JP7247716B2 - Liquid ejector - Google Patents

Description

The present invention relates to a liquid ejecting apparatus that ejects liquid such as ink.

2. Description of the Related Art Conventionally, as a liquid ejecting apparatus that ejects liquid such as ink, there is one that has a configuration as described in Japanese Patent Application Laid-Open No. 2002-200012. This liquid ejection device ejects ink droplets from the recording head while moving a carriage on which the recording head is mounted in the main scanning direction. After that, the recording sheet is conveyed in the sub-scanning direction. The entire surface of the recording sheet is printed by repeating the movement (printing operation) accompanied by the ejection operation and the conveyance (conveyance operation) of the recording sheet a plurality of times.

JP-A-2002-103595

During image formation, the carriage reciprocates in the main scanning direction. At this time, along with the movement of the carriage, an air flow is generated around the carriage. When the carriage starts moving on the outward path, there remains an airflow that has chased the carriage during the previous return path. This air flow may shift the landing position of the ejected liquid droplets with respect to the ejection operation in the subsequent forward pass. Moreover, in recent years, there has been a demand for higher resolution printing. For this reason, small-diameter droplets have come to be used frequently, and it has become necessary to take countermeasures against landing displacement of the droplets due to the air flow.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid ejecting apparatus capable of suppressing the influence of the air flow accompanying the movement of the ejection head on the landing positions of droplets ejected from the ejection head.

A liquid ejection apparatus according to one aspect of the present invention includes an ejection head having a plurality of nozzles, a head scanning mechanism that reciprocates the ejection head in a main scanning direction, and a sub-scanning mechanism that scans a recording medium perpendicularly to the main scanning direction. a medium conveying mechanism for conveying in a direction; a control unit; and a storage unit capable of storing image data of an image to be formed on a recording medium. a recording process for forming an image on a recording medium by ejecting liquid from the ejection head while moving in a first direction along the main scanning direction; After moving in the second direction along the direction, executing a set process of moving to the start position of the recording process of the next pass, and a medium conveying process of conveying the recording medium in the sub-scanning direction, Further, the control unit defines a range of a predetermined distance in the first direction from the position of the nozzle at the start position as an influence region, and sets the scanning distance over which the ejection head moves in the set process as a control distance. If the pass is a first state pass that does not include a continuous region of a predetermined dimension or more in the sub-scanning direction in the image within the affected region, the first distance is set as the control distance, and the next pass is: If the image in the affected area is a second state pass including a continuous area of a predetermined dimension or more in the sub-scanning direction, a second distance longer than the first distance is set as the control distance.

According to the above configuration, at the start of the recording process in the next pass, if there is a high possibility that the droplets will not land properly due to the air flow, the control distance is set to the first distance, which is longer than the normal (first distance). 2 distances. As a result, the air flow generated when the ejection head returns to the stop position for changing the direction for the next pass of the recording process is suppressed to the extent that it does not affect the impact of the droplets when the next recording process starts. . Therefore, it is possible to suppress the disturbance of the image due to the air flow.

According to the present invention, it is possible to provide a liquid ejecting apparatus capable of suppressing the impact of the airflow accompanying the movement of the ejection head on the landing positions of droplets ejected from the ejection head.

1 is a schematic diagram showing a schematic configuration of a liquid ejection device according to an embodiment; FIG. FIG. 2 is a top view of a recording medium and an ejection head; 3 is a block diagram showing a control system of the liquid ejection device; FIG. 4 is a flowchart showing print processing; 4A and 4B are diagrams for explaining movements of an ejection head during image formation; FIG. 4 is a flowchart showing a control distance adjustment procedure; 7A and 7B are drawings showing an operation example of the ejection head during the setting process; 9 is a flowchart showing a control distance adjustment procedure according to the second embodiment; FIG. 11 is a flowchart showing a control distance adjustment procedure according to the third embodiment; FIG.

Hereinafter, embodiments will be described with reference to the drawings. As a liquid ejecting apparatus, an ink ejecting apparatus that ejects ink onto a sheet-like recording medium will be described as an example.

(Embodiment 1)
FIG. 1 shows a schematic configuration of a liquid ejection device 1. As shown in FIG. The liquid ejection device 1 includes a paper feed tray 2 , a platen 3 , a paper discharge tray 4 and a medium transport path 5 . The paper feed tray 2 can accommodate a plurality of recording media P. As shown in FIG. The platen 3 is a flat plate member elongated in the left-right direction, and is arranged above the paper feed tray 2 . A discharge tray 4 is provided in front of the platen 3 . A medium transport path 5 connects the paper feed tray 2 with the paper discharge tray 4 . Media transport path 5 includes, for example, curved path 6 , straight path 7 and end path 8 . The curved path 6 extends from the rear portion of the paper feed tray 2 while curving upward to the vicinity of the rear portion of the platen 3 . The straight path 7 linearly extends forward from the end point of the curved path 6 , passes through the upper surface side of the platen 3 , and reaches near the front of the platen 3 . The end path 8 extends forward from the end point of the straight path 7 and reaches the discharge tray 4 .

The liquid ejection apparatus 1 includes an ejection head 15, a head scanning mechanism 10 that reciprocates the ejection head 15 in the main scanning direction, and a medium transport mechanism 20 that transports the recording medium P in the sub-scanning direction orthogonal to the main scanning direction. Prepare. The "main scanning direction" is horizontal, and the horizontal direction corresponds to the main scanning direction. The "sub-scanning direction" is the transport direction of the recording medium P on the platen 3 (extending direction of the straight path 7), and the front-rear direction (front is downstream) corresponds to the sub-scanning direction.

The head scanning mechanism 10 includes, for example, a carriage 11, a guide member (not shown), an endless belt (not shown), and a carriage motor 14 (see FIG. 3). The carriage 11 is supported by a guide member so as to be able to reciprocate in the main scanning direction, and is arranged above the platen 3 . The ejection head 15 has a nozzle surface in which a plurality of nozzles 16 (see FIG. 2) for ejecting droplets are opened. The ejection head 15 is mounted on the carriage 11 so that the nozzle surface faces downward and faces the upper surface of the platen 3 , and the nozzle surface is the lower surface of the ejection head 15 .

