JP2014148110A - Liquid jet device, and control method for the same - Google Patents

Abstract

A liquid ejecting apparatus capable of dealing with a landing target having unevenness and a curved surface, and a control method thereof.
A flying speed of a droplet ejected by a driving pulse generated after the driving pulse is higher than a flying speed of a droplet ejected by a driving pulse generated earlier in the driving signal. The control unit is configured to catch up and coalesce before the droplet ejected later is landed on the landing target with respect to the previously ejected droplet, and the control unit has a distance detected by the detection unit as the first distance. At a second distance longer than the distance, the number of application of the drive pulse included in the ejection drive signal to the pressure generating means is increased as compared with the first distance to change the number of droplets that merge during the flight. .
[Selection] Figure 3

Description

  The present invention relates to a liquid ejecting apparatus such as an ink jet recording apparatus, and a control method for the liquid ejecting apparatus, and in particular, drives the pressure generating means by applying a driving waveform included in a driving signal to the pressure generating means, The present invention relates to a liquid ejecting apparatus that ejects a liquid from a nozzle by causing a pressure fluctuation in a liquid in a pressure chamber communicating with the nozzle, and a control method for the liquid ejecting apparatus.

  The liquid ejecting apparatus includes an ejecting head and ejects (discharges) various liquids from the ejecting head. As this liquid ejecting apparatus, for example, there are image recording apparatuses such as an ink jet printer and an ink jet plotter. Recently, various types of liquid ejecting apparatuses are utilized by utilizing the feature that a very small amount of liquid can be accurately landed on a predetermined position. It is also applied to devices. For example, a display manufacturing apparatus for manufacturing a color filter such as a liquid crystal display, an electrode forming apparatus for forming an electrode such as an organic EL (Electro Luminescence) display or FED (surface emitting display), a chip for manufacturing a biochip (biochemical element) Applied to manufacturing equipment. The recording head for the image recording apparatus ejects liquid ink, and the color material ejecting head for the display manufacturing apparatus ejects solutions of R (Red), G (Green), and B (Blue) color materials. The electrode material ejecting head for the electrode forming apparatus ejects a liquid electrode material, and the bioorganic matter ejecting head for the chip manufacturing apparatus ejects a bioorganic solution.

  In recent years, by using a photocurable ink (photocurable liquid) that is cured by irradiating light (especially ultraviolet rays), various shapes and materials such as those having a three-dimensional shape such as irregularities and curved surfaces can be used. A printer configured to record an image or the like on a landing target has also been proposed (see, for example, Patent Document 1). In other words, after the ink is landed on the landing target, the ink is quickly cured by irradiating the light from the light irradiation means, so that the ink has a three-dimensional shape that is difficult to fix at the landing position, or the ink soaks. It can also be used for printing on materials such as resin films.

JP 2012-206087 A

  In the configuration in which the ink is ejected onto the landing target having the unevenness and the curved surface, the distance from the nozzle formation surface of the liquid jet head (recording head) to the landing target is longer than that when printing on the recording paper. . For example, in the configuration for printing on recording paper, it is about 1 mm to 1.5 mm, whereas in the configuration for ejecting ink to the landing target having the above unevenness and curved surface, there are cases where the length is about 5 mm to 10 mm. is there. As described above, when the distance from the nozzle formation surface to the landing target is long, the ink ejected from the nozzle of the liquid ejecting head may be misted without landing on the landing target. Further, in the configuration in which the liquid ejecting head is provided with the light irradiating means for curing the ink, the amount of light emitted from the light irradiating means to the landing ink on the landing target varies depending on the distance. The degree of ink curing will change. As a result, there is a problem that color unevenness occurs in a recorded image or the like.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a liquid ejecting apparatus capable of dealing with a landing target having unevenness and a curved surface, and a control method thereof. .

The liquid ejecting apparatus of the present invention has been proposed to achieve the above-described object, and includes a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a pressure that causes pressure fluctuations in the liquid in the pressure chamber. A liquid ejecting head having a generating means and capable of ejecting a liquid from the nozzle by the operation of the pressure generating means;
Drive signal generating means for generating a drive signal including a plurality of drive pulses for driving the pressure generating means to eject droplets from the nozzles within a unit period;
Detecting means for detecting a distance from the nozzle forming surface of the liquid jet head to the landing target;
Control means for controlling application of the drive pulse to the pressure generating means;
With
The flying speed of a droplet ejected by a driving pulse generated after a driving pulse generated earlier is higher than the flying speed of a droplet ejected by a driving pulse generated earlier in the driving signal, The droplets ejected later are configured to catch up and merge before the droplets ejected earlier land on the landing target,
When the distance detected by the detection means is longer than the first distance, the control means increases the number of application of the drive pulse included in the drive signal to the pressure generation means compared to the case of the first distance. And changing the number of droplets that coalesce during flight.

  According to the present invention, the flying speed of the droplet ejected by the driving pulse generated later is higher than the flying speed of the droplet ejected by the driving pulse generated earlier in the driving signal. The droplets ejected later are configured to catch up and merge with the droplets ejected earlier before landing on the landing target, and are included in the ejection drive signal according to the distance detected by the detection means The number of applied driving pulses to the pressure generating means is increased compared to the case of the first distance, and the number of droplets that merge during flight is changed, so that the flying speed and weight of the combined droplets increase. . The combined droplets can fly a longer distance without being misted, and can land on the landing target. As a result, it is possible to suppress problems such as deterioration in the image quality of recorded images and contamination in the apparatus due to droplets becoming mist. As a result, for example, it is possible to cope with printing on a landing target having a three-dimensional shape having a larger uneven step and a curved surface with a larger height difference.

