JP7501049B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device that ejects ink to form an image.

Conventionally, technology has been disclosed for determining whether or not to clean a nozzle when a nozzle discharge defect occurs in an image forming device such as an inkjet printer.

For example, Patent Document 1 discloses that when a nozzle discharge defect is detected, the number of points (image quality value) for the nozzle discharge defect is calculated using the results of the nozzle inspection and weighting information that weights and associates the discharge defect state with the image quality value of the print result, and when this number of points is within an acceptable range, an acceptable print process is executed without performing cleaning.

JP 2010-179577 A

If printing is performed without cleaning the defective nozzle, printing can begin more quickly because cleaning is not performed, but the image that the defective nozzle was supposed to print will not be printed. Generally, if there are localized areas where the image is not printed, users are quick to notice, but if there are areas where the image is not printed uniformly, such as in a newspaper, users tend not to notice the unprinted areas.

The above-mentioned patent document 1 does not take the above tendency into consideration, and depending on the image, unprinted areas may be printed in a way that is noticeable to the user, resulting in reduced print quality.

One aspect of the present invention aims to provide an image forming device that can start printing quickly without compromising print quality, even if there is a nozzle with an ejection abnormality.

In order to solve the above problem, an image forming device according to one aspect of the present invention includes a head having multiple nozzles that eject ink, a signal output unit that outputs a signal according to the ejection state of the multiple nozzles, and a control unit. After receiving a command to eject ink onto a medium, the control unit drives the head before ejecting ink onto the medium, and determines whether or not there is an abnormality in the ejection state for each of the multiple nozzles based on the signal from the signal output unit. Of the multiple nozzles, those determined to be abnormal in the ejection state are designated as specific nozzles, and those determined not to be abnormal in the ejection state are designated as normal nozzles, and the specific nozzles and some of the normal nozzles are set as non-ejection nozzles that do not eject ink, and the control unit controls the head to eject ink onto the medium based on the setting.

According to one aspect of the present invention, even if there is a nozzle with an ejection abnormality, printing can be started promptly without compromising print quality.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a schematic diagram showing connections in the vicinity of a cap unit included in the image forming apparatus shown in FIG. 1 . FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus shown in FIG. 1 . 4 is a flowchart illustrating a processing procedure of the image forming apparatus according to the embodiment of the present invention. 10 is a flowchart illustrating a process for detecting an ejection abnormality. 11 is a flowchart illustrating a process for printing with thinned nozzles. 11 is a flowchart illustrating a process for printing with thinned nozzles. FIG. 4 is a diagram showing an example of a mask pattern of a print mask. FIG. 11 is a diagram showing another example of a mask pattern of a print mask.

<Configuration of Image Forming Apparatus 1>
1 is a schematic diagram showing the configuration of an image forming apparatus 1 according to an embodiment of the present invention. As shown in Fig. 1, the image forming apparatus 1 includes a carriage 2, a sub-tank 3, an inkjet head 4, a platen 5, transport rollers (transport mechanism) 6 and 7, a maintenance unit 8 (including a purge mechanism), guide rails 9 and 10, a cartridge holder 11, and an ink cartridge 12.

Here, the direction from the carriage 2 toward the waste liquid storage section 63 described later is the X direction, the direction from the transport roller 6 toward the transport roller 7 is the Y direction, and the direction from the platen 5 toward the carriage 2 is the Z direction. The Z direction is the upward direction, and the direction opposite to the Z direction is the downward direction. The Y direction is the transport direction of the paper (medium) P.

The carriage 2 is supported by two guide rails 9 and 10 that extend in the scanning direction. The scanning direction is the X direction. The scanning direction is also perpendicular to the transport direction of the paper P and parallel to the nozzle surface 4B described later. The carriage 2 is connected to a carriage motor 31 (described later) via a belt (not shown) or the like. When the carriage motor 31 is driven by a control unit 23 (described later), the carriage 2 moves in the scanning direction along the guide rails 9 and 10. As a result, the inkjet head 4 moves between a maintenance position facing the cap unit 61 and a non-maintenance position not facing the cap unit 61. A so-called serial head method is used.

The subtank 3 is mounted on the carriage 2. Here, the image forming device 1 is provided with a cartridge holder 11, and four ink cartridges 12 are removably attached to the cartridge holder 11. The four ink cartridges 12 store black, yellow, cyan, and magenta ink, which are examples of liquid, respectively. The subtank 3 is connected to the four ink cartridges 12 via four tubes 13. In this way, four colors of ink are supplied from the four ink cartridges 12 to the subtank 3.

