Printing apparatus, printing method thereof, and program

Abstract

To provide a printer which can suppress reduction in the image quality due to a temperature difference of ink in a head.SOLUTION: A printer comprises: a head which has a plurality of nozzles arrayed in a first direction, a manifold communicating with the plurality of nozzles and a drive element applying discharge pressure to the ink; a first temperature sensor which detects a temperature difference between the ink in the upstream and ink in the downstream in the first direction in the manifold; and a control device. The plurality of nozzles have a first nozzle arranged on the upstream in the first direction and a second nozzle arranged on the downstream in the first direction. The control device executes the printing operation of causing the nozzles to discharge the ink to a printing medium on the basis of image data to constitute an image with the ink that landed on the printing medium, and the position correction operation of correcting discharge timing of the ink from the nozzles on the basis of the temperature difference such that a distance between the landing position of the ink discharged from the first nozzle and the landing position of the ink discharged from the second nozzle becomes short in the second direction.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] As a conventional printing apparatus, for example, the image forming apparatus of Patent Document 1 is known. This image forming apparatus includes a recording head that discharges a liquid, a carriage that reciprocates the recording head, and a tank that supplies the liquid to the recording head. The recording head has a pressure generating means that applies a pressure for discharging the liquid. In such an image forming apparatus, while reciprocating the recording head, the liquid is discharged from the recording head onto the recording medium, so that the liquid lands on the recording medium and an image is formed on the recording medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such an image forming apparatus, as the pressure generating means is driven during image formation, the liquid in the recording head is heated by the heat generated by the pressure generating means. On the other hand, the liquid is supplied to the recording head from the tank. Therefore, in the flow path where the liquid flows in the recording head, the temperature of the liquid becomes higher downstream than upstream where the liquid is supplied from the tank, and a temperature difference occurs in the liquid. The higher the temperature of this liquid, the lower the viscosity, and the faster the speed of the liquid discharged from the recording head. As a result, the landing position of the liquid on the recording medium is shifted.

[0005] In contrast, the image forming ejection device of Patent Document 1 corrects the landing position deviation of the liquid ejected from the recording head based on the temperature difference between the environmental temperature of the device and the temperature of the liquid. However, this image forming ejection device cannot correct the landing position deviation caused by the temperature difference of the liquid in the recording head, resulting in a deterioration of the image quality.

[0006] In view of such a situation, an object of the present invention is to provide a printing device, a printing method, and a program that can reduce the deterioration of image quality caused by the temperature difference of the liquid in the head.

Means for Solving the Problems

[0007] A printing device according to an aspect of the present invention includes a head having a plurality of nozzles arranged in a first direction, a manifold communicating with the plurality of nozzles, and a driving element for applying a discharge pressure to the ink, a first temperature sensor for detecting a temperature difference of the ink in the upstream and downstream of the first direction in the manifold, and a control device. The plurality of nozzles include a first nozzle arranged upstream in the first direction and a second nozzle arranged downstream in the first direction. The control device performs a printing operation of ejecting the ink from the nozzles onto a printing medium based on image data to form an image with the ink landed on the printing medium, and a position correction operation of correcting the ejection timing of the ink from the nozzles based on the temperature difference so that the distance between the landing position of the ink ejected from the first nozzle and the landing position of the ink ejected from the second nozzle in a second direction intersecting the first direction becomes shorter.

[0008] A printing method according to an aspect of the present invention includes a head having a plurality of nozzles arranged in a first direction, a manifold communicating with the plurality of nozzles, and a driving element that applies a discharge pressure to ink, and a first temperature sensor that detects a temperature difference of the ink upstream and downstream in the first direction in the manifold. The plurality of nozzles include a first nozzle disposed upstream in the first direction and a second nozzle disposed downstream in the first direction. The printing method of a printing apparatus includes a printing operation of discharging the ink from the nozzles onto a printing medium based on image data to form an image with the ink landed on the printing medium, and a position correction operation of correcting a discharge timing of the ink from the nozzles based on the temperature difference so that a distance between a landing position of the ink discharged from the first nozzle and a landing position of the ink discharged from the second nozzle in a second direction intersecting the first direction is shortened.

[0009] A program according to an aspect of the present invention causes a computer of a printing apparatus including a head having a plurality of nozzles arranged in a first direction, a manifold communicating with the plurality of nozzles, and a driving element that applies a discharge pressure to ink, and a first temperature sensor that detects a temperature difference of the ink upstream and downstream in the first direction in the manifold. The plurality of nozzles include a first nozzle disposed upstream in the first direction and a second nozzle disposed downstream in the first direction. Based on image data, the computer performs a printing operation of discharging the ink from the nozzles onto a printing medium to form an image with the ink landed on the printing medium, and a position correction operation of correcting a discharge timing of the ink from the nozzles based on the temperature difference so that a distance between a landing position of the ink discharged from the first nozzle and a landing position of the ink discharged from the second nozzle in a second direction intersecting the first direction is shortened.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a printing apparatus, a printing method, and a program that can reduce the deterioration of image quality caused by a temperature difference of liquid in a head.

[0011] The above object, other objects, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

Brief Description of the Drawings

[0012]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout all the drawings, and the overlapping descriptions thereof are omitted.

[0014] (Embodiment 1) <Configuration of the printing device> As shown in FIG. 1, the printing device 10 according to Embodiment 1 of the present invention is a device that discharges ink from the nozzles 21 of the head 20 onto the printing medium A to print an image on the printing medium A with the ink. Hereinafter, an example in which the printing device 10 is applied to an inkjet printer will be described, but the printing device 10 is not limited thereto. Further, the printing medium A is a sheet such as paper and cloth.

[0015] The printing device 10 is of a serial head type and includes a head 20, a platen 11, a conveying device 30, a scanning device 40, an ink cartridge 12, a first temperature sensor 13, a housing 14, and a control device 50. Note that the first direction in which a plurality of nozzles 21 are arranged is referred to as the front-rear direction, the second direction intersecting (for example, orthogonal) to the first direction is referred to as the left-right direction. Further, the direction intersecting (for example, orthogonal) to the front-rear direction and the left-right direction is referred to as the up-down direction. However, the arrangement of the printing device 10 is not limited thereto. Details of the head 20, the first temperature sensor 13, and the control device 50 will be described later.

[0016] The housing 14 houses the head 20, the platen 11, the conveying device 30, the scanning device 40, the ink cartridge 12, the first temperature sensor 13, and the control device 50. The platen 11 has a flat upper surface and defines the distance between the printing medium A disposed on the upper surface thereof and the lower surface of the head 20 provided opposite thereto.

[0017] The conveying device 30 has, for example, two conveying rollers 31 and a conveying motor 32 (Fig. 2). The two conveying rollers 31 sandwich the platen 11 therebetween in the front-rear direction and are arranged parallel to each other. The central axis of the conveying roller 31 extends in the left-right direction and is connected to the conveying motor 32. The conveying roller 31 rotates by the drive of the conveying motor 32 and conveys the printing medium A in the front-rear direction on the platen 11.

[0018] The scanning device 40 has a carriage 41, two guide rails 42, a scanning motor 43 (Fig. 2), and an endless belt 44. The carriage 41 mounts the head 20 and is supported by the two guide rails 42 so as to be movable in the left-right direction. The two guide rails 42 extend in the left-right direction above the platen 11 so as to sandwich the lower surface of the head 20 therebetween in the front-rear direction. The endless belt 44 extends in the left-right direction and is attached to the carriage 41 and the scanning motor 43. When the scanning motor 43 is driven, the endless belt 44 runs, and the carriage 41 reciprocates in the left-right direction along the guide rail 42. Thereby, the carriage 41 moves the head 20 in the forward and return paths in the left-right direction.

[0019] The ink cartridge 12 is, for example, a tank detachable from the housing 14 and stores ink. The ink cartridge 12 is connected to the head 20 by a tube 12a and supplies ink to the nozzles 21 of the head 20 via the tube 12a.

[0020] <Head> As shown in Fig. 1, a plurality of nozzles 21 are arranged at equal intervals in the front-rear direction to form a nozzle row. The plurality of nozzle rows are arranged at intervals in the left-right direction. The nozzles 21 open on the lower surface of the head 20. As shown in Fig. 3, the plurality of nozzles 21 in each nozzle row include an upstream nozzle 21a which is the first nozzle arranged in the front and a downstream nozzle 21b which is the second nozzle arranged in the rear in the front-rear direction.

[0021] The head 20 has, in addition to a plurality of nozzles 21 arranged in the front-rear direction, a manifold 22 communicating with the plurality of nozzles 21, and a drive element 24 (Fig. 2) that applies a discharge pressure to the ink. Further, the head 20 is mounted with the sub-tank 15 and the first temperature sensor 13. The manifold 22 extends in the front-rear direction and has a front end 22a which is one end thereof and a rear end 22b which is the other end. The plurality of individual flow paths 23 branch from the manifold 22 and are connected to the nozzles 21. In the front-rear direction, among the plurality of nozzles 21 in the nozzle row, the upstream nozzle 21a is closer to the front end 22a of the manifold 22 than the other nozzles 21 other than the upstream nozzle 21a, and the downstream nozzle 21b is closer to the rear end 22b of the manifold 22 than the other nozzles 21 other than the downstream nozzle 21b.

[0022] The sub-tank 15 is connected to the ink cartridge 12 (Fig. 1) by a tube 12a and is also connected to the front end 22a of the manifold 22. For this reason, the ink is supplied from the ink cartridge 12 to the sub-tank 15 by the tube 12a, flows into the manifold 22 from the sub-tank 15, and flows from the front end 22a to the rear end 22b in the manifold 22. The ink flows into the individual flow paths 23 while flowing through the manifold 22 and is supplied to the nozzles 21 through the individual flow paths 23.

[0023] The drive element 24 is a piezoelectric element, a heating element, an electrostatic actuator, etc., is provided for each nozzle 21, and drives to vary the volume of the individual flow path 23 connected to the nozzle 21. Thereby, a pressure for discharging the ink from the nozzle 21 is applied to the ink in the individual flow path 23.

[0024] The first temperature sensor 13 is a sensor such as a thermistor, and detects the temperature difference of the ink at the upstream (front in the front-rear direction) and the downstream (rear in the front-rear direction) in the manifold 22. For example, the first temperature sensor 13 has an upstream temperature sensor 13a and a downstream temperature sensor 13b. The upstream temperature sensor 13a is arranged near the front end 22a of the manifold 22 so as to detect the temperature of the ink at the front part in the manifold 22. The downstream temperature sensor 13b is arranged near the rear end 22b of the manifold 22 so as to detect the temperature of the ink at the rear part in the manifold 22.

[0025] <Configuration of the control device> As shown in FIG. 2, the control device 50 is, for example, a computer, and includes an interface 51, an arithmetic unit 52, and a storage unit 53. The interface 51 receives various data such as image data from external devices such as a computer, a camera, a network, and a recording medium. The image data is raster data or the like indicating an image printed on the printing medium A. Note that the control device 50 may be configured by a single device, or a plurality of devices may be distributed and configured so that they cooperate to perform the operation of the printing device 10.

