Ink jet printhead having solenoids controlling ink flow

• US 5,907,339 A
• Filed: 11/10/1994
• Issued: 05/25/1999
• Est. Priority Date: 11/10/1994
• Status: Expired due to Fees

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Diagraph Corporation (Illinois Tool Works Inc.)
• Inventors: Evans, Edward B., Droit, Jimmy L., Porter, Donald D.
• Primary Examiner(s): Yockey, David F.
• Application Number:
  US08/337,300
• Time in Patent Office: 1,657 Days
• Field of Search: 347/54, 347/20, 347/50, 335/213-215, 335/219, 335/220, 222/1, 222/146.5, 222/504, 118/313, 137/516.25, 137/883, 137/625.48, 137/870, 251/129.15, 251/231, 251/129.17, 251/331, 251/61.1, 251/84, 251/85, 251/333, 251/357, 361/160, 361/171, 361/187, 361/152, D08/399
• US Class Current: 347/54
• CPC Class Codes: B41J 2/04 generating single droplets or particles on demand
• CPC Class Codes: B41J 2002/041 Electromagnetic transducer

Abstract

A printhead for ink jet printing apparatus having a plurality of orifices for delivery of droplets of ink with delivery controlled by miniature solenoids, one for each orifice, each solenoid having a plunger directly engageable with a membrane to block flow of ink to a respective orifice and electromagnetically retractable from the membrane for flow of ink for delivery of a droplet of ink from the respective orifice, with provision for proportional valve action for each orifice. A removable and replaceable dot mask plate having a pattern of holes is sandwiched between a body and a back plate of the printhead and certain of the plungers of the solenoids are aligned with holes in the dot mask and, in a forward extended position, extend through the holes to engage the membrane. The dot mask masks or blocks other plungers of the printhead.

Claims

1. A printhead for ink jet printing apparatus comprising a body having a front face and a back face, a chamber in the body for ink under pressure, a plurality of ports extending from the chamber to the back face of the body, each of said ports having a back end at the back face of the body, a plurality of recesses, one for each of said ports, in the back face of the body adjacent but spaced from said back end of the port, a plurality of passages, one for each recess, each of said passages extending forward from a recess through the body toward the front of the body, a plurality of orifices at the front face of the body, one orifice for each of said passages, each of said passages extending forward through the body to an orifice for delivery of ink from the orifices onto a target surface moving relative to the body past said front face of the body, a flexible membrane on said back face of the body engageable therewith all around the back end of each of said ports and each of said recesses, and means for releasably holding the membrane in position pressed against the back face of the body around the back end of each of said ports to block flow of ink from said chamber out of the back end of each of said ports, said holding means comprising a plurality of solenoids, one for each of said ports, each of said solenoids comprising an electromagnetic coil having an axis, a forward end, a rearward end, a plunger movable within the coil on the axis of the coil and spring means for biasing the plunger in a forward direction, said plunger having a free end adjacent the said forward end of the solenoid constituting the forward end of the plunger, said plunger being movable axially within the coil of the solenoid between a forward extended position wherein said plunger extends forward from the forward end of the solenoid and a rearward retracted position spaced rearward from said forward extended position, the plunger being movable rearward against said spring bias on energization of the coil, means for mounting the solenoids in position at the back face of said body with the axis of each of said solenoids and each of said plungers generally aligned with a respective port of said plurality of ports and with the forward end of each of said solenoids proximate said membrane, each of the solenoids being so positioned at the backface of said body and each of the plungers being so disposed in the coil of the solenoid that when the coil of the solenoid is deenergized the plunger is in extended position with said free end of said plunger engaging the membrane and holding the membrane pressed under the bias of said spring means against the back face of the body around the back end of the respective port of said plurality of ports to block flow of ink out of the back end of the port, and when the coil is energized the plunger is retracted to release the membrane for flexing away from the back end of the respective port of said plurality of ports for delivery of ink therefrom, wherein the membrane has a front face in engagement with the back face of said body and a back face, wherein the printhead has a masking plate on the back face of the membrane, said masking plate having holes therein in a pattern for alignment with certain of the ports in the body, wherein said body has a predetermined thickness and the solenoid mounting means comprises a back plate of substantially greater thickness than that of said body removably assembled with the body at the back face of the body with the membrane and the masking plate sandwiched between the body and said back plate, said back plate having a plurality of holes therein, one for each of said ports, each of said holes in said back plate being aligned with a said respective port of said plurality of ports, each of said solenoids being mounted in a respective hole of said plurality of holes with the plunger of each of said solenoids movable toward and away from the back face of the membrane aligned with the back end of the said respective port, each of said plungers being biased in said forward direction by the spring means therefor, certain of said plungers being aligned with the holes in said masking plate and in the forward extended position thereof extending through the respective hole of said plurality of holes in the masking plate and engaging the membrane through said respective hole of said plurality of holes in the masking plate to press the membrane against the back face of the body around the said respective port of said plurality of ports to block flow of ink out of the back end of the port, the plunger being retracted on energization of the coil to release the membrane for flexing away from the back end of the said respective port of said plurality of ports for delivery of ink therefrom to the respective recess of said plurality of recesses, and thence through the respective passage of said plurality of passages to and out of the respective orifice of said plurality of orifices, said masking plate being removable and replaceable with another masking plate having a different pattern of holes.

