JP5834827B2 - Liquid ejection inspection apparatus, liquid ejection inspection method, printing apparatus, and program - Google Patents

Description

  The present invention relates to a liquid ejection inspection apparatus, a liquid ejection inspection method, a printing apparatus, and a program.

There is known a printing apparatus such as an ink jet printer having a head that discharges liquid such as ink to various media such as paper and film, and an internal sensor that detects a liquid state inside the head (for example, Patent Document 1).
Also known is a printing apparatus such as an ink jet printer having a head that discharges liquid such as ink to various media such as paper and film, and an external sensor that detects liquid discharge failure outside the head. (For example, Patent Document 2).

Japanese Patent No. 3794431 JP 2007-152888 A

In this ink jet printer, there are cases where nozzles are clogged and droplets cannot be ejected (ejection failure). As a result, missing dots occur, which causes the print image to deteriorate.
The discharge inspection for detecting such discharge failure includes an internal discharge inspection using an internal sensor and an external discharge inspection using an external sensor, but each discharge inspection has its respective drawbacks.
The present invention has been made in view of such circumstances, and an object of the present invention is to compensate for the respective drawbacks of the internal discharge inspection and the external discharge inspection.

The main invention for solving the above problems is:
An internal sensor for detecting the liquid state inside the head that discharges liquid to the medium;
An external sensor for detecting a liquid ejection failure outside the head;
Based on the detection results of the internal sensor and the external sensor, a controller that selects a recovery operation for recovering the ejection of liquid by the head from a plurality of types of recovery operations;
It is a liquid discharge inspection apparatus characterized by having.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

2 is a block diagram illustrating a configuration example of a printer 1. FIG. FIG. 2A is a cross-sectional view of the head 31, and FIG. 2B is a diagram showing an arrangement of nozzles. 3A to 3C are views showing the positional relationship between the head 31 and the ink suction unit 50. FIG. 3 is a schematic plan view showing a configuration of a cap 51. FIG. 5A and 5B are diagrams showing a positional relationship between the head 31 and the wiping unit 55. FIG. It is a figure explaining the inspection unit 70 in a head. FIG. 7A is a diagram illustrating a signal output according to the residual vibration of the piezo element. FIG. 7B is a diagram illustrating a signal output after the output of the operational amplifier passes through a high-pass filter including a capacitor and a resistor. FIG. 7C is a diagram illustrating a signal output after passing through the comparator. FIG. 8A is a diagram illustrating the outside-head inspection unit 80, and FIG. 8B is a block diagram illustrating the detection control unit 87. FIG. 9A is a diagram illustrating a drive signal, and FIGS. 9B and 9C are diagrams illustrating a voltage signal output from an amplifier. FIG. 10A is a diagram illustrating a state in which bubbles are mixed. FIG. 10B is a diagram showing a state of dry thickening. FIG. 10C is a diagram illustrating a state in which the paper dust is in close contact with the nozzle. FIG. 10D is a diagram illustrating a state in which paper dust is attached near the nozzle. It is a flowchart which shows the operation example of a missing dot inspection. It is a figure explaining the determination conditions in dot missing inspection operation.

At least the following matters will become apparent from the description of the present specification and the accompanying drawings.
That is, an internal sensor that detects a liquid state inside a head that discharges liquid to the medium;
An external sensor for detecting a liquid ejection failure outside the head;
Based on the detection results of the internal sensor and the external sensor, a controller that selects a recovery operation for recovering the ejection of liquid by the head from a plurality of types of recovery operations;
It is a liquid discharge inspection apparatus characterized by having.
According to such a liquid discharge inspection apparatus, the defect in each of the internal sensor used for the internal discharge inspection and the external sensor used for the external discharge inspection is compensated for, thereby improving the detection accuracy of the discharge failure and performing an appropriate recovery process. You can choose.

In addition, such a liquid discharge inspection apparatus,
The controller is
If it is determined from the detection result of the internal sensor that a liquid discharge failure has occurred based on the liquid state, and it is determined from the detection result of the external sensor that no liquid discharge failure has occurred, the internal sensor The detection results of the sensor and the external sensor may be acquired again to determine whether or not a liquid ejection failure has occurred.
According to such a liquid ejection inspection device, by performing re-inspection in such a case, it is not necessary to immediately perform a recovery operation, so that waste of consumed ink can be suppressed.

In addition, such a liquid discharge inspection apparatus,
The controller is
When it is determined from the detection result of the external sensor that a liquid ejection failure has occurred, the internal sensor detects from a plurality of types of recovery operations that differ in the amount of liquid consumed during the recovery operation. The recovery operation may be selected based on the liquid state.
According to such a liquid ejection inspection device, since an appropriate recovery operation is performed in consideration of the cause of ejection failure, waste of the amount of ink consumed for recovery can be suppressed.

In addition, a liquid discharge inspection apparatus is provided that includes an internal sensor that detects a liquid state inside a head that discharges liquid to a medium, an external sensor that detects a liquid discharge failure outside the head, and a controller. To do
Causing the controller to select a recovery operation for recovering the ejection of the liquid by the head from a plurality of types of recovery operations based on the detection results of the internal sensor and the external sensor;
A liquid discharge inspection method characterized by comprising:
According to such a liquid ejection inspection method, it is possible to improve the detection accuracy of ejection failure and to select an appropriate recovery process by compensating for the defects of the internal sensor and the external sensor.

A head that performs printing by discharging liquid onto the medium;
An internal sensor for detecting the state of the liquid in the head;
An external sensor for detecting a liquid ejection failure outside the head;
Based on the detection results of the internal sensor and the external sensor, a controller that selects a recovery operation for recovering the ejection of liquid by the head from a plurality of types of recovery operations;
It is a printing apparatus characterized by having.
According to such a printing apparatus, it is possible to improve the detection accuracy of ejection failure and to select an appropriate recovery process by compensating for the defects of the internal sensor and the external sensor.

In addition, in a liquid ejection inspection apparatus having an internal sensor that detects a liquid state inside a head that ejects liquid to a medium, an external sensor that detects a liquid ejection failure outside the head, and a controller,
A program for realizing a function of selecting, from a plurality of types of recovery operations, a recovery operation for recovering liquid ejection by the head based on detection results of the internal sensor and the external sensor.
According to such a program, it is possible to improve the detection accuracy of ejection failure and to select an appropriate recovery process by compensating for the defects of the internal sensor and the external sensor.

=== Embodiment ===
<<< About Liquid Discharge Inspection Apparatus >>>
The liquid ejection inspection device is used in a state of being incorporated in a printing device. Moreover, when using in a process, it can also be comprised as an exclusive apparatus. In the embodiments described below, a liquid discharge inspection apparatus incorporated in a printing apparatus will be described. Specifically, an ink jet printer 1 (hereinafter also simply referred to as “printer 1”) will be described as an example. In this case, the printer 1 is an example of a printing apparatus and an example of a liquid ejection inspection apparatus.

<<< Configuration Example of Printer 1 >>>
A configuration example of the printer 1 will be described with reference to FIGS. 1, 2A and 2B, FIGS. 3A to 3C, FIGS. 4, 5A and 5B. FIG. 1 is a block diagram of the printer 1. FIG. 2A is a cross-sectional view of the head. FIG. 2B is a diagram illustrating an arrangement of nozzles. 3A to 3C are views showing the positional relationship between the head 31 and the ink suction unit 50. FIG. FIG. 4 is a view of the cap 51 as viewed from above. 5A and 5B are diagrams showing a positional relationship between the head 31 and the wiping unit 55. FIG.