The medium transport mechanism 20 transports the recording media P one by one along the medium transport path 5 . The medium transport mechanism 20 includes, for example, a feed roller 21, a transport roller 22, a discharge roller 25, and a transport motor 29 (see FIG. 3). The feed roller 21 is provided directly above the paper feed tray 2 and contacts the recording medium P from above. The conveying roller 22 is arranged near the downstream end of the curved path 6 and forms a conveying roller section 24 together with the pinch roller 23 . The discharge roller 25 is arranged near the downstream end of the straight path 7 and forms a discharge roller portion 27 together with the spur roller 26 .

The recording medium P is sent to the conveying roller section 24 via the curved path 6 by the feeding roller 21 and sent to the discharge roller section 27 via the straight path 7 by the conveying roller section 24 . In the straight path 7, ink is ejected from the ejection head 15 onto the recording medium P supported on the platen 3, thereby forming an image on the recording medium P. As shown in FIG. The liquid ejection device 1 records an image on the recording medium P by alternately repeating scanning of the carriage 11 and transportation of the recording medium P. FIG. The recorded recording medium P is sent to the paper discharge tray 4 via the end path 8 by the discharge roller unit 27 and received by the paper discharge tray 4 .

FIG. 2 shows the recording medium P and the ejection head 15 as viewed from above. The nozzles 16 on the bottom surface of the head are also shown projected. A plurality of nozzles 16 are arranged in the sub-scanning direction to form a nozzle row 17 . Furthermore, a plurality of nozzle rows 17 are arranged side by side at intervals in the main scanning direction. Each nozzle row 17 corresponds to each liquid type (color, etc.). In this embodiment, as a mere example, four nozzle rows 17 are provided, sequentially from the left: a black row 17K that ejects black ink, a cyan row 17C that ejects cyan ink, and a yellow row 17Y that ejects yellow ink. , a magenta column 17M for ejecting magenta ink.

The movement path of the carriage 11 extends to both sides in the main scanning direction with the recording medium P conveying area interposed therebetween. There is a storage position (home position) of the ejection head 15 on one side (for example, right side) in the main scanning direction. When the power is turned off, the ejection head 15 is housed in the storage position and the nozzle surface is covered with the cap. A maintenance port for the ejection head 15 is provided on the other side (for example, the left side) in the main scanning direction. Here, maintenance (flushing and purging) is performed on the ejection head 15 .

FIG. 3 shows a control system of the liquid ejection device 1. As shown in FIG. The control unit 40 of the liquid ejecting apparatus 1 includes a CPU 41, a storage unit and an ASIC 45. The storage unit includes a ROM 42, a RAM 43 and an EEPROM 44. The liquid ejecting apparatus 1 has two motor driver ICs 46 and 47 and a head dry IC 48, and the ASIC 45 is connected to these driver ICs 46-48. The motor driver IC 46 drives the transport motor 29 , the motor driver IC 47 drives the carriage motor 14 , and the head driver IC 48 drives the actuator of the liquid ejection head 15 .

When the control unit 40 receives an input of a print job from a user or another communication device, the CPU 41 causes the RAM 43 to store image data (image data of an image to be formed on the recording medium P) related to the print job, and stores the image data in the ROM 42 . A print job execution command is output to the ASIC 45 based on the stored program. The ASIC 45 controls the driver ICs 46 to 48 based on this command, and executes print processing (see FIG. 4) based on the image data stored in the RAM 43 .

In the printing process, the motor driver IC 46 drives the transport motor 29 to rotate the feed roller 21, the transport roller 22 and the discharge roller 25 to transport the recording medium P on the platen 3 in the sub-scanning direction. The motor driver IC 47 drives the carriage motor 14 to reciprocate the carriage 11 and the ejection head 15 mounted thereon in the main scanning direction. The head driver IC 48 drives the actuator to eject ink from the nozzles 16 and vibrate the meniscus formed in the nozzles 16 .

The liquid ejection device 1 includes various sensors (for example, a leading edge detection sensor for detecting the position of the recording medium P, an encoder for detecting the position of the carriage, etc.). The control unit 40 controls the driver ICs 46 to 48 synchronously based on the signals from these sensors to form an image on the recording medium P. FIG.

In this embodiment, the direction from the other side (maintenance port side) to the one side (storage position side) in the main scanning direction is referred to as the "first direction", and the opposite direction is referred to as the "second direction". In addition, it is assumed that the printing process is executed by so-called "unidirectional printing", in which ink is ejected while the ejection head 15 is moving in the first direction, and is in a non-ejecting state while it is moving in the second direction. shall be

FIG. 4 shows the procedure of print processing executed for one sheet of recording medium P. As shown in FIG. Upon receiving the print job, the control unit 40 executes pre-printing processing (step S10). In pre-printing processing, the control unit 40 adjusts the meniscus, generates recording data, and causes the recording medium P to be supplied onto the platen 3 .

The controller 40 removes the cap from the nozzle surface and moves the ejection head 15 from the storage position to the maintenance port. At the maintenance port, the ejection head 15 is driven to perform a predetermined number of flashes. This renews the meniscus on the nozzle 16 . After that, the controller 40 drives the carriage motor 29 to move the ejection head 15 in the first direction. At this time, the ejection head 15 is accelerated to a predetermined scanning speed before reaching the start position of the printing process of the first pass. The "start position" is located on one side of the main scanning direction relative to the maintenance port, but on the other side of the main scanning direction with the platen 3 as a reference.

During this time, the control unit 40 stores the image data in the RAM 43 . The control unit 40 generates print data for the first pass based on this image data, and stores this in the RAM 43 as well. Thereafter, print data for each pass is generated until image formation on one print medium P is completed.