[0026] The storage unit 53 is a memory accessible from the arithmetic unit 52, and has a RAM and a ROM. The RAM temporarily stores various data such as image data and data converted by the arithmetic unit 52. The ROM stores programs and tables for performing various data processes. The arithmetic unit 52 includes, for example, a circuit such as a processor such as a CPU or an integrated circuit such as an ASIC, and controls each unit by executing a program stored in the ROM, and executes a printing operation and a position correction operation. Details of the printing operation and the position correction operation will be described later.

[0027] Such a control device 50 is electrically connected to a conveyance motor 32 of a conveyance device 30 via a conveyance drive circuit 33 and controls the drive of the conveyance motor 32. Thereby, the conveyance of the print medium A by the conveyance device 30 is controlled. Further, the control device 50 is electrically connected to a scanning motor 43 of a scanning device 40 via a scanning drive circuit 45 and controls the drive of the scanning motor 43. Thereby, the movement of the head 20 by the scanning device 40 is controlled.

[0028] Also, the control device 50 is electrically connected to a drive element 24 via a head drive circuit 25. The control device 50 outputs a control signal of the drive element 24 to the head drive circuit 25, and the head drive circuit 25 generates a drive signal based on the control signal and outputs it to the drive element 24. The drive element 24 drives according to the drive signal, and ink is ejected from the nozzles 21.

[0029] That is, the control device 50 divides the image of the image data into a plurality of regions and performs halftone processing on the image data for each region based on a predetermined look-up table stored in the storage unit 53. Thereby, the image data is converted into gradations that can be output by the printing device 10. The gradation of the converted image data corresponds to, for example, the ejection amount per drop of ink ejected from the nozzles 21. For this reason, the control device 50 selects one type of waveform signal from a plurality of types of waveform signals for each region according to the ink ejection amount based on the image data and generates waveform selection data.

[0030] The waveform signal is, for example, a pulse signal and has a non-ejection waveform signal for not ejecting ink from the nozzles 21 and an ejection signal for ejecting ink from the nozzles 21. The ejection signal has, for example, a small-droplet waveform signal for ejecting an amount of ink (small droplet) less than a predetermined amount, a medium-droplet waveform signal for ejecting a predetermined amount (medium droplet) of ink, and a large-droplet waveform signal for ejecting an amount of ink (large droplet) greater than the predetermined amount.

[0031] Then, the control device 50 divides the waveform selection data for each path and arranges them according to the order in which the ink is ejected from the nozzles 21 in the path. The control device 50 assigns the waveform selection data to the drive elements 24 corresponding to the nozzles 21 that eject the ink and the drive timings of the drive elements 24 corresponding to the landing positions of the ink, and outputs control data including the waveform selection data and four types of waveform signals to the head drive circuit 25. In this way, the control data defines the ejection amount of the ink according to the waveform selection data, the nozzles 21 that eject the ink, and the ejection timing of the ink according to the drive timing of the drive element 24.

[0032] The head drive circuit 25 selects one type of waveform signal based on the waveform selection data of the control data, and applies a voltage signal corresponding to the waveform of this waveform signal to the drive element 24 as a drive signal. As a result, the drive element 24 is driven according to the drive signal, the volume of the individual flow path 23 is changed, ejection pressure is applied to the ink, and the ink is ejected from the nozzle 21.

[0033] <Printing operation> In such a printing apparatus 10, the control device 50 acquires image data and executes a printing operation based on the image data. In the printing operation, for example, the control device 50 executes the forward path, which is the first path. In this forward path, the control device 50 moves the head 20 in the forward path, which is one direction in the left-right direction, and ejects ink from the head 20 onto the printing medium A. After this forward path, the control device 50 conveys the printing medium A forward. Then, after the conveyance of the printing medium A, the control device 50 executes the return path, which is the second path. In this return path, the control device 50 moves the head 20 in the return path, which is the other direction in the left-right direction, and ejects ink from the head 20 onto the printing medium A. After this return path, the control device 50 conveys the printing medium A forward. Hereinafter, the direction of movement of the head 20 will be described with the forward path direction being to the right and the return path direction being to the left, but the forward path and return path directions are not limited to this.

[0034] In this way, the printing apparatus 10 alternately repeats the path and the conveyance of the print medium A while alternately changing the forward path and the return path in the path, and proceeds with the printing operation of bidirectional printing. In this path, the ink ejected from the head 20 lands on the print medium A on the platen 11 facing the lower surface of the head 20. Dots of ink are formed at this landing position, and an image composed of the dots is printed on the print medium A.

[0035] In this printing operation, each time the ink is ejected, the drive element 24 is driven and the drive element 24 generates heat. Due to this heat generation, the ink in the manifold 22 is heated. On the other hand, ink is supplied to the manifold 22 from the sub-tank 15. For this reason, in the manifold 22, the temperature of the ink at the rear part becomes higher than the temperature of the ink at the front part flowing in from the sub-tank 15, and a temperature difference occurs in the ink in the manifold 22. The higher the temperature of this ink, the lower the viscosity, and among the nozzles 21 communicating with the manifold 22, the farther the rear nozzles 21 are from the upstream nozzle 21a, and the faster the speed of the ink ejected from the nozzle 21. For this reason, the landing position of the ink on the print medium A deviates from the desired position which is the landing position of the ink based on the image data when there is no temperature difference in the ink in the manifold 22. Therefore, the control device 50 performs a position correction operation to correct the landing position of the ink, thereby reducing the deviation of the landing position.

[0036] <Position correction operation> The control device 50 executes a position correction operation for correcting the ejection timing of the ink from the nozzle 21 based on the temperature difference so that the distance between the landing position of the ink ejected from the upstream nozzle 21a and the landing position of the ink ejected from the downstream nozzle 21b in the left-right direction becomes shorter.

[0037] For example, in the position correction operation, the control device 50 corrects the ejection timing of the ink in the return path so as to be later than the ejection timing of the ink based on the image data without correcting the ejection timing of the ink in the forward path.

[0038] Specifically, for example, the control device 50 causes ink to be ejected from a plurality of nozzles 21 arranged in the front-rear direction shown in FIG. 3 at ejection timings based on image data, thereby forming a straight-line image extending in the front-rear direction. Here, when there is no temperature difference in the ink in the manifold 22, the straight-line image extends in the front-rear direction as shown by the broken line in FIG. 4(a). However, since the temperature of the ink in the manifold 22 is higher toward the rear, among the plurality of nozzles 21 arranged along the manifold 22, the speed of the ink ejected from the rear nozzles 21 is faster. For this reason, the landing position of the ink from the rear nozzles 21 is shifted more upstream in the moving direction of the head 20. That is, in the forward path where the head 20 moves to the right, the forward path landing position B1 is arranged to be inclined more to the left toward the rear with respect to the front-rear direction, and in the return path where the head 20 moves to the left, the return path landing position B2 is arranged to be inclined more to the right toward the rear with respect to the front-rear direction. Therefore, the deviation distance in the left-right direction from the landing position of the ink from the upstream nozzle 21a is larger for the landing position of the ink from the rear nozzles 21. Also, the deviation distance between the landing position of the ink from the upstream nozzle 21a and the landing position of the ink from the downstream nozzle 21b is larger as the temperature difference becomes larger.

[0039] While the head 20 moves to the right in the forward path, ink is ejected from the plurality of nozzles 21. This forward path landing position B1 greatly deviates to the left from the upstream forward path landing position B1a of the ink from the upstream nozzle 21a toward the downstream forward path landing position B1b of the ink from the downstream nozzle 21b. Also, while the head 20 moves to the left in the return path immediately after the forward path, ink is ejected from the plurality of nozzles 21. This return path landing position B2 is arranged behind the forward path landing position B1 and greatly deviates to the left from the upstream return path landing position B2a of the ink from the upstream nozzle 21a toward the downstream return path landing position B2b of the ink from the downstream nozzle 21b.

[0040] These multiple forward landing positions B1 are shifted by a distance C1 each, and the multiple return landing positions B2 are also shifted by a distance C1 each. In contrast, the downstream forward landing position B1b of the forward landing positions B1 adjacent to each other in the front-rear direction and the upstream return landing position B2a of the return landing positions B2 are shifted by a distance C2 in the left-right direction. Since this shift distance C2 is larger than the shift distance C1, the path shift between the downstream forward landing position B1b and the upstream return landing position B2a is more noticeable.

[0041] Therefore, as shown in the example of FIG. 5, the control device 50 corrects the ink ejection timing based on a predetermined correspondence between the temperature difference of the ink in the front and rear in the manifold 22 and the correction value of the ink ejection timing. Here, the control device 50 acquires the temperature of the ink at the front part in the manifold 22 from the upstream temperature sensor 13a, and acquires the temperature of the ink at the rear part in the manifold 22 from the downstream temperature sensor 13b. The control device 50 acquires the temperature difference obtained by subtracting the temperature of the front part from the temperature of the rear part, and acquires the correction value corresponding to this temperature difference from the graph in FIG. 5. For example, when the temperature difference is 0 or more and less than E1, the correction value is 0; when the temperature difference is E1 or more and less than E2, the correction value is D1; when the temperature difference is E2 or more and less than E3, the correction value is D2; when the temperature difference is E3 or more and less than E4, the correction value is D3; when the temperature difference is E4 or more and less than E5, the correction value is D4. These temperature differences E1, E2, E3, E4, and E5 increase in this order, and the correction values D1, D2, D3, and D4 increase in this order. Thus, the larger the temperature difference, the larger the correction value.

[0042] The control device 50 acquires, as the drive timing of the drive element 24 corresponding to the ink landing position, the drive timing based on the image data from the control data of the return path. For example, when the temperature difference is equal to or greater than E2 and less than E3, the control device 50 corrects the control data of the return path so that all the discharge timings in the return path are corrected by a correction value D2 and become slower than the discharge timing based on the image data. As a result, as shown in FIG. 4(b), all the return path landing positions B2 formed by one return path are displaced to the left by a distance C3 from the desired position indicated by the dashed-dotted line. Due to this displacement distance C3, the path distance, which is the distance between the downstream forward path landing position B1b and the upstream return path landing position B2a in the left-right direction, is reduced compared to the deviation distance C2. Since the deviation of the landing positions between the paths is thus reduced, it is possible to reduce the deterioration of the image quality due to the temperature difference of the liquid in the head 20.

[0043] <Printing method> The printing method is executed by the control device 50 according to the flowchart of an example of the printing method shown in FIG. 6(a). First, the control device 50 acquires image data from an external device (step S1). The control device 50 executes a position correction operation. Here, the control device 50 acquires the ink discharge amount for each region from the image data, assigns waveform selection data corresponding to the discharge amount to the drive element 24 and the drive timing, and generates control data for the drive element 24 for each path. Then, the control device 50 executes a position correction operation for correcting so as to delay the discharge timing from the discharge timing based on the image data (step S2).

[0044] According to the flowchart shown in the example of FIG. 6(b), the control device 50 acquires, as the discharge timing based on the image data, the drive timing of the control data of the return path (step S21). Further, the control device 50 acquires the temperature difference of the ink in the manifold 22 based on the detected temperature of the first temperature sensor 13, and acquires a correction value corresponding to the temperature difference from the predetermined correspondence relationship in FIG. 5 (step S22). Then, the control device 50 corrects the discharge timing so as to delay by the correction value from the discharge timing based on the image data, and acquires this corrected control data (step S23).

