PRINT HEAD FOR INK JET PRINTER

Abstract: The present invention relates to a print head for an ink jet printer of the type which comprises a plurality of piezoelectric transducers (26) each having at least one electrode (30, 32), a housing member (24) for holding the transducers in spaced apart positions, a conductor member (50) including a plurality of separate electrical conductors (48) thereon and mounted in a fixed position adjacent to the tranducers, and a connector member (46) positioned adjacent to the transducers and the conductor member and providing an electrical connection between each electrode (30, 32) on the transducers and a corresponding one of the electrical conductors (48). According to the invention the print head is characterised in that the connector member (46) comprises a resilient body and a plurality of electrically conducting elements mounted on the body, and the connector member is positioned so that each electrically conducting element abuts against a respective electrode and a respective electrical conductor.

Description: This invention relates to a print head for an ink jet printer in which ink drops are generated on demand in response to suitable electrical signals. There have been known in the prior art ink jet printing systems in which an electromechanical transducer is selectively energised to produce ink drops on demand. US-A-3,683,212, US-A-4,390,886, and US-A-4,418,356, each discloses an ink jet drop-on-demand print head in which the electromechanical transducer is a piezoelectric tube. The requirements for a higher print rate and a greater resolution in printing has led to multi-nozzle drop-on-demand ink jet arrays. These arrays require densely packed piezoelectric transducers to minimise the size and weight of the print head, and to enhance print visibility during printing operations. Due to the close proximity of the piezoelectric transducers, wiring for the electrodes on the piezoelectric tubes is extremely difficult. In addition, sealing at both ends of the piezoelectric transducer is particularly difficult since alignment, registration and centring of a large number of individual piezoelectric tubes is not easily accomplished. Conventional methods used in fabricating piezoelectric driver assemblies include standard lead soldering techniques on the electrodes and epoxy bonding materials at both ends of the piezoelectric elements. However, the prior art technique offers little flexibility for repair and replacement in case of broken parts either during fabrication of the print head or in later use. US-A-4,584,591 and US-A-4,588,999 each shows an array of piezoelectric tubes which are clipped in place, soldered and incorporated into a moulded assembly. None of the prior art patents show an array of piezoelectric tubes which are "floating" inside a body member so that they are self-aligned and self-centred when the array is fixed in position between a manifold section and a fan-in section. DE-A-3 324 043 describes a print head for an ink jet printer having a plurality of transducers and and a connector having resilient electrically conducting elements for making connections to electrodes on the transducers. The transducers are mounted in housings but neither these housings nor the connector allow movement of the transducers within the housings. The object of the present invention is to provide an improved print head for an ink jet printer. The present invention relates to a print head for an ink jet printer of the type comprising a plurality of piezoelectric transducers each having at least one electrode, a housing member formed with a plurality of openings each adapted to contain a corresponding transducer so as to hold all the transducers in spaced apart positions, a conductor member including a plurality of separate electrical conductors thereon and mounted in a fixed position adjacent to the transducers, and a connector member positioned adjacent to the transducers and the conductor member and providing an electrical connection between each electrode on the transducers and a corresponding one of the electrical conductors. According to the invention the print head is characterised in that each of the openings is such as to allow a transducer contained therein to move, the connector member comprises a resilient body and a plurality of electrically conducting elements mounted on the body, the connector member is positioned so that each electrically conducting element abuts against a respective electrode and a respective electrical conductor, and the connector member allows each transducer to move within its corresponding opening. In order that the invention may be more readily understood an embodiment will now be described with reference to the accompanying drawings, in which: FIG. 1 is an exploded perspective view of a print head for a drop-on-demand ink jet printer embodying the present invention, FIG. 2 is a perspective view of the actuator section of the print head illustrated in FIG. 1, FIG. 3 is an exploded view of the actuator section illustrated in FIG. 2, FIG. 4 is a plan view of a flat gasket member used with the actuator section illustrated in FIGS. 1 and 2, FIG. 5 is an exploded view of an alternative actuator section for the print head illustrated in FIG 1, Fig. 6 is a partial view from below of the actuator section illustrated in FIG 5, sectioned along line 6-6 of FIG. 5, Fig. 7 is a partial side view of the actuator section illustrated in FIG 5, sectioned along line 7-7 of FIG. 5. Fig. 8 is a partial exploded view of a further alternative actuator section for the print head illustrated in FIG 1, and Fig. 9 is a partial front view of the actuator section illustrated in FIG. 8. The print head 10 illustrated in FIG 1 comprises an actuator section 12 to which liquid ink is supplied from ink supply section 14. Actuator section 12 provides the driving force to eject drops of liquid ink from orifices in a print element section 16. A fan-in section 18 provides ink channels which extend from the actuator section 12 to the print element section 16. The present invention is directed to the actuator section 12, and this section will be described in detail after a brief description of the other components of the print head 10. The ink supply section 14 comprises an ink supply means 11 which supplies a marking fluid