  The printer 1 ejects ink as an example of a liquid toward a medium such as paper, cloth, or film, and is connected to a computer CP so as to be communicable. Since the computer CP causes the printer 1 to print an image, print data corresponding to the image can be transmitted to the printer 1.

  As shown in FIG. 1, the printer 1 according to the present embodiment includes a transport unit 10 that transports a medium in the transport direction, a carriage unit 20, a head unit 30, a drive signal generation unit 40, and an ink suction unit 50. A wiping unit 55, a flushing unit 60, an in-head inspection unit 70, an out-head inspection unit 80, a detector group 90, a controller 100 that controls these units and controls the operation as the printer 1, have.

  The carriage unit 20 is for moving the head unit 30 (head 31). The carriage unit 20 includes a carriage 21 supported so as to be reciprocally movable in the movement direction along the guide rail, and a motor. The carriage 21 is configured to move integrally with the head 31 by driving the motor (see FIG. 3A). As for the position of the carriage 21 (head 31) on the guide rail (position in the moving direction), the controller 100 detects the rising edge and the falling edge in the pulse signal output from the encoder provided in the motor, and counts this edge. Can be obtained.

  The head unit 30 ejects ink to the medium conveyed on the platen by the conveyance unit 10. The head unit 30 includes a head 31 and a head controller HC. The head 31 ejects ink toward the medium. The head controller HC controls the head 31 based on the head control signal from the controller 100.

  As shown in FIG. 2A, the head 31 includes a case 32, a flow path unit 33, and a piezo element unit 34. The case 32 is a member for housing and fixing the piezoelectric element PZT and the like, and is made of, for example, a non-conductive resin material such as an epoxy resin.

  The flow path unit 33 includes a flow path forming substrate 33a, a nozzle plate 33b, and a vibration plate 33c. The nozzle plate 33b is bonded to one surface of the flow path forming substrate 33a, and the vibration plate 33c is bonded to the other surface. The flow path forming substrate 33 a is formed with a pressure chamber 331, an ink supply path 332, and voids and grooves that become the common ink chamber 333. The flow path forming substrate 33a is made of, for example, a silicon substrate. The nozzle plate 33b is provided with a nozzle group including a plurality of nozzles Nz. The nozzle plate 33b is made of a conductive plate-like member, for example, a thin metal plate. The nozzle plate 33b is connected to the ground line and has a ground potential. A diaphragm portion 334 is provided in a portion corresponding to each pressure chamber 331 in the diaphragm 33c. The diaphragm portion 334 is deformed by the piezo element PZT and changes the volume of the pressure chamber 331. In addition, the piezoelectric element PZT and the nozzle plate 33b are electrically insulated by interposing the vibration plate 33c, the adhesive layer, and the like.

  The piezo element unit 34 includes a piezo element group 341 and a fixed plate 342. The piezo element group 341 has a comb shape. Each of the comb teeth is a piezo element PZT. The front end surface of each piezo element PZT is bonded to an island portion 335 included in the corresponding diaphragm portion 334. The fixing plate 342 supports the piezo element group 341 and serves as a mounting portion for the case 32. The piezo element PZT is an example of an electromechanical conversion element. When a drive signal COM is applied, the piezo element PZT expands and contracts in the longitudinal direction, and gives a pressure change to the liquid in the pressure chamber 331. The ink in the pressure chamber 331 undergoes a pressure change due to a change in the volume of the pressure chamber 331. By utilizing this pressure change, ink droplets can be ejected from the nozzle Nz. Instead of the piezo PZT as the electromechanical conversion element, a structure may be adopted in which ink droplets are ejected by generating bubbles corresponding to the applied drive signal COM.

  As shown in FIG. 2B, the nozzle plate 33b is provided with a plurality of nozzle rows in which 180 nozzles (# 1 to # 180) are arranged at intervals of 180 dpi along the medium conveyance direction. Each nozzle row ejects ink of a different color. For example, four nozzle rows are provided on the nozzle plate 33b. Specifically, the black ink nozzle row K, the cyan ink nozzle row C, the magenta ink nozzle row M, and the yellow ink nozzle row Y.

  The drive signal generation unit 40 is for generating the drive signal COM. When the drive signal COM is applied to the piezo element PZT, the piezo element expands and contracts, and the volume of the pressure chamber 331 corresponding to each nozzle Nz changes. For this reason, the drive signal COM is applied to the head 31 at the time of printing processing, at the time of internal discharge inspection processing to be described later, at the time of external discharge inspection processing, or at the time of flushing processing performed for the nozzles Nz that are missing dots.

  As shown in FIGS. 3A to 3C and 4, the ink suction unit 50 includes a cap 51 and a slider member 52 that supports the cap 51 and is movable in an obliquely up and down direction. The cap 51 has a rectangular bottom portion (not shown) and a side wall portion 511 that rises from the periphery of the bottom portion, and has a thin box shape with an open upper surface facing the nozzle plate 33b. In a space surrounded by the bottom portion and the side wall portion 511, a sheet-like moisture retention member made of a porous member such as felt or sponge is disposed. A waste liquid tube 58 is connected to the bottom of the cap 51, and a suction pump (not shown) is connected to the middle of the waste liquid tube 58.

  As shown in FIG. 3A, when the carriage 21 is out of the home position (here, the right side in the moving direction), the cap 51 is sufficiently lower than the surface of the nozzle plate 33b (hereinafter also referred to as “nozzle surface”). Positioned on. 3B, when the carriage 21 moves to the home position side, the carriage 21 comes into contact with the contact portion 53 provided on the slider member 52, and the contact portion 53 moves together with the carriage 21 to the home position side. To do. When the contact part 53 moves to the home position side, the slider member 52 rises along the guide slot 54, and the cap 51 also rises accordingly. Finally, as shown in FIG. 3C, when the carriage 21 is positioned at the home position, the side wall portion 511 (porous member) of the cap 51 and the nozzle plate 33b come into close contact with each other. That is, the opening edge of the cap 51 is in contact with the nozzle surface.

  In this way, when the side wall portion 511 of the cap 51 and the nozzle surface are in close contact with each other, the ink suction unit 50 can perform pump suction. That is, when the suction pump (not shown) is operated in a state where the side wall portion 511 of the cap 51 and the nozzle surface are in close contact with each other, the ink suction unit 50 can make the space in the cap 51 negative pressure, so that the ink in the head 31 is discharged. It becomes possible to suck together with bubbles mixed in the head (in the nozzle). Thereby, the missing dot nozzle can be recovered.

