Patent Application
20160082722
Embodiments described herein relate to a drive method and a drive apparatus for the ink jet head used in an ink jet printer and the like.
An ink jet head comprises a plurality of pressure chambers for accommodating ink, a plurality of piezoelectric actuators arranged corresponding to each of the pressure chambers and a nozzle plate arranged on one end of each of the pressure chambers. A plurality of nozzles, which are connected with the pressure chambers, respectively, are formed on the nozzle plates to eject ink drops. Each piezoelectric plate vibrates a corresponding pressure chamber across a vibration plate.
A drive apparatus for such an ink jet head applies a drive pulse signal to piezoelectric actuators. Vibration is generated in pressure chambers according to the drive pulse signal when the internal volume of the pressure chambers is changed to eject ink drops from nozzles connected with the pressure chambers.
However, the vibration generated in the pressure chambers remains in the pressure chambers after the ink drops are ejected out, which hinders the stable ejection of following ink drops.
In an embodiment, a drive method for an ink jet head comprises: as a drive pulse, applying a first pulse for increasing and then restoring the volume of a pressure chamber and giving pressure vibration to the chamber in which ink are accommodated and then a second pulse for reducing and then restoring the volume of the pressure chamber to an actuator arranged corresponding to the pressure chamber.
In the drive method,
the second pulse is turned on at first point of time causing the pressure vibration amplitude at second point of time to be the same with that of generated by the first pulse when the first pulse is turned on,
The second point of time is the time when flow velocity of the ink nearby the nozzle inside the pressure chamber becomes 0 after the first point of time,
and the second pulse is turned off at the second point of time.
Embodiments of the drive method and the drive apparatus for an ink jet head provided herein are described below with reference to the accompanying drawings. First, the ink jet head 1 used in the embodiment is described with reference to
The ink jet head 1 comprises a drive device 2, a head substrate 3 and a manifold 4. The manifold 4 is equipped with an ink feed tube 5 and an ink discharging tube 6. The ink jet head 1 ejects the ink fed from an ink feeding unit (not shown) through the feed tube 5 out from each nozzle 13a according to a drive signal from the drive device 2. The part of the ink fed into the manifold 4 from the feed tube 5 which is not ejected out from each nozzle 13a is discharged from the discharging tube 6 to the ink feeder.
A plurality of parallel pressure chambers 11 are arranged in the head substrate 3 corresponding to the nozzles 13a, respectively. The bottom side (the bottom side in
In the ink jet head 1, a vibration plate 14 is adhered to the top face side of each pressure chamber 11, with whose top side stuck fast to one end of a plurality of piezoelectric members 15 arranged corresponding to the pressure chambers 11, respectively. The ink jet head 1 holds the other end of each piezoelectric member 15 with a holding member 16. Each piezoelectric member 15 is formed by laminating a plurality of piezoelectric layers 15a and electrode layers 15b alternatively. In the ink jet head 1, a pair of electrodes 17 are arranged in such a manner that each electrode layer 15b is sandwiched between the electrodes. The two electrodes 17 are electrically connected with the drive device 2.
A common liquid chamber 18 is formed in the head substrate 3 of the ink jet head 1. Ink is injected into the common liquid chamber 18 through the feed tube 5. The common liquid chamber 18 is connected with each pressure chamber 11 so that the injected ink is filled into each pressure chamber 11 and the nozzle 13a corresponding to the pressure chamber 11. By filling the pressure chambers 11 and the nozzles 13a with ink, an ink meniscus is formed in the nozzles 13a.
In the ink jet head 1 with a related structure, if a drive signal is applied from the drive device 2 to the piezoelectric member 15 through the electrodes 17, then the piezoelectric member 15 expands or contracts. With the expansion or contraction of the piezoelectric member 15, the vibration plate 14 is deformed such that vibration is given to the pressure chamber 11. Because of the vibration, the volume of the pressure chamber 11 changes, generating a pressure wave in the pressure chamber 11 to eject ink drops from the nozzle 13a. Here, the vibration plate 14 and the piezoelectric member 15 serve as an actuator which vibrates the pressure chamber 11. That is, as many actuators are arranged on the ink jet head 1 as the nozzles 13a.
Next, the drive device 2 is described. The drive device 2 comprises: a communication section 21, an operation section 22 and a drive signal generation section 23. The communication section 21 receives gradation data of an image to be printed from a host computer for controlling, for example, an ink jet printer. The operation section 22 calculates the number of drive pulse trains for each nozzle 13a based on the gradation data. The drive signal generation section 23 supplies a drive pulse signal to a piezoelectric member 15 corresponding to a nozzle 13a, the drive pulse signal having as many drive pulse trains as the number calculated by the operation section 22 for each nozzle 13a.
