JP2006248001A - Liquid discharge device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid discharge device which reduces the contamination of a machine interior due to a mist of a liquid and discharges the liquid with proper impact accuracy in accordance with a user's request. <P>SOLUTION: The liquid discharge device discharges so as to make the speed Vm of main dots 22m comparatively low when the distance PG between a printing surface 6a and a nozzle forming surface 12a is a prescribed value or larger, and reduces a mist of the the satellite dots 22s from the viewpoint of the discharge characteristics of ink droplets. When the distance PG is less than a prescribed value, the device discharges so as to make the speed of the main dots 22m comparatively fast and improves the impact accuracy of the main dots 22m. Consequently, the device can provide high image quality requested by the user. In performing borderless printing, the device generates static electricity by applying high voltage to an electrode 20, actively induces ink droplets 22m and 22s discharged to a dummy portion 5d and reduces a mist. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid ejecting apparatus that performs drawing by ejecting a liquid, such as an inkjet printer, a display manufacturing apparatus, an electrode forming apparatus, or a biochip manufacturing apparatus.

  2. Description of the Related Art Conventionally, an ink jet printer suitable for printing on paper is known as a liquid ejecting apparatus, and generally an ejecting head that ejects liquid (ink) from a minute nozzle to a carriage that reciprocates in a certain direction. It is a configuration equipped with. Then, the printing paper is fed in one direction, and the ejection head is reciprocated (scanned) perpendicularly to the feeding direction of the printing paper, thereby ejecting ink droplets on the printing paper to form an image.

When performing printing (so-called borderless printing) on the entire surface of the printing paper without leaving a margin at the edge of the printing paper using this inkjet printer, allowance for misalignment of the printing paper and carriage is taken into consideration. Thus, printing is performed on an area slightly larger than the size of the printing paper. That is, in order to perform printing without leaving margins on the front and rear edges (edges extending in the paper feed direction) and the left and right side edges (edges extending in the head scanning direction) of the printing paper, the ejection head for the printing paper Is expanded to the outside of these front and rear edges and side edges, and ink droplets are ejected. The ink droplets ejected toward the area outside the printing paper are absorbed by an ink absorbing member (such as a sponge) disposed on the back side of the printing paper facing the recording head.
However, the ink absorbing member is spaced apart from the back side of the printing paper, and the distance from the nozzle opening to the exposed surface of the ink absorbing member is the distance from the nozzle opening to the paper surface (hereinafter referred to as PG). Longer than that. For this reason, when ink droplets are ejected toward the area outside the printing paper, the ink droplets ejected from the nozzle opening decelerates due to air resistance, resulting in mist without reaching the ink absorbing member was there. In particular, if the volume (weight) of the ink droplet is reduced in order to improve the image quality, the degree of deceleration due to air resistance increases and the ink droplet tends to mist. Such mist ink adheres everywhere in the machine and causes so-called stains in the machine.

  In view of the above-mentioned problems, an ink jet printer that generates an electrostatic force in a case and collects ink that has been mist-generated by the action of the electrostatic force has been proposed (for example, Patent Document 1). That is, an electrode is disposed on the exposed surface of the above-described ink absorbing member, and an electric field is generated between the electrode and the nozzle opening forming surface, whereby the charged ink is captured by the electrode.

  By the way, some inkjet printers are configured so that the PG can be variably adapted to various printing papers (plain paper or dedicated paper whose surface is subjected to surface treatment). That is, when plain plain paper is used, PG is increased to prevent so-called paper rubbing (contact between the ejection head and the paper), and when dedicated paper suitable for high-quality printing is used, PG is reduced. Thus, the landing accuracy of the ink droplets is improved and the image quality is improved. In such a printer with variable PG, it is necessary to consider various conditions relating to the ejection of ink droplets that change according to the PG. For example, Patent Document 2 proposes a printer in which the ejection timing of ink droplets in bidirectional printing is configured to be variable according to PG.

JP 2003-305840 A JP 2004-314361 A

However, the above-described printer does not give any consideration to changes in the influence of misting on changes in PG. That is, when PG is large, the distance from the nozzle to the paper surface becomes long, so that mist ink is easily generated regardless of whether or not so-called borderless printing is performed. On the other hand, even when PG is small, when so-called borderless printing is performed, misted ink is likely to be generated for the reasons described above. As described above, the generation situation of the mist ink differs depending on the presence or absence of PG and borderless printing.
When the PG is large, it is difficult to sufficiently collect the mist ink even if the means according to Patent Document 1 is used. This is because the electrodes are arranged in the vicinity of the edge of the printing paper.

  By the way, the inventors of the present invention have found that the generation of mist ink can be suppressed to some extent even by reducing the discharge speed (hereinafter referred to as Vm) of the tip of the ink droplet by the discharge control of the discharge head. did. That is, in view of the fact that when Vm increases, the ink droplets extend in the ejection direction, and the tendency to be divided apart before reaching the paper surface is increased, which tends to cause misting. However, reducing Vm causes deterioration of image quality due to a decrease in landing accuracy, and in printing using dedicated paper, it is difficult to secure sufficient image quality required by the user using dedicated paper. Become.

  The present invention has been made in order to solve the above-described problems, and is a liquid ejecting apparatus capable of reducing in-machine contamination due to mist of liquid and ejecting liquid with suitable landing accuracy according to a user's request. The purpose is to provide.

