Head for image printing apparatus

Abstract: A head (1) for an image printing apparatus includes a housing (4), an air nozzle (11), an ink nozzle (13), a valve seat (15), a diaphragm (16), and an actuator (21). The housing (4) has a cylindrical body with a bottom to cause a nozzle head to oppose a printing surface e.g. paper (7) at a predetermined interval. The air nozzle (11) is connected to an air path (12) formed at a central portion of a front end face of the nozzle head (6). The ink nozzle (13) is formed coaxial with the air nozzle (11), connected to an external pressurized ink tank, and formed in the nozzle head (6). The valve seat (15) is formed in a rear opening end of the ink nozzle (13). The diaphragm (16) is in tight contact with the valve seat (15) and has a peripheral portion supported by the nozzle head (6). The actuator (21) is supported by a support member (18) in the housing (4) and its operation end is fixed on a central portion of a surface of the diaphragm (16).

Description: Background of the Invention The present invention relates to a head for injecting an ink as a pixel to a printing surface to form an image in an image printing apparatus for expressing gradation of a pixel as a minimum unit constituting an image in accordance with a change in recording area or printing density, (as described in earlier EP-A- 0 398 000, forming prior art pursuant to Art. 54(3) EPC). A printing image is constituted by a set of pixels as the minimum units of the image. An image printing apparatus capable of recording an image on the basis of image information of each pixel has been developed. In an image printing apparatus of this type, gradation of each pixel is expressed by changing a printing area of pixels or their printing density. Furthermore a conventional image printing apparatus of this type comprises an actuator controller arranged near an original image surface and a spray gun serving as a head electrically connected to the actuator controller through a solenoid valve. The spray gun is operated while the original image and paper are synchronously moved. An ink in an ink tank is guided through a flow path and sprayed from a nozzle to a paper surface by a siphon effect generated by an air pressure whose flow rate is controlled by the solenoid valve. At this time, the actuator controller outputs image information in units of pixels of the original image and ON/OFF-controls the solenoid valve. The ink is intermittently sprayed from the spray gun, and an image having gradation corresponding to the image information of the original image is printed on the printing surface. Since the head in the conventional image printing apparatus comprises a siphon type spray gun having the solenoid valve, as described above, the apparatus as a whole including the valve body becomes heavy and is difficult to handle. In addition, since this apparatus employs the valve structure, response is poor. Since an amount of ink is controlled by air as a compressed fluid, the response time is further prolonged, and reproducibility of image information is degraded. Adjustment and maintenance operations are cumbersome and time-consuming, and much labor and skills are required due to the above reasons. Summary of the Invention It is an object of the present invention to provide a nozzle for an image printing apparatus, capable of obtaining a clear image, improving printed matters, and achieving high response and excellent reproducibility of an image. It is another object of the present invention to provide a lightweight, compact nozzle for an image printing apparatus, which can be easily maintained and adjusted and can improve durability due to reduction in wear and fatigue. It is still another object of the present invention to provide a nozzle for an image printing apparatus, which can greatly improve performance of the printing apparatus due to constant supply of the ink. In order to achieve the above objects of the present invention, there is provided a head for an image printing apparatus according to claim 1. When the air source is operated, an ink sprayed from the ink nozzle is surrounded by the air sprayed from the air nozzle and travels straight with a controlled dispersion distribution. At this time, image information of each pixel of an original image is output from the actuator controller to ON/OFF-control the actuator. The actuator moves the diaphragm back and forth to close and open the valve seat. The ink is intermittently sprayed from the ink nozzle, and an image having gradation corresponding to the image information of the original image is printed on the printing surface. Brief Description of the Drawings Fig. 1 is a longitudinal sectional view of a head for an image forming apparatus according to earlier EP-A- 0 398 000 forming prior art pursuant to Art. 54(3) EPC. Fig. 2 is an enlarged longitudinal sectional view showing the main part of the image forming apparatus shown in Fig. 1; Fig. 3 is an enlarged longitudinal sectional view showing a head part in correspondence with Fig. 2 according to an embodiment of the present invention; Fig. 4 is a sectional view showing the overall structure of the head; and Fig. 5 is a sectional view of the head along the line V - V of Fig. 4. Figs. 1 and 2 show a head for an image printing apparatus (according to earlier EP-A- 0 398 000) to illustrate its general structure. Referring to Figs. 1 and 