[0045] In step S3 of FIG. 6(a), the control device 50 executes a printing operation while driving the driving element 24 with the corrected control data (step S3). As a result, since the return landing position B2 of the return path is displaced by the distance C3, the path distance between the downstream forward landing position B1b and the upstream return landing position B2a in the left-right direction becomes shorter than the deviation distance C2. Therefore, it is possible to reduce the deterioration of the image quality caused by the temperature difference of the liquid in the head 20.

[0046] <Modification 1> The printing apparatus 10 according to Modification 1 includes, in Embodiment 1, a carriage 41 that moves the head 20 in the forward path and the return path in the left-right direction. In the printing operation, the control device 50 alternately executes a forward path in which ink is ejected from the nozzles 21 while moving the head 20 in the forward path, and a return path in which ink is ejected from the nozzles 21 while moving the head 20 in the return path. In the position correction operation, the control device 50 corrects the ejection timing of the ink in either only the forward path or both the forward path and the return path among the forward path and the return path to be later than the ejection timing of the ink based on the image data.

[0047] Specifically, in the position correction operation of FIG. 6(b), the control device 50 acquires the drive timing of the drive element 24 from the control data of the forward path as the ejection timing based on the image data (step S21). Further, the control device 50 acquires the temperature difference of the manifold 22 from the detected temperature of the first temperature sensor 13, and acquires, for example, a correction value D2 corresponding to a temperature difference of E2 or more and E3 from a predetermined correspondence relationship such as FIG. 5 (step S22). Then, without correcting the ejection timing based on the image data of the return path, the control device 50 corrects the control data of the forward path with the correction value so that all the ejection timings in the forward path are later than the ejection timing based on the image data by the correction value.

[0048] The control device 50 executes a printing operation while driving the drive element 24 with the corrected control data (step S3). As a result, as shown in FIG. 7(a), in the forward path where the head 20 moves to the right, all the forward landing positions B1 in the forward path are displaced to the right by a distance C3 from the desired position shown by the two-dot chain line. For this reason, since the path-to-path distance becomes shorter than the deviation distance, it is possible to reduce the deterioration of the image quality due to the temperature difference of the liquid in the head 20.

[0049] Alternatively, in the position correction operation of FIG. 6(b), the control device 50 obtains the drive timing of the drive element 24 from the control data of the forward path and the return path as the discharge timing based on the image data (step S21). Further, the control device 50 obtains, for example, a correction value D2 corresponding to a temperature difference E2 or more and E3 of the manifold 22 from a predetermined correspondence relationship such as FIG. 5 (step S22). Then, the control device 50 corrects the control data of the forward path so that all the discharge timings in the forward path are delayed by a predetermined ratio (for example, D2×d%) of the correction value D2 from the discharge timing based on the image data. Further, the control device 50 corrects the control data of the return path so that all the discharge timings in the return path are delayed by the remaining ratio (for example, D2×(100 - d)%) of the correction value D2 from the discharge timing based on the image data.

[0050] The control device 50 executes a printing operation while driving the drive element 24 with the corrected control data (step S3). As a result, as shown in FIG. 7(b), in the forward path where the head 20 moves to the right, all the forward landing positions B1 in the forward path are displaced to the right by a predetermined ratio (for example, C3×d%) of the distance C3 from the desired position shown by the two-dot chain line. Also, in the return path where the head 20 moves to the left, all the return landing positions B2 in the return path are displaced to the left by the remaining ratio (for example, C3×(100 - d)%) of the distance C3 from the desired position shown by the one-dot chain line. Due to the sum of this displacement distance C3×d% and the displacement distance C3×(100 - d)%, the path-to-path distance becomes shorter than the deviation distance, so it is possible to reduce the deterioration of the image quality due to the temperature difference of the liquid in the head 20.

[0051] <Modification Example 2> In the printing apparatus 10 according to the modification example 2, in the first embodiment and the modification example 1, the return path is executed immediately after the forward path. The ink landing positions include the first ink landing position from the upstream nozzle 21a in the return path, the second ink landing position from the upstream nozzle 21a in the forward path, and the third ink landing position from the downstream nozzle 21b. When the temperature difference is the first temperature difference in the position correction operation, the control device 50 corrects the ejection timing of the ink in the return path so as to be slower than the ejection timing of the ink based on the image data such that the first landing position is arranged farther from the second landing position than the third landing position in the second direction. When the temperature difference is the second temperature difference greater than the first temperature difference, the control device 50 corrects the ejection timing of the ink in the return path so as to be slower than the ejection timing of the ink based on the image data such that the first landing position is arranged closer to the second landing position than the third landing position in the second direction.

[0052] Specifically, the graph of FIG. 8(a) shows the correspondence between the temperature difference of the ink in the manifold 22 and the deviation distance, which is the distance between the downstream landing position and the upstream landing position in the left-right direction. As shown in this graph, the larger the temperature difference, the larger the deviation distance. The rate of change of the deviation distance with respect to this temperature difference is larger when the temperature of the ink supplied from the sub-tank 15 to the manifold 22 is lower than the predetermined temperature Tl than when the temperature of the supplied ink is equal to or higher than the predetermined temperature Th. Therefore, when the temperature difference is E1, the deviation distance Cl at the supply temperature Tl is larger than the deviation distance Ch at the supply temperature Th.

[0053] Thus, when the supply temperature is as low as Tl, since the change in the deviation distance with respect to the temperature difference is large, there may be cases where the deviation distance cannot be sufficiently corrected by the correction value in FIG. 5. For this reason, for example, as shown in FIG. 8(a), in a small temperature range where the temperature difference is 0 or more and less than E1, as shown in FIG. 8(b), a predetermined correspondence relationship with a large correction value with respect to the temperature difference may be used in the position correction operation. The correction value in FIG. 8(b) is larger than the correction value in FIG. 5, and the width of the temperature difference in FIG. 8(b) is narrower than the width of the temperature difference in FIG. 5.

[0054] In the printing method, in step S22 of FIG. 6, the control device 50 acquires a correction value corresponding to the temperature difference from the predetermined correspondence relationship in FIG. 8(b). Then, the control device 50 corrects the ejection timing so as to delay the correction value from the ejection timing based on the image data. As a result, as shown in FIGS. 8(b) and 9, for example, when the temperature difference is equal to or more than a predetermined temperature difference E12 and less than E13, if the ejection timing is delayed by a correction value D12 from the ejection timing based on the image data, the return path landing position B2 is displaced to the left by a displacement distance C12 corresponding to the correction value D12 from the desired position. Thereby, the upstream return path landing position B2a2 of the return path landing position B2 coincides with or approaches the downstream forward path landing position B1b2 of the forward path landing position B1 in the left-right direction, and the inter-path distance decreases more than the deviation distance.

[0055] Also, when the temperature difference is smaller than the predetermined temperature difference, for example, 0 or more and less than E11, if the control device 50 corrects the ejection timing so as to delay the correction value D10 from the ejection timing based on the image data, the upstream return path landing position B2a0 of the return path landing position B2 is corrected to be displaced to the left more than the downstream forward path landing position B1b0 of the forward path landing position B0 by the displacement distance C10 corresponding to the correction value D10. Further, when the temperature difference is smaller than the predetermined temperature difference, for example, equal to or more than E11 and less than E12, similar to the case of 0 or more and less than E11, the upstream return path landing position B2a1 of the return path landing position B2 is corrected to be displaced to the left more than the downstream forward path landing position B1b1 of the forward path landing position B0 by the displacement distance C11 corresponding to the correction value D11.

[0056] On the other hand, when the temperature difference is greater than a predetermined temperature difference, for example, greater than or equal to E13 and less than E14, the control device 50 corrects the ejection timing to be delayed by a correction value D14 from the ejection timing based on the image data. Then, due to the displacement distance C13 corresponding to the correction value D13, the upstream return landing position B2a3 of the return path landing position B2 is corrected to be displaced to the right of the downstream forward path landing position B1b3 of the forward path landing position B0. Also, when the temperature difference is less than a predetermined temperature difference, for example, greater than or equal to E14 and less than E15, similar to the case where the temperature difference is greater than or equal to E13 and less than E14, due to the displacement distance C14 corresponding to the correction value D14, the upstream return landing position B2a4 of the return path landing position B2 is corrected to be displaced to the right of the downstream forward path landing position B1b4 of the forward path landing position B0.

[0057] At the corrected return path landing position B2 and the forward path landing position B1, the path distance between the upstream return landing position B2a and the downstream forward path landing position B1b in the left - right direction is the smallest at the predetermined temperature difference, and increases as the temperature difference deviates from the predetermined temperature. Also, at a temperature difference smaller than the predetermined temperature difference, the upstream return landing position B2a is to the left of the downstream forward path landing position B1b in the left - right direction, and the displacement distance based on the correction value is set to be larger than the deviation distance so that it is located away from the upstream forward path landing position B1a of the downstream forward path landing position B1b. On the other hand, at a temperature difference larger than the predetermined temperature difference, the upstream return landing position B2a is to the right of the downstream forward path landing position B1b in the left - right direction, and the displacement distance based on the correction value is set to be smaller than the deviation distance so that it is located near the upstream forward path landing position B1a of the downstream forward path landing position B1b. Thereby, even when the change in the deviation distance with respect to the temperature difference is large, since the path distance is shorter than the deviation distance, it is possible to reduce the deterioration of the image quality caused by the temperature difference of the liquid in the head 20.

[0058] <Modification Example 3> The printing apparatus 10 according to Modification 3 includes, in Embodiment 1 and Modifications 1-2, a case 16 that houses an ink cartridge 12 and a second temperature sensor 17 that detects the ambient temperature inside the case 16. In the position correction operation, the control device 50 corrects the ink ejection timing based on the ambient temperature in addition to the temperature difference.

[0059] Specifically, as shown in FIG. 1, the case 16 has an internal space, and the ink cartridge 12 is housed in the internal space. The second temperature sensor 17 is a sensor such as a thermistor, and is arranged, for example, in the vicinity of the ink cartridge 12 inside the case 16 so as to detect the temperature of the ink stored in the ink cartridge 12 inside the case 16. As shown in FIG. 2, the second temperature sensor 17 is connected to the control device 50 and outputs the detected temperature to the control device 50.

[0060] As shown in FIG. 8(a), in addition to the temperature difference of the ink in the manifold 22, the deviation distance of the landing position also varies depending on the temperature of the ink flowing into the manifold 22. This ink flows into the manifold 22 from the ink cartridge 12 inside the case 16 via the sub-tank 15. Therefore, the ambient temperature inside the case 16, which is the detected temperature by the second temperature sensor 17, corresponds to the temperature of the ink flowing into the manifold 22. Thus, the control device 50 acquires the detected temperature by the second temperature sensor 17 as the ambient temperature and acquires the temperature difference of the ink in the manifold 22 from the first temperature sensor 13.

[0061] Then, based on the environmental temperature and the temperature difference of the ink, the control device 50 obtains a correction value based on, for example, a predetermined relationship shown in FIG. 10. In FIG. 10, the correspondence relationship between the environmental temperature, the temperature difference of the ink, and the correction value is predetermined in a table and stored in the storage unit 53 such that the correction value increases as the temperature difference of the ink increases and the correction value also increases as the environmental temperature decreases. The control device 50 corrects the correction value and the ejection timing to delay the ejection timing of the ink based on the image data. Thereby, when the control device 50 performs the printing operation with the corrected ejection timing, at least one of the landing positions of the forward path landing position B1 and the return path landing position B2 is displaced by a displacement distance corresponding to the correction value from the desired position. Due to this displacement, the distance between the paths becomes shorter than the deviation distance, so that it is possible to reduce the deterioration of the image quality caused by the temperature difference of the liquid in the head 20.

