JP2015051511A - Image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording method for preventing reduction in an image quality of an image caused by an impact error of a droplet discharged from a recording head, in the case of a configuration in which a distance up to a recording medium from the recording head varies.SOLUTION: An image recording method is an image recording method for recording an image on a recording medium 208 by discharging ink from a discharge port by using a recording head 202 having a plurality of discharge ports, and when at least two among the plurality of discharge ports have different distances from each other from the recording medium 208, when a distance up to the recording medium 208 of the discharge port 206 on the near side from the recording medium 208 is denoted by h1, and a distance up to the recording medium 208 of the discharge port 207 on the distant side from the recording medium 208 is denoted by h2, and a discharge speed of the ink is denoted by v2, correction control of v2 is executed so as to satisfy a relation of v2≥(h2/h1)v1.

Description

  The present invention relates to an image recording method.

  2. Description of the Related Art Image recording apparatuses such as ink jet recording apparatuses are known that perform recording using a recording head in which a plurality of recording elements (hereinafter, also referred to as ejection ports) are integrated to improve recording speed. ing. Further, in recent years, there has been an increasing demand for colorization of recorded images, and those equipped with a plurality of types of recording heads that discharge color inks are generally used.

  In addition, against the background of recent technological advances in integrated arrangement of discharge ports, it has become possible to manufacture high-density and long recording heads. A long recording head with a high density of discharge ports is generally called a full multi-type long recording head. One recording is performed on a wide recording area corresponding to the long recording head. Proposals and implementations have been made to complete an image by scanning. According to this image recording apparatus, since both the recording speed and the image quality can be satisfied, further technical development is being advanced.

  In recent years, printers aiming at high-speed printing using such a long head have been developed, and a configuration for printing on a drum rotating at high speed is common. In such a configuration, printing is performed on the curved surface of the drum using an ink jet method, but recording from the recording head to the recording medium on the curved surface means that the recording medium depends on the position of the discharge port in the recording head. It means that the distance to will change.

  When the distance to the recording medium changes, the image quality varies depending on the distance. However, in order to solve this problem, Patent Document 1 changes the recording method according to the distance from the recording head to the recording medium. A method for printing is disclosed.

  That is, when the ejection control disclosed in Patent Document 1 is performed, the problem is that the dot density of the image varies due to the change in the distance from the recording head to the recording medium, by changing the ejection amount and the original data. It is addressed.

JP 2009-234191 A Japanese Patent No. 3423412 Japanese Patent No. 3313819

  However, it is known that the image quality of the obtained image is also deteriorated due to droplet landing error (ejection deviation). In the method of changing the ejection amount and the original data as disclosed in Patent Document 1, it is difficult to improve the deterioration of the image quality caused by the droplet landing error (ejection deviation).

  An object of the present invention is to provide an image recording method for preventing deterioration in image quality caused by landing errors of droplets ejected from a recording head when the distance from the recording head to the recording medium is changed. And

The image recording method of the present invention is an image recording method for recording an image on a recording medium by using a recording head having a plurality of ejection openings and ejecting ink from the ejection openings, and at least of the plurality of ejection openings. When the two have different distances from the recording medium, the distance from the recording port closer to the recording medium to the recording medium is h1, the ink ejection speed is v1, and the one farther from the recording medium. The distance from the ejection port to the recording medium is h2, and the ink ejection speed is v2.
v2 ≧ (h2 / h1) v1
The correction control of v2 is performed so as to satisfy the following formula.

  According to the present invention, it is assumed that the distance from the recording medium to the recording medium of the closer ejection opening (ejection opening A) is h1, the ink ejection speed is v1, and the ejection outlet (ejection opening B) far from the recording medium. If the distance to the recording medium is h2 and the ink ejection speed is v2, the correction control of v2 is performed so that h1, h2, and v1 are known and v2 ≧ (h2 / h1) v1 is satisfied. The landing accuracy from the discharge port B to the recording medium becomes equal to or higher than the landing accuracy from the discharge port A to the recording medium, and the image quality is improved.

  INDUSTRIAL APPLICABILITY The present invention can provide an image recording method for preventing deterioration in image quality caused by landing errors of droplets ejected from a recording head when the distance from the recording head to the recording medium is changed. .