By applying the pulse voltage of the drive pulse signal to the piezoelectric member 15, ink drops, the number of which is equivalent to that of pulse trains, are ejected out from the nozzle 13a of the pressure chamber 11 corresponding to the piezoelectric member 15. An ink jet recorder consisting of the ink jet head 1 and the drive device 2 converts the number of the ink drops into a pixel unit and adjusts the concentration of pixels to implement gradation printing to print an image, that is, the ink jet recorder prints in a multi-drop manner.
When a selection signal indicating the selection on four drops is input to the passing range selection circuits 232-1 to 232-n, the passing range selection circuits 232-1 to 232-n select the time range t0-t4 of the reference pulse signal as a whole passing range, as a result, the drive pulse signal PA4 is output. When the drive pulse signal PA4 is applied to the piezoelectric member 15, four drops of ink are ejected out from the nozzle 13a corresponding to the piezoelectric member 15.
The drive pulse signal PA3 is a signal obtained by removing the DRP waveform in the time range t0-t1 from the drive pulse signal (reference pulse signal) PA4. When a selection signal indicating the selection on three drops is input to the passing range selection circuits 232-1 to 232-n, the passing range selection circuits 232-1 to 232-n select the time range t1-t4 of the reference pulse signal as a passing range, as a result, the drive pulse signal PA3 is output. When the drive pulse signal PA3 is applied to the piezoelectric member 15, three drops of ink are ejected out from the nozzle 13a corresponding to the piezoelectric member 15.
The drive pulse signal PA2 is a signal obtained by removing the two DRP waveforms in the time range t0-t2 from the drive pulse signal (reference pulse signal) PA4. When a selection signal indicating the selection on two drops is input to the passing range selection circuits 232-1 to 232-n, the passing range selection circuits 232-1 to 232-n select the time range t2-t4 of the reference pulse signal as a passing interval, as a result, the drive pulse signal PA2 is output. When the drive pulse signal PA2 is applied to the piezoelectric member 15, two drops of ink are ejected out from the nozzle 13a corresponding to the piezoelectric member 15.
The drive pulse signal PA1 is a signal obtained by removing the three DRP waveforms in the time range t0-t3 from the drive pulse signal (reference pulse signal) PA4. When a selection signal indicating the selection on one drop is input to the passing range selection circuits 232-1 to 232-n, the passing range selection circuits 232-1 to 232-n select the interval t3-t4 of the reference pulse signal as a passing interval, as a result, the drive pulse signal PA1 is output. When the drive pulse signal PA1 is applied to the piezoelectric member 15, one drop of ink is ejected out from the nozzle 13a corresponding to the piezoelectric member 15.
When applying the ejection pulse SP (negative voltage pulse-on), the voltage applied to the piezoelectric member 15 is changed from Vm to −V1. At the point of time t11 the ejection pulse SP falls, the piezoelectric member 15 contracts with respect to the normal state; with the contraction, the vibration plate 14 stuck fast to the piezoelectric member 15 is deformed, increasing the volume of the pressure chamber 11. As the volume of the pressure chamber 11 is increased, a negative pressure is generated instantly in the pressure chamber 11.
The expansion of the pressure chamber 11 lasts after the time Ts elapsed. The pulse width Ts of the ejection pulse SP is set to ½ of the natural vibration period of the pressure chamber 11. In this embodiment, the natural vibration period is 4.6 μs, and the pulse width Ts is 2.3 μm. During Ts, ink flows from the common liquid chamber 18 into the pressure chamber 11. Further, the meniscus on the front end of the nozzle 13a backs to the side of the pressure chamber 11. The pressure in the pressure chamber 11 changes from a negative pressure to a positive pressure.
When rising the ejection pulse SP (negative voltage pulse-off), the voltage applied to the piezoelectric member 15 is changed back to Vm from −V1. At the point of time t12 the ejection pulse SP rises, the piezoelectric member 15 recovers to normal. With the recovery, the internal volume of the pressure chamber 11 returns to normal. At this time, a positive pressure is generated instantly in the pressure chamber 11, and with the pressure, the meniscus in the nozzle 13a advances.
The meniscus advances till ½ of the natural vibration period elapses (e.g. 2.3 μs) from the moment the ejection pulse SP rises, meanwhile, the pressure in the pressure chamber 11 changes again from a positive pressure to a negative pressure. Then, ink drops are separated from the ink inside the nozzle and ejected out. Then, applying the damping pulse DP (positive voltage pulse-on), the voltage applied to the piezoelectric member 15 is changed from Vm to V1 at the point of time t13, the volume of the piezoelectric member 15 increases. With the expansion, the vibration plate 14 stuck fast to the piezoelectric member 15 is deformed to make the pressure chamber 11 contract. A positive pressure is generated instantly in the pressure chamber 11 as the volume of the pressure chamber 11 contracts.