Further, the control unit 40 unrolls the first recording medium P from the paper feed tray 2 and supplies it onto the platen 3 . This paper feeding process is performed in synchronism with meniscus adjustment and print data generation.

When the ejection head 15 reaches the start position of the printing process of the first pass, the control unit 40 starts the process related to this pass. Note that "one pass" of the printing process is a series of processes including one recording process (step S11), one set process (step S13), and one medium transport process (step S14). be.

In the recording process S11, the control unit 40 moves the ejection head 15 in the first direction along the main scanning direction. In synchronization with this movement, the control unit 40 ejects ink from the nozzles 16 . As a result, a band-shaped image is formed on the recording medium P. As shown in FIG. Movement of the ejection head 15 and ink ejection are synchronized based on a signal from an encoder. Thus, one recording process is an ejection operation that the head scanning mechanism 10 and the ejection head 15 are caused to perform during one movement in the first direction.

After finishing the recording process S11, the control unit 40 determines whether or not the recording process of all passes to be executed in the print job has been finished (step S12). If not completed (S12: NO), the control unit 40 performs the setting process S13 and the medium transporting process S14, and connects the operation to the next pass.

In the set processing S13, after the recording processing S12 is completed, the ejection head 15 is moved in the second direction to the start position of the recording processing of the next pass. For this movement, the ejection head 15 once passes the next start position and moves in the second direction, switches the moving direction of the ejection head 15 at a stop position on the other side of the next start position, and moves in the first direction from this stop position. It includes a reversal operation of the ejection head 15 to move to the next start position while accelerating (see also FIG. 5). In this embodiment, so-called "unidirectional printing" is applied, and the ejection head 13 moves in the non-ejection state in the setting process S13. In the medium conveying process S14, the recording medium P is conveyed in the sub-scanning direction. If the ejection head 15 is moved in the first direction by the medium conveying process S14, it can just pass the start position of the printing process of the next pass. Although the setting process S13 and the medium transporting process S14 are shown sequentially in FIG. 4 for the sake of convenience, both the processes S13 and S14 may be performed in parallel. After both processes S13 and S14, the control unit 40 executes the recording process S11 from the start position of the recording process of the next pass.

The control unit 40 repeatedly executes a series of processes corresponding to "one pass" shown in S11 to S14. When the recording process for all passes is completed (S12: YES), the control unit 40 controls the medium transport mechanism 20 to discharge the recording medium P to the discharge tray 4 (step S15). This completes the printing process for one recording medium P. FIG.

If the recording medium P to be printed remains (S16: NO), the control section 40 returns the process to step S10. As the pre-printing process S10, generation of new recording data and supply of the recording medium P are performed. Meniscus adjustments are made as needed. After that, the control unit 40 shifts the process to step S11. If there is no recording medium P to be printed, the control section 40 completes the printing process. For example, the ejection head 15 is returned to the storage position and its nozzle face is covered with a cap. The nozzle surface may be cleaned or the meniscus may be adjusted prior to storage in the storage position. If there is no recording medium P to be printed (S16: YES), the printing process ends.

FIG. 5 shows movement of the ejection head 15 during image formation. A filled trapezoid is exemplified as an image to be formed. The movement speed of the carriage 11 is illustrated using arrows. A diagonally upward arrow indicates acceleration, a diagonally downward arrow indicates deceleration, and a horizontal arrow indicates constant speed.

In FIG. A1, the ejection head 15 is at the turning point where the moving direction is switched from the second direction to the first direction, that is, the stop position PA10 of the setting process S13. The stop position PA10 is separated in the second direction from the start position PA11 of the printing process of the next pass. The ejection head 15 moves from the stop position PA10 to the start position PA11 while accelerating in the first direction. The start position PA11 is also the end point of the set processing S13.

As shown in FIG. A2, the ejection head 15 starts the recording process S11 from the start position PA11. The ejection head 15 ejects ink from the nozzles 16 while moving in the first direction at a constant scanning speed. As a result, partial images are formed on the recording medium P. As shown in FIG. In FIG. A3, the ejection head 15 is at the end position PA12 of the recording process S11. When the end position is reached, the band-shaped partial image is completed, and ink ejection is stopped. Of the formed partial images, the pixels at one end are formed at the start position PA11, and the pixels at the other end are formed at the end position PA12.

As shown in FIG. A4, the end position PA12 is also the starting point of the set processing S13. The ejection head 15 starts decelerating from the end position PA12 and stops at the conversion position PA13. As shown in FIG. A5, the ejection head 15 straddles the formed partial image, moves in the second direction from the conversion position PA13, and stops at the stop position PA20.

The stop position PA20 corresponds to the stop position PA10 and is separated from the next start position PA21 in the second direction. The pixel at one end of the partial image for the next time (pass (2)) is on the second direction side of the pixel at one end of the partial image for this time (pass (1)). Accordingly, the stop position PA20 and the start position PA21 are set on the second direction side with respect to the stop position PA10 and the start position PA11, respectively. The stop position and start position change in the main scanning direction according to the position of the pixel at one end (the end on the recording start side) of the partial image formed in the recording process S11.

Referring to FIG. A6, ejection head 15 accelerates from stop position PA20 toward start position PA21. The ejection head 15 moves at a constant speed in the first direction from the start position PA21, which is also the end point of the setting process S13, while ejecting ink.

The operations shown in FIGS. A2 and A3 correspond to the recording process S11, and the operations shown in FIGS. A4 to A6 correspond to the set process S13. The recording process S11 is an operation from ejecting the first droplet to ejecting the last droplet in one pass. In order to form a partial image, the ejection head 15 moves at a constant speed and ejects liquid in synchronization therewith. The set process S13 is an operation from the end of the recording process S11 in one pass to the start of the recording process S11 in the next pass. The ejection head 15 accelerates, decelerates, and changes direction twice in order to connect two printing processes.

