JP2016087918A - Driving method of inkjet head and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve striking position accuracy by preventing fluctuation of a striking position of a droplet when continuously discharging a large droplet without lengthening a driving period.SOLUTION: A first driving signal PA and a second driving signal PB are applied in the order within one pixel period to a pressure generation means for discharging droplets by expansion or contraction of volume of a pressure chamber and the one pixel periods are repeated two times or more. The first driving signal PA has a first expansion pulse Pa1, a first contraction pulse Pa2, a second expansion pulse Pa3, a second contraction pulse Pa4, a pause time and a third contraction pulse Pa5 in the order, the first liquid droplet due to application of the first expansion pulse Pa1 and the first contraction pulse Pa2 and the second liquid droplet due to application of the second expansion pulse Pa3 and the second contraction pulse Pa4 are combined to one body during flying immediately after discharge, the second driving signal PB has an expansion pulse Pb1, a first contraction pulse Pb2, a pause time and a second contraction pulse Pb3 in the order and starts application of the first driving signal PA of a subsequent one pixel period while leaving a time of 4.5 AL or more from the rising of the expansion pulse Pb1 of the second driving signal PB.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an inkjet head driving method and an inkjet recording apparatus, and more particularly, to an inkjet head that can be driven at high speed while ensuring stability of landing position accuracy even when large droplets are continuously ejected. The present invention relates to a driving method and an ink jet recording apparatus.

  By driving the ink-jet head, droplets ejected from the nozzles of the ink-jet head are landed on the print medium to form pixels composed of dots. It is known to perform gradation expression by changing the dot diameter of one pixel. As a method of changing the dot diameter for this gradation expression, the method of changing the drive signal according to the dot size (Patent Document 1) or the number of application of the drive signal within one pixel period is the same. There is a method of changing the number of droplets ejected from a nozzle (Patent Document 2).

  In Patent Document 1 that changes the drive signal in accordance with the dot size, a drive signal with a smaller droplet volume and a slower droplet velocity is output ahead of other drive signals. Thereby, landing position deviations between droplets of different volumes are reduced.

  Further, in Patent Document 2 of a method for changing the number of droplets ejected from the same nozzle by applying a plurality of driving signals within one pixel period, the waveform of the final driving signal among the plurality of driving signals, The waveform of the initial drive signal to be operated at least once before the final drive signal is changed. Thereby, the difference in velocity of the droplets is eliminated, and the landing position accuracy is improved.

JP 2002-321360 A JP 2007-118278 A

  In the method of changing the drive signal according to the dot size and shifting the ejection timing for each drive signal as in Patent Document 1, the drive waveform of a droplet with a smaller volume is preceded by the drive waveform of other droplets. As a result, it is necessary to delay the discharge timing of medium droplets and large droplets. Therefore, the droplet driving cycle becomes long, and there is a problem in performing high-speed printing. Therefore, from the viewpoint of performing high-speed printing, a method of changing the number of applied drive signals within one pixel period as in Patent Document 2 is desirable.

  By the way, as a case where large droplets are continuously ejected, for example, it is known to form a solid image, and the large droplets are continuously formed using the techniques of Patent Document 1 and Patent Document 2, for example. Create a solid image. However, it has been found that the landing position accuracy of the large droplets deteriorates when the solid droplets are continuously ejected to form a solid image.

  The present inventors diligently studied the cause, and this deterioration of the landing position accuracy occurs when a large droplet is formed by applying a plurality of drive signals to the pressure generating means within one pixel period. Yes. Then, it has been found that among the large droplets ejected continuously when printing a solid image, the landing positions of the large droplets ejected in the second pixel period vary.

  Specifically, among the plurality of drive signals applied in the next one pixel cycle after the end of the first pixel cycle, variation in the landing position occurs in the droplets ejected from the nozzle by the first drive signal, As a result, the landing positions of the large droplets formed by the one pixel period vary. In addition, large droplets after the third pixel period also have a variation in landing positions, and there is a problem that density unevenness occurs in the solid image as a whole.

  Such variation in the landing position is affected by the pressure wave reverberation vibration remaining in the pressure chamber after the discharge of the liquid droplet in the previous one-pixel cycle, when the liquid droplet is discharged in the next one-pixel cycle. Is considered to be the cause. In this case, it is necessary to provide an interval between the last drive signal in the previous one pixel period and the first drive signal in the next one pixel period so that the pressure wave reverberation can be sufficiently attenuated. However, there is a problem that the drive cycle becomes long and the demand for high-speed printing cannot be satisfied.

  Accordingly, the present invention provides an inkjet head that can improve landing position accuracy by preventing variations in the landing positions of droplets when large droplets are continuously discharged without lengthening the driving cycle. It is an object to provide a driving method and an ink jet recording apparatus.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

1. Two drive signals of a first drive signal and a second drive signal are applied in this order within one pixel period to the pressure generating means for ejecting droplets from the nozzle by expanding or contracting the volume of the pressure chamber, and A method for driving an inkjet head that repeats one pixel cycle twice or more,
The first drive signal is:
A first expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A second expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A third contraction pulse that contracts the volume of the pressure chamber and expands after a predetermined time in this order, and discharges the first droplet from the nozzle by applying the first expansion pulse and the first contraction pulse. And causing the second droplet to be ejected from the nozzle by application of the second expansion pulse and the second contraction pulse and coalescing during flight immediately after ejection,
The second drive signal is:
An expansion pulse that expands the volume of the pressure chamber and contracts after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time, in this order,
After the rise of the expansion pulse of the second drive signal, a time of 4.5 AL or more (where AL is ½ of the acoustic resonance period of the pressure wave in the pressure chamber) is set to the next one pixel period. The method for driving an ink-jet head is characterized in that application of the first drive signal is started.

