Printing device, printing method and printing program

Abstract

To reduce consumptions of ink in identifying an abnormal nozzle and shorten a printing time.SOLUTION: A printing device 100 is provided with: an image forming part 20 that has a plurality of inkjet heads 30 for discharging ink to a recording medium and prints an image on the recording medium; a head control part 42 that obtains residual vibration waveforms generated after a plurality of nozzles which the inkjet heads 30 have are respectively driven and performs first determination of determining discharge states of the nozzles on the basis of the residual vibration waveforms; and a control part 50 that makes a second determined nozzle, which is the nozzle whose discharging state could not be determined in the first determination, discharge ink, and performs second determination of determining the discharge state thereof on the basis of the result of the discharging.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a printing apparatus, a printing method, and a printing program.

Background Art

[0002] In an inkjet printing apparatus, nozzle defects may occur in some of the nozzles of the line head during continuous printing. Since ink is no longer ejected from the defective nozzles, white streaks appear in the printed image. Such white streaks can be corrected so as not to be noticeable by adjusting the dot size of adjacent nozzles. However, with such a correction method, it is necessary to identify the position of the defective nozzle in advance. For example, Patent Document 1 discloses a technique for outputting a test pattern every few pages of printing and periodically identifying the position of defective nozzles because the state of the nozzles changes during continuous printing.

[0003] Patent Document 1 describes detecting abnormal ejection of droplets from nozzles based on the residual vibration of a diaphragm. Further, when receiving an abnormality determination, the arithmetic processing unit controls each part of the apparatus to print a nozzle check pattern for checking the nozzles. Further, it is described that each nozzle check pattern includes a plurality of patterns formed for each ink color by ejecting ink droplets using all the nozzles of the head. Further, it is described that the user visually checks the printed nozzle check pattern for the presence or absence of abnormal ejection of the nozzles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, conventionally, all nozzles of an inkjet head eject ink droplets to form a nozzle check pattern. A technique (Patent Document 1) is disclosed in which the position of a missing nozzle is specified by visually observing the formed nozzle check pattern. However, in the technique described in Patent Document 1, ink droplets are ejected from normal nozzles as well when printing the nozzle check pattern. For this reason, the technique described in Patent Document 1 has a problem of a large ink consumption in specifying a missing nozzle. Further, in the technique described in Patent Document 1, the user stops printing and visually checks for missing nozzles in the printed nozzle check pattern. For this reason, the technique described in Patent Document 1 has a problem of long printing time.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to reduce the ink consumption in specifying an abnormal nozzle and reduce the printing time.

Means for Solving the Problems

[0007] In order to solve the above problems, a printing apparatus of the present invention includes a plurality of inkjet heads that eject ink onto a recording medium, an image forming unit that prints an image on the recording medium, and a residual vibration waveform that is generated after each of a plurality of nozzles included in the inkjet head is driven. A head control unit that performs a first determination for acquiring the waveform and determining the ejection state of the nozzle based on the residual vibration waveform, and a second determination nozzle that is a nozzle for which the ejection state could not be determined in the first determination. And a control unit that ejects ink and performs a second determination for determining the ejection state based on the ejection result. Note that the above printing apparatus is an aspect of the present invention, and a printing method and a printing program reflecting one aspect of the present invention are also configured in the same manner as the above printing apparatus.

Effects of the Invention

[0008] According to the present invention having the above configuration, it is possible to reduce the ink consumption in specifying an abnormal nozzle and reduce the printing time. Problems, configurations, and effects other than the above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In this specification and the drawings, for components having substantially the same function or configuration, the same reference numerals are given and redundant explanations are omitted.

[0011] <One Embodiment> [Configuration Example of Printing Device] First, the configuration of a printing device 100 according to an embodiment of the present invention will be described. The printing device 100 is an example of an image forming device that forms an image on a recording medium by an electrophotographic method. The printing device 100 forms a color image on a recording medium by overlapping four-color images of Y (yellow), M (magenta), C (cyan), and K (black), for example. Hereinafter, the recording medium is also referred to as "paper".

