Impact Anomaly Detection Device

Abstract

To provide an impact abnormality detection device which prevents erroneous detection of an impact position abnormality due to an installation positional deviation of ink jet heads.SOLUTION: An impact abnormality detection device comprises: a test image data acquisition unit 61 which acquires test image data by reading a test pattern obtained by discharging ink from a line head in which a plurality of ink jet heads having a plurality of nozzles for discharging ink arrayed are arranged in the longitudinal direction of the ink jet head; a distance measurement unit 62 which measures a distance between two nozzles straddling a joint of the adjacent ink jet heads in the line head on the basis of the test image data; and an abnormality detection unit 63 which detects an impact position abnormality on the basis of the measured distance between the two nozzles and a theoretical value of the distance between the two nozzles considering the installation positional deviation between the adjacent ink jet heads.SELECTED DRAWING: Figure 3

Description

Technical Field

[0007]

[0001] The present invention relates to a landing abnormality detection device that detects an abnormality in the landing position of droplets ejected from a discharge head.

Background Art

[0002] Conventionally, an inkjet printing device has been proposed that performs a printing process by ejecting ink from an inkjet head onto a printing medium conveyed on a conveyance path.

[0003] In an inkjet printing device, due to a defect in the inkjet head or the like, the landing position of the ink ejected from the inkjet head onto the printing medium may deviate from the designed ideal landing position. When such an abnormality in the landing position of the ink occurs, the quality of the printed image deteriorates.

[0004] As a method for detecting an abnormality in the landing position of the ink as described above, for example, Patent Document 1 proposes a method of actually printing a test pattern and detecting an abnormality in the landing position based on the test pattern and the ideal landing position.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, as an inkjet printing device as described above, an inkjet printing device has been proposed that has a line head in which a plurality of inkjet heads are arranged in a direction orthogonal to the conveyance direction of the printing medium, and performs a printing process by ejecting ink from the line head onto the printing medium, thereby enabling high-speed printing processing.

[0007] Even in such inkjet printing apparatuses, a method for detecting abnormalities in the impact position by printing a test pattern can be considered, as described in Patent Document 1. Specifically, for example, as shown in Figure 11A, a straight line extending in the transport direction is printed by each nozzle of the inkjet head, and an abnormality in the impact position can be detected based on the amount of deviation between the position of the printed straight line and the position of the ideal straight line shown in Figure 11B.

[0008] However, in the case of an inkjet head printing device equipped with a line head composed of multiple inkjet heads as described above, the straight lines of the test pattern may be misaligned due to misalignment of the inkjet heads.

[0009] In such cases, simply detecting an anomaly in the impact position based on the amount of deviation shown in Figure 11B would not account for the aforementioned misalignment of the inkjet head's installation position for the ideal straight line position, which could lead to false detections.

[0010] In view of the above circumstances, the present invention aims to provide a projectile impact abnormality detection device that can prevent false detection of projectile impact position abnormalities caused by misalignment of the installation position of the inkjet head. [Means for solving the problem]

[0011] The projectile impact anomaly detection device of the present invention includes a test image data acquisition unit that reads a test pattern obtained by discharging liquid from a line head arranged in the longitudinal direction of a discharge head, which has a plurality of nozzles arranged in the discharge head for discharging liquid, and acquires test image data; a distance measurement unit that measures the distance between two nozzles that straddle the joint of adjacent discharge heads within the line head based on the test image data; and an anomaly detection unit that detects an anomaly in the projectile impact position based on the measured distance between the two nozzles and a theoretical value of the distance between the two nozzles that takes into account the misalignment of the installation position of adjacent discharge heads. [Effects of the Invention]

[0012] According to the impact abnormality detection device of the present invention, the distance between two nozzles that straddle the joint of adjacent discharge heads within the line head is measured, and impact position abnormalities are detected based on the measured distance between the two nozzles and a theoretical value of the distance between the two nozzles that takes into account the misalignment of the adjacent discharge heads. This prevents false detection of impact position abnormalities caused by misalignment of the inkjet heads. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows a schematic configuration of an inkjet printing apparatus using one embodiment of the bullet impact abnormality detection device of the present invention. [Figure 2] Top view of the head unit [Figure 3] Figure 1 shows a block diagram illustrating the schematic configuration of the control system of the inkjet printing apparatus. [Figure 4] A diagram showing an example of a test pattern. [Figure 5] Flowchart illustrating the bullet impact anomaly detection process in the first embodiment [Figure 6] A diagram illustrating the regions where the distance between nozzles spans the joint and regions where it does not. [Figure 7] Flowchart illustrating the impact anomaly detection process of the second embodiment [Figure 8] Flowchart illustrating the bullet impact anomaly detection process in the third embodiment [Figure 9] Flowchart illustrating the bullet impact anomaly detection process in the third embodiment [Figure 10] A diagram illustrating the movement of the starting point in the projectile impact anomaly detection process of the third embodiment. [Figure 11] Diagram illustrating conventional projectile impact anomaly detection processing. [Modes for carrying out the invention]