2. A printhead as set forth in claim 1 wherein each of the solenoids comprises an elongate casing having an axis extending lengthwise thereof, the coil of the solenoid being received in the casing coaxially therewith, the plunger of the solenoid being movable axially with respect to the coil and casing into and out of one end of the casing constituting the forward end of the casing, said spring means being interconnected between the casing and the plunger within the casing and biasing the plunger to move in said forward direction out of said forward end of the casing, each of said solenoids having the casing thereof fitted in a respective hole in the back plate with said forward end of the casing at the front end of said respective hole.

3. A printhead as set forth in claim 2 wherein, as to each solenoid, the coil is wound on a bobbin having a tubular barrel having opposite ends and flanges extending outwardly at said ends of the barrel, the flanges fitting in the casing, the flange at one end of the barrel constituting a forward flange and the flange at the other end of the barrel constituting a rearward flange.

4. A printhead as set forth in claim 3 wherein, as to each solenoid, the casing has a head at said forward end thereof toward the body, the plunger being axially movable in an opening in said head and in the tubular barrel of the bobbin.

5. A printhead as set forth in claim 4 wherein, as to each solenoid the bobbin is received in the casing with said forward flange thereof adjacent the head of the casing, said forward flange having an annular rim projecting toward and engaging the head of the casing.

6. A printhead as set forth in claim 5 wherein, as to each solenoid, the spring means comprises a washer-type spring having a periphery and a center held at said periphery thereof between said annular rim and said head of the casing and interconnected at said center thereof with the plunger.

7. A printhead as set forth in claim 6 wherein said washer-type spring comprises a peripheral ring and spring fingers extending radially inwardly from the ring, the plunger having an annular groove, the fingers having inner ends received in the groove.

8. A printhead as set forth in claim 7 wherein the barrel has an internal diameter and the plunger, where movable in the barrel, is of circular cross-section of smaller diameter than the internal diameter of the barrel and the spring fingers are of equal length so as to center the plunger in the barrel for anti-friction purposes.

9. A printhead as set forth in claim 8 wherein said annular rim projects toward and has an outer end engaging the head of the casing, said rim having an internal annular recess at said outer end thereof, said washer-type spring having the periphery thereof received in said internal annular recess.

10. A printhead as set forth in claim 3 having a magnetic core in the barrel of the bobbin.

11. A printhead as set forth in claim 10 wherein the magnetic core comprises a stem extending axially in the barrel of the bobbin from the end of the barrel opposite the head of the casing, the stem having a flange thereon at the back end thereof engaging the rearward flange of the bobbin.

12. A printhead as set forth in claim 11 wherein, as to each solenoid, the casing has a back end and is open at said back end and the solenoid has terminals for the coil extending back out of the back end of the casing.