[0012] FIG. 1 is a block diagram showing a configuration example of the printing device 100 according to the present embodiment. As shown in FIG. 1, the printing device 100 includes a paper feeding unit 11, an image forming unit 20, a reading unit 12, and a head control unit 42. The printing device 100 also includes a control unit 50, a storage unit 13, an operation display unit 14, and a communication interface (I / F) 15. Each component of the printing device 100 shown in the figure is connected by a bus B so that information data can be transmitted and received to and from each other. Note that FIG. 1 shows only the components of the printing device 100 related to the present invention, and the illustration and description of other components are omitted.

[0013] The paper feeding unit 11 is a container (paper feeding tray) that stores the paper on which image formation is performed by the image forming unit 20.

[0014] The image forming unit 20 has a function of printing an image on paper. The image forming unit 20 has four head units 21 (only one is shown in the figure) that eject Y, M, C, and K inks, respectively. Four-color images of Y, M, C, and K can be printed on paper by the four head units 21. The head unit 21 has a plurality of inkjet heads that eject ink onto the paper. The configuration of the head unit 21 will be described with reference to FIG. 2 described later.

[0015] The reading unit 12 is composed of an image sensor or the like, reads the image printed on the paper output from the image forming unit 20, and outputs the read image.

[0016] The head control unit 42 drives each nozzle in order to properly eject ink from the nozzles of each inkjet head 30 (see FIG. 2) of the head unit 21. The head control unit 42 selects a prestored voltage waveform pattern based on a control signal from the control unit 50. Further, the head control unit 42 generates a drive signal and drives the nozzles according to the selected voltage waveform pattern. Also, the head control unit 42 switches, according to the image data to be printed, whether to output a drive signal to each nozzle.

[0017] Further, the head control unit 42 acquires a residual vibration waveform that occurs after each of the plurality of nozzles included in the inkjet head 30 has been driven. The acquisition of the residual vibration waveform is measured and acquired by a residual vibration measurement circuit 200 shown in FIG. 5 described later. The head control unit 42 makes a first determination described later for determining the ejection state of each nozzle based on the acquired residual vibration waveform. Here, the ejection state includes a normal state in which the ejection operation of the nozzle is normal and an abnormal state in which the ejection operation of the nozzle is abnormal. Abnormalities in the ejection operation are, for example, ejection failure, non-ejection, and the like. Further, hereinafter, a nozzle whose ejection state is the normal state is referred to as a "normal nozzle", and a nozzle whose ejection state is the abnormal state is referred to as an "abnormal nozzle".

[0018] The control unit 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, and a RAM (Random Access Memory) 53. The control unit 50 is configured by, for example, a microprocessor or the like and performs overall control of the printing apparatus 100.

[0019] The CPU 51 controls the operations of each part within the printing apparatus 100. For example, the CPU 51 (control unit 50) controls the printing process in the image forming unit 20. Also, the CPU 51 (control unit 50) causes ink to be ejected from a second determination nozzle, which is a nozzle for which the ejection state could not be determined in the first determination described later. Thereafter, the CPU 51 (control unit 50) performs a second determination described later to determine the ejection state based on the ejection result. Note that a GPU (Graphics Processing Unit) may be used instead of the CPU 51, or the CPU 51 and the GPU may be used in combination.

[0020] The ROM 52 is composed of a storage medium such as a non-volatile memory, and stores programs, data, etc. that the CPU 51 executes and references.

[0021] The RAM 53 is composed of a storage medium such as a volatile memory, and temporarily stores information (data) necessary for each process performed by the CPU 51.

[0022] The storage unit 13 is composed of a non-transitory recording medium such as an HDD (Hard Disk Drive), for example. The storage unit 13 stores programs for the CPU 51 to control each part, an OS (Operating System), programs such as a controller, and data. Note that the storage unit 13 is not limited to an HDD, and may be a recording medium such as an SSD (Solid State Drive), a CD (Compact Disc)-ROM, a DVD (Digital Versatile Disc)-ROM, etc.

[0023] The operation display unit 14 is composed of a display unit including a display device such as an LCD (Liquid Crystal Display) or an organic EL (Electro-luminescence) display, and an operation unit including a mouse, a touch sensor, etc.

[0024] The communication interface (I / F) 15 is composed of a NIC (Network Interface Card), a modem, etc., establishes a connection with an external terminal device (not shown), and performs transmission and reception of various data.

