JP2000289234A - Imaging method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control liquid jet timing of a liquid jet head arranged in the carrying direction of a print medium accurately regardless of rotational fluctuation of a rotator for carrying the print medium. SOLUTION: The imaging apparatus comprises a drive sprocket 22 for carrying a print medium upon rotation, and a head fixing section for holding a plurality of inkjet heads 13B, 13C, 13M and 13Y provided with a liquid jet opening at a specified interval S in the carrying direction of a print sheet 15. The print sheet 15 is carried by rotating the drive sprocket 22 and an image is formed by ejecting liquid to the print sheet 15 from the liquid jet opening of the inkjet head. Carrying distance of the print sheet 15 per one revolution of the drive sprocket 22 is set equal to the interval S between adjacent inkjet heads 13B, 13C, 13M and 13Y.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus for forming an image by discharging liquid from a plurality of liquid discharge heads onto a print medium, and more particularly to a full line type ink jet printer. It is suitable.

[0002]

2. Description of the Related Art An ink or a liquid such as a processing liquid for adjusting the printability of the ink is ejected from an ejection port of an ink jet head, and a desired image is formed on a print medium such as paper, a resin film, or a cloth or metal. The ink jet printer that forms is excellent in quietness because the print head is not in contact with such a print medium,
The advantages are that the printing speed is high, high-density printing is possible, colorization is easy, and the entire apparatus can be downsized.

[0003] As one of such ink jet printers, a printer using a long, so-called full line type ink jet head in which discharge ports are arranged over the entire width of an image forming area of a print medium is known. FIG. 5 shows a schematic structure of the full line type ink jet printer. The ink jet printer is a process in which print media 2 such as sheets stacked on a paper feed tray 1 are fed out one by one, transferred onto a transport belt 3, and discharged from the transport belt 3 to a discharge tray 4. Then, the conveyor belt 3
A desired image is formed by a plurality of ink-jet heads 5, which are arranged immediately above, for example, four ink-jet heads 5 that respectively discharge black, cyan, magenta, and yellow inks. Usually, these inkjet heads 5 are arranged in the order of black, cyan, magenta and yellow inkjet heads 5 so that inks with higher optical density are ejected in order. If the position of the print medium 2 with respect to the inkjet head 5 is not accurately adjusted, image quality such as color misregistration will be degraded.

For this reason, conventionally, a stepping motor 6 is used to transport the print medium 2 on the transport belt 3, and the print medium 2 is driven based on the driving frequency of the stepping motor 6 and the relative position of each ink jet head 5. Ink ejection timing from each ink jet head 5 is calculated, and each ink jet head 5 is driven in synchronization with the stepping motor 6.

[0005]

In the conventional ink jet printer shown in FIG. 5, a component constituting a power transmission system provided between the stepping motor 6 and the conveyor belt 3, particularly a rotating body such as a driving pulley 7, is provided. Due to the eccentricity and assembly error of the print medium 2, the moving speed of the conveyor belt 3 is not always constant but slightly changes periodically.
In contrast, the ejection timing of the ink from the inkjet head 5 located on the downstream side in the transport direction of the print medium 2 may be shifted. As a result, the print medium 2
In this case, the ink cannot be ejected accurately to the position where printing is to be performed in advance, and the ejection position of the ink is shifted along the transport direction of the print medium 2, resulting in deterioration of image quality such as color shift. ing.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to accurately control the ejection timing of liquid from liquid ejection heads arranged in the direction of conveyance of a print medium even when the rotating body for conveying the print medium has uneven rotation. And a device therefor.

[0007]

According to a first aspect of the present invention, there is provided:
The print medium is transported by driving the rotating body for transporting the print medium, and the liquid is discharged from each of the discharge ports of the plurality of liquid discharge heads arranged at predetermined intervals in the transport direction of the print medium, and the image is printed on the print medium. Wherein the discharge timing of the liquid from the discharge port of the liquid discharge head is controlled on the basis of one rotation of the rotating body.

According to the present invention, even if the peripheral speed changes during one rotation of the rotator, there is no change in the transport amount of the print medium due to one rotation of the rotator. By controlling the ejection timing of the liquid from the ejection port of the liquid ejection head on the basis of the rotation, the ink is accurately ejected to the position where printing is to be performed on the print medium in advance.