The inkjet head 4 is mounted on the carriage 2. The inkjet head 4 is an example of a head unit. Four colors of ink are supplied to the inkjet head 4 from the subtank 3. The inkjet head 4 has a plurality of nozzles 4A that eject ink. The nozzles 4A are formed on a nozzle surface 4B, which is the lower surface of the inkjet head 4. Note that the scope of application of the present invention is not limited to an image forming device 1 equipped with an inkjet head 4 having a plurality of nozzles 4A, but is also applicable to an image forming device equipped with an inkjet head having one nozzle. The inkjet head 4 may eject more than four colors of ink.

The platen 5 is disposed below the inkjet head 4 and faces the nozzles 4A and the nozzle surface 4B. The platen 5 extends over the entire length of the paper P in the scanning direction and supports the paper P from below. The transport roller 6 is disposed upstream of the inkjet head 4 and the platen 5 in the transport direction. The transport roller 7 is disposed downstream of the inkjet head 4 and the platen 5 in the transport direction. The transport rollers 6 and 7 are connected to a transport motor 32 (described later) via gears (not shown). When the transport motor 32 is driven by the control unit 23, the transport rollers 6 and 7 rotate and the paper P is transported in the transport direction.

<Configuration of Maintenance Unit 8>
The maintenance unit 8 performs maintenance to restore the ejection state of the nozzle 4A. The maintenance unit 8 has a cap portion 61, a suction portion 62, a waste liquid storage portion 63, a first electrode E1, and a second electrode E2. The cap portion 61 is disposed so as to be shifted in the scanning direction relative to the platen 5. When the carriage 2 is disposed at the maintenance position by moving in the scanning direction relative to the platen 5, the nozzle 4A and the nozzle surface 4B face the cap portion 61.

Figure 2 is a schematic diagram showing the connection relationship near the cap unit 61 provided in the image forming device 1 shown in Figure 1. As shown in Figure 2, the inkjet head 4 has at least two nozzles, a first nozzle 41N and a second nozzle 42N. In other words, the inkjet head 4 has at least one first nozzle 41N and at least one second nozzle 42N.

The first nozzle 41N ejects the color inks of yellow, cyan, and magenta. The second nozzle 42N ejects black ink. In other words, the nozzle 4A is divided into the first nozzle 41N and the second nozzle 42N. Note that the scope of application of the present invention is not limited to image forming devices 1 that eject color inks and black ink, but can also be applied to image forming devices that eject ink of one color.

The cap part 61 has a first cap part 61A and a second cap part 61B. The cap part 61 is disposed at a position facing the inkjet head 4, and serves to cover the nozzle 4A of the inkjet head 4, thereby sealing the nozzle 4A.

The first cap part 61A is for sealing the first nozzle 41N of the inkjet head 4 by covering the first nozzle 41N, and has a first lip 61D. The first lip 61D protrudes upward from the bottom part 61C of the cap part 61 and surrounds the first electrode E1.

The second cap part 61B is adjacent to and shares a portion of the first lip 61D of the first cap part 61A, and covers the second nozzle 42N of the inkjet head 4 to seal the second nozzle 42N, and has a second lip 61E. The first lip 61D and the second lip 61E share the boundary between the first cap part 61A and the second cap part 61B. The second lip 61E protrudes upward from the bottom part 61C of the cap part 61 and surrounds the second electrode E2.

The cap portion 61 is connected to the cap displacement portion 33, which will be described later. The cap displacement portion 33 has a motor (not shown), a gear (not shown) connected to the motor, and a cam (not shown) driven by the gear. The motor is driven by the control portion 23, which drives the gear and the cam. The cap displacement portion 33 displaces the cap portion 61 to move up and down by driving the gear and the cam.

When the carriage 2 is placed in the maintenance position and the nozzle 4A and the cap part 61 are opposed to each other, the cap part 61 is raised by the cap displacement part 33, and the first lip 61D and the second lip 61E of the cap part 61 come into close contact with the nozzle surface 4B. This causes the nozzle 4A to be covered by the cap part 61. In other words, the first nozzle 41N is covered by the first cap part 61A, and the second nozzle 42N is covered by the second cap part 61B.

The cap portion 61 is not limited to a cap that covers the nozzle 4A by adhering closely to the nozzle surface 4B. The cap portion 61 may also cover the nozzle 4A by adhering closely to a frame (not shown) or the like that is arranged around the nozzle surface 4B of the inkjet head 4.