[0014] Hereinafter, an inkjet printing apparatus using an embodiment of the landing abnormality detection device of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by a method for detecting an abnormality in the landing position of ink droplets ejected from an inkjet head. First, the overall configuration will be described. FIG. 1 is a diagram showing a schematic configuration of the inkjet printing apparatus 1 of this embodiment. Note that the up-down, left-right directions shown in FIG. 1 are the up-down, left-right directions of the inkjet printing apparatus 1 of this embodiment. Also, the front side of the paper surface in FIG. 1 is the front direction, the back side of the paper surface is the back direction, and the front-back direction is the main scanning direction described later.

[0015] As shown in FIG. 1, the inkjet printing apparatus 1 of this embodiment includes a side paper feeding unit 10, an internal paper feeding unit 20, a printing processing unit 30, a paper discharging unit 40, a reversing unit 50, a control unit 60, an operation panel 70, and a scanner unit 80.

[0016] The printing processing unit 30, the internal paper feeding unit 20, and the control unit 60 are housed and installed in a housing formed of metal, resin, or the like. Also, the side paper feeding unit 10, the paper discharging unit 40, and the reversing unit 50 are installed in a state where a part is housed in the housing and a part projects outside the housing. Further, the scanner unit 80 is installed on the upper surface of the housing.

[0017] The side paper feeding unit 10 includes a paper feeding table 11 on which a printing medium P is placed, a primary paper feeding unit 12 that feeds out only the uppermost printing medium P from the paper feeding table 11 and conveys it onto the paper feeding conveyance path FR, and a secondary paper feeding unit 14 that conveys the printing medium P conveyed by the primary paper feeding unit 12 onto the circulation conveyance path CR.

[0018] The internal paper feeding unit 20 includes a paper feed tray 21a on which the printing medium P is placed, a primary paper feeding unit 22a that feeds only the uppermost printing medium P from the paper feed tray 21a and transports it onto the paper feed transport path FR, a paper feed tray 21b on which the printing medium P is placed, a primary paper feeding unit 22b that feeds only the uppermost printing medium P from the paper feed tray 21b and transports it onto the paper feed transport path FR, a paper feed tray 21c on which the printing medium P is placed, a primary paper feeding unit 22c that feeds only the uppermost printing medium P from the paper feed tray 21c and transports it onto the paper feed transport path FR, a paper feed tray 21d on which the printing medium P is placed, and a primary paper feeding unit 22d that feeds only the uppermost printing medium P from the paper feed tray 21d and transports it onto the paper feed transport path FR.

[0019] In this manner, the secondary paper feed unit 14 receives printing media P from the side paper feed unit 10 or the internal paper feed unit 20, as well as from the reversing unit 50, which will be described later.

[0020] Therefore, in the transport direction, there is a merging point just before the secondary paper feed section 14 where the transport path of the printing medium P fed from the internal paper feed section 20 and the transport path of the printing medium P with one side printed, transported from the reversal section 50, merge. Based on this merging point, the path on the paper feed mechanism side is called the paper feed transport path FR, and the other paths are called the circulating transport path CR.

[0021] The printing processing unit 30 includes a head unit 31 and an annular transport belt 133 provided opposite the head unit 31.

[0022] The conveyor belt 133 is formed from an annular endless belt and has numerous suction holes. The printing medium P fed from the secondary paper feed unit 14 is conveyed to the annular conveyor belt 133. The printing medium P is then attracted onto the conveyor belt 133 by suction from suction fans 131 and 132 installed on the underside of the conveying surface of the conveyor belt 133 and is conveyed at a predetermined conveying speed. As the printing medium P is conveyed by the conveyor belt 133, ink is ejected from the head unit 31 onto the printing medium P, thereby performing the printing process on the printing medium P.

[0023] The head unit 31 comprises four line heads 32a, 32b, 32c, and 32d, and a head holder 33 on which the four line heads 32a, 32b, 32c, and 32d are installed. Each line head 32a to 32d extends in a direction perpendicular to the transport direction (movement direction) of the printing medium P and ejects ink onto the printing medium P transported by the transport belt 133. As shown in Figure 1, the four line heads 32a to 32d are arranged at predetermined intervals along the transport path of the printing medium P. Each of the four line heads 32a to 32d ejects ink of a different color (for example, black, cyan, magenta, and yellow).

[0024] The head holder 33 is a component on which the inkjet heads 34 that make up each line head 32a to 32d are installed. Figure 2 is a top view from above showing the state in which the inkjet heads 34 that make up each line head 32a to 32d are installed in the head holder 33.

