JP2006056241A - Method and unit for jetting ink droplet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain the liquid amount of each ink droplet constant and to match the ink ejection speed between the ink droplets even if the size of the ink droplets differs to improve the precision of the hitting position of the ink droplets different in size, in a method for jetting ink droplets having three types of ink droplets in size to be jetted, a middle droplet, a small droplet about half size of the middle droplet and a large droplet about two times larger than the middle droplet. <P>SOLUTION: In the method for jetting ink droplets, a drive voltage pulse for the small droplets for jetting the small droplets at a predetermined speed is previously set to jet the ink droplets in each size with the drive voltage of the small droplet drive voltage pulse. The jetting pulse corresponding to the middle droplets and the large droplets, and the pulse width of jet stabilizing pulse, and the downtime width between the two pulses are made to be a predetermined time, to jet the ink droplets having the predetermined size at the jetting speed matching the jetting speed of the small droplets. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink droplet ejection method and an ink droplet ejection apparatus using an inkjet method.

  Conventionally, an inkjet printer head which is a printing apparatus using an inkjet method supplies ink from an ink supply source to an ink supply port of a head unit via an ink supply path, and a plate-type piezoelectric actuator mounted on the head unit, A predetermined pressure is selectively applied to a pressure chamber communicating with a large number of nozzle holes, and each ink is ejected from the nozzle holes.

  The ink jet method is simple in principle, easy to make multiple gradations and colors, and has a drop-on-demand type printing device that ejects only ink droplets used for printing. It is spreading rapidly due to low running costs.

  An example of the ink ejecting apparatus constituting the printing apparatus is shown in FIGS. The ink ejecting apparatus 200 shown in FIG. 4A includes an actuator substrate 201 in which an elongated groove-shaped ink chamber 213 extending in the thickness direction of the paper and a space 215 that does not contain ink are arranged across a side wall 217, and a cover plate. 202. The side wall 217 includes a lower wall 211 polarized in opposite directions P1 and P2 in the height direction of the side wall, and an upper wall 209. One end of each ink chamber 213 in the length direction has a nozzle 218 and the other end has a manifold for supplying ink. The end of the space 215 on the manifold side is closed so that ink does not enter. Electrodes 219 and 221 are provided as metal layers on both side surfaces of each side wall 217. Specifically, the side walls 217 and 217 adjacent to each other with the ink chamber 213 interposed therebetween and the electrodes 219 and 221 on both sides thereof are used as a set of actuators, and all the electrodes 219 on the side wall 217 inside the ink chamber 213 are grounded. In addition, the space electrodes 221 and 221 on the space 215 side are electrically connected to each other and connected to an output circuit for supplying a drive signal.

  Then, when the output circuit applies a voltage to the in-space electrodes 221 that are adjacent to each other with the ink chamber 213 interposed therebetween, the upper and lower portions of the side wall 217 are deformed in a piezoelectric thickness direction in the direction of increasing the volume of the ink chamber 213. For example, as shown in FIG. 4B, when the ink chamber 213b is driven, the voltage V is applied to the adjacent space electrodes 221c and 221d across the ink chamber 213b with all the ink chamber electrodes 219 grounded. When applied, an electric field in the direction of arrow V is generated on the side walls 217c and 217d, and the upper and lower portions of the side walls 217c and 217d are each subjected to piezoelectric thickness slip deformation in a direction increasing the volume of the ink chamber 213b. At this time, the pressure in the ink chamber 213b including the vicinity of the nozzle 218b decreases. This state is maintained for a one-way propagation time T in the ink chamber 213 of the pressure wave. In the meantime, ink is supplied from a manifold (not shown).

  The one-way propagation time T is a time required for the pressure wave in the ink chamber 213 to propagate in the longitudinal direction of the ink chamber 213, and the length L of the ink chamber 213 (not shown: in the thickness direction of the paper surface). Length) and the speed of sound a in the ink inside the ink chamber 213, T = L / a.

  According to the pressure wave propagation theory, the pressure in the ink chamber 213 is reversed and turned to a positive pressure just after the time T has elapsed from the application of the above voltage, but applied to the space electrodes 221c and 221d in accordance with this timing. Return the voltage being set to 0 (V = 0).

  Then, the side walls 217c and 217d return to the state before deformation, and pressure is applied to the ink. At that time, the pressure turned positive and the pressure generated when the side walls 217c and 217d return to the state before the deformation are added together, and a relatively high pressure is generated in a portion near the nozzle 218b of the ink chamber 213b. Ink droplets are ejected from nozzle 218b.

  More specifically, if the time from the application of the voltage to the return of the voltage to 0 (V = 0) deviates from the one-way propagation time T, the ink droplets are ejected, so that the energy efficiency decreases, and the one-way propagation. Since the injection is not performed at all when the time T is almost an even multiple, the time from the application of the voltage to the return of the voltage to 0 (V = 0) is usually equal to the one-way propagation time T. Since the energy efficiency is the highest and the flying speed of the ink droplet is the maximum, it is desirable to set it at least approximately an odd number.