The pressure chamber 11 contracts for a time of the pulse width Td (e.g. 0.9 us) of the damping pulse DP. Then, at the point of time t14 the voltage applied to the piezoelectric member 15 is changed back to Vm from V1 because of the falling of the damping pulse DP (positive voltage pulse-off), the piezoelectric member 15 recovers to normal. The turn-off of the positive voltage pulse makes the charging state of the piezoelectric member charged to V1 return back to Vm. With the recovery, the positive pressure in the pressure chamber 11 drops back to 0. Then, the residual vibration in the pressure chamber 11 is eliminated.
Next, the output timing of the damping pulse DP is described using the equivalent circuit 30 shown in
The equivalent circuit 30 is a circuit formed by connecting a series circuit (hereinafter referred to as an LCR circuit 32) consisting of a resistor R, a capacitor C and an inductor L with a voltage source 31. The resistance of the resistor R is 0.18Ω, the capacitance of the capacitor C is 0.69 uF, and the inductance of the inductor L is 0.736 uH. The equivalent circuit 30 represents the pressure chamber 11 of the ink jet head 1. The voltage generated at two terminals of the voltage source 31 is equivalent to the displacement of the actuator and can be deemed as a drive voltage applied to the actuator. The voltage generated at two terminals of the inductor L is equivalent to the pressure on the periphery of the nozzle 13a in the pressure chamber 11. On the periphery of the nozzle 13a in the pressure chamber 11, the circuit current is equivalent to the velocity of the ink flowing towards the nozzle. In the equivalent circuit 30, the voltage source 31 is connected with a voltmeter V in parallel; an ammeter (current meter) S is connected between the voltage source 31 and the resistor R, and the inductor L is connected with a voltmeter P in parallel. The flow velocity of the ink from the common liquid chamber 18 to the inlet of the pressure chamber 11 is reverse to that of the ink on the periphery of the nozzle 13a. For example, at the time t11 shown in
A pulse signal 41 having the DRP waveform shown in
At the point of time the 6.2 μs elapses from the point of time the ejection pulse SP falls (just before the damping pulse DP falls), the voltage (pressure) generated at two terminals of the inductor L becomes V1. The circuit current (flow velocity) becomes 0. The voltage (pressure) V1 is reverse in polarity to but equal in amplitude to the voltage (pressure) generated at two terminals of the inductor L at the point of time the ejection pulse SP falls. In this case, the voltage (pressure) generated at two terminals of the inductor L becomes 0 if the damping pulse DP falls at this point. In addition, the circuit current (flow velocity) becomes 0 as well. That is, the residual vibration of the pressure chamber 11 is eliminated.
The damping pulse DP should be raised at the time causing vibration of the voltage (pressure) generated at two terminals of the inductor L becomes V1 when the circuit current (flow velocity) becomes 0, which indeed eliminates the residual vibration of the pressure chamber 11. In other words, the residual vibration of the pressure chamber 11 cannot be eliminated if there is no point of time at which the voltage (pressure) generated at two terminals of the inductor L becomes V1 and the circuit current (flow velocity) becomes 0.
The amplitude of the voltage (pressure) generated at two terminals of the inductor L is changed by adjusting the time at which the damping pulse DP rises. In the case of the equivalent circuit 30, as shown in
The damping pulse DP is contained in the drive pulse signal to eliminate the residual vibration of the pressure chamber 11. As described above with reference to
Thus, as to the damping pulse DP in a DRP waveform, as shown in
The ‘satellite’ of the satellite canceling pulse CP refers to a satellite drop. An ink drop is usually ejected out from the nozzle 13a, leaving a trail. Then, when the ink drop is separated from the ink in the nozzle 13a, the trail part, that is, the called liquid column becomes a spherical satellite drop and flies following the main ink drop. The satellite drop flying at a lower speed is separated from the main liquid drop and impacts on a recording medium. Consequentially, printing quality is degraded due to the density unevenness and ghost caused by the satellite drop. The satellite canceling pulse CP is used to prevent the generation of a satellite drop.
During the period from t21 at which the ejection pulse SP drops to t22 at which the ejection pulse SP rises, the DRCRP waveform functions as a DRP waveform, that is, at the point of time t22 the voltage applied to the piezoelectric member 15 is changed back to Vm from −V1, the meniscus in the nozzle 13a starts to advance.
