for example, a ball screw or a ball spline, and the carriage motor 41 extending in the X-axis direction. It is possible to reciprocate.

In the state where the head unit 30 is moved to the printing position (X = X0), the control unit 6 conveys the label paper P in the X-axis direction, and at the same time from the plurality of ejection units 35 provided in the head unit 30 to the label paper P. The printing process is executed by ejecting ink based on the image data Img to the area where the label Lb is arranged.
In addition, when a discharge abnormality of the discharge unit 35 is found, the control unit 6 moves the head unit 30 to an initial position (X = Xini) facing the recovery mechanism 70 and executes the recovery process.

Although not shown in FIG. 2, the ink jet printer 1 includes four ink cartridges 31 filled with ink. Specifically, the four ink cartridges 31 are provided in a one-to-one correspondence with the four colors of yellow, cyan, magenta, and black, and are mounted on the carriage 32.
Each of the M ejection units 35 receives ink from any one of the four ink cartridges 31. As a result, each of the ejection units 35 can eject any one of the four colors, thereby enabling full color printing.
Note that the ink cartridge 31 may be installed in another place of the inkjet printer 1 instead of being mounted on the carriage 32. The ink jet printer 1 may further include an ink cartridge 31 filled with ink of a color different from the above four colors, or include only an ink cartridge 31 corresponding to a part of the four colors ( For example, the ink cartridge 31 may include only the ink cartridge 31 corresponding to black.

3 shows the arrangement position of the label Lb on the label paper P and the position of the label paper P and the head unit 30 when the ink jet printer 1 is viewed in plan (that is, when the ink jet printer 1 is viewed from the + Z direction). It is explanatory drawing which shows a relationship exemplarily.
On the label sheet P, a plurality of labels Lb are arranged. In this figure, two rows of labels Lb are arranged in the horizontal direction (Y-axis direction) so as to have an interval Δy, and a plurality of labels Lb are arranged in the vertical direction (X-axis direction) so as to have an interval Δx. The labeled paper P is illustrated.
Below, the area | region where label Lb is arrange | positioned planarly among the label paper P is called printing area | region Ap. Further, in the label sheet P, an area where the label Lb is not arranged in a plan view (that is, an area where an image is not formed by the printing process) is referred to as a non-printing area Ax. In addition, a region extending in the horizontal direction in the non-printing region Ax is referred to as a non-printing region AxH, and a region obtained by removing the non-printing region AxH from the non-printing region Ax (that is, in the vertical direction in the non-printing region Ax). The extended area) is referred to as a non-printing area AxV.
Note that the label paper P shown in FIG. 3 is merely an example of a recording medium on which the inkjet printer 1 can print an image. The recording medium on which an image can be printed by the inkjet printer 1 is not limited to the label paper P illustrated in this figure, and any recording medium can be used as long as it can be stored in the roll paper storage unit 43.

As shown in FIG. 3, the head unit 30 has a width equal to or larger than the width of the label paper P in the Y-axis direction when viewed in plan. As described above, the head unit 30 includes the M ejection units 35. Each of these M ejection units 35 includes one nozzle N. In other words, the head unit 30 is provided with M nozzles N (N [1], N [2],..., N [M]).
The head portion 30 illustrated in this figure has four nozzle rows each composed of a plurality of nozzles N (22 nozzles N in this drawing) extending in the lateral direction (Y-axis direction). Of the four nozzle rows, yellow (Y) ink is ejected from each nozzle N included in the first nozzle row, and magenta (from m each nozzle N included in the second nozzle row). M) ink is ejected, cyan (C) ink is ejected from each nozzle N included in the third nozzle row, and black (K) is ejected from each nozzle N included in the fourth nozzle row. Ink is ejected.
Further, the label sheet P is conveyed in the upward direction (+ X direction) in FIG. 3 at a predetermined speed Mv. Then, at the timing when the head unit 30 moves to a position facing the non-printing area Ax (label Lb) of the label paper P, the ink of each color is ejected from the nozzles N of each row, so that the full color is printed on the label Lb. An image can be formed.

  Next, the configuration of the head unit 30 and the ejection unit 35 provided in the head unit 30 will be described with reference to FIGS. 4 and 5.

  FIG. 4 is a schematic cross-sectional view of each ejection unit 35 provided in the head unit 30. The ejection unit 35 shown in FIG. 4 ejects ink (an example of “liquid”) in the cavity 141 (an example of “pressure chamber”) from the nozzle N by driving the piezoelectric element 120. The discharge unit 35 includes a nozzle plate 150 in which the nozzles N are formed, a cavity plate 242, a vibration plate 121, and a laminated piezoelectric element 201 formed by laminating a plurality of piezoelectric elements 120.

  The cavity plate 242 is formed into a predetermined shape (a shape in which a concave portion is formed), whereby the cavity 141 and the reservoir 143 are formed. The cavity 141 and the reservoir 143 communicate with each other via the ink supply port 142. The reservoir 143 communicates with the ink cartridge via the ink supply tube 311.

  In FIG. 4, the lower end of the laminated piezoelectric element 201 is joined to the diaphragm 121 through the intermediate layer 244. A plurality of external electrodes 248 and internal electrodes 249 are joined to the laminated piezoelectric element 201. That is, the external electrode 248 is bonded to the outer surface of the laminated piezoelectric element 201, and the internal electrode 249 is disposed between the piezoelectric elements 120 constituting the laminated piezoelectric element 201 (or inside each piezoelectric element). ing. In this case, the external electrode 248 and a part of the internal electrode 249 are alternately arranged so as to overlap in the thickness direction of the piezoelectric element 120.

Then, by supplying a drive signal Vin from the head driver 50 between the external electrode 248 and the internal electrode 249, the laminated piezoelectric element 201 is deformed as indicated by an arrow in FIG. The diaphragm 121 vibrates by expansion and contraction, and the vibration 121 vibrates due to this vibration. The volume of the cavity 141 (pressure in the cavity) is changed by the vibration of the vibration plate 121, and the ink (liquid) filled in the cavity 141 is discharged as a liquid from the nozzle N.
When the ink in the cavity 141 decreases due to the ink ejection, the ink is supplied from the reservoir 143. Further, ink is supplied to the reservoir 143 from the ink cartridge 31 via the ink supply tube 311.

  In addition, the arrangement pattern of the nozzles N formed on the nozzle plate 150 shown in FIG. 4 is arranged in a shifted manner, for example, like the nozzle arrangement pattern shown in FIG. The pitch between the nozzles N can be appropriately set according to the printing resolution (dpi: dot per inch).

  Next, another example of the discharge unit will be described. In the ejection part 35A shown in FIG. 5, the vibration plate 121A vibrates by driving the piezoelectric element 120A, and the ink (liquid) in the cavity 141A is ejected from the nozzle N. A stainless steel metal plate 254 is bonded to the stainless steel nozzle plate 150A on which the nozzle N is formed via an adhesive film 255, and a similar stainless steel metal plate 254 is further bonded thereto. They are joined via a film 255. Further, a communication port forming plate 256 and a cavity plate 257 are sequentially joined thereon.

  The nozzle plate 150A, the metal plate 254, the adhesive film 255, the communication port forming plate 256, and the cavity plate 257 are each formed into a predetermined shape (a shape in which a concave portion is formed). 141A and reservoir 143A are formed. The cavity 141A and the reservoir 143A communicate with each other through the ink supply port 142A. The reservoir 143 </ b> A communicates with the ink intake port 137.

  A diaphragm 121 </ b> A is installed in the upper surface opening of the cavity plate 257, and the piezoelectric element 120 </ b> A is joined to the diaphragm 121 </ b> A via the lower electrode 263. An upper electrode 264 is bonded to the opposite side of the piezoelectric element 120A from the lower electrode 263.

  When the head driver 50 supplies a drive signal Vin between the upper electrode 264 and the lower electrode 263, the piezoelectric element 120A vibrates, and the diaphragm 121A bonded thereto vibrates. The volume of the cavity 141A (pressure in the cavity) is changed by the vibration of the vibration plate 121A, and the ink (liquid) filled in the cavity 141A is ejected from the nozzle N.

  When ink is ejected and the amount of ink in the cavity 141A decreases, ink is supplied from the reservoir 143A. Ink is supplied from the ink intake 137 to the reservoir 143A.

Next, ink ejection will be described with reference to FIG.
When the drive signal Vin is supplied from the head driver 50 to the piezoelectric element 120 (120A) shown in FIG. 4 (FIG. 5), a Coulomb force is generated between the electrodes, and the diaphragm 121 (121A) is shown in FIG. 4 is bent upward in FIG. 4 (FIG. 5), and the volume of the cavity 141 (141A) is expanded as shown in FIG. 6B. In this state, when the voltage indicated by the drive signal Vin is changed by the head driver 50, the diaphragm 121 (121A) is restored by its elastic restoring force and exceeds the position of the diaphragm 121 (121A) in the initial state. As shown in FIG. 6C, the volume of the cavity 141 (141A) contracts rapidly. At this time, due to the compression pressure generated in the cavity 141 (141A), a part of the ink filling the cavity 141 (141A) is ejected as an ink droplet from the nozzle N communicating with the cavity 141 (141A).

The vibration plate 121 (121A) of each cavity 141 (141A) oscillates damped after the series of ink ejection operations is completed until the next ink ejection operation is started. Hereinafter, this damped vibration is also referred to as residual vibration.
The residual vibration of the vibration plate 121 (121A) includes the acoustic resistance r due to the shape of the nozzle N and the ink supply port 142 (142A), or the ink viscosity, the inertance m due to the ink weight in the flow path, and the vibration plate 121 (121A). And a natural vibration frequency determined by the compliance Cm.

A calculation model of residual vibration of the diaphragm 121 based on the above assumption will be described.
FIG. 7 is a circuit diagram showing a calculation model of simple vibration assuming residual vibration of the diaphragm 121. Thus, the calculation model of the residual vibration of the diaphragm 121 can be expressed by the sound pressure p, the inertance m, the compliance Cm, and the acoustic resistance r. When the step response when the sound pressure p is applied to the circuit of FIG. 7 is calculated for the volume velocity u, the following equation is obtained.
u = {p / (ω · m)} e ^−γt · sin (ωt)
ω = {1 / (m · Cm) −γ ² } ^1/2
γ = r / (2m)

  The calculation result obtained from this equation is compared with the experimental result in the residual vibration experiment of the vibration plate 121 after the ink droplets are separately ejected. FIG. 8 is a graph showing the relationship between the experimental value and the calculated value of the residual vibration of the diaphragm 121. As can be seen from the graph shown in FIG. 8, the two waveforms of the experimental value and the calculated value are almost the same.

  In the ejection unit 35, there is a case in which an ink droplet is not ejected normally from the nozzle N in spite of performing the ejection operation as described above, that is, a droplet ejection abnormality occurs. The cause of this discharge abnormality is (1) bubbles mixed in the cavity 141, (2) drying / thickening (fixing) of ink in the vicinity of the nozzle N, and (3) near the outlet of the nozzle N. Examples include paper dust adhesion.

  When this ejection abnormality occurs, typically, as a result, a droplet is not ejected from the nozzle N, that is, a non-ejection phenomenon of the droplet appears. In this case, the pixel dot in the image printed on the label paper P Omission occurs. Also, in the case of abnormal discharge, even if droplets are ejected from the nozzle N, the amount of droplets is too small or the flight direction (ballistic) of the droplets shifts and does not land properly. It still appears as missing pixels in the pixels. For this reason, in the following description, the droplet ejection abnormality is sometimes simply referred to as “dot missing”.

  In the following, based on the comparison result shown in FIG. 8, the residual vibration of the diaphragm 121 is calculated for each cause of the dot dropout (discharge abnormality) phenomenon (droplet non-discharge phenomenon) during the printing process that occurs in the discharge unit 35. At least one of the acoustic resistance r and the inertance m is adjusted so that the value matches the experimental value (substantially matches).

First, (1) mixing of bubbles into the cavity 141, which is one cause of missing dots, is examined. FIG. 9 is a conceptual diagram in the vicinity of the nozzle N when bubbles are mixed in the cavity 141. As shown in FIG. 9, the generated bubbles are assumed to be generated and attached to the wall surface of the cavity 141.
Thus, when bubbles are mixed in the cavity 141, it is considered that the total weight of the ink filling the cavity 141 is reduced and the inertance m is reduced. Further, as illustrated in FIG. 9, when bubbles are attached in the vicinity of the nozzle N, the diameter of the nozzle N is increased by the size of the diameter, and the acoustic resistance r is reduced. it is conceivable that.
Therefore, with respect to the case of FIG. 8 in which the ink is normally ejected, by setting both the acoustic resistance r and the inertance m to be small and matching with the experimental value of the residual vibration at the time of bubble mixing, as shown in FIG. A result (graph) was obtained. As can be seen from the graphs of FIGS. 8 and 10, when bubbles are mixed in the cavity 141, a characteristic residual vibration waveform having a frequency higher than that during normal ejection can be obtained. It should be noted that the attenuation rate of the amplitude of the residual vibration is reduced due to the decrease in the acoustic resistance r, and it can be confirmed that the residual vibration is slowly decreasing the amplitude.