2, a head 1 comprises a housing 4 located near a circumferential surface of a rotary cylinder 2 and supported by a support member 3. The support member 3 is reciprocated in the axial direction of the rotary cylinder 2 so as to be interlocked with rotation of the rotary cylinder 2. The housing 4 has a cylindrical shape having two closed ends and comprises a cylindrical body (hollow body) 5 having a bottom and a rectangular section, and a nozzle head 6 serving as a front bottom plate which closes an open end of the cylindrical body 5. The nozzle head 6 opposes to be spaced apart from a printing surface of, e.g., paper 7 mounted on the rotary cylinder 2 by a predetermined distance. The nozzle head 6 according to EP-A- 0 398 000 is formed by bonding front, middle, and rear plate 8, 9, and 10 which are divided in a direction of thickness. An air nozzle 11 is formed at the central portion of the front plate 8 such that the open end on the middle plate 9 side has a disc-like opening. The air nozzle 11 is connected to an external air source (not shown) through an air path 12 open to the disc-like opening end and defined between the front and middle plates 8 and 9. An ink nozzle 13 coaxial with the air nozzle 11 is formed at the central portion of the middle plate 9. A circular valve seat 15 surrounded by an annular ink reservoir 14 is formed at an open end of the rear portion of the ink nozzle 13. Reference numeral 16 denotes a circular diaphragm made of an elastic thin metal plate. The central portion of the diaphragm 16 is normally in tight contact with the valve seat 15, and the peripheral portion of the diaphragm 16 is supported and clamped between the middle and the rear plates 9 and 10 (according to EP-A- 0 398 000). The ink nozzle 13 is connected to an external pressurized ink tank (not shown) through an ink path 17 formed between the valve seat 15 and the diaphragm 16 and between the diaphragm 16 and the middle plate 9. The ink in the ink tank is pressurized and is supplied to the valve seat 15 through the ink path 17. The ink is then supplied to the ink nozzle 13 through a gap between the valve seat 15 and the diaphragm 16 which can be opened by an actuator 21 (to be described in detail later). A support member 18 is slidably fitted in the hollow portion of the housing 4. Bolts 19 are threadably fitted in the screw holes in the support member 18 through the wall portions of the housing 4, so that the support member 18 can be moved back and forth upon rotation of the bolts 19. Reference numeral 20 denotes a bolt which is threadably engaged with a screw hole formed in the housing 4 to fix the support member 18 after adjustment. The actuator or piezoelectric element 21, an operation end of which is integrally fixed with the central portion of the flat surface of the diaphragm 16, is mounted on the central portion of the support member 18 at its end face on the nozzle head 6. The piezoelectric element 21 is connected to the actuator controller. A drive signal corresponding to pixel information of an original image is input to the piezoelectric element 21 and is ON/OFF-controlled, the diaphragm 16 is moved back and forth to close and open the valve seat 15. The reciprocal movement of the piezoelectric element 21 is adjusted by the bolts 19 through the support member 18 to adjust a gap between the diaphragm 16 and the valve body 15. An operation of the head having the above arrangement will be described below. When compressed air is supplied from the air source for the head 1 to the nozzle head 6, this air is supplied to the air nozzle 11 through the air path 12 and is sprayed from the air nozzle 11. When the pressurized ink is supplied from the ink tank to the nozzle head 6, the ink is supplied to the valve seat 15 through the ink path 17 and the ink reservoir 14 and is sprayed from the ink nozzle 13 through a gap between the valve seat 15 and the diaphragm 16. The sprayed ink is surrounded by the air flow formed by the air sprayed from the air nozzle 11 and travels straight with a controlled dispersion distribution. The ink is then printed as a clear pixel on the printing surface of the paper 7. At this time, since the drive signal which is ON/OFF-controlled by image information of an original image is input to the piezoelectric element 21, the piezoelectric element 21 is ON/OFF-controlled to reciprocate the diaphragm 16 and hence open/close the valve seat 15. As a result, the ink passes through the valve seat 15 while the valve seat 15 is open. Therefore, an image having gradation corresponding to the image information of the original image can be printed on the printing surface of the paper 7. In order to change an amount of ink passing through the valve seat 15, the bolt 20 is loosened to move the piezoelectric element 21 backward together with the support member 18. The open end limit of the diaphragm 16 is changed to adjust a degree of opening of the valve seat 15. The amount of ink passing through the valve seat 15 is adjusted, and the adjusted amount of ink can be kept constant after the adjustment. In addition, when a voltage applied to the piezoelectric element 21 is changed, zero adjustment and opening adjustment of the valve seat 15 can be performed. In the head operated as described above, since a movable member is the diaphragm 16 made of a thin film, the operation of the actuator can be accurately transmitted. For