JP2007326280A - Inkjet recorder and method for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder capable of obtaining a gradation image with high quality by aligning center positions of recorded dots with each other in a whole range from a low gradation having few ejection dots to a high gradation having many ejection dots, and to provide a method for inkjet recording. <P>SOLUTION: This inkjet recorder comprises a memory means storing a time period from starting of ejection of each dot to arrival thereof on a recording medium obtained by measuring a speed in each ejection in a range from dot-recording of one ink droplet to dot-recording of the maximum number of ink droplets in a condition that a relative speed between at least a nozzle and the recording medium is set. The inkjet recorder further comprises a timing setting means for setting a timing of each of the ejections in the range from the dot-recording of one ink droplet to the dot-recording of the maximum number of ink droplets based on the stored time period from starting of ejection of each dot to arrival thereof on the recording medium. The ink droplet is ejected from the nozzle at the set timing of each ejection. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus and an ink jet recording method that perform dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from nozzles in accordance with gradation.

  This type of ink jet recording apparatus, for example, which performs dot recording of 7 gradations, expresses 1 gradation when forming 1 dot with 1 ink drop, and continuously 3 ink drops. When one dot is formed by sequentially ejecting three dots, three gradations are expressed, and when one dot is formed by sequentially discharging seven ink droplets sequentially, seven gradations are represented. ing.

Conventionally, in such an ink jet recording apparatus, for example, when performing dot recording of five gradations, when one dot is formed by one ink droplet, the third of the five pulse signals that can be generated. When one dot is formed with two ink droplets, the second and third pulse signals among the five possible pulse signals are generated, so that the center position of each dot is generated. And the center position of a region where one dot is to be formed are known (see, for example, Patent Document 1).
JP-A-6-297717 (paragraph “0096” etc.)

According to the method described in Patent Document 1, the discharge timing is determined on the assumption that the discharge speed is always constant both when forming one dot with one drop of ink droplet and when forming one dot with five drops of maximum drop. It was.
However, in practice, since the ejection speed of each drop is different, the ejection speed is different between forming one dot with one drop and forming one dot with five maximum drops. That is, the discharge speed when forming one dot with one drop is the slowest, the discharge speed when forming one dot with two drops, forming one dot with three drops, and forming one dot with four drops Becomes faster, and the ejection speed when forming one dot in the last five drops is the fastest.

  This is because the ink state at the nozzle position of the head changes quickly due to the inertia of the ink and the discharge mechanism when shifting from the stop state to the discharge mode at the first drop and the second drop when the number of discharges is low. This is because the ink and the discharge mechanism discharge in a resonance state after the third drop, and the discharge conditions are different.

  Therefore, in the thing of patent document 1, since the speed of each discharge differs in fact, the problem that all the center positions of each pixel cannot be made to occur occurs.

  The present invention has been made to solve such a problem, and the dot recording center position can be matched in all of the low gradation with a small number of ejections to the high gradation with a large number of ejections. An ink jet recording apparatus and an ink jet recording method capable of obtaining a high-quality gradation image are provided.

  The present invention is an inkjet recording apparatus that performs dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from the nozzle according to the gradation, with at least the relative speed between the nozzle and the recording medium being set, Storage means for storing the time from the discharge start of each discharge to the arrival at the recording medium obtained by measuring the speed of each discharge from dot recording with one drop of ink droplets to dot recording with the maximum number of drops; And a timing setting means for setting the timing of each ejection from the dot recording by one drop of ink droplets to the dot recording by the maximum number of drops based on the time from the ejection start to the arrival at the recording medium. In other words, ink droplets are ejected from the nozzles at each ejection timing set by the timing setting means.

  According to the present invention, all the dot recording center positions can be made to coincide in all of the low gradations with a small number of ejections and the high gradations with a large number of ejections, so that high-quality gradation images can be obtained. An apparatus and an ink jet recording method can be provided.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to a monochrome ink jet recording apparatus.
FIG. 1 is a diagram showing a mechanism part of an ink jet recording apparatus. A drum 12 that rotates in a direction of an arrow in the figure at a constant peripheral speed is provided in a main body case 11. A recording medium 15 such as a recording sheet to be fed is wound.