In the above configuration, each drive pulse has a first change element whose potential changes so as to expand the pressure chamber, and a potential change so that the pressure chamber expanded by the first change element contracts. A second change element that
It is desirable to adopt a configuration in which the potential change rate of the drive pulse generated after the previous drive pulse is set larger than the potential change rate of the drive pulse generated earlier in the drive signal.

  According to this configuration, the drive pulse generated later is set by setting the potential change rate of the drive pulse generated after the drive pulse larger than the potential change rate of the drive pulse generated earlier in the drive signal. The flying speed of the droplets ejected by the pulse can be increased.

Further, in the above configuration, an interval from the start end of the drive pulse generated earlier in the drive signal to the start end of the drive pulse generated after the previous drive pulse is generated in the liquid in the pressure chamber. When the period of pressure oscillation is Tc and the natural number is n,
n × 0.75 × Tc ≦ Δtp ≦ n × 1.25 × Tc
It is desirable to adopt a configuration that satisfies the above.

  According to this configuration, by setting the interval Δtp from the start end of the drive pulse generated earlier in the drive signal to the start end of the drive pulse generated after the drive pulse within the above range, the previous drive pulse By using the residual vibration after the droplet is ejected by the above, the flight speed of the droplet ejected by the subsequent drive pulse can be increased.

Further, in the above configuration, when the time from the start of the first change element to the start of the second change element of each drive pulse is Δtx and the period of the pressure vibration generated in the liquid in the pressure chamber is Tc ,
0.3 × Tc ≦ ΔTx ≦ 0.6 × Tc
It is desirable to adopt a configuration that satisfies the above.

  According to this configuration, by setting the time Δtx from the start end of the first change element to the start end of the second change element of each drive pulse to a value within the above range, the pressure oscillation caused by the first change element On the other hand, the pressure vibration generated by the second change element can be resonated to obtain a larger pressure vibration. As a result, a liquid having a relatively high viscosity, such as a photocurable liquid, can be efficiently ejected.

Further, in the above configuration, the drive signal generation means generates a non-ejection drive pulse that drives the pressure generation means to such an extent that a droplet is not ejected after the drive pulse,
The non-injection drive pulse includes a third change element whose potential changes so as to expand the pressure chamber,
It is desirable that the non-ejection drive pulse adopts a configuration in which the rear end portion of the droplet ejected from the nozzle by the drive pulse is drawn to the pressure chamber side by the third change element.

  According to this configuration, the non-ejection drive pulse causes the rear end portion of the droplet ejected from the nozzle by the drive pulse to be drawn to the pressure chamber side by the third change element, so that the droplet ejected by the drive pulse The rear end portion is drawn into the meniscus in the nozzle. Thereby, generation | occurrence | production of mist is suppressed.

In the above configuration, the time from the end of the second change element in the drive pulse to the start of the third change element in the non-ejection drive pulse is Δtpc, and the period of the pressure vibration generated in the liquid in the pressure chamber is Tc. When
0.3 × Tc ≦ Δtpc ≦ 1.5 × Tc
It is desirable to adopt a configuration that satisfies the above.

  According to this configuration, by setting the time Δtpc from the end of the second change element in the drive pulse to the start of the third change element in the non-ejection drive pulse to a value within the above range, It is possible to suppress the occurrence of mist without reducing the flying speed and weight of the ejected droplets.

  In the above configuration, it is desirable to employ a configuration in which the potential difference from the highest potential to the lowest potential of the non-ejection drive pulse is set to 50% or less of the potential difference from the highest potential to the lowest potential of the drive pulse.

  According to this configuration, the potential difference (drive voltage) from the high potential to the lowest potential of the non-ejection drive pulse is set to 50% or less of the potential difference from the highest potential to the lowest potential of the drive pulse. When a pulse is applied to the pressure generating means and driven, droplets are not ejected from the nozzle, and pressure vibration generated in the pressure chamber due to application of the non-ejection driving pulse can be suppressed low.

Furthermore, in the above configuration, the liquid is a photocurable liquid that is cured by light irradiation,
An irradiation means for irradiating light to the photocurable liquid that has landed on the landing target is provided,
The control means grasps the distance from the irradiation means to the landing target based on the detection means, and the integrated amount of light irradiated to the photocurable liquid on the landing target when the distance is relatively short Therefore, it is desirable to employ a configuration in which the amount of integrated irradiation of light applied to the photocurable liquid on the landing target is large when the distance is relatively long.
In this configuration, it is desirable that the liquid has a viscosity of 8 mPa · s to 20 mPa · s.

  According to this configuration, the distance from the irradiation unit to the landing target is grasped on the basis of the detection unit, and as the distance is longer, the cumulative amount of light irradiated from the irradiation unit to the photocurable liquid on the landing target is increased. Thus, even a landing target having a three-dimensional shape such as an uneven surface or a curved surface can be fixed while suppressing liquid bleeding and flowing out.

The method for controlling a liquid ejecting apparatus of the present invention includes a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a pressure generation unit that causes pressure fluctuation in the liquid in the pressure chamber. A liquid ejecting head capable of ejecting liquid from the nozzle by the operation of the means, and a drive signal generating means for generating a drive signal including a plurality of drive pulses for driving the pressure generating means to eject droplets from the nozzle within a unit period; And a control means for detecting the distance from the nozzle formation surface of the liquid jet head to the landing target, and a control means for controlling application of the drive pulse to the pressure generating means. And
The flying speed of a droplet ejected by a driving pulse generated after a driving pulse generated earlier is higher than the flying speed of a droplet ejected by a driving pulse generated earlier in the driving signal, The droplets generated later are configured to catch up and coalesce before the previously generated droplets land on the landing target,
According to the distance detected by the detection means, the number of application of the drive pulse included in the drive signal to the pressure generation means is increased as compared with the case of the first distance, so that the number of droplets that merge during flight is increased. It is characterized by changing.

