Patent Grant
RE38941
1. Field of the Invention
The invention relates to an ink droplet ejecting method and apparatus of an ink jet type.
2. Description of Related Art
According to a known ink jet printer of an ink jet type, the volume of an ink flow path is changed by deformation of a piezoelectric ceramic material. When the ink flow path volume decreases, the ink present in the ink flow path is ejected as a droplet from a nozzle. However, when the ink flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of printing head, multiple ink chambers are formed by partition walls of a piezoelectric ceramic material. An ink supply device, such as ink categories, are connected to one end of each of the multiple ink chambers. The opposite end of each of the ink chambers is provided with an ink ejecting nozzle (hereinafter referred to simply as “nozzles”). The partition walls are deformed in accordance with printing data to make the ink chambers smaller in volume, whereby ink droplets are ejected onto a printing medium from the nozzles to print, for example, a character of a figure.
An example of this type of ink jet printer is a drop-on-demand type ink jet printer that ejects ink droplets, which is popular because of a high ejection efficiency and a low running cost. An example of a drop-on-demand type ink jet printer is a shear mode type that uses a piezoelectric material, which is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
As shown in FIGS. 7(a) and 7(b), this type of ink droplet ejecting apparatus 600 includes a bottom wall 601, a top wall 602 and shear mode actuator walls 603 (shown in
A nozzle plate 617 having nozzles 618 (shown in
The one-way propagation time T is a time required for the pressure wave in the ink chamber 613 to propagate longitudinally through the same chamber. Given that the length of the ink chamber 613 is L and the velocity of sound in the ink present in the ink chamber 613 is a, the time T is determined to be T=L/a.
According to the theory of pressure wave propagation, upon lapse of time T, or an odd-multiple time thereof, after the above application of voltage, the internal pressure of the ink chamber 613 reverses into a positive pressure. In conformity with this timing, the voltage being applied to the electrode in the ink chamber 613c is returned to 0(V). As a result, the actuator walls 603e and 603f revert to their original state (FIGS. 7(a) and 7(b) before the deformation, whereby a pressure is applied to the ink. At this time, the above positive pressure, and the pressure developed by the reverting of the actuator walls 603e and 603f to their original state before the deformation, are added together to provide a relatively high pressure in the vicinity of the nozzle 618c in the ink chamber 613c, whereby an ink droplet is ejected from the nozzle 618c. An ink supply passage 626, shown in FIG. 7(b), that communicates with each of the ink chambers 613, is formed by members 627 and 628.
Conventionally, in this type of ink droplet ejecting apparatus 600, when an ink droplet of a small volume is to be ejected for enhancing the printing resolution, a control has been provided to decrease the driving voltage in multiple steps, for example. However, such a method of controlling the voltage in multiple steps leads to an increase in cost of a driver IC, etc., and attempting to reduce the volume of an ink droplet gives rise to the problem that even the speed of the ink droplet decreases. In order to obtain an ink droplet of a small volume without decreasing the ink droplet speed, it has been proposed to use in additional pulse of a low voltage level, after application of a jet pulse and before completion of ink ejection. However, this proposal also leads to an increase in cost of a driver IC, etc. because multiple voltages are needed as driving pulses.
The invention solves the above-mentioned problems, and it is an object of the invention to provide an ink droplet ejecting method and apparatus, wherein, after a driving waveform for a primary ejection of ink, only one additional pulse is added, thereby making it possible to obtain an ink droplet of a desired volume and also possible to minimize the decrease of the ink droplet speed.
In order to achieve this object, an ink droplet ejecting method is provided, wherein a jet pulse signal is applied to an actuator, for changing the volume of an ink chamber filed with ink, to generate a pressure wave within the ink chamber, thereby applying pressure to the ink and allowing a droplet of the ink to be ejected from a nozzle. Both the jet pulse signal and an additional pulse signal are applied to the actuator in accordance with a one-dot printing instruction. The jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage of the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The additional pulse signal has a pulse width of approximately 0.2T to 0.6T relative to the jet pulse signal, and a time difference between a fall timing of the jet pulse signal and a rise timing of the additional pulse signal is 0.3T to 0.7T.