  The wiping unit 55 has a wiper 56 that can contact the nozzle surface of the head 31. The wiper 56 is made of an elastic member having flexibility, and is provided at the end of the cap 51 (see FIG. 3A). When the cap 51 is maintained in the state shown in FIG. 3B, the wiper 56 according to the present embodiment is disposed in a state of protruding upward from the side wall portion 511 of the cap 51. That is, as shown to FIG. 5A, the front-end | tip part of the wiper 56 comes to be located above a nozzle surface. Thereafter, as shown in FIG. 5B, when the carriage 21 (head 31) moves in the moving direction (arrow direction in the figure) by driving the motor, the tip of the wiper 56 comes into contact with the nozzle surface of the head 31 and bends. Clean the nozzle surface. As a result, the wiping unit 55 can remove foreign matters such as paper dust attached to the nozzle surface, so that it is possible to normally eject ink from the nozzles clogged with the foreign matters.

  The flushing unit 60 is for receiving and storing ink ejected by the head 31 performing a flushing operation. As shown in FIG. 3B, the flushing operation is a state where a slight gap is opened between the nozzle surface and the opening edge of the cap 51, and a drive signal (piezo element) that is not related to an image to be printed is provided. The ink droplets are forcibly and continuously ejected from the nozzles. As a result, it is possible to prevent the ink in the head (inside the nozzle) from being thickened and dried and prevent the proper amount of ink from being ejected, so that the clogged nozzle recovers from the non-ejection state. It becomes possible.

  The in-head inspection unit 70 is for inspecting the state of the ink inside the head 31. That is, the in-head inspection unit 70 functions as an internal sensor that detects the ink state in the head 31 during an internal ejection inspection to be described later. The specific configuration of the in-head inspection unit 70 will be described in detail later.

  The outside head inspection unit 80 is for inspecting whether or not ink is ejected to the outside of the head 31. That is, the outside-head inspection unit 80 functions as an external sensor that detects an ink ejection failure outside the head 31 during an external ejection inspection described later. The specific configuration and the like of the outside head inspection unit 80 will be described in detail later.

  The controller 100 is a control unit for controlling the printer 1. As illustrated in FIG. 1, the controller 100 includes an interface unit 101, a CPU 102, a memory 103, and a unit control circuit 104. The interface unit 101 is for transmitting and receiving data between the host computer CP, which is an external device, and the printer 1. The CPU 102 is an arithmetic processing device for controlling the entire printer 1. The memory 103 is used to secure an area for storing a program of the CPU 102, a work area, and the like. The CPU 102 controls each unit by a unit control circuit 104 according to a program stored in the memory 103.

  The detector group 90 is for monitoring the situation in the printer 1. For example, the encoder 90 is a rotary encoder that is used to control the conveyance of a medium, a paper detection sensor that detects the presence or absence of a medium to be conveyed, and a carriage 21 ( Alternatively, there is a linear encoder for detecting the position of the head 31) in the moving direction.

<In-head inspection unit 70>
Here, the in-head inspection unit 70 will be described. The in-head inspection unit 70 is an internal sensor that detects an ink state in the head 31 during an internal ejection inspection to be described later.

(Principle of discharge inspection)
As shown in FIG. 2A, when the drive signal COM is applied to the piezo element PZT, the piezo element PZT is bent and the diaphragm 33c vibrates. Even when application of the drive signal COM to the piezo element PZT is stopped, residual vibration is generated in the diaphragm 33c. When the diaphragm 33c vibrates due to residual vibration, the piezo element PZT vibrates according to the residual vibration of the diaphragm 33c and outputs a signal. Therefore, residual vibration is generated in the diaphragm 33c, and a signal (frequency characteristic) of each piezoelectric element PZT can be obtained by detecting a signal generated in the piezoelectric element PZT at that time.

  Specifically, when the drive signal COM output from the drive signal generation unit 40 is applied to the corresponding piezo element PZT, the diaphragm 33c in contact with the piezo element PZT vibrates. The vibration of the diaphragm 33c does not stop immediately, but residual vibration occurs. For this reason, the piezoelectric element PZT vibrates according to the residual vibration and outputs a signal (back electromotive voltage). The signal is input to the in-head inspection unit 70. The in-head inspection unit 70 detects the frequency characteristic of the piezo element PZT based on the input signal. If this process is sequentially performed for the piezo elements PZT corresponding to the nozzles, the frequency characteristics of the piezo elements PZT can be detected. The frequency characteristics detected in this way vary depending on the ink state (normal, bubble contamination, ink thickening, paper dust adhesion) inside the head 31. That is, the vibration pattern of the residual vibration varies depending on the ink state (normal, mixed air bubbles, thickened ink, close contact with paper dust) in the head 31.

(Constitution)
FIG. 6 is an explanatory diagram of the configuration of the in-head inspection unit 70. The in-head inspection unit 70 includes an amplification unit 701 and a pulse width detection unit 702.

  The amplifying unit 701 removes a low-frequency component included in the signal from the piezo element 341 by a high-pass filter composed of a capacitor C1 and a resistor R1, and amplifies the signal with a predetermined amplification factor by the operational amplifier 701a. Next, the output of the operational amplifier 701a is passed through a high-pass filter composed of a capacitor C2 and a resistor R4, thereby converting it into a signal that vibrates up and down around the reference voltage Vref. Then, it is compared with the reference voltage Vref by the comparator 701b, and the signal is binarized depending on whether it is higher than the reference voltage Vref.

(Operation during inspection)
FIG. 7A is a diagram illustrating a signal output by the piezo element PZT according to the residual vibration. Since the frequency characteristics vary depending on the ink state in the head (normal, air bubbles mixed, ink thickening, paper dust adhesion), a unique voltage waveform (vibration pattern) corresponding to each ink state is output. It will be.

  FIG. 7B is a diagram illustrating a signal after the output of the operational amplifier 701a is passed through a high-pass filter including a capacitor C2 and a resistor R4, and a reference voltage Vref. That is, these are signals input to the comparator 701b.

  FIG. 7C is a diagram illustrating an output signal from the comparator 701b. That is, it is a signal input to the pulse width detector 702.

  When the pulse shown in FIG. 7C is input, the pulse width detection unit 702 resets the count value at the rising edge of the pulse, increments the count value for each subsequent clock signal, and counts at the rising edge of the next pulse. Is output to the CPU 102 of the controller 100. The CPU 102 can detect the period of the signal output from the piezo element PZT based on the count value output from the pulse width detection unit 702, that is, based on the detection result output from the in-head inspection unit 70.

  As described above, when the in-head inspection unit 70 outputs a vibration pattern having a frequency characteristic corresponding to the residual vibration, the controller 100 causes the ink state in the head (whether it is normal or air bubbles are mixed in the head). For example, whether there is an ejection failure due to ink, or due to an increase in ink viscosity, or whether foreign matter such as paper dust is in close contact with the nozzle Nz). Therefore, an appropriate recovery operation corresponding to each ink state can be performed.

<Outside head inspection unit 80>
Next, a configuration example of the outside-head inspection unit 80 will be described. The outside-head inspection unit 80 is an external sensor that detects a nozzle missing a dot by actually ejecting ink from each nozzle during external ejection inspection, which will be described later.

(Constitution)
FIG. 8A is a diagram illustrating the configuration of the outside-head inspection unit 80, and FIG. 8B is a block diagram illustrating the detection control unit 87.

  As shown in FIG. 8A, the outside head inspection unit 80 includes a detection electrode 513, a high voltage power supply unit 81, a first limiting resistor 82, a second limiting resistor 83, a detecting capacitor 84, an amplifier 85, A smoothing capacitor 86 and a detection control unit 87 are included. The nozzle plate 33b of the head 31 is grounded and functions as a part of the outside head inspection unit 80.

