Ink jet recording apparatus with density control function

Abstract: A multi-nozzle type ink jet recording apparatus arranged so as to eject ink from each of a plurality of ink nozzles (88-91) toward a writing surface by means of an electric field established due to an ink ejecting signal applied to each of ink nozzles. The ink jet recording apparatus includes a circuit (1) for generating a density information signal indicative of a recording density at every ink nozzle and a control unit (3) being responsive to the density information signal and having a plurality of memories (11-13). Each of the plurality of memories stores a density-to-signal characteristic being predetermined to correspond to one or more of the ink nozzles (88-90) and the density-signal characteristic represents the relation between the recording density and the ink ejecting signal indicative of an ink ejecting amount ejected from each of the ink nozzles. The control unit (3) selects one from the density-to-signal characteristics at every ink nozzle and generating the ink ejecting signal indicative of the ink ejecting amount determined on the basis of the density information signal from the density information signal generating (1) circuit in accordance with the selected density-to-signal characteristic, the generated ink ejecting signal being applied to the corresponding ink nozzle.

Description: BACKGROUND OF THE INVENTION The present invention relates generally to an ink jet recording apparatus, and more particularly to such an ink jet recording apparatus with a multi-nozzle type ink jet printing head which allows gradation control of the recording density when ink is ejected from each of a plurality of ink nozzles of the multi-nozzle type ink jet printing head toward a writing surface placed in opposed relation to the printing head. Various types of ink jet printers are devised heretofore and one known arrangement is to use a multi-nozzle ink jet printing head of the type wherein printing ink is ejected therefrom toward a writing surface by the aid of an electric field established between two types of electrodes and air-stream supplied from a pressurized air source. Such a multi-nozzle ink jet printing head is illustrated in U.S. Patent No. 4,555,717, for example. An important problem in such multi-nozzle ink jet printing heads relates to the lack of uniformity in recording thickness or density on a writing surface. This is due to the difference in characteristic between the nozzles of the multi-nozzle ink jet printing head. Document US-4 521 786 discloses a programmable controller for ink jet printheads which improves print quality by controlling pulse width and pulse amplitude of a drive pulse for each ink jet ejector. This programmable controller is used in a system wherein a control processor contains look-up tables necessary to provide the desired amplitude and width data of the drive pulse necessary for a desired drop ejection velocity and droplet size. However, no adaption of the drive pulse width to a desired print density is provided in the aparatuses of the prior art. It is therefore an object of the present invention to provide an improved ink jet recording apparatus which is capable of controlling the recording density while preventing the recording thickness irregularity due to the difference in characteristic between the nozzles of the multi-nozzle printing head. This object is achieved by an ink jet printer according to claim 1. Alternatively, this object is achieved by an ink jet recording apparatus according to claim 4. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing a multi-nozzle type ink jet printing head which may be employed for an ink jet recording apparatus according to an embodiment of the present invention; Fig. 2 is a block diagram showing a conventional ink ejecting signal generation control circuit; Fig. 3 is a graphic diagram showing a density-to-pulse width of the ink ejecting signal used in the conventional ink ejecting signal generation control circuit of Fig. 2; Fig. 4 is a graphic illustration for describing the difference in density-pulse width characteristic between the ink nozzles of a multi-nozzle type ink jet printing head; Fig. 5 is a block diagram showing a pulse-width control circuit of the ink jet recording apparatus in accordance with the embodiment of the present invention; and Fig. 6 is a graphic diagram showing density-to-pulse width characteristics used in the pulse-width control circuit of Fig. 5. DETAILED DESCRIPTION OF THE INVENTION Prior to describing an embodiment of the present invention, a brief description of a conventional ink jet printing apparatus will be made first with reference to Figs. 1 to 4 for a better understanding of the present invention. A prior multi-nozzle ink jet printing head, as shown in Fig. 1, comprises an insulating air-ink nozzle plate 81 having a plurality of air-ink nozzles 82 to 85 successively arranged in a row at a predetermined interval. A common electrode 86 is attached at the circumferential portions of the plurality of air-ink nozzles 82 to 85 to a surface of