The suction unit 62 has a suction pump 62P and a switching unit 62V. The suction pump 62P is a tube pump or the like, and is connected to a motor (not shown) by gears. The switching unit 62V, the suction pump 62P, and the waste liquid storage unit 63 are connected via a tube 64. The switching unit 62V is switchably connected to the first cap unit 61A and the second cap unit 61B via the tube 64. The switching unit 62V is a rubber valve, and is connected to a motor (not shown) by gears.

The switching unit 62V switches between the flow path from the first cap unit 61A to the suction pump 62P and the flow path from the second cap unit 61B to the suction pump 62P by driving a motor. The suction unit 62 selectively discharges ink from inside the first cap unit 61A and the second cap unit 61B by the switching unit 62V. In other words, the suction unit 62 discharges ink from inside the cap unit 61.

In the maintenance unit 8, when the suction pump 62P is driven by the control unit 23, the ink inside the first cap part 61A and the ink inside the second cap part 61B are discharged into the waste liquid storage part 63. The waste liquid storage part 63 stores the ink discharged from inside the cap part 61 by the suction part 62. In other words, the waste liquid storage part 63 stores the ink discharged from inside the first cap part 61A and the second cap part 61B by the suction part 62.

The first electrode E1 is disposed inside the first cap portion 61A, and ink ejected from the first nozzle 41N can land on the first electrode E1. The second electrode E2 is disposed inside the second cap portion 61B, and ink ejected from the second nozzle 42N can land on the second electrode E2. When the carriage 2 is disposed in the maintenance position, the first electrode E1 faces the first nozzle 41N, and the second electrode E2 faces the second nozzle 42N. The first electrode E1 and the second electrode E2 are disposed inside the cap portion 61 and are provided on the bottom portion 61C.

The image forming device 1 further includes a high-voltage circuit 21, a signal output unit 22, and a control unit 23, as shown in FIG. 2. The first electrode E1 and the second electrode E2 have a rectangular planar shape, are made of a conductive material, and are connected to the high-voltage circuit 21. A predetermined positive potential is applied to the first electrode E1 and the second electrode E2 by the high-voltage circuit 21. Meanwhile, the inkjet head 4 is connected to the ground GND. This generates a predetermined potential difference between the inkjet head 4 and the first electrode E1 and the second electrode E2. The high-voltage circuit 21 is connected to the ground GND.

The signal output unit 22 has a first detection unit 22A and a second detection unit 22B. The first detection unit 22A is electrically connected to the first electrode E1 and detects that ink has been ejected from the first nozzle 41N toward the first electrode E1. The second detection unit 22B is electrically connected to the second electrode E2 and detects that ink has been ejected from the second nozzle 42N toward the second electrode E2. The detection of ink by the signal output unit 22 when ink lands on the first electrode E1 will be described in detail below. When ink lands on the second electrode E2, the same process is performed as when ink lands on the first electrode E1, and therefore a description thereof will be omitted.

The inkjet head 4 is connected to ground GND, and the potential of the inkjet head 4 is maintained as close to 0V as possible. A potential of 600V is applied to the first electrode E1 by the high-voltage circuit 21. This creates a potential difference of 600V between the inkjet head 4 and the first electrode E1.

When the inkjet head 4 ejects ink from the first nozzle 41N toward the first electrode E1 while the carriage 2 is in the maintenance position, the negatively charged ink approaches the first electrode E1. When the ink lands on the first electrode E1, a negative charge is transferred to the first electrode E1, and the voltage value of the first electrode E1 drops. To explain it more simply, a phenomenon similar to current flowing from the first electrode E1 to the inkjet head 4 via the ejected ink occurs.

Using this principle, the signal output unit 22 determines whether or not ink has been ejected from the nozzle 4A onto the electrode. Furthermore, in the ink detection described above, it is possible to grasp not only whether or not ink has been ejected, but also various states of the nozzle 4A. For example, it is possible to confirm whether or not the ink ejected from the inkjet head 4 is of a normal size depending on the magnitude of the voltage waveform detected by the signal output unit 22 and the length of time from when the ejection signal is output by the control unit 23 until the ink lands. The ejection signal is a signal that commands the inkjet head 4 to eject ink.

Furthermore, the detection results from the signal output unit 22 can be used to check the blockage status of the nozzle 4A, the increase in ink viscosity, the presence or absence of splashes, the bending of the ink, the presence of air bubbles in the ink, etc.