  The present invention provides a discharge head that discharges liquid as droplets from a nozzle, a scanning unit that moves the discharge head relative to a discharge target, and a discharge target that faces the discharge head. A support member that supports the discharge member, an electrostatic force generation means that generates an electrostatic force at a position adjacent to the support member, and whether or not the discharge head discharges the liquid droplets including an area of an edge of the discharge target The electrostatic force selection means for selecting whether or not the electrostatic force is generated, the PG changing means for changing the distance between the discharge object and the nozzle: PG, and a binary value synchronized with the relative movement of the discharge head Gradation control data for each nozzle, and discharge control means for discharging droplets from the nozzle under conditions according to the gradation data, wherein the discharge control means has the PG equal to or greater than a predetermined value. If the PG is less than a predetermined value, the second droplet corresponding to the first value is discharged. A liquid discharge apparatus that discharges the liquid droplet under conditions, wherein the liquid droplet discharged under the first condition is faster than the liquid droplet discharged under the second condition. : Vm is slow.

  According to the liquid ejection apparatus of the present invention, the ejection control unit can change the ejection conditions of the droplets according to PG. That is, when the PG is larger than a predetermined value with respect to one value of the gradation data, the generation of a so-called misted liquid is suppressed by discharging a droplet having a slow Vm, and when the PG is smaller than the predetermined value, the liquid having a high Vm is discharged. The droplets are ejected to ensure high landing accuracy. Further, depending on whether or not so-called borderless printing is performed, an electrostatic force is generated as necessary to actively collect the misted liquid. Thus, in-machine contamination due to misted liquid is reduced regardless of the presence or absence of PG and borderless printing, and sufficient landing accuracy is ensured even in the mode of small PG that prioritizes image quality.

Preferably, in the liquid ejecting apparatus, the amount of droplets ejected according to the first and second conditions is substantially the same.
According to the liquid ejecting apparatus of the present invention, the amount of droplets ejected under different conditions depending on the PG is substantially the same, so there is not much difference in the gradation of the image after landing on the ejection target. Not give.

Preferably, in the liquid ejection apparatus, the ejection head includes pressure generation means that is driven by an electric pulse to generate pressure on the liquid in the vicinity of the nozzle, and the ejection control means satisfies the first condition. Any one of the corresponding first electric pulse or the second electric pulse corresponding to the second condition is selected and applied to the pressure generating means.
More preferably, the discharge control means includes drive signal generation means for generating a drive signal in which the first electric pulse and the second electric pulse are combined at different timings within one cycle, In the discharge control corresponding to this value, any one of the first and second electric pulses is selected from the drive signal and applied to the pressure generating means.

  According to the liquid ejection apparatus of the present invention, by selecting one of the electric pulses having different modes (shape, size, etc.) and applying it to the pressure generating means, the first and second conditions can be achieved with a simple configuration. Droplets can be ejected. Preferably, if the first or second electrical pulse is selected from the drive signal by timing control, a signal line for each electrical pulse is not required, and the circuit configuration can be simplified.

Preferably, in the liquid ejection apparatus including the drive signal generation unit, the ejection control unit may perform the first and second electric pulses in the drive signal in ejection control corresponding to other values of the gradation data. Both are selected and applied to the pressure generating means.
More preferably, in the drive signal, the second electric pulse has a timing later than that of the first electric pulse.

  According to the liquid ejection device of the present invention, by selecting both the first and second electric pulses, a larger amount of liquid droplets are ejected than the liquid droplets ejected by each single electric pulse, and this is reduced. It is possible to discharge droplets corresponding to other values of tone data. That is, it is not necessary to prepare independent electric pulses corresponding to other values, and multi-gradation can be realized with a simple configuration. Preferably, if the second electric pulse is set at a timing later than that of the first electric pulse, the liquid ejected later catches up with the liquid ejected earlier. It can be landed on the object in a state of being integrated or close to being integrated. Thus, the image quality can be improved.

Preferably, in the liquid ejecting apparatus, the liquid is a colored ink containing a pigment.
According to the liquid ejection apparatus of the present invention, it is possible to effectively reduce in-machine contamination while using a pigment ink that has a high viscosity and easily generates a mist of liquid.

Preferably, in the liquid ejecting apparatus, when the amount of droplets corresponding to the one value is 6 ng to 8 ng, Vm according to the first condition is 7.5 m / s to 8.5 m / s. It is characterized by being.
More preferably, Vm according to the second condition is 9.5 m / s to 10.5 m / s.

  According to the liquid ejecting apparatus of the present invention, it is possible to effectively reduce in-machine contamination due to the mist of liquid. In addition, preferably, by setting Vm according to the second condition to 9.5 m / s to 10.5 m / s, it is possible to suitably balance the landing accuracy and the degree of liquid mist formation in the mode where the PG is small. .

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
Note that the embodiments described below are preferred specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these forms.

FIG. 1 is a schematic perspective view showing an example of the internal structure of the liquid ejection apparatus.
In FIG. 1, a printer 100 as a liquid discharge device is a device that draws (prints) an image or the like by discharging ink as a liquid onto a printing surface 6a of a sheet 6 as a discharge target. The printer 100 includes a steel frame base 9, an ejection head 12 that ejects ink, a carriage 1 on which the ejection head 12 is mounted, and a scanning unit that reciprocates (main scans) the carriage 1 in a certain direction. And a platen 5 that supports the paper 6 from the back side. Here, the frame base 9 forms the basis of the entire mechanism by its rigidity and weight, and also functions as an electrical ground.

  For example, four colors of black, magenta, cyan, and yellow are used as the ink ejected from the ejection head 12 and are accommodated in an ink cartridge 7 mounted on the carriage 1. A lead-out portion (not shown) for leading out ink is provided at the bottom of the ink cartridge 7. The ink cartridge 7 is coupled to an ink introduction portion (not shown) provided in the discharge head 12, and ink is supplied to the discharge head 12. To supply.