Next, (2) drying (fixing, thickening) of ink near the nozzle N, which is another cause of missing dots, will be examined. FIG. 11 is a conceptual diagram in the vicinity of the nozzle N when the ink in the vicinity of the nozzle N in FIG. 4 is fixed by drying. As shown in FIG. 11, when the ink in the vicinity of the nozzle N is dried and fixed, the ink in the cavity 141 is confined in the cavity 141. Thus, it is considered that the acoustic resistance r increases when the ink near the nozzle N is dried and thickened.
Therefore, by setting the acoustic resistance r to be large with respect to the case of FIG. 8 in which the ink has been normally ejected, and matching with the experimental value of the residual vibration at the time of ink dry adhesion (thickening) near the nozzle N, The result (graph) as shown in FIG. 12 was obtained. The experimental values shown in FIG. 12 indicate that the ink cannot be ejected because the ink in the vicinity of the nozzle N is dried and thickened without leaving the cap (not shown) for several days. This is a measurement of the residual vibration of the diaphragm 121 in a state where the ink is fixed. As can be seen from the graphs of FIGS. 8 and 12, when the ink near the nozzle N is fixed by drying, the frequency becomes extremely lower than that during normal ejection, and the characteristic residual vibration in which the residual vibration is overdamped. A waveform is obtained. This is because when the vibration plate 121 is drawn downward in FIG. 4 to eject ink droplets, the ink flows from the reservoir 143 into the cavity 141 and then the vibration plate 121 moves upward in FIG. This is because the diaphragm 121 cannot vibrate abruptly because there is no escape route for ink in the cavity 141 (because it is overdamped).

Next, (3) paper dust adhesion near the nozzle N exit, which is yet another cause of missing dots, will be examined. FIG. 13 is a conceptual diagram of the vicinity of the nozzle N when paper dust adheres to the vicinity of the nozzle N outlet of FIG. As shown in FIG. 13, when paper dust adheres to the vicinity of the outlet of the nozzle N, the ink oozes out from the cavity 141 through the paper dust, and ink cannot be ejected from the nozzle N. As described above, when paper dust adheres to the vicinity of the outlet of the nozzle N and the ink oozes out from the nozzle N, the ink in the cavity 141 and the amount of the oozing out increase from the normal state as seen from the vibration plate 121. Thus, the inertance m is considered to increase. Further, it is considered that the acoustic resistance r is increased by the paper dust fibers adhering to the vicinity of the outlet of the nozzle N.
Therefore, in contrast to the case of FIG. 8 in which the ink has been ejected normally, both the inertance m and the acoustic resistance r are set large to match the experimental value of residual vibration when paper dust adheres to the vicinity of the nozzle N outlet. As a result, a result (graph) as shown in FIG. 14 was obtained. As can be seen from the graphs of FIGS. 8 and 14, when paper dust adheres near the outlet of the nozzle N, a characteristic residual vibration waveform having a frequency lower than that during normal ejection is obtained.
From the graphs shown in FIGS. 12 and 14, it is understood that the frequency of residual vibration is higher in the case of paper dust adhesion than in the case of ink drying.

Here, in the case where the ink near the nozzle N is dried and thickened, and in the case where the paper dust is attached near the outlet of the nozzle N, the vibration of the attenuation is compared with the case where the ink droplets are normally ejected. The frequency is low. In order to identify the cause of these two missing dots (ink non-ejection: ejection abnormality) from the residual vibration waveform of the diaphragm 121, for example, a comparison is made with a predetermined threshold in the frequency, period and phase of the damped vibration. Alternatively, it can be specified from the periodic change of residual vibration (damped vibration) or the attenuation rate of amplitude change. In this way, the ejection abnormality of each ejection unit 35 is detected based on the change in the residual vibration of the diaphragm 121 when ink droplets are ejected from the nozzles N in each ejection unit 35, in particular, the change in the frequency thereof. Can do. Further, by comparing the residual vibration frequency in that case with the residual vibration frequency during normal ejection, the cause of the ejection abnormality can be specified.
The ink jet printer 1 according to the present embodiment detects a discharge abnormality by analyzing residual vibration.

  Next, the configuration and operation of the head driver 50 (the drive signal generation unit 51, the ejection abnormality detection unit 52, and the switching unit 53) will be described with reference to FIGS.

FIG. 15 is a block diagram illustrating a configuration of the drive signal generation unit 51 in the head driver 50. As shown in FIG. 15, the drive signal generation unit 51 has a one-to-one correspondence with a set of the shift register SR, the latch circuit LT, the decoder DC, and the transmission gates TGa and TGb on the M ejection units 35. So that it has M. Hereinafter, the elements constituting the M sets may be referred to as a first stage, a second stage,..., An M stage in order from the top in the drawing (in FIG. 15, for convenience of illustration, a shift register is referred to as “stage”). The number of stages is displayed only for SR).
Although details will be described later, in the present embodiment, the M ejection units 35 are divided into Q groups with the K ejection units 35 as one group (provided that K and Q are M = 2 or more natural numbers satisfying K × Q) That is, the 1st to Kth stages are referred to as the first group, the (K + 1) th to (2K) th stages are referred to as the second group, and the (M−K + 1) th to Mth stages are referred to as the Qth group. Similarly, for each component of the drive signal generation unit 51, the first stage to the K stage are the first group, the (K + 1) stage to the (2K) stage are the second group,..., (M−K + 1) stage to M. The stage may be referred to as the Qth group.
Although details will be described later, the discharge abnormality detection unit 52 has Q discharge abnormality detection circuits DT (DT [1], DT [2],..., DT [Q so as to correspond to the Q groups on a one-to-one basis. ]).

The drive signal generator 51 is supplied with a clock signal CL, a print signal SI, a latch signal LAT, a change signal CH, and a drive waveform signal Com (Com-A, Com-B) from the controller 6.
Here, the print signal SI is a digital signal that defines the amount of ink ejected from each ejection section 35 (each nozzle N) when forming one dot of an image.
More specifically, the print signal SI according to the present embodiment defines the amount of ink ejected from each ejection unit 35 (each nozzle N) by two bits, an upper bit MSB and a lower bit LSB. 6 is serially supplied to the drive signal generator 51 in synchronization with the clock signal CL. By controlling the amount of ink ejected from each ejection unit 35 by this print signal SI, each dot of the label paper P can express four gradations of non-recording, small dots, medium dots, and large dots. It becomes possible.

  Each of the shift registers SR temporarily holds the serially supplied print signal SI for every 2 bits corresponding to each ejection unit 35. Specifically, M shift registers SR of 1 stage, 2 stages,..., M stages corresponding to M ejection units 35 on a one-to-one basis are cascade-connected to each other and serially supplied print signals. SI is sequentially transferred to the subsequent stage according to the clock signal CL. When the print signal SI is transferred to all of the M shift registers SR, the supply of the clock signal CL is stopped, and each of the M shift registers SR has 2 bits corresponding to itself among the print signals SI. Keep the minute data.

  Each of the M latch circuits LT simultaneously latches the print signals SI for 2 bits corresponding to the respective stages held in the M shift registers SR at the timing when the latch signal LAT rises. In FIG. 15, SI [1], SI [2],..., SI [M] are respectively latched by the latch circuits LT corresponding to the 1-stage, 2-stage,. A 2-bit print signal SI is shown.

By the way, the printing operation period, which is a period in which the inkjet printer 1 forms an image on the label paper P and performs printing, includes a plurality of unit operation periods Tu.
Then, the control unit 6 assigns the unit operation period Tu to either the unit print operation period Tp for performing the printing process or the unit detection operation period Tt for performing the discharge abnormality detection process. Therefore, the printing operation period includes a plurality of unit printing operation periods Tp and a plurality of unit detection operation periods Tt. That is, in each unit operation period Tu included in the printing operation period, either the printing process or the ejection abnormality detection process is executed. Hereinafter, the unit printing operation period Tp and the unit detection operation period Tt may be simply referred to as a unit operation period Tu. In the present embodiment, it is assumed that the unit operation period Tu has a predetermined time length.
Hereinafter, the unit printing operation period Tp and the unit detection operation period Tt will be described in detail.

The unit printing operation period Tp is a printing signal SI [1], SI [2] for 2 bits in which each of the M ejection units 35 is latched by the latch circuit LT in order for the inkjet printer 1 to perform a printing process. ,..., SI [M] (i.e., ejection or non-ejection operation), and the non-recording, small dots, medium dots, or large This is a period for forming M dots that can be expressed by four gradations of dots.
Each unit printing operation period Tp includes a control period Tcp1 and a control period Tcp2 subsequent thereto. In the present embodiment, the control periods Tcp1 and Tcp2 have the same time length.

On the other hand, the unit detection operation period Tt is an operation defined by the 2-bit print signal SI [m] latched by the latch circuit LT in order for the ink jet printer 1 to perform discharge abnormality detection processing. It is a period to perform. Each unit detection operation period Tt includes a control period Tct1 and a control period Tct2 subsequent thereto.
In the present embodiment, the unit detection operation period Tt has a time length equal to the unit printing operation period Tp, and the control periods Tct1 and Tct2 have a time length equal to the control periods Tcp1 and Tcp2.
Hereinafter, the control period Tcp1 and the control period Tct1 may be collectively referred to as a control period Tc1, and the control period Tcp2 and the control period Tct2 may be collectively referred to as a control period Tc2.
The controller 6 supplies the print signal SI to the drive signal generator 51 every unit operation period Tu (Tp or Tt), and the latch circuit LT every unit operation period Tu (Tp or Tt). The print signals SI [1], SI [2],..., SI [M] are latched.

The decoder DC decodes the 2-bit print signal SI latched by the latch circuit LT, and outputs selection signals Sa and Sb in the control periods Tc1 and Tc2, respectively.
FIG. 16 is an explanatory diagram (table) showing the contents of decoding performed by the decoder DC. As shown in this figure, the content indicated by the print signal SI [m] corresponding to m stages (m is a natural number satisfying 1 ≦ m ≦ M) is, for example, (MSB, LSB) = (1, 0). In this case, in the control period Tc1 (Tcp1 or Tct1), the m-stage decoder DC sets the selection signal Sa to the high level H, sets the selection signal Sb to the low level L, and controls the control period Tc2 (Tcp2 or Tcp2). At Tct2), the selection signal Sa is set to the low level L and the selection signal Sb is set to the high level H.
Note that in the unit detection operation period Tt, the contents indicated by the print signal SI [m] are limited to two types (MSB, LSB) = (1, 1) or (0, 0). In order to facilitate understanding of the operation of DC, the case of (MSB, LSB) = (1, 0) is illustrated. The contents of the print signal SI [m] in the unit detection operation period Tt will be described later.

Returning to FIG.
As shown in FIG. 15, the drive signal generator 51 includes a set of M transmission gates TGa and TGb so as to correspond to the M ejection units 35 on a one-to-one basis.
The transmission gate TGa is turned on when the selection signal Sa is at the H level and turned off when the selection signal Sa is at the L level. The transmission gate TGb is turned on when the selection signal Sb is at the H level and turned off when the selection signal Sb is at the L level.
For example, in the m-th stage, when the content indicated by the print signal SI [m] is (MSB, LSB) = (1, 0), the transmission gate TGa is turned on in the control period Tc1 (Tcp1 or Tct1). The transmission gate TGb is turned off, and the transmission gate TGb is turned on and the transmission gate TGb is turned on in the control period Tc2 (Tcp2 or Tct2).

The drive waveform signal Com-A is supplied to one end of the transmission gate TGa, and the drive waveform signal Com-B is supplied to one end of the transmission gate TGb. The other ends of the transmission gates TGa and TGb are commonly connected to the output end OTN to the switching unit 53.
When the transmission gate TGa is turned on, the drive waveform signal Com-A is output to the output terminal OTN, and when the transmission gate TGb is turned on, the drive waveform signal Com-B is output to the output terminal OTN. .
As a result, from the m-stage output terminal OTN, the drive waveform signal Com-A or Com-B selected for each of the control periods Tc1 and Tc2 by the m-stage transmission gates TGa and TGb is used as the drive signal Vin [m]. This is output and supplied to the m-stage ejection unit 35 via the switching unit 53.

  FIG. 17 is a timing chart for explaining the operation of the drive signal generator 51 in the unit printing operation period Tp. As shown in FIG. 17, the unit printing operation period Tp is defined by the latch signal LAT output from the control unit 6. Each unit printing operation period Tp is composed of control periods Tcp1 and Tcp2 of the same time length defined by the latch signal LAT and the change signal CH.

  As shown in FIG. 17, the drive waveform signal Com-A supplied from the control unit 6 in the unit printing operation period Tp includes the unit waveform PA1 arranged in the control period Tcp1 in the unit printing operation period Tp, and the control period. This is a waveform in which unit waveforms PA2 arranged at Tcp2 are continuous. The potentials at the start and end timings of the unit waveform PA1 and the unit waveform PA2 are both the reference potential Vc. Further, as shown in this figure, the potential difference between the potential Va11 and the potential Va12 of the unit waveform PA1 is larger than the potential difference between the potential Va21 and the potential Va22 of the unit waveform PA2. Therefore, when the piezoelectric element 120 included in each discharge unit 35 is driven by the unit waveform PA1, the amount of ink discharged from the nozzle N included in the discharge unit 35 is discharged when driven by the unit waveform PA2. It is larger than the amount of ink.