the insulating air-ink nozzle plate 81. In parallel to the air-ink nozzle plate 81 is provided an ink nozzle plate 87 having a plurality of ink nozzles 88 to 91 successively arranged in a row and aligned with the air-ink nozzles 82 to 85 with one-to-one correspondance therebetween. The respective ink nozzles 88 to 91 are coupled to an ink chamber 93 with ink which is in turn coupled through an ink supply passage 92 to an ink source, not shown. On the other hand, the respective air-ink nozzles 82 to 85 are coupled through an air chamber 95 and an air supply passage 94 to an air source, not shown so that air supplied from the air supply passage 94 makes an air stream 96 because of the ink nozzle plate 87 and is then discharged curvedly from the air-ink nozzles 82 to 85. Control electrodes 100 whose number corresponding to the number of the ink nozzles 88 to 91 are independently provided at the circumferential portions of the ink nozzles 88 to 91 and on the rear surface of the ink nozzle plate 87 facing the ink chamber 93. An electric field is established between the common electrode 86 and the control electrodes 100 to form meniscuses in the ink nozzles 88 to 91 and, in response to selective application of ink-ejection control signals 96 to 99 to the control electrodes 100, the meniscuses in the selected ink nozzles are extended toward the air-ink nozzles 82 to 85 and carried by the air-stream 96 so as to be ejected as inkdroplets from the corresponding air-ink nozzles. This type ink jet printing head is arranged to cause ink to discharge due to an electrostatic force produced in response to the application of the ink-ejection control signals 96 to 99 which are pulse signals, respectively. The ink-discharging amount, i.e., recording density, is substantially proportional to the pulse width, or length, of each of the ink-ejection control signals applied to the control electrodes 88 to 91 and thus controllable under control of the pulse width thereof. One known ink-ejection control arrangement will be described hereinbelow with reference to Fig. 2 which is a block diagram showing a device for generating the ink-ejection control pulse signals which are in turn applied to n ink nozzles of a multi-nozzle type ink jet printing head such as illustrated in Fig. 1. In Fig. 2, the control pulse generating device 110 comprises a pulse width control circuit 152 which produces pulse signals 111 to 114 with pulse widths corresponding to N-bit input signals 101 to 104 respectively having information relating to the recording densities in correspondance with the respective ink nozzles 141 to 144 of the multi-nozzle type ink jet printing head 140. The produced pulse signals 111 to 114 are respectively supplied through amplifiers 121 to 124 to the control electrodes of the ink nozzles 141 to 144. Also included in the control pulse generating device 110 is a memory 153 which stores density-pulse width characteristic curves as illustrated in Fig. 3. In operation, in response to inputs of the N-bit density information signals 101 to 104, the memory is controlled to convert them into ℓ-bit pulse width information signals respectively corresponding to the inputted density information signals 101 to 104 which are in turn supplied to the pulse width control circuit 152 which produces the corresponding one-bit pulse width signals 111 to 114 and supplies them through the amplifiers 121 to 124 to the control electrodes of the ink nozzles 141 to 144, resulting in ink discharges with amounts corresponding to the density information. However, this arrangement causes recording density irregularity irrespective of application of control signals with the same pulse width, because of the difference in the density-pulse width characteristic between the ink nozzles as shown in Fig. 4. Referring now to Fig. 5, there is illustrated a control pulse generating unit according to an embodiment of the present invention designated at numeral 1, which may be coupled to a multi-nozzle type ink jet printing head such as shown in Fig. 1 and which comprises a pulse width control circuit 2 for, at every ink nozzles, producing a pulse signal with the width corresponding to a N-bit density information signal inputted from the external circuit. Also included in the control pulse generating unit 1 are a first memory 11 to a m th memory 13 (m = integer not less than 2) which store density-pulse width characteristic curves as shown in Fig. 6, respectively. Although it is better in general that a density-pulse width characteristic curve is determined at every ink nozzle so that the number n of the ink nozzles equals to the number m of the density-pulse width characteristic curves, it is sufficient in practice that m density-pulse width characteristic curves are prepared and one of the m density-pulse width characteristic curves is selected to be closer to the density-pulse characteristic curve of each of the n ink nozzles (n > m). Illustrated at numeral 3 is a memory designating circuit for specifying memories in correspondance with the ink nozzles, respectively, which is presetable from