The main scanning mechanism 8 includes a timing belt 3 that transmits power to the carriage 1 and a guide rod 4 that supports the carriage 1 and defines the moving direction thereof. The timing belt 3 is driven by a main scanning motor 2 such as a DC motor. Thus, when the main scanning motor 2 is rotationally driven, the ejection head 12 mounted on the carriage 1 is guided by the guide rod 4 installed on the printer 100 and reciprocates (main scanning) in the extending direction of the guide rod 4. .
The guide rod 4 is moved in the vertical direction in the figure while maintaining the extension direction by the PG changing means 15 provided on the side surface of the frame base 9, and the nozzle forming surface of the discharge head 12 is moved by the movement. It is possible to change the distance PG (see FIG. 4) between 12a and the printing surface 6a. The guide rod is moved by a mechanism and a drive motor (not shown).

  The paper 6 is transported (sub-scanned) in a direction orthogonal to the main scanning direction by a transport mechanism 16 (see FIG. 3) that constitutes scanning means including the platen 5. The conveyance of the paper 6 is performed by driving the sub-scanning motor 14.

  In the above-described configuration, the ink is ejected as droplets (ink droplets) from the nozzles 79 (see FIG. 2) of the ejection head 12 while the ejection head 12 is moved relative to the paper 6 to thereby obtain a desired value on the printing surface 6a. An ink droplet is landed at the position and an image or the like is formed.

A maintenance mechanism 10 serving as a suction unit is disposed at a home position that is a non-recording area of the printer 100.
The maintenance mechanism 10 includes a cap member 13 which is a box-shaped elastic member whose upper side in the figure is open. The cap member 13 is intended to maintain the nozzle 79 in an unused state by sealing (capping) the opening of the nozzle 79 in close contact with the nozzle forming surface 12a of the ejection head 12 (see FIG. 2). . Further, by operating a suction pump (not shown) that communicates with a communication port (not shown) in the inner bottom portion of the cap member 13 from the capping state, the sealed space is decompressed to reduce the nozzle 79 (FIG. 2). Ink) can be forcibly sucked from
In the vicinity of the printing area side of the cap member 13, a wiping means 11 having an elastic member molded in a plate shape is arranged so as to be able to advance and retreat in the horizontal direction with respect to the movement locus of the ejection head 12. The wiping means 11 is configured to wipe the nozzle forming surface 12a (see FIG. 2) of the ejection head 12 as necessary when the carriage 1 reciprocates toward the cap member 13 side.

FIG. 2 is a cross-sectional view of the main part showing an example of the internal structure of the ejection head.
As shown in FIG. 2, the ejection head 12 is bonded to the case 71, which is formed of a resin or the like, the comb-like piezoelectric vibrator 21 housed in the housing chamber 72 of the case 71, and the case 71. The flow path unit 74 is provided.

  The upper end side of the piezoelectric vibrator 21 in the drawing is fixed to the inner wall of the storage chamber 72 via a metal substrate 73, and the movable end portion 21 a in the lower side of the drawing is an island portion 89 of the flow path unit 74. It is joined to. Further, the flow path unit 74 is configured by laminating a nozzle plate 80 and an elastic plate 77 on both sides with a flow path forming plate 75 interposed therebetween.

  The piezoelectric vibrator 21 is formed by cutting a plate-like vibrator plate in which common internal electrodes 21c and individual internal electrodes 21d are alternately stacked with a piezoelectric body 21b interposed therebetween, and cutting the comb-like shape in accordance with the dot formation density. It is. Then, by applying a potential difference between the common internal electrode 21c and the individual internal electrode 21d, each piezoelectric vibrator 21 expands and contracts in the vibrator longitudinal direction orthogonal to the stacking direction.

  The flow path forming plate 75 includes a plurality of pressure generating chambers 81, a plurality of ink supply units 82 that communicate with at least one end of each pressure generation chamber 81, and a common ink that is a common liquid chamber that communicates with each ink supply unit 82. The chamber 83 is a plate-like member in which the chamber 83 is formed. The flow path forming plate 75 is manufactured, for example, by etching a silicon wafer. Ink supply to the common ink chamber 83 is performed from an outlet (not shown) corresponding to each color ink of the ink cartridge 7 (see FIG. 1) through an ink supply pipe 84 formed in the case 71.

  The nozzle plate 80 is a plate-like member formed of a metal such as SUS, and nozzles 79 are formed corresponding to the plurality of pressure generating chambers 81 to form a nozzle forming surface 12a. The nozzle plate 80 is electrically connected to the frame base 9 (see FIG. 1) via a lead wire indicated by a virtual line, and is in a grounded state. This is because if the discharge head 12 is charged and discharge through the nozzle plate 80 occurs, the drive circuit 33 (see FIG. 5) for driving the piezoelectric vibrator 21 may be destroyed. This is a measure to prevent such an accident.

  The elastic plate 77 is laminated on the surface of the flow path forming plate 75 opposite to the nozzle plate 80, and a double structure in which a polymer film such as PPS is laminated as an elastic film 88 on the lower surface side of the stainless steel plate 87. It is. Then, an island portion 89 for abutting and fixing the piezoelectric vibrator 21 is formed by etching the portion of the stainless plate 87 corresponding to the pressure generating chamber 81.

In the ejection head 12 having the above configuration, by extending the piezoelectric vibrator 21 in the longitudinal direction of the vibrator, the island portion 89 is pressed toward the nozzle plate 80 side, and the elastic film 88 around the island portion 89 is deformed. The pressure generating chamber 81 contracts. When the piezoelectric vibrator 21 is contracted in the longitudinal direction from the contracted state of the pressure generating chamber 81, the pressure generating chamber 81 expands due to the elasticity of the elastic film 88.
Such driving of the piezoelectric vibrator 21 is performed by an electric pulse (see FIG. 6) applied between the common internal electrode 21c and the individual internal electrode 21d. The application of this electric pulse causes a pressure fluctuation in the ink in the pressure generating chamber 81, and an ink droplet is ejected from the nozzle 79. That is, the piezoelectric vibrator 21 and the pressure generating chamber 81 constitute a pressure generating unit.