[0025] The head holder 33 is composed of a box-shaped support member, and the bottom surface of the head holder 33 has a plurality of mounting holes into which each inkjet head 34 is fitted and installed. The mounting holes are through holes and are formed so that the ink ejection surface of each inkjet head 34 is exposed to the outside of the bottom surface of the head holder 33.

[0026] Each inkjet head 34 has multiple nozzles that eject ink onto the printing medium P, and these multiple nozzles are arranged in a direction perpendicular to the transport direction of the printing medium P.

[0027] The dotted rectangles shown in Figure 2 indicate the areas where the six inkjet heads 34, which make up each line head 32a to 32d, are located.

[0028] As shown in Figure 2, each line head 32a to 32d has two rows of heads, each consisting of three inkjet heads 34 arranged at equal intervals in a direction perpendicular to the transport direction of the printing medium P (front-to-back direction), and these two rows of heads are arranged in a staggered pattern so as to overlap by a predetermined number of nozzles.

[0029] For example, when printing a straight line extending perpendicular to the transport direction of the printing medium P using the line head 32a, ink is ejected from the two rows of heads constituting the line head 32a at different timings depending on the distance between the rows of heads, and as a result, a straight line is printed by the six inkjet heads 34 constituting the line head 32a. The same applies to the other line heads 32b to 32d. In this embodiment, adjacent inkjet heads 34 refer to the two inkjet heads 34 that print the joint portion when printing a straight line as described above.

[0030] The printing medium P printed by the printing processing unit 30 is transported along the circulating transport path CR by transport rollers and the like placed on the circulating transport path CR. The circulating transport path CR is equipped with a switching mechanism 43 that switches between guiding the printing medium P transported along the circulating transport path CR to the paper discharge unit 40 or recirculating it along the circulating transport path CR. Specifically, the switching mechanism 43 switches between the transport path on the paper discharge unit 40 side and the transport path on the reversing unit 50 side.

[0031] The paper discharge unit 40 has a tray-shaped paper discharge table 41 that protrudes from the housing of the inkjet printing device 1, and a pair of paper discharge rollers 42 that discharge the printing medium P onto the paper discharge table 41. The printing medium P, guided to the transport path on the paper discharge unit 40 side by the switching mechanism 43, is discharged onto the paper discharge table 41 by the paper discharge rollers 42.

[0032] The reversing unit 50 includes a reversing table 51 for reversing the printing medium P, and a reversing roller 52 that transports the printing medium P from the circulating transport path CR to the reversing table 51 and returns the printing medium P that has been transported to the reversing table 51 back onto the circulating transport path CR.

[0033] The printing medium P, guided to the reversal section 50 by the switching mechanism 43, is transported from the circulating transport path CR to the reversal table 51 by the reversal roller 52, and then returned from the reversal table 51 to the circulating transport path CR, thereby being transported on the circulating transport path CR with its front and back sides reversed. The reversed printing medium P is then transported again toward the printing processing unit 30 by a plurality of rollers, such as the transport roller 53, provided on the circulating transport path CR.

[0034] The control panel 70 consists of a touch panel with a liquid crystal display, and displays various setting input screens and accepts various setting inputs, such as instructions to start printing. In addition, the control panel 70 displays information regarding the abnormal impact location when an abnormal impact location is detected.

[0035] The scanner unit 80 photoelectrically reads the printed image on the printing medium P to acquire read image data and outputs the read image data to the control unit 60. In this embodiment, the scanner unit 80 reads the printing medium P on which a test pattern for detecting bullet impact abnormalities is printed, and outputs the read test image data to the control unit 60. The test pattern may be, for example, a linear pattern printed by each nozzle of each inkjet head 34, which will be described in detail later.

[0036] Figure 3 is a block diagram showing the schematic configuration of the control system of the inkjet printing apparatus 1 according to this embodiment.

[0037] The control unit 60 controls the entire inkjet printing apparatus 1 and includes a CPU (Central Processing Unit), semiconductor memory, and a hard disk. The control unit 60 controls the operation of each part of the inkjet printing apparatus 1 by executing a program pre-stored in a storage medium such as semiconductor memory or a hard disk, and by operating electrical circuits.

[0038] In particular, the control unit 60 of this embodiment acquires test image data of the test pattern output from the scanner unit 80 as described above, and detects abnormalities in the landing position of ink droplets ejected from each nozzle of each inkjet head 34 based on the acquired test image data.

[0039] Specifically, as shown in Figure 3, the control unit 60 includes a test image data acquisition unit 61, a distance measurement unit 62, and an anomaly detection unit 63.

[0040] As described above, the test image data acquisition unit 61 acquires test image data obtained by scanning the test pattern with the scanner unit 80.