  In recent years, it has been desired to change the size of ejected ink droplets for gradation expression. In this case, in order to improve the printing quality, the size of the ink droplets to be ejected is three types of large, medium and small balls, and it is necessary to stably and reliably eject these ink droplets. It is.

For this purpose, a drive voltage pulse is applied to an actuator for changing the volume of the ink flow path filled with ink, and ink droplets are ejected from the ink nozzles, and printing for one pixel is performed once to a plurality of times. When forming by ejecting droplets, the drive voltage pulse is composed of an ejection pulse for ejecting ink and an ejection stabilization pulse for suppressing pressure wave oscillation in the ink, and the ejection pulse and the ejection stabilization By controlling the pulse width of the pulse and the duration of the pause between these two pulses, there are already ink droplet ejection methods in which the size of the ejected ink droplet is three types: large, medium and small. It has been published. (For example, refer to Patent Document 1).
JP 2001-301206 A (page 1-11, FIG. 1)

  The rising timing and pulse width (that is, time width) of each of at least one ejection pulse and at least one ejection stabilization pulse in the drive pulse signals for large, medium, and small balls for gradation printing In the conventional method, first, a reference center ball is created. Based on the profile of the drive pulse signal when the center ball is created, the droplet volume of the small ball and the large ball is the same as the droplet volume of the center ball. The rising timing and the pulse width of at least one injection pulse and at least one injection stabilization pulse in each of the driving pulse signals for small balls and large balls are determined so as to be approximately half and approximately twice. In this case, the pulse width of each of the at least one ejection pulse in the drive pulse signal for the center ball is set to a pulse width such that the ejection time 1T coincides with the one-way propagation time T described above.

  Therefore, for example, when obtaining the driving pulse signal for the small ball and the large ball based on the driving pulse signal for the middle ball having one ejection pulse, the ejection pulse has one ejection pulse having a pulse width shorter than the one-way propagation time T. A small driving pulse signal is obtained, and a large driving pulse signal having two ejection pulses each having a pulse width shorter than the one-way propagation time T is obtained.

  When gradation printing was performed with three types of droplets to be ejected, small balls, medium balls, and large balls, it was found that the print quality was not always constant. Therefore, it is desired to further improve the printing accuracy even when gradation printing is performed by changing the size of the ejected droplets.

  Possible causes of poor print quality include cases where the ink droplet volume error for each of the large, medium, and small droplets is different, and the ejection speed (also referred to as the flying speed) of each droplet is different. It is done. For this purpose, it is desired to match the ejection speeds in addition to keeping the droplet volume of each of the large, medium, and small ink droplets constant.

  In order to solve the above problems, the object of the present invention is to divide the size of the ink droplets to be ejected into three: a middle ball, a small ball that is approximately half the middle ball, and a large ball that is approximately twice the middle ball. In each type of ink droplet ejection method, the droplet volume of each ink droplet is kept constant, and even if the ink droplet size is different, the ejection speed between the ink droplets is made to coincide with each other. Another object of the present invention is to provide an ink droplet ejection method or an ink droplet ejection device capable of improving the accuracy of the landing position of the ink droplet.

  In order to achieve the above object, according to a first aspect of the present invention, an ink droplet is ejected from an ink nozzle by applying a driving voltage pulse having a plurality of pulses to an actuator that changes the volume of an ink flow path. When forming a minute print by ejecting at least one ink droplet, the size of the ink droplet to be ejected is set to a central ball having a predetermined droplet amount and a droplet amount smaller than the set droplet amount. There are three types of ink droplet ejection methods: a small ball and a large droplet with a larger droplet amount than the set droplet amount. When printing one pixel, at least in order to form the small droplet, A first drive pulse signal is set to eject one of the droplets at a predetermined ejection speed, and the first drive is performed to eject at least one droplet to form the middle or large ball. Having the same voltage as the pulse signal, A second driving pulse signal is set in which the width of each of the plurality of pulses corresponding to the middle ball or the large ball and the time width between each of the plurality of pulses are set to a predetermined time, The ink droplets of the respective sizes are ejected at an ejection speed that matches the ejection speed of the small balls.

According to the invention according to claim 1 having the above-described configuration, for example, the center ball having a predetermined droplet amount as in claim 3 and the center ball, regardless of the size of the dot to be formed, Even if three types of droplets of approximately half the amount of droplets and large balls having a droplet amount of about twice that of the middle ball are formed, the size of each ink droplet can be maintained, Since the droplet ejection speeds are substantially the same, the accuracy of the landing positions of the ink droplets of the respective sizes is improved, and the print quality can be kept good.
According to a second aspect of the present invention, when forming a center ball, a signal for a center ball, which is a kind of the second drive signal set for the center ball, is used as an actuator to eject at least one droplet. When the droplets are ejected to form a large ball, the second drive signal set for the large ball is used for ejecting at least one droplet, Since a large ball signal different from the signal is applied to the actuator to eject droplets, fine setting and control are possible.
According to a fourth aspect of the present invention, the drive voltage pulse includes at least one ejection pulse for ejecting at least one ink droplet and at least one ejection stabilization pulse for suppressing pressure wave oscillation in the ink chamber. It is characterized by comprising.
According to the fourth aspect of the invention having the above-described configuration, since any of the drive voltage pulses is a set of the ejection pulse and the ejection stabilization pulse, it is possible to always stably discharge the droplet.