  The conditions for ejecting the ink droplets can be controlled by the mode (shape, component gradient, etc.) of the electric pulse applied to the piezoelectric vibrator 21. As a result, a plurality of types having different characteristics such as quantity and speed can be controlled. Ink droplets can be properly used as needed. Specific control for this will be described in detail later.

FIG. 3 is an enlarged plan view showing a part around the platen. 4 is a cross-sectional view taken along line AA in FIG.
As shown in FIG. 3, the transport mechanism 16 includes a platen 5 and transport rollers 19 a and 19 b that transport the paper 6 to the platen 5. The transport rollers 19a and 19b are arranged to face each other, and transport the paper 6 in the direction of the arrow F with the paper 6 interposed therebetween. Further, the transport roller 19a is a driven roller, and the transport roller 19b is a drive roller.

  3 and 4, the platen 5 is disposed to face the ejection head 12, supports the paper 6 at a position where ink droplets are ejected, and the distance PG between the nozzle forming surface 12a and the printing surface 6a. It prescribes. The platen 5 includes a support member 17 formed of plastic or the like, and a liquid-absorbing member 18 formed of sponge or the like, and as illustrated, a support portion 5a that contacts the back surface 6b of the paper 6; Dummy portions 5b, 5c, 5d, and 5e where the liquid absorbing member 18 is exposed are formed. Since the exposed surface of the liquid absorbing member 18 is lower than the surface on which the support member 17 supports the paper 6, it does not come into contact with the paper 6.

3 and 4, the dummy portions 5 b, 5 c, 5 d, and 5 e are used when performing so-called borderless printing in which printing is performed without leaving a margin at the edge of the paper 6. In other words, at the position of the paper 6 shown in the drawing, printing is performed with the print area extended to the dummy portion 5d, so that printing is performed without leaving a margin on the side edge portion 6c of the paper 6. The ejected ink droplets 22m and 22s are absorbed by the liquid absorbing member 18. For this reason, the support portion 5a is not stained with ink, and the stain on the support portion 5a is not transferred to the next sheet 6.
Similarly, the dummy portion 5b is used when printing the upper edge portion 6d of the paper 6, and the dummy portion 5c is used when printing the lower end portion of the paper 6 (the end portion facing the upper edge portion 6d). Also, borderless printing is performed on the edge portion of the paper 6 facing the side edge portion 6c in the same manner. Further, the dummy portion 5e is provided for the same purpose as the dummy portion 5d in order to correspond to the paper 6 of various sizes.

The platen 5 also includes an electrode 20 (shown by hatching in FIG. 3 for convenience) disposed on the exposed liquid absorbing member 18 in the dummy portions 5b, 5c, 5d, and 5e. The electrode 20 is formed of a metal wire or the like, and a coating for preventing corrosion is formed on the surface thereof.
The electrode 20 is electrically connected to the high-voltage power supply 50 by a conducting wire indicated by a virtual line, and a high voltage is applied as necessary. When the high voltage power supply 50 applies a voltage to the electrode 20, an electric field (electrostatic force) is generated between the nozzle forming surface 12 a of the ejection head 12 maintained at the ground potential and the electrode 20. That is, the electrode 20 and the high-voltage power supply 50 constitute an electrostatic force generating means.

  In FIG. 4, the ink droplets 22m and 22s ejected from the ejection head 12 are called main dots and satellite dots, respectively. The main dots 22m and the satellite dots 22s are originally ejected as a single unit, but are divided into a leading end portion and a trailing end portion in the ejection direction due to the nonuniformity of the speed generated in the ink droplets. For this reason, the speed Vm of the main dot 22m is relatively fast, and the speed Vs of the satellite dot 22s is relatively slow.

  Generally, the amount of satellite dots 22s is smaller than the amount of main dots 22m, and the influence of deceleration due to air resistance is large. For this reason, the satellite dots 22s are likely to be in a so-called mist state that loses speed and floats in the air. Such misted ink causes in-machine stains and paper stains.

  The balance of the amount and speed of the main dots 22m and the satellite dots 22s varies depending on the electric pulse (see FIG. 6) applied to the piezoelectric vibrator 21 (see FIG. 2). In particular, it has been found that there is a strong correlation between the velocity Vm of the main dot 22m and this balance. That is, if the discharge is performed under the condition that Vm becomes faster, the speed Vs of the satellite dot 22s becomes smaller, and the tendency of the satellite dot 22s to become mist becomes stronger. Further, when ejection is performed under such a condition that Vm becomes faster, the satellite dots 22s may be further subdivided into a plurality of ink droplets. Such a tendency is more conspicuous when a pigment ink having a high viscosity is used. That is, it can be said that the pigment ink easily generates a mist ink.

  As can be seen from this explanation, it is possible to reduce the generation of misted ink by performing ejection under conditions such that Vm becomes small. However, Vm affects the landing accuracy of the main dot 22m, and consequently the image quality. That is, when Vm becomes smaller, the landing accuracy of the main dot 22m is lowered, and the image quality tends to be lowered.

  The degree of generation of misted ink also varies depending on the distance PG between the nozzle forming surface 12a and the printing surface 6a. This is because, when the distance PG is large, the distance until the discharged satellite dots 22s reach the printing surface 6a becomes long, and thus the rate of satellite dots 22s that lose speed and do not reach the printing surface 6a increases.

  On the other hand, the distance PG is closely related to the selection of the paper 6. In other words, when using paper with a low stiffness, the PG has a relatively large state (large PG state) in order to prevent contact between the ejection head 12 and the paper 6 (so-called paper rubbing), and the thick dedicated to the thick When paper is used, priority is given to the landing accuracy of the main dot 22m to make the PG relatively small (PG small state).