  The drive waveform signal Com-B supplied from the control unit 6 in the unit printing operation period Tp is a waveform obtained by continuing the unit waveform PB1 arranged in the control period Tcp1 and the unit waveform PB2 arranged in the control period Tcp2. is there. The potentials at the start and end timing of the unit waveform PB1 are both the reference potential Vc, and the unit waveform PB2 is kept at the reference potential Vc over the control period Tcp2. Further, the potential difference between the potential Vb11 of the unit waveform PB1 and the reference potential Vc is smaller than the potential difference between the potential Va21 and the potential Va22 of the unit waveform PA2. Even if the piezoelectric element 120 included in each discharge unit 35 is driven by the unit waveform PB1, ink is not discharged from the nozzle N included in the discharge unit 35. Similarly, when the unit waveform PB2 is supplied to the piezoelectric element 120, ink is not ejected from the nozzle N.

As described above, the M latch circuits LT have the print signals SI [1], SI [2], the timing at which the latch signal LAT rises, that is, the timing at which the unit operation period Tu (Tp or Tt) starts. ..., SI [M] is output.
Further, as described above, the m-stage decoder DC changes the contents of the table shown in FIG. 16 in each of the control periods Tc1 (Tcp1 or Tct1) and Tc2 (Tcp1 or Tct1) according to the print signal SI [m]. Based on this, selection signals Sa and Sb are output.
Further, as described above, the m-stage transmission gates TGa and TGb select either the drive waveform signal Com-A or Com-B based on the selection signals Sa and Sb, and drive the selected drive waveform signal Com. Output as signal Vin [m].

The waveform of the drive signal Vin output from the drive signal generation unit 51 in the unit printing operation period Tp will be described with reference to FIGS. 15 to 17 and FIG.
When the content of the print signal SI [m] supplied in the unit print operation period Tp is (MSB, LSB) = (1, 1), the selection signals Sa and Sb are respectively at the H level in the control period Tcp1. Since it is at the L level, the drive waveform signal Com-A is selected by the transmission gate TGa, and the unit waveform PA1 is output as the drive signal Vin [m]. In addition, since the selection signals Sa and Sb are at the H level and the L level in the control period Tcp2, the drive waveform signal Com-A is selected by the transmission gate TGa, and the unit waveform PA2 is output as the drive signal Vin [m]. The
That is, as shown in FIG. 18, when the content of the print signal SI [m] is (MSB, LSB) = (1, 1), it is supplied to the m-stage ejection units 35 during the unit print operation period Tp. The waveform of the drive signal Vin [m] to be generated is a waveform DpAA including the unit waveform PA1 and the unit waveform PA2.
As a result, the m-stage ejection unit 35 ejects a medium amount of ink based on the unit waveform PA1 and a small amount of ink based on the unit waveform PA2 in the unit printing operation period Tp. Since the ink ejected twice is combined on the label paper P, large dots are formed on the label paper P.

When the content of the print signal SI [m] supplied in the unit print operation period Tp is (MSB, LSB) = (1, 0), the selection signals Sa and Sb are respectively at the H level in the control period Tcp1. Since it is at the L level, the drive waveform signal Com-A is selected by the transmission gate TGa, and the unit waveform PA1 is output as the drive signal Vin [m]. In addition, since the selection signals Sa and Sb are at the L level and the H level in the control period Tcp2, the drive waveform signal Com-B is selected by the transmission gate TGb, and the unit waveform PB2 is output as the drive signal Vin [m]. The
That is, as shown in FIG. 18, when the content of the print signal SI [m] is (MSB, LSB) = (1, 0), it is supplied to the m-stage ejection units 35 during the unit print operation period Tp. The waveform of the drive signal Vin [m] to be generated is a waveform DpAB including the unit waveform PA1 and the unit waveform PB2.
As a result, the m-stage ejection unit 35 ejects a medium amount of ink based on the unit waveform PA1 during the unit printing operation period Tp, and a medium dot is formed on the label paper P.

When the content of the print signal SI [m] supplied in the unit print operation period Tp is (MSB, LSB) = (0, 1), the selection signals Sa and Sb are respectively at the L level in the control period Tcp1. Since it is at the H level, the drive waveform signal Com-B is selected by the transmission gate TGb, and the unit waveform PB1 is output as the drive signal Vin [m]. In addition, since the selection signals Sa and Sb are at the H level and the L level in the control period Tcp2, the drive waveform signal Com-A is selected by the transmission gate TGa, and the unit waveform PA2 is output as the drive signal Vin [m]. The
That is, as shown in FIG. 18, when the content of the print signal SI [m] is (MSB, LSB) = (0, 1), it is supplied to the m-stage ejection units 35 during the unit print operation period Tp. The waveform of the drive signal Vin [m] to be generated is a waveform DpBA including the unit waveform PB1 and the unit waveform PA2.
As a result, the m-stage ejection unit 35 ejects a small amount of ink based on the unit waveform PA2 in the unit printing operation period Tp, and a small dot is formed on the label paper P.

When the content of the print signal SI [m] supplied in the unit print operation period Tp is (MSB, LSB) = (0, 0), the selection signals Sa and Sb are respectively at the L level in the control period Tcp1. Since it is at the H level, the drive waveform signal Com-B is selected by the transmission gate TGb, and the unit waveform PB1 is output as the drive signal Vin [m]. Further, since the selection signals Sa and Sb are at the L level and the H level in the control period Tcp2, the drive waveform signal Com-A is selected by the transmission gate TGb, and the unit waveform PB2 is output as the drive signal Vin [m]. The
That is, as shown in FIG. 18, when the content of the print signal SI [m] is (MSB, LSB) = (0, 0), it is supplied to the m-stage ejection units 35 during the unit print operation period Tp. The waveform of the drive signal Vin [m] to be generated is a waveform DpBB including the unit waveform PB1 and the unit waveform PB2.
As a result, no ink is ejected from the m-stage ejection units 35 in the unit printing operation period Tp, and no dots are formed on the label paper P (non-recording).

  FIG. 19 is a timing chart for explaining the operation of the drive signal generator 51 in the unit detection operation period Tt. As shown in FIG. 19, the unit detection operation period Tt is defined by the latch signal LAT output from the control unit 6. Each unit detection operation period Tt includes control periods Tct1 and Tct2 having the same time length defined by the latch signal LAT and the change signal CH.

As shown in FIG. 19, the drive waveform signal Com-A supplied from the control unit 6 in the unit detection operation period Tt includes the unit waveform PA1-T arranged in the control period Tct1 in the unit detection operation period Tt, and The unit waveform PA2-T arranged in the control period Tct2 is a continuous waveform.
In the present embodiment, the potential of the unit waveform PA1-T changes from the potential Va11 to the potential Va12 in the control period Tcp1, similarly to the unit waveform PA1. For this reason, when the piezoelectric element 120 included in each discharge unit 35 is driven by the unit waveform PA1-T, medium ink is discharged from the nozzle N included in the discharge unit 35.
Note that the potential at the start timing of the unit waveform PA1-T and the potential at the end timing of the unit waveform PA2 are both the reference potential Vc. Further, the potential indicated by the drive waveform signal Com-A in the unit detection operation period Tt becomes the potential Va12 in the control period Tct1, and then is maintained at the potential Va12 until immediately before the end of the control period Tct2.

The drive waveform signal Com-B supplied from the control unit 6 in the unit detection operation period Tt is:
The waveform is the same as that of the drive waveform signal Com-B supplied from the control unit 6 in the unit printing operation period Tp.
The switching period designation signal Sc shown in FIG. 19 will be described later.

Next, the waveform of the drive signal Vin output from the drive signal generation unit 51 in the unit detection operation period Tt will be described with reference to FIG.
As described above, in the unit detection operation period Tt, the contents of the print signal SI [m] supplied from the control unit 6 are two types (MSB, LSB) = (1, 1) or (0, 0). Limited.
When the content of the print signal SI [m] supplied in the unit detection operation period Tt is (MSB, LSB) = (1, 1), the selection signals Sa, Sb are set in the control period Tct1 and the control period Tct2. Since they are at the H level and the L level, respectively, the drive waveform signal Com-A is selected by the transmission gate TGa. In this case, the waveform of the drive signal Vin [m] supplied to the m-stage ejection unit 35 in the unit detection operation period Tt, as shown in FIG. 20, is a unit waveform PA1-T and a unit waveform PA2-T. A waveform DpT including The m-stage ejection unit 35 ejects a medium amount of ink based on the unit waveform PA1-T in the unit detection operation period Tt.
When the content of the print signal SI [m] supplied in the unit detection operation period Tt is (MSB, LSB) = (0, 0), the selection signals Sa and Sb are set in the control period Tct1 and the control period Tct2. The drive waveform signal Com-B is selected by the transmission gate TGb because they are at the L level and the H level, respectively. In this case, the waveform of the drive signal Vin [m] supplied to the m-stage ejection units 35 in the unit detection operation period Tt is a waveform DpBB as shown in FIG. Therefore, ink is not ejected from the m-stage ejection section 35.

As described above, in the unit detection operation period Tt, the inkjet printer 1 according to the present embodiment drives the ejection unit 35 with the drive signal Vin having the waveform DpT to eject ink, and the resulting cavity of the ejection unit 35 is generated. 141 detects a change in electromotive force of the piezoelectric element 120 based on a pressure change inside 141 as a residual vibration signal Vout. And the discharge abnormality detection process which performs the determination about whether the discharge part 35 has discharge abnormality based on the residual vibration signal Vout is performed.
In the present embodiment, as an ejection abnormality detection process, a case where the ejection state is determined based on residual vibration generated in the ejection section 35 when the ejection section 35 is driven so that ink is ejected from the nozzle N is illustrated. However, the present invention is not limited to such an embodiment, and the ejection abnormality detection process is performed when the ejection unit 35 is driven so that ink is not ejected from the nozzle N. The discharge state may be determined on the basis of residual vibration generated. That is, in the present embodiment, the ejection abnormality detection process will be described by exemplifying the case of non-ejection inspection, but the present embodiment similarly applies to the case of ejection inspection.
When the ejection abnormality detection process is executed without ejecting ink, the potential difference between the potential Va11 and the potential Va12 in the waveform DpT shown in FIG. 20 (unit waveform PA1-T shown in FIG. 19) is expressed as the waveform DpT. What is necessary is just to set it as a small value compared with the time of discharge so that ink may not be discharged from the nozzle N even if the discharge part 35 is driven with the drive signal Vin which has.

In the present embodiment, the control unit 6 (CPU 61), for each unit detection operation period Tt, for each of the first group to the Qth group, one discharge from among the K discharge units 35 constituting each group. The unit 35 is selected as a target for the ejection abnormality detection process. In other words, in each unit detection operation period Tt, the control unit 6 selects Q ejection units 35 from among the M ejection units 35 as ejection units 35 (“target ejection” as targets of ejection abnormality detection processing. As an example).
Then, in each unit detection operation period Tt, the control unit 6 is supplied with the drive signal Vin having the waveform DpT to the selected Q ejection units 35, and the other (MQ) units that are not selected. The printing signal SI (and the drive waveform signal Com) is generated so that the drive signal Vin having the waveform DpBB is supplied to the discharge unit 35, and these signals are supplied to the drive signal generation unit 51.
In addition, the control unit 6 sets the switching control signal Sw so that the residual vibration signal Vout output from the selected Q number of ejection units 35 is supplied to each of the Q number of ejection abnormality detection circuits DT. This is generated and supplied to the switching unit 53. Specifically, the control unit 6 selects one of the K ejection units 35 constituting the q-th group (q is a natural number satisfying 1 ≦ q ≦ Q) that is selected as the target of the ejection abnormality detection process. The switching control signal Sw is generated so that the residual vibration signal Vout output from the discharge unit 35 is output to the discharge abnormality detection circuit DT [q] provided corresponding to the q-th group.

  In addition, the control unit 6 sets the K discharge units 35 constituting each group to a unit detection operation period so that all of the K discharge units 35 constituting each group are subjected to discharge abnormality detection processing. One discharge unit 35 is selected in a predetermined order for each Tt. In the present embodiment, the K ejection units 35 constituting each group are selected one by one for each unit detection operation period Tt in order of increasing number of stages. As a result, all of the K discharge units 35 constituting each group are selected when the K unit detection operation periods Tt have elapsed, and all the discharge units 35 are included during the K unit detection operation periods Tt. Discharge abnormality detection processing can be performed for.

FIG. 21 is a block diagram illustrating the configuration of the switching unit 53 in the head driver 50 and the electrical connection relationship between the switching unit 53, the ejection abnormality detection unit 52, the head unit 30, and the drive signal generation unit 51. is there.
As shown in FIG. 21, the switching unit 53 includes 1 to M M switching circuits U (U [1], U [2],. U [M]). The m-stage switching circuit U [m] includes an m-stage ejection unit 35 (strictly speaking, a piezoelectric element 120), an m-stage output end OTN included in the drive signal generation unit 51, or an ejection abnormality detection unit 52. It is electrically connected to any one of the ejection abnormality detection circuits DT provided.
Hereinafter, in each switching circuit U, a state in which the ejection unit 35 and the output end OTN of the drive signal generation unit 51 are electrically connected is referred to as a first connection state. In addition, a state in which the discharge unit 35 and the discharge abnormality detection circuit DT of the discharge abnormality detection unit 52 are electrically connected is referred to as a second connection state.
Note that the M switching circuits U [1], U [2],..., U [M] are Q groups, each of which includes K switching circuits U as well as the M ejection units 35. It is divided into.

  As shown in FIG. 21, the ejection abnormality detection unit 52 includes Q ejection abnormality detection circuits DT [1] to DT [Q] provided to correspond to the Q groups on a one-to-one basis. That is, each of the K switching circuits U configuring the q-th group is electrically connected in common to the ejection abnormality detection circuit DT [q] provided corresponding to the q-th group.