  That is, a paper feed cassette 16 is provided at the bottom of the main body case 11, and the recording medium 15 placed on the placement plate 17 of the paper feed cassette 16 is taken out one by one by the feed roller 18, and the paper feed roller The recording medium 15 manually fed from the manual feed tray 19 that is openably and detachably attached to the side of the main body case 11 is fed to the paper feed rollers 13 and 14 by the feed roller 20. It is like that. The feeding switching means 21 performs switching between feeding by the feeding roller 18 and feeding by the feeding roller 20.

  A charging roller 22 is disposed on the drum 12 so as to oppose the recording medium 15 fed from the paper feeding rollers 13 and 14 to the drum surface. In addition, a printing mechanism in which an inkjet recording head 23 in which a large number of ink discharge nozzles are arranged in a line at a predetermined pitch is arranged on the drum 12 so as to be movable in the direction of the rotation axis of the drum 12 that is the nozzle arrangement direction. 24 are arranged opposite to each other. Accordingly, the recording medium 15 is conveyed in a direction substantially perpendicular to the nozzle arrangement direction of the inkjet recording head 23 by the rotation of the drum 12.

  The printing mechanism 24 includes a reciprocating mechanism 25 on which the ink jet recording head 23 is mounted, a motor unit 26 having a reciprocating rod and a linear motor, and an advancing / retreating means 27. The head 23 is moved forward and backward with respect to the drum 12. The reciprocating mechanism 25 is controlled to move in the direction of the rotation axis of the drum 12 by the motor unit 26, so that the ink jet recording head 23 is reciprocated in the direction of the rotation axis of the drum 12, that is, the recording line direction. ing.

  The drum 12 is provided with a peeling claw 28 that can be inserted between the drum surface and the recording medium 15, and the recording medium 15 peeled by the peeling claw 28 is discharged to a recording medium discharging / conveying mechanism 29. ing. The recording medium discharging / conveying mechanism 29 includes a belt conveyor 30 that contacts the non-recording surface of the recording medium 15 and a pressing unit 31 that presses the recording medium 15 against the surface of the belt conveyor 30.

  A discharge roller 32 is disposed on the upper side of the main body case 11 so as to discharge the recording medium 15 conveyed by the belt conveyor 30 to the outside of the main body case 11. In the main body case 11, a drum motor 33 that rotates the drum 12, an ink cassette 34 that serves as an ink supply source, an ink buffer 35 that temporarily stores ink from the ink cassette 34, and ink in the ink buffer 35 are stored. An ink supply tube 36 that supplies the ink jet recording head 23 is accommodated.

  In addition, a feed motor that rotationally drives the feed roller 18, a discharge motor that drives the recording medium discharge transport mechanism 29, an ink temperature sensor as an ink temperature detection means that detects ink temperature, and recording by the feed roller 18 A feeding sensor that detects the start of feeding of the medium 15, a suction sensor that detects the suction state of the recording medium 15 with respect to the surface of the drum 12, and a discharge sensor that detects the discharge of the recording medium 15 to the recording medium discharge and transport mechanism 29. Etc. are provided.

  In the ink jet recording apparatus, at the time of printing, for example, the recording medium 15 is taken out from the paper feed cassette 16 by the paper feed roller 18 and sent to the paper feed rollers 13 and 14. This is detected by the feed sensor. Then, the recording medium 15 is fed to the rotating drum 12 by the paper feed rollers 13 and 14 and wound. That is, the recording medium 15 is attracted and wound around the surface of the drum 12 by the charging roller 22. The winding sensor detects this winding.

  When the winding is detected, image recording on the recording medium 15 is started. That is, the recording medium 15 is rotated and conveyed in the direction in which the nozzles are arranged in the inkjet recording head 23, that is, the direction orthogonal to the line direction by the rotation of the drum 12, and is transferred from each nozzle of the inkjet recording head 23 to the recording medium 15. Image recording is performed by selectively ejecting ink at a predetermined timing based on the image signal.