According to a second aspect of the present invention, a rotating body for transporting a print medium by driving and rotating, and a plurality of liquid discharge heads having discharge ports for discharging a liquid are formed in the transport direction of the print medium. And a head mounting portion for holding the print medium at a predetermined interval, while driving and rotating the rotating body to convey the print medium, and discharging an image onto the print medium from the discharge port of the liquid discharge head to form an image. In the image forming apparatus to be formed, a conveyance distance of the print medium per one rotation of the rotating body is set to be equal to an interval between adjacent liquid ejection heads.

According to the present invention, even if the peripheral speed changes during one rotation of the rotating body, the amount of transport of the print medium by one rotation of the rotating body does not change. By setting the transport distance of the print medium per rotation and the distance between the adjacent liquid discharge heads to be the same, the ink is accurately discharged to the position where the print medium is to be printed in advance.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the first and second embodiments of the present invention, a plurality of liquid discharge heads may discharge inks of different hues.

Further, the liquid may be a processing liquid for adjusting the printability of the ink and / or the ink ejected onto the print medium.

The liquid discharge head may have discharge ports arranged over the entire width of the print area of the print medium.

In the image forming apparatus according to the second aspect of the present invention, the liquid discharge head may have a discharge energy generating section for discharging liquid droplets from the discharge port. May have an electrothermal conversion element that generates thermal energy that causes film boiling in the liquid.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an image forming apparatus capable of realizing the image forming method according to the present invention is applied to a full line type ink jet printer will be described in detail with reference to FIGS. The present invention is not limited to the above embodiments, and may be further combined or applied to technologies in other fields that include similar problems.

FIG. 1 shows a schematic structure of this embodiment.
FIG. 2 shows a cross-sectional structure taken along the line II. That is, the ink jet printer according to the present embodiment includes a paper feeding device 11, a paper conveying device 12, a plurality (four in the illustrated example) of ink jet heads 13B, 13C, 13M, 13Y, and a stacker 14.

The paper supply device 11 for supplying print paper 15 as a print medium to the ink jet printer includes a paper supply tray 1 on which the print paper 15 is stacked.
6, print paper 1 loaded on the paper feed tray 16
5, a separation guide 18 that causes the print papers 15 stacked on the paper feed tray 16 to be fed out one by one from the top in accordance with the rotation of the pickup rollers 17, and side edges of the print papers 15. Print paper 1 so that the edge is parallel to the transport direction.
5, a skew correcting member 19 for correcting skew.
It has a pair of carry-out rollers 20 and the like for guiding the print paper 15 fed by the pickup roller 17 to the paper transport device 12.

A paper transport device 12 for guiding the print paper 15 to the outlet of the ink-jet printer is provided with a plurality of (three in the illustrated example) transport toothed belts (hereinafter referred to as toothed belts) for transporting the paper. Abbreviated) 21;
A driving sprocket 22 and a driven sprocket 23 around which the toothed belt 21 is wound, a transport motor 24 for driving the toothed belt 21 via the driving sprocket 22 as a rotating body in the present invention, and a driven sprocket 23 , A press roller 25 for guiding the print paper 15 onto the toothed belt 21, a paper sensor 26 for detecting the leading end position of the print paper 15 fed onto the toothed belt 21, and the print paper 1 on the toothed belt 21.
And a pair of paper discharge rollers 27 for guiding the nozzle 5 to the outlet of the ink jet printer. Further, the transport motor 24 employs a stepping motor, and can control the moving amount of the toothed belt 21 according to the driving pulse amount.

The ink jet heads 13B, 13C, 13M, and 13Y for forming an image on the print paper 15 by ejecting ink droplets from an ejection port (not shown) are arranged so that the ejection port faces downward immediately above the toothed belt 21. They are arranged at a predetermined interval S corresponding to the pitch circle diameter of the driving sprocket 22, and are arranged in order from the upstream side for black ink, cyan ink, magenta ink, and yellow ink.
In addition, these inkjet heads 13B, 13C, 1
The interval S between 3M and 13Y is 2πr, where r is the pitch circle radius of the driving sprocket 22 and π is the pi, ie, the toothed belt 2 corresponding to one rotation of the driving sprocket 22.
This corresponds to the movement amount of 1.