[0025] Next, the configuration of the nozzle bottom surface of the head unit 21 will be described. FIG. 2 is a diagram showing the configuration of the nozzle bottom surface (the liquid ejection surface of the nozzle) of the head unit 21 of the printing apparatus 100 according to the present embodiment. As shown in FIG. 2, the head unit 21 has eight inkjet heads 30. The eight inkjet heads 30 are arranged in a staggered pattern in two rows. Further, in each row, four inkjet heads 30 are arranged at a predetermined interval along the direction orthogonal to the paper conveyance direction (the paper width direction). The inkjet head 30 includes a diaphragm and a piezoelectric actuator that displaces the diaphragm. Further, the inkjet head 30 includes a cavity (pressure chamber) filled with ink as a liquid therein and whose internal pressure is increased or decreased by the displacement of the diaphragm. Further, the inkjet head 30 includes a plurality of nozzles that communicate with the cavity and eject ink as droplets by the increase or decrease of the pressure in the cavity.

[0026] FIG. 3 is a diagram showing a test pattern P1 for identifying abnormal nozzles in the prior art. As shown in FIG. 3, the test pattern P1 is composed of image data corresponding to the positions of the respective inkjet heads 30 of the head unit 21. In FIG. 3, only the test pattern P1 corresponding to one head unit 21 is shown. Actually, the test pattern includes four test patterns P1 corresponding to each of the four head units 21 (four colors). In the prior art, the user observes a test chart on which the test pattern is printed. The user identifies abnormal nozzles by checking the positions of white streaks, light-colored images, etc. on the test chart. FIG. 4 is an enlarged view of a test chart including white streaks. In FIG. 4, the white portion surrounded by the dashed-dotted line is the white streak corresponding to the missing nozzle.

[0027] [Configuration example of residual vibration measurement circuit] Next, the configuration of the residual vibration measurement circuit 200 in the printing apparatus 100 will be described. After the nozzle is driven, the residual vibration measurement circuit 200 measures and acquires the residual vibration waveform of the nozzle. The period and amplitude of the residual vibration waveform of an abnormal nozzle are smaller than those of the residual vibration waveform of a normal nozzle, respectively. Therefore, the residual vibration measurement circuit 200 can identify an abnormal nozzle by analyzing the residual vibration waveform of the nozzle. FIG. 5 is a block diagram showing the configuration of the residual vibration measurement circuit 200 in the printing apparatus 100 according to the present embodiment.

[0028] As shown in FIG. 5, the residual vibration measurement circuit 200 includes a drive substrate 40 and an inkjet head 30. In FIG. 5, for convenience of explanation, only one inkjet head 30 is shown. Actually, all the inkjet heads 30 included in the head unit 21 are connected to the drive substrate 40 as shown in FIG. 5.

[0029] The drive substrate 40 drives the inkjet head 30 and performs various controls related to the ink ejection operation of the inkjet head 30. The drive substrate 40 includes a drive circuit 41, a head control unit 42, an AMP (Amplifier) 43, and an ADC (Analog Digital Converter) 44. The drive circuit 41 is connected to a drive circuit 32 (described later) of the inkjet head 30. Further, the head control unit 42 is connected to the drive circuit 32 and a MUX (Multiplexer) 33 (described later) of the inkjet head 30.

[0030] The drive circuit 41 includes a CPU 411, a DAC (Digital Analog Converter) 412, and a power supply circuit 413. The CPU 411 sets a drive voltage and outputs a drive voltage set value to the DAC 412. The DAC 412 converts the drive voltage set value into an analog signal and outputs it to the power supply circuit 413. The power supply circuit 413 generates a drive voltage using the analog signal input from the DAC 412 and outputs it to the drive circuit 32 (described later) of the inkjet head 30.

[0031] The head control unit 42 is composed of an FPGA (Field Programmable Gate Array) or the like. Based on the control signal from the control unit 50, the head control unit 42 selects a pre-stored voltage waveform pattern to generate a drive signal. In the following description, the "drive signal" is also referred to as the "drive waveform". The head control unit 42 outputs the generated drive waveform to a drive circuit 32 (described later) of the inkjet head 30 to drive the nozzles. Also, in the measurement operation of the residual vibration waveform of the nozzles, the head control unit 42 drives the nozzles so as not to eject ink.