  At the time of an external discharge inspection process to be described later, as shown in FIGS. 3B and 8A, the cap 51 is disposed so as to face the nozzle surface with a predetermined distance d. In the space surrounded by the side wall portion 511 of the cap 51, as shown in FIG. 4, a moisturizing member 512 and a wire-shaped detection electrode 513 are arranged. For this reason, the nozzle plate 33b and the detection electrode 513 are arranged to face each other with a predetermined distance d.

  The detection electrode 513 is set to a high potential of about 600 V to 1 kV during an external discharge inspection process described later. As shown in FIG. 4, the detection electrode 513 connects the frame portion provided in a double rectangular shape, the diagonal line portion connecting the diagonal portions of the frame portion, and the midpoints on each side of the frame portion. And a cross. With this structure, it is uniformly charged over a wide range. In addition, when the ink solvent of this embodiment is a conductive liquid (for example, water) and the detection electrode 513 is set to a high potential while the moisturizing member 512 is moist, the surface of the moisturizing member 512 has the same potential. Also in this respect, the area where ink is ejected from the nozzle is uniformly charged over a wide range.

  The high-voltage power supply unit 81 is a power supply that makes the detection electrode 513 in the cap 51 have a predetermined potential. The high-voltage power supply unit 81 of this embodiment is configured by a DC power supply of about 600 V to 1 kV, and the operation is controlled by a control signal from the detection control unit 87.

  The first limiting resistor 82 and the second limiting resistor 83 are disposed between the output terminal of the high-voltage power supply unit 81 and the detection electrode 513, and limit the current flowing between the high-voltage power supply unit 81 and the detection electrode 513. . In the present embodiment, the first limiting resistor 82 and the second limiting resistor 83 have the same resistance value (for example, 1.6 MΩ), and the first limiting resistor 82 and the second limiting resistor 83 are connected in series. As shown, one end of the first limiting resistor 82 is connected to the output terminal of the high voltage power supply unit 81, the other end is connected to one end of the second limiting resistor 83, and the other end of the second limiting resistor 83 is connected to the detection electrode. Connect to 513.

  The detection capacitor 84 is an element for extracting a potential change component of the detection electrode 513, and one conductor is connected to the detection electrode 513 and the other conductor is connected to the amplifier 85. By interposing the detection capacitor 84 therebetween, the bias component (DC component) of the detection electrode 513 can be removed, and the signal can be easily handled. In this embodiment, the detection capacitor 84 has a capacity of 4700 pF.

  The amplifier 85 amplifies and outputs a signal (potential change) appearing at the other end of the detection capacitor 84. The amplifier 85 of this embodiment is configured with a gain of 4000 times. As a result, the potential change component can be acquired as a voltage signal having a change width of about 2 to 3V. The set of the detection capacitor 84 and the amplifier 85 corresponds to a kind of detection unit, and detects an electrical change generated in the detection electrode 513 caused by ejection of an ink droplet.

  The smoothing capacitor 86 suppresses a rapid change in potential. The smoothing capacitor 86 of this embodiment has one end connected to a signal line connecting the first limiting resistor 82 and the second limiting resistor 83, and the other end connected to the ground. And the capacity | capacitance is 0.1 micro F.

  The detection control unit 87 controls the outside-head inspection unit 80 based on the control by the controller 100. As illustrated in FIG. 8B, the detection control unit 87 includes a register group 87a, an AD conversion unit 87b, a voltage comparison unit 87c, and a control signal output unit 87d. The register group 87a includes a plurality of registers. Each register stores a determination result for each nozzle Nz, a voltage threshold for determination, and the like. The AD conversion unit 87b converts the amplified voltage signal (analog value) output from the amplifier 85 into a digital value. The voltage comparison unit 87c compares the amplitude value based on the amplified voltage signal with a voltage threshold value. The control signal output unit 87d outputs a control signal for controlling the operation of the high-voltage power supply unit 51.

(Principle of discharge inspection)
When ink is ejected from the nozzles of the nozzle plate 33 b, the potential of the detection electrode 513 changes. This potential change is detected by the detection capacitor 84 and the amplifier 85, and a detection signal is output to the detection control unit 87. Even if ink is ejected from the abnormal nozzle, since the ink is not ejected outside the head 31, the potential of the detection electrode 513 does not change, and no voltage change appears in the detection signal.

  Specifically, the nozzle plate 33b is set to the ground potential, and the detection electrode 513 disposed on the cap 51 is set to a high potential of about 600V to 1kV. Since the nozzle plate 33b is set to the ground potential, the ink droplet ejected from the nozzle also has the ground potential. The nozzle plate 33b and the detection electrode 513 are opposed to each other with a predetermined distance d (see FIG. 8A), and ink droplets are ejected from the detection target nozzle. When the ink droplet is ejected, the electrical change caused on the detection electrode 513 side due to this is acquired by the detection control unit 87 as the voltage signal SG via the detection capacitor 84 and the amplifier 85. Then, the detection control unit 87 determines whether or not the ink droplet has been normally ejected from the detection target nozzle based on the amplitude value (potential change) in the voltage signal SG.

  That is, as shown in FIG. 8A, by arranging the nozzle plate 33b and the detection electrode 513 at a predetermined interval d, these members can behave like a condenser. Generally, it is known that when the distance d between two conductors constituting a capacitor changes, the charge Q stored in the capacitor changes. When ink is ejected from the ground potential nozzle plate 33b toward the high potential detection electrode 513, the distance d between the ground potential ink droplet and the detection electrode 513 changes, and the distance between the two conductors of the capacitor is changed. As when d changes, the electric charge Q stored in the detection electrode 513 changes (the capacitance of the capacitor changes). When the capacitance in the capacitor is reduced, the amount of charge that can be stored between the nozzle plate 33b and the detection electrode 513 is reduced, so that excess charge is transferred from the detection electrode 513 to each limiting resistor. It moves to the high voltage power supply unit 81 side through 82 and 83. That is, a current flows toward the high voltage power supply unit 81. On the other hand, when the capacitance increases or the decreased capacitance returns, the charge moves from the high-voltage power supply unit 81 to the detection electrode 613 side through the limiting resistors 82 and 83. That is, a current flows toward the detection electrode 613. When such a current (also referred to as a discharge inspection current If for convenience) flows, the potential of the detection electrode 513 changes. The change in the potential of the detection electrode 513 also appears as a change in the potential of the other conductor (conductor on the amplifier 85 side) in the detection capacitor 84. Therefore, it is possible to determine whether or not an ink droplet has been ejected by monitoring the potential change of the other conductor.

(Operation during inspection)
FIG. 9A is a diagram illustrating an example of a drive signal COM used at the time of ejection inspection, and FIG. 9B illustrates a voltage signal SG output from the amplifier 55 when ink is ejected from a nozzle by the drive signal COM of FIG. 9A. FIG. 9C is a diagram illustrating a voltage signal SG which is a discharge inspection result of a plurality of nozzles (# 1 to # 10). As shown in FIG. 9A, the drive signal COM has a plurality of drive waveforms W (for example, 24) for ejecting ink from the nozzles in the first half period TA of the repetition period T, and is constant at an intermediate potential in the second half period TB. Is maintained. The drive signal generation unit 40 repeatedly generates a plurality of drive waveforms W (24 drive waveforms) every repetition period T. This repetition period T corresponds to the time required for inspection of one nozzle.