  The inkjet recording head 23 performs dot recording by ejecting one or a plurality of ink droplets of the same volume from each nozzle, and expresses gradation by controlling the number of ejected ink droplets. Record images using the drop method. Here, for example, a maximum of seven ink droplets can be ejected continuously to record an image with seven gradations.

  FIG. 2 is a block diagram showing the configuration of the control unit, which stores a CPU (central processing unit) 41 constituting the control unit main body, program data for controlling the respective units by the CPU 41, calculation formulas for determining the ejection timing of seven ink droplets, and the like. The P-ROM 42 constituting the storage means, the P-RAM 43 used for data processing such as computation and temporary storage of data, the PC interface 44 communicating with the personal computer 100, and the PC interface 44 received from the personal computer 100 An image memory 45 for storing image data is provided. The CPU 41 and the P-ROM 42 constitute timing setting means.

  The drum motor drive circuit 46 for driving the drum motor 33, the feed motor drive circuit 48 for driving the feed motor 47, the discharge motor drive circuit 50 for driving the discharge motor 49, and the keyboard 51 are controlled to control the key signal. A keyboard control circuit 52 for capturing, a display control circuit 54 for driving a display 53 made of an LCD or LED, an ink temperature sensor 55, and a temperature sensor control circuit 56 for capturing a temperature detection signal from the ink temperature sensor 55. A sensor control circuit 58 that controls various sensors 57 that detect the conveyance state of the recording medium 15 such as a feeding sensor, an adsorption sensor, and a discharge sensor and takes in detection signals from these sensors is provided.

  The CPU 41, P-ROM 42, P-RAM 43, PC interface 44, image memory 45, drive circuits 46, 48, 50 and control circuits 54, 56, 58 are electrically connected to each other by a pass line 59.

  After the image data stored in the image memory 45 is converted into bit data by the gradation conversion circuit 60, the gradation conversion is performed by performing a dithering process or the like according to the discharge gradation resolution of the inkjet recording head 23. The tone conversion circuit 60 supplies the tone-converted image data to the inter-tone speed correction circuit 61.

  The inter-tone speed correction circuit 61 constitutes a correction means, and is controlled by the CPU 41. Each ink droplet is ejected by correcting the speed between gradations using a calculation formula stored in the P-ROM 42. The discharge timing is adjusted. The inter-tone speed correction circuit 61 supplies the image data subjected to the speed correction between the gradations to the block dividing circuit 62.

  The block division circuit 62 performs block division according to the number of nozzles of the ink jet recording head 23 and supplies the image data obtained by the block division to the image transfer circuit 63. Then, the image data is transferred from the image transfer circuit 63 to the head driver 64, and the head driver 64 drives the inkjet recording head 23 based on the image data.

In the ink jet recording apparatus having such a configuration, adjustment of the ejection timing of each ink droplet from the nozzle is performed as follows.
Parameters that can be input from various sensors such as ink temperature, head temperature, ink type, etc., and parameters such as image recording resolution, recording speed, and distance between the recording medium 15 and the nozzles are input from the personal computer 100 and the keyboard 51 as ejection adjustment parameters. There is information that can be done. In this embodiment, a sensor using only an ink temperature sensor is shown as an example.

  The ink discharge speed of each ink droplet at each dot size (each gradation) under a certain condition is evaluated before shipment from the factory, and a discharge start timing difference at each dot size based on this is set in the P-ROM 42 in advance. To do. How much the timing changes due to the change of the parameters is evaluated in advance before shipment from the factory, and is set in the P-ROM 42 as a calculation formula.

  The CPU 41 detects the ink temperature, the resolution of image recording, the recording speed, and the distance between the recording medium 15 and the nozzles as parameters at the time of image recording. Correction data is added to the ink ejection timing. The inter-tone speed correction circuit 61 supplies the corrected image data to the block division circuit 62.