[0062] <Modification Example 4> In the above, the control device 50 corrected the ejection timing of all the nozzles 21 communicating with the manifold 22 with a correction value corresponding to the temperature difference between the upstream and downstream of the ink in the manifold 22. On the other hand, in the printing apparatus 10 according to the modification example 4, for each one or a plurality of nozzles 21 among the plurality of nozzles 21 communicating with the manifold 22, the ejection timing of the ink is corrected with a correction value corresponding to the temperature difference.

[0063] Specifically, in FIG. 11, the correspondence relationship between the temperature difference of the ink and the rank of the nozzle 21 and the correction value of the ejection timing is predetermined in a table and stored in the storage unit 53. In FIG. 11, the temperature difference of the ink before and after in the manifold 22 is shown in the horizontal direction, and the larger the temperature difference, the larger the correction value. In the vertical direction, the rank of the nozzles 21 arranged in order from the front along the manifold 22 is shown. The upstream nozzle 21a is the first nozzle 21, and the downstream nozzle 21b is the 79th nozzle 21. The larger the rank of this nozzle 21, the larger the distance from the upstream nozzle 21a in the front-rear direction, and the larger the temperature difference from the upstream nozzle 21a, so the correction value is larger. For example, the nozzle 21 has a middle nozzle 21 between the upstream nozzle 21a and the downstream nozzle 21b. Since the downstream nozzle 21b is farther from the upstream nozzle 21a than the middle nozzle 21, the temperature of the ink in the downstream nozzle 21b is higher than that in the middle nozzle 21. Therefore, the temperature difference of the ink between the upstream nozzle 21a and the downstream nozzle 21b is larger than the temperature difference of the ink between the upstream nozzle 21a and the middle nozzle 21, and the correction value for the downstream nozzle 21b is larger than the correction value for the middle nozzle 21.

[0064] In step S22, the control device 50 refers to the predetermined correspondence relationship in FIG. 11 and obtains a correction value for each nozzle 21 from the temperature difference of the ink based on the first temperature sensor 13. For example, when the temperature difference is 5°C, the control device 50 obtains a correction value of 0 for the first to ninth nozzles 21, a correction value of 1 for the tenth to nineteenth nozzles 21, a correction value of 2 for the twentieth to thirty-ninth nozzles 21, a correction value of 3 for the fortieth to fifty-ninth nozzles 21, and a correction value of 4 for the sixtieth to seventy-ninth nozzles 21. Then, the control device 50 does not correct the ink ejection timing from the first to ninth nozzles 21, but corrects the ink ejection timing from the tenth to nineteenth nozzles 21 to be slower by the correction value 1 from the ejection timing based on the image data. The control device 50 also performs the same correction of delaying the ink ejection timing by each correction value from the ejection timing based on the image data for the twentieth to thirty-ninth, fortieth to fifty-ninth, and sixtieth to seventy-ninth nozzles 21 as for the tenth to nineteenth nozzles 21.

[0065] When the control device 50 performs the printing operation with the corrected ejection timing, at least one of the landing positions of the forward path landing position B1 and the return path landing position B2 is displaced from the desired position by a displacement distance corresponding to the correction value. As a result, the displacement distance and the landing position of the ink ejected from the nozzle 21 according to the temperature of the ink are corrected. Therefore, in the left-right direction, the distance between the upstream forward path landing position B1a and the downstream forward path landing position B1b, the distance between the downstream forward path landing position B1b and the upstream return path landing position B2a, and the distance between the upstream return path landing position B2a and the downstream return path landing position B2b become shorter than the deviation distance, so that the deterioration of the image quality due to the temperature difference of the liquid in the head 20 can be reduced.

[0066] <Modification 5> The printing apparatus 10 according to Modification 5 is a line head type as shown in FIG. 12 in Embodiment 1 and Modifications 3-4, and does not include the scanning apparatus 40 in FIG. 1, but includes a head unit 120, a platen 11, a conveyance apparatus 30, an ink cartridge 12, a first temperature sensor 13, a housing 14, and a control apparatus 50. The head unit 120 includes a plurality (for example, four) of heads 20, namely, a first head 20a, a second head 20b, a third head 20c, and a fourth head 20d, and these heads 20 are arranged side by side from left to right in this order. In the head unit 120, these heads 20 are arranged along the left-right direction, and adjacent heads 20 are arranged shifted in the front-rear direction. For this reason, the plurality of heads 20 are arranged side by side in the left-right direction so as to be staggered one by one in the front-rear direction. In the head 20, a manifold 22 extends in the left-right direction, and a plurality of nozzles 21 are arranged along the manifold 22 in the left-right direction to form a nozzle row. The plurality of heads 20 are arranged such that the plurality of nozzles 21 are spaced at equal intervals in the left-right direction and extend longer than the printing medium A in the left-right direction.

[0067] In the printing operation, the control apparatus 50 discharges ink from the nozzles 21 by driving a driving element 24 while conveying the printing medium A forward by the conveyance apparatus 30. For this reason, as shown in FIG. 13, the ink landing positions B3 from the first head 20a, the ink landing position B4 from the second head 20b, the ink landing position B5 from the third head 20c, and the ink landing position B6 from the fourth head 20d are arranged from left to right. Here, if there is a temperature difference between the front and rear ink in the manifold 22, as shown in FIG. 13(a), even when trying to print an image of a straight line indicated by a broken line, the landing positions B3, B4, B5, and B6 based on the image are shifted rearward from the desired positions. Here, the upstream landing position Ba from the upstream nozzle 21a is closest to the desired landing position, and the downstream landing position Bb from the downstream nozzle 21b is shifted by a distance C4 from the desired landing position and is the farthest. For this reason, the control apparatus 50 executes a position correction operation for correcting the ink discharge timing from the nozzles 21 based on the temperature difference so that the distance between the upstream landing position Ba and the downstream landing position Bb in the front-rear direction becomes shorter.

[0068] In step S22, for example, the control device 50 refers to the predetermined correspondence relationship in FIG. 11, and obtains a correction value for each nozzle 21 from the temperature difference of the ink based on the first temperature sensor 13. Then, in step S23, as shown in FIG. 13(b), the control device 50 corrects the ejection timing for each nozzle 21 so as to delay the correction value from the ejection timing based on the image data. Then, when the control device 50 performs the printing operation with the corrected ejection timing, the downstream landing position Bb is displaced forward by a displacement distance corresponding to the correction value. Therefore, in the front-rear direction, since the distance between the upstream landing position Ba and the downstream landing position Bb at each of the landing positions B3, B4, B5, and B6 is shorter than the deviation distance C4, it is possible to reduce the deterioration of the image quality caused by the temperature difference of the liquid in the head 20.

[0069] (Embodiment 2) In the printing apparatus 10 according to Embodiment 2, in Embodiment 1 and Modification Examples 1-5, the control device 50, the image is composed of a plurality of dots. The control device 50 executes a density correction operation for correcting the ejection amount of the ink for the dots based on the image data so that the density difference of the image in the first direction becomes small, based on the temperature difference.

[0070] For example, in the density correction operation, the control device 50 corrects the ejection amount of the ink for the dots at a ratio based on the temperature difference to 0 from among the plurality of dots.

[0071] <Density correction operation> Specifically, the control device 50 acquires the ink ejection amount from the image data and controls the drive element 24 with control data corresponding to the ejection amount. As a result, as shown in FIG. 14, ink is ejected from the nozzles 21 by driving the drive element 24, ink dots are formed on the printing medium A, and an image is printed by the dots. In this case, since the plurality of dots F formed by one pass are ejected from the nozzles 21 arranged in the front-rear direction in the head 20, they are arranged in the front-rear direction. Also, since the ink is ejected from each nozzle 21 while the head 20 moves right or left, the dots are arranged in the left-right direction. The dots F arranged in the left-right direction form a dot row f.

[0072] Here, due to the heat generation of the drive element 24 and the supply of ink from the sub-tank 15 to the manifold 22, the temperature of the ink becomes higher toward the rear in the manifold 22. Along with this, if the drive element 24 is driven by a middle ball waveform signal to eject ink from the nozzles 21 communicating with the manifold 22 and arranged in the front-rear direction, the ink ejection amount will be larger for the rear nozzles 21. Therefore, as shown in FIG. 14, in the dots F formed by the forward path, the upstream forward path dot Fa of the ink from the foremost upstream nozzle 21a is the smallest, the dots F toward the rear are larger, and the downstream forward path dot Fb of the ink from the last downstream nozzle 21b is the largest. For the dots F formed by the return path, similarly to the dots F, the dots F toward the rear are larger. In this way, the dots become larger toward the rear, and the density of the image composed of the dots becomes higher toward the rear. Therefore, the control device 50 performs a density correction operation to correct the ink ejection amount and reduce density unevenness in the image.

[0073] In the concentration correction operation, the control device 50 corrects the discharge amount based on the temperature difference of the ink according to a predetermined correspondence relationship shown in the example of FIG. 15. In the table of FIG. 15, the correction ratio (%) of the discharge amount is predetermined for the temperature difference of the ink and the rank of the nozzle 21 and stored in the storage unit 53. In this table, the temperature difference of the ink before and after in the manifold 22 is shown in the horizontal direction. The greater the temperature difference, the greater the correction ratio of the discharge amount. In the vertical direction, the rank of the nozzle 21 arranged in order from the front along the manifold 22 is shown. The first nozzle 21 is the upstream nozzle 21a arranged at the forefront. The rank increases for the nozzles 21 further back, and the 79th nozzle at the end is the downstream nozzle 21b arranged at the rearmost. For example, when the temperature difference is 4°C, the correction ratio for the 1st - 9th nozzles 21 is 0%, the correction ratio for the 10th - 39th nozzles 21 is 1%, the correction ratio for the 40th - 59th nozzles 21 is 2%, and the correction ratio for the 60th - 79th nozzles 21 is 3%. Thus, as the rank of the nozzle 21 increases, the distance from the upstream nozzle 21a in the front - rear direction increases, and the temperature difference from the upstream nozzle 21a increases, so the correction ratio of the discharge amount is large.

[0074] The correction ratio of the discharge amount is the ratio of the number of dots that correct the discharge amount of the ink forming the dots among the dots based on the image data arranged in the left - right direction, and is represented by the number of correction dots / the number of dots based on the image data × 100. The number of dots based on the image data is the number of dots F formed by the ink from a certain nozzle 21 in one pass, and is the number of dots F in the dot sequence f.

[0075] For example, as shown in FIG. 14, the control device 50 associates the rank of dot F based on the image data arranged from front to back among the dots F formed in one pass with the rank of the nozzles 21 arranged from front to back along the manifold 22. The control device 50 corrects the ink ejection amount based on the image data by a correction ratio corresponding to the temperature difference and the rank of the nozzle 21. For example, when the correction ratio is 3%, among the dots F of the dot sequence f in FIG. 16(a), the ejection amount is corrected to 0 every 33rd dot F33 from the ejection amount based on the image data. For this reason, no ink is ejected from the nozzle 21 at the 33rd ejection timing, and as shown in FIG. 16(b), in the dot sequence f, the dot F33 corresponding to the 33rd ejection timing is not formed on the print medium A.