  In addition, the degree of generation of mist ink varies depending on whether or not so-called borderless printing is performed. In borderless printing, the ink droplets 22m and 22s are ejected toward the exposed surface of the liquid absorbent member 18 having a long distance from the nozzle forming surface 12a, so that the speed is lost and the liquid absorbent member 18 is not reached. This is because the proportion of satellite dots 22s increases.

3 and 4, the electrode 20 disposed on the liquid-absorbing member 18 has a function of attracting the mist ink generated in the vicinity of the dummy portions 5b, 5c, 5d, and 5e in borderless printing. It is.
Since the sheet 6 is charged to the positive electrode by rubbing against each member of the conveyance mechanism 16 in the conveyance process, the ink droplets 22m and 22s ejected by the electric field formed between the sheet 6 and the nozzle forming surface 12a are negative. Is charged. For this reason, by applying a high voltage potential of the positive electrode to the electrode 20, such charged ink droplets 22 m and 22 s are actively attracted by an electrostatic force and can be collected by the liquid absorbing member 18. it can.

  As can be seen from the above description, the generation of the mist ink is intertwined with factors such as ejection conditions (applied electric pulses), distance PG, borderless printing, and electrostatic force generated by the electrode 20. These elements are also related to the type of paper 6 and the landing accuracy (image quality). For this reason, the printer 100 (see FIG. 1) of the present embodiment is configured such that the operating conditions change according to the type (distance PG) of the paper 6 and the presence / absence of borderless printing. The generation can be reduced, and suitable printing can be performed according to the user's request. Details will be described later.

Next, the electrical configuration of the printer will be described with reference to FIGS. FIG. 5 is a block diagram showing the electrical configuration of the printer. FIG. 6 is a timing diagram illustrating an example of a control signal.
As shown in FIG. 5, the printer 100 includes a print controller 23 and a drive circuit 33 that constitute discharge control means, a piezoelectric vibrator 21 that constitutes pressure generation means, and scanning means (main scanning mechanism 8 and transport mechanism 16). Are provided with a main scanning motor 2 and a sub scanning motor 14 for driving the PG, a PG changing motor 51 for driving the PG changing means 15, and a high voltage power source 50 and an electrode 20 constituting electrostatic force generating means. Here, the print controller 23 is accommodated in a control box provided on the back side of the frame base 9 (see FIG. 1), and the drive circuit 33 is mounted on the ejection head 12.

  The print controller 23 includes an external interface (external I / F) 25, a RAM 26, a ROM 27, a control unit 28, an oscillation circuit 29 that generates a clock signal (CK), and a drive signal that generates a drive signal (COM). A drive signal generation circuit 30 as generation means and an internal interface (internal I / F) 31 are provided.

  The external I / F 25 receives print data composed of, for example, a character code, a graphic function, image data, and the like from a host computer (PC) 32. A busy signal (BUSY) and an acknowledge signal (ACK) are output to the host computer 32 through the external I / F 25.

  The RAM 26 temporarily stores print data received via the external I / F 25, or temporarily stores gradation data generated by decoding (translating) the print data by the control unit 28. It also functions as a work memory for the control unit 28.

  The ROM 27 stores font data, graphic functions, and the like in addition to a control program (control routine) for performing various data processing.

  The drive signal (COM) generated by the drive signal generation circuit 30 is an electric signal for applying to the piezoelectric vibrator 21 and driving it. As shown in FIG. 6, the drive signal (COM) has the same electric pulse PS1 arranged in the period T1, electric pulse PS3 arranged in the period T2, and electric pulse PS2 arranged in the period T3. They are coupled at an intermediate potential to form one cycle. Each of the electric pulses PS1 to PS3 has an aspect in which the shape and the inclination of the component are different, and is designed so that ink droplets having different characteristics are ejected by being applied to the piezoelectric vibrator 21. . The period T of the drive signal (COM) is synchronized with the main scanning timing of the ejection head 12 (see FIG. 1) by the main scanning mechanism 8, and by ejecting ink droplets at each period, the paper 6 ( Printing can be performed at a constant resolution.

Returning to FIG. 5 again, the control unit 28 performs various controls according to the control program stored in the ROM 27. For example, the print data is analyzed to determine the type of paper, and the distance PG (see FIG. 4) defined for each paper is recognized. Then, if necessary, the PG changing motor 51 is driven to be in the “PG large state” or “PG small state”.
Further, the control unit 28 analyzes the print data to determine whether or not to perform so-called borderless printing. When borderless printing is performed, the control unit 28 switches the internal switch of the high-voltage power supply 50 and applies a high voltage to the electrode 20. Supply. Further, when no borderless printing is performed, the high voltage is not supplied to the electrode 20. That is, the control unit 28 functions as an electrostatic force selection unit.

The control unit 28 further generates various control signals for performing discharge control, and supplies them to the drive circuit 33 through the internal I / F 31. For example, the control unit 28 decodes (translates) the print data to generate gradation data (2 bits) for each nozzle for each period T (see FIG. 6), and the gradation for each nozzle group (nozzle row). Data is combined to generate a data signal (SI).
Further, the control unit 28 generates an allocation signal (SP) according to the PG large state / small state. Here, the assignment signal (SP) defines the assignment of the electric pulses PS1 to PS3 (see FIG. 6) in the drive signal (COM) corresponding to the value of the gradation data.
Further, the control unit 28 generates a latch signal (LAT) and a channel signal (CH). Here, the latch signal (LAT) and the channel signal (CH) define the application timing of the electric pulses PS1 to PS3 (see FIG. 6) constituting the drive signal (COM) to the piezoelectric vibrator 21 (see FIG. 6). (See FIG. 6).

  As shown in FIG. 5, the drive circuit 33 of the ejection head 12 includes a shift register circuit including a first shift register 36 and a second shift register 37, and a latch circuit including a first latch circuit 39 and a second latch circuit 40. , A decoder 42, a control logic 43, a level shifter 44, and a switch circuit 45 are provided.