On the other hand, when ink is not ejected from the first nozzle 41N, the voltage value of the first electrode E1 hardly changes. Note that here, a positive potential is applied to the first electrode E1 and the second electrode E2 by the high voltage circuit 21, but a negative potential may also be applied to the first electrode E1 and the second electrode E2 by the high voltage circuit 21.

In addition, although the cap portion 61 has been described here as having a first cap portion 61A and a second cap portion 61B, this is not limited to this. The cap portion 61 may cover all of the nozzles 4A together, and the suction portion 62 may discharge ink from inside the cap portion 61. In this case, the suction portion 62 does not have a switching portion 62V, and only has a suction pump 62P. Furthermore, at least one electrode is disposed inside the cap portion 61, and the signal output portion 22 is connected to the at least one electrode.

Furthermore, even when two or more electrodes are arranged inside the cap unit 61, the image forming device 1 may include either the first detection unit 22A or the second detection unit 22B as the signal output unit 22. In this case, the signal output unit 22 may be configured to calculate the average value of the voltage values of the two or more electrodes and output the average value to the control unit 23. The signal output unit 22 may also be configured to be controlled by the control unit 23 so that the signal output unit 22 detects the ejection of ink by shifting the timing at which it detects each of the voltage values of the two or more electrodes.

The cap displacement unit 33 is configured to displace the cap unit 61 up and down by driving a motor, but may also be configured to displace the carriage 2 or the inkjet head 4 up and down. In this way, the cap displacement unit 33 becomes a mechanism that displaces the cap unit 61 relatively by the movement of the carriage 2 or the inkjet head 4.

<Electrical Configuration of Image Forming Apparatus 1>
Fig. 3 is a block diagram showing the electrical configuration of the image forming apparatus 1 shown in Fig. 1. As shown in Fig. 3, the image forming apparatus 1 includes an inkjet head 4, a carriage motor 31, a transport motor 32, and a cap displacement unit 33. The operation of the image forming apparatus 1 is controlled by a control unit 23.

The control unit 23 has an ASIC (Application Specific Integrated Circuit) 41, a CPU (Central Processing Unit) 42, a ROM (Read Only Memory) 43, a RAM (Random Access Memory) 44, and a flash memory 45. The ASIC 41 and the CPU 42 are examples of a control unit, and the ROM 43, the RAM 44, and the flash memory 45 are examples of a storage unit.

The ASIC 41 generates and outputs control signals for controlling access to the ROM 43, RAM 44, and flash memory 45 based on the address signal, bus control signal, etc. output from the CPU 42. This enables the CPU 42 to fetch instruction codes and read data from the ROM 43, RAM 44, and flash memory 45, and to write data to the RAM 44 and flash memory 45.

In addition, the ASIC 41 generates control signals for controlling the inkjet head 4, carriage motor 31, transport motor 32, cap displacement unit 33, suction pump 62P, switching unit 62V, high voltage circuit 21 and signal output unit 22 based on the address signal, bus control signal, etc. output from the CPU 42, and outputs the control signals to each unit.

The ROM 43 stores a boot program, a control program for controlling the image forming device 1, and the like. The RAM 44 stores working data and the like. The control program stored in the ROM 43 may be transferred to the RAM 44, and the CPU 42 may execute the control program stored in the RAM 44. The flash memory 45 can retain data even if the power supply to the image forming device 1 is cut off, so that data that is referenced by the control program every time and data that will be required for subsequent processing can be stored.

By executing a control program stored in ROM 43 or RAM 44, the CPU 42 controls the carriage motor 31, transport motor 32, cap displacement unit 33, suction pump 62P, switching unit 62V, high voltage circuit 21, and signal output unit 22 within the image forming device 1, thereby realizing the functions of the control unit 23 of the image forming device 1. The control unit 23 also drives the cap displacement unit 33 and suction unit 62 to execute a discharge process that discharges ink remaining inside the cap unit 61.

The control unit 23 may be one in which only the CPU 42 performs various processes, one in which only the ASIC 41 performs various processes, or one in which the CPU 42 and the ASIC 41 work together to perform various processes. The control unit 23 may be one in which a single CPU 42 performs processes independently, or one in which multiple CPUs 42 share the processing. The control unit 23 may be one in which a single ASIC 41 performs processes independently, or one in which multiple ASICs 41 share the processing.

The image forming device 1 may further include a display unit (not shown), such as a display, and an operation unit (not shown) including switches and a touch panel. The control unit 23 also controls the display unit, and the operation unit transmits a signal to the control unit 23 in response to an operation by a user.