2. In the first drive signal,
The pulse width of the first expansion pulse is 0.4 AL or more and 2.0 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
2. The method of driving an ink jet head according to claim 1, wherein a pulse width of the third contraction pulse is not less than 0.8 AL and not more than 1.2 AL.

3. In the second drive signal,
The expansion pulse has a pulse width of 0.8 AL or more and 1.2 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
3. The ink jet head driving method according to claim 1 or 2, wherein a pulse width of the second contraction pulse is not less than 0.8 AL and not more than 1.2 AL.

4). An inkjet head having pressure generating means for discharging droplets from the nozzle by expanding or contracting the volume of the pressure chamber; and a drive control means for outputting a drive signal for driving the pressure generating means,
The drive control means is an ink jet recording apparatus that applies two drive signals of a first drive signal and a second drive signal to the pressure generating means in this order within one pixel period, and repeats the one pixel period twice or more. There,
The first drive signal is:
A first expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A second expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A third contraction pulse that contracts the volume of the pressure chamber and expands after a predetermined time in this order, and discharges the first droplet from the nozzle by applying the first expansion pulse and the first contraction pulse. And causing the second droplet to be ejected from the nozzle by application of the second expansion pulse and the second contraction pulse and coalescing during flight immediately after ejection,
The second drive signal is:
An expansion pulse that expands the volume of the pressure chamber and contracts after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time, in this order,
The drive control means starts the application of the first drive signal of the next one pixel period after a time of 4.5 AL or more from the rising edge of the expansion pulse of the second drive signal. Inkjet recording apparatus.

5). In the first drive signal,
The pulse width of the first expansion pulse is 0.4 AL or more and 2.0 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
5. The ink jet recording apparatus according to claim 4, wherein a pulse width of the third contraction pulse is not less than 0.8 AL and not more than 1.2 AL.

6). In the second drive signal,
The expansion pulse has a pulse width of 0.8 AL or more and 1.2 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
6. The ink jet recording apparatus according to 4 or 5, wherein a pulse width of the second contraction pulse is not less than 0.8 AL and not more than 1.2 AL.

  According to the present invention, there is provided an inkjet head capable of improving the landing position accuracy by preventing variations in the landing positions of droplets when large droplets are continuously discharged without increasing the driving cycle. A driving method and an ink jet recording apparatus can be provided.

1 is a schematic configuration diagram showing an example of an ink jet recording apparatus according to the present invention. It is a figure which shows an example of an inkjet head, (a) is a partially notched perspective view, (b) is sectional drawing seen from the side surface FIG. 2 is an explanatory diagram illustrating an example of an inkjet driving method according to the present invention, where (a) illustrates an example of a first drive signal, and (b) illustrates an example of a second drive signal. (A)-(c) is explanatory drawing which shows discharge operation | movement of an inkjet head. (A) is a conceptual diagram of a droplet ejected by a first drive signal, (b) is a conceptual diagram of a droplet ejected by a second drive signal. Explanatory drawing of an example of the drive method which discharges the inkjet large droplet continuously in this invention (A) is a figure explaining other examples of the 1st drive signal, (b) is a figure explaining other examples of the 2nd drive signal. Explanatory drawing showing blurring of landing when discharging large inkjet droplets continuously

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an example of an ink jet recording apparatus according to the present invention.

  In the inkjet recording apparatus 1, the transport mechanism 2 sandwiches a print medium 7 made of paper, plastic sheet, fabric, or the like by a pair of transport rollers 22, and rotates the transport roller 21 by a transport motor 23 in the Y direction (sub-scanning). Direction). An inkjet head (hereinafter referred to as a head) 3 is provided between the transport roller 21 and the transport roller pair 22. The head 3 is mounted on the carriage 5 so that the nozzle surface side faces the recording surface 71 of the print medium 7, and is electrically connected to the drive control unit 8 constituting the drive control means in the present invention via the flexible cable 6. Has been.

  The carriage 5 is driven along a guide rail 4 spanned across the width direction of the print medium 7 by a driving unit (not shown) along the XX ′ direction (main scanning direction) substantially orthogonal to the sub-scanning direction. ) Is provided so as to be reciprocally movable. The head 3 moves the recording surface 71 of the print medium 7 in the main scanning direction as the carriage 5 reciprocates, and in the course of this movement, ejects droplets from the nozzles according to the image data to record an inkjet image. It is supposed to be.

  2A and 2B are diagrams illustrating an example of the head 3, in which FIG. 2A is a partially cutaway perspective view, and FIG. 2B is a cross-sectional view viewed from the side.

  The head 3 has a channel substrate 30 in which a large number of narrow grooves 31 and partitions 32 are alternately arranged. A cover substrate 33 is provided on the upper surface of the channel substrate 30 so as to block all the channels 31 above. A nozzle plate 34 is bonded to the end surfaces of the channel substrate 30 and the cover substrate 33.