The above-described ink jet heads 13B, 1
Stacker 1 from which print paper 15 on which an image is formed by ink droplets ejected from 3C, 13M, 13Y is discharged
Reference numeral 4 denotes a discharge tray 28 on which the print paper 15 on which an image is formed is stacked, and a pair of feed rollers 29 for guiding the print paper 15 sent from the discharge rollers 28 to the discharge tray 28.

Therefore, the sheet transporting device 1 is
The print paper 15 guided to 2 is guided onto a toothed belt 21 driven by a transport motor 22. When the print paper 15 is an inkjet head 13B, 13C,
When passing directly below 13M and 13Y, an image is formed by ink droplets ejected from each ejection port. After the image is formed in this manner, the print paper 15 is guided onto the paper discharge tray 28 by the paper discharge rollers 27 driven in synchronization with the transport motor 22. In this case, as shown in FIG. 3, which schematically shows an image formed on the print paper 15, the amount of movement of the print paper 15 by one rotation of the driving sprocket 22 and the distance between the adjacent inkjet heads 13
Since the intervals S of B, 13C, 13M, and 13Y coincide with each other, even when rotational unevenness due to eccentricity of the drive sprocket 22 or the like occurs, each of the inkjet heads 13B, 13C, 13M, 1
It is possible to accurately match the ejection positions of the ink droplets by 3Y, and to form an image of good quality without color shift.

Incidentally, B, C, M and Y in FIG.
Indicate ejection areas of black ink, cyan ink, magenta ink, and yellow ink, respectively, which are precisely aligned in a direction perpendicular to the print paper transport direction (left direction in FIG. 3). It will be understood that it is.

In the above-described embodiment, the printing paper 15 is conveyed by using the toothed belt 21.
It is also possible to provide a similar function by arranging them along the transport direction of

FIG. 4 shows a schematic structure of another embodiment of such a sheet conveying device. Members having the same functions as those of the above-described embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. It shall be omitted. That is, a plurality of (five in the illustrated example) roller shafts 31 rotatably attached to the frame 30 at predetermined intervals are integrally provided with a transport roller 32 for transporting print paper. A drive gear 33 having the same pitch circle diameter is attached to one end of each of the roller shafts 31. The adjacent drive gears 33 are meshed with each other via an idle gear 34 rotatably attached to the frame 30, and the drive gear 33 and the idle gear 34 have the same pitch circle diameter. A transport motor 22 having the same function as that of the previous embodiment is attached to a roller shaft 31 located on the downstream end side in the print paper transport direction, and all the transport rollers 32 are rotated synchronously by the transport motor 22. It has become.

The ink jet head has an interval corresponding to the pitch circle diameter of the drive gear 33 and the idle gear 34, that is, the pitch circle radius of the drive gear 33 and the idle gear 34 is represented by r, and the circumferential ratio is represented by 2πr. Are arranged in the same manner as in the previous embodiment.

Therefore, also in this embodiment, the driving gear 33
Since the amount of movement of the print paper by one rotation of the print head coincides with the distance between adjacent inkjet heads, even if rotation unevenness occurs due to eccentricity of the drive gear 33, etc. It is possible to accurately match the ejection positions of the ink droplets by the inkjet head, and to form an image of good quality without color shift.

The present invention includes a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for discharging the liquid. This provides an excellent effect in an image forming apparatus using an ink jet type liquid ejection head which causes a change. According to such a method, it is possible to achieve higher density and higher definition of the print.

The typical configuration and principle are described in, for example, US Pat. No. 4,723,129 and US Pat.
It is preferable to use the basic principle disclosed in Japanese Patent Application No. 0796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or the flow path holding the liquid. Heat energy is generated by applying at least one drive signal to the electrothermal transducer to give a rapid temperature rise exceeding nucleate boiling corresponding to print information, thereby causing film boiling on the heat working surface of the liquid discharge head. As a result, bubbles in the liquid corresponding to this drive signal one-to-one can be formed, which is effective. By the growth and shrinkage of the bubble, the liquid is discharged through the discharge port to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of the liquid having particularly excellent responsiveness can be achieved, which is more preferable. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in U.S. Pat. No. 4,313,124 relating to the rate of temperature rise of the heat acting surface are adopted, more excellent printing can be performed.