the external. In the memory designating circuit 3 are preset and stored addresses of the memories 11 to 13 which respectively prestore the density-pulse width characteristic curves corresponding to the respective ink nozzles of a multi-nozzle type ink jet printing head used in this ink jet recording apparatus. In response to inputting of each of N-bit density information signals for the respective ink nozzles to the control pulse generating unit 1, the memory designating circuit generates a k-bit memory address signal on the basis of each of the density information signals at every nozzle and the pulse width control circuit 2 obtains a ℓ-bit pulse width information signal on the basis of each of the density information signals and the density-pulse width characteristic curve stored in the corresponding memory (k and ℓ are positive integers). The pulse width control circuit 2 further produces a one-bit pulse signal with width corresponding to each of the pulse width information signals which is in turn supplied to the control electrode of each of the ink nozzles after amplified by amplifying means. It should be understood that the foregoing relates to only a preferred embodiment of the present invention, and that it is intended to cover all changes and modifications of the embodiment of the invention herein used for the purposes of the disclosure, which do not constitute departures from the scope of the invention as defined in the appended claims.

Claims: An ink jet printer comprising: ink jet printing head means having a plurality of ink nozzles (141-144) each ejecting ink toward a writing surface, characterized by means (11-13) for storing a plurality of predetermined density-pulse width characteristic curves each representing a relation between a desired recording density and a therefore required pulse width of an ink ejecting signal to be applied to a respective one of said plurality of ink nozzles (141-144); and control means (1) for selecting one of said plurality of predetermined density-pulse width characteristic curves in correspondence with said respective one of said plurality of ink nozzles (141-144) and generating said ink ejecting signal in accordance with said selected density-pulse width characteristic curve, whereby for each of said plurality of ink nozzles (141-144) one of said plurality of predetermined density-pulse width characteristic curves is selected. An ink jet printer according to claim 1, characterized in that said ink jet printing head means is a signal head and said plurality of ink nozzles (141-144) are integrally arranged in a row. An ink jet printer according to claim 1, characterized in that said ink jet printing head means comprises a plurality of ink jet printing heads (140) each having one of said plurality of ink nozzles (141-144) . An ink jet recording apparatus comprising: a multi-nozzle type ink jet printing head having a plurality of ink nozzles (141-144) each ejecting ink toward a writing surface, characterized by electrode means (86,100) for establishing an electric field due to ink ejecting signals applied to said electrode means (86,100), so as to eject ink from each of said plurality of ink nozzles (141-144) by means of said electric field; density determining means (2) for generating density information signals each indicative of a recording density at a respective one of said plurality of ink nozzles (141-144) of said multi-nozzle type ink jet printing head; and control means (1) responsive to said density determining means (2) and having memory means (11-13) storing a plurality of density-pulse width characteristic curves each being predetermined to correspond to one or more of said ink nozzles (141-144) and each representing a relation between said recording density and a therefore required pulse width of a respective one of said ink ejecting signals indicative of an ink ejecting amount ejected from said one or more of said ink nozzles (141-144), for selecting a respective one of said density-pulse width characteristic curves for each ink nozzle (141-144), and for generating said one of said ink ejecting signals indicative of said ink ejecting amount determined on the basis of said density information signal from said density determining means (2) in accordance with said selected density-pulse width characteristic curve, each of said one of said ink ejecting signals being applied to said electrode means (86,100). An ink jet recording apparatus according to claim 4, characterized in that said electrode means (86,100) of said multi-nozzle type ink jet printing head comprise a common electrode (86) and a plurality of control electrodes (100) each being provided in correspondence with each of said plurality of ink nozzles (88-91) and positioned in opposed relation to said common electrode, said pulse signal with a width corresponding to said density information signal being applied to said corresponding control electrode (100) .

Inventors: IWASAWA TOSHIYUKI, MIURA MASAYOSHI, IWASAWA, TOSHIYUKI, MIURA, MASAYOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: B41J2
IPC codes: B41J2