In the invention according to claim 5, when the one-way propagation time of the pressure wave in the ink is T, after setting the first drive pulse signal, the pulse width of the ejection pulse included in the second drive pulse signal is set. It is characterized by being set shorter than the one-way propagation time T.
According to a sixth aspect of the present invention, when the one-way propagation time of the pressure wave in the ink is T, after setting the first drive pulse signal, the pulse of the ejection pulse included in the second drive pulse signal The width is set longer than the one-way propagation time T.

  According to the invention which concerns on Claim 5 or 6 which has said structure, selecting either the pulse width shorter than the said one-way propagation time T, and a long pulse width for the injection pulse of a center ball and a large ball is set. A wide range of program settings are possible.

  The invention according to claim 7 is the pulse width of the ejection pulse of the first drive pulse signal, the time width during which the ejection pulse and the ejection stabilization pulse are paused, and the pulse width of the ejection stabilization pulse. Is (0.75T-0.6T-0.35T), the pulse width of the injection pulse of the second drive pulse signal of the center ball, a pause between the injection pulse and the injection stabilization pulse And the pulse width of the injection stabilization pulse is (0.74T-1.725T-1.525T) or (1.3T-1.725T-1.525T).

  According to the invention according to claim 7 having the above-described configuration, it is possible to set the inner ball of the injection speed that matches the injection speed of the small ball to each of the pulse width shorter than the one-way propagation time T and the long pulse width. .

  According to an eighth aspect of the present invention, the second driving pulse signal of the large ball includes the two injection pulses and the one injection stabilization pulse, the pulse width of the first injection pulse, the first injection pulse, and the second injection pulse. The duration of the pause between the injection pulses, the pulse width of the second injection pulse, the duration of the pause between the second injection pulse and the injection stabilization pulse, the duration of the injection stabilization pulse The pulse width is (0.72T-1T-0.72T-1.925T-1.4T) or (1.6T-1T-1.6T-1.925T-1.4T). .

According to the invention which concerns on Claim 8 which has said structure, the large ball of the injection speed which matched the injection speed of the small ball can be set to each of the pulse width shorter than the one-way propagation time T, and a long pulse width.
In order to achieve the above object, an invention according to claim 9 is provided by a medium ball constituted by a set amount of ink, a small ball constituted by an amount of ink smaller than the set amount, and an amount of ink larger than the set amount An ink ejecting apparatus that forms dots selected from a large ball configured, and ejects ink droplets from the nozzle by changing a nozzle, an ink chamber connected to the nozzle, and a volume of the ink chamber. An actuator, and a controller that applies a drive pulse signal having a plurality of pulses to the actuator to eject at least one droplet in order to form a dot corresponding to one pixel, and the controller forms a small ball In order to eject at least one droplet, it is set for a small ball and ejects the droplet at a set ejection speed A small ball formation control unit that applies the first drive pulse signal to the actuator as the drive pulse signal, and a medium ball or a large ball to eject at least one droplet to form a medium ball or a large ball. , Having the same voltage as the first drive pulse signal, the width of each of the plurality of pulses and the pause time between each of the plurality of pulses are set to predetermined values, respectively, A non-small ball formation control unit that applies a second drive pulse signal that causes the droplets to be formed to be ejected at a speed equal to the set ejection speed of the small balls to the actuator as the drive pulse signal.
According to the invention of claim 9 having the above-described configuration, it is possible to make the ejection speeds of the droplets constituting the dots substantially the same regardless of the size of the dots to be formed. As a result, the accuracy of the ink droplet landing position is improved, and the print quality can be kept good.
The invention according to claim 10 is a type of the second drive signal set for the middle ball so that the formation control unit other than the small balls ejects at least one droplet to form the middle ball. A middle ball formation control unit that applies a signal to the actuator; and a second driving signal set for a large ball to eject at least one droplet to form a large ball, It has a large ball formation control unit that applies a signal different from the signal for the central ball to the actuator, and since it has a control unit for the central ball and a control unit for the large ball, fine setting and control are possible. It becomes possible.

  According to the present invention, it is possible to make the ejection speeds of the droplets constituting the dots substantially the same regardless of the size of the dots to be formed. As a result, the accuracy of the ink droplet landing position is improved, and the print quality can be kept good.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 3.