The structure of the liquid discharge head is a combination of a discharge port, a liquid path, and an electrothermal converter as disclosed in each of the above-mentioned specifications (the electrothermal converter is arranged along the liquid path). U.S. Pat. No. 6,059,055 discloses a configuration in which a disposed linear liquid flow path or an electrothermal converter is disposed in a region where a heat acting portion is bent in addition to a liquid flow path and a right-angled liquid flow path directly facing the discharge port. Patent No. 4558333 and US Patent No. 44596
The configuration using the specification of No. 00 is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slit is used as a discharge portion of an electrothermal transducer for a plurality of electrothermal transducers, and an aperture for absorbing a pressure wave of thermal energy is provided. The effects of the present invention are effective even if the configuration is based on JP-A-59-138461, which discloses a configuration corresponding to the ejection unit. That is, according to the present invention, printing can be performed reliably and efficiently regardless of the form of the liquid discharge head.

The effect of the present invention can be further stabilized by adding a recovery means or a preliminary auxiliary means for making the state of liquid discharge from the liquid discharge head proper as a configuration of the image forming apparatus of the present invention. It is preferable because it can be performed.
Specific examples thereof include a capping unit for the liquid discharge head, a cleaning unit, a pressurizing or sucking unit, a preheating unit that performs heating using an electrothermal converter, another heating element, or a combination thereof. ,
Preliminary ejection means for performing ejection other than printing can be used.

Regarding the type and number of mounted liquid ejection heads, inks of the same hue or a plurality of inks may be provided corresponding to a plurality of inks having different optical densities. . That is, for example, the print mode of the image forming apparatus is not limited to the print mode of only the mainstream color such as black, but may be configured integrally with the liquid ejection head or by a combination of a plurality of liquid ejection heads.
The present invention is extremely effective also in an apparatus provided with at least one of the printing modes of full-color printing using different colors, such as multiple colors or mixed colors. In this case, it is also effective to discharge a processing liquid (printability improving liquid) for adjusting the printability of the ink to the print medium from a dedicated or common liquid discharge head according to the type of print medium and the print mode.

Further, in the embodiment of the present invention described above, a material which solidifies at room temperature or lower and softens or liquefies at room temperature may be used, or in the case of an ink jet system, the liquid itself is 30 ° C. to 70 ° C. In general, the temperature is adjusted within the range described above to control the temperature so that the viscosity of the liquid is in the stable ejection range. Therefore, a liquid that is in a liquid state when the used print signal is applied may be used. In addition, in order to positively prevent the temperature rise due to thermal energy by using it as the energy of the state change from the solid state to the liquid state, or to prevent the liquid from evaporating, it is solidified in a standing state and liquefied by heating. May be used. In any case, such as a liquid that is liquefied by application of heat energy according to a print signal and a liquid is discharged, and a liquid that already starts to solidify when it reaches a print medium,
The present invention is also applicable to a case where a material that liquefies for the first time by applying heat energy is used. The liquid in such a case is, as described in JP-A-54-56847 or JP-A-60-71260, in a state where it is held as a liquid or solid substance in the concave portion or through hole of the porous sheet. Alternatively, it may be configured to face the electrothermal converter. In the present invention, the most effective one for each of the above-mentioned liquids is to execute the above-mentioned film boiling method.

The form of the image forming apparatus according to the present invention can be used not only as an image output terminal of an information processing apparatus such as a computer, but also as a copying apparatus combined with a reader or the like, as well as a facsimile apparatus having a transmitting / receiving function. The printing medium may be in the form of a printing device. The printing medium may be a sheet or long paper or cloth, or a plate-shaped wood, stone, resin, glass, metal, or the like, or may be a three-dimensional printing medium. Examples include three-dimensional structures.