  The head 3 shown in the present embodiment is an independent drive type head in which the channel 31 is divided into an ejection channel 311 for ejecting ink and a dummy channel 312 for not ejecting ink, and illustrates a preferable aspect in the present invention. The discharge channel 311 and the dummy channel 312 are alternately arranged to form a channel row. One end of the discharge channel 311 communicates with the outside via a nozzle 341 formed in the nozzle plate 34.

  The other end of each channel 31 is formed so as to gradually become a shallow groove with respect to the channel substrate 30. A common channel 331 is formed in the cover substrate 33. The other end of each discharge channel 311 communicates with this common flow path 331. The common channel 331 is closed by the plate 35. An ink supply port 351 is formed in the plate 35. Ink is supplied from the ink supply pipe 352 into the common flow path 331 and the ejection channels 311 via the ink supply port 351.

  The partition wall 32 is made of a piezoelectric element such as PZT which is an electrical / mechanical conversion means. In the present embodiment, the partition wall 32 made of a piezoelectric element in which the upper wall portion 321 and the lower wall portion 322 are polarized in opposite directions is illustrated. However, the portion made of the piezoelectric element in the partition wall 32 may be only the upper wall portion 321, for example, and may be in at least part of the partition wall 32. Since the partition walls 32 and the channels 31 are alternately arranged in parallel, one partition wall 32 is shared by the adjacent channels 31 and 31.

  Drive electrodes (not shown in FIG. 2) are formed on the inner surface of the channel 31 from the wall surfaces to the bottom surface of both partition walls 32 and 32. When a drive signal of a predetermined voltage is applied from the drive control unit 8 to the two drive electrodes arranged with the partition wall 32 in between, the partition wall 32 is bordered by the joint surface between the upper wall portion 321 and the lower wall portion 322. Shear deformation. When two adjacent partition walls 32 and 32 are shear-deformed in opposite directions, the volume of the discharge channel 311 sandwiched between the partition walls 32 and 32 expands or contracts, and a pressure wave is generated inside. As a result, a pressure for ejection is applied to the ink in the ejection channel 311.

  The head 3 shown in this embodiment is a shear mode type head that discharges ink in the discharge channel 311 from the nozzle 341 when the partition wall 32 undergoes shear deformation, and is a preferable aspect in the present invention. The shear mode type head can efficiently eject droplets by using a rectangular wave described later as a drive signal.

  In this head 3, the channel 31 (discharge channel 311) defined by the channel substrate 30, the partition wall 32, the cover substrate 33, and the nozzle plate 34 is an example of the pressure chamber in the present invention. These drive electrodes are an example of the pressure generating means in the present invention.

  The drive control unit 8 generates a drive signal for discharging droplets from the nozzle 341. The generated drive signal is applied to the head 3. Specifically, the drive signal is applied to each drive electrode formed on the partition wall 32 of the head 3.

  In the present invention, the drive signal generated by the drive control unit 8 and applied to the head 3 includes the first drive signal PA shown in FIG. 3A and the second drive signal PB shown in FIG. Yes. The second drive signal PB is a drive signal for ejecting a droplet having a smaller droplet amount at a relatively higher speed than the droplet ejected by the first drive signal PA.

  Specific configurations of the first drive signal PA and the second drive signal PB will be described with reference to FIG.

  A first drive signal PA shown in FIG. 3A is a drive signal for forming a droplet having a larger droplet amount at a lower speed than the second drive signal PB.

  The first drive signal PA expands the volume of the channel 31 and contracts after a predetermined time. The first expansion pulse Pa1 has a pulse width PWA1 and the first pulse width PWA2 contracts the volume of the channel 31 and expands after a certain time. The contraction pulse Pa2, the second expansion pulse Pa3 with a pulse width PWA3 that expands the volume of the channel 31 and contracts after a certain time, and the second contraction pulse with a pulse width PWA4 that contracts the volume of the channel 31 and expands after a certain time Pa4, the rest period of the width PWA5 in which no pulse is applied, and the third contraction pulse Pa5 of the pulse width PWA6 that contracts the volume of the channel 31 and expands after a certain time, in this order.

  The first expansion pulse Pa1 of the first drive signal PA shown in the present embodiment is a pulse that rises from the reference potential 0 to + Von and falls to the reference potential 0 after a certain time.

  The first contraction pulse Pa2 is a pulse that falls from the reference potential 0 to -Voff and rises to the reference potential 0 after a certain time.

  The second expansion pulse Pa3 is a pulse that rises from the reference potential 0 to + Von and falls to the reference potential 0 after a certain time.

  The second contraction pulse Pa4 is a pulse that falls from the reference potential 0 to -Voff and rises to the reference potential 0 after a certain time.

  The pause time is a time for maintaining the reference potential 0.

  The third contraction pulse Pa5 is a pulse that falls from the reference potential 0 to -Voff and rises to the reference potential 0 after a certain time.

  In the first drive signal PA, the first contraction pulse Pa2 continuously falls to −Voff from the reference voltage 0, which is the end of the fall of the first expansion pulse Pa1, without any pause time.

  Further, the second expansion pulse Pa3 continuously rises from the reference voltage 0, which is the end of the rise of the first contraction pulse Pa2, to + Von without any pause time.