  First, a drive signal COM is applied to a piezo element corresponding to a certain nozzle to be inspected over a repetition period T. Then, ink droplets are continuously ejected from the nozzles targeted for ejection inspection in the first half period TA (for example, 24 shots are hit). As a result, the potential of the detection electrode 513 changes, and the amplifier 85 outputs the potential change to the detection control unit 87 as a voltage signal SG (sine curve) shown in FIG. 9B.

  Then, the detection control unit 87 calculates the maximum amplitude Vmax (difference between the maximum voltage VH and the minimum voltage VL) from the voltage signal SG in the inspection period (T) of the nozzle to be inspected, and determines the maximum amplitude Vmax and the predetermined threshold value TH. Compare If ink is ejected from the nozzle to be inspected according to the drive signal COM, the potential of the detection electrode 513 changes, and the maximum amplitude Vmax of the voltage signal SG becomes larger than the threshold value TH. On the other hand, if ink is not ejected from the nozzle to be inspected due to clogging or the amount of ejected ink is small, the potential of the detection electrode 513 does not change or the potential change is small. The maximum amplitude Vmax of the signal SG is equal to or less than the threshold value TH.

  After the drive signal COM is applied to the piezo element corresponding to a certain nozzle, the drive signal COM is repeatedly applied to the piezo element corresponding to the next inspection target nozzle over the period T, so that one nozzle to be inspected. Every time, the drive signal COM is applied to the piezo element corresponding to the nozzle over the repetition period T. As a result, as shown in FIG. 9C, the detection control unit 87 can acquire the voltage signal SG in which the potential change of the sine curve occurs for each repetition period T.

  For example, in the result of FIG. 9C, since the maximum amplitude Vmax of the voltage signal SG corresponding to the inspection period of the nozzle # 5 is smaller than the threshold value TH, the detection control unit 57 determines that the nozzle # 5 is a missing dot nozzle. Since the maximum amplitude Vmax of the voltage signal SG corresponding to each inspection period of the other nozzles (# 1 to # 4 and # 6 to # 10) is equal to or greater than the threshold value TH, the detection control unit 87 determines that the other nozzles are normal nozzles. It is judged that.

<<< Operation Example of Printer 1 >>>
<Overall operation>
Here, the overall operation of the printer 1 will be described. In the printer 1 according to the present embodiment, the controller 100 controls objects (conveyance unit 10, carriage unit 20, head unit 30, drive signal generation unit 40, ink suction unit 50, wiping) according to a computer program stored in the memory 103. The unit 55, the flushing unit 60, the in-head inspection unit 70, and the out-head inspection unit 80) are controlled to perform each process. Therefore, this computer program has a code for controlling a control target in order to execute these processes.

  Specifically, the controller 100 performs print command reception, paper feed operation, dot formation operation, transport operation, paper discharge determination, and print end determination in print processing, and dot dropout inspection operation in dot dropout inspection processing. , Perform recovery operation. Each process will be briefly described below.

  The reception of the print command is a process of receiving a print command from the computer CP. In this process, the controller 100 receives a print command via the interface unit 101.

  The paper feeding operation is an operation of moving a medium to be printed and positioning it at a print start position (so-called cue position). In this operation, the controller 100 moves the medium by driving the transport motor.

  The dot forming operation is an operation for forming dots on the medium. In this operation, the controller 100 drives the carriage 21 or outputs a control signal to the head 31. At this time, the drive signal COM generated by the drive signal generation unit 40 is applied to the piezo element PZT, whereby ink is ejected from the nozzle Nz. Thereby, ink is intermittently ejected from the nozzle Nz during the movement of the head 31, and dots are formed on the medium.

  The transport operation is an operation for moving the medium in the transport direction. The controller 100 can form dots at positions different from the dots formed by the previous dot formation operation by driving the transport motor.

  The print end determination is a determination as to whether or not to continue printing. The controller 100 makes a print end determination based on the presence or absence of print data for the medium to be printed.

  The dot missing inspection operation is an operation for inspecting whether or not there is a discharge failure (dot missing). The controller 100 acquires the detection result from the in-head inspection unit 70 and the detection result from the outside-head inspection unit 80 at a predetermined timing when the printing process is not performed, and sets in advance based on a combination of these detection results. An appropriate recovery operation is selected from the plurality of types of recovery operations performed. This dot dropout inspection operation will be described in detail later.

  The recovery operation is an operation for recovering the head 31 in a defective discharge state to a normal state where ink can be normally discharged. The controller 100 performs any one of a flushing operation, an ink suction operation, and a wiping operation according to the cause of the ejection failure.

  Here, in the printer 1 according to the present embodiment, performing the recovery operation according to the cause of the ejection failure has the following merits.

  When performing the flushing operation, the ink suction operation, and the wiping operation, the amount of ink consumed for recovery is different. For example, since the wiping operation is an operation of cleaning (wiping) the nozzle surface with the wiper 56, the amount of ink consumed for recovery is extremely small. On the other hand, since the flushing operation is an operation of discharging the ink in the head together with the thickened and dried ink, the amount of ink consumed for recovery is larger than the amount of ink consumed during the wiping operation. Further, the ink suction operation is an operation of sucking the ink in the head together with bubbles mixed with the ink, and the amount of ink consumed for recovery is larger than the amount of ink consumed during the flushing operation. For this reason, for example, when a discharge failure occurs due to paper dust adhering to the nozzle surface, the flushing operation or the ink suction operation can be performed despite the fact that it can be recovered by selecting the wiping operation. If selected, the amount of ink consumed for recovery is wasted.

  For this reason, in the printer 1 according to the present embodiment, an appropriate one of a plurality of types of recovery operations set in advance is selected based on the combination of the detection result of the in-head inspection unit 70 and the detection result of the outside inspection unit 80. By selecting an appropriate recovery operation, it is possible to suppress wasteful ink consumption.

<About missing dot detection operation>
Next, the dot dropout inspection operation will be described with reference to FIGS. 10A to 10D, FIG. 11, and FIG. FIG. 10A is a diagram illustrating a state in which bubbles are mixed. FIG. 10B is a diagram illustrating a state where the ink is thickened and dried. FIG. 10C is a diagram illustrating a state in which foreign matter such as paper dust is in close contact with the nozzle. FIG. 10D is a diagram illustrating a state in which a foreign substance such as paper dust has adhered to the vicinity of the nozzle. FIG. 11 is a flowchart illustrating an operation example of the missing dot inspection. FIG. 12 is a diagram for explaining determination conditions in the dot dropout inspection operation.

  As shown in FIG. 11, first, the controller 100 performs an internal ejection inspection process on the head 31 with the head 31 positioned at the home position (see FIG. 3C) (S101). In this internal ejection inspection process, the detection result of the in-head inspection unit 70 is acquired to inspect for the presence of ejection failure (dot missing) due to the ink state in the head. As a result of detection by the in-head inspection unit 70, the internal discharge inspection results in a normal ink state (no missing dots), an abnormal discharge due to bubble contamination (see FIG. 10A), Either an abnormal discharge has occurred due to ink thickening / drying (see FIG. 10B), or an abnormal discharge has occurred due to a foreign matter such as paper dust coming into close contact with the nozzle Nz (see FIG. 10C). The controller 100 can obtain the result.