  FIG. 1 shows a waveform of a driving voltage pulse according to the present invention, (a) shows a driving voltage pulse for a small ball, (b) shows a driving voltage pulse for a middle ball, and (c) Indicates driving voltage pulses for large balls. FIG. 2 is a list showing the ejection speed for each drive voltage pulse. FIG. 3 shows the ink ejecting apparatus, and is a cross-sectional view showing a state where the ink chamber is not deformed.

  The ink ejecting apparatus according to the present embodiment includes an actuator and a flow path block. Among these, the actuator has an actuator 100 that uses the longitudinal vibration of the piezoelectric body instead of the actuator 200 that uses the slip deformation of the piezoelectric layer described with reference to FIG.

  As shown in FIG. 3, the actuator 100 has seven piezoelectric layers 121a, 122a, 121b, 122b, 121c, 122c, 121d having electrode layers formed on the surface thereof, and the electrode layers are not formed. It is a laminate of a single piezoelectric layer 123a, 123b. The actuator 100 is fixed to a flow path block 130 in which a plurality of ink chambers 113 are formed so as to straddle the ink chambers 113. These piezoelectric layers are stacked in order from the bottom (ink chamber 113 side) in FIG.

  Among the piezoelectric layers on which the electrodes are formed, the piezoelectric layer 121a located at the lowest layer and the piezoelectric layers 121b, 121c, and 121d have a common electrode extending across each ink chamber 113. 111b is formed. In addition, individual electrodes 111a are formed on the surfaces of the piezoelectric layers 122a, 122b, and 122c so as to individually face the corresponding ink chambers 113.

  By alternately laminating these piezoelectric layers, an active portion (pressure generating portion) 124 that actually expands and contracts when a voltage is applied between the individual electrode 111a and the common electrode 111b is formed in the ink chamber in the actuator 100. 113 side is formed. The active portion 124 corresponds to a region surrounded by a broken line in FIG. On the other hand, the two piezoelectric layers 123a and 123b located on the opposite side of the ink chamber 113 function to restrict the displacement of the active portion 124, and as a whole, the actuator 100 is applied to the ink chamber 113 by applying a voltage. It is designed to be displaced to the side. Each piezoelectric layer has a thickness of 30 μm, and the actuator 100 has a thickness of about 270 μm.

  On the other hand, a plurality of ink chambers 113 are formed on the surface of the flow path block 130 to which the actuator 100 is fixed as described above. The flow path block 130 mainly includes a flow path member 130a in which an ink chamber 113 is formed and a nozzle plate 130b in which a plurality of ink nozzles 118 for discharging ink are formed. The ink chamber 113 as a whole has a rectangular shape elongated in a direction perpendicular to the paper surface, and one end communicates with the ink nozzle 118 and the other end communicates with a manifold (not shown). The external dimensions are 40 μm deep, 250 μm wide and 1700 μm long.

  In the ink ejecting apparatus of the present embodiment, when a voltage is applied between the individual electrode 111a and the common electrode 111b, the piezoelectric layer in the region surrounded by the broken line in FIG. 3 extends in the stacking direction due to the piezoelectric effect. . As a result, the actuator 100 is deformed in a convex shape toward the ink chamber 113, so that the volume of the ink chamber 113 is reduced. In the present embodiment, a so-called “fill-before-fire” driving method is employed. According to this “pulling” driving method, in a normal state (that is, in a non-ejecting state), a state in which a voltage is applied to all the individual electrodes 111a is maintained, and the volumes of all the ink chambers 113 are reduced. Maintained in a state. When a drive command is received, the voltage applied to the individual electrode corresponding to the command is released (that is, the applied voltage is set to 0) immediately before the ink droplet discharge timing, and the corresponding operation is performed. The volume of the ink chamber is returned to the original volume (that is, the volume is increased). When the volume is restored, ink is drawn from the manifold into the ink chamber. Thereafter, a voltage is applied to the individual electrode 111a again, and the volume of the ink chamber is reduced, whereby ink droplets are ejected from the ink chamber. As described in the Background section, in the “pulling” driving method, ink is supplied before discharge, and the pressure fluctuation in the discharge direction is superimposed on the pressure fluctuation at the time of ink supply. By performing (volume reduction of the ink chamber), it is also possible to perform efficient ink ejection.

  In order to change the volume of the ink chamber 113 as described above, a drive voltage pulse is applied to the actuator 100. The driving voltage pulse is applied to at least one ejection pulse for ejecting at least one ink droplet by setting the voltage applied to the individual electrode to 0 at the normal time and to the individual electrode at the normal time. And a jet stabilization pulse that suppresses pressure wave oscillation in the ink by setting the voltage to 0. In the description of the present embodiment, the pulse width in the at least one ejection pulse and the pulse width in the ejection stabilization pulse both mean a period in which no voltage is applied to the individual electrode 111a (voltage 0). is doing. In addition, the resting time width between the ejection pulse and the ejection stabilization pulse and the resting time width between each of the ejection pulses are periods in which a voltage is applied to the individual electrode 111a. I mean.