  Further, the second contraction pulse Pa4 continuously falls from the reference voltage 0, which is the end of the fall of the second expansion pulse Pa3, to −Voff without any pause time.

  On the other hand, the second drive signal PB shown in FIG. 3B is a drive signal for forming a droplet having a smaller droplet amount at a higher speed than the first drive signal PA.

  The second drive signal PB has an expansion pulse Pb1 having a pulse width PWB1 that expands the volume of the channel 31 and contracts after a certain time, and a first contraction pulse that has a pulse width PWB2 that contracts the volume of the channel 31 and expands it after a certain time. Pb2 and a second contraction pulse Pb3 having a pulse width PWB4 of which the volume of the channel 31 is contracted and expanded after a certain time after a pause time of a width PWB3 in which no pulse is applied are provided in this order.

  The expansion pulse Pb1 of the second drive signal PB shown in the present embodiment is a pulse that rises from the reference potential 0 and falls to the reference potential 0 after a certain time.

  The first contraction pulse Pb2 is a pulse that falls from the reference potential 0 and rises to the reference potential 0 after a certain time.

  The pause time is a time for maintaining the reference potential 0.

  The second contraction pulse Pb3 is a pulse that falls from the reference potential 0 and rises to the reference potential 0 after a predetermined time.

  In the second drive signal PB, the first contraction pulse Pb2 continuously falls without any pause time from the end of the fall of the expansion pulse Pb1.

  Note that the first drive signal PA and the second drive signal PB of the present embodiment are illustrated with the reference potential set to 0 potential, but are not particularly limited.

  Next, the droplet discharge operation of the head 3 when applied to the drive electrode using each pulse of the first drive signal PA and the second drive signal PB will be described with reference to FIGS.

  FIG. 4 shows a part of a cross section obtained by cutting the head 3 in a direction orthogonal to the length direction of the channel 31. Here, a case where droplets are ejected from the central channel 31B (ejection channel 311) in FIG. 4 will be described.

  FIG. 5A is a conceptual diagram of droplets ejected when the first drive signal PA is applied, and FIG. 5B is a droplet ejected when the second drive signal PB is applied. FIG.

  First, the case where the first drive signal PA is applied will be described.

  In the neutral state of the partition walls 32B and 32C to which the drive signal is not applied (FIG. 4A), the drive electrodes 36A and 36C are grounded and applied to + Von by the first expansion pulse Pa1 in the first drive signal PA to the drive electrode 36B. Then, an electric field is applied to each of the partition walls 32B and 32C, and the volume of the channel 31B sandwiched between the partition walls 32B and 32C expands due to bending toward each other (FIG. 4B). As a result, negative pressure is generated in the channel 31B, and ink flows.

  When the application of the first expansion pulse Pa1 ends, the electric potential falls to the reference potential 0, the electric field applied to the partition walls 32B and 32C disappears, the volume of the channel 31B contracts from the expanded state, and the partition walls 32B and 32C return to the neutral state (FIG. 4). (A)). When the first contraction pulse Pa2 continues to fall from the reference potential 0 to −Voff without any pause time, an electric field in the opposite direction to that of the first expansion pulse Pa1 is applied to the partition walls 32B and 32C. The volume of 31B is immediately contracted (FIG. 4C). At this time, a large positive pressure is applied to the ink in the channel 31 </ b> B, and the ink is pushed out from the nozzle 341. As a result, the first droplet 101 shown in FIG.

  When the application of the first contraction pulse Pa2 ends, the reference potential rises to 0, the volume of the channel 31B expands from the contracted state, and the partition walls 32B and 32C return to the neutral state (FIG. 4A).

  Hereinafter, the fluctuation from the reference potential 0 of the expansion pulse to + Von, or the fluctuation from the reference potential 0 of the contraction pulse to −Voff is abbreviated in terms of the application of each pulse of the drive signal.

  Following the neutral state of the first contraction pulse Pa2, the volume of the channel 31B immediately becomes inflated when applied by the second expansion pulse Pa3 without any rest time, and a negative voltage is generated in the channel 31B. A pressure is generated (FIG. 4B). For this reason, the pulling force acts on the first droplet 101 protruding from the nozzle 341 toward the nozzle 341 side, and the droplet velocity is suppressed. Ink flows again by the negative pressure generated in the channel 31B.

  When application of the second expansion pulse Pa3 ends, the volume of the channel 31B contracts from the expanded state, and the partition walls 32B and 32C return to the neutral state (FIG. 4A). Then, the second contraction pulse Pa4 is applied without any pause time, and the volume of the channel 31B immediately contracts (FIG. 4C). At this time, a large positive pressure is applied to the ink in the channel 31B, and the ink is further pushed out following the first droplet 101 ejected from the nozzle 341 by the first expansion pulse Pa1 and the first contraction pulse Pa2, and is eventually pushed out. The second ink droplet 102 having a large droplet velocity is ejected from the nozzle 341 (FIG. 5A).

  After the application of the second contraction pulse Pa4 is completed and the partition walls 32B and 32C return to the neutral state, the third contraction pulse Pa5 is applied after a pause. As a result, the volume of the channel 31B is contracted again (FIG. 4C). When the application of the third contraction pulse Pa5 is completed, the volume of the channel 31B expands, and the partition walls 32B and 32C are returned to the neutral state again (FIG. 4A). Even when the partition walls 32B and 32C return to the neutral state after the application of the second contraction pulse Pa4, a pressure wave (pressure wave reverberation vibration) that repeats reversal positively or negatively every 1 AL remains in the channel 31B. The third contraction pulse Pa5 is a pulse for applying a pressure for canceling the pressure wave reverberation vibration in the channel 31B.

