Ink-jet recording device and method for controlling the same

Abstract: An electrostatic ink-jet recording device which provides stable printing by preventing too much charged toner from gathering around an ink discharge aperture even if the charged toner has not been discharged for a long time. If the charged toner is not to be discharged, the potential difference between the electrophoretic electrode and the discharge electrode is so controlled as to suppress electrophoretic movement of the charged toner toward the ink discharging aperture, or the potential difference is made zero (100, 34). If the charged toner is to be discharged, the voltage applied to the discharge electrode is kept lower than the voltage applied to the electrophoretic electrode for a predetermined period of time before discharging a jet of the charged toner (110, 28).

Description: BACKGROUND OF THE INVENTION The present invention generally relates to an ink-jet recording device, and particularly, to an electrostatic ink-jet recording device in which a recording is achieved by controlling coloring particles in a pigmentary ink through the electrophoretic effect and discharging a jet of coloring particles by means of electrostatic force. An example of such a recording device is shown in FIG. 1. In FIG. 1, the ink-jet recording device comprises an ink chamber 201 filled with pigmentary ink, an electrophoretic electrode 203 for gathering the coloring particle 206 or charged toner around an ink discharge aperture 202 by means of the electrophoretic effect, and a discharge electrode 205 for discharging a jet of charged toner gathered around the ink discharge aperture toward a recording object 207 to record on. The ink chamber 201 is provided within a dielectric member 208. The ink discharge aperture 202 is provided in the dielectric member 208 for communicating the inside and the out side of the ink chamber 201. The discharge electrode 205 has a long and narrow form disposed in the ink discharging direction, and has its end pointed like a needle so as to facilitate electric field concentration on the end. The electrophoretic electrode 203 is fixed as one body on the side and back surfaces of the dielectric member 208. A grounded facing electrode 214 is provided facing the ink discharge aperture 202 via the recording object 207. The pigmentary ink comprises petroleum organic solvent (isoparaffin) and coloring particles 206 of thermoplastic resin colored with electrification control agent or toner dispersed in the organic solvent. The toner is charged apparently positive by the zeta potential. The recording object 204 is ordinary paper. The electrophoretic electrode 203 and the discharge electrode 205 is connected to a voltage driver (not shown) for applying predetermined voltages with a polarity opposite from that of the coloring particle 206 to the electrodes 203 and 205 in predetermined timing. FIG. 2 is a diagram showing the voltages applied to the electrophoretic electrode 203 and the discharge electrode 205 in printing operation of the recording device of FIG. 1. In FIG. 2, if a constant voltage V1 is applied to the electrophoretic electrode 203 as shown in FIG. 2A, forming an electric field in the ink chamber 201 filled with pigmentary ink, then the coloring particles 206 in the pigmentary ink move at an electrophoretic speed toward the ink discharge aperture 202 by the action of the electric field, and eventually gather around the ink discharge aperture 202. If a pulse voltage V2 with a duration of T2 is applied to the discharge electrode 205 with the coloring particles 206 gathered around the ink discharge aperture, then a jet of coloring ink is discharged in synchronism with the pulse voltage V2 from the ink discharge aperture 202 in the form of a flying particle group 207, which adheres to the recording object 204. Subsequently, the electric field formed by the electrophoretic electrode 203 causes coloring particles 206 to be supplied to the ink discharge aperture 202. Thus, the discharge of coloring particles is repeated, resulting in a formation of an image on the recording object 204. However, in the conventional ink-jet recording device as described above, the coloring particles 206 keep moving toward the ink discharge aperture 202 as long as the constant voltage V1 shown in FIG. 2 is applied to the electrophoretic electrode 203. If no coloring particle 206 has been discharged from the ink discharge aperture 202 for a long time, then too many coloring particles will gather around the ink discharge aperture 202, causing an obstruction in the ink discharge aperture 202. This prevents stable discharging of coloring particles 202, having