[0032] The AMP 43 inputs and amplifies the residual vibration waveform from a MUX 33 (described later) of the inkjet head 30. The ADC 44 converts the residual vibration waveform amplified by the AMP 43 into a digital signal and outputs it to the head control unit 42.

[0033] The head control unit 42 makes a first determination regarding the ejection state of the nozzles using the residual vibration waveform input from the ADC 44. Also, the head control unit 42 outputs the result of the first determination regarding the ejection state of the nozzles to the control unit 50. The result of the first determination includes the position information of each of the identified normal nozzles, abnormal nozzles, and nozzles for which the ejection state could not be determined (second determination nozzles).

[0034] As shown in FIG. 5, the inkjet head 30 has a driving IC (Integrated Circuit) 31 and a plurality of nozzles (nozzle 1 to nozzle n) that eject ink. The driving IC 31 has a driving circuit 32, a MUX 33, and two-channel switches (switches 34_1 to 34_n) equal in number to the nozzles. The output side of each switch (switches 34_1 to 34_n) is connected to each nozzle, respectively. The input terminal on the ON side of each switch is connected to the output side of the driving circuit 32. The driving circuit 32 amplifies the driving voltage input from the head control unit 42 and applies the driving waveform input from the head control unit 42 to each nozzle to drive each nozzle. The input terminal on the OFF side of each switch is connected to the input side of the MUX 33. When each switch is set to the ON side, the nozzle connected to the turned-on switch is driven by the driving waveform. When each switch is set to the OFF side, the MUX 33 acquires the residual vibration waveform generated in the nozzle connected to the turned-off switch and outputs it to the head control unit 42.

[0035] Next, the determination of the nozzle ejection state based on the residual vibration waveform measured by the residual vibration measurement circuit 200 will be described. FIG. 6 is a diagram for explaining the determination of the nozzle ejection state based on the residual vibration waveform of the nozzle in the printing apparatus 100 according to the present embodiment. FIG. 6A is a diagram for explaining the determination of the nozzle ejection state based on the period of the residual vibration waveform. FIG. 6B is a diagram for explaining the determination of the nozzle ejection state based on the amplitude of the residual vibration waveform.

[0036] The waveform W10 shown in FIG. 6A represents the driving waveform. The waveform W21 represents the residual vibration waveform measured after driving a normal nozzle. The waveform W22 represents the residual vibration waveform measured after driving an abnormal nozzle. T nom represents the period of the residual vibration waveform (waveform W21) of the normal nozzle. T th is smaller than the period (T nom ) of the residual vibration waveform of the normal nozzle and represents a period threshold appropriately set based on T nom . T defrepresents the period of the residual vibration waveform (waveform W22) of the abnormal nozzle. In the present embodiment, when the period of the acquired residual vibration waveform is smaller than the period threshold (T th ), the head control unit 42 determines that the ejection state of the nozzle from which the residual vibration waveform is acquired is an abnormal state. Conversely, when the period of the acquired residual vibration waveform is larger than the period threshold (T th ), the head control unit 42 determines that the ejection state of the nozzle from which the residual vibration waveform is acquired is a normal state. When the period of the acquired residual vibration waveform is in the vicinity of the period threshold (T th ), it is difficult to determine the ejection state of the nozzle. Therefore, in the present embodiment, a predetermined range from the period threshold (T th ) is registered in advance as a period range in which the ejection state cannot be determined.

[0037] Since the waveforms W10, W21, and W22 shown in FIG. 6B are the same as the respective waveforms shown in FIG. 6A, redundant descriptions are omitted. A nom represents the amplitude of the residual vibration waveform (waveform W21) of the normal nozzle. A th is smaller than the amplitude of the residual vibration waveform of the normal nozzle (A nom ) and represents an amplitude threshold appropriately set based on A nom . A def represents the amplitude of the residual vibration waveform (waveform W22) of the abnormal nozzle. In the present embodiment, when the amplitude of the acquired residual vibration waveform is smaller than the amplitude threshold (A th ), the head control unit 42 determines that the ejection state of the nozzle from which the residual vibration waveform is acquired is an abnormal state. Conversely, when the amplitude of the acquired residual vibration waveform is larger than the amplitude threshold (A th ), the head control unit 42 determines that the ejection state of the nozzle from which the residual vibration waveform is acquired is a normal state. When the amplitude of the acquired residual vibration waveform is in the vicinity of the amplitude threshold (A th ), it is difficult to determine the ejection state of the nozzle. Therefore, in the present embodiment, a predetermined range from the amplitude threshold (A th ) is registered in advance as an amplitude range in which the ejection state cannot be determined.