The meniscus advances till ½ of the natural vibration period elapses (e.g. 2.3 μs) from the point of time the ejection pulse SP rises, then, the ink liquid column is to be separated from the nozzle 13a after the time Tw2 (e.g. 3.25 us) elapses. At this time, the satellite canceling pulse CP rises (positive voltage pulse-on). The volume of the piezoelectric member 15 increases at the point of time t23 the voltage applied to the piezoelectric member 15 is changed from Vm to V1 due to the rise of the satellite canceling pulse CP. With the expansion, the vibration plate 14 stuck fast to the piezoelectric member 15 is deformed to make the pressure chamber 11 contract. A positive pressure is generated instantly in the pressure chamber 11 as the pressure chamber 11 contracts. With the pressure, the ink liquid column is pushed out from the pressure chamber 11. As a result, the liquid column and the ink drop are separated from the ink in the nozzle together and ejected out from the nozzle 13a. Thus, no satellite drop is generated.
The pressure chamber 11 keeps in a contracted state for a time equivalent to the pulse width Tc (e.g. 1.85 us) of the satellite canceling pulse CP. Tc is the time needed for the separation of the liquid column from the ink in the nozzle 13a and the following ejection of the whole separated liquid column out from the nozzle 13a. Then, the piezoelectric member 15 recovers to normal at the point of time t24 the voltage applied to the piezoelectric member 15 is changed back to Vm from V1 due to the falling of the satellite canceling pulse CP (positive voltage pulse-off). With the recovery, the internal volume of the pressure chamber 11 returns to normal and is kept in the normal state for Tw3 (e.g. 1.3 us). Then, the volume of the piezoelectric member 15 increases again at the point of time t25 the voltage applied to the piezoelectric member 15 is changed from Vm to V1 due to the rise of the damping pulse DP. With the expansion, the vibration plate 14 stuck fast to the piezoelectric member 15 is deformed to make the pressure chamber 11 contract. As the pressure chamber contracts, a positive pressure is generated instantly in the pressure chamber 11.
The pressure chamber 11 is kept in the contracted state for a time equivalent to the pulse width Td (e.g. 0.95 us) of the damping pulse DP, then, the piezoelectric member 15 recovers to normal again at the point of time t26 the voltage applied to the piezoelectric member 15 is changed back to Vm from V1 due to the falling of the damping pulse DP. With the recovery, the positive pressure in the pressure chamber 11 is changed to 0. Then, the residual vibration in the pressure chamber 11 is eliminated.
Next, the output timing of the satellite canceling pulse CP is described with reference to the equivalent circuit 30 shown in
A pulse signal 51 having the DRC waveform shown in
At the point of time 5.55 μs elapses from the moment the ejection pulse SP falls, the ink drop is to be separated from the nozzle 13a. At this time, the voltage (pressure) generated at two terminals of the inductor L is approximate to ‘0’. Here, the satellite canceling pulse CP rises, which reduces the volume of the pressure chamber 11 to push out the ink liquid column. Then, at the point of time 7.4 μs elapses from the moment the ejection pulse SP falls, the liquid column is ejected out from the nozzle 13a. At this time, the voltage (pressure) generated at two terminals of the inductor L is approximate to ‘0’ again. Here, if the satellite canceling pulse falls, then the internal volume of the pressure chamber 11 returns to normal, the pressure in the pressure chamber 11 drops sharply, making the ink which is not ejected out but left nearby the nozzle return back into the pressure chamber. In this way, the liquid column is separated from the ink in the nozzle, thereby inhibiting the generation of a satellite drop.
However, as shown in
Though DRCRP waveform eliminates both the satellite drop and the residual vibration as mentioned above, it takes longer time for one drive pulse train of the waveform compared with the DRC or DRP waveform.
Especially in a case where a multi-drop manner which includes multiple pulse trains of waveforms for sub drops in a dot, using DRCRP waveform for every sub drop takes longer waveform time and degrades the print speed. But in this case, DRCRP waveform is necessary only at the last waveform for the last sub drop in the multiple drops with the following reason.
It's because, in the case of the multi-drop manner, generated satellites at any time prior to the last ink sub drop will be gathered with the following liquid drop and never reaches on the printing medium alone, which causes no deterioration of the print quality.
In this embodiment, as shown in
Further, in this embodiment, as shown in
Because of using the backward justified manner for placing each waveform for each sub drop, the waveform PA4 including 3 DRP waveforms prior to 1 DRCRP waveform can be used as a reference drive waveform.
Thus, the reference drive waveform generation portion 231 of the drive signal generation section 23 shown in
Further, the present invention is not limited to the embodiments above.
For example, the aforementioned embodiments are described as a drive apparatus and a drive method for the ink jet head 1 having the structure shown in
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