It is a figure which shows the conceptual structure of the image recording apparatus of this invention. It is a figure which shows the positional relationship of the recording head of this invention, and a drum. It is a figure which shows the state which the droplet in this invention flies. It is a figure which shows the pattern for measuring the discharge speed in this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a conceptual configuration of an image recording apparatus according to the first embodiment of the present invention. The present invention is an invention for performing optimum printing mainly in a system in which the distance from the recording head to the recording medium is different, and an image recording apparatus that performs printing on a drum-shaped recording medium is a representative example of the present invention. .

  The image recording apparatus of the present embodiment is a full-line type color inkjet recording apparatus in which long recording heads 103, 104, 105, and 106 are arranged in parallel in the recording medium conveyance direction. Here, the color ink jet recording apparatus includes a recording head 103 that ejects yellow ink, a recording head 104 that ejects magenta ink, a recording head 105 that ejects cyan ink, and a recording head 106 that ejects black ink. Each recording head has substantially the same configuration, and in the following description, unless there is a particular need to distinguish, these are collectively referred to as a recording head.

  In the recording head, there are formed an ink discharge port for discharging ink, a common liquid chamber, and a liquid flow path to be described later for guiding ink from the common liquid chamber to each ink discharge port. Each liquid flow path is provided with an electrothermal converter (heater) as discharge energy generating means for generating thermal energy. The heater is electrically connected to the control device via a head driver. The driving / stopping of the heater is controlled in accordance with an on / off signal (discharge / non-discharge signal) sent from the control device.

  The ink ejected from these recording heads lands on the recording drum 102 to form an image.

  Next, the relationship between the recording head 202, which is a characteristic part of this embodiment, and the printing drum 201, which is a recording medium, will be described with reference to FIG. The discharge port surface 205 of the recording head 202 is disposed so as to be parallel to the central axis of the print drum 201. Further, chips 203 and 204 are arranged in the recording head 202 in the drum rotation direction. Each of the chips 203 and 204 has a plurality of ejection port arrays, and the distance to the printing drum 201 differs depending on the position of the ejection port array.

  In the chip 203, the distance between the discharge port array closest to the drum and the drum is h1, and the distance between the discharge port array farthest from the drum and the drum is h2. At this time, how the image quality of the image decreases for each ejection port array will be described with reference to FIG.

FIG. 3 is a schematic diagram when droplets fly from a certain chip toward a recording medium. In this figure, it is assumed that the ejected droplets land with a certain amount of deviation from the ideal landing position. If the distance from the ejection port 206 closer to the recording medium to the recording medium 208 is h1, and the distance from the ejection port 207 farther from the recording medium to the recording medium 208 is h2, the landing deviation amount is the same when the flight speed is the same. They are y1 and y2, respectively. Here, the relationship of the following equation is established between y1 and y2.
y2 = y1 × (h2 / h1)
As described above, when the amount of landing position deviation differs for each ejection port array, the degree of image quality deterioration varies for each ejection port array, and a good image cannot be obtained.

  Therefore, by changing the ejection speed for each position of the ejection port array and aligning the landing time to the recording medium for each ejection port array, it is possible to align the amount of landing deviation for each ejection port array.

As shown in FIG. 2, assuming that the distance from the chip to the drum is h1 and h2, and the ejection speeds when ejecting ink from the respective ejection port arrays are v1 and v2, respectively, In order to align the arrival time to reach
h1 / v1 = h2 / v2
It only has to be. Here, typically, h1 and h2 are very short, less than 1 mm, and v1 and v2 are as fast as about 15 m / s. Therefore, deceleration due to air resistance after ink ejection is negligible, and v1, v2 was assumed to be constant from ejection to landing.

Rewriting the above formula,
v2 = (h2 / h1) × v1
If the discharge speed is made variable so as to maintain the relational expression, the landing accuracy is equivalent.

In actual implementation of the present invention, it is obvious that the higher the discharge speed v, the higher the landing accuracy and the image quality.
v2 ≧ (h2 / h1) × v1
If it controls so that it may become, the effect of invention will be acquired.

  As a means for changing the discharge speed, a PWM (Pulse Width Modulation) method for changing the pulse width for driving the discharge heater is suitable. Since the control of the discharge speed in the PWM method is already widely known in the invention such as Patent Document 2, detailed description thereof is omitted here.

  However, if it is attempted to control the discharge speed using the PWM method, the discharge amount may be changed at the same time depending on the form of the discharge outlet. Therefore, in the present invention, a head shading method that reduces the influence of the change in the discharge amount and adjusts the apparent density by adjusting the density of the original image that is the source of printing in response to the problem that the discharge amount changes. Use. The density referred to here is an optical density (OD value) and is defined by OD = −log (reflectance).