[0038] The determination of the ejection state of the nozzles based on the period and amplitude of the residual vibration waveform in the head control unit 42 is the first determination. In the first determination, the head control unit 42 determines that it cannot determine the ejection state of the nozzle for which the residual vibration waveform is measured in any of the following cases. For example, when the period of the residual vibration waveform is within a preset period range in which the ejection state cannot be determined. Or when the amplitude of the residual vibration waveform is within a preset amplitude range in which the ejection state cannot be determined.

[0039] Note that in this embodiment, it is assumed that the period range and amplitude range for determining the ejection state of the nozzles in the first determination are registered in advance. However, the present invention is not limited to this. For example, the control unit 50 of the printing apparatus 100 may dynamically adjust the period range and amplitude range based on the determination result of the second determination described later.

[0040] In this embodiment, the printing apparatus 100 outputs (prints) a test chart only for the nozzles (second determination nozzles) for which the ejection state could not be determined. Therefore, the period range and amplitude range in which the ejection state cannot be determined are the output ranges of the test chart.

[0041] Next, with reference to FIGS. 7 and 8, the identification of the nozzles based on the residual vibration waveform will be described. FIG. 7 is a diagram for explaining the identification of the nozzles based on the period of the residual vibration waveform in the printing apparatus 100 according to this embodiment. The horizontal axis in FIG. 7 represents a number (referred to as the nozzle number) that can identify the position of each nozzle. The vertical axis in FIG. 7 represents the period of the residual vibration waveform, for example, in microseconds (μs). The dashed line in FIG. 7 indicates the period threshold (T th ). The range between the dashed lines in FIG. 7 indicates the period range in which the ejection state cannot be determined, that is, the output range of the test chart. In FIG. 7, the periods of the residual vibration waveforms corresponding to the nozzles with nozzle numbers 0 to 12 are shown as examples, and the illustration of the periods of the residual vibration waveforms corresponding to other nozzles is omitted.

[0042] When the period of the residual vibration waveform of the nozzle is within the period range shown in the figure, the head control unit 42 identifies the nozzle as an output target of the test chart. The nozzles that are output targets of the test chart are indicated by triangular marks in Fig. 7. When the period of the residual vibration waveform of the nozzle is greater than the period threshold (T th ) and exceeds the period range, the head control unit 42 identifies the nozzle as a normal nozzle. The normal nozzles are indicated by black circle marks in Fig. 7. When the period of the residual vibration waveform of the nozzle is smaller than the period threshold (T th ) and exceeds the period range, the head control unit 42 identifies the nozzle as an abnormal nozzle. The abnormal nozzles are indicated by square marks in Fig. 7.

[0043] Fig. 8 is a diagram for explaining the identification of nozzles based on the amplitude of the residual vibration waveform in the printing apparatus 100 according to the present embodiment. The horizontal axis in Fig. 8 represents numbers that can identify the positions of the respective nozzles, and the vertical axis in Fig. 8 represents the amplitude of the residual vibration waveform, for example, in units of volts (V). The dashed line in Fig. 8 indicates the amplitude threshold (A th ). The range between the dashed lines in Fig. 8 indicates an amplitude range in which the discharge state cannot be determined, that is, the output range of the test chart. Note that Fig. 8 shows, as an example, the amplitudes of the residual vibration waveforms corresponding to the nozzles numbered 0 to 12, similar to Fig. 7.

[0044] When the amplitude of the residual vibration waveform of the nozzle is within the amplitude range shown in the figure, the head control unit 42 identifies the nozzle as an output target of the test chart. The nozzles that are output targets of the test chart are indicated by triangular marks in Fig. 8. When the amplitude of the residual vibration waveform of the nozzle is greater than the amplitude threshold (A th ) and exceeds the amplitude range, the head control unit 42 identifies the nozzle as a normal nozzle. The normal nozzles are indicated by black circle marks in Fig. 8. When the amplitude of the residual vibration waveform of the nozzle is smaller than the amplitude threshold (A th ) and exceeds the period range, the head control unit 42 identifies the nozzle as an abnormal nozzle. The abnormal nozzles are indicated by square marks in Fig. 8.