[0041] Here, we will describe an example of a test pattern. Figure 4 shows an example of a test pattern printed by each nozzle of two adjacent inkjet heads 34. For the sake of clarity, we will describe a test pattern printed by some of the nozzles, and assume that the joints of the two adjacent inkjet heads 34 do not overlap, as described above. Even if the joints of the two adjacent inkjet heads 34 overlap, the overlap area will only use the nozzles of one of the two inkjet heads 34, so the explanation is the same as below.

[0042] In Figure 4, two adjacent inkjet heads 34 are shown as the first inkjet head 34A and the second inkjet head 34B. The white circles shown within the first inkjet head 34A and the second inkjet head 34B represent nozzles, and each white circle representing a nozzle is numbered from 1 to 15 for explanatory purposes.

[0043] Below the first inkjet head 34A and the second inkjet head 34B, a test pattern consisting of straight lines printed by each nozzle is shown. As shown in Figure 4, the test pattern is printed with straight lines extending in the transport direction. Each straight line in the test pattern is labeled with the nozzle number that printed it. In the example shown in Figure 4, the test pattern printed by nozzles 0 through 15 is shown.

[0044] As shown in Figure 4, a test pattern is printed with a predetermined number of nozzle spacings within the same range in the transport direction of the printing medium P, so that the lines printed by each nozzle do not overlap.

[0045] In the example shown in Figure 4, the first printing area R1 has test patterns printed for each of the four nozzles, specifically for nozzles 0, 4, 8, and 12. Next, test patterns are printed in the second printing area R2 below the first printing area R1, and in the second printing area R2, test patterns are printed for each of the four nozzles, similar to the first printing area R1. However, in the second printing area R2, the test patterns are printed shifted by one nozzle length in a direction perpendicular to the transport direction compared to the first printing area R1. Specifically, the second printing area R2 has test patterns printed for nozzles 1, 5, 9, and 13.

[0046] Similarly, for the third printing area R3 and the fourth printing area R4, test patterns are printed for each of the four nozzles within the third printing area R3 and the fourth printing area R4, with a shift of one nozzle width. Specifically, test patterns for nozzles 2, 6, 10, and 14 are printed in the third printing area R3, and test patterns for nozzles 3, 7, 11, and 15 are printed in the fourth printing area R4.

[0047] Although Figure 4 only shows test patterns printed by some of the nozzles, linear test patterns are printed by all nozzles of all inkjet heads 34. In addition, test patterns for each color are printed in different ranges depending on the transport direction of the printing medium P. The test image data acquisition unit 61 then acquires test image data by reading the test patterns printed by all of the nozzles.

[0048] The distance measuring unit 62 measures the nozzle-to-nozzle distance based on the test image data acquired by the test image data acquisition unit 61. Here, the nozzle-to-nozzle distance refers to the distance between two nozzles within one inkjet head, or the distance between two nozzles that straddle the joint of adjacent inkjet heads in a direction perpendicular to the transport direction. Specifically, in the test pattern shown in Figure 4, the distance between two adjacent straight lines in a direction perpendicular to the transport direction is the nozzle-to-nozzle distance. In Figure 4, "a" represents the distance between two nozzles within one inkjet head, and "b" represents the distance between two nozzles that straddle the joint of adjacent inkjet heads. In this embodiment, the distance between two nozzles within one inkjet head is called the first nozzle-to-nozzle distance, and the distance between two nozzles that straddle the joint of adjacent inkjet heads is called the second nozzle-to-nozzle distance.

[0049] The abnormality detection unit 63 detects abnormalities in the landing position of ink droplets ejected from each nozzle based on the distance between the first and second nozzles measured by the distance measuring unit 62.

[0050] Specifically, the anomaly detection unit 63 calculates the difference between the first nozzle-to-nozzle distance and the theoretical value of the first nozzle-to-nozzle distance, and detects it as an impact position anomaly if the difference exceeds a preset threshold. The anomaly detection unit 63 also calculates the difference between the second nozzle-to-nozzle distance and the theoretical value of the second nozzle-to-nozzle distance, and detects it as an impact position anomaly if the difference exceeds a preset threshold.

[0051] Here, the first theoretical nozzle distance is a theoretical value obtained from the ideal landing positions of two nozzles within a single inkjet head. The second theoretical nozzle distance is a theoretical value obtained from the ideal landing positions of two nozzles that straddle the joint between adjacent inkjet heads. The second theoretical nozzle distance is set to a theoretical value that also takes into account the amount of misalignment in the installation position of adjacent inkjet heads, and is a different value from the first theoretical nozzle distance.

[0052] If the abnormality detection unit 63 detects an abnormal impact position, the control unit 60 displays the detection of the abnormal impact position on the operation panel 70, as well as the location of the abnormal impact position. This allows the user to replace the inkjet head 34 that is experiencing the abnormal impact position.