an adverse influence on the quality of the printed images. GB 2031344 A discloses an ink recording apparatus. A recording head has a nozzle defining an elongate opening. A plurality of narrow control electrodes are arranged in a closely spaced array along the length of the opening. A grounding electrode is located behind a recording sheet at a location where it is arranged to be fed past the opening. The ink which is fed through the nozzle to the opening is shot in small drops at the recording sheet in accordance with the potential differences between an adjacent control electrode and the grounding electrode. By selectively varying the potential of the control electrodes a desired ink pattern can be produced on the recording sheet. WO93/11866 discloses a method and apparatus for the production of discrete agglomerations of particulate matter. A method and apparatus is provided for the generation of agglomerations of particulate material in a liquid. Agglomerations are built up at a point under the effect of an electric field and ejected by electrostatic means. The size of the agglomeration is dependent upon the strength of the electric field, point geometry, the nature of the liquid and the nature of the particles. Agglomerations of particles in the range of from 1 to 500 microns are produced. The invention is useful for non-impact printing and other applications where delivery of agglomerations of particles is useful such as in inhalable pharmaceuticals. The above and other problems in the prior art are solved and advances are made by the present invention. It is an object of the invention to provide an electrostatic ink-jet recording device for providing a stable printing by preventing too many coloring particles to gather around the ink discharge aperture. SUMMARY OF THE INVENTION According to the invention, an electrostatic ink-jet recording device provides stable printing by preventing too much charged toner or too many coloring particles from gathering around an ink discharge aperture even if the charged toner has not been discharged for a long time. If the charged toner is not to be discharged, the potential difference between the electrophoretic electrode and the discharge electrode is so controlled as to suppress electrophoretic movement of the charged toner toward the ink discharging aperture, or the potential difference is made zero. This prevents the gathering of too much toner around the ink discharge aperture. If the charged toner is to be discharged, the voltage applied to the discharge electrode is kept lower than the voltage applied to the electrophoretic electrode for a predetermined period of time before discharging a jet of the charged toner. This enables sufficient charged toner to gather around the ink discharge aperture. BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic diagram showing a part involved in printing in a conventional ink-jet recording device; FIGs. 2A and 2B are diagrams showing the voltages applied to the electrophoretic electrode and the discharge electrode in printing operation of the recording device of FIG. 1; FIG. 3 is a schematic diagram showing a relevant part of an exemplary arrangement of an ink-jet recording device according to the present invention; FIG. 4 is a flow chart showing a flow of operation executed by a controller under the control of a program stored in a ROM; and FIGs. 5A and 5B are diagrams showing the voltages applied to the electrophoretic electrode and the discharge electrode in printing operation of the controller unit of FIG. 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 3, an illustrative embodiment of the invention will be described in the following. FIG. 3 is a schematic diagram showing a relevant part of an exemplary arrangement of an ink-jet recording device according to the present invention. In FIG. 3, the elements denoted by the same numerals as those of FIG. 1 are identical to corresponding elements of FIG. 1, and accordingly their description is omitted. As shown in FIG. 3, the controller unit 100 comprises an input interface 113 for receiving printing data including print control codes from an external device (not shown), a voltage supplier 111 connected to the electrophoretic electrode 203 and the discharge electrode 205 for supplying voltages thereto, and a controller 110 connected with the input interface 113 and the electrophoretic electrode 205 via bus lines for analyzing the printing data and giving instructions to the voltage supplier 111. Specifically, the controller 110 comprises a read only memory (ROM) 115 for storing a program for controlling the recording device, a random access memory (RAM) 119 for storing data