[0045] In the present embodiment, a nozzle for which the ejection state cannot be determined, that is, a nozzle that is the output target of the test chart, is the target of the second determination in the control unit 50 and is referred to as a "second determination nozzle". The second determination is to determine the nozzles for which the ejection state could not be determined in the first determination, that is, the second determination nozzles. Further, the second determination is a determination process that uses a determination method using a test chart or a determination method for detecting ejected droplets of the nozzle for the second determination nozzles.

[0046] Next, the test chart output by the printing apparatus 100 will be described. FIG. 9 is a diagram showing an image of a test chart for nozzle identification printed by the printing apparatus 100 according to the present embodiment. Only a portion of the test chart corresponding to one inkjet head 30 is shown in FIG. 9. Illustrations and descriptions of portions corresponding to other inkjet heads 30 are omitted. FIG. 9A is a diagram showing an image of a test chart for nozzle identification output in the prior art. FIG. 9B is a diagram showing a test chart for nozzle identification output by the printing apparatus 100 of the present invention.

[0047] As shown in FIG. 9A, in the prior art, ink is ejected from all nozzles to output a test chart. The image portion surrounded by the dashed-dotted line in the figure is the image portion corresponding to the missing nozzle.

[0048] On the other hand, in the printing apparatus 100, the control unit 50 controls the image forming unit 20 to print only the test chart corresponding to the second determination nozzles. The control unit 50 performs the second determination based on the ejection result of the second determination nozzles. Here, the ejection result is, for example, a read image of the test chart read by the reading unit 12 (see FIG. 9B). In the test chart shown in FIG. 9B, images are not printed at positions corresponding to nozzles other than the second determination nozzles, that is, normal nozzles and abnormal nozzles. This is because the normal nozzles and the abnormal nozzles are controlled not to eject ink.

[0049] At a position corresponding to the second determination nozzle, there are those with an image printed (drawn with a solid line) and those without an image printed (enclosed by a dashed line and drawn with a broken line). In FIG. 9B, in order to indicate the position corresponding to the missing nozzle, the position is drawn with a broken line, but actually, there is no image at that position. The nozzles corresponding to the positions where the image is printed (the positions drawn with a solid line) are specified as normal nozzles in the second determination. Also, the nozzles corresponding to the positions where the image is not printed (the positions drawn with a broken line) are specified as abnormal nozzles in the second determination.

[0050] As can be seen by comparing FIG. 9A and FIG. 9B, in the printing apparatus 100, the ink consumption in specifying abnormal nozzles is much less than in the prior art. That is, according to the printing apparatus 100, the ink consumption in specifying abnormal nozzles can be reduced.

[0051] Note that the second determination in the control unit 50 is not limited to the determination method using a test chart. For example, there may be provided a detection unit that detects each ejected droplet of each nozzle of the inkjet head 30. In this case, the control unit 50 performs the second determination based on the detection result (ejection result) of the detection unit corresponding to the second determination nozzle. When the control unit 50 detects an ejected droplet by the detection unit, it determines that the nozzle corresponding to the detection unit is a normal nozzle. Also, when the control unit 50 does not detect an ejected droplet by the detection unit, it determines that the nozzle corresponding to the detection unit is a missing nozzle.

[0052] [Procedure of printing process] Next, the procedure of the printing process in the printing apparatus 100 will be described. The printing process in the printing apparatus 100 includes the above-described first determination and second determination. The first determination and the second determination are executed during the printing process for a plurality of recording media (papers) set in the printing job. Also, the first determination is executed during the time between pages of the recording media during the printing process. FIG. 10 is a flowchart showing the procedure of the printing process in the printing apparatus 100 according to the present embodiment. The processes described below start when the printing job is executed.

[0053] First, the control unit 50 of the printing apparatus 100 starts the printing set in the print job (S10).

[0054] Next, the head control unit 42 measures the residual vibration waveform of each nozzle during the time between pages of the paper (S11).