such as liquid ink to a manifold 13. Manifold 13 includes a plurality of openings which connect with corresponding openings in the actuator section 12, in order to feed the liquid ink to each of a plurality of transducers in actuator section 12. A transducer gasket (not shown) is provided to seal all the ink paths between the ink supply section 14 and the actuator section 12 in fluid tight relation. The fan-in section 18 comprises a plurality of ink channels, one end of each of which is positioned to mate with a corresponding one of the transducers in actuator section 12, and this mating interface is maintained in fluid tight relation by another transducer gasket (not shown). As the ink channels extend through the fan-in section 18 toward the print element section 16, the spacing of the ink channels converges from the spacing of the transducers in actuator section 12 to the spacing of the orifices in print element section 16. The print element section 16 comprises an orifice plate substrate 21 in which are formed a plurality of openings in registration with the ink channels in fan-in section 18, and the interface is maintained in fluid tight relation by a further gasket member (not shown). An orifice plate 22 has a plurality of nozzles or orifices 23 in registration with the openings in orifice plate substrate 21. The orifice plate substrate 21 provides support for the fragile orifice plate 22, and the orifice plate 22 is permanently bonded to the orifice plate substrate 21. The diameter of each of the ink channels through the fan-in section 18, the gasket member 20, and the orifice plate substrate 21 is chosen to provide a good acoustic impedance match in order to minimise reflections of the ejection pressure wave in each channel of the ink drop generator. In the embodiment shown in Figs. 2 and 3 the actuator section 12 comprises a plurality of piezoelectric tubes 26 which are held in position by a tube housing member 24. Tube housing member 24 can be a moulded plastic part, for example, and comprises a plurality of openings into which the piezoelectric tubes 26 engage with a close fit. The piezoelectric tubes 26 are coated, both inside and outside, with a conductive material that is resistant to corrosion by the liquid ink. Near each end of the tube 26 a gap in the form of a ring 28 is formed on the outside of the tube. No conductive material is present in each ring 28. The rings 28 have the effect of producing two electrodes on the tube. The first electrode 30 comprises the portions of conductive material formed on the inside of the tube, around the ends of the tube, and on the outside of the tube near the ends of the tube. The second electrode 32 comprises the portion of conductive material formed in the centre portion of the outside of the tube between the two rings 28. The first electrode 30 is connected to a reference potential and the second electrode 32 carries the drive signal for each of the piezoelectric tubes 26. The active portion of each tube 26 is the centre portion, that is, the portion between the two rings 28. When an electric pulse is applied to the centre portion electrode 32 of a piezoelectric tube 26, the tube momentarily contracts and generates a pressure wave in the ink inside the tube. A portion of this pressure wave travels forward along the channel from the centre portion of the tube 26 and the forward travelling pressure wave causes the ejection of a drop of ink from the corresponding orifice 23 when the pressure wave reaches the print element section 16. In the embodiment shown in Figs 2 and 3, the actuator section 12 is divided into two symmetrical halves. The actuator section 12 comprises a supporting frame 34 having two identical halves 36 fastened together and two identical module blocks 38 of piezoelectric tubes 26. Each module block 38 (FIG. 3) is made of an inexpensive, non-conductive material such as plastic with two columns each having a selected number of holes 40 through its entire length. These holes 40 are made just large enough for free insertion of the piezoelectric tubes 26. Two slots 42, 44 are provided on each side of each block 38 to expose the signal electrodes 32 and the reference electrodes 30 of the piezoelectric tubes 26 in the block. Two electrical connector members 46 are provided to connect each electrode 30, 32 to a corresponding electrical conductor 48 on a flat cable conductor 50. Each electrical conductor member 46 comprises a resilient body member 52 which is electrically non-conductive and which has electrically conductive rings 54 at spaced intervals on its other surface so that electrical contact is made between each one of the conductors 48 and a corresponding one of the electrodes 30 or 32 of the piezoelectric transducers 26. The completed actuator section 12 is fastened to the ink supply section 14 and the fan-in section 18 by suitable screws, clamps or clips. A flat gasket member 56 (FIG. 4) having openings corresponding to holes 40 is placed on each end of the actuator section 12. The control signals to produce the desired printed data are coupled to corresponding ones of conductors 48. The print head design has many advantages both in fabrication and in operation. The design permits easy repair and replacement of all the components of the print head either at the time of fabrication or in later operation of the print head. No soldering is required for electrical contact, and no epoxy or other bonding material is needed to hold the piezoelectric tubes in position since the piezoelectric tubes 26 are essentially floating inside the modular block 38 and are self-aligned and self-centered when the actuator section 12 is fastened in place between the ink supply section 14 and the fan-in section 18. As the number of modules required for a high resolution print head increases, the alternative embodiment shown in FIGS. 5-7 makes it easier to retain the relative registration among modules. The print head actuator section is shown in an exploded view in FIG. 5, and comprises a body member 58 having a plurality of holes 60 which are arranged in a plurality of rows and extend through the entire body member 58. A recess 62 is provided in each end of body member 58 in the face extending normal to the holes 60 to provide step overhangs 64. A printed circuit board 66 is provided with a plurality of holes 