[0034]

According to the present invention, the discharge timing of the liquid from the discharge port of the liquid discharge head is controlled with reference to one rotation of the rotating body for transporting the print medium.
Even if there is uneven rotation of the rotating body due to eccentricity or the like, the amount of conveyance of the print medium by one rotation of the rotating body does not change, and ink is accurately applied to a position where printing is to be performed on the print medium in advance. Discharge can be performed, and the occurrence of color misregistration can be fundamentally prevented, and an image of good quality can be formed.

Similarly, since the conveyance distance of the print medium per one rotation of the rotating body and the interval between the adjacent liquid ejection heads are set to be the same, the rotational unevenness of the rotating body due to eccentricity or the like is reduced. Even if there is, there is no change in the transport amount of the print medium due to one rotation of the rotating body, ink can be ejected accurately to the position where printing is to be performed on the print medium in advance, and occurrence of color misregistration is reduced. It is possible to form an image of good quality by fundamentally blocking.

[Brief description of the drawings]

FIG. 1 is a conceptual view of a mechanism showing a schematic structure of an embodiment in which an image forming apparatus according to the present invention is applied to an ink jet printer.

FIG. 2 is a view taken along the line II-II of the embodiment shown in FIG.

FIG. 3 is a schematic diagram sequentially showing a printing process according to the embodiment shown in FIG. 1;

FIG. 4 is a plan view corresponding to FIG. 2 of another embodiment of the present invention.

FIG. 5 is a conceptual view of a mechanism showing a schematic structure of a conventional ink jet printer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Paper feeder 12 Paper feeder 13B, 13C, 13M, 13Y Ink jet head 14 Stacker 15 Print paper 16 Paper feed tray 17 Pickup roller 18 Separation guide 19 Skew straightening member 20 Unloading roller 21 Conveyor toothed belt 22 Drive sprocket 23 Driven sprocket 24 Transport motor 25 Press roller 26 Paper sensor 27 Discharge roller 28 Discharge tray 29 Feed roller 30 Frame 31 Roller shaft 32 Transport roller 33 Drive gear 34 Idle gear S Ink head interval B Black ink ejection area C Cyan Color ink ejection area M Magenta ink ejection area Y Yellow ink ejection area

Claims (10)

[Claims] 1. A printing medium transporting rotary body is driven to transport a print medium, and a liquid is ejected from each ejection port of a plurality of liquid ejection heads arranged at a predetermined interval in the transport direction of the print medium. An image forming method for forming an image on a print medium, wherein a timing of discharging liquid from a discharge port of the liquid discharge head is controlled based on one rotation of the rotating body. Method. 2. The image forming method according to claim 1, wherein the plurality of liquid discharge heads discharge inks of different hues. 3. The image forming method according to claim 1, wherein the liquid is a processing liquid for adjusting printability of the ink and / or the ink ejected to a print medium. 4. The liquid discharge head according to claim 1, wherein the discharge ports of the liquid discharge head are arranged over the entire width of a print area of the print medium. Image forming method. 5. A rotating body for transporting a print medium by driving and rotating, and a plurality of liquid ejection heads having ejection ports for ejecting liquid are held at predetermined intervals in the transport direction of the print medium. An image forming apparatus, comprising: a head mounting portion, for driving and rotating the rotator to convey the print medium and discharging a liquid from a discharge port of the liquid discharge head to the print medium to form an image. An image forming apparatus, wherein a conveyance distance of the print medium per one rotation of the rotating body is set to be equal to an interval between adjacent liquid ejection heads. 6. The image forming apparatus according to claim 5, wherein the plurality of liquid discharge heads discharge inks of different hues, respectively. 7. The image forming apparatus according to claim 5, wherein the liquid is a processing liquid for adjusting printability of the ink and / or the ink ejected to a print medium. 8. The liquid discharge head according to claim 5, wherein the liquid discharge heads have discharge ports arranged over the entire width of a print area of the print medium. Image forming device. 9. The image forming apparatus according to claim 5, wherein the liquid discharge head has a discharge energy generating unit for discharging a droplet from the discharge port. 10. The image forming apparatus according to claim 9, wherein the discharge energy generation unit includes an electrothermal conversion element that generates thermal energy that causes liquid to cause film boiling.