According to the above method, the ink present in the ink chamber is about to rush out from the nozzle at the leading edge and the trailing edge of the jet pulse signal, and with the additional pulse signal which is subsequently applied halfway at the above timing, a part of the ink droplet which is rushing out from the nozzle is pulled back. Consequently, it is possible to reduce the size of the flying ink droplet after ejection, and hence possible to attain a high printing resolution easily. Further, since it is not necessary to change the driving voltage to reducing the size of the ink droplet, the cost is reduced and the ink droplet speed is only minimally decreased.
In accordance with another aspect of the ink droplet ejecting method, the jet pulse signal and the additional pulse signal have the same peak value. According to this method, a single drive voltage source is sufficient to obtain a small-sized ink droplet, and therefore the cost can be reduced.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides controls so that, in accordance with a one-dot printing instruction, a jet pulse signal and an additional pulse signal are applied to the actuator from the driving power source, thereby causing the ink present in the ink chamber to be ejected. The controller provides control so that the jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the laps of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The controller also provides control so that the additional pulse signal has a pulse width of approximately 0.2T to 0.6T relative to the jet pulse signal, and a time difference between a fall timing of the jet pulse signal and a rise timing of the additional pulse signal is 0.3T to 0.7T.
This structure provides the same advantages as the corresponding method in accordance with the invention discussed above.
In accordance with another aspect of this ink droplet ejecting apparatus, the jet pulse signal and the additional pulse signal have the same peak value. This structure provides the same advantages as the corresponding aspect of the method in accordance with the invention discussed above.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides control so that in accordance with a one-dot printing instruction, a jet pulse signal for ejecting the ink present in the ink chamber and an additional pulse signal for withdrawing a part of an ink droplet which has rushed out from a nozzle in accordance with the jet pulse signal, are applied from the driving power source to the actuator. The controller determines whether or not the additional pulse signal is to be used. According to the apparatus, the volume of ink droplet can be adjusted by either applying, or not applying, the additional pulse signal in accordance with a preset resolution.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides control so that, in accordance with a one-dot printing instruction, a jet pulse signal for ejecting the ink present in the ink chamber and an additional pulse signal for withdrawing a part of an ink droplet which has rushed out from a nozzle in accordance with the jet pulse signal, are applied to the actuator from the driving power source. The controller provides controls so that a time difference from the application of the jet pulse signal up to the application of the additional pulse signal, and the pulse width of the additional pulse signal, can be adjusted. According to this apparatus, since a control is provided so that the time difference from the application of the jet pulse signal up to the application of the additional pulse signal can be adjusted in accordance with a preset resolution, it is possible to adjust the volume of an ink droplet.
In accordance with another aspect of this ink droplet ejecting apparatus, the jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The pulse width of the additional pulse signal is controlled so as to be adjustable in the range of approximately 0.2T to 0.6T relative to the jet pulse signal, and the time difference is controlled so as to be adjustable in the range of approximately 0.3T to 0.7T from a trailing edge of the jet pulse signal up to a leading edge of the additional pulse signal. According to this apparatus, the decrease of the ink catalyst speed is minimized, so that the same advantages can be attained as the ink droplet ejecting apparatus discussed above.
According to the invention, as set forth above, by adding a predetermined additional pulse signal to a jet pulse signal for a one-dot printing instruction, a small volume ink droplet can be provided at high speed, without decreasing the ink droplet speed. Further, since the volume of an ink droplet can be adjusted as desired, it is possible to obtain a desired printing resolution easily.
Further, unlike the conventional art, multiple driving voltages are not required to reduce the size of an ink droplet. One driving voltage source is sufficient, and it is not necessary to change the driving voltage, thus reducing the cost.