  The shift registers 36 and 37, the latch circuits 39 and 40, the decoder 42, and the switch circuit 45 are provided for each piezoelectric vibrator 21 provided for each nozzle 79 (see FIG. 2) of the ejection head 12. . In synchronization with the clock signal (CK), gradation data of lower bits and upper bits of the data signal (SI) is serialized in the first shift register 36 and the second shift register 37 provided for each nozzle. Is transmitted.

  The gradation data from the print controller 23 is 2-bit data as described above, and the non-recording is (00) and the small dots are (4) for four gradations including non-recording, small dots, medium dots, and large dots. 01), medium dots are represented by (10), and large dots are represented by (11). The gradation data has an independent value for each nozzle, and ejection control is performed for each nozzle as follows.

As shown in FIG. 5, a first latch circuit 39 is electrically connected to the first shift register 36. Similarly, a second latch circuit 40 is electrically connected to the second shift register 37. When a latch signal (LAT) from the print controller 23 is input to each of the latch circuits 39 and 40, the first latch circuit 39 latches the lower bit data of the gradation data, and the second latch circuit 40 Latch the upper bits of key data.
As described above, the circuit unit including the first shift register 36 and the first latch circuit 39 and the circuit unit including the second shift register 37 and the second latch circuit 40 each function as a memory circuit. That is, these circuit units temporarily store gradation data before being input to the decoder 42.

  The gradation data latched by the latch circuits 39 and 40 is input to the decoder 42. The decoder 42 decodes (translates) the gradation data with reference to the assignment signal (SP), and generates pulse selection data. This pulse selection data is composed of, for example, 3 bits, and each bit data is information indicating application / non-application (ON / OFF) of a drive signal (COM) at a timing signal (see FIG. 6) described later. It is.

  On the other hand, a timing signal from the control logic 43 is also input to the decoder 42. This timing signal is generated by the control logic 43 based on the latch signal (LAT) and the channel signal (CH) (see FIG. 6).

  The pulse selection data translated by the decoder 42 is input to the level shifter 44 every time the timing defined by the timing signal (see FIG. 6) arrives in order from the upper bit side. That is, the most significant bit data of the pulse selection data is input to the level shifter 44 at the first timing in the recording cycle, the second bit data at the second timing, and the least significant bit data at the third timing. 44 respectively.

  The level shifter 44 functions as a voltage amplifier. When the bit data of the pulse selection data is “1”, for example, a voltage that can drive the switch circuit 45, for example, a drive voltage of about several tens of volts is supplied to the switch circuit 45. . On the other hand, when the bit data of the pulse selection data is “0”, for example, such a drive voltage is not supplied to the switch circuit 45.

  Thus, while the voltage boosted by the level shifter 44 is supplied to the switch circuit 45, the drive signal (COM) is applied to the piezoelectric vibrator 21. That is, in FIG. 6, when the most significant bit of the selection data is “1”, for example, the electric pulse PS1 in the period T1, and when the second bit of the selection data is “1”, for example, the electric pulse in the period T2. When the third bit of the selection data is “1”, for example, PS3, the electric pulse PS2 of the period T3 is applied to the piezoelectric vibrator 21, and ink droplets corresponding to the electric pulses PS1 to PS3 are ejected from the nozzle 79. (See FIG. 2).

  As described above, the printer 100 according to the present embodiment has an electrical configuration in which the electrical pulses PS1 to PS3 corresponding to ink droplets having different characteristics are selected by controlling the application timing of the drive signal (COM). A signal line for each electric pulse is not required, and the circuit configuration is simple.

  Next, the printing operation of the printer will be described along the flowchart of FIG. 7 with reference to FIG. FIG. 7 is a flowchart showing a control flow relating to the printing operation of the printer.

  In FIG. 5, the printing operation is executed by a command from a host computer (PC) 32 connected to the printer 100. The user inputs conditions such as “paper type”, “resolution”, “whether to perform borderless printing” or the like through the user interface on the host computer 32 in the print command. Information regarding the conditions and image data generated according to these conditions are sent as print data to the print controller 23 (step S0 in FIG. 7). The print data sent to the print controller 23 is analyzed by the control unit 28.

  First, the control unit 28 sets a drive signal (COM) based on information relating to the resolution included in the print data (step S1 in FIG. 7). The control unit 28 reads drive signal (COM) generation information corresponding to the selected print mode and sends the information to the drive signal generation circuit 30.

  Next, the control unit 28 recognizes the distance PG (see FIG. 4) to be set based on the information regarding the paper type included in the print data (step S2 in FIG. 7). For example, when the paper is plain plain paper or the like, it is recognized that printing is performed in the PG large state. If the paper is a thick special paper, it is recognized that printing is performed in the small PG state.

  Next, based on the recognition in step S2, the control unit 28 drives the PG changing motor 51 as necessary to set the PG large state or the PG small state (step S3 in FIG. 7). In the present embodiment, the distance PG (see FIG. 4) in the large PG state is 1.5 mm, and the distance PG (see FIG. 4) in the small PG state is 1.2 mm.

  Next, the control unit 28 sets the assignment signal (SP) based on the recognition in step S2 (step S4 in FIG. 7). As described above, the assignment signal (SP) is information defining assignment of selection of the electric pulses PS1 to PS3 (see FIG. 6) for the gradation data, and the gradation data sent from the print controller 23 is decoded by the decoder 42. This is referred to when decoding into selected data. The assignment signal (SP) has different contents depending on the distance PG recognized in step S2, that is, different electric pulses are generated for the same gradation data in the PG large state and in the PG small state. May be selected. Details will be described later.