As shown in FIG. 21, the control unit 6 supplies a switching control signal Sw [m] for controlling the connection state of the switching circuit U [m] to the m-th switching circuit U [m].
Specifically, the control unit 6 performs switching control so that all the switching circuits U [1], U [2],..., U [M] are set to the first connection state in the unit printing operation period Tp. Signals Sw [1], Sw [2],..., Sw [M] are output. That is, in the unit printing operation period Tp, each of the M ejection units 35 is electrically connected to the output end OTN of the drive signal generation unit 51, and the drive signal Vin is supplied from the drive signal generation unit 51.

On the other hand, during the unit detection operation period Tt, the control unit 6 is supplied with the drive signal Vin from the drive signal generation unit 51 to each of the M ejection units 35 and is selected as the target of the ejection abnormality detection process. The operation of the switching unit 53 is controlled so that the residual vibration signal Vout from the discharge unit 35 is output to the discharge abnormality detection unit 52.
More specifically, the control unit 6 connects the switching circuit U [m] to the first connection in the entire unit detection operation period Tt when the m-stage ejection units 35 are not the target of the ejection abnormality detection process. A switching control signal Sw [m] for setting the state is supplied to the switching circuit U [m].
On the other hand, when the m-stage ejection unit 35 is the target of the ejection abnormality detection process, the control unit 6 performs the switching circuit U while the potential indicated by the switching period designation signal Sc shown in FIG. 19 is VH. In the switching period Td in which [m] is set to the first connection state and the potential indicated by the switching period specification signal Sc is VL, the switching control signal Sw [to set the switching circuit U [m] to the second connection state. m] is supplied to the switching circuit U [m].

Here, the switching period Td is a period for detecting residual vibration generated in the ejection unit 35 to which the drive signal Vin having the waveform DpT is supplied in the unit detection operation period Tt. Specifically, as shown in FIG. 19, the switching period Td starts after the drive waveform signal Com-A (that is, the waveform DpT) in the unit detection operation period Tt changes from the potential Va11 to the potential Va12. This is a period determined to end before Va12 changes to the reference potential Vc.
The ejection abnormality detection unit 52 detects a change in electromotive force of the piezoelectric element 120 of the ejection unit 35 during the switching period Td as a residual vibration signal Vout.
Further, the switching period designation signal Sc shown in FIG. 19 is a signal generated in the control unit 6 and is a signal that becomes the potential VL in the switching period Td and becomes the potential VH in a period other than the switching period Td.

FIG. 22 is a block diagram illustrating a configuration of the ejection abnormality detection circuit DT included in the ejection abnormality detection unit 52 of the head driver 50.
As shown in FIG. 22, the ejection abnormality detection circuit DT includes a detection unit 55 that outputs a detection signal NTc that represents a time length of one cycle of residual vibration of the ejection unit 35 based on the residual vibration signal Vout, and a detection signal. A determination unit 56 that determines the presence or absence of discharge abnormality in the discharge unit 35 and the discharge state when there is a discharge abnormality based on NTc, and outputs a determination result signal Rs representing the determination result.
Among these, the detection unit 55 generates the waveform shaping unit 551 that generates a shaped waveform signal Vd obtained by removing noise components and the like from the residual vibration signal Vout output from the discharge unit 35, and the detection signal NTc based on the shaped waveform signal Vd. A measuring unit 552 to be generated.

The waveform shaping unit 551 is, for example, a high-pass filter for outputting a signal in which a frequency component in a lower range than the frequency band of the residual vibration signal Vout is attenuated, or a frequency component in a higher range than the frequency band of the residual vibration signal Vout. Including a low-pass filter or the like for outputting a signal in which noise is attenuated, and a configuration capable of outputting a shaped waveform signal Vd in which the frequency range of the residual vibration signal Vout is limited and noise components are removed.
The waveform shaping unit 551 is a negative feedback amplifier for adjusting the amplitude of the residual vibration signal Vout, or a voltage follower for converting the impedance of the residual vibration signal Vout and outputting the low impedance shaped waveform signal Vd. The structure containing these etc. may be sufficient.

  The measuring unit 552 includes a shaped waveform signal Vd obtained by shaping the residual vibration signal Vout in the waveform shaping unit 551, a mask signal Msk generated by the control unit 6, and a threshold value determined by the potential at the amplitude center level of the shaped waveform signal Vd. The potential Vth_c, the threshold potential Vth_o determined to be higher than the threshold potential Vth_c, and the threshold potential Vth_u determined to be lower than the threshold potential Vth_c are supplied. Based on these signals and the like, the measurement unit 552 outputs the detection signal NTc and a validity flag Flag indicating whether or not the detection signal NTc is a valid value.

FIG. 23 is a timing chart showing the operation of the measurement unit 552.
As shown in this figure, the measuring unit 552 compares the potential indicated by the shaped waveform signal Vd with the threshold potential Vth_c, and becomes high when the potential indicated by the shaped waveform signal Vd is equal to or higher than the threshold potential Vth_c. When the potential indicated by the waveform signal Vd is less than the threshold potential Vth_c, the comparison signal Cmp1 that is at a low level is generated.
Further, the measuring unit 552 compares the potential indicated by the shaped waveform signal Vd with the threshold potential Vth_o, and when the potential indicated by the shaped waveform signal Vd is equal to or higher than the threshold potential Vth_o, the measurement unit 552 indicates a high level. When the potential is lower than the threshold potential Vth_o, the comparison signal Cmp2 that is at a low level is generated.
Further, the measurement unit 552 compares the potential indicated by the shaped waveform signal Vd with the threshold potential Vth_u, and becomes high when the potential indicated by the shaped waveform signal Vd is less than the threshold potential Vth_u, and indicates the shaped waveform signal Vd. When the potential is equal to or higher than the threshold potential Vth_u, the comparison signal Cmp3 that becomes high level is generated.
The mask signal Msk is a signal that becomes a high level only for a predetermined period Tmsk after the supply of the shaped waveform signal Vd from the waveform shaping unit 551 is started. In this embodiment, the detection signal NTc is generated only for the shaped waveform signal Vd after the lapse of the period Tmsk in the shaped waveform signal Vd, so that the noise component superimposed immediately after the start of the residual vibration is removed. A high detection signal NTc can be obtained.

The measurement unit 552 includes a counter (not shown). The counter starts counting a clock signal (not shown) at time t1 when the potential indicated by the shaped waveform signal Vd is first equal to the threshold potential Vth_c after the mask signal Msk falls to a low level. . That is, the counter is the earlier of the timing at which the comparison signal Cmp1 first rises to the high level after the mask signal Msk falls to the low level, or the timing at which the comparison signal Cmp1 first falls to the low level. Counting starts at time t1, which is the timing.
The counter then finishes counting the clock signal at time t2, which is the timing at which the potential indicated by the shaped waveform signal Vd becomes the threshold potential Vth_c for the second time after starting counting, and the obtained count value Is output as a detection signal NTc. That is, the counter is earlier of the timing at which the comparison signal Cmp1 rises to the high level for the second time after the mask signal Msk falls to the low level, or the timing at which the comparison signal Cmp1 falls to the low level for the second time. At time t2, which is the other timing, the counting is finished.
As described above, the measuring unit 552 generates the detection signal NTc by measuring the time length from the time t1 to the time t2 as the time length for one cycle of the shaped waveform signal Vd.

By the way, when the amplitude of the shaped waveform signal Vd is small as shown by the one-dot chain line in FIG. 23, there is a high possibility that the detection signal NTc cannot be measured accurately. In addition, when the amplitude of the shaped waveform signal Vd is small, even if it is determined that the discharge state of the discharge unit 35 is normal based only on the result of the detection signal NTc, there is actually a discharge abnormality. There is a possibility that has occurred. For example, when the amplitude of the shaped waveform signal Vd is small, it can be considered that ink cannot be ejected because ink is not injected into the cavity 141.
Therefore, in the present embodiment, it is determined whether or not the amplitude of the shaped waveform signal Vd has a sufficient magnitude for measurement of the detection signal NTc, and the result of the determination is output as the validity flag Flag. .
Specifically, the measurement unit 552 determines that the potential indicated by the shaped waveform signal Vd exceeds the threshold potential Vth_o during the period when the counter is counting, that is, the period from time t1 to time t2. When the value is lower than the signal Vth_u, the value of the validity flag Flag is set to a value “1” indicating that the detection signal NTc is valid. In other cases, the validity flag Flag is set to “0”. The sex flag Flag is output. More specifically, in the period from time t1 to time t2, the measurement unit 552 causes the comparison signal Cmp2 to rise from the low level to the high level and then falls to the low level again, and the comparison signal Cmp3 changes from the low level to the high level. The value of the validity flag Flag is set to “1” when falling to the low level again after rising to the level, and the value of the validity flag Flag is set to “0” in other cases.

  As described above, in the present embodiment, the measurement unit 552 generates the detection signal NTc indicating the time length of one cycle of the shaped waveform signal Vd, and the shaped waveform signal Vd is sufficient for measuring the detected signal NTc. Since it is determined whether or not the amplitude has a large magnitude, it is possible to detect the ejection abnormality more accurately.

The determination unit 56 determines the ink discharge state in the discharge unit 35 based on the detection signal NTc and the validity flag Flag, and outputs the determination result as a determination result signal Rs.
FIG. 24 is an explanatory diagram for explaining the contents of determination in the determination unit 56. As shown in this figure, the determination unit 56 sets the time length indicated by the detection signal NTc to the threshold value NTx1, the threshold value NTx2 indicating a time length longer than the threshold value NTx1, and the threshold value NTx3 indicating a time length longer than the threshold value NTx2. Compare with each of the above.
Here, the threshold value NTx1 is the time length of one period of residual vibration when bubbles are generated in the cavity 141 and the frequency of residual vibration becomes high, and one period of residual vibration when the ejection state is normal. It is a value for indicating the boundary with the time length of.
The threshold value NTx2 is a time length corresponding to one period of residual vibration when paper dust adheres to the vicinity of the nozzle N outlet and the frequency of residual vibration is low, and one period of residual vibration when the ejection state is normal. This is a value to indicate the boundary with the minute time length.
The threshold value NTx3 is the time length of one period of residual vibration when the frequency of residual vibration becomes lower than when paper dust adheres due to ink sticking or thickening in the vicinity of the nozzle N, and the nozzle N outlet. It is a value for indicating a boundary with a time length corresponding to one cycle of residual vibration when paper dust adheres in the vicinity.

As shown in FIG. 24, when the value of the validity flag Flag is “1” and “NTx1 ≦ NTc ≦ NTx2” is satisfied, the determination unit 56 indicates that the ink ejection state in the ejection unit 35 is normal. And a value “1” indicating that the ejection state is normal is set for the determination result signal Rs.
Further, when the value of the validity flag Flag is “1” and “NTc <NTx1” is satisfied, the determination unit 56 determines that the ejection abnormality has occurred due to the bubbles generated in the cavity 141. For the determination result signal Rs, a value “2” indicating that ejection abnormality due to bubbles has occurred is set.
Further, when the value of the validity flag Flag is “1” and “NTx2 <NTc ≦ NTx3” is satisfied, the determination unit 56 generates a discharge abnormality due to paper dust adhering to the vicinity of the nozzle N outlet. The value “3” indicating that a discharge abnormality due to paper dust has occurred is set for the determination result signal Rs.
Further, when the value of the validity flag Flag is “1” and “NTx3 <NTc” is satisfied, the determination unit 56 determines that an ejection abnormality has occurred due to ink thickening in the vicinity of the nozzle N. Determination is made, and a value “4” is set for the determination result signal Rs, which indicates that an ejection abnormality due to ink thickening has occurred.
Further, when the value of the validity flag Flag is “0”, the determination unit 56 sets a value “5” indicating that an ejection abnormality has occurred for some reason, such as ink not being injected. To do.

  As described above, the determination unit 56 determines whether or not a discharge abnormality has occurred in the discharge unit 35, and outputs the determination result as the determination result signal Rs. For this reason, the control unit 6 suspends the printing process as necessary (strictly, suspends the printing operation period) and discharges the head unit 30 in the initial position (X = Xini), and an appropriate recovery process according to the cause of the ejection abnormality indicated by the determination result signal Rs can be executed.

  Note that the determination in the determination unit 56 may be executed by the control unit 6 (CPU 61). In this case, the discharge abnormality detection circuit DT of the discharge abnormality detection unit 52 may be configured to include the determination unit 56 and output the detection signal NTc generated by the detection unit 55 to the control unit 6.

Next, the overall flow of printing processing, ejection abnormality detection processing, and recovery processing executed in the inkjet printer 1 will be described.
FIG. 25 is a flowchart showing the operation of the inkjet printer 1. This flowchart is started when the image data Img is supplied from the host computer 9 with the power of the inkjet printer 1 turned on, and the CPU 61 executes the control program stored in the storage unit 62.

When the image data Img is supplied from the host computer 9, the CPU 61 of the control unit 6 outputs a driver control signal Ctr1 to the carriage motor driver 401 to move the head unit 30 to the printing position (X = X0) and supply it. The driver control signal Ctr2 is output to the paper motor driver 402, and the conveyance of the label paper P is started so that the ejection unit 35 can eject ink onto the label paper P (step S110).
The label paper P is positioned so that at least some of the M ejection parts 35 included in the head unit 30 can eject ink onto the label paper P (printing area Ap and non-printing area Ax). Is conveyed, a printing operation period is started, and steps S120 to S160 described below are executed.
Note that the CPU 61 controls the motor driver 40 so that the label paper P is conveyed in the + X direction at a predetermined speed Mv during the printing operation period in which steps S120 to S160 are executed.