The carriage motor 31 moves the carriage 2 in the scanning direction along the guide rails 9, 10. The transport motor 32 transports the paper P in the transport direction by rotating the transport rollers 6, 7. The cap displacement unit 33 displaces the first cap portion 61A and the second cap portion 61B so that the first lip 61D and the second lip 61E contact and separate from the inkjet head 4. In other words, the cap displacement unit 33 displaces the cap portion 61 so that the lips of the cap portion 61 contact and separate from the inkjet head 4.

<Processing of Image Forming Apparatus 1>
4 is a flow chart for explaining the processing procedure of the image forming apparatus 1 according to the embodiment of the present invention. First, the control unit 23 controls the signal output unit 22 to detect the ink ejection of the nozzle rows corresponding to black (K), yellow (Y), cyan (C) and magenta (M) of the nozzle 4A. The control unit 23 receives the signal output from the signal output unit 22 and stores the ejection state of each nozzle in the nozzle rows corresponding to the four colors (S1). Details of this process will be described later.

Next, the control unit 23 determines whether the printed portion is monochrome printing using the black nozzle row, or color printing using the black, yellow, cyan, and magenta nozzle rows (S2). If it is monochrome printing (S2, monochrome printing), the control unit 23 obtains the detection result for the black nozzle row detected by the signal output unit 22, and determines whether the number of nozzles with ejection abnormalities is greater than a predetermined value (threshold value) (S3). Note that a nozzle determined to have an ejection abnormality is also called an abnormal nozzle (specific nozzle), and a nozzle not determined to have an ejection abnormality is also called a normal nozzle.

If the number of abnormal ejection nozzles in the black nozzle row is greater than a predetermined value (S3, Yes), the control unit 23 determines that maintenance is necessary, performs maintenance control such as flushing and purging using the maintenance unit 8 (S4), and performs printing without thinning out the nozzles (S5). On the other hand, if the number of abnormal ejection nozzles in the black nozzle row is equal to or less than a predetermined value (S3, No), maintenance control such as flushing and purging using the maintenance unit 8 is not performed, and printing is performed with the nozzles in the black nozzle row thinned out (S6). Details of this nozzle thinning printing will be described later.

In the case of color printing (S2, color printing), the control unit 23 acquires the detection results for each of the nozzle rows of black, yellow, cyan, and magenta detected by the signal output unit 22, and creates and stores the nozzle numbers of the nozzles with ejection abnormalities during color printing based on the nozzle numbers of the nozzle rows with ejection abnormalities (S7). In the following description, each nozzle row will be described as having 100 nozzles.

For example, suppose that the 10th and 20th nozzles in the black nozzle row are judged to have an ejection abnormality, and the 10th and 30th nozzles in the yellow nozzle row are judged to have an ejection abnormality. Furthermore, suppose that the 40th nozzle in the cyan nozzle row is judged to have an ejection abnormality, and the 20th and 50th nozzles in the magenta nozzle row are judged to have an ejection abnormality. In this case, any nozzle number that is judged to have an ejection abnormality is determined to have an ejection abnormality, and the nozzle numbers with ejection abnormalities during color printing are set to 10, 20, 30, 40, and 50.

Next, the control unit 23 calculates the number of nozzles with ejection abnormalities from the nozzle numbers of the nozzles with ejection abnormalities, and sets this as the number of nozzles with ejection abnormalities during color printing (S8). The control unit 23 then determines whether the number of nozzles with ejection abnormalities during color printing is greater than a predetermined value (threshold value) (S9).

If the number of nozzles with ejection abnormalities during color printing is greater than a predetermined value (S9, Yes), the control unit 23 determines that maintenance is necessary, performs maintenance control such as flushing and purging using the maintenance unit 8 (S10), and performs printing without thinning out the nozzles (S11). Also, if the number of nozzles with ejection abnormalities during color printing is equal to or less than a predetermined value (S9, No), maintenance control such as flushing and purging using the maintenance unit 8 is not performed, and printing is performed with nozzles thinned out in the nozzle rows during color printing (S12). Note that during color printing, the same thinning method is applied to the nozzle rows of the four colors. Details of this nozzle thinning printing will be described later.

Figure 5 is a flow chart for explaining the process of detecting an ejection abnormality (S1). First, the control unit 23 controls the signal output unit 22 to detect whether there is an ejection abnormality among black (K) nozzles 1 to 100 (S21). Then, the control unit 23 stores the nozzle number of the black nozzle that has an ejection abnormality (S22).