  Subsequently, the controller 100 performs an external ejection inspection process (S102). In this external ejection inspection process, the detection result of the inspection unit 80 outside the head is acquired, thereby inspecting for the presence of ejection failure (dot missing) due to the fact that ink droplets are not ejected outside the head. Then, as a result of detection by the outside-head inspection unit 80, the ink droplets are normally ejected toward the outside of the head (no missing dots), and the ink droplets are normally ejected toward the outside of the head. The controller 100 can acquire any result of not being performed (with missing dots).

  Next, the controller 100 determines whether there is a discharge defect (dot missing) from the detection result of the in-head inspection unit 70 acquired by the internal discharge inspection process and the detection result of the external head inspection unit 80 acquired by the external discharge inspection process. An appropriate recovery operation is selected based on the determination condition. As shown in FIG. 12, this determination condition is set so that an appropriate recovery operation is selected for each combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection.

  Specifically, the controller 100 determines in step S103 that the determination result is No. 1 from the combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection, that is, as shown in FIG. As described above, the internal discharge inspection result is normal (“◯”: no missing dot) and the external discharge inspection result is normal (“◯”: no missing dot). Since the head 31 is in a normal state in which no ejection failure has occurred, the process is terminated as it is.

  Subsequently, when the controller 100 determines in step S103 that the determination result is any one of No. 2, 3, and 4 from the combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection, the re-inspection is performed. I do. That is, as shown in FIG. 12, the result of the internal discharge inspection is abnormal due to the mixing of bubbles (“× (bubble)”: dot missing), and the result of the external discharge inspection is normal (“◯”: The result of the internal ejection test is abnormal due to ink thickening (“× (thickening)”: dot missing) and the result of the external ejection test is normal ( “○”: No missing dot) or internal discharge inspection result is abnormal due to paper dust contact (“× (contact paper powder)”: dot missing) and external discharge inspection result Is determined to be normal (“◯”: no missing dot), the process returns to step S101 to perform re-inspection.

  At this time, if the controller 100 determines that the determination result is No. 2, the controller 100 is in an abnormal state due to air bubble mixing by internal discharge inspection (see FIG. 10A) and is in a normal state by external discharge inspection. Can be detected. Further, when it is determined that the determination result is No. 3, it is possible to detect an abnormal state due to ink thickening by an internal discharge inspection (see FIG. 10B) and a normal state by an external discharge inspection. it can. Further, when it is determined that the determination result is No. 4, the abnormal state due to the adhesion of paper dust is detected by the internal discharge inspection (see FIG. 10C), and the normal state is detected by the external discharge inspection. Can do.

  As described above, when it is determined that the determination result is any of No. 2, 3, and 4, that is, the result of the internal discharge inspection is abnormal and the result of the external discharge inspection is determined to be normal. In some cases, the results were different, so a re-examination was performed. As a result, it is possible to improve the inspection accuracy of todd loss, and it is not necessary to perform the recovery operation immediately, so that waste of consumed ink can be suppressed.

Subsequently, when the controller 100 determines in step S103 that the determination result is No. 5 or No. 8 from the combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection, the wiping process is performed. (S104). That is, as shown in FIG. 12, the result of the internal ejection inspection is normal (“◯”: no missing dot), and the result of the external ejection inspection is abnormal (“×”: missing a dot). Judgment condition or internal discharge inspection result is abnormal due to paper dust contact (“× (contact paper powder)”: dot missing) and external discharge inspection result is abnormal (“×”: dot If it is determined that any one of the determination conditions is present, a wiping process is performed. In this wiping process, while the head 31 moves from the home position (see FIGS. 3B, 5A, and 5B), a recovery operation is performed by the wiping unit 55 to remove foreign matters such as paper dust from the nozzle surface. Become.

  At this time, when it is determined that the determination result is No. 5, the controller 100 can detect the normal state by the internal discharge inspection and the abnormal state by the external discharge inspection.

  As described above, even when the result of the internal discharge inspection is normal and the result of the external discharge inspection is abnormal, that is, when the detection results are different, the wiping operation is performed without performing the re-inspection. The reason for this is as follows.

  From this combination of detection results, it can be determined that ink droplets are not ejected outside the head even though the ink state in the head is normal. This is because it can be estimated that a foreign matter such as paper dust that is not in close contact with Nz has adhered to the vicinity of the nozzle Nz, and that a discharge abnormality has occurred (see FIG. 10D).

  Here, if only the external discharge inspection is performed, the controller 100 can detect that the result of the external discharge inspection is abnormal (even if it can detect that a discharge failure has occurred). The cause of the failure cannot be identified. That is, it is possible to determine whether the head is attached in a state where the paper dust is in close contact with the nozzle surface as shown in FIG. 10C or in a state where the paper dust is not in close contact as shown in FIG. 10D. Can not. On the contrary, if only the internal discharge inspection is performed, the controller 100 determines that the result of the internal discharge inspection is normal, and thus detects the discharge failure even though the discharge failure has occurred. You can't do that. In the present embodiment, for each of these drawbacks, the paper powder adheres to the nozzle surface without being in close contact by determining the combination of the external discharge inspection result and the internal discharge inspection result (see FIG. 10D), it is possible to specify that a discharge failure has occurred. Therefore, the defects of the internal discharge test and the external discharge test are compensated for, and the inspection accuracy can be improved.

  On the other hand, when it is determined that the determination result is No. 8, the controller 100 is in an abnormal state due to the adhesion of paper powder by the internal discharge inspection (see FIG. 10C) and is abnormal by the external discharge inspection. Can be detected.

  As described above, when the result of the internal ejection test is abnormal and the result of the external ejection test is also abnormal, the ink droplets are ejected outside the head because the paper powder is in close contact with the nozzle surface. Since the cause of the ejection failure can be specified when there is no state (see FIG. 10C), the wiping operation is performed without performing re-inspection.

  Therefore, when there is an abnormality in the result of the external ejection inspection, the recovery operation (wiping operation) is selected based on the result of the internal ejection inspection (paper powder adhesion), so that appropriate recovery according to the cause of the ejection failure is achieved. The operation is performed, and waste of ink consumed for recovery can be suppressed.

  Next, when the wiping process in step 104 is completed, the process returns to step S101 and re-inspection is performed. The reason why the re-inspection is performed after the wiping process is completed is as follows.

  This is because when the paper dust adhering to the nozzle surface is wiped off in the wiping process, the wiper 56 touches the nozzle Nz, so that the ink meniscus may collapse and cause missing dots. In this way, by performing re-inspection after the wiping process is completed, it is possible to improve the detection accuracy of missing dots.

  Subsequently, in Step S103, when the controller 100 determines that the determination result is No. 6 from the combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection, the controller 100 performs ink suction processing (S105). That is, as shown in FIG. 12, the result of the internal discharge inspection is abnormal due to the mixing of bubbles (“× (bubble)”: dot missing), and the result of the external discharge inspection is abnormal (“×”: If it is determined that the determination condition “with missing dots” is satisfied, ink suction processing is performed. In this ink suction process, the recovery operation by the ink suction unit 50 is performed, and bubbles mixed in the head are sucked together with the ink in the head.