[0055] Next, the head control unit 42 makes a first determination regarding the ejection state of each nozzle based on the measured residual vibration waveform of each nozzle (S12). In this process, the head control unit 42 identifies the nozzles based on the period of the measured residual vibration waveform of each nozzle and based on the period of the residual vibration waveform described in FIG. 7. Further, the head control unit 42 identifies the nozzles based on the amplitude of the measured residual vibration waveform of each nozzle and based on the amplitude of the residual vibration waveform described in FIG. 8. Also, in this process, the head control unit 42 outputs the result of the first determination to the control unit 50.

[0056] Next, the control unit 50 determines whether there are nozzles (second determination nozzles) for which the ejection state cannot be determined in the result of the first determination (S13).

[0057] When the control unit 50 determines that there are no second determination nozzles in the result of the first determination (NO in S13), it performs the process of S17 described later.

[0058] On the other hand, when the control unit 50 determines that there are second determination nozzles in the result of the first determination (YES in S13), it controls the image forming unit 20 to print a test chart (S14). In this process, the control unit 50 outputs a test chart corresponding only to the second determination nozzles to the non-image area of the page to be printed next. When the test chart does not fit in the non-image area of one page of paper, the control unit 50 controls the image forming unit 20 to print the test chart in the non-image areas of a plurality of pages of paper. By outputting the test chart to the non-image area of the paper, paper can be saved and the printing time can also be shortened.

[0059] Next, the reading unit 12 reads the printed test chart and outputs a read image to the control unit 50 (S15).

[0060] Next, the control unit 50 performs a second determination based on the read image of the test chart (S16). In the second determination, as described with reference to FIG. 9, the control unit 50 determines the ejection state of each of the second determination nozzles. Note that, in S16, an example of performing the second determination using the read image of the test chart is shown. The present invention is not limited to this, and the second determination may be performed using the detection result by a detection unit that detects the ejected droplets of the nozzles.

[0061] In the case of NO in S13, or after the process of S16, the control unit 50 determines whether to perform image correction (S17). In this process, when the control unit 50 determines that there are no abnormal nozzles, it determines not to perform image correction, and S17 becomes a NO determination. On the other hand, when the control unit 50 determines that there are abnormal nozzles, it determines to perform image correction, and S17 becomes a YES determination.

[0062] When the control unit 50 determines to perform image correction (YES in S17), it performs image correction on the image corresponding to the position of the identified abnormal nozzle (S18). As an image correction method, for example, there is a method of increasing the size of the ejected droplets of the nozzles around the abnormal nozzle.

[0063] On the other hand, when the control unit 50 determines not to perform image correction (NO in S17), or after the process of S18, it determines whether printing is completed (S19). In this process, when the printing of all pages included in the print job is completed, the control unit 50 determines that the printing is completed, and S19 becomes a YES determination. When the printing of all pages included in the print job is not completed, the control unit 50 determines that the printing is not completed, and S19 becomes a NO determination.

[0064] When the control unit 50 determines that the printing is not completed (NO in S19), it returns to S11 and repeats the execution of S11 to S19.

[0065] On the other hand, when the control unit 50 determines that printing has been completed (YES in S19), the printing process ends.

[0066] [Effect] As described above, the printing apparatus 100 according to the present embodiment measures the residual vibration waveforms of the nozzles of each inkjet head during the inter-sheet time of the printing process. The printing apparatus 100 makes a first determination regarding the ejection state of each nozzle based on the periods and amplitudes of the measured residual vibration waveforms of the nozzles. Further, the printing apparatus 100 automatically makes a second determination only for the nozzles for which the ejection state cannot be determined (second determination nozzles). In the second determination, the printing apparatus 100 controls to eject ink only from the second determination nozzles. The printing apparatus 100 identifies abnormal nozzles based on the ejection results of the second determination nozzles. Therefore, according to the printing apparatus 100 according to the present embodiment, it is possible to reduce the ink consumption amount in identifying abnormal nozzles and reduce the printing time.