  After the printing operation period is started, the CPU 61 detects that the head unit 30 is on the printing area Ap of the label paper P in the first unit operation period Tu after the current time (hereinafter referred to as “target unit operation period Tu”). It is determined whether or not it is located (on label Lb) (step S120).

Specifically, in step S120, the CPU 61 calculates the movement distance of the label paper P from the start of conveyance of the label paper P to the start of the target unit operation period Tu, and the calculated movement of the label paper P. Based on the distance, the relative position in the X-axis direction of the head unit 30 with respect to the label paper P (hereinafter referred to as “label position Xp”) is obtained. Here, the on-label position Xp is, for example, a distance in the X-axis direction from a predetermined portion of the label paper P (for example, an end portion of the label paper P) to the head unit 30.
Next, in step S120, the CPU 61 determines that the head unit 30 moves the label sheet in the target unit operation period Tu based on the on-label position Xp and the information related to the shape of the label sheet P stored in the storage unit 62. It is determined whether or not it is located on the print area Ap in P. Here, the information relating to the shape of the label paper P is, for example, information about the size of the label paper P, the position of the print area Ap on the label paper P, and the like.

In the present embodiment, in step S120, the CPU 61 calculates the on-label position Xp in the target unit operation period Tu, thereby determining whether or not the head unit 30 is positioned on the print area Ap in the target unit operation period Tu. However, the present invention is not limited to such an embodiment.
For example, in step S110, the CPU 61 calculates in advance the on-label position Xp for each of the plurality of unit operation periods Tu included in the printing operation period, and each of the plurality of unit operation periods Tu based on the calculation result. Alternatively, it may be determined whether or not the head unit 30 is positioned on the printing area Ap. In this case, in step S120, the CPU 61 obtains a determination result corresponding to the target unit operation period Tu from the plurality of determination results obtained in step S110, so that the head unit 30 prints in the target unit operation period Tu. What is necessary is just to determine whether it is located on the area | region Ap.
Further, instead of explicitly obtaining the on-label position Xp in the unit operation period Tu, it is determined whether there is data to be printed in the unit operation period Tu in the image data Img, so that the unit operation period Tu. It may be determined whether or not the head unit 30 is positioned on the printing area Ap of the label paper P.

  As shown in FIG. 25, when the determination result in step S120 is affirmative, that is, when the head unit 30 is positioned on the print area Ap in the target unit operation period Tu, the CPU 61 performs unit printing in the target unit operation period Tu. An operation period Tp is assigned and the printing process is executed (step S130).

Specific processing contents of the CPU 61 in step S130 are as follows.
First, as shown in FIG. 17, the CPU 61 sets ink to be ejected from each of the M ejection units 35 in the target unit operation period Tu before the target unit operation period Tu (unit print operation period Tp) is started. The print signal SI that defines the amount is supplied to the drive signal generator 51 together with the clock signal CL.
In addition, the CPU 61 supplies the latch signal LAT, the change signal CH, and the drive waveform signal Com to the drive signal generation unit 51 in the target unit operation period Tu. Note that the drive waveform signal Com that the CPU 61 supplies to the drive signal generation unit 51 in step S130 includes a drive waveform signal Com-A including unit waveforms PA1 and PA2, and unit waveforms PB1 and PB2, as shown in FIG. A drive waveform signal Com for print processing including the drive waveform signal Com-B.
Further, the CPU 61 switches the switching control signal Sw [1] so that all the M switching circuits U of the switching unit 53 are in the first connection state over the target unit operation period Tu in the target unit operation period Tu. To Sw [M] are supplied to the switching unit 53.

  As shown in FIG. 25, when the determination result in step S120 is negative, that is, when the head unit 30 is positioned on the non-printing area AxH in the target unit operation period Tu, the CPU 61 performs the unit in the target unit operation period Tu. The detection operation period Tt is assigned, and the ejection abnormality detection process is executed (step S140).

Specific processing contents of the CPU 61 in step S140 are as follows.
First, before starting the target unit operation period Tu (unit detection operation period Tt), the CPU 61 sets the discharge units 35 to be subjected to the discharge abnormality detection process to the respective discharge units belonging to the first to Qth groups. A total of Q is selected from each of the 35.
Next, before starting the target unit operation period Tu, the CPU 61 generates a print signal SI that defines the amount of ink to be discharged from each of the M ejection units 35 in the target unit operation period Tu together with the clock signal CL. This is supplied to the drive signal generator 51.
The CPU 61 is supplied with the drive signal Vin having the waveform DpT to the Q ejection units 35 selected as the target of the ejection abnormality detection process, and (M−Q) ejection units that are not selected. For 35, the content of the print signal SI is set so that the drive signal Vin having the unit waveforms PB1 and PB2 is supplied. More specifically, the CPU 61 sets (MSB, LSB) = (1, 1) as the print signal SI [m] corresponding to the ejection unit 35 selected as the target of the ejection abnormality detection process, and ejects not selected. The print signal SI [m] corresponding to the part 35 is set to (MSB, LSB) = (0, 0).
In addition, the CPU 61 supplies the latch signal LAT, the change signal CH, and the drive waveform signal Com to the drive signal generation unit 51 in the target unit operation period Tu. Note that the drive waveform signal Com that the CPU 61 supplies to the drive signal generation unit 51 in step S140 includes a drive waveform signal Com-A including unit waveforms PA1-T and PA2-T, and a unit waveform PB1, as shown in FIG. And the drive waveform signal Com-B including the drive waveform signal Com-B including PB2.
In addition, in the target unit operation period Tu, the CPU 61 causes the switching circuit U [m] corresponding to the ejection unit 35 selected as the target of the ejection abnormality detection process to be connected in the second connection in the switching period Td of the target unit operation period Tu. The switching circuit U [m] corresponding to the ejection unit 35 that has not been selected is in the first connection state over the target unit operation period Tu. The switching control signals Sw [1] to Sw [M] are supplied to the switching unit 53.
Further, the CPU 61 uses the contents of the Q determination result signals Rs generated by the discharge abnormality detection unit 52 based on the Q residual vibration signals Vout output from the selected Q discharge units 35 as the discharge abnormality detection result. The data is stored in the storage unit 62 as data. Here, the discharge abnormality detection result data is data in which the number of stages of the discharge unit 35 in which discharge abnormality is found and the value indicated by the determination result signal Rs corresponding to the discharge unit 35 are associated with each other. The ejection abnormality detection result data is stored in the storage unit 62 at least until a recovery process described later is executed.

As shown in FIG. 25, when the discharge abnormality detection process in the target unit operation period Tu is completed, the CPU 61, based on the discharge abnormality detection result data stored in the storage unit 62,
It is determined whether recovery processing is necessary (step S150).
Specifically, the CPU 61 refers to the ejection abnormality detection result data, and determines that the recovery process is necessary when the number of ejection units 35 in which ejection abnormality is present is greater than a predetermined allowable number. When the number of ejection units 35 that are abnormal in ejection is equal to or less than a predetermined allowable number, it is determined that the recovery process is unnecessary.
Note that the determination criterion in the determination according to the present embodiment is an example, and the determination may be performed using a criterion that is appropriately determined according to the image quality required for the printing process performed by the inkjet printer 1. For example, it may be determined that the recovery process is necessary when a predetermined number of ejection units 35 that are abnormal in ejection exist in the X-axis direction or the Y-axis direction.

If the CPU 61 determines in step S150 that the recovery process is necessary, the CPU 61 interrupts the printing operation period and advances the process to step S180.
On the other hand, if the CPU 61 determines in step S150 that the recovery process is unnecessary, the process proceeds to step S160 without interrupting the printing operation period.

Note that when the CPU 61 performs the printing process in step S <b> 130 despite the presence of the ejection unit 35 that is abnormal in ejection, the ejection unit 35 that is abnormal in ejection regardless of the content of the image data Img. The print signal SI may be generated so as not to eject ink from the printer.
In this case, the CPU 61 uses the discharge amount specified by the image data Img as the discharge amount from the discharge unit 35 corresponding to the same color adjacent in the X-axis direction or the Y-axis direction with respect to the discharge unit 35 that is abnormal in discharge. The print signal SI may be generated so as to increase the number of the print signals SI. As a result, even when there is an ejection portion 35 with abnormal ejection, it is possible to keep the degree of degradation of the image quality of the image formed on the label Lb of the label paper P small.

As shown in FIG. 25, when the printing process in the target unit operation period Tu is completed in step S130, or when the determination result in step S150 is negative, the CPU 61 advances the process to step S160.
In step S160, the CPU 61 determines whether or not all the printing processes for the label paper P have been completed based on the image data Img and the like. When the determination result in step S160 is affirmative, the CPU 61 ends the series of processes shown in FIG. If the determination result in step S160 is negative, that is, if printing on the label paper P has not been completed, the CPU 61 can execute the printing process or the ejection abnormality detection process in the next unit operation period Tu. Then, the conveyance of the label paper P is continued (step S170), and the process proceeds to step S120.

  On the other hand, when the determination result in step S150 is affirmative, that is, when it is determined that the recovery process is necessary, the CPU 61 stops the conveyance of the label paper P and moves the head unit 30 to the initial position (X = Xini). (Step S180). Thereby, the printing operation period is interrupted.

Thereafter, the CPU 61 executes a recovery process using the recovery mechanism 70 (step S190).
More specifically, the CPU 61 controls the operation of the recovery mechanism 70 (and the head driver 50) to wipe off foreign matters such as paper dust attached to the nozzle plate 150 with a wiper (not shown), the cavity 141. Ink ejection from the ejection unit 35 is performed by performing recovery processing such as pumping processing for sucking thickened ink and bubbles by a tube pump (not shown) and flushing processing for preliminarily ejecting ink from the ejection unit 35. Return the state to normal.
At this time, the CPU 61 selects and executes one or more processes suitable for recovering the discharge state of the discharge unit 35 from the flushing process, the wiping process, the pumping process, and the like based on the discharge abnormality detection result data. May be.

  After the recovery process is completed, the CPU 61 advances the process to step S110 to restart the conveyance of the label sheet P and the printing operation period to execute the printing process and the ejection abnormality detection process.

  Thus, in this embodiment, during the printing operation period, without stopping the conveyance of the label paper P (that is, while the head unit 30 remains in the printing position (X = X0)), the printing process and the ejection abnormality are performed. Both detection processes are executed.

In order to clarify the effect of the inkjet printer 1 performing printing based on the flowchart shown in FIG. 25, an inkjet printer that performs the ejection abnormality detection process at the initial position (X = Xini) (Referred to as “inkjet printer”).
The comparative inkjet printer is configured in the same manner as the inkjet printer 1 according to the present embodiment, except that the control program stored in the storage unit 62 is different from the inkjet printer 1.

FIG. 26 is a flowchart showing the operation of the inkjet printer according to the comparative example. In this flowchart, the CPU 61 of the proportional inkjet printer (hereinafter referred to as “a proportional CPU”) receives the supply of image data Img from the host computer 9, and the proportional CPU is stored in the storage unit 62. It is started by executing the stored control program related to the proportionality.
When the image data Img is supplied from the host computer 9, the proportional CPU outputs a driver control signal Ctr1 and a driver control signal Ctr2 as in step S110 of FIG. Then, the conveyance of the label paper P is started so that the ink can be discharged (step S110t).
In the printing operation period, the CPU according to the proportionality determines whether or not the number of printing processes executed after the last execution of the recovery process is equal to or less than a predetermined number (step S120t).
If the determination result in step S120t is affirmative, that is, if the number of printing processes executed after the recovery process is less than or equal to a predetermined number, the CPU in the proportional manner is the same as that in step S130 in FIG. The printing process is executed at Tu (step S130t), and then it is determined whether or not all the printing processes for the label paper P have been completed (step S160t) as in step S160 of FIG.
When the determination result of step S160t is affirmative, the CPU according to the comparative example ends the series of processes illustrated in FIG. 26, and when the determination result of step S160t is negative, in the next unit operation period Tu, The process advances to step S120t while continuing the conveyance of the label paper P (step S170t) so that the printing process or the ejection abnormality detection process can be executed.

Further, as shown in FIG. 26, when the determination result of step S120t is negative, that is, when the printing process is executed more times than the predetermined number after the recovery process is executed last, the comparison is made. As with step S180 in FIG.
The conveyance of the label paper P is stopped, and the head unit 30 is moved to the initial position (X = Xini) (step S200t). Thereby, the printing operation period is interrupted.
Thereafter, the CPU according to the proportionality performs the ejection abnormality detection process for all the ejection units 35 included in the ink jet printer according to the proportionality (step S210t).
After the discharge abnormality detection process in step S210t is completed,
As in step S150 in FIG. 25, it is determined whether or not a recovery process is necessary (step S220t). If the determination result of step S220t is affirmative, the CPU related to the proportionality executes the recovery process using the recovery mechanism 70 (step S230t), similarly to step S190 of FIG. 25, and after the recovery process ends, The process proceeds to step S110t. On the other hand, if the determination result in step S220t is negative, the CPU related to the proportionality advances the process to step S110t without executing the recovery process.