[0053] Next, the flow of the projectile impact anomaly detection process in the first embodiment will be explained with reference to the flowchart shown in Figure 5.

[0054] First, the control unit 60 controls each of the line heads 32a, 32b, 32c, and 32d of the head unit 31 to print the test pattern described above (S10).

[0055] Next, the printed medium P on which the test pattern is printed is placed in the scanner unit 80 by the user and read by the scanner unit 80 (S12), and the read test image data is acquired by the test image data acquisition unit 61.

[0056] Next, the control unit 60 reads and sets a first theoretical value T1 for the distance between nozzles, which is pre-stored in a storage medium such as a semiconductor memory (S14). The control unit 60 also reads and sets a second theoretical value T2[N] for the distance between nozzles, which is pre-stored in a storage medium such as a semiconductor memory (S16). The first theoretical value T1 and the second theoretical value T2[N] for the distance between nozzles may be set and input by the user using an operation panel 70 or the like.

[0057] The control unit 60 then determines whether the currently measured nozzle-to-nozzle distance belongs to an area that straddles the joint of adjacent inkjet heads 34 or to an area that does not straddle the joint, and decides whether to use the first theoretical nozzle-to-nozzle distance T1 or the second theoretical nozzle-to-nozzle distance T2[N] depending on the area to which it belongs.

[0058] Figure 6 is a diagram illustrating the areas where the two nozzles described above straddle the seam and the areas where they do not. In Figure 6 and the following explanation, for the sake of simplicity, we will describe the case where there are four inkjet heads 34, i.e., three areas where the nozzles straddle the seam. However, as mentioned above, when there are six inkjet heads 34 included in each line head 32a to 32d, five areas where the nozzles straddle the seam are set.

[0059] In Figure 6, Area1 is defined as the region that does not straddle the seam, and Area2[1]~[3] is defined as the region that straddles the seam. The numbers in parentheses in Area2[1]~[3] indicate the location of the seam. Similarly, N in the second theoretical nozzle distance T2[N] mentioned above also indicates the location of the seam.

[0060] The control unit 60 then determines whether the current distance between nozzles being measured belongs to Area 1 or Area 2[1]~[3] as shown in Figure 6 (S18).

[0061] If the nozzle-to-nozzle distance to be measured belongs to Area 1 (S18, Area 1), the control unit 60 obtains a first theoretical value T1 for the nozzle-to-nozzle distance (S20) and measures the nozzle-to-nozzle distance L to be measured as the first nozzle-to-nozzle distance (S28).

[0062] The control unit 60 then calculates the absolute value of the difference between the first theoretical nozzle-to-nozzle distance T1 and the measured nozzle-to-nozzle distance L, and determines whether or not this absolute value exceeds a preset threshold (S30). If the absolute value exceeds the threshold (S30, YES), the control unit 60 detects it as an abnormal impact location (S32). On the other hand, if the absolute value is within the threshold (S30, NO), the control unit 60 considers that no abnormal impact location has occurred. If the measurement of all nozzle-to-nozzle distances has not been completed (S34, NO), the control unit 60 returns to S18 and performs the impact abnormality detection process for the next nozzle-to-nozzle distance to be measured. If the measurement of all nozzle-to-nozzle distances has been completed (S34, YES), the impact abnormality detection process ends.

[0063] Furthermore, in S18, the control unit 60 obtains a second theoretical value T2[1] for the distance between nozzles of the current measurement target if it belongs to Area2[1] (S18, Area2[1]) (S22), obtains a second theoretical value T2[2] for the distance between nozzles if it belongs to Area2[2] (S18, Area2[2]), and obtains a second theoretical value T2[3] for the distance between nozzles if it belongs to Area2[3] (S18, Area2[3]).

[0064] The control unit 60 then measures the distance L between the nozzles to be measured as the second distance between the nozzles (S28), calculates the absolute value of the difference between the measured distance L and one of the theoretical values ​​T2[1] to T2[3] of the second distance between the nozzles, and determines whether or not that absolute value exceeds a preset threshold (S30).

[0065] The control unit 60 detects an abnormal impact location (S32) if the absolute value exceeds the threshold (S30, YES). On the other hand, if the absolute value is within the threshold (S30, NO), it is assumed that no abnormal impact location has occurred. If the control unit 60 has not completed measuring all the distances between nozzles (S34, NO), it returns to S18 and performs the abnormal impact detection process for the next target nozzle distance to be measured. If the measurement of all the distances between nozzles has been completed (S34, YES), it terminates the abnormal impact detection process.

[0066] According to the inkjet printing apparatus of this embodiment, the distance between two nozzles that straddle the joint of adjacent inkjet heads 34 is measured, and an abnormality in the projectile's landing position is detected based on the measured distance between the two nozzles and a second theoretical value of the distance between nozzles that takes into account the misalignment of the adjacent ejection heads. This prevents false detection of abnormalities in the projectile's landing position caused by misalignment of the inkjet heads.