68 having the same spacing as holes 60 in body member 58. A plurality of electrical conductors 70 are provided on the printed circuit board 66. Each conductor 70 extends from a respective one of the holes 68 to the edge of the printed circuit board 66. Piezoelectric tubes 26 are inserted in each of the holes 60 in body member 58, and the end of each piezoelectric tube 26 is inserted through a corresponding one of the holes 68 in the printed circuit board 66. Gasket member 74 has a corresponding plurality of holes and the end of each the piezoelectric tubes 26 in also inserted partially through a corresponding one of the holes in gasket member 74. A slot 72 is provided along each row of holes 60 within the recessed face of body member 58. When the actuator section is assembled, as shown in FIG. 6, an electrical connector member 46 is positioned within each slot 72 to make electrical contact between each one of the electrodes 30, 32 on the piezoelectric tubes 26 and a corresponding one of the conductors 70 on printed circuit board 66. As shown in FIG. 7, the step overhangs 64 on the top and bottom of body member 58 provide positive stops when the actuator section 12 is clamped between the manifold section 14 and the fan-in section 18, thereby preventing over-compression of the gasket members 74. In the embodiment shown in FIGS. 5-7, one slot 72, and one connector member 46 is needed for each column of piezoelectric tubes. However, in a further alternative arrangement shown in FIGS. 8 and 9, two adjacent columns of piezoelectric tubes can utilise one slot and one connector member. As shown in FIG. 9, the piezoelectric tubes 26 in adjacent columns are staggered, and a slot 76 is cut in body member 78 which extends between two adjacent columns of piezoelectric tubes 26a and 26b. A connector member 46w is provided which has the size and shape, when placed in slot 76, to make electrical contact with each one of the electrodes 30, 32 on piezoelectric tubes 26a and 26b and a corresponding one of the conductors 82a or 82b on a printed circuit board 80. In other respects this arrangement is similar to that shown in FIGS. 5-7. Several embodiments of the invention have been described, each of which has the advantage of modular design of the actuator section of a print head for an ink jet printer and fabrication advantages which include no soldering operations and no bonding operations. The print heads described are repairable should one or more components require replacement. The modular designs also offer additional advantages in terms of piezoelectric tube registration and alignment.

Claims: A print head for an ink jet printer comprising a plurality of piezoelectric transducers (26; 26a, 26b) each having at least one electrode (30, 32), a housing member (24; 58; 78) formed with a plurality of openings (40; 60) each adapted to contain a corresponding transducer so as to hold all said transducers in spaced apart positions, a conductor member (50; 66; 80) including a plurality of separate electrical conductors (48; 70; 82) thereon and mounted in a fixed position adjacent to said transducers, and a connector member (46; 46W) positioned adjacent to said transducers and said conductor member and providing an electrical connection between each electrode (30; 32) on said transducers and a corresponding one of said electrical conductors (48; 70; 82), characterised in that each of said openings (40; 60) is such as to allow a transducer (26; 26a, 26b) contained therein to move, said connector member (46; 46W) comprises a resilient body and a plurality of electrically conducting elements mounted on the body, and said connector member is positioned so that each electrically conducting element abuts against a respective electrode (30, 32) and a respective electrical conductor (48; 70; 82), and said connector member allows each transducer to move within its corresponding opening. A print head as claimed in Claim 1 characterised in that said connector member comprises an elongated resilient electrically non-conductive body (52) having spaced apart electrically conducting elements (54) on the outer surface thereof. A print head as claimed in either of the preceding claims characterised in that said conductor member comprises a flat conductor cable (50). A print head as claimed in either claim 1 or Claim 2 characterised in that said conductor member comprises a printed circuit board (66; 80). A print head as claimed in any one of the preceding claims characterised in that each transducer (26) comprises an elongated body having at least one electrode formed on its outer surface. A print head as claimed in Claim 6 characterised in that the body of each transducer is made of electrically non-conducting material and each electrode is formed by a corresponding coating (30, 32) of electrically conducting material on said body. A print head as claimed in any one of the preceding claims characterised in that said housing member comprises a plurality of openings (40; 60), each adapted to receive a corresponding transducer (26), and in that each transducer (26) is a close fit in its corresponding openings (40; 60). A print head as claimed in any one of the preceding claims in which each transducer (26) is formed with two electrodes (30, 32) and comprising two conductor members (50; 66; 80) each including a plurality of separate electrical conductors (48; 70; 82) thereon and mounted in a fixed position adjacent to said transducers, and two connector members (46; 46W) positioned adjacent to said transducers and said conductor member and providing an electrical connection between each electrode (30; 32) on said transducers and a corresponding one of said electrical conductors (48; 70; 82), characterised in that each connector member (46) comprises a resilient body and a plurality of electrically conducting elements mounted on the body, each connector member is positioned so that each electrically conducting element abuts against a respective electrode and a respective electrical conductor, and each connector member allows each transducer to move within its corresponding opening.

Inventors: BAIER, WALTER FRANZ, DRAGO, GARY A., LEE, FRANCIS CHEE-SHUEN, MILLS, ROSE NEAL, MOSSBRUGGER, HORST GEBHART
Applicants: LEXMARK INTERNATIONAL, INC.
Application year: 1987
Main classification: B41J2
IPC codes: B41J2