2 is a block diagram illustrating an electrical configuration of a printer. FIG. FIG. 2 is a front view of a main part for explaining the internal configuration of the printer. It is a wave form diagram explaining the structure of a drive signal. FIG. 3 is a perspective view illustrating a configuration of a recording head. FIG. 3 is a cross-sectional view of a main part illustrating the configuration of a recording head. It is a graph which shows the change of the flying speed of the ink when changing the space | interval of drive pulses. It is a graph which shows the relationship between the distance from the nozzle formation surface of the ink droplet ejected from the nozzle, and the flying speed of the said ink droplet. It is a schematic diagram explaining a recording operation.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In the embodiments described below, various limitations are made as preferred specific examples of the present invention. However, the scope of the present invention is not limited to the following description unless otherwise specified. However, the present invention is not limited to these embodiments. In the following, an ink jet recording apparatus (hereinafter referred to as a printer) will be described as an example of the liquid ejecting apparatus of the invention.

  FIG. 1 is a block diagram for explaining the electrical configuration of the printer 1, and FIG. 2 is a front view of a main part for explaining the internal configuration of the printer 1. The external device 2 is an electronic device that handles images, such as a computer or a digital camera. The external device 2 is communicably connected to the printer 1 and causes the printer 1 to print an image or text on the recording medium 12 (landing target, recording target). 1 to send.

  The printer 1 in this embodiment includes a printer controller 7 and a print engine 13. As shown in FIG. 2, the recording head 6 which is a kind of liquid ejecting head is fixed to the bottom surface side of the carriage 16 on which the ink cartridge 17 is mounted. The carriage 16 is configured to reciprocate along the guide rod 18 by the carriage moving mechanism 4. That is, the printer 1 sequentially transports the recording medium 12 by the transport mechanism 3 and moves the recording head 6 relative to the printing surface of the recording medium 12 by the carriage moving mechanism 4 while the nozzles 36 ( Ink is ejected from (see FIG. 5), and the ink is landed on the recording medium 12, thereby recording an image or the like.

  The printer controller 7 is a type of control means in the present invention, and is a control unit that controls each part of the printer. The printer controller 7 includes an interface (I / F) unit 8, a CPU 9, a storage unit 10, and a drive signal generation unit 11. The interface unit 8 transmits / receives printer status data when sending print data or a print command from the external device 2 to the printer 1 or outputting status information of the printer 1 to the external device 2 side. The CPU 9 is an arithmetic processing device for controlling the entire printer. The memory | storage part 10 is an element which memorize | stores the data used for the program and various control of CPU9, and contains ROM, RAM, and NVRAM (nonvolatile memory element). The CPU 9 controls each unit according to a program stored in the storage unit 10.

  The drive signal generator 11 generates an analog voltage signal based on waveform data relating to the waveform of the drive signal. The drive signal generator 11 amplifies the voltage signal to generate the drive signal COM. For example, the drive signal generation unit 11 in the present embodiment generates a drive signal COM including two or more drive pulses DP shown in FIG. Details of the drive signal COM will be described later.

  Next, the print engine 13 will be described. As shown in FIG. 1, the print engine 13 includes a recording head 6, a carriage moving mechanism 4, a transport mechanism 3, and a linear encoder 5. Further, the recording head 6 is provided with a head control unit 14, a piezoelectric element 28, a gap detection unit 19, and a light irradiation unit 20. The carriage moving mechanism 4 includes a carriage 16 to which the recording head 6 is attached, and a drive motor (for example, a DC motor) that travels the carriage 16 via a timing belt or the like (not shown). The mounted recording head 6 is moved in the main scanning direction. The transport mechanism 3 includes a paper feed motor, a paper feed roller, and the like, and sequentially feeds the recording medium 12 such as recording paper onto the platen to perform sub-scanning. Further, the linear encoder 5 outputs an encoder pulse corresponding to the scanning position of the recording head 6 mounted on the carriage 16 to the printer controller 7 as position information in the main scanning direction. The printer controller 7 can grasp the scanning position (current position) of the recording head 6 based on the encoder pulse received from the linear encoder 5 side.

  FIG. 4 is a perspective view illustrating the configuration of the recording head 6, and FIG. 5 is a cross-sectional view of the main part illustrating the internal configuration of the recording head 6. The recording head 6 in the present embodiment is composed of a pressure generating unit 23 and a flow path unit 24, and these are integrated in an overlapped state. The pressure generating unit 23 includes a pressure chamber plate 26 that partitions the pressure chamber 25, a communication port plate 27 having a supply side communication port 30 and a first communication port 32a, and a diaphragm 29 on which the piezoelectric element 28 is mounted. It is configured by stacking and integrating by firing or the like. The flow path unit 24 includes a supply port plate 33 having a supply port 31 and a second communication port 32b, a reservoir plate 35 having a reservoir 34 and a third communication port 32c, and a nozzle plate having a nozzle 36 formed therein. It is comprised by adhere | attaching the plate member which consists of 37 in a laminated state. The nozzle plate 37 includes a plurality of (for example, 360) nozzles 36 arranged in a row to form a nozzle row. This nozzle row is provided for each color of ink, for example.