[0067] Furthermore, as in the above embodiment, by using a first theoretical value for the distance between nozzles that does not cross a joint, and a second theoretical value for the distance between nozzles that does cross a joint, which is different from the first theoretical value, it is possible to detect abnormalities in the impact position with high accuracy for all nozzles.

[0068] Next, the impact anomaly detection process of the second embodiment will be described. In the description of the impact anomaly detection process of the first embodiment described above, Area2[1]~[3] was set for each joint position as a second theoretical value of the nozzle distance used when the distance between two nozzles belongs to a region that straddles the joint of adjacent inkjet heads 34, but it is not limited to this.

[0069] In the second embodiment, a second theoretical value for the distance between nozzles is calculated using a first theoretical value for the distance between nozzles, which is used when the distance between the two nozzles falls within a region that does not cross a joint, and an amount of installation position deviation calculated in advance for each joint location. Figure 7 is a flowchart illustrating the impact anomaly detection process when the second theoretical value for the distance between nozzles is calculated using the first theoretical value for the distance between nozzles and an amount of installation position deviation calculated in advance for each joint location, as described above.

[0070] The processes S40 to S44 shown in Figure 7 are the same as those in S10 to S14 of the first embodiment shown in Figure 5. Then, in S46, the control unit 60 reads and sets the amount of misalignment H[N] of the joints of adjacent inkjet heads 34 from a storage medium such as a semiconductor memory. The N in the amount of misalignment H[N] is a number indicating the position of the joint.

[0071] The installation position deviation amount H[N] is a value that is calculated in advance. Specifically, for each joint, the distance between nozzles spanning the joint is measured and the average value is obtained. The installation position deviation amount H[N] is calculated by calculating the difference between this average value and the first theoretical value T1 of the distance between nozzles, and this value is stored in the storage medium in advance. Note that the installation position deviation amount H[N] for each joint may be calculated by the control unit 60, or it may be set and input by the user using the operation panel 70 or the like.

[0072] Then, in S48, the control unit 60 determines whether the current distance between nozzles being measured belongs to Area 1 or Area 2[1]~[3] as shown in Figure 6.

[0073] Then, if the distance between nozzles to be measured belongs to Area 1 (S48, Area 1), the control unit 60 obtains a first theoretical value T1 for the distance between nozzles (S50). Also, if the distance between nozzles to be measured belongs to Area 2[1] (S48, Area 2[1]), the control unit 60 adds the first theoretical value T1 for the distance between nozzles and the installation position displacement H[1] to obtain a second theoretical value for the distance between nozzles (S52). Furthermore, if the distance between nozzles to be measured belongs to Area2[2] (S48, Area2[2]), the control unit 60 adds the first theoretical value of the distance between nozzles T1 and the installation position deviation H[2] to obtain the second theoretical value of the distance between nozzles (S54). If the distance between nozzles to be measured belongs to Area2[3] (S48, Area2[3]), the control unit 60 adds the first theoretical value of the distance between nozzles T1 and the installation position deviation H[3] to obtain the second theoretical value of the distance between nozzles (S56).

[0074] The subsequent processing in S58 to S64 is the same as the processing in S28 to S34 of the first embodiment shown in Figure 5.

[0075] According to the impact anomaly detection process of the second embodiment described above, the amount of installation position deviation H[N] is calculated in advance, and the first theoretical value of the distance between nozzles T1 and the amount of installation position deviation H[N] are added to obtain the second theoretical value of the distance between nozzles. As a result, the accuracy of the second theoretical value of the distance between nozzles can be improved, and impact anomalies can be detected with higher accuracy.

[0076] Next, the impact anomaly detection process of the third embodiment will be described. In the impact anomaly detection process of the second embodiment, the distance between nozzles that cross the joints was measured and the average value was obtained to calculate the installation position deviation amount H[N]. However, in the case of a test pattern such as that shown in Figure 4, there are only four distances between nozzles that cross the joints, and the accuracy of the installation position deviation amount H[N] decreases because the sample size is small. If the number of test patterns is increased in the transport direction and printed, the sample size will increase, but the test pattern will become longer in the transport direction, which may result in larger printing paper.

[0077] The third embodiment is a method for calculating the installation position deviation amount H[N] with higher accuracy without increasing the number of test patterns in the transport direction, as described above. Figures 8 and 9 are flowcharts illustrating the impact anomaly detection process of the third embodiment.

[0078] First, steps S70 and S72 shown in Figure 8 are the same as steps S10 and S12 in the first embodiment shown in Figure 5.