  In this way, by applying the first drive signal PA to the drive electrodes, the second expansion pulse Pa3 follows the first droplet 101 having a small droplet velocity by the first expansion pulse Pa1 and the first contraction pulse Pa2. The second droplet 102 having a high droplet velocity due to the second contraction pulse Pa4 is ejected from the same nozzle 341.

  The droplet 100 at the beginning of ejection has a form in which the first droplet 101 and the second droplet 102 are continuous, but the ejection speed of the second droplet 102 is larger than that of the first droplet 101. These merge into a single droplet 100 during flight immediately after ejection. In this droplet 100, since the first droplet 101 having a relatively small droplet velocity and the second droplet 102 having a relatively large droplet are combined during the flight, one droplet having the same droplet amount is ejected from the nozzle. Compared with the case of discharging from the nozzle 341, the droplet velocity becomes slower.

  Further, since the droplet speed of the droplet 100 is low, the amount of satellite is suppressed as compared with the case where one droplet having the same droplet amount is ejected from the nozzle 341. That is, satellites are generally generated when the tail formed so as to extend backward accompanying the ejected main droplet is separated from the main droplet. The length of the tail becomes longer as the droplet velocity increases, and the satellite is easily separated at a position away from the main droplet.

  If the satellite is separated at a position away from the main droplet, the landing position of the satellite is also greatly separated from the main droplet, which causes a reduction in image quality. In other words, as long as the satellites are separated in close proximity to the main droplets, they land at approximately the same position, so there is little effect on the image quality. According to the first drive signal PA, since the droplet can be discharged at a low speed even when the droplet amount is increased, the tail length associated with the droplet 100 (main droplet) can be shortened, and the position close to the main droplet. Will be able to separate the satellites. Therefore, the satellite amount can be suppressed while discharging the droplet 100 having a large droplet amount. For this reason, there is no problem that the satellite when the droplet 100 is discharged deteriorates the image quality.

  In the present invention, the droplet velocity is calculated by recognizing a droplet image by a droplet observation device and obtaining an elapsed time from ejection and a position coordinate at which the droplet exists. Specifically, the droplet velocity is calculated from the distance at which the droplet flies for 50 μs from the position 500 μm away from the nozzle surface. The elapsed time from the ejection can be calculated by synchronizing the drive signal output to the inkjet head and the observation strobe. Further, the position coordinates of the droplet can be calculated by performing image processing on the flying image.

  As a preferred example of each pulse width of the first drive signal PA, the pulse width PWA1 of the first expansion pulse Pa1 is 0.4 AL or more and 2.0 AL or less, and the pulse width PWA2 of the first contraction pulse Pa2 is 0.3 AL or more. The pulse width PWA3 of the second expansion pulse Pa3 is 0.8 AL or more and 1.2 AL or less, the pulse width PWA4 of the second contraction pulse Pa4 is 0.3 AL or more and 0.7 AL or less, and the pause time width PWA5 is 0 The pulse width PWA6 of the third contraction pulse Pa5 is 0.8 AL or more and 1.2 AL or less.

  In addition, AL is an abbreviation for Acoustic Length, and is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber (channel 31). AL measures the flying speed of a droplet discharged when a rectangular wave driving signal is applied to the driving electrode, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. It is determined as the pulse width that maximizes the droplet flight speed. The pressure wave generated in the channel 31 by expanding or contracting the volume of the channel 31 repeatedly reverses positively or negatively every 1 AL, so that the AL that is the time for maintaining each pulse is appropriately selected. Thus, the pressure in the channel 31 can be appropriately controlled.

  The pulse is a rectangular wave having a constant voltage peak value. The pulse width is defined as the time between 10% rise of voltage from 0V and 10% fall from peak value voltage when 0V is 0% and peak value voltage is 100%.

  Furthermore, a rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably within ¼ of AL.

  Next, a case where the second drive signal PB is applied will be described.

  In the neutral state of the partition walls 32B and 32C to which the drive signal is not applied (FIG. 4A), when the drive electrodes 36A and 36C are grounded and the expansion pulse Pb1 in the second drive signal PB is applied to the drive electrode 36B, the partition walls 32B and 32C are bent and deformed toward each other, and the volume of the channel 31B sandwiched between the partition walls 32B and 32C expands (FIG. 4B). As a result, negative pressure is generated in the channel 31B, and ink flows.

  When the application of the expansion pulse Pb1 is completed, the volume of the channel 31B contracts from the expanded state, and the partition walls 32B and 32C return to the neutral state (FIG. 4A). Then, the first contraction pulse Pb2 is applied without any pause time, and the volume of the channel 31B immediately contracts (FIG. 4C). At this time, a large pressure is applied to the ink in the channel 31 </ b> B, and the ink is pushed out from the nozzle 341. Thereby, the droplet 200 shown in FIG. 5B is ejected from the nozzle 341.