  At this time, when it is determined that the determination result is No. 6, the controller 100 can detect an abnormal state due to air bubble mixing by the internal discharge inspection and an abnormal state by the external discharge inspection. .

  As described above, when the result of the internal ejection inspection is abnormal and the result of the external ejection inspection is also abnormal, the ink droplets are not ejected outside the head because the air bubbles are mixed. The cause of the ejection failure can be specified (see FIG. 10A), so that the ink suction operation is performed without performing re-inspection.

  Therefore, when there is an abnormality in the result of the external discharge inspection, the recovery operation (ink suction operation) is selected based on the result of the internal discharge inspection (bubble mixing), so that an appropriate recovery operation according to the cause of the discharge failure And waste of the amount of ink consumed for recovery can be suppressed.

  Subsequently, in step S103, when the controller 100 determines that the determination result is No. 7 from the combination of the detection result of the internal discharge inspection and the detection result of the external discharge inspection, the controller 100 performs a flushing process (S106). That is, as shown in FIG. 12, the result of the internal ejection inspection is abnormal due to ink thickening (“× (thickening)”: dot missing), and the result of the external ejection inspection is abnormal (“× ": Dot missing"), the head 31 is moved to a position shifted from the home position (see FIG. 3B), and the flushing process is performed. In this flushing process, the recovery operation by the flushing unit 60 is performed, and the thickened ink is discharged out of the head.

  At this time, if the controller 100 determines that the determination result is No. 7, the controller 100 detects an abnormal state due to ink thickening by an internal discharge inspection and an abnormal state by an external discharge inspection. Can do.

  As described above, when the result of the internal ejection inspection is abnormal and the result of the external ejection inspection is also abnormal, the ink is in a thickened state, so that the ink droplet is not ejected outside the head. If there is, the cause of the ejection failure can be specified (see FIG. 10B), so the flushing operation is performed without performing re-inspection.

  Therefore, when there is an abnormality in the result of the external ejection inspection, the recovery operation (flushing operation) is selected based on the result of the internal ejection inspection (thickening of ink), so that appropriate recovery according to the cause of the ejection failure is achieved. The operation is performed, and waste of ink consumed for recovery can be suppressed.

<<< Effectiveness of Printer 1 According to the Present Embodiment >>>
As described above, the printer 1 according to this embodiment includes the head 31 that performs printing by ejecting ink onto a medium, the in-head inspection unit 70 that detects the ink state inside the head 31, and the outside of the head 31. The recovery operation for recovering the ink discharge by the head 31 is set in advance based on the detection results of the inspection unit 80 outside the head for detecting defective ink discharge and the inspection unit 70 inside the head and the inspection unit 80 outside the head. And a controller 100 that selects from a plurality of types of recovery operations.

  When ink is filled from the ink cartridge to the head, bubbles are mixed in, the ink (liquid) is not discharged from the nozzle Nz for a long time, the ink is thickened and dried, or foreign matter such as paper dust adheres to the nozzle Nz Otherwise, the nozzle Nz may be clogged. When the nozzle Nz is clogged in this way, ink is not ejected when ink should be ejected from the nozzle Nz, and dot missing occurs (ejection failure). The missing dot means a phenomenon in which dots are not formed where ink is originally ejected from the nozzles Nz and dots are to be formed. If dot omission occurs, it causes image quality degradation. As described above, there are various reasons for missing dots, such as air bubbles, thickening / drying of ink, and adhesion of foreign matters such as paper dust. Therefore, internal ejection inspection (in-head inspection unit 70) or external ejection inspection (outside of the head) In some cases, the inspection unit 80) alone cannot be specified. For example, in the external ejection inspection, even if an abnormal state in which ink droplets are not ejected from the nozzle to the outside of the head can be detected, is the cause of the ejection failure caused by paper dust that is in close contact with the nozzle surface (see FIG. 10C), or whether it is due to paper dust that does not adhere to the nozzle surface (see FIG. 10D). Also, in the internal discharge inspection, from the inspection result, the cause of the discharge failure is due to air bubbles mixing (see FIG. 10A), due to thickening / drying of ink (see FIG. 10B), or paper dust adhered to the nozzle surface. Even if it is possible to determine whether it is any of the above (refer to FIG. 10C), it is not possible to determine the one based on paper dust that does not adhere to the nozzle surface (see FIG. 10D). On the other hand, in the present embodiment, not only the detection result of the external discharge inspection but also the detection result of the internal discharge inspection is acquired, so that the cause of the discharge failure adheres to the nozzle based on the combination of the respective detection results. It is possible to determine whether it is due to the paper dust (see FIG. 10C) or the paper dust that does not adhere to the nozzle surface (see FIG. 10D). As described above, in the invention according to the present embodiment, the nozzles Nz that are missing dots (also referred to as dot missing nozzles and non-ejection nozzles) are detected based on the detection results of the in-head inspection unit 70 and the outside head inspection unit 80. In order to make up for the mutual shortcomings of internal discharge inspection and external discharge inspection, the cause of dot dropout is identified from the combination of the respective inspection results, and the recovery action suitable for each cause is selected, thereby creating a dot. Ink was normally ejected from the nozzle. As a result, the defects of the in-head inspection unit 70 (internal sensor) and the out-of-head inspection unit 80 (external sensor) can be compensated for each other, the detection accuracy of ejection failure can be improved, and an appropriate recovery process can be performed. Can be done.

  Further, the controller 100 determines from the detection result of the in-head inspection unit 70 that an ink ejection failure has occurred based on the ink state in the head, and the ink ejection failure from the detection result of the outside-head inspection unit 80. When it is determined that the ink does not occur, the detection results of the in-head inspection unit 70 and the out-head inspection unit 80 are obtained again to determine whether or not an ink ejection failure has occurred. As described above, when dot missing is detected in the internal ejection inspection and dot missing is not detected in the external ejection inspection, ink is ejected outside the head although there is an abnormality in the head. Therefore, by performing re-inspection, it is not necessary to perform the recovery operation immediately, so it is possible to suppress waste of consumed ink.

  In addition, when the controller 100 determines from the detection result of the out-of-head inspection unit 80 that an ink ejection failure has occurred, the controller 100 performs a plurality of types of recovery operations with different amounts of liquid consumed during the recovery operation. Therefore, the recovery operation is selected based on the ink state detected by the in-head inspection unit 70. In other words, when dot missing is detected in both the internal ejection test and the external ejection test, the ink is not ejected outside the head due to an abnormality in the head. The recovery action was selected to eliminate the cause. For this reason, an appropriate recovery operation considering the cause of ejection failure is performed, and wasteful ink consumption can be suppressed.