Referring to FIGS. A4 to A6, as the ejection head 15 moves from the switching position PA13 to the stop position PA20 in the setting process S13, an airflow is generated around the carriage 11 in the second direction. This air flow is hereinafter referred to as "return wind". The distance between the stop position PA20 and the start position PA21 is usually within the range required to increase the moving speed from zero to the scanning speed in the recording process S11 according to the acceleration that can be achieved by the carriage motor 14. The distance is set as short as possible. The time required from the stop position PA20 to the start position PA21 is very short, and the recording process S11 is started with the return wind remaining. Therefore, there is a possibility that landing deviation (a phenomenon in which droplets are swept away by the return air and deviate from the originally intended landing position in the second direction) occurs in pixels at one end of the partial image and in the vicinity thereof.

Therefore, in the present embodiment, the scanning distance (hereinafter referred to as control distance) that the ejection head 15 moves in the setting process S13 is adjusted in order to suppress the landing deviation. Since the landing deviation caused by the return air does not pose a problem near the conversion position PA13 (especially in unidirectional printing), the distance from the end position PA12 to the conversion position PA13 is determined so that the ejection head 15 can move in the second direction as quickly as possible. It is set to the constant distance required for deceleration for any pass so that it can be started. In adjusting the control distance, the distance between the start position PA21 and the stop position PA20 is adjusted by displacing the stop position PA20 in the main scanning direction. When the ejection head 15 moves in the second direction from the conversion position PA13 in the set processing S13, the ejection head 15 passes the next start position PA21. The distance from PA12 to the starting position PA21 via the turning position PA13 remains unchanged regardless of the adjustment of the control distance. The "control distance" may be macroscopically grasped as the entire scanning distance in the set processing S13, or microscopically grasped as the distance between the start position PA21 and the stop position PA20 except for the part where the distance is unchanged. However, it is the distance including the distance excluding this constant distance part.

FIG. 6 shows the procedure for setting the control distance. First, the control unit 40 acquires image data of an unprocessed pass (step S20). The unprocessed image data typically corresponds to image data related to the next recording process. The control unit 40 analyzes the acquired image data (step S21) and extracts a "continuous area". Then, the control unit 40 determines whether the obtained unprocessed path is the "first state path" or the "second state path" (steps S22 and S23).

The 'first state pass' is a pass that does not include a 'continuous area' having a predetermined dimension L1 or more in the sub-scanning direction in the image within the 'influence area'. The "second state pass" is the opposite, and is a pass that includes a "continuous area" having a predetermined dimension L1 or more in the sub-scanning direction in the image within the "influence area". In path determination, first, it is determined whether or not the image within the area of influence includes a continuous area in the acquired path (S22). If a continuous area is included (S22: YES), it is determined whether or not the continuous area has a predetermined dimension L1 or more in the sub-scanning direction (S23).

If either of the two determination results is negative, the acquired path is the first state path, and the control unit 40 sets the control distance to the first distance (step S24). If both of the two determination results are yes, the acquired path is the second state path, and the control unit 40 sets the control distance to a second distance longer than the first distance (step S25). The stopping position for the second state path is further in the second direction from the starting position than the stopping position for the first state path. Therefore, the second distance is longer than the first distance.

The “influence area” is an area in which the return wind that causes recognizable impact deviation remains if the recording process is performed without adjustment of the control distance, and is the area from the position of the nozzle 16 at the start position PA21. The range is a predetermined distance in one direction.

An example of an area of influence will be described. After the ejection head 15 is moved in the second direction by a certain distance by the liquid ejecting apparatus 1 and then reversed in the first direction, a test pattern is printed in the first direction. For example, the test pattern consists of a plurality of line segments (35 mm in length in the sub-scanning direction and 1 mm in length in the main scanning direction) arranged in the main scanning direction. formed by The return wind shifts the droplets to the second direction side of the line segment, creating dots that land poorly. Here, a rectangular area set corresponding to each line segment is defined as a sampling area. Each sampling area is set with a gap of 0.5 mm from the corresponding line segment, and has a length of 10 mm in the sub-scanning direction and a length of 5 mm in the main scanning direction. Dots within the sampling area are bad dots and are counted. The number of defective dots decreases with increasing distance from the start position PA21 in the first direction. This is considered to be because the ejection timing of the droplets becomes later as the distance from the start position PA21 increases, and the return wind weakens with the lapse of time. In this embodiment, the position of a line segment corresponding to less than 15 defective dots is used as the boundary of the affected area. Note that the strength of the return wind depends on the movement distance of the ejection head 15 from the switching position PA13 to the start position PA20 in the setting process, or the movement of the ejection head 15 in the second direction and returning to the start position PA20 after passing the start position PA20. The width of the affected area (or the position of the boundary) also changes in the main scanning direction.

A "continuous area" is an area composed of a plurality of pixels arranged at unit intervals corresponding to the resolution in the sub-scanning direction, and is a partial image in which a plurality of pixels are continuously arranged in the sub-scanning direction. Say.

As described above, when a continuous area having a predetermined size L1 or more is included in the sub-scanning direction within the affected area of a certain pass (when the pass is the second state pass), the set processing performed before the printing processing , the control distance is set to a longer second distance (S25). Since the next recording process is executed after the ejection head 15 has moved a longer distance, the required round trip time between the start position and the stop position becomes longer. Therefore, the recording process can be started with the return wind weakened. Therefore, it becomes difficult for the return wind to cause deviation in landing.

On the other hand, if the continuous area within the affected area of a certain pass is less than the predetermined size L1 (if the pass is the first state pass), the impact deviation is not conspicuous even if the control distance is not adjusted to be longer. Therefore, the control distance is set to a shorter first distance (S24) to speed up the printing process.