A preferred embodiment of the invention will be described in detail with reference to the following figures wherein:
FIG. 4(a) is a diagram showing how the ink droplet speed changes upon application of various driving waveform signals and
FIG. 4(b) is a diagram showing how the ink droplet volume changes upon application of various driving waveform signals;
FIGS. 5(a)-5(e) are drawings showing how an ink droplet is ejected from a nozzle upon application of a conventional driving waveform signal;
FIGS. 6(a)-6(e) are diagrams showing how an ink droplet is ejected from a nozzle upon application of a driving waveform signal according to the invention;
FIG. 7(a) is a longitudinal sectional view of an ink jet portion of a printing head, and
FIG. 7(b) is a transverse sectional view thereof;
An embodiment of the invention will be described hereinunder with reference to the drawings. The structure of a mechanical portion of an ink droplet ejecting apparatus of this embodiment is the same as that shown in FIGS. 7(a) and 7(b), referred to above, and therefore an explanation thereof is omitted.
An example of specific dimensions of this ink droplet ejecting apparatus, indicated as 600, will now be described. The length L of an ink chamber 613 is 9 mm. As to the dimensions of a nozzle 618, its diameter on an ink droplet ejection side is 40 μm, its diameter on the ink chamber 613 side is 72 μm, and its length is 100 μm. In an experiment, the viscosity of 25° C. of ink used was about 2 mPas and the surface tension thereof was 30 mN/m. The ratio of the above length L to a sonic velocity, a, in the ink present within the ink chamber 613, i.e., L/a (=T) was 10 μsec.
The wave width Wa of the jet pulse signal A is set equal to the ratio, L/a (=T), of the foregoing length L to a sonic velocity, a, in the ink present in the ink chamber 613, or corresponds to an odd-multiple time thereof (a value peculiar to a head), for example, 10 μsec, that a time difference, d, between a fall timing of the jet pulse signal A and a rise timing of the additional pulse signal B is 0.3T to 0.7T, that is, approximately 3 to 7 μsec, and that the wave width Wb of the additional pulse signal B is 0.2T to 0.6T, that is, approximately 2 to 6 μsec. The total time of the time difference, d, and the wave width, Wb, is approximately 5 to 13 μsec. At the wave width Wb, the additional pulse signal B does not cause ejection of an ink droplet. The pulse cycle in the case of printing the next dot in a continuous manner is 100 μsec, assuming that the driving frequency is 10 kHz.
Next, an example of a controller for implementing the driving waveform 10 will be described with reference to
Input terminals 181 and 183 are for inputting pulse signals to adjust the voltage to be applied to the electrode 619 in each ink chamber 613, to E(V) or 0(V). The charging circuit 182 includes resistors R101, R102, R103, R104, R105 and transistors TR101, TR102.
When an ON signal (+5V) is applied to the input terminal 181, the transistor TR101 conducts through resistor 101, so that an electric current flows from a positive power source 187, passes through resistor R103, and flows from the collector to the emitter of transistor TR101. Consequently, a divided voltage of the voltages applied to the resistor R104 and R105, which are connected to the positive power source 187, increases and so does the electric current flowing in the base of the transistor TR102, providing conduction between the emitter and the collector of the transistor TR102. A voltage of 20(V) from the positive power source 187 is applied to the terminal 191A of the capacitor 191 via the collector and emitter of the transistor TR102 and resistor R120.
The following description is now provided regarding the discharge circuit 184. The discharge circuit 184 includes resistors R106, R107 and a transistor TR103. When an ON signal (+5V) is applied to the input terminal 183, the transistor TR103 turns conductive via resistor R106 and the terminal 191A on the resistor R120 side of the capacitor 191 is grounded via resonator R120, so that the electric charge imposed on the actuator wall 603 of the ink chamber 613 shown in FIGS. 7(a), 7(b) and 8 is discharged.
Reference will now be made to the pulse control circuit 186 which generates pulse signals to be received by the input terminal 181 of the charging circuit 182 and the input terminal 183 of the discharge circuit 184. A CPU 110 is provided in the pulse control circuit 186 which performs various arithmetic operations. To the CPU 110 are connected, a RAM 112 for the storage of printing data and various other data, and a ROM 114 which stores sequence data for generating ON-OF signals in accordance with control program and timing in the pulse control circuit 186. In the ROM 114, as shown in
In the control program storage area 114A, as shown in
The CPU 110 is further connected to an I/O bus 116 for transmission and reception of various data. A printing data receiving circuit 118 and pulse generations 120 and 122 are also connected to the I/O bus 116. The output of the pulse generator 120 is connected to the input terminal 181 of the charging circuit 182, while the output of the pulse generator 122 is connected to the input terminal 183 of the discharge circuit 184.