  Table 1 shows a table used when performing head shading control. Assume that there are five types of pulses A to E used in the PWM system.

When the pulse C is used as a reference, the pulse A and the pulse B are drive pulses whose discharge speed is faster than that of the pulse C. At the same time, the discharge amount is 20% higher for the pulse A and 10% higher for the pulse B, respectively. turn into. Therefore, if the density of the original image is set to -20% when using pulse A and -10% when using pulse B, the apparent density is almost the same as when printing with pulse C.

  Similarly, the pulse D and the pulse E are drive pulses whose discharge speed is slower than that of the pulse C, and at the same time, the discharge amount is 10% when the pulse D and 20% when the pulse E, respectively. Therefore, if the density of the original image is + 10% when using pulse D and + 20% when using pulse E, the apparent density is almost the same as when printing with pulse C, as before.

  Next, a method for detecting the discharge speed will be described. In order to detect the ejection speed from the recording head, a method of calculating from the deviation of the landing position of the ejected ink is desirable. A pattern for detecting the discharge speed from the landing position is shown in FIG. A new striped pattern 502 having a relationship that complements the striped pattern 501 printed in the reference ejection port array is printed in the ejection port array whose discharge speed is desired.

  Patterns 503 to 505 are discharge timings 1 from the discharge port array whose discharge speed is to be measured, with respect to the pattern 506 which is printed so as to have a complementary relationship between the reference discharge port array and the discharge port array whose discharge speed is to be measured. They are shifted pixel by pixel. Similarly, the patterns 507 to 510 are also shifted in the opposite direction on the time axis from the patterns 503 to 505.

  If the discharge speed of the reference discharge port array is exactly the same as the discharge speed of the discharge port array for which the discharge speed is desired, the pattern 506 is a complementary pattern without a striped gap. In the case where the ejection speed of the ejection port array serving as a reference is different from the ejection speed of the ejection port array for which it is desired to know the ejection speed, the patterns other than the pattern 506 are complementary patterns having no striped gaps.

  For example, it is assumed that the pattern 507 shifted by one pixel from the reference discharge port array has a complementary relationship without a gap. If the printer is 472 dots / cm (1200 dpi), the landing position is shifted by about 21 μm. Assuming that the distance between the head and the recording drum is 1 mm, the rotational speed of the drum is 1 m / s, and the discharge speed of the reference discharge port array is 15.0 m / s, the discharge speed of the discharge port array whose discharge speed is to be measured is 14.6 m / s. Here, the ejection speed of the ejection port array serving as a reference was set based on the design center value (about 15 m / s) when ejection was performed with a normal pulse.

  As described above, it is possible to obtain a relative discharge speed difference from the reference discharge port array by observing which pattern has a complementary relationship.

  Next, the distance from the recording head to the recording medium may be a value measured by a laser length measurement method as shown in Patent Document 3, or a design value obtained from design data of the printer body. Good.

  A good image can be obtained by controlling the discharge speed so as to satisfy the formula of v2 ≧ (h2 / h1) × v1 from the information on the discharge speed and distance obtained in this way.

  Next, the timing for performing the correction control shown in the present invention will be described. According to the present invention, the effect can be obtained by performing correction control when the distance from the recording head to the recording medium and the ejection speed of the droplets are known. First, as the timing when the two points are known, the time of factory shipment can be considered. At the time of shipment from the factory, it becomes possible to know the distance from the recording head to the recording medium in a state having a manufacturing error inherent to the printer body. In addition, it is possible to know the ejection speed of a recording head mounted on the recording head with a manufacturing error. If correction control is performed based on these two eigenvalues at the time of shipment from the factory, it is possible for the user to immediately perform high-quality printing with the correction work already completed.

  In addition, the eigenvalues of these two points change due to replacement of the recording head due to consumption of the recording head. For this reason, it is desirable to perform correction work even when the recording head is replaced.

  Further, printing is performed by winding the recording medium around a drum. However, since the distance from the recording head to the recording medium varies depending on the thickness of the recording medium, it is desirable to perform a correction operation for this.

  In addition, the droplet ejection speed may change over time depending on the frequency of use of the printhead, so the correction work can be performed arbitrarily by the user periodically or irregularly according to the printhead usage history. Is also suitable.

(Second Embodiment)
In the first embodiment, a form in which printing is performed with a full multi-head on a drum-shaped recording medium has been shown, but the present invention is not limited to that form. For example, the present invention is also effective in a so-called serial printer that performs printing while a recording head scans a flat recording medium such as paper.