=== Other Embodiments ===
Although the present embodiment is mainly described for a printing apparatus (liquid ejection inspection apparatus), disclosure of a liquid ejection inspection method and the like is also included. Further, the present embodiment is intended to facilitate understanding of the present invention and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<Printing device>
In the above embodiment, an ink jet printer has been described as an example of a printing apparatus. However, the present invention is not limited to this. For example, a printing apparatus that discharges liquid other than ink may be used. The present invention can be used in various printing apparatuses including a liquid ejecting head that discharges a minute amount of liquid droplets. In addition, a droplet means the state of the liquid discharged from the said printing apparatus, and shall include what pulls a tail in granular shape, tear shape, and thread shape. The liquid here may be any material that can be ejected by the printing apparatus. For example, it may be in a state in which the substance is in a liquid phase, such as a liquid with high or low viscosity, sol, gel water, other inorganic solvents, organic solvents, solutions, liquid resins, liquid metals (metal melts ) And a liquid as one state of a substance, as well as a material in which particles of a functional material made of a solid such as a pigment or metal particles are dissolved, dispersed or mixed in a solvent. Further, representative examples of the liquid include ink and liquid crystal as described in the above embodiment. Here, the ink includes general water-based inks and oil-based inks, and various liquid compositions such as gel inks and hot melt inks. Specific examples of printing apparatuses include, for example, liquids that are dispersed or dissolved in materials such as liquid crystal displays, EL (electroluminescence) displays, surface-emitting displays, and electrode materials and color materials used in the manufacture of color filters. It may be a printing apparatus that discharges biological organic materials used in biochip manufacturing, a printing apparatus that is used as a precision pipette and discharges a sample liquid, a textile printing apparatus, a microdispenser, or the like. In addition, transparent resin liquids such as UV curable resins are used to form micro hemispherical lenses (optical lenses) that are used in optical devices, such as printers that eject lubricant oil to precision machines such as watches and cameras. You may employ | adopt the printing apparatus which discharges etching liquid, such as an acid or an alkali, in order to etch the printing apparatus discharged on a board | substrate, a board | substrate. The present invention can be applied to any one of these printing apparatuses.

  Further, the printing apparatus in the above embodiment may be a so-called serial scanning type printer including the carriage unit 20, or the carriage unit 20 is not included, and the head unit 30 (head 31) does not reciprocate. A so-called line scanning printer may be used.

<Internal sensor>
In the above embodiment, as an example of the in-head inspection unit 70 (internal sensor), an actuator such as a piezo element vibrates the vibration plate, and detects a change in the frequency characteristics (vibration pattern) of residual vibration generated on the vibration plate. Although what has been described (FIGS. 6 and 7) has been described, the present invention is not limited to this. For example, the change in the frequency characteristics of the residual vibration may be detected from the vibration of the actuator itself such as a piezo element, not limited to the diaphragm.

  The internal sensor only needs to be able to inspect the state of the ink inside the head 31, and as the internal sensor, a signal from the piezo element PZT to which the drive signal COM is applied may be input to the in-head inspection unit 70. As the internal sensor, a signal from the piezo element PZT to which the drive signal COM is not applied may be input to the in-head inspection unit 70, and a sensor other than the piezo element PZT may be used as the internal sensor.

<External sensor>
In the above embodiment, as an example of the outside-head inspection unit 80 (external sensor), a charged ink droplet is ejected from a nozzle toward a detection electrode, and an electrical change occurring in the electrode is detected. (Refer to FIG. 8A and FIG. 8B) has been described, but is not limited thereto.

  For example, a detector having a light source and an optical sensor may be used as the external sensor. Specifically, such a detector detects that an ink droplet ejected from the nozzle to the outside of the head has passed between the light source and the optical sensor and blocked light between the light source and the optical sensor. . If the ink droplet blocks the light, it is determined that the ink has been ejected normally. If the ink droplet does not block the light, it is determined that the ejection has failed (dot missing).

  A reading device (scanner or the like) or an imaging device (line sensor camera or the like) may be used as an external sensor. Specifically, an image is printed on a medium based on the image data, the image after printing is read by a scanner (imaged by a camera), and the read data (image data captured by a camera) read by the scanner and the image data are combined. In comparison, the ejection failure of the nozzle may be detected.

<Dot missing detection operation>
In the above-described embodiment, the case where the dot missing detection operation is performed at a predetermined timing when the printing process is not performed has been described as an example. However, the present invention is not limited to this. For example, the printing process is performed. During the middle, a missing dot detection operation may be performed.

1 printer, 10 transport unit,
20 carriage unit, 21 carriage,
30 head units, 31 heads,
32 cases, 33 flow path units,
33a flow path forming substrate, 33b nozzle plate,
331 pressure chamber, 332 ink supply path,
333 Common ink chamber, 334 Diaphragm part,
335 islands, 34 piezo element units,
341 piezo element group, 342 fixing plate,
40 drive signal generator, 50 ink suction unit,
51 cap, 511 side wall,
512 moisturizing member, 513 detection electrode,
52 slider member, 53 contact part,
54 long hole, 55 wiping unit,
56 Wiper, 58 Waste tube,
60 flushing units, 70 in-head inspection units,
701 amplifier, 701a operational amplifier,
701b comparator, 702 pulse width detector,
80 head inspection unit, 81 high voltage unit,
82 first limiting resistor, 83 second limiting resistor,
84 detection capacitor, 85 amplifier,
86 smoothing capacitor, 87 detection control unit,
90 detectors, 100 controllers,
CP computer, Nz nozzle, PZT piezo element

Claims (6)

An internal sensor for detecting the liquid state inside the head that discharges liquid to the medium;
An external sensor for detecting a liquid ejection failure outside the head;
Based on the detection results of the internal sensor and the external sensor, a controller that selects a recovery operation for recovering the ejection of liquid by the head from a plurality of types of recovery operations;
A liquid discharge inspection apparatus comprising: The liquid discharge inspection apparatus according to claim 1,
The controller is
If it is determined from the detection result of the internal sensor that a liquid discharge failure has occurred based on the liquid state, and it is determined from the detection result of the external sensor that no liquid discharge failure has occurred, the internal sensor A liquid discharge inspection apparatus, wherein the detection result of the sensor and the external sensor is obtained again to determine whether or not a liquid discharge failure has occurred. The liquid discharge inspection apparatus according to claim 1 or 2,
The controller is
When it is determined from the detection result of the external sensor that a liquid ejection failure has occurred, the internal sensor detects from a plurality of types of recovery operations that differ in the amount of liquid consumed during the recovery operation. A liquid discharge inspection apparatus, wherein a recovery operation is selected based on the liquid state. Preparing a liquid ejection inspection apparatus having an internal sensor that detects a liquid state inside a head that ejects liquid to a medium, an external sensor that detects a liquid ejection failure outside the head, and a controller When,
Causing the controller to select a recovery operation for recovering the ejection of the liquid by the head from a plurality of types of recovery operations based on the detection results of the internal sensor and the external sensor;
A liquid discharge inspection method characterized by comprising: A head for performing printing by discharging liquid onto a medium;
An internal sensor for detecting the state of the liquid in the head;
An external sensor for detecting a liquid ejection failure outside the head;
Based on the detection results of the internal sensor and the external sensor, a controller that selects a recovery operation for recovering the ejection of liquid by the head from a plurality of types of recovery operations;
A printing apparatus comprising: In a liquid ejection inspection apparatus having an internal sensor that detects a liquid state inside a head that ejects liquid to a medium, an external sensor that detects a liquid ejection failure outside the head, and a controller,
A program for realizing a function of selecting a recovery operation for recovering liquid ejection by the head from a plurality of types of recovery operations based on detection results of the internal sensor and the external sensor.

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