example, the actuator comprises the piezoelectric element 21, as described in this embodiment, high response can be obtained, and pixels having excellent reproducibility can be formed. Since the ON/OFF drive signals are input to the piezoelectric element 21, an amount of ink applied to the unit printing area can be changed in accordance with a change in duty ratio of the signal, thus facilitating gradation expressions. Now, Figs. 3 to 5 show an embodiment of the present invention. Fig. 3 shows a main part of a head in correspondence with Fig. 2, Fig. 4 is a sectional view thereof, and Fig. 5 is a sectional view thereof along the line V - V in Fig. 4. A housing 4 of a head 30 of this embodiment comprises a cylindrical body 5 having a bottom. A disc-like cap 32 having an air nozzle 11 at its central portion is fitted in a recess of a disc-like flange 31 fixed at the distal end of the housing 5. An air path 12, an ink path 17, and an ink nozzle 13 fitted in the air nozzle 11 are formed in the flange 31. A valve seat 15 and a diaphragm 16 are arranged behind the ink nozzle 13. Reference numeral 7'denotes an air reservoir; and 8', an ink reservoir. A piezoelectric element 21 is housed in a cylindrical case 33, and the cylindrical case 33 is fitted in the hollow portion of the body 5. The case 33 is fixed by a holder 34 fitted in a groove in the body 5 and bolts 35. Reference numeral 120 denotes a bolt for fixing the case 33. An operation of the head 30 having the above arrangement is the same as previously described, and a detailed description thereof will be omitted. In the embodiment described above, the actuator comprises the piezoelectric element 21, but is not limited to this. In a head for an image forming apparatus according to the present invention, as has been described above, a housing supported by a support member comprises a cylindrical member having a bottom, an air nozzle and an ink nozzle coaxial with the air nozzle are formed at a central portion of the nozzle head in the housing. The air nozzle and the ink nozzle are connected to an air source and a pressurized ink tank, respectively. The peripheral portion of a diaphragm which is in tight contact with a valve seat formed at the opening end of the rear portion of the ink nozzle is supported by the nozzle head. An actuator, an operation end of which is in contact with the central portion of the flat surface of the diaphragm, is supported by a support member which can be reciprocated in the housing. Since the ink sprayed from the ink nozzle is surrounded by air sprayed from the air nozzle and travels straight with a controlled dispersion distribution, a clear image can be obtained, and the quality of the printed matters can be improved. In addition, the valve seat is opened and closed upon ON/OFF operations of the actuator to control the densities of the pixels by the ON durations of the drive signals, so that high response can be obtained, and pixels having excellent reproducibility can be obtained. Since the movable portion is formed of a diaphragm of a thin film, an operation of the actuator can be accurately transmitted, and a higher response can be obtained. At the same time, a lightweight, compact apparatus can be obtained, and maintenance and adjustment can be facilitated. Since the stroke of the diaphragm is very short, wear and fatigue of the diaphragm can be minimized to improve durability. The flow rate of the ink can be adjusted by a simple operation and the adjusted amount of ink can be maintained constant after adjustment, thereby greatly improving the performance of the apparatus.

Claims: A head (30) for an image printing apparatus, comprising a housing (4), having a hollow body (5) with a bottom, for causing a nozzle head (6) to oppose a printing surface (7) at a predetermined interval; an air nozzle (11) connected to an air path (12) formed at a central portion of a front end face of said nozzle head (6); an ink nozzle (13) formed coaxial with said air nozzle (11), connected to an external pressurized ink tank by an ink path (17), and formed in said nozzle head (6); a valve seat (15) formed in a rear opening end of said ink nozzle (13); a diaphragm (16) which is in tight contact with said valve seat (15) and a peripheral portion of which is supported by said nozzle head (6); and an actuator (21) which is supported by a support member (18) in said housing (4) and an operation end of which is fixed on a central portion of a surface of said diaphragm (16), wherein said nozzle head (6) comprises a cap (32) having said air nozzle (11) formed therein, and a disc-like flange (31) having said air path (12) and said ink path (17) formed therein. A head according to claim 1; characterized by actuator adjusting means (20;120) for adjusting a degree of opening interval between said valve seat (15) and said diaphragm (16); and actuator fixing means (19;35) for fixing said actuator (21). A head according to claim 2, characterized in that said actuator adjusting means (20;120) and said actuator fixing means (19;35) comprise screw bolts. A head according to any preceding claim, characterized in that said actuator (21) comprises a piezoelectric element.

Inventors: ARAUCHI RYUJI, ENDOH YASUJI, TOMITA TOSHIKAZU, ARAUCHI, RYUJI, ENDOH, YASUJI, TOMITA, TOSHIKAZU
Applicants: KOMORI PRINTING MACH, KOMORI CORPORATION
Application year: 1990
Main classification: B41J2
IPC codes: B41J2