The present invention relates to ink jet printing and in particular discloses a planar thermoelastic bend actuator ink jet printer.
The present invention further relates to the field of drop on demand ink jet printing.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207 to 220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electrostatic ink jet printing.
U.S. Pat. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electrothermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
According to the invention there is provided an ink jet nozzle assembly including a nozzle chamber having a nozzle, the chamber including a movable portion configured for movement to effect ejection of ink from the chamber via said nozzle, the assembly further including an actuator attached to or formed integrally with the movable portion, the actuator having an electrically conductive portion and an electrically resistive portion such that upon passing a current through both said portions, said actuator is caused to deform elastically to effect said movement of said movable portion.
Preferably said electrically conductive portion and said electrically resistive portion are respective surfaces of a thermal actuator arm.
According to the invention there is further provided an ink jet nozzle assembly including:
a nozzle chamber having an inlet in fluid communication with an ink reservoir and a nozzle through which ink from the chamber can be ejected;
a chamber including a fixed portion and a movable portion, relative movement between the fixed portion and the movable portion in an ejection phase reducing an effective volume of the chamber, and alternate movement in a refill phase enlarging the effective volume of the chamber; and
a thermal actuator to eject ink from said nozzle chamber via said nozzle, said thermal actuator comprising a lower planar surface constructed from a highly electrically conductive material interconnected to an upper planar surface constructed from an electrically resistive material such that upon passing a current between said planar surfaces, said thermal actuator is caused to bend so as to effect movement of said movable portion and cause ink to be ejected through said nozzle.
Preferably the movable portion includes the nozzle and the fixed portion is mounted on a substrate.
Preferably the fixed portion includes the nozzle mounted on a substrate.
Preferably said actuator is attached to a substrate and further includes a stiff paddle portion which increases bending of said actuator near a point where it is attached to the substrate.
Preferably said stiff paddle is formed of silicon nitride.
Preferably said actuator further includes an expansion coating having a high coefficient of thermal expansion on top of said upper planar surface so as to increase bending of said actuator.
Preferably said expansion coating comprises substantially polytetrafluoroethylene.
Preferably between said upper planar surface and said lower planar surface there is provided a gap, formed upon etching away of a deposited sacrificial material.
Preferably said upper planar surface includes a plurality of etchant holes provided so as to allow a more rapid etching of said sacrificial layer during construction.
Preferably said upper planar surface comprises substantially Indium Tin Oxide (ITO).
Preferably said lower planar surface comprises substantially metal.
Preferably said upper and lower surfaces are further coated with a passivation material.
Preferably said nozzle is formed on a silicon wafer using micro-electro mechanical systems construction techniques.