Next, the control unit 28 selects whether or not an electrostatic force is generated based on information on whether to perform borderless printing included in the print data (step S5 in FIG. 7). That is, when performing borderless printing, the internal switch of the high-voltage power supply 50 is switched to supply a high voltage to the electrode 20. Thereby, it is possible to reduce the mist of the satellite dots 22s (see FIGS. 3 and 4) in the vicinity of the dummy portions 5b, 5c, 5d, and 5e.
On the other hand, when no borderless printing is performed, the high voltage is not supplied to the electrode 20. The electrode 20 can be attracted because the ink droplets 22m and 22s (see FIGS. 3 and 4) in the vicinity of the dummy portions 5b, 5c, 5d, and 5e are almost ineffective when borderless printing is not performed. Thereby, excessive power consumption can be suppressed.

  When the processing from steps S1 to S5 is completed, the print controller 23 performs various controls of the printing operation (step S6 in FIG. 7). Specifically, gradation data is generated by decoding print data, main scanning control is performed by driving the main scanning motor 2, sub-scanning control is performed by driving the sub-scanning motor 14, and ejection control described above is performed. . Thus, printing under the conditions set by the user is completed.

FIG. 8 is a diagram showing the relationship between gradation data, selection data, and applied electric pulses, where (a) is a diagram related to the PG large state, and (b) is a diagram related to the PG small state.
The decoding of the gradation data by the assignment signal (SP) set in the above-described step S3 and the application of the electric pulse by the generated selection pulse are specifically performed according to the relationship shown in FIG. This will be specifically described below.

  As shown in FIG. 8, gradation data (01) representing small dots is decoded into selection data (010) regardless of the large PG state / small PG state, and the electric pulse PS3 is converted into the piezoelectric vibrator 21 (see FIG. 2). ). Thereby, a relatively small amount (for example, about 2 ng) of ink droplets is ejected as small dots from the nozzle 79 (see FIG. 2).

  The gradation data (10) as one value representing the medium dot is decoded into selection data (100) as shown in FIG. 8A in the case of the large PG state, and the electric pulse PS1 is converted into the piezoelectric vibrator. 21 (see FIG. 2). Thereby, a moderate amount (for example, 6 ng to 8 ng) of ink droplets is ejected from the nozzle 79 (see FIG. 2) as a medium dot according to the first condition. In the case of the PG small state, as shown in FIG. 8B, the selection data (001) is decoded and the electric pulse PS2 is applied to the piezoelectric vibrator 21. Thereby, a moderate amount (for example, 6 ng to 8 ng) of ink droplets is ejected from the nozzle 79 (see FIG. 2) as a medium dot according to the second condition.

  Here, between the medium dots ejected by the electric pulse PS1 (first condition) and the medium dots ejected by the electric pulse PS2 (second condition), the main dot is different depending on the mode of the electric pulse to be applied. The speed Vm of 22 m (see FIG. 4) is different. That is, Vm related to the large PG state (first condition) is slower than Vm related to the small PG state (second condition).

This is because, in the large PG state in which ink droplets are likely to mist, Vm is made relatively slow to reduce mist formation from the viewpoint of ink droplet characteristics. On the other hand, in the small PG state, since ink droplets are less likely to be misted, Vm is increased to improve the landing accuracy of ink droplets, and consequently the image quality. Printing in the small PG state is performed when the user requests high image quality, such as when using thick special paper, but even in such a case, a high level of image quality required by the user can be provided. Is possible.
Note that the medium dots according to the first condition and the medium dots according to the second condition have almost the same discharge amount, and have almost no effect on the gradation when an image or the like is formed. Does not reach.

  As shown in FIG. 8, gradation data (11) as another value representing a large dot is decoded into selection data (101) regardless of the large PG state / small PG state, and electric pulses PS1 and PS2 are piezoelectric. Applied to the vibrator 21 (see FIG. 2). As a result, both the medium dots according to the first and second conditions are ejected from the nozzle 79 (see FIG. 2), and land on the paper 6 (see FIG. 1) as a large dot.

As described above, since the large dots can be ejected using the electrical pulses PS1 and PS2 related to the medium dots, it is not necessary to prepare an independent electrical pulse for ejecting the large dots. Therefore, the configuration of the common pulse (COM) can be simplified, and in particular, the period T (see FIG. 6) can be shortened, so that the printing speed can be improved.
Further, since the electric pulse PS2 is arranged at a timing later than the electric pulse PS1, the medium dot according to the second condition having a relatively fast Vm catches up with the medium dot according to the first condition having a relatively slow Vm. Large dots can be landed on the printing surface 6a (see FIG. 4) of the paper 6 in an integrated or nearly integrated state. Thereby, the image quality can be improved.

In the above-described embodiment, when the ejection amount of the medium dots is 6 ng to 8 ng, the Vm of the medium dots according to the PG large state (first condition) may be 7.5 m / s to 8.5 m / s. preferable. At this time, the mist formation of the satellite dots 22s (see FIG. 4) is preferably reduced.
Further, it is preferable that the Vm of the medium dot relating to the PG small state (second condition) is 9.5 m / s to 10.5 m / s. At this time, suitable landing accuracy can be ensured while the mist formation of the satellite dots 22s (see FIG. 4) is moderately suppressed.

  In addition, the effect of reducing mist formation in the above-described embodiment becomes more remarkable in the case of a printer using pigment ink that has high viscosity and is likely to cause mist formation of satellite dots 22s (see FIG. 4).