In the same manner, the control unit 23 controls the signal output unit 22 to detect whether there is an ejection abnormality among the yellow (Y) nozzles 1 to 100 (S23). The control unit 23 then stores the nozzle number of the yellow nozzle that has an ejection abnormality (S24).

In the same manner, the control unit 23 controls the signal output unit 22 to detect whether there is an ejection abnormality among the cyan (C) nozzles 1 to 100 (S25). Then, the control unit 23 stores the nozzle number of the cyan nozzle that has an ejection abnormality (S26).

In the same manner, the control unit 23 controls the signal output unit 22 to detect whether there is an ejection abnormality among magenta (M) nozzles 1 to 100 (S27). Then, the control unit 23 stores the nozzle number of the magenta nozzle that has an ejection abnormality (S28).

Figures 6 and 7 are flow charts for explaining the process of printing with thinned nozzles (S6, S12). First, the control unit 23 determines whether the printed portion is text printing or solid printing (S31). For example, if the print duty ratio of the printed portion is lower than a predetermined value, it is determined to be text printing, and if the print duty ratio is higher than a predetermined value, it is determined to be solid printing.

Here, the print duty is calculated as Sb/Sa x 100 (%), where Sa is the area of the entire paper being printed on and Sb is the cumulative area of the printed portion. In addition, it may be possible to determine whether the printed portion is text printing or solid printing from the printer description language (commands) of the print data.

If the printing portion is solid printing (S31, solid printing), processing proceeds to step S34 in FIG. 7. Also, if the printing portion is text printing (S31, text printing), the control unit 23 selects a printing mask for nozzle thinning printing, which prints masks at equal intervals in the transport direction, from among various mask patterns (S32). Here, a mask pattern with a narrow printing mask distance in the nozzle direction is selected as the printing mask for text printing. This makes it possible to mask normal nozzles so that the period between ejection-enabled nozzles and non-ejection nozzles becomes smaller.

Next, the control unit 23 masks the print data with the selected print mask (thinning out nozzles) and performs the printing process (S33). As shown on the right side of Figure 6, when the nozzles with abnormal ejection are the fourth and fifth nozzles, print mask 1 is used to determine the nozzles after masking (non-ejecting nozzles). In print mask 1, ◯ indicates that the nozzle will not be masked, and × indicates that the nozzle will be masked. Therefore, the nozzles after masking (non-ejecting nozzles) are the even-numbered nozzles and the fifth nozzle. Here, printable nozzles marked with ◯ after masking are called ejectable nozzles. In other words, print mask 1 can be said to be a pattern that masks normal nozzles so that the cycle between ejectable nozzles and non-ejecting nozzles is minimized.

If the printing portion is solid printing (S31, solid printing), the control unit 23 selects the printing mask with the narrower printing mask distance in the nozzle direction from among multiple printing masks for nozzle thinning printing that print masks at equal intervals in the transport direction, and calculates the maximum value (MAX value) and minimum value (MIN value) of the number of prints / (number of prints + number of non-prints) (S34).

As shown on the right side of Figure 7, when the nozzles with abnormal ejection are the fourth and fifth nozzles, print mask 1 is used to determine the masked nozzles (non-ejecting nozzles). Then, the control unit 23 calculates the value of print count / (print count + non-print count) (hereinafter referred to as the print rate) in order from the top. First, since the first nozzle is an ejection capable nozzle and the second nozzle is a non-ejection nozzle, the print rate is 0.5. Furthermore, since the third nozzle is an ejection capable nozzle and the fourth to sixth nozzles are non-ejection nozzles, the print rate is 0.25. By repeating the same process, the maximum print rate becomes 0.5 and the minimum becomes 0.25. Therefore, the difference between the maximum and minimum values is 0.25.

Next, the control unit 23 selects the print mask with the wider print mask distance in the nozzle direction from among the multiple print masks for nozzle thinning printing that are printed at equal intervals in the transport direction, and calculates the maximum and minimum print rates (S35).

As shown on the right side of Figure 7, when the nozzles with abnormal ejection are the fourth and fifth nozzles, print mask 2 is used to determine the masked nozzles (non-ejecting nozzles). The control unit 23 then calculates the print rate in order from the top. First, nozzles 1 to 3 are ejection capable nozzles and nozzles 4 to 5 are non-ejecting nozzles, so the print rate is 0.6. Furthermore, nozzles 6 to 7 are ejection capable nozzles and nozzle 8 is a non-ejecting nozzle, so the print rate is 0.66. By repeating the same process, the maximum print rate becomes 0.75 and the minimum becomes 0.6. Therefore, the difference between the maximum and minimum values is 0.15.