In order to set a long control distance, the presence of a continuous area is a condition. Even if there is a pixel in the area of influence, if a plurality of pixels are not continuous in the sub-scanning direction, the landing deviation will not be noticeable, so the control distance is set to the normal first distance. This prevents the time required for the setting process S13 from becoming unnecessarily long, and speeds up the printing process. Furthermore, in the present embodiment, the predetermined dimension L1 as a threshold for judging the continuity of pixels is set to 1.0 mm as an example. Even if there is a continuous area within the affected area, if it is less than the predetermined dimension L1 in the sub-scanning direction, the impact deviation is not conspicuous. Therefore, the control distance is set to the normal first distance, and speeding up of the printing process is achieved.

An example of the operation of the ejection head 15 in the setting process S13 will be described with reference to FIG. FIG. 7 shows the relationship between the moving speed and time for the ejection head 15 during the setting process S13. The time on the horizontal axis also indicates the position of the ejection head 15 at that time. For example, time tA12 corresponds to position PA12 whose last two digits have the same number in FIG.

FIG. 7A is an operation example when the control distance is set to the first distance. That is, the pass following this set operation is the first state pass. Even if the control distance remains the first distance, in the recording process following this set process, the poor landing due to the air flow does not become apparent. The operation at this time will be described with reference to FIG. 5 as well.

In the printing process, the ejection head 15 moves in the first direction at a speed V1, and finishes printing at the position PA12 at time tA12. In the subsequent set process, the liquid ejection head 13 decelerates and stops at position PA13 at time tA13. A turning position PA13 is a turning point in the first direction.

The ejection head 15 immediately reverses its movement direction and accelerates in the second direction to a speed V2 (V2>V1). Then, the ejection head 13 decelerates while moving at the speed V2, and stops at the stop position PA20 at time tA20. The stop position PA20 is a turning point in the second direction.

The ejection head 15 again immediately reverses its movement direction and accelerates in the first direction to the velocity V1. The ejection head 15 reaches the speed V1 at time tA21 and simultaneously reaches the start position PA21 where the setting process ends.

FIG. 7B is an operation example when the control distance is set to the second distance. That is, the pass following this set operation is the second state pass. If the control distance remains the normal first distance, in the recording process subsequent to this setting process, poor landing due to the air flow will become apparent.

In this case, the ejection head 15 is scanned in the second direction at the speed V2 for a longer time and a longer distance. Accordingly, the position of the turning point (stop position PA20) in the second direction is moved away from the start position PA21, and the control distance becomes longer than the first distance.

As described above, this operation example is characterized in that the turning point (stop position PA20) in the second direction is kept away from the print area in unidirectional printing, thereby increasing the control distance. As a result, the start of the recording process can be intentionally delayed, and the airflow remaining after the set process can be weakened until the next recording process is started. Therefore, in the next recording process, it is possible to prevent the landing of the droplets from being disturbed. Note that the second distance is set so that the scanning time is extended in the range of 0.1 to 1.0 seconds from the viewpoint of sufficiently weakening the airflow and not impairing the speeding up of the printing process.

[Thickening measures]
By the way, when the control distance is set to the second distance, the liquid near the nozzle 16 is exposed to the air for a longer time. During this time, the viscosity of the liquid progresses, and there is a possibility that the ejection characteristics will deteriorate. Therefore, in the present embodiment, when the control distance is the second distance (when the next pass is the second state pass), non-ejection flushing (vibration of the liquid in the nozzle 16 in the non-ejection state) is performed during the set process. action to give). From the viewpoint of recovery of ejection characteristics, this non-ejection flushing is performed while moving from the stop position PA20 to the start position PA21. As a result, even if the setting process takes a long time, the liquid in the nozzle 16 can be effectively stirred and fresh liquid can be ejected.

[Scanning speed of set processing]
When the control distance is set to the second distance, deceleration in the setting process may be started from one side in the main scanning direction, and the low speed region may be longer than when the control distance is set to the first distance. As a result, the airflow is weakened, and the influence of the airflow can be reduced. Therefore, even if the second distance is not so long as compared to the first distance, it is possible to suppress impact disturbance in the next recording process.

[Acceleration in next recording process]
When it is determined that the next pass is in the second pass state, the acceleration when moving in the first direction from the stop position (initial acceleration of the recording process of the next pass) compared to the case of the first state pass may be larger than it would be if it were the first state path. As a result, it becomes easier to generate an air flow that opposes the remaining air flow, and it is possible to suppress impact disturbance due to the remaining air flow. Therefore, it is allowed to set the influence area small, and the opportunities for adjusting the control distance can be reduced.

[Dimensions of influence area]
In this embodiment, the dimensions of the affected area are variably set based on the following various viewpoints. As the size of the region of influence decreases, the probability that it will contain continuous regions decreases, and the probability that the next pass will be determined to be the first state pass increases. By reducing the control distance adjustment opportunities as much as possible, it is possible to achieve both high-speed printing and suppression of poor landing.

(1. Position of nozzle row)
As shown in FIG. 3, on the nozzle surface of the ejection head 15, a plurality of nozzle rows 17 are arranged side by side at intervals in the main scanning direction. At this time, the dimensions of the affected area may be set for each nozzle row. Specifically, with respect to the moving direction (first direction) of the carriage during the printing process, the dimension of the affected area may be set smaller for the nozzle row located in the direction opposite to the first direction.

For example, when droplets are made to land at the same location, the degree of influence of the air flow differs depending on the position of the nozzle row 17 . When a nozzle row positioned upstream with respect to the direction of movement of the carriage faces a certain airflow, the nozzle row positioned downstream faces the following. Subsequent air streams touch the nozzle face a longer distance to reach that point. Since contact with the nozzle face also weakens the airflow, the downstream rows of nozzles face even more weakened airflow. Therefore, the degree of influence of the air flow on the downstream nozzle row is smaller than that on the upstream nozzle row. The area of influence corresponding to the downstream nozzle row may have a smaller dimension in the main scanning direction than the area of influence corresponding to the upstream nozzle row. In this way, the next pass may be the first state pass for some of the nozzle rows, and the second state pass for the remaining nozzle rows.