  When application of the first contraction pulse Pb2 ends, the volume of the channel 31B expands from the contracted state, and the partition walls 32B and 32C return to the neutral state (FIG. 4A). Then, the second contraction pulse Pb3 is applied with a certain pause time. As a result, the volume of the channel 31B is contracted again (FIG. 4C).

  When the application of the second contraction pulse Pb3 is completed, the volume of the channel 31B expands and the partition walls 32B and 32C are returned to the neutral state again (FIG. 4A). The second contraction pulse Pb3 is a pulse for applying a pressure in the channel 31B that cancels the pressure wave reverberation oscillation in the channel 31B after the application of the first contraction pulse Pb2.

  As a preferred example of each pulse width of the second drive signal PB, the pulse width PWB1 of the expansion pulse Pb1 is 0.8 AL to 1.2 AL, and the pulse width PWB2 of the first contraction pulse Pb2 is 0.3 AL to 0.00. 7AL or less, the pause time width PWB3 is 0.3 AL or more and 0.7 AL or less, and the pulse width PWB4 of the second contraction pulse Pb3 is 0.8 AL or more and 1.2 AL or less.

  When the drive control unit 8 forms a large droplet within one pixel period, the first drive signal PA and the second drive signal PB described above are applied in this order within one pixel period T as shown in FIG. Apply. As a result, within one pixel period T, at least two droplets, that is, the droplet 100 having a large droplet amount based on the first drive signal PA and the droplet 200 having a small droplet amount based on the second drive signal PB are ejected from the nozzle 341. Then, the droplets 100 and 200 are combined into a large droplet during the flight. This large droplet lands on the print medium 7 to form a pixel composed of one large dot.

  For example, when large droplets are ejected continuously as in the case of printing a solid image, the drive control unit 8 repeats this one-pixel period T twice or more continuously. At this time, as shown in FIG. 6, the drive control unit 8 starts the application of the first drive signal PA of the next one pixel period T from the rising edge of the expansion pulse Pb1 of the second drive signal PB, and the first expansion pulse Pa1. The time t1 until starting up is set to 4.5 AL or more.

  Originally, in order to increase the landing accuracy, the second contraction pulse Pb3 of the second drive signal PB is made to act so as to cancel the pressure wave reverberation vibration in the channel 31, and then the time until the first drive signal PA is sufficiently increased. If it takes, landing accuracy can be raised. However, when large droplets are continuously ejected, the element of the pressure wave reverberation vibration attenuation in the channel 31 when the first drive signal PA is applied must be taken into consideration, and the second contraction pulse of the second drive signal PB is taken into consideration. It is not easy to uniquely define the time from Pb3 to the first drive signal PA. Therefore, paying attention to the time t1 from the expansion pulse Pb1 of the second drive signal PB to the first expansion pulse Pa1 of the first drive signal PA, it is set in a range where there is little landing blur.

  Thereby, it is possible to prevent variations in the landing positions of droplets when large droplets are continuously discharged without lengthening the driving cycle, and it is possible to improve landing position accuracy.

  From the viewpoint of improving the landing position accuracy, the time t1 is preferably as long as possible. However, since the driving cycle is increased accordingly, from the viewpoint of performing high-speed printing by shortening the driving cycle, it is preferably 6.0 AL or less.

  In the first drive signal PA, the voltage value of the first expansion pulse Pa1 is equal to the voltage value of the second expansion pulse Pa3, and the voltage value of the first contraction pulse Pa2, the second contraction pulse Pa4, and the third contraction pulse Pa5. Are preferably equal to each other. Since at least two power sources are sufficient, the number of power sources can be reduced. Thereby, the circuit configuration of the drive control unit 8 can be simplified.

  When the voltage values of the first expansion pulse Pa1 and the second expansion pulse Pa3 of the first drive signal PA are VH2, and the voltage values of the first contraction pulse Pa2 and the second contraction pulse Pa4 are VH1, | VH2 | / | VH1 | = 2/1 is preferable. Accordingly, the return of the ink meniscus in the nozzle 341 is promoted, and high frequency driving is possible. In particular, flight stabilization when using high viscosity ink can be achieved.

  Also in the second drive signal PB, it is preferable that the voltage value of the first contraction pulse Pb2 and the voltage value of the second contraction pulse Pb3 are equal for the same reason as the first drive signal PA.

  For the same reason as the first drive signal PA, when the voltage value of the expansion pulse Pb1 of the second drive signal PB is VH2, and the voltage values of the first contraction pulse Pb2 and the second contraction pulse Pb3 are VH1, | VH2 It is preferable that | / | VH1 | = 2/1. The voltage values of VH1 and VH2 are preferably the same in the first drive signal PA and the second drive signal PB from the viewpoint of further simplifying the circuit configuration of the drive control unit 8.

  The first drive signal PA and the second drive signal PB are preferably rectangular waves. As a result, the droplets can be discharged efficiently and the drive voltage can be kept low. In particular, since the shear mode type head 3 shown in the present embodiment can generate the pressure wave in phase with respect to the application of the drive signal composed of the rectangular wave, the droplet can be efficiently discharged. In addition, the drive voltage can be further reduced. In addition, since the rectangular wave can be easily generated by using a simple digital circuit, the circuit configuration can be simplified as compared with the case of using a trapezoidal wave having an inclined wave.