As such, the difference between the maximum and minimum printing rates is smaller when print mask 2 is used compared to when print mask 1 is used, so the control unit 23 determines that the quality of solid printing is not degraded when print mask 2 is used, and adopts the ejection-enabled nozzles and non-ejection nozzles masked with print mask 2.

Finally, the control unit 23 masks the print data using the print mask with the smaller difference between the maximum and minimum print rate values (using ejection-enabled nozzles and non-ejection nozzles) and performs printing (S36).

<Example of print mask pattern>
Fig. 8 is a diagram showing an example of a mask pattern of a print mask. MP1-1 is the same as the mask pattern of print mask 1 shown in Figs. 6 and 7. Moreover, MP1-2 has an arrangement opposite to that of MP1-1. These MP1-1 and MP1-2 are mask patterns with the narrowest print mask distance. When using a mask pattern with the narrowest print mask distance (masking normal nozzles so that the period between ejection enabled nozzles and non-ejection nozzles is the smallest), the control unit 23 will appropriately select and use one of these two mask patterns.

MP2-1 to MP2-3 are mask patterns with the second narrowest print mask distance, and each has a different print mask position. MP3-1 to MP3-4 are mask patterns with the next narrowest print mask distance (masking normal nozzles so that the period between ejection-enabled nozzles and non-ejection nozzles is the next smallest), and each has a different print mask position.

Figure 9 is a diagram showing another example of a mask pattern of a print mask. MP4-1 to MP4-4 are mask patterns in which two print masks and two non-print masks are lined up, and the positions of the print masks and non-print masks differ in each mask pattern. MP5-1 to MP5-5 are mask patterns in which two print masks and three non-print masks are lined up, and the positions of the print masks and non-print masks differ in each mask pattern. These multiple mask patterns are stored in ROM 43, flash memory 45, etc.

In this way, the control unit 23 performs the process shown in FIG. 7 using various print masks shown in FIG. 8 and FIG. 9 to select a print mask with a small difference between the maximum and minimum print rates, and prints so as not to degrade the quality of solid printing. Note that the mask pattern of the print mask is not limited to those shown in FIG. 8 and FIG. 9, and other print masks may be used.

In addition, when printing on the print area, the control unit 23 may eject a first amount of droplets if the ejection nozzle is not adjacent to a non-ejection nozzle, and eject a second amount of droplets greater than the first amount of droplets if the ejection nozzle is adjacent to a non-ejection nozzle.

As described above, according to the image forming device 1 of this embodiment, regardless of the ejection state, after determining whether or not there is an abnormality in the ejection state, ink can be ejected onto the medium without performing any additional processing. At this time, by including some of the normal nozzles as non-ejecting nozzles, areas where ink is not ejected can be dispersed on the medium. This makes the areas where ink is not ejected less noticeable than when the areas where ink is not ejected are locally present on the medium. Therefore, printing can be started promptly without degrading the quality of the image.

In addition, printing starts before maintenance (flushing, purging) processes, so printing can begin promptly.

In addition, the non-ejecting nozzles are set so that their arrangement is uniform, which reduces the number of areas where ink is not ejected locally and allows the areas where ink is not ejected to exist uniformly. This allows the user to perceive solid printing as light solid printing, for example.

In addition, non-ejecting nozzles are set when the print duty is equal to or greater than a threshold, making it possible to avoid printing images in which the areas where ink is not ejected are easily noticeable to the user.

In addition, depending on the print duty of the area to be printed, it is determined whether to print solid or text, and the mask pattern is then determined, so that the arrangement of non-ejecting nozzles can be optimized.

In addition, in the case of color printing, the arrangement of non-ejecting nozzles in multiple ink ejection nozzle rows corresponding to the three primary colors (yellow, cyan, magenta) is made the same, which makes it possible to suppress color unevenness and prevent a decrease in color printing quality.

In addition, the amount of droplets ejected from an ejection-enabled nozzle adjacent to a non-ejection nozzle is increased compared to when the nozzle is not adjacent to a non-ejection nozzle, making it possible to reduce the area where droplets are missing and preventing a decrease in print quality.

Furthermore, because the head is a serial head type, the head structure can be simplified.

The above describes an example of the application of the present invention to a printer that ejects ink from nozzle 4A to record on recording paper P, but the present invention is not limited to this. It can also be applied to printers that record images on recording media other than recording paper, such as T-shirts, sheets for outdoor advertising, cases for mobile devices such as smartphones, cardboard, and plastic components. It can also be applied to liquid ejection devices that eject liquids other than ink, such as liquid resins and metals.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Configurations obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present invention.