(2. Print mode)
The liquid ejecting apparatus 1 has multiple types of print modes. The moving speed of the ejection head 13 differs for each printing mode. For example, in the "fine mode", a relatively high-quality image is formed, but the ejection head 15 moves at a low speed. In the "draft mode", an image of relatively low image quality is formed, but the ejection head 15 moves at high speed. In the "normal mode", an image having an intermediate image quality is formed, and the moving speed is also intermediate.

At this time, the liquid ejection apparatus 1 moves the liquid ejection head 13 at different speeds depending on the print mode. That is, the moving speed to the stop position immediately before the recording process is faster in the order of fine mode, normal mode, and draft mode. Correspondingly, the residual air flow also increases in this order. Therefore, the liquid ejecting apparatus 1 reduces the affected areas of different dimensions according to the print mode. For example, the lower the speed mode, the smaller the influence region may be set. In low-speed mode, there are fewer opportunities to adjust the control distance, so printing can be speeded up without degrading image quality.

On the other hand, in the fine mode, the size of droplets ejected from the nozzles 16 is relatively small in order to form a relatively high-quality image, and in the draft mode, the size of droplets ejected from the nozzles 16 is relatively small. big. Smaller droplets are more likely to be disturbed by air currents. Therefore, the liquid ejecting apparatus 1 may set a smaller influence area for a print mode with a larger droplet size. The larger the droplet size in the recording mode, the less opportunities there are to adjust the control distance, so printing can be speeded up without degrading image quality.

(3. Width of recording sheet, scanning distance of previous pass)
The liquid ejecting apparatus 1 moves the ejecting head 15 farther to the stop position immediately before the recording process as the width dimension that can be printed on a plurality of types of recording sheets P having different dimensions in the main scanning direction is larger. The greater the movement, the greater the residual airflow impacting the subsequent recording process.

The liquid ejection device 1 has an influence region with different dimensions according to the width dimension of the recording sheet P. FIG. The smaller the width dimension, the smaller the dimension of the area of influence to be set. Thereby, the control distance is set according to the width dimension of the recording sheet P. FIG. When the width dimension becomes smaller, the dimension of the affected area becomes smaller, and the chances of being judged as being in the second pass state decrease, so printing can be speeded up without degrading image quality.

(4. Image size)
In the liquid ejection apparatus 1, when one recording process is completed, the ejection head 15 is reversed and moved toward the next recording start position. For example, in FIG. 5, the ejection head 15 moves in the main scanning direction from the stop position of position PA13 to the stop position of position PA20. The greater the distance traveled, the greater the residual airflow impacting the subsequent recording process. The moving distance at this time depends on the size of the previously formed image.

Therefore, the liquid ejecting apparatus 1 has influence regions with different dimensions according to the moving distance between the two stop positions in the setting process. The control distance is set according to the dimensions of the previously formed image. That is, the smaller the size of the formed image, the smaller the size of the region of influence. Since the opportunities for adjusting the control distance are reduced accordingly, the printing speed can be increased without degrading the image quality.

(5. Viscosity)
If the viscosity of the liquid ejected from the ejection head 15 is high, the ejection speed is lowered, and the air flow tends to cause the landing disturbance. Therefore, the liquid ejecting apparatus 1 sets the dimension of the affected region to be smaller as the viscosity of the liquid is higher. Since the opportunities for adjusting the control distance are reduced accordingly, the printing speed can be increased without degrading the image quality. Note that the control unit may determine the viscosity by referring to a table that preliminarily defines the relationship between the usage period of the liquid and the viscosity.

(6. Paper space gap)
If the gap between the nozzle surface and the recording sheet (hereinafter referred to as the "paper surface gap") is large, the airflow will easily pass under the nozzle, and the flight distance of the droplets will be long, resulting in impact disturbance due to the airflow. Cheap. Therefore, the liquid ejecting apparatus 1 sets the dimension of the affected area smaller as the paper gap is narrower. Since the opportunities for adjusting the control distance are reduced accordingly, the printing speed can be increased without degrading the image quality. Note that even with the same liquid ejection device 1, the paper surface gap can be changed depending on the recording mode, and can also be changed depending on the recording sheet used.

(7. Borderless printing)
The liquid ejection apparatus 1 can execute a "borderless mode" in the printing process. In this borderless mode, the image forming range extends to the outside of the recording sheet P in the main scanning direction.

That is, in the borderless mode, droplets land on the outer side of the recording sheet P in the vicinity of the start position of the recording process. Therefore, even if there is a continuous area within this area, the image quality will not be substantially hindered. Therefore, in borderless mode, this area may be excluded from the influence area. As a result, the affected area can be set to be small, so it is possible to avoid an unnecessary increase in scan time and print processing time.

(Embodiment 2)
When the remaining airflow passes under the nozzle surface, it mainly flows in the main scanning direction at the center of the nozzle surface in the sub-scanning direction. At the end of the nozzle surface in the sub-scanning direction, the component in the sub-scanning direction is added to the component in the main scanning direction. Therefore, at the end of the nozzle row 16, the discharged droplets may deviate from the strip-shaped recording area in the sub-scanning direction. Here, one image is completed by connecting strip-shaped recording areas in the sub-scanning direction. Therefore, at the seam between the recording areas, the image quality defect is likely to be conspicuous due to the overlapping of the above-described landing defects. Therefore, in the present embodiment, the control distance is set as follows to suppress image quality defects.

The flowchart of FIG. 8 shows the control distance setting procedure according to the second embodiment. The control unit 40 acquires image data of an unprocessed pass (step S30). The unprocessed image data is typically image data for the next recording process. Then, in step S31, the control unit 40 analyzes this image data and extracts continuous regions. In subsequent step S32, the control unit 40 detects whether or not the image within the area of influence includes a continuous area.