  It is preferable that the diameter of the droplet 200 ejected by the second drive signal PB is smaller than the diameter of the nozzle 341. By making the droplet 200 smaller in diameter than the diameter of the nozzle 341, the satellite suppression effect can be further enhanced.

  Here, the diameter of the nozzle 341 is the nozzle opening diameter at the tip in the ejection direction. If the nozzle opening shape at the tip of the nozzle 341 in the ejection direction is circular, it indicates the diameter, and if not, it is the diameter of the circle when replaced with a circle having the same area as the opening area at the tip of the nozzle 341 in the ejection direction. .

  The diameter of the droplet refers to the diameter when the droplet is spherical, and when the droplet is not spherical, the diameter of the sphere when the volume is replaced with the same sphere.

  It is preferable that the diameter of the droplet 100 ejected by the first drive signal PA is larger than the diameter of the nozzle 341. By setting the droplet 100 to have a diameter larger than the diameter of the nozzle 341, it is possible to form a dot as large as possible on the print medium 7. The diameter of the droplet 100 is a diameter in a state where the first droplet 101 and the second droplet 102 are integrated into one droplet.

  Of course, the diameter of the droplet 200 ejected by the second drive signal PB is smaller than the diameter of the nozzle 341, and the diameter of the droplet 100 ejected by the first drive signal PA is larger than the diameter of the nozzle 341. It is more preferable that

  In the above description, each drive signal has a + Von expansion pulse and a −Voff contraction pulse. However, the present invention is not limited to this. That is, the deformation of the partition wall 32 can be caused by a voltage difference between two drive electrodes provided so as to sandwich the partition wall 32. Therefore, when ejection is performed from the channel 31B shown in FIG. 4 using the first drive signal PA, as shown in FIG. 7A, the first expansion pulse of + Von is applied to the drive electrode 36B in the channel 31B as the ejection channel. The same applies when Pa1 and second expansion pulse Pa3 are applied, and + Voff first contraction pulse Pa2, second contraction pulse Pa4, and third contraction pulse Pa5 are applied to drive electrodes 36A and 36C of adjacent channels 31A and 31C. Can be driven.

  Similarly, when ejection is performed from the channel 31B shown in FIG. 4 using the second drive signal PB, as shown in FIG. 7B, the drive electrode 36B in the channel 31B as the ejection channel expands to + Von. Even if the pulse Pb1 is applied and the + Voff first contraction pulse Pb2 and the second contraction pulse Pb3 are applied to the drive electrodes 36A and 36C of the adjacent channels 31A and 31C, the same driving can be performed.

  When the first drive signal PA and the second drive signal PB shown in FIGS. 7A and 7B are used, each drive signal can be configured with only a positive voltage, and therefore the configuration of the drive control unit 8 is further simplified. Can do.

  Further, in the above description, the head 3 is exemplified as one in which the partition wall 32 between adjacent channels 31 and 31 is shear-deformed, but the pressure generating means in which the upper wall or the lower wall of the channel is configured by a piezoelectric element such as PZT. The upper wall or the lower wall may be subjected to shear deformation.

  In addition, the inkjet head in the present invention is not limited to the shear mode type. For example, an ink jet of a type in which one wall surface of a pressure chamber is formed by a vibration plate, and the vibration plate is vibrated by a pressure generating means constituted by a piezoelectric element such as PZT, and pressure for ejection is applied to ink in the pressure chamber. It may be a head.

  In addition, the inkjet head in the present invention is not limited to ejecting droplets while scanning and moving in the main scanning direction with respect to the printing medium 7. For example, it may be a line-type inkjet head that is formed in a long shape extending in the width direction of the print medium 7 and that records an image in one pass by transporting and moving the print medium 7 in one direction.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  A shear mode independent drive type ink jet head (nozzle number = 256, nozzle diameter = 24 μm, AL = 3.7 μs) shown in FIG. 2 was prepared. As the ink, UV curable ink was used at 40 ° C. The viscosity of the ink at the time of use was 0.01 Pa · s.

As the first drive signal and the second drive signal, the rectangular-wave first drive signal PA and second drive signal PB shown in FIGS. 3A and 3B were used. Each pulse width was as follows.
(First drive signal)
First expansion pulse: 0.8 AL
First contraction pulse: 0.4 AL
Second expansion pulse: 1.0 AL
Second contraction pulse: 0.5 AL
Rest time: 0.5AL
Third contraction pulse: 1.0 AL
(Second drive signal)
Expansion pulse: 1.0AL
First contraction pulse: 0.5 AL
Rest time: 0.5AL
Second contraction pulse: 1.0 AL

  The first drive waveform and the second drive waveform are successively applied in this order within one pixel cycle, and this one-pixel cycle is continuously repeated at a drive frequency of 27.0 kHz. By observing with a droplet observation device, landing blur was evaluated by the following method. The result is shown in FIG.

  The period of the first drive signal (the time from the rise of the first expansion pulse to the rise of the expansion pulse of the second drive signal) is set to 5.2AL, and the cycle of the second drive signal (the first to the first pulse from the rise of the expansion pulse). The time until the rise of the first expansion pulse of the drive signal was changed to 4.2AL, 4.5AL, 4.7AL, 5.0AL, 5.5AL, 6.0AL.