for use in operation of the recording device, and a central processing unit (CPU) 117 for controlling the operation of the recording device under the control of the program stored in ROM 115. Referring to FIGs. 4 and 5, operation of the ink-jet recording device 10 of FIG. 3 will be now described, FIG. 4 is a flow chart showing a flow of operation executed by the controller 110 under the control of a program stored in the ROM 115. FIG. 5 is a diagram showing the voltages applied to the electrophoretic electrode 203 and the discharge electrode 205 in a printing operation of the controller unit 100 of FIG. 3. In FIG. 4, when the ink-jet recording device 10 is activated, the controller 110 enters the flow at step 20, and proceeds to step 22, where the CPU 117 controls the voltage supplier 111 to apply a voltage V1 of the same polarity as the coloring particles 206 have to the electrophoretic electrode 203 and the discharge electrode 205. At this time, no electric field is formed between the electrophoretic electrode 203 and the discharge electrode 205, causing no electrostatic force to act on the coloring particles 206 in the ink. In step 204, a check is made to see if any printing data has been input. If not, the flow returns to step 24. If the answer is YES in step 24, the controller 110 analyzes the input printing data to see if a jet of toner is to be discharged in step 26. If so, the controller 110 proceeds to step 28, where the controller 110 controls the voltage supplier 111 to supply the discharge electrode 205 with a voltage V2 lower than the voltage V1, e.g., 0V in this embodiment. This causes an electric field to be formed between the electrophoretic electrode 203 and the discharge electrode 205 causing the coloring particles 206 in the ink to gather around the ink discharge aperture 202 by means of the electrophoretic effect. Then, the controler 110 waits for a predetermined period of time in step 30. If the predetermined period of time has elapsed, the controller 110 proceeds to step 32 to control the voltage supplier 111 to apply a pulse voltage of a value V3 with a pulse width of T2 to the discharge voltage 205 in step 32. The predetermined period of time is preferably set long enough for a sufficient quantity of coloring particles to gather around the ink discharge aperture 203.Once a pulse voltage V3 is applied to the discharge electrode 205, an electric field is formed between the discharge electrode 205 and the facing electrode 214, a group of coloring particles 206 are pulled apart from the top of the ink meniscus into a group of flying particles 206A to adhere to the recording object 204 forming a dot. Subsequently, after moving the recording object 204, the procedures from step 24 to step 32 are repeated resulting in a desired printing on the surface of the recording medium. On the other hand, if the answer is NO in step 26, the controller 110 controls, in step 34, the voltage supplier 111 to supply the discharge electrode 205 with the voltage V1 which is equal to the voltage applied to the electrophoretic electrode 203. This ceases the formation of the electric field between the electrophoretic electrode 203 and the discharge electrode 205, and accordingly the electrophoretic movement of the coloring particles 206, preventing too many coloring particles 206 from gathering around the ink discharge aperture 202. After completing the action of step 34, the controller returns to step 24. As described above, stopping charged particles 206 from gathering around the ink discharge aperture 202 as long as coloring particles have not to be discharged permits preventing too many coloring particles from gathering around the ink discharge aperture, resulting in a stability of printed image without an obstruction in the ink discharge aperture 202. Further, if coloring particles 206 are to be discharged in printing, the discharge of coloring particles 206 is guaranteed because coloring particles are gathered around the ink discharge aperture 202 in advance. The voltage applied to the electrophoretic electrode 203 is always kept at a constant value V1 even when the electrophoretic movement of coloring particles is stopped, which eliminates the need of a complicated control system for controlling the voltage applied to the electrophoretic electrode 203. This contributes to a simplification of the control system and accordingly a reduction in cost. It is noted that the voltage which is applied to the discharge electrode 205 during a predetermined period of time before the discharge of coloring particles 206 has not to be necessarily zero, if it is lower than the voltage applied to the electrophoretic electrode 203.