[0076] Then, the ratio of correcting this ejection amount to 0 is increased as the rank of the nozzle 21 increases, that is, the more rearward the nozzle 21 is. Thereby, the ratio of dots not being formed increases more in the rearward dot sequence f. For this reason, reduction of the density in the rear part of the image is achieved, and uniformity of the density of the image in the front-rear direction is achieved.

[0077] <Printing method> The printing method of the printing apparatus 10 is executed by the control device 50 according to the flowchart shown in the example of FIG. 17(a). In the flowchart of FIG. 17(a), a density correction operation is executed between steps S1 and S2 in the flowchart of FIG. 6(a). This density correction operation is executed by the control device 50 according to the flowchart shown in the example of FIG. 17(b).

[0078] Specifically, first, the control device 50 acquires image data from an external device (step S1). The control device 50 executes a density correction operation for correcting the ejection amount of ink based on the image data (step S4). Here, in the density correction operation of FIG. 17(b), the control device 50 acquires the ejection amount of ink from the image data for each dot formed by the ink (step S41). Further, the control device 50 acquires the temperature difference of the ink in the manifold 22 based on the detected temperature of the first temperature sensor 13. Then, the control device 50 acquires, for each nozzle 21, the correction ratio of the ejection amount corresponding to the temperature difference and the rank of the nozzle 21 from a predetermined correspondence relationship shown in FIG. 15 (step S42). The control device 50 corrects the ejection amount of ink for the dots of the correction ratio to 0 from the ejection amount based on the image data among the dots formed by the ink from each nozzle 21 in one pass (step S43).

[0079] Then, the control device 50 selects a waveform signal for each dot F according to the ejection amount corrected by the density correction operation and the ejection amount based on the other image data, and generates waveform selection data. The control device 50 allocates the waveform selection data to the driving element 24 and the driving timing, and generates control data for the driving element 24 for each pass. Then, the control device 50 executes a position correction operation for correcting the ejection timing of the ink according to the driving timing of the driving element 24 (step S2).

[0080] Then, the control device 50 executes a printing operation while driving the driving element 24 with the control data in which the ejection amount and the ejection timing of the ink are corrected (step S3). As a result, the greater the temperature difference between the front and rear inks in the manifold 22, and the more the rear nozzles 21 among the plurality of nozzles 21 arranged along the manifold 22, the greater the correction ratio of the ejection amount. For this reason, the ratio of not ejecting ink in one pass increases for the rear nozzles 21, and the ratio of not forming dots increases for the rear dot rows. Therefore, due to the temperature difference of the liquid in the head 20, density unevenness where the density becomes higher towards the rear can be reduced, and deterioration of image quality can be reduced.

[0081] <Modification Example 6> In Modification Example 6, in the second embodiment, the dots include first dots and second dots larger than the first dots. In the density correction operation, the control device 50 corrects the ink ejection amount for the dots in a ratio based on the temperature difference to 0 for all the dots including the first dots and the second dots. Hereinafter, the first dots are referred to as small dots Fs, and the second dots are referred to as large dots Fl, but the first dots and the second dots are not limited to these dots.

[0082] Specifically, the control device 50 obtains the ink ejection amount for each dot formed by the ink such that the smaller the gradation pixel value of the image data, the larger the ink ejection amount. As a result, medium dots are formed by medium ink for pixel values within a predetermined range, small dots Fs are formed by small ink for pixel values smaller than the predetermined range, and large dots Fl are formed by large ink for pixel values larger than the predetermined range. In the example of FIG. 18(a), ink is ejected from a certain nozzle 21 according to the image data through the forward path, and the small dots Fs and the large dots Fl are arranged in order from the right in the dot column f in sizes corresponding to the gradation.

[0083] In contrast, in step S43 of FIG. 17(b), the control device 50 corrects the discharge amount of dot F based on the temperature difference to 0 from the discharge amount based on the image data. For example, the control device 50 acquires the correction ratio corresponding to the temperature difference of the ink for each rank of the nozzles 21 based on the predetermined correspondence relationship of FIG. 15. When the temperature difference is 4° C., among the dots based on the image data for each of the nozzles 21 from the 60th to the 79th, the discharge amount for the dots with a correction ratio of 3% is corrected to 0. At this time, as shown in FIG. 18(b), among all the dots F including the small dots Fs and the large dots Fl in the dot column f, the discharge amount for every 33rd dot F33 is corrected to 0 from the small dot or the large dot. For this reason, ink is not discharged from the nozzle 21 every 33rd discharge timing, and in the dot column f, the dot F33 corresponding to the 33rd discharge timing is not formed on the printing medium A. This correction ratio is larger as the temperature difference in the manifold 22 is larger, and is also larger for the rear dot column f. Thus, the reduction of the density in the rear part of the image is achieved, and the density uniformity of the image in the front-rear direction is achieved.

[0084] <Modification Example 7> In the printing apparatus 10 according to Modification Example 7, in Embodiment 2, the dots include the first dot and the second dot larger than the first dot. In the density correction operation, the control device 50 corrects the discharge amount of the ink for the first dot at a ratio based on the temperature difference from the first dot to 0, and corrects the discharge amount of the ink for the second dot at a ratio based on the temperature difference from the second dot to 0.

[0085] Specifically, in the example of FIG. 18(a), when ink is ejected from a certain nozzle 21 according to image data through the forward path, small dots Fs and large dots Fl are sequentially formed from the right in the dot sequence f. On the other hand, in step S42 of FIG. 17(b), for example, the control device 50 acquires a correction ratio corresponding to the temperature difference of the ink for each nozzle 21 rank based on the predetermined correspondence relationship of FIG. 15. In step S43, when the temperature difference is 4°C, the control device 50 corrects the ejection amount of dots corresponding to a correction ratio of 3% among the dots based on the image data for each of the 60th to 79th nozzles 21 to 0.

[0086] At this time, as shown in FIG. 18(c), among the small dots Fs in the dot sequence f, the ejection amount for every 33rd small dot Fs33 from the first small dot Fs1 is corrected from the small ball to 0. Also, among the large dots Fl in the dot sequence f, the ejection amount for every 33rd large dot Fl33 from the first large dot Fl1 is corrected from the large ball to 0. In this way, according to each dot F of the small dot Fs and the large dot Fl, ink is not ejected from the nozzle 21 at the 33rd ejection timing, and in the dot sequence f, the small dot Fs and the large dot Fl corresponding to the 33rd ejection timing are not formed on the printing medium A. Thereby, the reduction of the density at the rear of the image is achieved, and the density uniformity of the image in the front-rear direction is achieved.

[0087] <Modification Example 8> The printing apparatus 10 according to Modification Example 8, in Embodiment 2 and Modification Examples 6-7, the dot F includes a fifth dot and a sixth dot arranged continuously in the first direction, and a seventh dot arranged continuously with the fifth dot in the second direction. In other words, in the first direction, there are no other dots between the fifth dot and the sixth dot. Also, in the second direction, there are no other dots between the fifth dot and the seventh dot. In the density correction operation, the control device 50 corrects the ejection amount of the ink for the seventh dot instead of the fifth dot so that the ejection amounts of the ink for both the fifth dot and the sixth dot are not corrected.

[0088] Specifically, as shown in FIG. 3, the plurality of nozzles 21 communicating with the manifold 22 include a front nozzle 21c and a rear nozzle 21d arranged continuously with the front nozzle 21c behind the front nozzle 21c. In other words, there are no other nozzles 21 between the front nozzle 21c and the rear nozzle 21d. In the example of FIG. 19(a), when ink is ejected from the front nozzle 21c and the rear nozzle 21d according to the image data through the forward path, the front dots Fc formed by the front nozzle 21c are arranged side by side from the right in order from the first front dot Fc1, and the rear dots Fd formed by the rear nozzle 21d are arranged side by side from the right in order from the first rear dot Fd1. The dot row f in which the rear dot Fd1 is arranged in the left - right direction is arranged continuously after the dot row f in which the front dot Fc1 is arranged in the left - right direction. In other words, in the front - rear direction, there is no other dot row f between the rear dot Fd1 and the front dot Fc1.

[0089] On the other hand, in step S42 of FIG. 17(b), for example, the control device 50 acquires a correction ratio corresponding to the temperature difference of the ink for each nozzle 21 rank based on the predetermined correspondence relationship of FIG. 15. In step S43, the control device 50 corrects the ejection amount of the dot F corresponding to the correction ratio to 0 among the dots F based on the image data. For example, when the correction ratio is 3% and the ejection amount based on the image data is medium - sized, as in the example of FIG. 19(b), the control device 50 corrects the ejection amount of the front dots Fc based on the image data from medium - sized to 0 for every 33rd front dot Fc33 in order from the first dot Fc1. Also, the control device 50 corrects the ejection amount of the rear dots Fd based on the image data from medium - sized to 0 for every 33rd rear dot Fd33 in order from the first dot Fd1. As a result, the front dot Fc33 whose ejection amount is corrected and the rear dot Fd33 whose ejection amount is corrected may be arranged continuously in the front - rear direction. In this case, the regions where the dot F is not formed are arranged in the front - rear direction, and since there are no other dots between the front dot Fc33 whose ejection amount is corrected and the rear dot Fd33 whose ejection amount is corrected, it looks like a so - called white streak.

[0090] Therefore, as in the example of FIG. 19(c), the control device 50 corrects the ejection amount for the rear dot Fd1 arranged continuously to the right of this rear dot Fd33 to 0 from the middle dot without correcting the ejection amount for the rear dot Fd33 among the front dot Fc33 and the rear dot Fd33 arranged continuously in the front-rear direction. As a result, since the dots F for which the ejection amount is corrected to 0 based on the image data are not arranged in the front-rear direction, the generation of white streaks is suppressed, and the deterioration of image quality due to the white streaks is reduced.

[0091] Note that instead of the rear dot Fd1, the ejection amount for the rear dot Fd32 arranged continuously to the left of the rear dot Fd33 may be corrected to 0 from the middle dot. Also, among the front dot Fc33 and the rear dot Fd33 arranged continuously in the front-rear direction, the ejection amount for the front dot Fc33 may not be corrected to 0 from the middle dot, and the ejection amount for the front dot Fc1 arranged continuously to the right of this front dot Fc33 may be corrected to 0 from the middle dot.

[0092] <Modification Example 9> The printing apparatus 10 according to Modification Example 9 includes, in Embodiment 2 and Modification Examples 6-8, dots including an eighth dot, a ninth dot, and a tenth dot arranged continuously in the second direction. In other words, there are no other dots between the eighth dot and the ninth dot in the second direction. Also, there are no other dots between the ninth dot and the tenth dot in the second direction. In the density correction operation, the control device 50 corrects the ejection amount of ink for the tenth dot instead of the ninth dot so that the ejection amounts of ink for both the eighth dot and the ninth dot are not corrected.