As described above, the proportional inkjet printer stops the conveyance of the label paper P, interrupts the printing operation period, and then moves the head unit 30 to the initial position (X = Xini) to detect ejection abnormality. Execute the process. Therefore, the proportional inkjet printer needs to interrupt the printing operation period every time the printing process is executed a predetermined number of times, and the time from the start to the end of printing on the label paper P is the inkjet printer according to the present embodiment. Longer than 1.
In particular, when the conveyance of the label paper P is stopped, the label paper P remains in the + X direction even after the conveyance is stopped due to the inertial force of the label paper P stored in the roll paper storage unit 43 in a roll shape. Continue moving. For this reason, when the printing operation period is restarted after the conveyance of the label paper P is stopped in order to execute the ejection abnormality detection process, the label paper P is moved by the amount that the label paper P has moved after the conveyance stops. It is necessary to align the label paper P such as returning to the X direction.
Compared with the inkjet printer 1 according to the present embodiment, the inkjet printer according to the comparative example is more likely to stop the conveyance of the label paper P and interrupt the printing operation period. There is also a high possibility that the time from the start to the end of printing becomes longer.
On the other hand, the inkjet printer 1 according to the present embodiment executes both the printing process and the ejection abnormality detection process without stopping the conveyance of the label paper P during the printing operation period. Compared with a printer, the time from the start to the end of printing on the label paper P can be shortened.

Hereinafter, an operation image of the printing process and the ejection abnormality detection process in the printing operation period of the inkjet printer 1 in the present embodiment will be described with reference to FIGS.
27 to 30, for easy understanding, the head unit 30 includes 12 ejection units 35 and the ejection abnormality detection unit 52 includes three ejection abnormality detection circuits DT [1] to DT [. 3] will be described as an example. That is, in this example, the case where the twelve discharge units 35 are divided into the first group to the third group by four, that is, the case where M = 12, Q = 3, and K = 4 will be described as an example. To do.
In this example, twelve nozzles N corresponding to the twelve ejection units 35 are represented by symbols N [1] to N [12].

FIG. 27 is an explanatory diagram showing a relationship between the label upper position Xp, which is a relative position of the label paper P with respect to the head unit 30, and the unit operation period Tu.
In this figure, the head unit 30 is located at the printing position (X = X0), and as a result of the label paper P being conveyed upward (+ X direction) at the speed Mv, the position Xp of the head unit 30 on the label is The case of moving is shown. However, in this figure, for convenience of description, the head portion 30 itself is shown as moving downward in the figure. Further, in this drawing, for convenience of description, only the head unit 30 in a part of the unit operation periods Tu among the plurality of unit operation periods Tu is shown.
Further, in this figure, a plurality of unit operation periods Tu included in the printing operation period are represented in order by adding numerals to the symbols Tu such as Tu1, Tu2, Tu3,..., Tu10,. In addition, the on-label position Xp in the unit operation periods Tu1, Tu2, Tu3,..., Tu10 is represented by adding a number to the code Xp as Xp1, Xp2, Xp3,.

In the label paper P in this example, as shown in FIG. 27, the print areas Ap (labels Lb) are arranged in Xp2 to Xp3, Xp6 to Xp7, and Xp10 among the on-label positions Xp1 to Xp10. . Therefore, among the unit operation periods Tu1 to Tu10 shown in the figure, each of Tu2, Tu3, Tu6, Tu7, and Tu10 is a unit printing operation period Tp, and each of Tu1, Tu4, Tu5, Tu8, and Tu9. Is the unit detection operation period Tt.
In this figure, the five unit printing operation periods Tp are represented in order by adding numerals to the reference Tp as Tp1, Tp2,..., Tp5. In addition, the five unit detection operation periods Tt are also expressed in order by adding a number to the reference Tt, such as Tt1, Tt2,..., Tt5.

28 and 29 are explanatory diagrams for explaining the operation of the ink jet printer 1 (particularly, the ejection unit 35) in each of the unit operation periods Tu1 to Tu10 shown in FIG.
In these drawings, “●” represents the nozzle N corresponding to the ejection unit 35 selected as the target of the ejection abnormality detection process, and “◯” represents the ejection unit 35 that was not the target of the ejection abnormality detection process. Represents a nozzle N corresponding to, and “Δ” represents a nozzle N corresponding to the ejection unit 35 used in the printing process.

FIG. 28A shows the operation of the nozzle N (ejection unit 35) in the unit detection operation period Tt1, which is the first unit operation period Tu1 of the printing operation period.
In the unit detection operation period Tt1, a total of Q (three) ejection units 35, one for each group, are selected from the M (12) ejection units 35 as targets for ejection abnormality detection processing. Is done.
Specifically, the discharge unit 35 corresponding to the nozzle N [1] is selected from the first group, the discharge unit 35 corresponding to the nozzle N [5] is selected from the second group, and from the third group. The discharge unit 35 corresponding to the nozzle N [9] is selected.
Then, a drive signal Vin having a waveform DpT is supplied to these three ejection portions 35, and ink is ejected from the respective nozzles N [1], N [5], N [9], and based on the residual vibration. Thus, a determination is made as to whether or not there is a discharge abnormality.

  FIG. 28B shows the operation of the nozzle N in the unit operation periods Tu2 and Tu3 (unit print operation periods Tp1 and Tp2) of the print operation period. In the unit printing operation periods Tp1 and Tp2, the ejection units 35 corresponding to the nozzles N [2] to N [5] and N [8] to N [11] are driven based on the drive signal Vin. Thus, an image is formed on the label Lb in the printing area Ap.

FIG. 28C shows the operation of the nozzle N (ejection unit 35) in the unit operation periods Tu4 and Tu5 (unit detection operation periods Tt2 and Tt3).
In the unit detection operation period Tt2, each group is selected from the discharge units 35 other than the Q (three) discharge units 35 selected in the unit detection operation period Tt1 among the M (12) discharge units 35. A total of Q (three) discharge units 35 are selected as targets for the discharge abnormality detection process.
Specifically, three ejection units 35 corresponding to the nozzles N [2], N [6], and N [10] are selected as targets of ejection abnormality detection processing, respectively. On the other hand, a determination is made as to whether or not there is a discharge abnormality.
Similarly, in the unit detection operation period Tt3, the discharge units 35 other than 2Q (six) discharge units 35 selected in the unit detection operation periods Tt1 and Tt2 out of the M (12) discharge units 35 are used. From the inside, a total of Q (three) ejection units 35, one for each group, are selected as targets for ejection abnormality detection processing.
Specifically, three ejection units 35 corresponding to the nozzles N [3], N [7], and N [11] are respectively selected as targets for the ejection abnormality detection process, and the ejection units 35 are selected. On the other hand, a determination is made as to whether or not there is a discharge abnormality.

  FIG. 29A shows the operation of the nozzle N in the unit operation periods Tu6 and Tu7 (unit print operation periods Tp3 and Tp4) of the print operation period. In the unit printing operation periods Tp3 and Tp4, the ejection units 35 corresponding to the nozzles N [2] to N [5] and N [8] to N [11] are driven based on the drive signal Vin. Thus, an image is formed on the label Lb in the printing area Ap.

FIG. 29B shows the operation of the nozzle N (ejection unit 35) in the unit operation periods Tu8 and Tu9 (unit detection operation periods Tt4 and Tt5).
In the unit detection operation period Tt4, among the discharge units 35 other than the 3Q (9) discharge units 35 selected in the unit detection operation periods Tt1 to Tt3 among the M (12) discharge units 35, A total of Q (three) ejection units 35, one for each group, are selected as targets for ejection abnormality detection processing.
Specifically, three ejection units 35 corresponding to the nozzles N [4], N [8], and N [12] are respectively selected as targets for the ejection abnormality detection process, and the ejection units 35 are On the other hand, a determination is made as to whether or not there is a discharge abnormality. As a result, the ejection abnormality detection process for all the ejection units 35 is executed.
Thereafter, in the unit detection operation period Tt5, the ejection abnormality detection process for the M ejection units 35 is started again.

FIG. 30 is a diagram summarizing the operations of the nozzles N in the unit operation periods Tu1 to Tu10 shown in FIGS.
As shown in FIG. 30, the ink jet printer 1 according to the present embodiment performs the ejection abnormality detection process in the non-printing area AxH1 at the label upper position Xp1 in the unit operation period Tu1, and on the label in the unit operation periods Tu2 and Tu3. The printing process is executed in the printing area Ap at the positions Xp2 and Xp3, the ejection abnormality detection process is executed in the non-printing area AxH2 at the on-label position Xp4 and Xp5 in the unit operation periods Tu4 and Tu5, and the label is displayed in the unit operation periods Tu6 and Tu7. One or a plurality of unit operation periods Tu for executing the ejection abnormality detection process and one or a plurality of unit operations for executing the print process, such as executing the print process in the print areas Ap at the upper positions Xp6 and Xp7. The period Tu is repeated.

That is, the printing operation period in the present embodiment is a first period that is one or more unit detection operation periods Tt in which the ejection abnormality detection process is executed, and a period after the first period has elapsed, and the printing process is executed. A second period that is one or more unit printing operation periods Tp, and a third period that is a period after the elapse of the second period and that is one or more unit detection operation periods Tt for executing the ejection abnormality detection process; And at least a fourth period that is one or a plurality of unit printing operation periods Tp in which the printing process is executed after the elapse of the third period.
The ejection abnormality detection process in the first period is referred to as “first operation”, the printing process in the second period is referred to as “second operation”, and the ejection abnormality detection process in the third period is referred to as “third operation”. And the printing process in the fourth period may be referred to as a “fourth operation”.

  As described above, in the present embodiment, since the printing process and the ejection abnormality detection process are both performed without stopping the conveyance of the label paper P during the printing operation period, the conveyance of the label paper P is stopped. Compared with the case where the ejection abnormality detection process is executed at the initial position (X = Xini) or the like, the overall processing time of printing can be shortened.

  In the present embodiment, the printing process is executed in the printing area Ap, and the ejection abnormality detection process is executed in the non-printing area Ax. For this reason, it is possible to prevent the ink ejected from the nozzle N from landing on the label Lb in order to perform the ejection abnormality detection process, and it is possible to prevent the image quality from being deteriorated due to the ejection abnormality detection process.

In the present embodiment, the unit printing operation period Tp and the unit detection operation period Tt are temporally separated, and the driving waveform signal Com for printing is supplied to the driving signal generation unit 51 in the unit printing operation period Tp. In the unit detection operation period Tt, the drive waveform signal Com for discharge abnormality detection processing is supplied to the drive signal generation unit 51.
For this reason, it is not necessary to incorporate a waveform for the ejection abnormality detection process in the drive waveform signal Com supplied to the drive signal generation unit 51 in the unit printing operation period Tp, and the waveform of the drive waveform signal Com in the printing process is printed. A suitable waveform can be obtained, and an improvement in image quality or an improvement in printing speed can be realized.

In the present embodiment, in the printing operation period, one or more unit operation periods Tu for executing the ejection abnormality detection process and one or more unit operation periods Tu for executing the printing process are repeated.
For this reason, when a discharge abnormality occurs in a certain discharge unit 35, it is possible to prevent the discharge unit 35 in which the discharge abnormality has occurred from being used for a long time in the printing process. In other words, even when a discharge abnormality occurs, it is possible to minimize the deterioration in image quality by minimizing the influence thereof.

  In the example illustrated in FIGS. 27 to 30, the case where a plurality of nozzles N are arranged in one row in the head unit 30 is illustrated, but for example, as shown in FIG. 3, the nozzles are arranged in four rows. It may be. In this case, the unit detection operation period Tt may be a period in which all the four nozzle arrays are located in the non-printing area AxH.

In the present embodiment, the inkjet printer 1 includes one drive signal generation unit 51, but may include a plurality of drive signal generation units 51. For example, when the head unit 30 includes a plurality of nozzle rows, the head unit 30 may include a plurality of drive signal generation units 51 that correspond one-to-one with the plurality of nozzle rows. In this case, the control unit 6 may supply different drive waveform signals Com to the plurality of drive signal generation units 51.
For example, it is assumed that the inkjet printer 1 includes a head unit 30 having four nozzle rows and four drive signal generation units 51 corresponding to the four nozzle rows in a one-to-one relationship. In this case, the control unit 6 sends a drive waveform signal for print processing to each of the four drive signal generation units 51 based on whether each of the four nozzle rows is positioned on the print region Ap. Either one of Com or the drive waveform signal Com for ejection abnormality detection processing may be selectively supplied. More specifically, the control unit 6 outputs a drive waveform for ejection abnormality detection processing to the drive signal generation unit 51 corresponding to the nozzle row located on the non-printing area AxH among the four nozzle rows. A drive waveform signal Com for print processing may be supplied to the drive signal generation unit 51 that supplies the signal Com and corresponds to the nozzle row located on the print region Ap. That is, the control unit 6 provides a unit operation period Tu for each nozzle row, and in accordance with the on-label position Xp of each nozzle row, the unit printing operation period Tp or the unit detection operation period Tt in the unit operation period Tu in each nozzle row. Either of these may be assigned. Accordingly, it is possible to simultaneously execute the ejection abnormality detection process for the nozzle row located on the non-printing area AxH and the printing process for the nozzle row located on the printing area Ap. It becomes possible to detect abnormal discharge.