Claims: A method for controlling the voltages applied to an electrophoretic electrode (203) and a discharge electrode (205) of a recording head in an electrostatic ink-jet printer wherein recording is achieved by discharging a jet of charged toner (206) from an ink discharging aperture (202) by controlling said voltages, the method comprising the step of: in case when said charged toner (206) is not to be discharged, controlling the potential difference between said electrophoretic electrode (203) and said discharge electrode (205) wherein the voltage applied to the electrophoretic electrode (203) is always kept at a constant value (V1), so as to suppress electrophoretic movement of said charged toner toward said ink discharging aperture. A method according to claim 1, wherein said step of controlling the potential difference comprises the step of making said potential difference zero. A method according to claim 2, wherein said making said potential difference zero comprises equalizing said voltage (V2) applied to said discharge electrode (205) with said voltage (V1) applied to said electrophoretic electrode (203). A method according to claim 1, further comprising the step of: in case when said charged toner (206) is to be discharged, controlling said potential difference so as to cause said electrophoretic movement of charged toner (206) toward said ink discharging aperture (202) for a predetermined period of time before discharging a jet of said charged toner (206). A method of claim 4, wherein said step of controlling said potential difference comprises the step (28) of controlling said potential difference such that said voltage applied to said discharge electrode is lower than said voltage applied to said electrophoretic electrode for said predetermined period of time before discharging said jet of said charged toner (206). A method of claim 5, wherein said controlling said voltage applied to said discharge electrode includes: keeping said voltage applied to said discharge electrode zero for said predetermined period of time before discharging said jet of said charged toner (206). An electrostatic ink-jet recording device which provides stable printing by preventing too much charged toner from gathering around an ink discharge aperture even if said charged toner has not been discharged for a long time, the recording device (10) comprising: a recording head comprising, an ink chamber (201) containing ink filled with charged toner (206) and having an ink discharging aperture (202) connecting the inside and the outside of said ink chamber (201), an electrophoretic electrode (203) for gathering said charged toner around said ink discharge aperture (202) by means of the electrophoretic effect, and a discharge electrode (205) for discharging a jet of charged toner (206) gathered around said ink discharge aperture (202) toward a recording object (204) to record on; and means (110, 28, 30, 32) for controlling the voltages applied to said electrophoretic electrode and said discharge electrode wherein the voltage applied to the electrophoretic electrode (203) is always kept at a constant value (V1), to cause said discharging a jet of said charged toner thereby to effect recording on said recording object. said means comprising: suppressing means (110, 34), being adapted to be operative in case when said charged toner is not to be discharged, for controlling the potential difference between said electrophoretic electrode and said discharge electrode so as to suppress electrophoretic movement of said charged toner toward said ink discharging aperture. An electrostatic ink-jet recording device of claim 7, wherein said means for controlling the potential difference comprises means (110, 34) for making said potential difference zero. An electrostatic ink-jet recording device of claim 7, wherein said means for making said said potential difference zero comprises means (110, 34) for equalizing said voltage applied to said discharge electrode with said voltage applied to said electrophoretic electrode. An electrostatic ink-jet recording device of claim 7, further comprising: means (110, 28), operative in case when said charged toner is to be discharged, for controlling said potential difference so as to cause said electrophoretic movement of charged toner toward said ink discharging aperture for a predetermined period of time before discharging a jet of said charged toner. An electrostatic ink-jet recording device of claim 10, wherein said means for controlling said potential difference comprises: means (110, 28) for keeping, a state in which said voltage applied to said discharge electrode is lower than said voltage applied to said electrophoretic electrode, for said predetermined period of time before discharging said jet of said charged toner. An electrostatic ink-jet recording device of claim 11, wherein said means for keeping said voltage applied to said discharge electrode includes: means (110, 28) for keeping said voltage applied to said discharge electrode zero for said predetermined period of time before discharging said jet of said charged toner.

Inventors: HAGIWARA YOSHIHIRO, MINEMOTO HITOSHI, SHIMA KAZUO, SUETSUGU JUNICHI, UEMATSU RYOSUKE, HAGIWARA, YOSHIHIRO, MINEMOTO, HITOSHI, SHIMA, KAZUO, SUETSUGU, JUNICHI, UEMATSU, RYOSUKE
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1996
Main classification: B41J2
IPC codes: B41J2