  The ejection stabilization pulse is generated by applying at least one ejection pulse, and is for reducing the pressure wave vibration in the ink chamber 113 remaining. For example, the ejection stabilization pulse returns the volume of the ink chamber 113 at the timing when the pressure in the ink chamber 113 generated by the ejection pulse rises, lowers the pressure, and then at the timing when the pressure falls. It acts to increase the pressure by reducing the volume, and this action suppresses the residual pressure wave vibration described above.

  In the present embodiment, since the ejection stabilization pulse is generated after the ejection pulse, the amount of ink droplets to be ejected can always be kept constant.

  Therefore, to change the amount of ejected ink droplets, change the applied voltage, change the pulse width of the ejection pulse, or change the timing of the ejection pulse and the ejection stabilization pulse. Can be done.

  As described above, it is possible to increase / decrease the amount of ink droplets and keep the droplet amount constant, but the ink liquids of small balls, medium balls, and large balls each having a predetermined droplet amount Even if droplets are ejected, the printing state is not stable unless the ejection speeds of the respective droplets match.

  Next, driving voltage pulses for ejecting ink droplets of small balls, medium balls, and large balls according to the present embodiment will be described with reference to FIGS.

  FIG. 1A shows a driving voltage pulse for a small ball, a waveform A1 is a conventional driving voltage pulse, and a waveform A2 shows a new driving voltage pulse according to the present invention. Further, FIG. 1B shows a driving voltage pulse for a center ball, a waveform B1 is a conventional driving voltage pulse, and waveforms B2 and B3 show a new driving voltage pulse according to the present invention. Yes. Further, FIG. 1C shows a driving voltage pulse for a large ball, a waveform C1 is a conventional driving voltage pulse, and a waveform C2 and a waveform C3 show a new driving voltage pulse according to the present invention. .

  Conventionally, the driving voltage pulse A1 for small balls and the driving voltage pulse C1 for large balls are set with reference to the driving voltage pulse B1 for middle balls, respectively.

  For this purpose, the pulse width E2 of the ejection pulse E in the drive voltage pulse B1 for the center ball is set to a time that matches the one-way propagation time T, and the applied voltage is V1. Further, at this time, the pulse width E1 of the ejection pulse E of the driving voltage pulse A1 for the small balls, which is about half the amount of the droplets of the middle ball, is 0.75T, which is shorter than the one-way propagation time T. Yes. Furthermore, the driving voltage pulse C1 for a large ball, which is about twice the amount of droplets as the middle ball, has a pulse width E3 of both the first injection pulse and the second injection pulse of 1.2T, The applied voltage is set to V1 (for example, 23 volts) in the same manner as the drive voltage pulse B1 for the center ball.

  The conventional driving voltage pulse A1 for small balls includes a pulse width E1 of the injection pulse E, a time width F1 between the injection pulse E and the injection stabilization pulse G, and a pulse width of the injection stabilization pulse G. G1 is set to (0.75T-0.6T-0.35T).

  Further, the driving voltage pulse B1 for the conventional center ball includes the pulse width E2 of the ejection pulse E, the time width F2 during which the ejection pulse E and the ejection stabilization pulse G are paused, and the ejection stabilization pulse G. The pulse width G2 of (1T-1.725T-1.525T) is set.

  Further, the driving voltage pulse C1 for the conventional large ball includes a pulse width E3 of the first injection pulse, a time width F3 between the first injection pulse and the second injection pulse, and the second injection pulse. A pulse width E3, a pause time width F4 between the second injection pulse and the injection stabilization pulse, and a pulse width G3 of the injection stabilization pulse are respectively (1.2T-1T-1.2T-1). .925T-1.4T).

  In addition, the above-mentioned conventional droplet amounts are 5 pl (picoliter) for small balls, 10 pl for medium balls, and 20 pl for large balls, respectively.

  However, when the injection speed at this time was measured, when the applied voltage V1 was 23 volts and the temperature was 25 ° C., as shown in FIG. 2, the injection speed of the conventional small ball (waveform A1) was 6.8 m / s. Yes, the injection speed of the middle ball (waveform B1) was 9.2 m / s, and the injection speed of the large ball (waveform C1) was 9.2 m / s. That is, it is clear that the middle ball and the large ball have a desired injection speed of 9 m / s, but the injection speed of the small balls is slower than that.

  The ejection speed and the amount of liquid droplets are determined by measuring the ejection speed by taking a stroboscopic image of an ink droplet at a point of 0.5 mm from the nozzle outlet and measuring the ink volume after a number of ejection experiments. The ink droplet amount for one time can be obtained.

  Since the driving voltage pulse A1 for the small ball is applied with the ejection stabilization pulse G immediately after the pulse width E1 (0.75T) of the ejection pulse E (after 0.6T), the ejected liquid droplet is pulled back. The injection speed is reduced by receiving influence.