<B. Second Embodiment>
In the first embodiment described above, the ejection abnormality detection process is executed in the non-printing area AxH extending in the horizontal direction (Y-axis direction).
On the other hand, the inkjet printer according to the second embodiment performs the ejection abnormality detection process in the non-printing area AxV extending in the vertical direction in addition to the non-printing area AxH extending in the horizontal direction. This is different from the ink jet printer 1 according to the first embodiment.

The inkjet printer according to the second embodiment is different from the inkjet printer 1 according to the first embodiment in the control program stored in the storage unit 62, and the drive waveform signal Com and the switching period designation signal Sc output by the control unit 6. However, it is comprised similarly to the inkjet printer 1 which concerns on 1st Embodiment except for a different point from the inkjet printer 1 which concerns on 1st Embodiment.
Hereinafter, the drive waveform signal Com and the switching period designation signal Sc output from the control unit 6 of the inkjet printer according to the second embodiment will be described.

The control unit 6 according to the second embodiment outputs the drive waveform signal Com (Com-A, Com-B) for print processing shown in FIG. 17 in both the unit printing operation period Tp and the unit detection operation period Tt. Output. Further, the control unit 6 according to the second embodiment has the potential VL during a part of the control period Tc1 in which the unit waveform PA1 is at the potential Va12 in both the unit printing operation period Tp and the unit detection operation period Tt. In other periods, the switching period designation signal Sc that becomes the potential VH is output. Furthermore, the control unit 6 according to the second embodiment prints the print signal so that the drive signal Vin having the waveform DpAB shown in FIG. 18 is supplied to the discharge unit 35 selected as the target of the discharge abnormality detection process. Generate SI.
Thereby, the ink jet printer according to the second embodiment drives both the formation of the medium dot in the printing area Ap (label Lb) and the ejection abnormality detection process in the non-printing area AxH or the non-printing area AxV having the waveform DpAB. This is performed using the signal Vin.
For this reason, the inkjet printer according to the second embodiment can execute the ejection abnormality detection process in addition to the printing process in the unit printing operation period Tp (note that the ejection abnormality detection process is performed in the unit detection operation period Tt). Run).

FIG. 31 is an explanatory diagram illustrating an operation image of the ink jet printer according to the second embodiment. In FIG. 31, as in FIG. 27, the head unit 30 includes twelve ejection units 35, the ejection abnormality detection unit 52 includes three ejection abnormality detection circuits DT, and the twelve ejection units 35 include the first group. To the third group, that is, M = 12, Q = 3, and K = 4.
Hereinafter, the operation of the inkjet printer according to the second embodiment will be described with reference to the example shown in FIG.

In the unit detection operation period Tt, the control unit 6 according to the second embodiment includes a maximum of one discharge unit 35 from each of the M discharge units 35, and a maximum of Q discharge units 35 in total. And selected as the target of the discharge abnormality detection process.
However, in this selection, unlike the first embodiment, when the unit printing operation period Tp arrives, the ejection unit 35 that can eject ink to the printing area Ap is preferentially selected.
For example, in the example shown in FIG. 31, in the unit operation period Tu1, which is the unit detection operation period Tt, it is possible to eject ink to the print region Ap when the unit print operation period Tp among the 12 ejection units 35 has arrived. A total of three discharge units 35, one from each group, are selected by the control unit 6 from the discharge units 35. Specifically, in this example, the discharge unit 35 corresponding to the nozzles N [2], N [5], and N [9] is selected by the control unit 6. In other words, the example shown in FIG. 31 is different from the example shown in FIG. 27 in that the ink in the printing area Ap in the unit operation period Tu2 is replaced with the nozzle N [1] that does not eject ink in the printing area Ap in the unit operation period Tu2. The ejection unit 35 corresponding to the nozzle N [2] capable of ejecting is selected in the unit operation period Tu1. Then, by supplying the drive signal Vin having the waveform DpAB to the three selected ejection units 35, the ejection abnormality detection process for the three ejection units 35 is executed.

Next, in the unit printing operation period Tp, the control unit 6 according to the second embodiment selects a non-printing area from among the ejection units 35 excluding the ejection unit 35 that has already been selected among the M ejection units 35. A maximum of one ejection unit 35 capable of ejecting ink to AxV is selected from each group as a target of ejection abnormality detection processing.
For example, in the example shown in FIG. 31, in the unit operation period Tu2 that is the unit printing operation period Tp, among the 12 ejection units 35, the ejection unit 35 is capable of ejecting ink to the non-printing area AxV. Among the ejection units 35 other than the ejection unit 35 selected in the unit detection operation period Tt1, at most one ejection unit 35 in each group and a total of up to three ejection units 35 are targeted for ejection abnormality detection processing. Selected. Specifically, in this example, three ejection units 35 corresponding to the nozzles N [1], N [6], and N [12] are respectively selected as targets for ejection abnormality detection processing, and these A determination is made as to whether or not there is a discharge abnormality in the discharge unit 35.

Thereafter, similarly, in the unit operation period Tu3 that is the unit printing operation period Tp, the ejection unit 35 that has not been selected so far corresponds to the nozzle N [7] that can eject ink to the non-printing area AxV. One ejection unit 35 is selected.
Further, in the unit operation period Tu4 that is the unit detection operation period Tt, 3 corresponding to the nozzles N [3], N [8], and N [10] among the ejection units 35 that have not been selected so far. The number of ejection units 35 is selected.

  As described above, the printing operation period in the present embodiment is a first period that is one or a plurality of unit detection operation periods Tt in which the ejection abnormality detection process is executed, and a period after the elapse of the first period. A second period that is one or a plurality of unit printing operation periods Tp for executing the discharge abnormality detection process, and a one or a plurality of unit detection operation periods Tt that are a period after the elapse of the second period and that execute the discharge abnormality detection process. And a fourth period that is a period after the elapse of the third period and that is one or a plurality of unit printing operation periods Tp for executing the printing process and the ejection abnormality detection process.

As described above, in the second embodiment, since the ejection abnormality detection process is executed in addition to the printing process in the unit printing operation period Tp, compared with the case where only the printing process is executed in the unit printing operation period Tp. The period required for performing the ejection abnormality detection process for all of the M ejection units 35 can be shortened.
For this reason, in the second embodiment, it is possible to detect the ejection abnormality at an early stage, and it is possible to suppress the possibility that the image quality is deteriorated due to the ejection abnormality.

  In the second embodiment, in the unit printing operation period Tp, the ejection unit 35 that can eject ink to the non-printing area AxV is selected as the target of the ejection abnormality detection process, but ink can be ejected to the printing area Ap. Of the discharge units 35, the discharge unit 35 to which the drive signal Vin having the waveform DpAB is supplied may be selected as the target of the discharge abnormality detection process. In this case, the selected ejection unit 35 executes the printing process and is selected as an ejection abnormality detection process target.

<C. Modification>
Each of the above forms can be variously modified. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the following examples can be appropriately combined within a range that does not contradict each other.

<Modification 1>
The ink jet printer according to the above-described embodiment performs one printing process or one ejection abnormality detection process in the unit operation period Tu having a predetermined time length. The time length for performing one printing process may be variable.
That is, the ink jet printer has a normal printing mode (an example of “first printing mode”) in which printing is performed at a normal speed (first printing speed) and a high-speed printing mode in which printing is performed at a high speed (second printing speed) ( One example of “second printing mode”) may be capable of executing two printing operation modes.

  FIG. 32 is a timing chart for explaining the operation of the ink jet printer according to this modification. In the following description of this modification, as an example, an operation mode in which printing is performed at the same speed as the above-described embodiment is a normal printing mode, and an operation mode in which printing is performed at a higher speed than in the above-described embodiment. Is set to the high-speed printing mode.

When the ink jet printer is operated in the high-speed printing mode, the control unit 6 according to the present modification partitions a unit high-speed operation period TuF having a time length shorter than the unit operation period Tu as shown in FIG. The latch signal LAT and the change signal CH are output. As shown in this figure, the unit high-speed operation period TuF is divided into high-speed control periods TcF1 and TcF2 having the same time length by the change signal CH.
In addition, when the ink jet printer is operated in the normal printing mode, the control unit 6 according to the present modification generates a latch signal LAT and a change signal CH that divide the unit operation period Tu as shown in FIG. Output.
FIG. 32 shows a case where the unit high-speed operation period TuF has a time length that is half the unit operation period Tu as an example.

Further, as shown in FIG. 32A, the control unit 6 according to the present modification has a waveform obtained by compressing the unit waveforms PA1, PA2, PB1, and PB2 (see FIG. 17) in the time axis direction in the high-speed printing mode. Drive waveform signals Com-A and Com-B having unit waveforms PA1F, PA2F, PB1F, and PB2F are output.
Specifically, in the high-speed printing mode, as shown in FIG. 32A, the drive waveform signal Com-A includes the unit waveform PA1F arranged in the high-speed control period TcF1 and the unit arranged in the high-speed control period TcF2. The waveform PA2F is a continuous waveform, and the drive waveform signal Com-B is a waveform in which the unit waveform PB1F arranged in the high speed control period TcF1 and the unit waveform PB2F arranged in the high speed control period TcF2 are made continuous. It becomes.

Furthermore, in the high-speed printing mode, the control unit 6 according to this modification drives the motor driver 40 so that the label paper P is conveyed at a conveyance speed MvF that is higher than the conveyance speed Mv in the normal printing mode. This speed MvF is determined according to the ratio of the time length of the unit high-speed operation period TuF and the unit operation period Tu.
In the example of FIG. 32, since the unit high-speed operation period TuF has a time length that is half the unit operation period Tu, the speed MvF is, for example, twice the speed Mv.

When printing is performed in the high-speed printing mode, one ejection abnormality detection process may be executed in each unit high-speed operation period TuF. That is, when printing is performed in the high-speed printing mode, the ejection abnormality detection process may be executed at a high speed as well (hereinafter, “the ejection abnormality detection process is performed at high speed is simply referred to as“ ejection abnormality in the high-speed printing mode ”). To perform detection processing ”).
For example, as in the case of the ink jet printer according to the second embodiment, when the drive waveform signal Com for print processing and the drive waveform signal Com for discharge abnormality detection processing have the same waveform, the unit waveform PA1F is The ejection abnormality detection process may be executed in the high-speed printing mode by supplying the drive signal Vin having the ejection signal 35 to the ejection unit 35.

On the other hand, like the ink jet printer according to the first embodiment, the drive waveform signal Com for print processing and the drive waveform signal Com for discharge abnormality detection processing are:
If they have different waveforms, the printing process may be performed in the high-speed printing mode shown in FIG. 32A, and the ejection abnormality detection process may be performed in the normal printing mode shown in FIG.
Specifically, when performing the printing process, the control unit 6 outputs the latch signal LAT, the change signal CH, and the drive waveform signal Com shown in FIG. When performing, the latch signal LAT, the change signal CH, and the drive waveform signal Com shown in FIG. 32B may be output.
However, even in this case, it is preferable that the conveyance speed of the label paper P is kept as constant as possible. Therefore, the inkjet printer according to the present modification performs the printing process in the high-speed printing mode and transports the label paper P at the speed MvF during the printing operation period even when the ejection abnormality detection process is performed in the normal printing mode.
For this reason, when performing printing in the high-speed printing mode, compared to performing printing in the normal printing mode, the first period in which the ejection abnormality detection process is performed, the second period in which the printing process is performed, and the ejection abnormality detection process are performed. In the third period to be executed and the fourth period in which the printing process is executed, the time length is shortened to (Mv ÷ MvF) times. Therefore, in this case, the number of ejection units 35 that are targets of ejection abnormality detection processing in the first period and the number of ejection units 35 that are targets of ejection abnormality detection processing in the third period are also (Mv ÷ MvF) times. To decrease.
However, even when printing is performed in the high-speed printing mode, by performing the ejection abnormality detection process in the normal printing mode, a period for detecting residual vibration in one ejection abnormality detection process, for example, the time of the switching period Td Since the length can be made sufficiently long, it is possible to accurately detect the residual vibration and accurately detect the ejection abnormality.

<Modification 2>
In the embodiment and the modification described above, in the ejection abnormality detection process, the ejection unit 35 is driven so that ink is ejected from the nozzle N, thereby detecting the residual vibration generated in the ejection unit 35 and whether there is an ejection abnormality. However, the present invention is not limited to such an embodiment, and the residual vibration generated in the discharge unit 35 is detected by driving the discharge unit 35 so that ink is not discharged from the nozzle N. The presence or absence of ejection abnormality may be determined.

For example, in the first embodiment described above, an ejection abnormality detection process is performed so that ink is not ejected from the nozzles N by adjusting the potential difference between the potential Va11 and the potential Va12 in the unit waveform PA1-T shown in FIG. The discharge unit 35 that is the target of the above may be driven.
Further, for example, in the second embodiment described above, the waveform DpBB is supplied instead of the waveform DpAB to the ejection unit 35 that is the target of the ejection abnormality detection process (see FIG. 18), so that the nozzle N The ejection unit 35 may be driven so as not to eject ink.
By executing the ejection abnormality detection process without ejecting ink, it is possible to prevent the ink ejected from the nozzle N from landing on the label Lb in order to perform the ejection abnormality detection process. It is possible to prevent the image quality from being deteriorated.

<Modification 3>
In the embodiment and the modification described above, the M ejection units 35 are equally divided into Q groups each including K units, but the present invention is not limited to such a mode. The M ejection units 35 may be appropriately classified according to the number of ejection abnormality detection circuits DT.
For example, among the Q sets, there may be two sets with different numbers of ejection units 35. Further, for example, in the case where the ejection abnormality detection unit 52 includes one ejection abnormality detection circuit DT, etc., the M ejection units 35 do not have to be divided (that is, M = 1 ejections with Q = 1). The part 35 may be divided into one set).