  Even in a flat recording medium such as paper, it is conceivable that the distance to the recording medium differs for each ejection port in the recording head due to a manufacturing error of the paper transport mechanism of the printer, undulation of the paper, or the like. At that time, the image quality of the image at a location where the distance to the recording medium is long is deteriorated.

  In order to carry out the present invention, it is only necessary to know the distance from the recording head to the recording medium and the droplet discharge speed. The droplet ejection speed may be the method described in the first embodiment of the present invention.

  The distance from the recording head to the recording medium is preferably measured accurately and at high speed by using the laser length measurement method.

(Third embodiment)
In addition to the method shown in the first embodiment, the following method is effective. In the diagram showing the positional relationship between the recording head and the recording drum shown in FIG. 2, the distance between the central portion of the recording head and the printing drum is the shortest, and the recording chip 203 and the recording chip 204 are symmetrical with respect to that point. It is in. That is, the recording chip 203 and the recording chip 204 have the same distance from the drum. Therefore, if the discharge speed is measured and corrected by the method shown in the first embodiment on one of the recording chips 203 or 204, the same correction amount may be applied to the other chip. .

  By using the method as described above, the correction work can be shortened and usability is improved.

(Fourth embodiment)
In the first to third embodiments, a method of measuring the discharge speed on the printer body is used, but the discharge speed is measured in advance at the factory that produces the printhead, and the memory provided in the printhead The discharge speed information may be written in the data and correction may be performed based on the information. By using this method, the user can further shorten the correction work, and the usability is greatly improved.

(Other embodiments)
In the above-described embodiment, an example in which the landing position deviation is detected and the ejection speed is calculated using a striped pattern that complements each other in the ejection port arrays where it is desired to detect the landing position deviation. In addition, a method such as printing and reading a pattern such as a vernier caliper memory, a method of detecting a landing position shift using an optical device such as a scanner, or a reading of the position shift by human eyes can be used. An input method may be used.

  Further, as a means for controlling the discharge amount, the PWM method has been described as an example, but other methods such as a method for changing the voltage applied to the heater, or a combination of both may be used.

  In the above embodiment, an image recording apparatus using a recording head having a discharge port for discharging a fixed amount of droplets has been described as an example, but a discharge port capable of discharging droplets of different liquid amounts is provided. The present invention can also be applied to a recording head. Further, the present invention can be applied to recording heads that discharge light and dark inks having different densities in the same hue in addition to inks such as yellow, cyan, magenta, and black.

  The present invention provides a particularly excellent effect in a recording apparatus using an ink jet recording head that performs recording by ejecting ink in a discharge port as flying ink droplets using thermal energy among ink jet recording methods. is there.

  Furthermore, the present invention is also effective when the recording head is fixed to the apparatus main body. Alternatively, it is also effective for a replaceable chip type that can be electrically connected to the apparatus main body and supplied with ink from the apparatus main body by mounting the recording head on the apparatus main body. Further, the present invention is also effective for a cartridge type recording head in which an ink tank is provided integrally with the recording head itself.

102, 201 Print drums 103 to 106, 202 Recording head 206 Discharge port 207 closer to the recording medium Discharge port 208 farther from the recording medium Recording medium

Claims (5)

An image recording method for recording an image on a recording medium by ejecting ink from the ejection ports using a recording head having a plurality of ejection ports,
When at least two of the plurality of ejection openings have different distances from the recording medium,
The distance from the recording port closer to the recording medium to the recording medium is h1, the ink ejection speed is v1,
The distance from the discharge port farther from the recording medium to the recording medium is h2, and the ink discharge speed is v2.
v2 ≧ (h2 / h1) v1
And v2 is controlled so as to satisfy the following formula.   The image recording method according to claim 1, wherein the v2 is controlled by a Pulse Width Modulation method.   The image recording method according to claim 1, wherein a distance from the discharge port to the recording medium is measured by a laser length measurement method.   4. The image recording method according to claim 1, wherein the recording medium has a drum shape, and an ejection port surface of the recording head is disposed so as to be parallel to a central axis of the recording medium.   The discharge port surface has at least one set of recording chips arranged in line symmetry with respect to a straight line in which the distance between the discharge port surface and the recording medium is the shortest, and one of the recording chips in each set 5. The image recording method according to claim 4, wherein the correction amount used in the correction control is applied to the other recording chip.

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