  A piezoelectric element 28 is disposed on the outer surface of the vibration plate 29 opposite to the pressure chamber 25 corresponding to each pressure chamber 25. The illustrated piezoelectric element 28 is a so-called flexural vibration mode piezoelectric element, and includes a piezoelectric body 28c sandwiched between a drive electrode 28a and a common electrode 28b. When a drive signal (drive pulse) is applied to the drive electrode of the piezoelectric element 28, an electric field corresponding to the potential difference is generated between the drive electrode 28a and the common electrode 28b. This electric field is applied to the piezoelectric body 28c, and is deformed according to the strength of the electric field applied with the piezoelectric body 28c. That is, as the potential of the drive electrode 28a is increased, the central portion in the width direction (nozzle row direction) of the piezoelectric layer 28c is bent toward the inner side of the pressure chamber 25 (the side closer to the nozzle plate 37), and the volume of the pressure chamber 25 is increased. The diaphragm 29 is deformed so as to decrease. On the other hand, as the electric potential of the drive electrode 28a is lowered (closer to 0), the central portion of the piezoelectric layer 28c in the short direction is deflected to the outside of the pressure chamber 25 (side away from the nozzle plate 37), and the volume of the pressure chamber 25 is increased. The diaphragm 29 is deformed so as to increase. Here, in the diaphragm 29, the portion sealing the opening of the pressure chamber 25 functions as an operating surface in the present invention. The area of the working surface is slightly larger than the opening area of the pressure chamber 25 sealed by the working surface. Thereby, the operating surface can be easily bent inward or outward from the opening surface of the pressure chamber 25. In the illustrated configuration, it is possible to adopt a configuration in which the drive electrode 28a and the common electrode 28b are reversed.

  Here, the printer 1 according to the present invention is configured so that an image or the like can be printed even on a recording medium 12 having a three-dimensional shape such as unevenness or a curved surface on a printing surface (surface on which ink is landed). Yes. More specifically, photocurable ink is ejected from the nozzles 36 of the recording head 6 to land on the recording medium 12, and the landed ink is irradiated with light from the light irradiation unit 20, so that the ink is applied onto the recording medium 12. Fix quickly. Thereby, even on the recording medium 12 having a three-dimensional shape such as unevenness and a curved surface, it is possible to print a fine image while suppressing ink bleeding and flowing out. As the photocurable ink, one having a viscosity of 8 mPa · s or more and 20 mPa · s or less at room temperature (for example, 25 ° C.) is used. As shown in FIG. 2, the light irradiation unit 20 is provided on each side surface of the carriage 17, and light is irradiated by the light irradiation unit 20 located on the rear side in the traveling direction according to the moving direction of the carriage 17. Thus, curing of the ink that has landed on the recording medium 12 is promoted. This light irradiation part 20 is comprised from light sources, such as a light emitting diode.

  With respect to such a recording medium 12, the distance from the nozzle forming surface of the recording head 6 (the surface on the ink ejection side of the nozzle plate 37) to the recording medium 12 is as shown in FIG. 12a and the recess 12b are different (SG1 <SG2). For this reason, when the ink is ejected under the same conditions (the amount of ink ejected and the flying speed) between the convex portion 12a and the concave portion 12b, the flying distance of the ink droplets in the scanning direction of the recording head 6 is different. Problems such as a relative landing position shift occur. That is, in the concave portion 12b, the time until the ink droplets land is longer than in the case of the convex portion 12a. Therefore, the movement distance in the main scanning direction becomes longer, and the landing position shift is caused accordingly. End up. Further, since the distance from the nozzle forming surface is long in the recess 12b, the ink ejected from the nozzle 36 may stall during flight and may be misted without landing on the recess 12b. Similarly, since the distance from the light irradiation unit 20 to the recording medium 12 differs between the convex portion 12a and the concave portion 12b in the recording medium 12, the amount of light irradiated to the landing ink on the recording medium 12 is the distance. Therefore, there is also a problem that the degree of ink curing changes. For this reason, in the printer 1 according to the present invention, the gap detection unit 19 detects the distance from the nozzle formation surface of the recording head 6 to the recording medium 12 and performs control according to the detected distance. Hereinafter, this point will be described.

First, the drive signal COM will be described.
FIG. 3 is a waveform diagram for explaining the configuration of the drive signal COM generated by the drive signal generation circuit 43.
The drive vibration COM in the present embodiment is configured such that a total of five drive pulses are generated within the generation period T of the drive signal COM1. More specifically, four drive pulses DP1 to DP4 and one cut drive pulse CP for suppressing mist (a kind of non-injection drive pulse) are generated in this order. The drive pulse DP in the present embodiment includes a first waveform element p1 (corresponding to the first change element in the present invention) in which the potential is displaced from the reference potential Eb to the negative electrode (first polarity) side with a constant gradient, A second waveform element p2 that maintains the rear end potential of the first waveform element p1 for a certain period of time, and a third waveform element that changes with a constant gradient from the rear end potential of the second waveform element p2 to the reference potential Eb. Due to p3 (corresponding to the second change element in the present invention), an inverted trapezoidal waveform is obtained.

  When the drive pulse DP is applied to the piezoelectric element 28, first, the piezoelectric element 28 is bent toward the outside of the pressure chamber 25 (side away from the nozzle plate 37) by the first waveform element p1. As a result, the pressure chamber 25 expands from the reference volume to the expansion volume. By this expansion, the meniscus in the nozzle 36 is drawn to the pressure chamber 25 side, and ink is supplied into the pressure chamber 25 from the reservoir 34 side through the supply port. The expansion state of the pressure chamber 25 is maintained over the application period of the second waveform element p2. Subsequently, the third waveform element p3 causes the central portion in the width direction of the piezoelectric element 28 to be greatly bent toward the inner side of the pressure chamber 25 (the side close to the nozzle plate 37). As a result, the pressure chamber 25 rapidly contracts from the expansion volume to the contraction volume. Due to the rapid contraction of the pressure chamber 25, the ink in the pressure chamber 25 is pressurized to generate pressure vibration, and an ink droplet (a kind of droplet) is ejected from the nozzle 36.