The CPU 110 controls the pulse generators 120 and 122 in accordance with the sequence data stored in the driving waveform data storage area 114B of the ROM 114. Therefore, by having various patterns of the foregoing timing stored beforehand in the driving waveform data storing area 114B of the ROM 114, it is possible to apply a driving pulse of the driving waveform 10 shown in
The same number of pulse generators 120, 122, charging circuit 182 and discharge circuit 184 are provided as the number of nozzles used. Although the above description is directed to controlling one nozzle, the same control can also be applied to the other nozzles.
Reference is now made to the results of ink droplet ejection tests conducted in accordance with the driving method of this embodiment. FIGS. 4(a) and (b) are characteristic diagrams showing changes in ink droplet speed and one-dot link droplet volume in various combinations of the time difference, d, and the wave width, Wb, in connection with the driving waveform 10 shown in FIG. 1. In both figures, broken lines represent values of ink droplet speed (8 m/s) and ink droplet volume, 45 pl (picoliter), obtained by using only the jet pulse A for the ejection of ink. The values of ink droplet volume obtained by using both jet pulse signal A and additional pulse signal B are all smaller than the values when only the jet pulse signal A is used. Particularly, in any of the combinations 0.3T to 0.5T as time difference, d, and 0.2T to 0.67T as wave width, Wb, of the additional pulse signal B a considerably reduction in the size of ink droplet is attained. In comparison with the use of only the jet pulse signal A, the ink droplet speed decreases partially (at the time difference, d, of 0.3T), but in many of the other cases (0.5T to 0.7T in the time difference, d), the ink droplet speed does not decrease very much. By using the additional pulse signal B in such combination ranges of time difference and wave width as mentioned above, the ink droplet speed does not decrease very much, and a small ink droplet is obtained as compared with the use of only the jet pulse signal A.
FIGS. 5(a)-5(e) show the manner in which an ink droplet is ejected from a nozzle by applying only the jet pulse signal A to the actuator with respect to one dot, and FIGS. 6(a)-6(e) show the manner in which an ink droplet is ejected from the nozzle by using both jet pulse signal A and additional pulse signal B as in the embodiment of the invention shown in FIG. 1. In
On the other hand, as shown in
Although an embodiment of the invention has been described above, the invention is not limited therein. For example, although the main driving signal used in the above embodiment has only one jet pulse A, it may be a driving signal that includes two jet pulses. Also, regarding the ink droplet ejecting apparatus 600, no limitation is placed on the structure described in the above embodiment. Further, a similar apparatus can be used that is opposite in polarizing direction of the piezoelectric material.
Although in the above embodiment, air chambers 615 are formed on both sides of each ink chamber 613, ink chambers may be formed in a directly adjacent manner with no air chamber 615 therebetween. Further, although the actuator used in the above embodiment is a shear mode type, a structure may be used wherein layers of a piezoelectric material are laminated together and a pressure wave is generated by a deformation in the laminated direction. No limitation is imposed on the piezoelectric material. Further, any other material can be used insofar as a pressure wave is generated in each ink chamber.
| Number | Date | Country | Kind |
|---|---|---|---|
| 9-346722 | Dec 1997 | JP | national |
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| 5903286 | Takahashi | May 1999 | A |
| 6095630 | Horii et al. | Aug 2000 | A |
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| Number | Date | Country |
|---|---|---|
| 59-133066 | Jul 1984 | JP |
| 63-71355 | Mar 1988 | JP |
| 63-094850 | Apr 1988 | JP |
| 63-247051 | Oct 1988 | JP |
| A-63-247051 | Oct 1988 | JP |
| 01-101160 | Apr 1989 | JP |
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| 04-189144 | Jul 1992 | JP |
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| A-9-29960 | Feb 1997 | JP |
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| 10-157100 | Jun 1998 | JP |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09201129 | Nov 1998 | US |
| Child | 10788047 | US |