An example of investigating the ink ejection speed for each dot size under specific constant conditions is shown.
For example, when performing dot recording of seven gradations, seven ink droplets are sequentially ejected from the nozzle and land on the recording medium 15. When the ink droplets fly, the interval between the first drop, which is the first ink droplet, the second drop, which is the second ink droplet, the third drop, which is the third ink droplet, is gradually narrowed. Will come together. This is because the discharge speed of the first drop and the second drop is slower than that of the third drop. Then, after the first to third drops are combined and landed on the recording medium 15, the fourth to seventh drops land on the recording medium 15 sequentially with a certain time interval.

  FIG. 3 is a graph showing an example of the ejection speed from 1-drop dot recording to 7-drop dot recording under certain conditions.

  For this reason, when the distance between the nozzle and the recording medium 15 and the conveyance speed of the recording medium 15 are determined to be a certain condition, each dot size is ejected, or after the ejection starts, the ink lands on the recording medium 15. Measure the time until. For example, the time from the start of ejection until landing on the recording medium 15 is measured. The result is stored in the P-ROM 42 as the landing time on the recording medium 15 of each dot size under a certain condition.

  In the same manner, the landing time from the start of ejection for each dot size when the recording conditions are different to the landing on the recording medium 15 is calculated, and the landing time on the recording medium 15 of each dot size under a certain condition Is stored in the P-ROM 42 as correction data.

  For example, it is assumed that the landing time on the recording medium 15 is t1 to t7 from a dot size of one gradation by one drop under a certain condition to a dot size of seven gradations by seven drops. This indicates that the landing time is shifted by a time difference of t7-t1, for example, when the dot size of 1 drop and the dot size of 7 drop are started at the same time. That is, the landing position is shifted. If the distance between the nozzle and the recording medium 15 increases, the movement distance with respect to the time difference of t7-t1 increases, and the landing position further shifts.

  For this reason, instead of starting discharge at the same time when discharging each dot size under a certain condition, recording is performed by advancing the discharge start time for small dot sizes recorded using 1 to 3 drops. It is possible to match the landing position on the medium with the landing position of the first ink droplet of a large dot size recorded using 4 drops or more, particularly 7 drops, and the image quality can be improved.

  When the ejection timing of all the dot sizes is set assuming that the ink ejection speed is constant at both 1 drop and 7 drop, as shown in FIG. 4, the recording medium 15 conveyed in the direction indicated by the arrow in the figure. As shown in FIG. 5, the ink landing starts when the tip of the ink passes through the nozzle position of the inkjet recording head 23, and the landing position when dot recording (one gradation) of 1 drop is performed. The position is a distance L1 from the front end of the recording medium 15.

Similarly, when a dot size (7 gradations) consisting of 7 drops is recorded, the landing position is at a distance L2 (<L1) from the tip of the recording medium 15, as shown in FIG. This is because the discharge speed of the dot size of one gradation is slower than the discharge speed of the dot size of seven gradations, and the time for flying a certain distance becomes longer.
As a result, as shown in FIG. 7, there is a difference between the landing position of the dot recording D1 having a dot size of 7 gradations and the landing position of the dot recording D2 having a dot size of 1 gradation, resulting in image quality deterioration.

  In contrast, in the present embodiment, it is assumed that the ejection speed of ink droplets from 1 drop to 7 drops is different as shown in FIG. That is, when the number of drops is one and seven, it is assumed that the landing time on the recording medium 15 is longer, and the tip of the recording medium 15 is positioned at the nozzle position of the inkjet recording head 23 as shown in FIG. Ink ejection from the nozzle is started at an early timing before passing through the nozzle.

As a result, the landing position of the dot recording D2 on the recording medium 15 can be made coincident with the landing position of the dot recording D1 having a dot size of 7 gradations as shown in FIG. That is, both can be landed at a distance L2 from the front end of the recording medium 15.
As a result, as shown in FIG. 10, the landing position of the dot recording D1 having the dot size of 7 gradations and the landing position of the dot recording D2 having the dot size of 1 gradation can be matched. As a result, the center positions of dot recording can be matched in all of the low gradation with a small number of ejections and the high gradation with a large number of ejections, and a high-quality gradation image can be obtained.