[0079] Then, after acquiring the test image data, the control unit 60 sets N in the installation position misalignment amount H[N] to 1 (S74). In this embodiment, N is a number indicating the position of the joint, but it is also a number assigned to the inkjet head 34. Specifically, as shown in Figure 10, each inkjet head 34 is numbered in the order in which they are arranged in their arrangement direction (a direction perpendicular to the transport direction of the printing medium P). The joint between the Nth inkjet head 34 and the (N+1)th inkjet head 34 is defined as the joint at position N. Therefore, the installation position misalignment amount at the joint between the Nth inkjet head 34 and the (N+1)th inkjet head 34 is expressed as the installation position misalignment amount H[N].

[0080] Then, as shown in Figure 10, the control unit 60 uses a test pattern to measure the actual distance from a predetermined nozzle in the Nth inkjet head 34 to a nozzle that is a predetermined number of nozzles away from that starting point, and obtains the measured value A (S76). In this embodiment, the first number of nozzles is the number of nozzles corresponding to the theoretical value T1 of the distance between first nozzles.

[0081] Next, the control unit 60 uses a test pattern to measure the actual distance from the starting nozzle set in S76 to the N+1th nozzle in the inkjet head 34, which is a number of nozzles away from the starting nozzle set in S76, and obtains the measured value B (S78). The above-mentioned preset second number of nozzles is the number of nozzles corresponding to the first nozzle-to-nozzle distance theoretical value T1 used when obtaining the measured value A, multiplied by M (where M is a natural number of 2 or more).

[0082] Next, the control unit 60 moves the starting nozzle position set within the Nth inkjet head 34 towards the N+1th inkjet head 34 (S80).

[0083] Then, if the position obtained by adding the first number of nozzles to the starting position after movement is within Area 1 as described above (S82, YES), the control unit 60 measures the measured value A in S76 and the measured value B in S78, and moves the starting position again (S80).

[0084] The control unit 60 repeats the process from S76 to S80 until the position obtained by adding the first nozzle number to the starting point after movement is outside Area 1. If the position obtained by adding the first nozzle number to the starting point after movement is outside Area 1 (S82, NO), it calculates the average of the multiple measured values ​​A and the average of the multiple measured values ​​B measured up to that point (S84).

[0085] The control unit 60 then calculates the theoretical value B of the measurement B by multiplying the average value of measurement A by M, and subtracts the average value of measurement B from the theoretical value B to calculate the installation position displacement H [N].

[0086] Next, the control unit 60 moves the starting nozzle position to the N+1th inkjet head 34 (S88) and increments N by 1 (S90).

[0087] Then, if the value of N is not the number of the last inkjet head (in this embodiment, N ≤ 3) (S92, NO), the process from S76 to S90 is repeated. In S92, if the value of N is the number of the last inkjet head (in this embodiment, N = 4), the control unit 60 sets the average value of all measured values ​​A as the first theoretical value T1 of the nozzle distance described above.

[0088] The subsequent processing steps S96 to S112 shown in Figure 9 are the same as the processing steps S48 to S64 in the second embodiment shown in Figure 7.

[0089] According to the impact anomaly detection process of the third embodiment described above, the installation position deviation amount H[N] can be calculated with higher accuracy without increasing the number of test patterns downwards, as described above.

[0090] It should be noted that the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the embodiments described above. For example, all the components shown in the embodiments may be combined as appropriate. It goes without saying that various modifications and applications are possible without departing from the spirit of the invention.

[0091] The following further notes are disclosed regarding the present invention. (Note)

[0092] In the projectile impact anomaly detection device of the present invention, the distance measuring unit measures the distance between two nozzles in the discharge head as the first nozzle distance based on test image data, and measures the distance between two nozzles that straddle the joint of adjacent discharge heads as the second nozzle distance. The anomaly detection unit can detect projectile impact position anomalies based on the first nozzle distance and the theoretical value of the distance between the two nozzles in the discharge head, and can also detect projectile impact position anomalies based on the second nozzle distance and the theoretical value of the distance between two nozzles that takes into account the misalignment of the installation position of adjacent discharge heads.

[0093] In the projectile impact anomaly detection device of the present invention, the anomaly detection unit can calculate a theoretical distance between two nozzles that takes into account the installation position misalignment of adjacent discharge heads by adding a pre-calculated amount of installation position misalignment to the theoretical distance between two nozzles in the discharge head.