  As described above, in the conventional ink ejecting method, in order to eject a small amount of droplets of 5 pl based on the ejection condition of the center ball, a decrease in ejection speed is inevitable. In order to meet the demand for higher image quality, which requires fine droplets, the pulse width E1 of the injection pulse E can be made even narrower. Become. Further, if the pulse width E1 of the ejection pulse E is narrowed, the ink ejection characteristics may become unstable, and the practical limit is close. Of course, in order to compensate for the decrease in the injection speed, there is also a method of increasing the drive voltage only when injecting small balls, but this requires a separate drive power supply, which means large size and high cost. It is disadvantageous in terms.

  By the way, this injection speed can be increased by changing the waveform of the drive voltage pulse or increasing the applied voltage.

  However, it is easier to change the applied voltage than to change the predetermined waveform of the drive voltage pulse. In addition, a smaller drive power source not only reduces the burden on the circuit, but is also advantageous in terms of cost. Therefore, a common power source is used regardless of the size of the droplets to be ejected, and the ejection speed of the small balls is the ejection speed of the medium balls or the large balls, which is a desired ejection speed of about 9 m / The applied voltage to be s was determined.

  Therefore, by observing the pulse waveform for the above-mentioned small balls, an applied voltage for matching the small-ball injection speed with the above-mentioned medium-ball and large-ball injection speeds is obtained, and the conventional applied voltage V1 (for example, 23 volts) is determined. An applied voltage V2 (for example, 25 volts) was obtained.

  Next, when driving voltage pulses of a middle ball having a droplet amount of 10 pl and a large ball having a droplet amount of 20 pl were obtained at the applied voltage V2, the desired voltage was changed only by changing the pulse width of each ejection pulse. Droplet volume and jetting speed were obtained. Further, it is a waveform that maintains the resting time width between the ejection pulse and the ejection stabilization pulse and the pulse width of the ejection stabilization pulse as they are, and the driving voltage pulses B2, B3 of the center ball, and The large drive voltage pulses C2 and C3 could be obtained.

  In this way, the applied voltage is changed from V1 (for example, 23 volts) to V2 (for example, 25 volts), and the pulse width of the injection pulse is shorter than the one-way propagation time T or longer than the one-way propagation time T, respectively. By merely changing the pulse width, it is possible to obtain the driving voltage pulses B2 and B3 for the middle ball and the driving voltage pulses C2 and C3 for the large ball.

  The drive voltage pulse B2 for the center ball according to the present embodiment includes the pulse width E4 of the injection pulse, the time width F2 during which the injection pulse and the injection stabilization pulse are paused, and the injection stabilization pulse. The pulse width G2 is (0.74T-1.725T-1.525T). Furthermore, the pulse width E5 of the injection pulse of the drive voltage pulse B3, the time width F2 between the injection pulse and the injection stabilization pulse, and the pulse width G2 of the injection stabilization pulse are (1.3T− 1.725T-1.525T).

  As described above, when the small balls are ejected with the driving voltage pulse A2, the driving voltage pulse B2 using the ejection pulse having the pulse width E4 shorter than the one-way propagation time T and the ejection having the pulse width E5 longer than the one-way propagation time T are used. Two kinds of driving voltage pulses, ie, a driving voltage pulse B3 using a pulse, can eject a middle ball having a droplet amount approximately twice that of the small ball.

  Next, the large driving voltage pulse C2 according to the present embodiment includes a pulse width E6 of the first injection pulse, a time width F3 during which the first injection pulse and the second injection pulse are stopped, The pulse width E6 of the two injection pulses, the pause time width F4 between the second injection pulse and the injection stabilization pulse, and the pulse width G3 of the injection stabilization pulse are (0.72T-1T-0. 72T-1.925T-1.4T). Further, the pulse width E7 of the first injection pulse, the time width F3 during which the drive voltage pulse C3 is paused between the first injection pulse and the second injection pulse, the pulse width E7 of the second injection pulse, the first The pause time width F4 between the two injection pulses and the injection stabilization pulse, and the pulse width G3 of the injection stabilization pulse are (1.6T-1T-1.6T-1.925T-1.4T). It is.

  As described above, when ejecting a small ball with the driving voltage pulse A2 and ejecting a large ball with the driving voltage pulse C2 or C3, the driving voltage pulse C2 using an ejection pulse having a pulse width E6 shorter than the one-way propagation time T; Two kinds of driving voltage pulses, ie, a driving voltage pulse C3 using an ejection pulse having a pulse width E7 longer than the one-way propagation time T, can eject a large ball having a droplet amount approximately twice that of the middle ball.

  When the ejection speed of each ink droplet at this time was measured by the method as described above, the ejection speed of the small ball (waveform A2) was 9.0 m / s as shown in FIG. The jet speed of the large ball of the waveform C2 was 9.2 m / s. Moreover, the injection speed of the center ball of the waveform B3 was 9.3 m / s, and the injection speed of the large ball of the waveform C3 was 9.2 m / s. In other words, the ejection speed of ink droplets of any size of small balls, medium balls, and large balls can be made to match approximately 9 m / s.