[0093] Specifically, in the example of FIG. 20(a), when ink is ejected from a certain nozzle 21 according to image data through the forward path, small dots Fs and large dots Fl are sequentially formed from the right in the dot sequence f. On the other hand, in step S42 of FIG. 17(b), for example, the control device 50 acquires a correction ratio corresponding to the temperature difference of the ink for each nozzle 21 rank based on the predetermined correspondence relationship of FIG. 15. In step S43, when the temperature difference is 4°C, the control device 50 corrects the ejection amount of dots F with a correction ratio of 3% among the dots based on the image data for each of the 60th to 79th nozzles 21 to 0. As a result, as shown in FIG. 20(b), among the small dots Fs in the dot sequence f based on the image data, the ejection amount for every 33rd small dot Fs33 is corrected from the small droplet to 0. Also, among the large dots Fl in the dot sequence f based on the image data, the ejection amount for every 33rd large dot Fl33 is corrected from the large droplet to 0. In this case, the small dots Fs33 whose ejection amount is corrected and the large dots Fl33 whose ejection amount is corrected may be arranged continuously in the left-right direction. In this case, regions where dots F are not formed are arranged in the left-right direction, and since there are no other dots between the small dots Fs33 whose ejection amount is corrected and the large dots Fl33 whose ejection amount is corrected, a local density decrease occurs.

[0094] Therefore, as in the example of FIG. 20(c), the control device 50 does not correct the ejection amount for the small dots Fs33 among the small dots Fs33 and large dots Fl33 arranged continuously in the left-right direction, but corrects the ejection amount for the small dots Fs1 arranged continuously in the left-right direction with these small dots Fs33 from the small droplet to 0. As a result, since the dots F whose ejection amount is corrected to 0 based on the image data are not arranged continuously in the left-right direction, that is, since there are small dots Fs33 between the large dots Fl33 and the small dots Fs1, the occurrence of local density decrease is suppressed, and the deterioration of image quality due to local density decrease is reduced. Note that instead of the small dots Fs1, the ejection amount for the large dots Fl32 arranged continuously in the left-right direction with the large dots Fl33 may be corrected from the large droplet to 0.

[0095] <Modification Example 10> The printing apparatus 10 according to Modification 10 includes, in Embodiment 2 and Modifications 8-9, dots including a third dot upstream of a predetermined position in the first direction and a fourth dot downstream of the predetermined position in the first direction. In the density correction operation, the control device 50 corrects the ink discharge amount for the third dot so that the size of the third dot based on the temperature difference is larger than the size of the dot based on the image data, starting from the third dot. In the density correction operation, the control device 50 corrects the ink discharge amount for the fourth dot so that the size of the fourth dot based on the temperature difference is smaller than the size of the dot based on the image data, starting from the fourth dot.

[0096] Specifically, in the density correction operation, in step S42 of FIG. 17(b), the control device 50 acquires, for each nozzle 21, a correction ratio based on the temperature difference of the ink, based on a table of a predetermined correspondence shown in the example of FIG. 21. In the table of FIG. 21, the correction ratio (%) of the discharge amount is predetermined for the temperature difference of the ink and the rank of the nozzle 21 and is stored in the storage unit 53. In the horizontal direction in this table, the temperature difference of the ink before and after in the manifold 22 is shown, and the larger the temperature difference, the larger the correction ratio of the discharge amount.

[0097] In the vertical direction, the order of the nozzles 21 arranged in order from the front along the manifold 22 is shown. The correction ratio for the nozzles 21 of a predetermined order is 0%. The smaller the order is than the predetermined order, and the larger the order is than the predetermined order, the larger the correction ratio of the discharge amount. For example, the nozzles 21 of a predetermined order are the nozzles 21 arranged at the center in the front-rear direction, or a plurality of nozzles 21 including the central nozzle 21. When the temperature difference is 4 °C, the 30th to 49th nozzles 21 are the nozzles 21 of a predetermined order, and the correction ratio for this nozzle 21 is 0%. The correction ratio for the 20th to 29th nozzles 21 whose order is smaller than this predetermined order, and the 50th to 59th nozzles 21 whose order is smaller than this predetermined order is 1%. Further, the correction ratio for the 10th to 19th nozzles 21 whose order is smaller than these nozzles 21, and the 60th to 69th nozzles 21 whose order is larger is 2%. Further, the correction ratio for the 1st to 9th nozzles 21 whose order is smaller than these nozzles 21, and the 70th to 79th nozzles 21 whose order is larger is 3%.

[0098] In step S43 of FIG. 17(b), the control device 50 corrects the discharge amount so as to be larger than the discharge amount based on the image data for the nozzles 21 whose order is smaller than the predetermined order, that is, the nozzles 21 in front of the predetermined position in the front-rear direction. Further, the control device 50 corrects the discharge amount so as to be smaller than the discharge amount based on the image data for the nozzles 21 whose order is larger than the predetermined order, that is, the nozzles 21 behind the predetermined position in the front-rear direction.

[0099] For example, when the temperature difference is 4°C, the ink ejection amounts from the 30th to 49th nozzles 21 are not corrected. In contrast, for the 1st to 9th nozzles 21 and the 60th to 79th nozzles 21, among the dots based on the image data shown in Fig. 22(b), the ejection amounts for the dots with a correction ratio of 3% are corrected. At this time, the control device 50 corrects the ejection amounts of the 1st to 9th nozzles 21 so that the 33rd small dot Fs33 based on the image data shown in Fig. 22(b) becomes the large dot Fl33 as shown in Fig. 22(a), increasing the ejection amount from the small droplet to the large droplet. Also, the control device 50 corrects the ejection amounts of the 60th to 79th nozzles 21 so that the 33rd large dot Fl33 based on the image data shown in Fig. 22(b) becomes the small dot Fs33 as shown in Fig. 22(c), decreasing the ejection amount from the large droplet to the small droplet.

[0100] As a result, among the dots in the image, the size of dot F is larger in front of the predetermined position, and the ratio of the dots that become larger increases as the temperature difference becomes larger and as the dots in front become larger. Also, among the dots in the image, the size of dot F is smaller behind the predetermined position, and the ratio of the dots that become smaller increases as the temperature difference becomes larger and as the dots behind become smaller. Thereby, the density increases more towards the front and decreases more towards the back in the image, so that the density of the image in the front-back direction is equalized.

[0101] <Modification Example 11> In the printing apparatus 10 according to Modification Example 11, in Embodiment 2, the control device 50 corrects the ejection amount of ink for the dots so that the size of a ratio of dots based on the temperature difference becomes larger than the size of the dots based on the image data from among a plurality of dots in the density correction operation.

[0102] Specifically, in the density correction operation, at step S42 in FIG. 17(b), the control device 50 acquires, for each nozzle 21, a correction ratio based on the temperature difference of the ink based on a table of a predetermined correspondence relationship shown in the example of FIG. 23. In the table of FIG. 23, the correction ratio (%) of the discharge amount is predetermined for the temperature difference of the ink and the rank of the nozzle 21 and is stored in the storage unit 53. In this table, the temperature difference of the ink before and after in the manifold 22 is shown in the horizontal direction, and the larger the temperature difference, the larger the correction ratio of the discharge amount.

[0103] Also, in the vertical direction, the ranks of the nozzles 21 arranged in order from the front along the manifold 22 are shown. For example, when the temperature difference is 4°C, the correction ratio for the 1st - 9th nozzles 21 is 4%, the correction ratio for the 10th - 29th nozzles 21 is 3%, the correction ratio for the 30th - 49th nozzles 21 is 2%, the correction ratio for the 50th - 69th nozzles 21 is 1%, and the correction ratio for the 70th - 79th nozzles 21 is 0%. Thus, the smaller the rank of the nozzle 21, that is, the closer the nozzle 21 is to the upstream nozzle 21a, the larger the correction ratio of the discharge amount.

[0104] In step S43 of FIG. 17(b), for example, when the temperature difference is 4° C., regarding the ink ejection amounts from the 10th to 29th nozzles 21, the control device 50 corrects the ejection amounts for the dots corresponding to 3% of the dots based on the image data shown in FIG. 22(b) to be larger than the ejection amounts based on the image data. That is, in the dot sequence f, the control device 50 corrects the ejection amount so that the 33rd small dot Fs33 based on the image data shown in FIG. 22(b) becomes a large dot Fl33 as shown in FIG. 22(a), changing the ejection amount from a small droplet to a large droplet. At this time, when the 33rd dot F among all the dots F included in the dot sequence f is a small dot, the ejection amount may be corrected from a small droplet to a large droplet. Also, among the small dots F included in the dot sequence f, the ejection amount for the 33rd small dot may be corrected from a small droplet to a large droplet. In this way, in the image, the size of the dots F in the front is large, and the ratio of the dots that become large increases as the temperature difference is larger and as the dots F in the front are closer. As a result, the density in the image increases more towards the front, thereby achieving uniform density of the image in the front-rear direction.

[0105] Note that also in Modifications 10 and 11, when the ejection amounts for the fifth dot and the sixth dot arranged continuously in the first direction are corrected, since there is no blank between the fifth dot and the sixth dot, there is a risk of appearing as so-called black streaks. For this reason, as in Modification 8, the control device 50 corrects the ejection amount of the ink for the seventh dot instead of the fifth dot so that the ejection amounts of the ink for both the fifth dot and the sixth dot are not corrected in the density correction operation. Thereby, the generation of black streaks is reduced, and the deterioration of the image quality due to black streaks can be suppressed.

[0106] <Modification 12> In the printing apparatus 10 according to Modification 12, in Embodiment 2, the control device 50 corrects the ejection amount of the ink for the dots so that the sizes of a ratio of the dots based on the temperature difference are smaller than the sizes of the dots based on the image data from among a plurality of dots in the density correction operation.

[0107] Specifically, in the density correction operation, in step S42 of FIG. 17(b), the control device 50 acquires, for each nozzle 21, a correction ratio based on the temperature difference of the ink, based on a table of a predetermined correspondence relationship shown in the example of FIG. 24. In the table of FIG. 24, the correction ratio (%) of the discharge amount is predetermined for the temperature difference of the ink and the rank of the nozzle 21 and is stored in the storage unit 53. In this table, the temperature difference of the ink before and after in the manifold 22 is shown horizontally, and the greater the temperature difference, the greater the correction ratio of the discharge amount.

[0108] Also, vertically, the ranks of the nozzles 21 arranged in order from the front along the manifold 22 are shown. For example, when the temperature difference is 4°C, the correction ratio for the 1st - 9th nozzles 21 is 0%, the correction ratio for the 10th - 39th nozzles 21 is 1%, the correction ratio for the 40th - 59th nozzles 21 is 2%, the correction ratio for the 50th - 69th nozzles 21 is 2%, and the correction ratio for the 60th - 79th nozzles 21 is 3%. Thus, the greater the rank of the nozzle 21, that is, the more downstream the nozzle 21, the farther it is from the upstream nozzle 21a, and the greater the temperature difference from the upstream nozzle 21a, so the correction ratio of the discharge amount is greater.