[0094] In the projectile impact anomaly detection device of the present invention, when adjacent discharge heads are designated as a first discharge head and a second discharge head, the distance measuring unit measures the distance from a predetermined nozzle position in the first discharge head to a nozzle in the first discharge head that is a predetermined number of nozzles away from the starting nozzle, and obtains a first measurement value. It also measures the distance from the starting nozzle to a nozzle in the second discharge head that is a predetermined number of nozzles away from the starting nozzle, and obtains a second measurement value. The position of the starting nozzle is then moved within the first discharge head. While moving, multiple first and second measurement values ​​are taken, and the anomaly detection unit calculates a first average value, which is the average of the multiple first measurement values, and a second average value, which is the average of the multiple second measurement values. The amount of misalignment of the installation position is calculated by subtracting the second average value from the first average value multiplied by M (where M is a natural number greater than or equal to 2). The anomaly detection unit can then add the calculated amount of misalignment of the installation position to the theoretical value of the distance between the two nozzles in the discharge head to calculate a theoretical value of the distance between the two nozzles that takes into account the misalignment of the installation position of the adjacent discharge head. [Explanation of Symbols]

[0095] 1. Inkjet printing device 10. Side paper feed section 11 Paper feed tray 12 Primary paper feed section 14 Secondary paper feed section 20 Internal paper feed section 21a Paper feed tray 21b Paper feed tray 21c Paper feed tray 21d Paper feed stand 22a~22d Primary paper feed section 30 Printing Processing Unit 31 Head Unit 32a~32d Line head 33 Head holder 34 inkjet heads 34A First inkjet head 34B Second inkjet head 40 Paper output section 41 Paper output tray 42 Paper output roller 43 Mechanism 50 Reversal section 51 Reversing platform 52 Reversible Roller 53 Conveyor rollers 60 Control Unit 61 Test Image Data Acquisition Unit 62 Distance measuring unit 63 Anomaly detection unit 70 Control Panel 80 Scanner section 131,132 Suction fan 133 Conveyor belt CR Circulation Transport Route FR paper feed transport path P Print media R1 First printing range R2 Second printing area R3 Third printing range R4 Fourth printing range

Claims

1. A test image data acquisition unit acquires test image data by reading a test pattern obtained by discharging the liquid from a line head which is arranged in the longitudinal direction of a discharge head, and which has a discharge head in which a plurality of nozzles for discharging liquid are arranged, A distance measuring unit measures the distance between two nozzles that straddle the joint of adjacent discharge heads within the line head, based on the test image data, An impact anomaly detection device comprising an anomaly detection unit that detects an anomaly in the impact position deviation based on the measured distance between the two nozzles and a theoretical value of the distance between the two nozzles that takes into account the misalignment of the installation position of the adjacent discharge heads.

2. The distance measuring unit measures the distance between two nozzles in the discharge head as the first nozzle distance based on the test image data, and measures the distance between two nozzles that straddle the joint of adjacent discharge heads as the second nozzle distance. The projectile impact abnormality detection device according to claim 1, wherein the abnormality detection unit detects an abnormality in the impact position based on the distance between the first nozzles and a theoretical value of the distance between the two nozzles in the discharge head, and detects an abnormality in the projectile impact position deviation based on the distance between the second nozzles and a theoretical value of the distance between the two nozzles that takes into account the misalignment of the installation position of the adjacent discharge head.

3. A test image data acquisition unit that reads a test pattern obtained by discharging a liquid from a line head which is arranged in the longitudinal direction of a discharge head, and which has a plurality of nozzles for discharging a liquid arranged therein, and acquires test image data, A distance measuring unit measures the distance between two nozzles that straddle the joint of adjacent discharge heads within the line head, based on the test image data, The system includes an abnormality detection unit that detects an abnormality in the point of impact based on the measured distance between the two nozzles and a theoretical value of the distance between the two nozzles that takes into account the misalignment of the installation position of the adjacent discharge heads. The projectile impact anomaly detection device calculates a theoretical distance between two nozzles that takes into account the installation position misalignment of adjacent discharge heads by adding a pre-calculated amount of installation position misalignment to the theoretical distance between two nozzles in the discharge head.

4. When the adjacent discharge heads are designated as a first discharge head and a second discharge head, the distance measuring unit measures the distance from a predetermined nozzle position in the first discharge head to a nozzle in the first discharge head that is a predetermined number of nozzles away from the starting nozzle, and obtains a first measurement value. It also measures the distance from the starting nozzle to a nozzle in the second discharge head that is a predetermined number of nozzles away from the starting nozzle, and obtains a second measurement value. The unit measures multiple first and second measurement values ​​while moving the starting nozzle position within the first discharge head. The anomaly detection unit calculates a first average value which is the average of a plurality of first measurement values, and also calculates a second average value which is the average of a plurality of second measurement values. The amount of displacement in the installation position is calculated by subtracting the second average value from the value obtained by multiplying the first average value by M (where M is a natural number of 2 or more). The projectile impact anomaly detection device according to claim 3, wherein the anomaly detection unit adds the calculated installation position displacement to the theoretical value of the distance between the two nozzles in the discharge head, and calculates a theoretical value of the distance between the two nozzles that takes into account the installation position displacement of the adjacent discharge head.

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