For example, when the ejection abnormality detection unit 52 includes one ejection abnormality detection circuit DT, M switching circuits provided in a one-to-one correspondence with the M ejection units 35 in the switching unit 53 illustrated in FIG. U is provided so that all of the M ejection portions 35 can be electrically connected to the one ejection abnormality detection circuit DT.
FIG. 33 is an operation image of the printing process and the discharge abnormality detection process when the number of discharge abnormality detection circuits DT included in the discharge abnormality detection unit 52 is one in the inkjet printer 1 according to the first embodiment. FIG. 33 illustrates a case where the head unit 30 includes twelve ejection units 35, as in FIG.
As shown in FIG. 33, when the discharge abnormality detection unit 52 includes one discharge abnormality detection circuit DT, one discharge unit 35 is selected as the target of discharge abnormality detection processing in each unit detection operation period Tt. Is done. Therefore, the discharge abnormality detection process for the twelve discharge units 35 is executed in the unit detection operation periods Tt1 to Tt12.

Note that, regardless of how the M ejection units 35 included in the head unit 30 are divided (or not divided), the printing operation period is a first period during which the ejection abnormality detection process is performed, A second period in which the printing process is performed after the first period has elapsed, a third period in which the ejection abnormality detection process is performed after the second period has elapsed, and after the third period has elapsed And a fourth period in which the printing process is executed.
Then, when the number of ejection units 35 to be subjected to ejection abnormality detection processing in the first period is “α” and the number of ejection units 35 to be ejection abnormality detection processing in the third period is “β”, The following equation is established between the number “M” of the ejection units 35 included in the head unit 30 and the above “α” and “β” (where α and β are natural numbers of 1 or more). .
M ≧ α + β

<Modification 4>
In the embodiment and the modification described above, all of the M ejection units 35 are targeted for ejection abnormality detection processing. However, the present invention is not limited to such an aspect, and Of these, only a part of the ejection units 35 may be targeted for ejection abnormality detection processing.
For example, among the M ejection units 35, only the ejection unit 35 that can eject ink onto the printing area Ap in the unit printing operation period Tp (that is, the ejection unit 35 used for printing) is ejected during the printing operation period. The target of the abnormality detection process may be used.

FIG. 34 is an operation image of the ejection abnormality detection process when only the ejection unit 35 used for printing is the target of the ejection abnormality detection process in the example shown in FIG.
In the example illustrated in FIG. 34, eight ejection units 35 corresponding to the nozzles N [2] to N [5] and N [8] to N [11] are used for printing. Therefore, in the example shown in this figure, only the discharge units 35 corresponding to the eight nozzles N are targeted for discharge abnormality detection processing, and the other discharge units 35 corresponding to the four nozzles N are detected as discharge abnormality detection. Excluded from processing. In this case, since the discharge abnormality detection processing of the discharge unit 35 used for printing can be executed in the unit detection operation periods Tt1 to Tt3, for example, all the discharge units 35 (12 pieces as shown in FIG. Compared with the case where the discharge unit 35) is the target of the discharge abnormality detection process, the period required for the discharge abnormality detection process can be shortened. As a result, it is possible to quickly find an ejection abnormality in the ejection unit 35 used for printing.

<Modification 5>
In the embodiment and the modification described above, the drive waveform signal Com includes two signals of Com-A and Com-B. However, the present invention is not limited to such a mode, and the drive waveform signal Com is It may be composed of one signal (for example, Com-A), or may be composed of three or more signals (for example, Com-A, Com-B, Com-C, etc.).
In the embodiment and the modification described above, the drive waveform signal Com represents both the print processing waveform and the ejection abnormality detection processing waveform by one signal (Com-A). However, the drive waveform signal Com supplies a signal representing a waveform for printing processing and a signal representing a waveform for ejection abnormality detection processing as different signals. May be. For example, when the drive waveform signal Com includes Com-A and Com-B, the drive waveform signal Com-A is a signal representing a waveform for printing processing, and the drive waveform signal Com-B is a waveform for ejection abnormality detection processing. It is good also as a signal showing.
The number of bits of the print signal SI is not limited to 2 bits, and may be determined as appropriate depending on the gradation to be displayed and the number of signals included in the drive waveform signal Com.

<Modification 6>
In the embodiment and the modification described above, the ink jet printer is a line printer as shown in FIG. 3, but may be a serial printer. For example, instead of the head unit 30 shown in FIG. 3, an inkjet printer having a head unit whose width in the Y-axis direction is narrower than the width of the label paper P, and the main scanning direction of the carriage is the Y-axis direction. Also good. Also in the serial printer, the printing process is performed in the printing area Ap on the label paper P, and the ejection abnormality detection process is performed in the non-printing area Ax, so that the printing speed is reduced due to the ejection abnormality detection process. This can be prevented.
In the above-described embodiments and modifications, the ink jet printer ejects ink from the nozzles N by vibrating the diaphragm 121 of the piezoelectric element 120. However, the present invention is limited to such an embodiment. For example, a so-called thermal method in which a heating element (not shown) provided in the cavity 141 generates heat to generate bubbles in the cavity 141 to increase the pressure inside the cavity 141 and thereby discharge ink. It may be. In this case, the ejection abnormality detection unit may detect whether or not ink is ejected from the ejection unit, for example, by an optical method. Even in a thermal ink jet printer, when the ejection abnormality detection process on the label paper P is performed, it is possible to prevent the printing speed from being lowered due to the ejection abnormality detection process.
In short, the ink jet printer only needs to be able to execute the ejection abnormality detection process on the label paper P, and the ejection abnormality detection unit detects the physical quantity of the operation of the ejection unit after the drive signal Vin is supplied. Anything that can do that.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 4 ... Feed position moving part, 6 ... Control part, 30 ... Head part, 32 ... Carriage, 35 ... Discharge part, 40 ... Motor driver, 41 ... Carriage motor, 42... Feeding motor, 50... Head driver, 51... Drive signal generation unit, 52... Discharge abnormality detection unit, 53 ... Switching unit, 55 ... Detection unit, 56 ... Determination unit, 551. Waveform shaping unit, 552 ... measurement unit, 70 ... recovery mechanism, 120 ... piezoelectric element, 121 ... diaphragm, 141 ... cavity, Ap ... printing area, Ax ... non-printing area, DT ... discharge Abnormality detection circuit, Lb ... label, N ... nozzle, P ... label paper, U ... switching circuit.

Claims (6)

A printing apparatus that discharges liquid onto a recording medium to form an image on a printing area of the recording medium,
A head unit including M (M is an integer of 2 or more) ejection units capable of ejecting the liquid by driving based on a drive signal;
A drive signal generation unit that generates the drive signal for driving the discharge unit to discharge or not discharge the liquid based on a print control signal;
A detection unit that detects a vibration of the liquid in the target discharge unit that occurs after the drive signal is supplied to the target discharge unit among the M discharge units, and generates a detection signal;
A determination unit that determines a discharge state of the liquid in the target discharge unit based on the detection signal;
A relative position moving unit that moves a relative position of the head unit with respect to the recording medium based on a movement control signal;
By controlling the drive of the ejection unit by supplying the print control signal to the drive signal generation unit,
While controlling the relative position of the head unit with respect to the recording medium by supplying the movement control signal to the relative position moving unit,
A control unit for selecting the target discharge unit from the M discharge units;
With
The controller is
Of the printing operation period in which the relative position of the head unit with respect to the recording medium is controlled such that at least some of the M ejection units can eject liquid onto the recording medium,
In the first period,
Among the M ejection units, α (α is an integer satisfying 1 ≦ α <M) among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium. , Select as the target discharge unit,
Of the printing operation period, in a second period started after the first period has elapsed,
A part or all of the ejection units capable of ejecting liquid to the print area are driven to eject the liquid, thereby forming an image on the print area of the recording medium,
Of the printing operation period, in a third period started after the second period has elapsed,
The liquid can be ejected to an area other than the print area of the recording medium in the ejection parts excluding the α ejection parts selected as the target ejection parts in the first period from the M ejection parts. Out of the discharge units, β discharge units (β is an integer satisfying 1 ≦ β ≦ M−α) are selected as the target discharge units,
Of the printing operation period, in a fourth period started after the third period has elapsed,
A part or all of the ejection units capable of ejecting liquid to the print area are driven to eject the liquid, thereby forming an image on the print area of the recording medium,
A first printing mode for printing at a first printing speed and a second printing mode for printing at a second printing speed faster than the first printing speed can be executed;
When printing is performed in the first printing mode, the number of target ejection units selected by the control unit in the first period is
More than the number of target ejection units selected by the control unit in the first period when printing is performed in the second printing mode,
A printing apparatus characterized by that. A printing apparatus that discharges liquid onto a recording medium to form an image on a printing area of the recording medium,
A piezoelectric element that is displaced in response to a drive signal;
A pressure chamber in which the liquid is filled and the internal pressure is increased or decreased by displacement of the piezoelectric element based on the drive signal;
A nozzle that communicates with the pressure chamber and discharges the liquid filled in the pressure chamber by increasing or decreasing the pressure in the pressure chamber;
A head unit comprising M discharge units (where M is a natural number of 2 or more);
A drive signal generator for generating the drive signal based on a print control signal;
The electromotive force of the piezoelectric element of the target discharge unit, which is generated after the drive signal is supplied to the target discharge unit among the M discharge units, based on the change in the pressure inside the pressure chamber of the target discharge unit. A detection unit that detects a change in the detection signal and generates a detection signal;
A determination unit that determines a discharge state of the liquid in the target discharge unit based on the detection signal;
A relative position moving unit that moves a relative position of the head unit with respect to the recording medium based on a movement control signal;
By controlling the drive of the ejection unit by supplying the print control signal to the drive signal generation unit,
While controlling the relative position of the head unit with respect to the recording medium by supplying the movement control signal to the relative position moving unit,
A control unit for selecting the target discharge unit from the M discharge units;
With
The controller is
Of the printing operation period in which the relative position of the head unit with respect to the recording medium is controlled such that at least some of the M ejection units can eject liquid onto the recording medium,
In the first period,
Among the M ejection units, α (α is an integer satisfying 1 ≦ α <M) among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium. , Select as the target discharge unit,
Of the printing operation period, in a second period started after the first period has elapsed,
A part or all of the ejection units capable of ejecting liquid to the print area are driven to eject the liquid, thereby forming an image on the print area of the recording medium,
Of the printing operation period, in a third period started after the second period has elapsed,
The liquid can be ejected to an area other than the print area of the recording medium in the ejection parts excluding the α ejection parts selected as the target ejection parts in the first period from the M ejection parts. Out of the discharge units, β discharge units (β is an integer satisfying 1 ≦ β ≦ M−α) are selected as the target discharge units,
Of the printing operation period, in a fourth period started after the third period has elapsed,
A part or all of the ejection units capable of ejecting liquid to the print area are driven to eject the liquid, thereby forming an image on the print area of the recording medium,
A first printing mode for printing at a first printing speed and a second printing mode for printing at a second printing speed faster than the first printing speed can be executed;
When printing is performed in the first printing mode, the number of target ejection units selected by the control unit in the first period is
More than the number of target ejection units selected by the control unit in the first period when printing is performed in the second printing mode,
A printing apparatus characterized by that. The controller is
In the second period,
Of the α target ejection units selected by the control unit in the first period,
From the target ejection unit, which has determined that the determination unit is in a state in which liquid cannot be ejected based on the drive signal, the liquid is not ejected,
Forming an image in a print area of the recording medium;
Wherein the printing apparatus according to claim 1 or 2. In the printing operation period,
The target discharge unit selected by the control unit is
A part or all of the M ejection parts;
Characterized in that, the printing apparatus according to any one of claims 1 to 3. The printing device is a line printer;
Characterized in that, the printing apparatus according to any one of claims 1 to 4. M discharge units (M is an integer of 2 or more) capable of discharging liquid based on the drive signal,
A control method for a printing apparatus that discharges liquid onto a recording medium to form an image in a printing area of the recording medium,
In a printing operation period in which at least some of the M ejection units can eject liquid onto the recording medium,
Among the M ejection units, α (α is an integer satisfying 1 ≦ α <M) among the ejection units capable of ejecting the liquid to an area other than the printing area of the recording medium. Performing a first operation for determining whether or not the liquid can be discharged based on the drive signal;
After completion of the first operation, the liquid is ejected to a part or all of the ejection units capable of ejecting the liquid to the print area, thereby forming an image on the print area of the recording medium. Perform the action,
After the end of the second operation, in the ejection units excluding the α ejection units that are the targets of the determination in the first operation from the M ejection units, in areas other than the print area of the recording medium Of the ejection units capable of ejecting the liquid, the third operation of performing the determination is performed on β (β is an integer that satisfies 1 ≦ β ≦ M−α) ejection units,
After completion of the third operation, the liquid is ejected to a part or all of the ejection units capable of ejecting the liquid to the print area, thereby forming an image on the print area of the recording medium. run the operation,
A printing operation is possible in a first printing mode for printing at a first printing speed and a second printing mode for printing at a second printing speed faster than the first printing speed;
When printing is performed in the first printing mode, the number of ejection units determined in the first operation is
More than the number of ejection units determined in the first operation when printing is performed in the second printing mode,
A control method for a printing apparatus.

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