[0109] In step S43 of FIG. 17(b), for example, when the temperature difference is 4° C., regarding the ink ejection amounts from the 60th to 79th nozzles 21, the control device 50 corrects the ejection amounts for the dots corresponding to 3% of the correction ratio among the dots based on the image data shown in FIG. 22(b) to be less than the ejection amounts based on the image data. That is, the control device 50 corrects the 33rd large dot Fl33 based on the image data shown in FIG. 22(b) to be a small dot Fs33 as shown in FIG. 22(c), and corrects the ejection amount from the large dot based on the image data to a small dot. At this time, when the 33rd dot F among all the dots F included in the dot sequence f is a large dot, this ejection amount may be corrected from the large dot to the small dot. Also, the ejection amount for the 33rd large dot among the large dots F included in the dot sequence f may be corrected from the large dot to the small dot. In this way, in the image, the size of the dots F at the rear is small, and the ratio of the dots that become smaller increases as the temperature difference is larger and as the dots F at the rear are more. As a result, since the density of the image decreases more towards the rear, the density uniformity of the image in the front-rear direction is achieved.

[0110] In addition, also in Modifications 10 and 12, when the ejection amounts for the fifth dot and the sixth dot arranged continuously in the first direction are corrected, since there are no other dots between the fifth dot and the sixth dot, there is a possibility of appearing as a so-called white streak. Therefore, as in Modification 8, the control device 50 corrects the ejection amount of the ink for the seventh dot instead of the fifth dot so that the ejection amounts of the ink for both the fifth dot and the sixth dot are not corrected in the density correction operation. Thereby, the generation of white streaks is reduced, and the deterioration of the image quality due to white streaks can be suppressed.

[0111] <Modification 13> In the case of Modification 13, in Embodiment 2, the printing operation of the printing apparatus 10 includes a first mode, a second mode in which color development is enhanced compared to the first mode, and a third mode in which the ink consumption is reduced compared to the first mode. The dots include a third dot upstream of a predetermined position in the first direction and a fourth dot downstream of the predetermined position in the first direction. In the density correction operation, when performing the printing operation in the first mode, the control device 50 corrects the ink ejection amount for the third dot so that the size of the third dot at a ratio based on the temperature difference becomes larger than the size of the dot based on the image data from the third dot, and corrects the ink ejection amount for the fourth dot so that the size of the fourth dot at a ratio based on the temperature difference becomes smaller than the size of the dot based on the image data from the fourth dot. In the density correction operation, when performing the printing operation in the second mode, the control device 50 corrects the ink ejection amount for the dots so that the size of the dots at a ratio based on the temperature difference becomes larger than the size of the dots based on the image data from a plurality of dots based on the image data. In the density correction operation, when performing the printing operation in the third mode, the control device 50 corrects the ink ejection amount for the dots to be recorded so that the size of the dots at a ratio based on the temperature difference becomes smaller than the size of the dots based on the image data from a plurality of dots based on the image data.

[0112] Specifically, when performing the printing operation in the first mode in step S3 of FIG. 17(a), in the density correction operation, in step S42 of FIG. 17(b), the control device 50 obtains a correction ratio for each nozzle 21 based on the temperature difference of the ink according to a predetermined correspondence shown in the example of FIG. 21. Then, in the process of step S43, similar to Modification 10, the control device 50 corrects the discharge amount of the nozzles 21 in front of a predetermined position in the front-rear direction to be larger than the discharge amount based on the image data. Also, the control device 50 corrects the discharge amount of the nozzles 21 behind a predetermined position in the front-rear direction to be smaller than the discharge amount based on the image data. As a result, among the dots in the image, the size of the dots F in the front is large, and the ratio of the dots that become large is larger for a larger temperature difference, and is also larger for the dots F in the front. Also, among the dots in the image, the size of the dots F in the rear is small, and the ratio of the dots that become small is larger for a larger temperature difference, and is also larger for the dots F in the rear. As a result, the density of the image increases more towards the front and decreases more towards the rear, so that the density uniformity of the image in the front-rear direction is achieved.

[0113] Also, when performing the printing operation in the second mode in step S3 of FIG. 17(a), in the density correction operation, in step S42 of FIG. 17(b), the control device 50 obtains a correction ratio for each nozzle 21 based on the temperature difference of the ink according to a predetermined correspondence shown in the example of FIG. 23. Then, in the process of step S43, similar to the process in Modification 11, the control device 50 corrects the discharge amount of the dots corresponding to the correction ratio among the dots based on the image data to be larger than the discharge amount based on the image data. As a result, while enhancing the color development of the image, the size of the dots F in the front of the image is large, and the ratio of the dots that become large is larger for a larger temperature difference, and is also larger for the dots F in the front. As a result, the density of the image increases more towards the front, so that the density uniformity of the image in the front-rear direction is achieved.

[0114] Also, when executing the printing operation in the third mode in step S3 of FIG. 17(a), in the density correction operation, in step S42 of FIG. 17(b), the control device 50 obtains a correction ratio for each nozzle 21 based on the temperature difference of the ink according to a predetermined correspondence relationship shown in the example of FIG. 24. Then, in the process of step S43, the control device 50 corrects the discharge amount of the dots corresponding to the correction ratio among the dots based on the image data to be less than the discharge amount based on the image data, in the same way as the process in Modification 12. Thereby, while reducing the ink consumption, in the image, the size of the dots F at the rear is small, and the ratio of the dots that become smaller is larger for a larger temperature difference, and also larger for the rear dots F. As a result, since the density of the image decreases more towards the rear, the density uniformity of the image in the front-rear direction is achieved.

[0115] <Modification 14> In the printing apparatus 10 according to Modification 16, in Embodiment 2 and Modifications 6-9, the printing medium A includes a landing possible region G1 which is a region where ink can land, and a mask region G0 which is a region where the discharge amount of ink is corrected to 0 in the density correction operation. Here, for example, there are more mask regions G0 towards the downstream in the first direction on the printing medium A.

[0116] Specifically, in the density correction operation in step S4 of FIG. 17(a), in step S41 of FIG. 17(b), the control device 50 divides the image data corresponding to the printing medium A into a plurality of regions as shown in FIG. 25(a), and obtains the discharge amount of ink for each of these regions based on the harmony. Also, the control device 50 obtains, for each nozzle 21, a correction ratio of the discharge amount corresponding to the temperature difference of the ink in the manifold 22 and the rank of the nozzle 21 from the predetermined correspondence relationship shown in FIG. 15 (step S42).

[0117] Here, the control device 50 associates the ranking of the area G of the image data arranged in order from the front with the ranking of the nozzles 21 arranged in order from the front along the manifold 22. The control device 50 corrects the ink ejection amount for the area G of the correction ratio to 0 from the ejection amount based on the image data among the areas G where ink is ejected from the nozzles 21. As a result, among the areas G with small, medium, and large ejection amounts in the area row g where a plurality of areas G are arranged in the left - right direction, the area G with the correction ratio is set as the mask area G0 with an ejection amount of 0. Also, the area G other than the mask area is set as the landing - possible area G1.

[0118] Then, in the position - correction operation of step S2 in FIG. 17(a), the control device 50 selects a waveform signal corresponding to the corrected ejection amount and other ejection amounts to generate waveform - selection data, and assigns the waveform - selection data to the driving element 24 and the driving timing. Then, in the printing operation of step S3 in FIG. 17(a), the control device 50 corrects the driving timing so that it is slower than the ejection timing based on the image data, using the driving timing as the ink ejection timing. Then, in the printing operation of step S3 in FIG. 17(a), the control device 50 outputs control data with the ink ejection amount and ejection timing corrected to the driving element 24 via the head - driving circuit 25. As a result, ink is ejected onto the printing medium A by driving the driving element 24, and as shown in FIG. 25(c), dots F based on the image data are not formed in the mask area G0, and dots F based on the image data are formed in the landing - possible area G1.

[0119] And the ratio of the mask area G0 whose ejection amount is corrected to 0 in the area row g is made larger for the rear area row g. As a result, the ratio of the dots F not being formed increases for the rear dot row f. Since this mask area G0 is larger as the temperature difference in the manifold 22 is larger and also larger for the rear area row g, the density reduction at the rear of the image is achieved, and the density uniformity of the image in the front - rear direction is achieved.

[0120] In addition, in Modification 16 as well, when the mask region G0 is set in two regions arranged continuously in the first direction, dots are not formed between the two regions, so there is a risk of appearing as so-called white streaks. For this reason, as in Modification 8, in the density correction operation, the control device 50 corrects the ink ejection amount for the seventh dot to 0 instead of the fifth dot so that the ink ejection amounts for both the fifth dot and the sixth dot are not corrected. As a result, the region G of the seventh dot is set as the mask region G0. Therefore, the generation of white streaks due to the mask region G0 is reduced, and the deterioration of image quality due to white streaks can be suppressed.

[0121] <Modification 15> The printing apparatus 10 according to Modification 15 includes, in Embodiment 2 and Modifications 6 - 14, a case 16 that houses the ink cartridge 12 and a second temperature sensor 17 that detects the ambient temperature inside the case 16. In the density correction operation, the control device 50 corrects the ink ejection amount based on the ambient temperature detected by the second temperature sensor 17 in addition to the temperature difference.

[0122] Specifically, as shown in FIG. 1, the case 16 houses the ink cartridge 12. The second temperature sensor 17 detects the temperature inside the case 16 as the ambient temperature and outputs it to the control device 50. Since the temperature of the ink flowing into the manifold 22 depends on the ambient temperature, the size of the dot F also varies depending on the ambient temperature as well as the temperature difference before and after in the manifold 22. Therefore, the control device 50 acquires the detected temperature by the second temperature sensor 17 as the ambient temperature and also acquires the temperature difference of the ink in the manifold 22 from the first temperature sensor 13.

[0123] The control device 50 acquires, for each nozzle 21, a correction ratio corresponding to the temperature difference of the ink based on a predetermined relationship shown in the example of FIG. 15, FIG. 21, FIG. 23, or FIG. 24. Further, the control device 50 acquires a magnification corresponding to the ambient temperature based on a table showing a predetermined correspondence between the ambient temperature and the magnification shown in the example of FIG. 26. Then, the control device 50 multiplies the correction ratio by the magnification to correct the correction ratio. In FIG. 26, as the ambient temperature is lower, the viscosity change with respect to the temperature difference is larger, so the magnification becomes larger and the corrected correction ratio becomes larger. The control device 50 corrects the ejection amount of the ink for the dots with the corrected correction ratio among the dots based on the image data from the ejection amount based on the image data. As a result, since the reduction amount of the size or the number of the dots F constituting the image becomes larger toward the rear of the image, the density unevenness of the image in the front-rear direction can be reduced.

[0124] <Other Modification Examples> In all of the above-described embodiments and modification examples, the first temperature sensor 13 includes an upstream temperature sensor 13a and a downstream temperature sensor 13b, and the control device 50 acquires the difference between the detected temperatures of these temperature sensors as the temperature difference of the ink before and after in the manifold 22. However, the method for acquiring the temperature difference is not limited to this. For example, the first temperature sensor 13 has a reference contact and a measurement contact of a thermocouple, and this reference contact is arranged in the vicinity of the upstream of the manifold 22, and the measurement contact is arranged in the vicinity of the downstream of the manifold 22. Thereby, the first temperature sensor 13 detects the temperature difference of the ink before and after in the manifold 22 and outputs it to the control device 50.

[0125] In all of the above-described embodiments and modification examples, a thermistor is used for the first temperature sensor 13, but the first temperature sensor 13 is not limited to this. For example, when the drive element 24 is arranged above or in the vicinity of the manifold 22, the current of the drive element 24 due to residual vibration and the capacitance of the drive element 24 depend on the temperature of the ink in the manifold 22. For this reason, a sensor that detects the current of the drive element 24 due to residual vibration and a sensor that detects the capacitance of the drive element 24 are used as the first temperature sensor 13.