Here, the relationship between the dot recording D1 having a dot size of 7 gradations and the dot recording D2 having a dot size of 1 gradation has been described here. This is based on the same idea.
As a method for obtaining the discharge speed of each drop and the landing time on the recording medium 15, there are a method of observing and measuring an actual discharge state with a camera, and a method of using a scale and a piezoelectric element.

  As shown in FIG. 11, the scale is used by arranging a pan 71 a of the scale 71 at a distance L 3 from the ink jet recording head 23, and the scale 71 detects a change in weight from the start of ink discharge from the head 23. Measure the time until.

In the method using a piezoelectric element, as shown in FIG. 12, a piezoelectric element 72 is arranged at a distance L3 from the ink jet recording head 23, and the piezoelectric element 72 generates a voltage from the start of ink discharge from the head 23. Measure the time to complete.
The distance L3 corresponds to the actual distance between the nozzles of the head 23 and the recording medium 15.

Next, a specific calculation method will be described.
Under the following conditions, when dot recording with a dot size of only one drop and dot recording with a dot size of 7 drops are ejected at the same time, a landing deviation of 0.04 mm occurs on the recording medium 15.

That is, in dot recording of dot size by 7 drops,
Flight time = distance / discharge speed = 1mm / 10m / sec
= 0.001m ÷ 10m / sec = 0.0001sec
Medium movement amount = medium speed × flight time = 1 m / sec × 0.0001 sec = 0.1 mm
Also, in dot recording of dot size with 1 drop,
Flight time = distance / discharge speed = 1mm / 7m / sec
= 0.0014m / 10m / sec = 0.00014sec
Media movement amount = medium speed × flight time = 1 m / sec × 0.00014 sec = 0.14 mm
Therefore, the landing position deviation of 0.14 mm−0.1 mm = 0.04 mm occurs.

  The landing position deviation is eliminated by making the ejection start timing at the time of 1 drop earlier than the ejection start timing at the time of 7 drops by the medium conveyance time of 0.04 mm for the landing deviation of 0.04 mm.

Discharge timing correction amount = 0.04 mm / 1 m / sec = 0.00004 m / 1 m / sec
= 0.00004sec = 0.04m sec
In the ejection speed calculation based on the difference in ink type, temperature, and distance from the recording medium, the parameters can be changed and the same can be obtained by the above method.

  Conversion formulas are obtained from these results, or are tabulated as a matrix and recorded in the P-ROM 42, and the discharge timing is adjusted according to the parameters in actual operation. By ejecting ink from the inkjet recording head 23 using the ejection timing at each dot size (each gradation) adjusted in this way, the landing positions of the inks of the respective dot sizes in the line direction on the recording medium 15 are matched. be able to.

  Further, in this embodiment, assuming that the ink spreads in a circular shape on the recording medium substantially around the position where the first ink droplet has landed, from the discharge start time of each drop until the first ink droplet has landed on the recording medium. However, as the relative speed with the recording medium increases, the landing position deviation between the first dot and the second dot increases, and the ink spreads in an elliptical shape instead of a circular shape. This case can be dealt with by calculating the time until landing by obtaining the center coordinates assuming an elliptical shape.

1 is a diagram showing a mechanism part of an ink jet recording apparatus according to an embodiment of the present invention. The block diagram which shows the structure of the control part in the embodiment. 6 is a graph showing the relationship between the number of drops from the head and the ink ejection speed. FIG. 3 is a diagram illustrating a positional relationship between a discharge start and a recording medium when an ink discharge speed is constant. FIG. 4 is a diagram illustrating a landing position on a dot-size recording medium composed of one drop when the ink ejection speed is constant. The figure which shows the landing position to the recording medium of the dot size which consists of 7 drops when the discharge speed of an ink is made constant. The figure which compares and shows the landing position to the recording medium in FIG.5 and FIG.6. FIG. 10 is a diagram illustrating a positional relationship between a discharge start and a recording medium when an ink discharge speed is 1 drop and is slower than 7 drops. FIG. 6 is a diagram illustrating a landing position on a 1-drop recording medium when an ink ejection speed is 1 drop when compared with 7 drops. FIG. 10 is a diagram showing a comparison of landing positions on a recording medium in FIGS. 6 and 9. The figure which shows the method of calculating | requiring the discharge speed of each drop, and the landing time to a recording medium using a scale. The figure which shows the method of calculating | requiring the discharge speed of each drop, and the landing time to a recording medium using a piezoelectric element.