The present invention is not limited to the above-described embodiment. For example, the liquid-absorbing member 18 of the platen 5 is formed by foaming by mixing a conductive material such as carbon into polyethylene or polyurethane, and this is used as an electrode of the electrostatic force generating means. May be. If it does in this way, the recovery capability of mist improves with the capture capability of mist by the liquid absorption property of electrode itself.
Further, the setting of the distance PG is not limited to the mode in which the distance PG is automatically adjusted based on the print data as in the above-described embodiment, and may be manually set by the user. Further, in such a case, the liquid ejection device may include a sensor that detects the state of the PG, and the control unit 28 may switch the allocation signal (SP) according to the detection result of the sensor.
In addition, the setting of the distance PG is not limited to a mode in which the PG large state and the PG small state are switched to two stages as in the above-described embodiment, and is a mode in which the value is continuously changed. Also good. In such a case, the setting of the assignment signal (SP) can be switched depending on whether the distance PG is equal to or greater than a predetermined value.
The gradation data in the above-described embodiment is 2 bits (four values), but the present invention can also be applied to a liquid ejecting apparatus processed with gradation data of 1 bit to 3 bits or more.
Moreover, each structure of each embodiment can combine these suitably, can be abbreviate | omitted, or can be combined with the other structure which is not illustrated.

FIG. 2 is a schematic perspective view illustrating an example of an internal structure of a liquid ejection device. FIG. 3 is a main part cross-sectional view showing an example of the internal structure of the ejection head. The top view which expanded and showed a part of platen periphery. AA sectional drawing of FIG. FIG. 2 is a block diagram illustrating an electrical configuration of the printer. The timing diagram which shows an example of a control signal. The flowchart which shows the control flow which concerns on the printing operation of a printer (A) is a figure which shows the relationship between the gradation data in a PG large state, selection data, and the applied electric pulse. FIG. 5B is a diagram showing a relationship between gradation data, selection data, and applied electric pulses in a small PG state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carriage, 2 ... Main scanning motor, 3 ... Timing belt, 4 ... Guide rod, 5 ... Platen, 5a ... Supporting part, 5b-5e ... Dummy part, 6 ... Paper, 6a ... Printing surface, 6b ... Back surface, 6c ... side edge, 6d ... upper edge, 8 ... main scanning mechanism constituting scanning means, 9 ... frame base, 12 ... discharge head, 12a ... nozzle forming surface, 14 ... sub-scanning motor, 15 ... PG change Means 16, transport mechanism constituting scanning means 17, support member 18, liquid absorbing member 19 a, 19 b transport rollers 20, electrodes constituting electrostatic force generating means 21, pressure generating means Piezoelectric vibrator, 21a ... movable end, 21b ... piezoelectric body, 21c ... common internal electrode, 21d ... individual internal electrode, 22m ... main dot (ink droplet) as droplet, 22s ... satellite dot (ink) drop , 23: Print controller constituting discharge control means, 25 ... External I / F, 26 ... RAM, 27 ... ROM, 28 ... Control section functioning as electrostatic force selection means, 29 ... Oscillator circuit, 30 ... Drive signal generating means Drive signal generation circuit, 31 ... internal I / F, 32 ... host computer, 33 ... drive circuit constituting discharge control means, 36 ... first shift register, 37 ... second shift register, 39 ... first latch circuit 40 ... second latch circuit, 42 ... decoder, 43 ... control logic, 44 ... level shifter, 45 ... switch circuit, 50 ... high voltage power supply constituting electrostatic force generating means, 51 ... motor for changing PG, 79 ... nozzle, 81 ... pressure generating chamber constituting pressure generating means, 100 ... printer as liquid ejection device.

Claims (9)

An ejection head for ejecting liquid as droplets from a nozzle;
Scanning means for moving the discharge head relative to the discharge target;
A support member disposed to face the discharge head and supporting the discharge target;
An electrostatic force generating means for generating an electrostatic force at a position adjacent to the support member;
An electrostatic force selection means for selecting whether or not the electrostatic force is generated depending on whether or not the ejection head includes the edge region of the ejection target and ejects the droplet;
A distance between the discharge object and the nozzle: PG changing means for changing PG;
Discharge control means for generating gradation data of binary or more synchronized with the relative movement of the discharge head for each nozzle, and discharging droplets from the nozzle under conditions according to the gradation data,
When the PG is greater than or equal to a predetermined value, the ejection control unit ejects the droplet under a first condition corresponding to one value of the gradation data, and the PG is less than the predetermined value Is a liquid ejecting apparatus that ejects the liquid droplet under a second condition corresponding to the one value,
The liquid ejecting apparatus according to claim 1, wherein the liquid droplet ejected under the first condition has a lower velocity Vm at the front end of the liquid droplet than the liquid ejected according to the second condition.   The liquid discharge apparatus according to claim 1, wherein the amount of liquid droplets discharged under the first and second conditions is substantially the same. The ejection head includes pressure generating means that is driven by an electric pulse to generate pressure on the liquid in the vicinity of the nozzle,
The discharge control unit selects one of the first electric pulse corresponding to the first condition or the second electric pulse corresponding to the second condition and applies the selected one to the pressure generating unit. The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting apparatus is a liquid ejecting apparatus. The ejection control means includes drive signal generation means for generating a drive signal in which the first electric pulse and the second electric pulse are combined at different timings within one cycle,
The discharge control corresponding to the one value selects one of the first and second electric pulses from the drive signal and applies the selected one to the pressure generating means. Liquid discharge device.   In the discharge control corresponding to another value of the gradation data, the discharge control unit selects both the first and second electric pulses in the drive signal and applies them to the pressure generation unit. The liquid ejection device according to claim 4, wherein the liquid ejection device is a liquid ejection device.   6. The liquid ejection apparatus according to claim 5, wherein, in the driving signal, the second electric pulse has a timing later than that of the first electric pulse.   The liquid ejecting apparatus according to claim 1, wherein the liquid is a colored ink containing a pigment.   2. The Vm according to the first condition is 7.5 m / s to 8.5 m / s when the amount of droplet corresponding to the one value is 6 ng to 8 ng. The liquid ejection device according to any one of Items 7 to 7. The liquid ejection apparatus according to claim 8, wherein Vm according to the second condition is 9.5 m / s to 10.5 m / s.

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