[0126] Specifically, by driving the driving element 24, a pressure wave is supplied to the ink, causing the ink to be ejected from the nozzle 21 or causing the meniscus formed on the nozzle 21 to oscillate. The pressure wave does not immediately disappear when the ink is ejected from the nozzle 21 or the meniscus formed on the nozzle 21 oscillates, but remains in the ink as residual vibration. This residual vibration deforms the stationary driving element 24 and generates an electric current from the driving element 24. The electric current generated by this residual vibration and the amplitude of the residual vibration of the ink have a predetermined correspondence. Further, since the amplitude of the residual vibration of the ink depends on the viscosity of the ink and the viscosity of the ink depends on the temperature of the ink, the amplitude of the residual vibration and the temperature of the ink have a predetermined correspondence. Therefore, based on a table showing the predetermined correspondence between the electric current of the driving element 24 generated by the residual vibration and the temperature of the ink, the temperature of the ink can be obtained from the electric current of the driving element 24. Thus, the sensor that detects the electric current of the driving element 24 due to the residual vibration is used as the first temperature sensor 13.

[0127] In addition, the driving element 24 is disposed via a diaphragm (not shown) between the individual flow path 23. Since the thickness of the diaphragm is as thin as several μm to several tens of μm or the material of the diaphragm has thermal conductivity such as SUS, the heat of the ink flowing through the individual flow path 23 is transmitted to the driving element 24 via the diaphragm. Further, when the driving element 24 is a piezo, the capacitance of the driving element 24 is affected by the temperature of the ink flowing through the individual flow path 23. That is, the capacitance of the driving element 24 depends on the temperature of the ink in the manifold 22. Therefore, based on a table of the predetermined correspondence between the capacitance of the driving element 24 and the temperature of the ink in the manifold 22, the temperature of the ink can be obtained from the capacitance of the driving element 24. Thus, the sensor that detects the capacitance of the driving element 24 when driving the driving element 24 is used as the first temperature sensor 13.

[0128] Note that the above-described embodiments may be combined with each other as long as they do not exclude each other. Also, from the above description, many improvements and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and provided for the purpose of teaching those skilled in the art the best mode of carrying out the present invention. Without departing from the spirit of the present invention, the details of its structure and / or function can be substantially changed.

Industrial Applicability

[0129] The present invention can be applied to a printing apparatus, a printing method, and a program that can reduce a decrease in image quality caused by a temperature difference of a liquid in a head.

Explanation of Reference Numerals

[0130] 10: Printing apparatus 12: Ink cartridge 13: First temperature sensor 16: Case 17: Second temperature sensor 20: Head 21: Nozzle 22: Manifold 24: Driving element 41: Carriage 50: Control device

Claims

1. A head having a plurality of nozzles arranged in a first direction, a manifold communicated with the plurality of nozzles, and a driving element for applying a discharge pressure to the ink, a first temperature sensor for detecting a temperature difference of the ink upstream and downstream in the first direction in the manifold, a control device, wherein the plurality of nozzles have a first nozzle arranged upstream in the first direction and a second nozzle arranged downstream in the first direction, the control device performs a printing operation of discharging the ink from the nozzles onto a printing medium based on image data to form an image with the ink landed on the printing medium, and a position correction operation of correcting the discharge timing of the ink from the nozzles based on the temperature difference so that the distance between the landing positions of the ink discharged from the first nozzle and the landing position of the ink discharged from the second nozzle in a second direction intersecting the first direction is shortened. A printing apparatus.

2. A carriage for moving the head in a forward path and a return path in the second direction, the control device in the printing operation, alternately executes a forward path for discharging the ink from the nozzles while moving the head in the forward path and a return path for discharging the ink from the nozzles while moving the head in the return path, in the position correction operation, corrects the discharge timing of the ink in any one of only the forward path, only the return path, and both the forward path and the return path among the forward path and the return path to be slower than the discharge timing of the ink based on the image data. The printing apparatus according to claim 1.

3. The control device corrects the discharge timing of the ink in the return path to be slower than the discharge timing of the ink based on the image data without correcting the discharge timing of the ink in the forward path in the position correction operation. The printing apparatus according to claim 2.

4. The return path is executed immediately after the forward path, the landing positions of the ink include a first landing position of the ink from the first nozzle in the return path, a second landing position of the ink from the first nozzle in the forward path, and a third landing position of the ink from the second nozzle in the forward path. In the position correction operation, the control device when the temperature difference is the first temperature difference, corrects the ejection timing of the ink in the return path so that the first landing position is arranged farther from the second landing position than the third landing position in the second direction, and delays the ejection timing of the ink in the return path from the ejection timing of the ink based on the image data; The printing apparatus according to claim 2 or 3, wherein when the temperature difference is a second temperature difference greater than the first temperature difference, the ejection timing of the ink in the return path is corrected so that the first landing position is arranged closer to the second landing position than the third landing position in the second direction, and the ejection timing of the ink in the return path is delayed from the ejection timing of the ink based on the image data.

5. a case for accommodating an ink cartridge; a second temperature sensor for detecting the ambient temperature in the case, and The printing apparatus according to any one of claims 1 to 4, wherein the control device corrects the ejection timing of the ink based on the ambient temperature in addition to the temperature difference in the position correction operation.

6. The image is composed of a plurality of dots, The printing apparatus according to any one of claims 1 to 5, wherein the control device executes a density correction operation of correcting the ejection amount of the ink based on the temperature difference so that the density difference of the image in the first direction becomes small, with respect to the dots based on the image data.

7. The printing apparatus according to claim 6, wherein in the density correction operation, the control device corrects the ejection amount of the ink for the dots at a ratio based on the temperature difference to 0 from among the plurality of dots.

8. The dots include a first dot and a second dot larger than the first dot, The printing apparatus according to claim 7, wherein in the density correction operation, the control device corrects the ejection amount of the ink for the dots at a ratio based on the temperature difference to 0 from among all the dots including the first dot and the second dot.

9. The dots include a first dot and a second dot larger than the first dot, In the density correction operation, the control device corrects the ejection amount of the ink for the first dots at a ratio based on the temperature difference to 0 from among the first dots, The printing apparatus according to claim 7, wherein the discharge amount of the ink with respect to the second dot is corrected to 0 from the second dot by a ratio based on the temperature difference.

10. The dot includes a third dot upstream of a predetermined position in the first direction and a fourth dot downstream of the predetermined position in the first direction. In the density correction operation, the control device corrects the discharge amount of the ink with respect to the third dot so that the size of the third dot by a ratio based on the temperature difference becomes larger than the size of the dot based on the image data, from the third dot. The printing apparatus according to claim 6, wherein the discharge amount of the ink with respect to the fourth dot is corrected so that the size of the fourth dot by a ratio based on the temperature difference becomes smaller than the size of the dot based on the image data, from the fourth dot.

11. The printing apparatus according to claim 6, wherein in the density correction operation, the control device corrects the discharge amount of the ink with respect to the dot so that the size of the dot by a ratio based on the temperature difference becomes larger than the size of the dot based on the image data, from a plurality of the dots.

12. The printing apparatus according to claim 6, wherein in the density correction operation, the control device corrects the discharge amount of the ink with respect to the dot so that the size of the dot by a ratio based on the temperature difference becomes smaller than the size of the dot based on the image data, from a plurality of the dots.

13. The printing operation includes a first mode, a second mode in which color development is enhanced compared to the first mode, and a third mode in which the ink consumption is reduced compared to the first mode. The dot includes a third dot upstream of a predetermined position in the first direction and a fourth dot downstream of the predetermined position in the first direction. In the density correction operation, the control device When performing the printing operation in the first mode corrects the discharge amount of the ink with respect to the third dot so that the size of the third dot by a ratio based on the temperature difference becomes larger than the size of the dot based on the image data, from the third dot. corrects the discharge amount of the ink with respect to the fourth dot so that the size of the fourth dot by a ratio based on the temperature difference becomes smaller than the size of the dot based on the image data, from the fourth dot. When performing the printing operation in the second mode, the ejection amount of the ink for the dots is corrected so that the size of a proportion of the dots based on the temperature difference is larger than the size of the dots based on the image data from among the plurality of dots. The printing apparatus according to claim 6, wherein when performing the printing operation in the third mode, the ejection amount of the ink for the dots is corrected so that the size of a proportion of the dots based on the temperature difference is smaller than the size of the dots based on the image data from among the plurality of dots.

14. The printing apparatus according to claim 7, wherein the printing medium includes a landing area where the ink can land and a mask area where the ejection amount of the ink is corrected to zero in the density correction operation.

15. The printing apparatus according to claim 14, wherein the mask area increases downstream in the first direction on the printing medium.

16. The dots include a fifth dot and a sixth dot arranged continuously in the first direction, and a seventh dot arranged continuously with the fifth dot in the second direction. The printing apparatus according to any one of claims 6 to 15, wherein in the density correction operation, the control device corrects the ejection amount of the ink for the seventh dot instead of the fifth dot so that the ejection amounts of the ink for both the fifth dot and the sixth dot are not corrected.

17. The dots include an eighth dot, a ninth dot, and a tenth dot arranged continuously in the second direction. The printing apparatus according to any one of claims 6 to 16, wherein in the density correction operation, the control device corrects the ejection amount of the ink for the tenth dot instead of the ninth dot so that the ejection amounts of the ink for both the eighth dot and the ninth dot are not corrected.

18. A case for accommodating an ink cartridge. A second temperature sensor for detecting the ambient temperature inside the case. The printing apparatus according to any one of claims 6 to 17, wherein in the density correction operation, the control device corrects the ejection amount of the ink based on the ambient temperature detected by the second temperature sensor in addition to the temperature difference.

19. A head having a plurality of nozzles arranged in a first direction, a manifold communicating with the plurality of nozzles, and a drive element that applies a discharge pressure to ink, A first temperature sensor that detects a temperature difference of the ink upstream and downstream in the first direction in the manifold, A printing method for a printing apparatus in which the plurality of nozzles have a first nozzle arranged upstream in the first direction and a second nozzle arranged downstream in the first direction, A printing operation of discharging the ink from the nozzles onto a printing medium based on image data and forming an image with the ink landed on the printing medium, A position correction operation of correcting the discharge timing of the ink from the nozzles based on the temperature difference so that the distance between the landing positions of the ink discharged from the first nozzle and the ink discharged from the second nozzle in a second direction intersecting the first direction is shortened.

20. A head having a plurality of nozzles arranged in a first direction, a manifold communicating with the plurality of nozzles, and a drive element that applies a discharge pressure to ink, A first temperature sensor that detects a temperature difference of the ink upstream and downstream in the first direction in the manifold, A program for a computer of a printing apparatus in which the plurality of nozzles have a first nozzle arranged upstream in the first direction and a second nozzle arranged downstream in the first direction, A printing operation of discharging the ink from the nozzles onto a printing medium based on image data and forming an image with the ink landed on the printing medium, A position correction operation of correcting the discharge timing of the ink from the nozzles based on the temperature difference so that the distance between the landing positions of the ink discharged from the first nozzle and the ink discharged from the second nozzle in a second direction intersecting the first direction is shortened.

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