  With respect to the time Δtx from the beginning of the first waveform element p1 to the beginning of the third waveform element p3 of each drive pulse DP, when the period of pressure vibration (natural vibration period) generated in the ink in the pressure chamber 25 is Tc. 0.3 × Tc ≦ Δtx ≦ 0.6 × Tc. By doing so, it is possible to resonate the pressure vibration generated by the third waveform element p3 with respect to the pressure vibration generated by the first waveform element p1, thereby obtaining a larger pressure vibration. Thereby, it is possible to efficiently eject a relatively high-viscosity liquid like the above-described photocurable ink. Note that the drive voltage and waveform elements of the first drive pulse DP1 are such that the ink droplet flying speed Vm1 is 6 m / s or more when ink is ejected independently by the first first drive pulse DP1 in the unit period T. The slope (potential change rate) is adjusted.

Here, the Tc is uniquely determined for each recording head by the shape, size, rigidity, and the like of each part such as the nozzle 36, the pressure chamber 25, and the ink supply path (supply side communication port 30 and supply port 31). . This inherent vibration period Tc can be expressed by the following equation (A), for example.
Tc = 2π√ [[(Mn × Ms) / (Mn + Ms)] × Cc] (A)
In the formula (A), Mn is an inertance in the nozzle 36, Ms is an inertance in the ink supply path, and Cc is a compliance of the pressure chamber 25 (represents a volume change per unit pressure and a degree of softness). In the above formula (A), the inertance M indicates the ease of movement of the liquid in the flow path such as the nozzle 36, in other words, the mass of the liquid per unit cross-sectional area. Then, assuming that the density of the fluid is ρ, the cross-sectional area of the surface perpendicular to the flow direction of the fluid in the flow path is S, and the length of the flow path is L, the inertance M is approximated by the following equation (B). Can do.
M = (ρ × L) / S (B)
Note that Tc is not limited to that defined by the above formula (A), and may be any vibration cycle that the pressure chamber 25 of the recording head 6 has.

  Here, the waveform configuration and the pulse width (time from the start end to the rear end of the pulse) of each drive pulse DP1 to DP4 are the same, but regarding each drive voltage (potential difference from the maximum potential to the minimum potential), first, The drive voltage of the drive pulse DP generated later is higher than the drive voltage of the generated drive pulse DP (the drive voltage DP is gradually increased as the drive pulse DP is generated later in the unit period T). ) Is set. Specifically, the drive voltage of the first drive pulse DP1 is V1, the drive voltage of the second drive pulse DP2 is V2, the drive voltage of the third drive pulse DP2 is V3, and the drive voltage of the fourth drive pulse DP4 is V4. V1 <V2 <V3 <V4. As the drive voltage increases, the slopes of the first waveform element p1 and the third waveform element p3, that is, the potential change rate increases, so that the displacement of the piezoelectric element 28 is steep when the piezoelectric element 28 is driven. As a result, a larger pressure fluctuation occurs in the pressure chamber 25. Accordingly, the drive pulse DP (second drive pulse) generated after the flying speed Vm of the ink droplet (first droplet) ejected by the drive pulse DP (first drive pulse) generated earlier. The flying speed Vm of the ink droplet (second droplet) ejected by the is higher. It is also possible to employ a configuration in which the drive voltage and the pulse width are fixed and the potential change rates of the first waveform element p1 and the third waveform element p3 are changed.

  In addition, regarding the time Δtp from the first end of the first drive pulse generated first (start end of the first waveform element p1) to the start end of the second drive pulse (start end of the first waveform element p1), n × It is set within the range of 0.75 × Tc ≦ Δtp ≦ n × 1.25 × Tc. Here, n is a natural number. By setting Δtp within the above range, the flying speed of the ink droplet ejected by the subsequent second drive pulse can be further increased by utilizing the residual vibration accompanying the ejection of the ink by the previous first drive pulse. Can be increased. Further, in the present embodiment, the time Δtp is set to be shorter for the combination of the first drive pulse and the second drive pulse generated on the rear side in the time series. Specifically, with respect to Δtp1 of the set of the first drive pulse DP1 and the second drive pulse DP2, Δtp2 of the set of the second drive pulse DP2 and the third drive pulse DP3, the third drive pulse DP3 and the fourth drive pulse DP4. Are set shorter in the order of Δtp3 (Δtp1> Δtp2> Δtp3). However, the flying speed Vm of the ink droplet ejected by the driving pulse DP generated later is set to be higher than the flying speed Vm of the ink droplet ejected by the driving pulse DP generated earlier. Therefore, Δtp1 = Δtp2 = Δtp3 can also be set as long as it is within the range of Δtp.

  By configuring each drive pulse DP in this way, when a plurality of drive pulses DP are continuously applied to the piezoelectric element 28 within the same period T, the preceding ink droplet is ejected by the previous first drive pulse. The ink droplet (second droplet) ejected by the subsequent second driving pulse catches up with (the first droplet) until it reaches the recording medium 12 and merges. As a result, the flying speed and weight of the combined ink droplets are increased as compared with the case of one ink droplet. Accordingly, as the number of ink droplets to be merged during flight increases, the flying speed and weight of the ink droplets after merger increase, so that it is possible to reach a longer distance without causing mist during flight. .

FIG. 6 is a graph showing a change in the flying speed Vm of the ink when the interval (time) Δtp between the drive pulses is changed. In the figure, the value of Vm indicated by the horizontal broken line is the flying speed Vm1 of the ink droplet when ink is ejected independently by the first first driving pulse DP1 in the period T. The flying speed when two drops are combined during flight is Vm2, the flying speed when three drops are combined during flight is Vm3, and the flying speed when four drops are combined during flight is Vm4. Yes.
When ink is ejected by the first drive pulse DP1, the ink and the meniscus in the pressure chamber 25 vibrate with a period Tc. In a state where this vibration has not converged, the flying speed when an ink droplet is ejected by a subsequent drive pulse varies according to the phase of the residual vibration. That is, when the time Δtp is changed, the flight speed is periodically changed as shown in FIG. The flight speed change period also substantially coincides with Tc. Ink is ejected at a flying speed higher than the flying speed Vm1 by setting the interval Δtp between the drive pulses within the above range of n × 0.75 × Tc ≦ Δtp ≦ n × 1.25 × Tc. The In addition, the flight speed can be further increased by setting a shorter value (n is smaller) within the above range. For this reason, in the present embodiment, Δtp1 is set to 3.75 × Tc ≦ Δtp ≦ 6.25 × Tc, Δtp2 is set to 3 × Tc ≦ Δtp ≦ 5 × Tc, and Δtp3 is 2.25 × Tc. ≦ Δtp ≦ 3.75 × Tc is set. Thereby, a plurality of ink droplets can be more reliably combined while flying toward the recording medium.