Explanation of symbols

  23... Inkjet recording head, 41... CPU (central processing unit), 42... P-ROM, 61.

Claims (6)

In an inkjet recording apparatus that performs dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from a nozzle according to the gradation,
From the discharge start of each discharge obtained by measuring the speed of each discharge from dot recording by one drop of ink droplets to dot recording by the maximum number of drops in a state where at least the relative speed between the nozzle and the recording medium is set Storage means for storing time until arrival at the recording medium;
Timing for setting the timing of each ejection from the dot recording by one drop of ink droplets to the dot recording by the maximum number of drops based on the time from the ejection start of each ejection stored in the storage means to the arrival at the recording medium Comprising setting means,
An ink jet recording apparatus, wherein ink droplets are ejected from the nozzles at each ejection timing set by the timing setting means. In an inkjet recording apparatus that performs dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from a nozzle according to the gradation,
From the discharge start of each discharge obtained by measuring the speed of each discharge from dot recording by one drop of ink droplets to dot recording by the maximum number of drops in a state where at least the relative speed between the nozzle and the recording medium is set Storage means for storing time until arrival at the recording medium;
Ink temperature detecting means for detecting the ink temperature;
Correction means for correcting the time from the discharge start of each discharge stored in the storage means to the arrival at the recording medium according to the ink temperature detected by the ink temperature detection means;
Timing for setting the timing of each ejection from dot recording by one drop of ink droplets to dot recording by the maximum number of drops based on the time from the start of ejection of each ejection corrected by the correcting means to arrival at the recording medium Comprising setting means,
An ink jet recording apparatus, wherein ink droplets are ejected from the nozzles at each ejection timing set by the timing setting means.   When the relative speed between the nozzle and the recording medium is different from a set value, the time from the discharge start of each discharge stored in the storage means to the arrival at the recording medium is corrected according to the difference in relative speed. Item 3. The ink jet recording apparatus according to Item 1 or 2. When performing dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from the nozzle according to the gradation,
From the discharge start of each discharge obtained by measuring the speed of each discharge from dot recording by one drop of ink droplets to dot recording by the maximum number of drops in a state where at least the relative speed between the nozzle and the recording medium is set The time until arrival at the recording medium is stored in the storage means in advance,
Based on the time from the start of each stored discharge until arrival at the recording medium, the timing of each discharge from dot recording by one drop of ink droplets to dot recording by the maximum number of drops is set,
An ink jet recording method, wherein ink droplets are ejected from the nozzles at the set ejection timings. When performing dot recording on a recording medium that is conveyed by changing the number of ink droplets ejected from the nozzle according to the gradation,
From the discharge start of each discharge obtained by measuring the speed of each discharge from dot recording by one drop of ink droplets to dot recording by the maximum number of drops in a state where at least the relative speed between the nozzle and the recording medium is set The time until arrival at the recording medium is stored in the storage means in advance,
At the time of dot recording, the time stored from the discharge start of each discharge to the arrival at the recording medium, which is stored in the storage unit according to the detected ink temperature, is corrected,
Based on the corrected time from the start of ejection to arrival at the recording medium, the timing of each ejection from dot recording by one drop of ink droplets to dot recording by the maximum number of drops is set,
An ink jet recording method, wherein ink droplets are ejected from the nozzles at the set ejection timings.   When the relative speed between the nozzle and the recording medium is different from a set value, the time from the discharge start of each discharge stored in the storage means to the arrival at the recording medium is corrected according to the difference in relative speed. Item 3. The inkjet recording method according to Item 1 or 2.

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