[0067] Note that the present invention is not limited to the above-described embodiments, and it goes without saying that various other application examples and modifications can be made without departing from the gist of the present invention described in the claims. For example, the above-described embodiments have described the configuration of the printing apparatus in detail and specifically in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace a part of the configuration of the embodiments described here with the configuration of other embodiments, and further, it is possible to add the configuration of other embodiments to the configuration of a certain embodiment. Also, it is possible to add, delete, or replace a part of the configuration of the embodiments with other configurations. Also, the control lines and information lines show those considered necessary for explanation, and do not necessarily show all the control lines and information lines on the product. In practice, it may be considered that almost all the components are interconnected.

Explanation of Reference Numerals

[0068] 1~n... Nozzles, 11... Paper feeding unit, 12... Reading unit, 13... Memory unit, 14... Operation display unit, 15... Communication interface, 20... Image forming unit, 21... Head unit, 30... Inkjet head, 31... Driving IC, 32, 41... Driving circuit, 33... MUX, 34... Switch, 40... Driving substrate, 42... Head control unit, 43... AMP, 44... ADC, 50... Control unit, 51, 411... CPU, 52... ROM, 53... RAM, 100... Printing device, 200... Residual vibration measurement circuit, 412... DAC, 413... Power supply circuit

Claims

1. An image forming unit having a plurality of inkjet heads that eject ink onto a recording medium, and that prints an image on the recording medium; A head control unit that acquires a residual vibration waveform generated after each of a plurality of nozzles included in the inkjet head is driven, and performs a first determination to determine a discharge state of the nozzle based on the residual vibration waveform; A control unit that ejects ink to a second determination nozzle, which is a nozzle for which the discharge state could not be determined in the first determination, and performs a second determination to determine the discharge state based on a discharge result; and A printing apparatus.

2. In the first determination, when the period of the residual vibration waveform is within a preset period range in which the discharge state cannot be determined, or when the amplitude of the residual vibration waveform is within a preset amplitude range in which the discharge state cannot be determined, the head control unit determines that the discharge state of the nozzle for which the residual vibration waveform was measured cannot be determined. The printing apparatus according to claim 1.

3. A reading unit that reads an image printed on the recording medium; The control unit controls the image forming unit to print a test chart corresponding to the second determination nozzle, and performs the second determination based on a read image of the test chart read by the reading unit, which is the discharge result. The printing apparatus according to claim 2.

4. A detection unit that detects discharge droplets of each of the plurality of nozzles; The control unit performs the second determination based on a detection result of the detection unit corresponding to the second determination nozzle, which is the discharge result. The printing apparatus according to claim 2.

5. The first determination and the second determination are executed during printing processing for a plurality of the recording media. The printing apparatus according to claim 2.

6. The first determination is executed during a time between pages of the recording medium during printing processing. The printing apparatus according to claim 5.

7. The control unit controls the image forming unit to print the test chart in a non-image area of the recording medium. The printing apparatus according to claim 3.

8. When the test chart does not fit in the non-image area of the recording medium of one page, the control unit controls the image forming unit to print the test chart in the non-image areas of a plurality of pages of the recording medium. The printing apparatus according to claim 7.

9. In the measurement operation of the residual vibration waveform of the nozzle, the head control unit drives the nozzle so as not to eject ink. The printing apparatus according to claim 2.

10. The ejection state includes a normal state in which the ejection operation of the nozzle is normal and an abnormal state in which the ejection operation of the nozzle is abnormal. The printing apparatus according to claim 2.

11. A printing method in a printing apparatus including an image forming unit having a plurality of inkjet heads that eject ink onto a recording medium to print an image, a step of obtaining a residual vibration waveform generated after each of a plurality of nozzles included in the inkjet head is driven, and performing a first determination for determining an ejection state of the nozzle based on the residual vibration waveform; a step of performing a second determination for ejecting ink onto a second determination nozzle that is a nozzle for which the ejection state cannot be determined in the first determination, and determining the ejection state based on an ejection result. Printing method.

12. A printing program in a printing apparatus including an image forming unit having a plurality of inkjet heads that eject ink onto a recording medium to print an image, a process of obtaining a residual vibration waveform generated after each of a plurality of nozzles included in the inkjet head is driven, and performing a first determination for determining an ejection state of the nozzle based on the residual vibration waveform; a process of causing a computer to perform a second determination for ejecting ink onto a second determination nozzle that is a nozzle for which the ejection state cannot be determined in the first determination, and determining the ejection state based on an ejection result. Printing program.

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