If there is no continuous area in the image within the area of influence (S32: NO), the control unit 40 sets the control distance to the first distance (S33). If the continuous area is within the influence area (S32: YES), the control unit 40 shifts the process to step S34. At step S<b>34 , the control unit 40 determines whether or not the end of the continuous area corresponds to the end of the nozzle row 16 .

If it does not correspond to the end of the nozzle row 16 (S34: NO), the control unit 40 moves the process to step S35. Here, as in step S24 of FIG. 6, the control unit 40 determines whether or not the continuous area has a length L1 or more in the sub-scanning direction. If the length is less than L1 (S35: NO), the control unit 40 sets the control distance to the first distance (S33). If the length is equal to or longer than L1 (S35: YES), the control unit 40 shifts the process to step S37. At step S37, the control unit 40 sets the control distance to a second distance that is longer than the first distance.

If it corresponds to the end of the nozzle row 16 (S34: YES), the control unit 40 shifts the process to step S36. Here, it is determined whether or not the continuous area has a length L2 or more in the sub-scanning direction. This length L2 is smaller than the length L1. For example, if length L1 is set to 1.0 mm as described above, length L2 is set to 0.8 mm. If the length is less than L2 (S36: NO), the control unit 40 sets the control distance to the first distance (S33). If the distance is equal to or longer than the length L2 (S36: YES), the control unit 40 sets the control distance to the second distance (S37).

In this way, when the edge of the continuous area corresponds to the edge of the nozzle row 16, the control distance is set with the smaller length L2 as the threshold. As a result, it is possible to suppress overlapping of defective landing portions at the joints of the band-shaped recording areas, and to maintain the image quality.

(Embodiment 3)
The liquid ejection device 1 is required to be compact, the platen 3 is set as small as possible according to the width of the recording sheet P that can be handled, and the ejection head 15 is designed so that the platen 3 can be scanned to both outer sides in the main scanning direction. Although the scanning range is set, the scanning range is also set to be as narrow as possible, thereby miniaturizing the housing that defines the overall dimensions of the liquid ejecting apparatus 1 . Therefore, when setting the second distance, the second distance cannot be increased indefinitely due to restrictions on the scanning range and housing size, and the maximum value of the second distance is naturally determined. On the other hand, it is conceivable that the second distance required to prevent impact disturbance may exceed this maximum value. Therefore, in the present embodiment, when the second distance originally desired to be set exceeds the maximum value, the second distance is set to the maximum value, and then the alternative processing necessary for suppressing the disturbance of the landing is executed.

The flowchart of FIG. 9 shows the control distance setting procedure according to the third embodiment. The control unit 40 acquires image data of an unprocessed pass (step S40). The unprocessed image data is typically image data for the next recording process. Then, the control unit 40 analyzes this image data to extract a continuous area (S41), determines whether or not the image within the affected area includes a continuous area (S42), and determines whether the continuous area has a predetermined dimension L1 or more. It is determined whether or not (S43). If there is no continuous area in the image within the affected area (S42: NO) or if the continuous area is less than the predetermined dimension L1 (S43: NO), the controller 40 sets the control distance to the first distance (S44). If there is a continuous area of the predetermined dimension L1 or more within the influence area (S42: YES, S43: YES), the control unit 40 sets the control distance to the temporary second distance (S45). Next, the control unit 40 determines whether or not this temporary second distance exceeds the maximum value of the liquid ejection device 1 (S46). In other words, the control unit 40 determines whether or not the stop position PA20 provisionally set to extend the control distance exceeds the limit of the scanning range. If the maximum value is not exceeded (if the tentatively set stop position PA20 is within the scanning range) (S46: NO), the tentative second distance is set as is as the control distance (S47). If the maximum value is exceeded (S46: YES), the control distance is set from the temporary second distance to the maximum value of the second distance (S48), and an alternative process (S50) is executed. At least one of a plurality of processes exemplified below is executed as the alternative process S50.

[Alternative process]
The alternative process S50 may be a standby process. The standby process is a process of stopping the movement of the ejection head for a predetermined time between the stop position PA20 and the start position PA21. With this standby process, even if the scanning distance cannot be sufficiently extended and the scanning time cannot be secured sufficiently, the recording process can be started with the airflow weakened after the lapse of the predetermined time, and the impact disturbance can be suppressed.

The alternative process S50 may be a deceleration process. The deceleration process is a process of reducing the moving speed of the ejection head in the set process. By this deceleration processing, the scanning time can be lengthened even if the scanning distance cannot be sufficiently extended, so that the printing processing can be started with the air flow weakened, and the impact disturbance can be suppressed.

The alternative process S50 may be a diameter increasing process. The diameter-enlarging process is a process for increasing the size of droplets ejected from the nozzles 16 within the affected area. As described above, if the droplet size is small, it is likely to be affected by the air flow, and the landing disturbance is likely to occur. By increasing the droplet size instead of shortening the control distance from the original desired setting, the landing disturbance can be suppressed.

(Modification)
Although the embodiments have been described so far, the above configuration is an example, and can be changed, added, and/or deleted as appropriate within the scope of the present invention.

The liquid ejecting apparatus 1 can also set one and the other of the main scanning directions as the first direction in which the recording process is performed. In other words, the liquid ejection device 1 can also be configured to allow bi-directional printing.

In this case, the set process is the operation of the ejection head 15 from the end of the printing process in the previous pass to the start of the printing process in the next pass, and the scanning distance during that time is the control distance. In bi-directional printing, the set process has one stop position where the liquid ejection head 15 is reversed.

The liquid ejecting apparatus 1 can set the control distance based on the above-described procedure even when performing this bidirectional printing, and can suppress landing defects of droplets due to the air flow.