  FIG. 7 is a graph showing the relationship between the distance from the nozzle formation surface of the ink droplet ejected from the nozzle 36 and the flying speed Vm of the ink droplet. As shown in the figure, the flying speed Vm of the ink droplet tends to decrease as the ink droplet moves away from the nozzle formation surface. However, as the number of ink droplets combined during flight increases with respect to the flight velocity Vm1 when ink is ejected solely by the first drive pulse DP1, the decrease in flight velocity is suppressed. I understand. In particular, when four ink droplets are combined using all of the drive pulses DP1 to DP4, the distance from the nozzle formation surface is 3 mm or more, and the flying speed Vm4 is hardly changed from the initial speed. As a result, a plurality of ink droplets can be combined more reliably, and even when the distance from the nozzle forming surface to the recording medium is long, the ink droplets can be reliably landed by the recording medium.

  FIG. 8 is a schematic diagram for explaining a recording operation for printing an image or the like on the surface of the recording medium 12 by ejecting ink droplets from the nozzles 36 of the recording head 6 and landing on the recording medium 12. In the figure, a recording head 6 mounted on a carriage 16 ejects ink droplets from nozzles 36 while moving from the left side to the right side with respect to the recording medium 12. Here, the printer controller 7 recognizes the distance SG from the nozzle formation surface of the recording head 6 to the recording medium 12 based on the detection signal from the gap detection unit 19, and according to the distance SG, the driving pulse in the driving signal COM. The number of DP applied to the piezoelectric element 28 is changed. For example, when ink is ejected onto the convex portion 12a in the recording medium 12 (FIG. 8A), the distance SG1 to the recording medium 12 is relatively short (for example, 1 mm or less), and therefore the drive signal COM Only the first drive pulse DP1 is selected and applied to the piezoelectric element 28. Accordingly, only one ink droplet Id1 is ejected from the corresponding nozzle 36. The ink droplet Id1 can land on the convex portion 12a of the recording medium 12 without being misted if the distance is SG1 or less.

On the other hand, when ink is ejected to the recess 12b in the recording medium 12 (FIG. 8B), the distance SG2 to the recording medium 12 is relatively long (for example, 2 mm or more). The first drive pulse DP1 and the next second drive pulse DP2 are selected and sequentially applied to the piezoelectric element 28. As a result, two ink droplets Id1 and a subsequent ink droplet Id2 are ejected from the corresponding nozzle 36 continuously. These ink droplets coalesce and fly before reaching the recording medium 12. As described above, since the flying speed and weight of the combined droplets increase, the combined ink droplets can land on the concave portion 12b of the recording medium 12 without being misted even at the distance SG2. it can.
However, when a plurality of ink droplets are combined in this way, the amount of ink that lands on the concave portion 12b increases more than originally, and accordingly, the printer controller 7 causes the number of dots to be formed in the concave portion 12b. The total amount of ink that lands on the entire concave portion 12b of the recording medium 12 is reduced. Thereby, it is possible to suppress the occurrence of unevenness in the density of the image printed on the recording medium 12.

  Similarly, when the distance SG3 to the recording medium 12 is longer than SG2 (for example, 3 mm or more) (FIG. 8C), the printer controller 7 uses all the drive pulses DP1 to DP4 in the drive signal COM. These are selected and sequentially applied to the piezoelectric elements 28. As a result, a total of four ink droplets of the ink droplet Id1 and the subsequent Id2, Id3, and Id4 are ejected from the corresponding nozzle 36 in succession. These ink droplets coalesce and fly before reaching the recording medium 12, and can land on the concave portion 12b of the recording medium 12 without being misted even at the distance SG3. Further, when ink is ejected by the last fourth drive pulse DP4, the tail drive is suppressed by applying the cut drive pulse CP to the piezoelectric element 28, thereby preventing the generation of mist (details will be described later). ).

  During the recording operation described above, the ink is irradiated by irradiating light toward the ink landed on the recording medium 12 from the light irradiation unit 20 (20a in FIG. 8) located behind the carriage 16 in the traveling direction. Is cured to promote fixing. Here, based on the detection signal from the gap detection unit 19, the printer controller 7 changes the integrated amount of light irradiation by the light irradiation unit 20. For example, if it is determined based on the detection signal from the gap detection unit 19 that the convex portion 12a in the recording medium 12 is directly below the light irradiation unit 20 (the distance from the light irradiation unit 20 to the recording medium 12 is short), the printer controller 7 adjusts the light irradiation unit 20 to set a relatively weak light amount. On the other hand, when it is determined that the concave portion 12b in the recording medium 12 is directly below the light irradiation unit 20 (the distance from the light irradiation unit 20 to the recording medium 12 is long), the printer controller 7 changes the light irradiation unit 20 to Adjust to a higher light intensity.