  As described above, when forming printing for one pixel by discharging ink droplets from one time to a plurality of times, the size of the ink droplets to be ejected is set to a center ball having a predetermined droplet amount, In the ink droplet ejecting method that uses three types of droplets, that is, a small ball having a droplet amount approximately half that of a central ball and a large ball having a droplet amount approximately twice that of the central ball, the driving voltage pulse is ejected by ejecting ink. It consists of a pulse E and a jet stabilization pulse G that suppresses pressure wave vibrations in the ink, and jets the small balls at a predetermined jet speed in advance for small balls whose jetting characteristics tend to be unstable compared to others. The small droplet driving voltage pulse V2 is set, and the ink droplets of the respective sizes are ejected by the driving voltage of the small ball driving voltage pulse, and the respective corresponding to the medium ball and the large ball. Injection pulse E and the injection stability By setting the pulse width of the pulse G and the time width F between the two pulses to be a predetermined time, the size of the ink droplets to be ejected is approximately half that of the middle ball and the middle ball. Even small balls and large balls that are almost twice as large as the above-mentioned medium balls can maintain the size of their droplets and match their ejection speed to the ejection speed suitable for ink jet printing. It is possible to improve the accuracy of the landing position of the droplet and improve the printing quality.

  Further, when the one-way propagation time of the pressure wave in the ink is T, after setting the driving voltage pulse for the small balls, the ejection pulses of the middle ball and the large ball are pulse widths shorter than the one-way propagation time T, respectively. Alternatively, both pulse widths longer than the one-way propagation time T can be set, a program can be set using at least one drive voltage pulse, and a wide range of program settings can be made.

  The ink droplet ejection apparatus according to the present embodiment includes a controller 300 shown in FIG. The controller 300 includes a computer including a CPU, a ROM, a RAM, and the like, and a drive circuit in terms of hardware. The controller 300 may employ a known hardware configuration. Here, description of the hardware configuration is omitted. The controller 300 uses the power supplied from the connected power supply 302 to generate a drive pulse signal to be output to the actuator 100 based on the input print data signal.

  In the figure, the controller 300 is shown as a functional block. The controller 300 includes a small ball formation control unit 304 as a functional unit that outputs a driving pulse signal for forming small balls to the actuator 100, and a functional unit that outputs a driving pulse signal for forming dots other than small balls to the actuator 100. The small formation control unit 306 is provided. The non-small ball formation control unit 306 includes a middle ball formation control unit 308 and a large ball formation control unit 310 as functional units for outputting drive pulse signals for forming the middle ball and the large ball to the actuator 100, respectively. I have. The small ball formation control unit 304, the middle ball formation control unit 308, and the large ball formation control unit 310 function selectively according to the dots to be formed, generate the drive pulse signal in the manner described above, and output the signal to the actuator 100. Output to. Since the detailed description of the drive pulse signal has been described above, it is omitted here.

  In the above-described embodiment, a so-called “fill-before-fire” driving method is employed in order to eject ink droplets. However, during normal operation (that is, in a non-ejecting state), no voltage is applied to the individual electrodes, and when a drive command is received, voltage is selectively applied to the individual electrodes to reduce the volume of the corresponding ink chamber. A so-called “fire-before-fill” drive system in which ink droplets are ejected from the ink chamber and then the voltage is quickly released to return the volume of the ink chamber and supply ink from the manifold. Even if it is adopted, the present invention can be similarly applied.

The waveform of the drive voltage pulse which concerns on this invention is shown, (a) shows the drive voltage pulse for small balls, (b) shows the drive voltage pulse for medium balls, (c) shows for large balls Drive voltage pulses are shown. It is a list figure which shows the ejection speed in each drive voltage pulse. FIG. 2 is a cross-sectional view illustrating the ink ejecting apparatus according to the present embodiment and a state in which the ink chamber is not deformed. FIGS. 4A and 4B show another ink ejecting apparatus, in which FIG. 4A is a cross-sectional view showing a state where the ink flow path is not deformed, and FIG. 4B is a cross-sectional view showing a state where the ink flow path is deformed. It is a functional block diagram which shows the function of a controller.