1: liquid ejection device, 10: head scanning mechanism, 15: ejection head, 16: nozzle, 17: nozzle row, 20: medium transport mechanism, 40: control unit, 42: ROM, 43: RAM, 44: EEPROM, P : recording medium, PA10, PA20: stop position, PA11, PA21: start position of recording processing, S11: recording processing, S13: setting processing, S14: medium conveying processing

Claims (21)

an ejection head having a plurality of nozzles;
a head scanning mechanism that reciprocates the ejection head in a main scanning direction;
a medium transport mechanism for transporting a recording medium in a sub-scanning direction orthogonal to the main scanning direction;
a control unit;
a storage unit capable of storing image data of an image to be formed on a recording medium,
The control unit, in one pass,
a recording process of forming an image on a recording medium by ejecting liquid from the ejection head while moving the ejection head in a first direction along the main scanning direction;
a setting process of moving the ejection head to a start position of the recording process of the next pass after the recording process is completed, through movement in the second direction along the main scanning direction;
a medium conveying process of conveying the recording medium in the sub-scanning direction;
and run
When a range of a predetermined distance in the first direction from the position of the nozzle at the start position is defined as an influence region, and a scanning distance over which the ejection head moves in the set process is defined as a control distance,
Furthermore, the control unit
setting a first distance as the control distance when the next pass is a first state pass in which the image in the affected area does not include a continuous area of a predetermined size or more in the sub-scanning direction;
If the next pass is a second state pass that includes a continuous area of a predetermined size or more in the sub-scanning direction in the image within the affected area, a second distance longer than the first distance is set as the control distance. set,
Liquid ejection device. The continuous area is an area composed of a plurality of pixels arranged at unit intervals corresponding to the resolution in the sub-scanning direction, and the plurality of pixels are continuously arranged in the sub-scanning direction by a predetermined dimension or more. is an arranged partial image,
The liquid ejection device according to claim 1. The predetermined dimension of the continuous area in the sub-scanning direction is 1.0 mm.
The liquid ejection device according to claim 1 or 2. In the setting process, the control unit adjusts the control distance by displacing, in the main scanning direction, a stop position for switching the moving direction of the ejection head between the first direction and the second direction. do,
The liquid ejection device according to any one of claims 1 to 3. The ejection head has a plurality of nozzle rows in which the plurality of nozzles are arranged in the sub-scanning direction, and the plurality of nozzle rows are arranged side by side at intervals in the main scanning direction,
The control unit sets the size of the influence area smaller for the nozzle row positioned in the direction opposite to the first direction in the main scanning direction.
The liquid ejection device according to any one of claims 1 to 4. In the recording process, the control unit sets the size of the affected area to be smaller for a recording mode having a lower moving speed in the main scanning direction.
The liquid ejection device according to any one of claims 1 to 5. In the recording process, the control unit sets the dimension of the affected area to be smaller for a recording medium having a smaller dimension in the main scanning direction.
The liquid ejection device according to any one of claims 1 to 6. In the recording process, the control unit sets the dimension of the affected area to be smaller in a recording mode in which the size of droplets ejected from the nozzle is larger.
The liquid ejection device according to any one of claims 1 to 7. When the stop position is a position where the direction of movement of the ejection head is switched between the first direction and the second direction,
When the image is formed in the previous pass, the controller controls that the smaller the moving distance of the ejection head moving in the main scanning direction from the stop position on one side of the image to the stop position on the other side of the image, setting a smaller dimension for the region of influence in the next pass;
The liquid ejection device according to any one of claims 1 to 8. wherein, in the recording process, the lower the viscosity of the liquid ejected from the ejection head, the smaller the size of the affected area is set;
The liquid ejection device according to any one of claims 1 to 9. wherein, in the recording process, the smaller the distance between the recording medium being conveyed by the medium conveying mechanism and the ejection head, the smaller the size of the affected area is set;
The liquid ejection device according to any one of claims 1 to 10. In the recording process, the control unit is capable of executing printing in a borderless mode in which liquid is ejected based on the image data to the outside of the recording medium. setting the size of the affected area smaller than in the case of printing in which the liquid based on the image data is ejected only inside the medium;
The liquid ejection device according to any one of claims 1 to 11. The ejection head is provided with a nozzle row in which a plurality of the nozzles are arranged in the sub-scanning direction,
When an end in the sub-scanning direction of the continuous region included in the image within the influential region corresponds to a nozzle at an end of the nozzle array, the control unit adjusts a predetermined dimension in the sub-scanning direction of the continuous region. 0.8 mm;
The liquid ejection device according to any one of claims 1 to 12. The control unit sets the size of the area of influence small and shortens the second distance.
The liquid ejection device according to any one of claims 2 to 13. When the next pass is the second state pass, the control unit performs non-ejection flushing to vibrate the nozzles of the ejection head in a non-ejection state.
The liquid ejection device according to any one of claims 1 to 14. The control unit starts decelerating the ejection head from the middle of the recording process in one pass.
The liquid ejection device according to any one of claims 1 to 15. When the stop position is a position where the direction of movement of the ejection head is switched between the first direction and the second direction,
When the next pass is the second state pass, the control unit increases acceleration when moving in the first direction from the stop position compared to when the next pass is the first state pass.
The liquid ejection device according to any one of claims 1 to 16. When the stop position is a position where the direction of movement of the ejection head is switched between the first direction and the second direction,
When forming an image in the previous pass, the control unit controls that the moving distance of the ejection head moving in the main scanning direction from the stop position on one side of the image to the stop position on the other side of the image reaches a predetermined value. If it exceeds, the second distance is set to a settable maximum value in the setting process, and an alternative process, which is an operation of the ejection head with the lapse of time, is executed.
The liquid ejection device according to any one of claims 1 to 17. The control unit executes, as the alternative process, a standby process of stopping the ejection head for a predetermined time between the stop position and the start position in the set process.
19. A liquid ejection device according to claim 18. The control unit executes, as the alternative process, a deceleration process that reduces the moving speed of the ejection head in the set process.
20. The liquid ejection device according to claim 18 or 19. wherein, as the alternative process, in the recording process, the control unit sets a larger droplet size to be ejected from the nozzle within the affected area;
The liquid ejection device according to any one of claims 18-20.

Images