  In this way, by changing the integrated amount of light irradiation by the light irradiation unit 20 according to the distance from the light irradiation unit 20 to the recording medium 12, landing is performed regardless of the distance from the light irradiation unit 20 to the recording medium 12. Since the amount of light applied to the ink can be made as uniform as possible, the degree of curing of the ink on the recording medium 12 can be made uniform. As a result, unevenness in the density and color of the image printed on the recording medium 12 is suppressed. The distance from the light irradiation unit 20 to the recording medium 12 includes the detection signal from the gap detection unit 19 (19a, 19b), the gap between the gap detection unit 19 (19a, 19b) and the light irradiation unit 20, and the carriage 16. It can be grasped from the moving speed. Further, when the light irradiation unit 20 is a light emitting diode, the light amount from the light irradiation unit 20 can be adjusted by changing the number of times that the light irradiation unit 20 blinks at high speed, or by changing the number of light emitting units provided with a plurality of light emitting diodes. This can be realized by changing the number of scans of 16.

Next, the cut drive pulse CP (a kind of non-ejection drive pulse in the present invention) will be described.
When a relatively high-viscosity liquid such as a photo-curable ink is ejected, a phenomenon that the trailing end portion of the droplet extends like a tail (claw) tends to occur. When the tail portion is separated from the droplet main body, the separated portion may be misted. When this mist occurs, the mist may adhere to the recording medium 12 and the image quality of the recorded image or the like may deteriorate, or the constituent members inside the printer 1 may be soiled to cause a failure. In particular, since the flying speed Vm4 of the ink droplet ejected by the fourth drive pulse DP4 generated last in the drive signal COM is the highest, mist is likely to occur. For this reason, in the printer 1 according to the present invention, when ink is ejected by the fourth drive pulse DP4, the cut drive pulse CP is applied to the piezoelectric element 28 following the fourth drive pulse DP4. It is comprised so that mist formation may be suppressed.

  The cut drive pulse CP in the present embodiment includes a first cut waveform element p11 (corresponding to a third change element in the present invention), a second cut waveform element p12 (maintenance element), and a third cut waveform element. p13 (return element). The first cut waveform element p11 is a waveform element in which the potential changes (falls) at a constant gradient that does not cause ink to be ejected from the reference potential Eb to the expansion potential E5, and the second cut waveform element p12 includes the expansion potential E5. Is a constant waveform element. The third cut waveform element p13 is a waveform element that restores (increases) the potential with a gentle constant gradient from the expansion potential E5 to the reference potential Eb. The drive voltage V5 of the cut drive pulse CP is set to 50% or less of the drive voltage V4 of the fourth drive pulse V4. Thus, when the cut drive pulse DPC is applied to the piezoelectric element 28 and driven, the ink is not ejected from the nozzle 36, and the pressure vibration generated in the pressure chamber 25 by the application of the cut drive pulse DPC. Can be kept low.

  When the cut drive pulse DPC configured in this way is applied to the piezoelectric element 28, first, the central portion of the piezoelectric element 28 is deflected to the outside of the pressure chamber 25 by the first cut waveform element p11, and the volume of the pressure chamber 25 is increased. Increase. Accordingly, the meniscus is drawn to the pressure chamber 25 side. As a result, the trailing end of the ink droplet ejected by the fourth drive pulse DP4 is drawn into the meniscus. The pressure chamber 25 expands from the reference volume corresponding to the reference potential Eb to the expansion volume corresponding to the expansion potential E5. By this expansion, the meniscus is drawn to the pressure chamber 25 side. And the expansion state of this pressure chamber 25 is maintained over the application period of the 2nd cut waveform element p12. Thereafter, the third cut waveform element p13 is applied, the central portion of the piezoelectric element 28 bends inside the pressure chamber 25, and returns to the reference state corresponding to the reference potential Eb.

  Here, regarding the time Δtpc from the end of the third waveform element p3 of the fourth drive pulse DP4 to the start of the first cut waveform element p11 of the cut drive pulse CP, 0.3 × Tc ≦ Δtpc ≦ 1.5 × It is set within the range of Tc. When Δtpc is shorter than 0.3 Tc, the fourth driving pulse draws more ink droplets ejected from the nozzles 36 than necessary into the meniscus, resulting in a problem that the flying speed and amount of the ink droplets are reduced. is there. On the other hand, when Δtpc is longer than 1.5 × Tc, the ink droplets ejected from the nozzles 36 by the fourth drive pulse are separated from the meniscus, so that mist reduction cannot be achieved. Therefore, by setting Δtpc to a value within the above range, it is possible to suppress the occurrence of mist without reducing the flying speed and weight of the ink droplet ejected from the nozzle 36 by the fourth drive pulse. It becomes.

  By the way, the present invention is not limited to the above-described embodiment, and various modifications can be made based on the description of the scope of claims.

The waveform configuration of the drive pulse DP is not limited to that exemplified in the above embodiment. At least a first change element whose potential changes so as to expand the pressure chamber, and a second change element whose potential changes so as to contract the pressure chamber expanded by the first change element. Any voltage waveform may be used.
Similarly, the waveform configuration of the cut drive pulse DPC is not limited to that exemplified in the above embodiment. The voltage waveform may include at least a third change element whose potential changes so as to expand the pressure chamber.
In the configuration capable of simultaneously generating a plurality of drive signals, in addition to the first drive signal for generating the drive pulse DP, a second drive signal for generating the cut drive pulse DPC is generated, and the cut drive pulse is generated. It is also possible to adopt a configuration in which the generation timing of DPC is set so as to correspond to each drive pulse in the first drive signal. According to this configuration, for example, when three droplets are merged, the last drive pulse is the third drive pulse DP3 in the above example, so the corresponding cut drive pulse after the third drive pulse DP3. By applying DPC to the piezoelectric element, it is possible to suppress mist caused by the ink ejected by the third drive pulse DP3.

  In the above embodiment, the so-called flexural vibration type piezoelectric element 28 is exemplified as the pressure generating means. However, the present invention is not limited to this, and for example, a so-called longitudinal vibration type piezoelectric element can be employed. In this case, with respect to the exemplified drive pulse DP and cut drive pulse DPC, the waveform is a waveform in which the direction of potential change, that is, the top and bottom are inverted.