Reference Signs List 1 Image forming apparatus 4 Inkjet head 4A Multiple nozzles 8 Maintenance unit 22 Signal output unit 23 Control unit

Claims (8)

a head having a plurality of nozzles for ejecting ink;
a signal output unit that outputs a signal in response to the ejection state of the plurality of nozzles;
A storage unit;
A control unit.
The control unit is
after receiving a command to eject ink onto a medium, and before ejecting ink onto the medium, driving the head, and determining whether or not there is an abnormality in the ejection state for each of the plurality of nozzles based on the signal from the signal output unit;
Among the plurality of nozzles, those determined to be abnormal in terms of the ejection state are designated as specific nozzles, and those determined not to be abnormal in terms of the ejection state are designated as normal nozzles, and the specific nozzles and some of the normal nozzles are set as non-ejection nozzles that do not eject ink,
Controlling the head so as to eject ink onto the medium based on the setting ;
the storage unit stores a plurality of patterns of masks for masking some of the normal nozzles to set them as non-ejection nozzles;
The control unit is
Calculate the print duty of the area where ink is ejected;
An image forming apparatus characterized in that, when setting the non-ejecting nozzles, if the ratio of the printing duty is equal to or greater than a threshold value, a mask that reduces the period between the non-ejecting nozzles and the ejection-enabled nozzles that eject ink is applied from among a plurality of mask patterns stored in the memory unit . a head having a plurality of nozzles for ejecting ink;
a signal output unit that outputs a signal in response to the ejection state of the plurality of nozzles;
A control unit.
The control unit is
after receiving a command to eject ink onto a medium, and before ejecting ink onto the medium, driving the head, and determining whether or not there is an abnormality in the ejection state for each of the plurality of nozzles based on the signal from the signal output unit;
Among the plurality of nozzles, those determined to be abnormal in terms of the ejection state are designated as specific nozzles, and those determined not to be abnormal in terms of the ejection state are designated as normal nozzles, and the specific nozzles and some of the normal nozzles are set as non-ejection nozzles that do not eject ink,
An image forming device characterized in that, based on the setting , the head is controlled so that when a nozzle that is not set as a non-ejecting nozzle is not adjacent to the non-ejecting nozzle, the amount of droplets ejected from the nozzle is set to a first droplet amount, and when the nozzle is adjacent to the non-ejecting nozzle, the amount of droplets ejected from the nozzle is set to a second droplet amount that is greater than the first droplet amount, while ejecting ink onto the medium. The control unit is
Controlling the head to perform a flushing process to discharge liquid from the plurality of nozzles;
3. The image forming apparatus according to claim 1, further comprising: a control unit that controls the head so as to start ejecting ink onto a medium after the determination is made, regardless of the result of the determination, without causing the flushing process to be performed. A purge mechanism for performing a purge process to discharge liquid from the plurality of nozzles is further provided,
The control unit is
4. The image forming apparatus according to claim 1, further comprising: a control unit that controls the head so as to start ejecting ink onto a medium after the determination is made, regardless of the result of the determination, without causing the purge mechanism to perform the purge process. The plurality of nozzles are arranged in a line in a predetermined direction,
5. The image forming apparatus according to claim 1, wherein the control unit sets the non-ejection nozzles so that an arrangement of the non-ejection nozzles is uniform in the predetermined direction. The control unit is
When the print duty is equal to or greater than the threshold value, a first pattern mask in which the interval between the non-ejection nozzles and the ejection enabled nozzles is a predetermined interval and a second pattern mask in which the interval between the non-ejection nozzles and the ejection enabled nozzles is smaller than the predetermined interval are applied to set the non-ejection nozzles,
2. The image forming apparatus according to claim 1 , wherein when the print duty is smaller than the threshold value, the non-ejecting nozzles are set by applying only the mask of the second pattern. the head has a plurality of nozzle rows each configured with the plurality of nozzles aligned in a predetermined direction,
the plurality of nozzle rows eject yellow, cyan, and magenta inks, respectively;
The image forming apparatus according to claim 1 , wherein the control unit sets the non-ejecting nozzles in each of the plurality of ink ejection nozzle rows such that the positions of the non-ejecting nozzles in the predetermined direction are the same. a transport mechanism that transports the medium in a transport direction;
8. The image forming apparatus according to claim 1, further comprising: a carriage on which the head is mounted and which is movable in a scanning direction perpendicular to the transport direction.

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