Explanation of symbols

A1 Drive voltage pulse (conventional Kodama)
A2 Drive voltage pulse (new Kodama)
B1 Drive voltage pulse (conventional center ball)
B2 Drive voltage pulse (new center ball)
B3 Drive voltage pulse (new center ball)
C1 Drive voltage pulse (conventional large ball)
C2 Drive voltage pulse (new big ball)
C3 Drive voltage pulse (new big ball)
E ejection pulse E1 to E7 pulse width G ejection stabilization pulse T one-way propagation speed 100 actuator 113 ink chamber 118 nozzle

Claims (10)

When a drive voltage pulse having a plurality of pulses is applied to an actuator that changes the volume of the ink flow path to eject ink droplets from the ink nozzles, and printing for one pixel is formed by ejecting at least one ink droplet In addition, the size of the ink droplets to be ejected is determined as follows: a medium ball having a predetermined droplet amount, a small ball having a droplet amount smaller than the set droplet amount, and a large ball having a droplet amount larger than the set droplet amount. There are three types of ink droplet ejection methods,
When printing for one pixel,
In order to form the small balls, a first drive pulse signal is set to eject at least one droplet at a predetermined ejection speed,
In order to form at least one droplet to form the middle ball or large ball, the width of each of the plurality of pulses having the same voltage as the first driving pulse signal and corresponding to the middle ball or the large ball is ejected. And setting a second drive pulse signal in which the pause time interval between each of the plurality of pulses is set to a predetermined time,
An ink droplet ejecting method, wherein the ink droplets having respective sizes are ejected at an ejection speed that matches the ejection speed of the small balls.   When forming the center ball, in order to eject at least one droplet, the droplet is ejected by applying a signal for the center ball, which is a kind of the second drive signal set for the center ball, to the actuator. When a large ball is formed, a large ball signal different from the middle ball signal is a kind of the second driving signal set for the large ball so as to eject at least one droplet. The ink ejecting method according to claim 1, wherein droplets are ejected by being applied to an actuator.   The liquid amount of the small balls is approximately half of the liquid amount set for the medium balls, and the liquid amount of the large balls is approximately twice the liquid amount for the medium balls. Ink ejection method.   The drive voltage pulse includes at least one ejection pulse for ejecting at least one ink droplet, and at least one ejection stabilization pulse for suppressing pressure wave oscillation in the ink chamber. The ink ejecting method according to claim 1.   When the one-way propagation time of the pressure wave in the ink is T, after setting the first drive pulse signal, the pulse width of the ejection pulse included in the second drive pulse signal is set shorter than the one-way propagation time T. The ink droplet ejection method according to claim 1, wherein the ink droplet ejection method is performed.   When the one-way propagation time of the pressure wave in the ink is T, after setting the first drive pulse signal, the pulse width of the ejection pulse included in the second drive pulse signal is set longer than the one-way propagation time T. The ink droplet ejection method according to claim 1, wherein the ink droplet ejection method is performed.   The pulse width of the injection pulse of the first drive pulse signal, the time width during which the injection pulse and the injection stabilization pulse are paused, and the pulse width of the injection stabilization pulse are (0.75T-0. 6T-0.35T), the pulse width of the injection pulse of the second drive pulse signal of the center ball, the time width during which the injection pulse and the injection stabilization pulse are paused, the injection stability The pulse width of the activating pulse is (0.74T-1.725T-1.525T) or (1.3T-1.725T-1.525T), according to any one of claims 1 to 6, The ink droplet ejection method according to claim.   The second driving pulse signal of the large ball includes two injection pulses and one injection stabilization pulse, and the pulse width of the first injection pulse, the pause between the first injection pulse and the second injection pulse. Time width, pulse width of the second injection pulse, resting time width between the second injection pulse and the injection stabilization pulse, and pulse width of the injection stabilization pulse are (0.72T− 1T-0.72T-1.925T-1.4T) or (1.6T-1T-1.6T-1.925T-1.4T) 2. An ink droplet jetting method according to 1. Ink ejection for forming dots selected from a medium ball composed of a set amount of ink, a small ball composed of an amount of ink smaller than the set amount, and a large ball composed of an amount of ink larger than the set amount. A device,
A nozzle, an ink chamber connected to the nozzle, an actuator for ejecting an ink droplet from the nozzle by changing the volume of the ink chamber, and at least one droplet to form a dot corresponding to one pixel A controller for applying a drive pulse signal having a plurality of pulses to the actuator to inject,
The controller is
In order to form a small ball, a small ball formation is applied to the actuator as a drive pulse signal, which is set for the small ball to eject at least one liquid droplet and ejects the liquid droplet at a set ejection speed. A control unit;
In order to form at least one droplet to form at least one medium ball or large ball, it is set for the medium ball or large ball and has the same voltage as the first drive pulse signal, and the width of each of the plurality of pulses and The second drive is configured such that the pause time between each of the plurality of pulses is set to a predetermined value, and the droplets forming the middle ball or the large ball are ejected at a rate equal to the set ejection speed of the small ball. A formation control unit other than small balls that applies a pulse signal to the actuator as the drive pulse signal;
An ink droplet ejecting apparatus comprising: The non-small ball formation control unit applies a signal, which is a kind of the second drive signal set for the medium ball, to the actuator so as to eject at least one droplet to form the middle ball. A ball formation control unit and a type of the second driving signal set for a large ball in order to eject at least one droplet to form a large ball, which is the signal for the middle ball The ink droplet ejecting apparatus according to claim 11, further comprising a large ball formation control unit that applies a signal to the actuator.

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