  The present invention is not limited to a printer as long as it is a liquid ejecting apparatus that ejects liquid onto a landed object having a three-dimensional shape such as unevenness, and various ink jet recording apparatuses such as a plotter, a facsimile machine, a copier, and a recording The present invention can also be applied to a liquid ejecting apparatus other than the apparatus, for example, a display manufacturing apparatus, an electrode manufacturing apparatus, a chip manufacturing apparatus, and the like. In the display manufacturing apparatus, a solution of each color material of R (Red), G (Green), and B (Blue) is ejected from the color material ejecting head. Moreover, in an electrode manufacturing apparatus, a liquid electrode material is ejected from an electrode material ejection head. In the chip manufacturing apparatus, a bioorganic solution is ejected from a bioorganic ejecting head.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 6 ... Recording head, 7 ... Printer controller, 11 ... Drive signal production | generation part, 19 ... Gap detection part, 20 ... Light irradiation part, 25 ... Pressure chamber, 28 ... Piezoelectric element, 36 ... Nozzle

Claims (10)

A liquid ejector that has a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a pressure generation unit that causes a pressure fluctuation in the liquid in the pressure chamber, and can eject the liquid from the nozzle by the operation of the pressure generation unit Head,
Drive signal generating means for generating a drive signal including a plurality of drive pulses for driving the pressure generating means to eject droplets from the nozzles within a unit period;
Detecting means for detecting a distance from the nozzle forming surface of the liquid jet head to the landing target;
Control means for controlling application of the drive pulse to the pressure generating means;
With
The flying speed of a droplet ejected by a driving pulse generated after a driving pulse generated earlier is higher than the flying speed of a droplet ejected by a driving pulse generated earlier in the driving signal, The droplets ejected later are configured to catch up and merge before the droplets ejected earlier land on the landing target,
When the distance detected by the detection means is longer than the first distance, the control means increases the number of application of the drive pulse included in the drive signal to the pressure generation means compared to the case of the first distance. And changing the number of droplets that coalesce during flight. Each of the drive pulses has a first change element whose potential changes so as to expand the pressure chamber, and a second change whose potential changes so as to contract the pressure chamber expanded by the first change element. Change elements, and
2. The potential change rate of a drive pulse generated after the previous drive pulse is set larger than a potential change rate of a drive pulse generated earlier in the drive signal. The liquid ejecting apparatus according to 1. In the drive signal, the interval from the start of the drive pulse generated earlier to the start of the drive pulse generated after the drive pulse generated earlier is Δtp, and the period of the pressure vibration generated in the liquid in the pressure chamber is Tc. When the natural number is n,
n × 0.75 × Tc ≦ Δtp ≦ n × 1.25 × Tc
The liquid ejecting apparatus according to claim 2, wherein: When the time from the start end of the first change element to the start end of the second change element of each drive pulse is Δtx, and the period of pressure oscillation generated in the liquid in the pressure chamber is Tc,
0.3 × Tc ≦ ΔTx ≦ 0.6 × Tc
The liquid ejecting apparatus according to claim 2, wherein: The drive signal generation means generates a non-ejection drive pulse that drives the pressure generation means to such an extent that droplets are not ejected after the drive pulse,
The non-injection drive pulse includes a third change element whose potential changes so as to expand the pressure chamber,
5. The liquid according to claim 4, wherein the non-ejection driving pulse causes the rear end portion of the droplet ejected from the nozzle by the driving pulse to be drawn into the pressure chamber side by the third change element. Injection device. When the time from the end of the second change element in the drive pulse to the start of the third change element in the non-ejection drive pulse is Δtpc, and the period of the pressure vibration generated in the liquid in the pressure chamber is Tc,
0.3 × Tc ≦ Δtpc ≦ 1.5 × Tc
The liquid ejecting apparatus according to claim 5, wherein:   The potential difference from the highest potential to the lowest potential of the non-ejection drive pulse is set to 50% or less of the potential difference from the highest potential to the lowest potential of the drive pulse. Liquid ejector. The liquid is a photocurable liquid that is cured by light irradiation,
An irradiation means for irradiating light to the photocurable liquid that has landed on the landing target is provided,
The control means grasps the distance from the irradiation means to the landing target based on the detection means, and the integrated amount of light irradiated to the photocurable liquid on the landing target when the distance is relatively short The amount of integrated irradiation of light applied to the photocurable liquid on the landing target when the distance is relatively long is large. Liquid ejector.   9. The liquid ejecting apparatus according to claim 1, wherein the liquid has a viscosity of 8 mPa · s or more and 20 mPa · s or less. A liquid ejector that has a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a pressure generation unit that causes a pressure fluctuation in the liquid in the pressure chamber, and can eject the liquid from the nozzle by the operation of the pressure generation unit A head, driving signal generating means for generating a driving signal including a plurality of driving pulses for ejecting droplets from the nozzles by driving the pressure generating means within a unit period, and the landing target from the nozzle forming surface of the liquid ejecting head A control method for a liquid ejecting apparatus, comprising: a detecting unit that detects a distance to the pressure generating unit; and a control unit that controls application of the drive pulse to the pressure generating unit.
The flying speed of a droplet ejected by a driving pulse generated after a driving pulse generated earlier is higher than the flying speed of a droplet ejected by a driving pulse generated earlier in the driving signal, The liquid droplets ejected later are configured to catch up and merge before the liquid droplets ejected earlier land on the landing target,
According to the distance detected by the detection means, the number of application of the drive pulse included in the drive signal to the pressure generation means is increased as compared with the case of the first distance, so that the number of droplets that merge during flight is increased. A control method for a liquid ejecting apparatus, wherein the control method is changed.

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