  As an evaluation method of landing blur, the synchronization timing of the camera is adjusted so that the droplet is positioned at a position where the nozzle is lowered by 1.0 mm, and the horizontal droplet coordinate at the height position is measured 100 times. The standard deviation σ was calculated from the distribution of

  As is clear from FIG. 8, the first drive waveform and the second drive waveform were applied successively in this order, and the period t1 of the second drive signal was changed as described above. When the period t1 of the second drive signal is 4.5 AL or more, the landing blur σ is 6 μm or less at a droplet speed of 6 to 8 m / s normally used for inkjet, and large droplets are continuously generated. Even if it is discharged, the landing position accuracy can be improved.

  Even at 4.2 AL or less, the landing blur σ exceeds 6 μm by about 0.2 μm at a droplet speed of 6 to 8 m / s, but the blur is very large at 10 m / s or more, and the ejection becomes extremely unstable. .

1: Inkjet recording device 2: Conveying mechanism 21: Conveying roller 22: Conveying roller pair 23: Conveying motor 3: Inkjet head 30: Channel substrate 31: Channel 311: Discharge channel 312: Dummy channel 32: Partition 321: Upper wall 322 : Lower wall part 33: Cover substrate 331: Common flow path 34: Nozzle plate 341: Nozzle 35: Plate 351: Ink supply port 352: Ink supply pipe 4: Guide rail 5: Carriage 6: Flexible cable 7: Print medium 71: Recording surface 8: Drive controller 100: Droplet 101: First droplet 100: Second droplet 200: Droplet PA: First drive signal Pa1: First expansion pulse Pa2: First contraction pulse Pa3: Second expansion Pulse Pa4: Second contraction pulse Pa5: Third contraction pulse PWA1 to PWA , PWA6: Pulse Width PWA5: pause time PB: second driving signal Pb1: expansion pulse Pb2: first decreasing pulse Pb3: second decreasing pulse PWB1, PWB2, PWB4: Pulse width PWB 103: pause time T: 1 pixel period

Claims (6)

Two drive signals of a first drive signal and a second drive signal are applied in this order within one pixel period to the pressure generating means for ejecting droplets from the nozzle by expanding or contracting the volume of the pressure chamber, and A method for driving an inkjet head that repeats one pixel cycle twice or more,
The first drive signal is:
A first expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A second expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A third contraction pulse that contracts the volume of the pressure chamber and expands after a predetermined time in this order, and discharges the first droplet from the nozzle by applying the first expansion pulse and the first contraction pulse. And causing the second droplet to be ejected from the nozzle by application of the second expansion pulse and the second contraction pulse and coalescing during flight immediately after ejection,
The second drive signal is:
An expansion pulse that expands the volume of the pressure chamber and contracts after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time, in this order,
After the rise of the expansion pulse of the second drive signal, a time of 4.5 AL or more (where AL is ½ of the acoustic resonance period of the pressure wave in the pressure chamber) is set to the next one pixel period. The method for driving an ink-jet head is characterized in that application of the first drive signal is started. In the first drive signal,
The pulse width of the first expansion pulse is 0.4 AL or more and 2.0 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
2. The method of driving an ink jet head according to claim 1, wherein a pulse width of the third contraction pulse is not less than 0.8 AL and not more than 1.2 AL. In the second drive signal,
The expansion pulse has a pulse width of 0.8 AL or more and 1.2 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
3. The method of driving an ink jet head according to claim 1, wherein a pulse width of the second contraction pulse is not less than 0.8 AL and not more than 1.2 AL. An inkjet head having pressure generating means for discharging droplets from the nozzle by expanding or contracting the volume of the pressure chamber; and a drive control means for outputting a drive signal for driving the pressure generating means,
The drive control means is an ink jet recording apparatus that applies two drive signals of a first drive signal and a second drive signal to the pressure generating means in this order within one pixel period, and repeats the one pixel period twice or more. There,
The first drive signal is:
A first expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A second expansion pulse for expanding the volume of the pressure chamber and contracting after a certain time;
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A third contraction pulse that contracts the volume of the pressure chamber and expands after a predetermined time in this order, and discharges the first droplet from the nozzle by applying the first expansion pulse and the first contraction pulse. And causing the second droplet to be ejected from the nozzle by application of the second expansion pulse and the second contraction pulse and coalescing during flight immediately after ejection,
The second drive signal is:
An expansion pulse that expands the volume of the pressure chamber and contracts after a certain time;
A first contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time;
A certain pause time without applying a pulse,
A second contraction pulse for contracting the volume of the pressure chamber and expanding after a predetermined time, in this order,
The drive control means starts the application of the first drive signal of the next one pixel period after a time of 4.5 AL or more from the rising edge of the expansion pulse of the second drive signal. Inkjet recording apparatus. In the first drive signal,
The pulse width of the first expansion pulse is 0.4 AL or more and 2.0 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
5. The ink jet recording apparatus according to claim 4, wherein a pulse width of the third contraction pulse is not less than 0.8 AL and not more than 1.2 AL. In the second drive signal,
The expansion pulse has a pulse width of 0.8 AL or more and 1.2 AL or less,
The pulse width of the first contraction pulse is not less than 0.3 AL and not more than 0.7 AL,
The width of the pause time is 0.3 AL or more and 0.7 AL or less,
6. The ink jet recording apparatus according to claim 4, wherein a pulse width of the second contraction pulse is not less than 0.8 AL and not more than 1.2 AL.

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