Ink jet apparatus

This application is a continuation of application Ser. No. 10/365,117, filed Feb. 11, 2003 now U.S. Pat. No. 6,739,690, which is incorporated herein by reference.

Drop on demand ink jet technology for producing printed media has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an ink jet image is formed by selective placement on a receiver surface of ink drops emitted by a plurality of drop generators implemented in a printhead or a printhead assembly. For example, the printhead assembly and the receiver surface are caused to move relative to each other, and drop generators are controlled to emit drops at appropriate times, for example by an appropriate controller. The receiver surface can be a transfer surface or a print medium such as paper. In the case of a transfer surface, the image printed thereon is subsequently transferred to an output print medium such as paper.

A known ink jet drop generator structure employs an electromechanical transducer to displace ink from an ink chamber into a drop forming outlet passage, and it can be difficult to control drop velocity and/or drop mass.

FIG. 1 is a schematic block diagram of an embodiment of a drop-on-demand drop emitting apparatus.

FIG. 2 is a schematic block diagram of an embodiment of a drop generator that can be employed in the drop emitting apparatus of FIG. 1 .

FIG. 3 is a schematic depiction of an embodiment of a drive signal that can be employed to drive the drop generator of FIG. 2 .

FIG. 4 is a schematic depiction of another embodiment of a drive signal that can be employed to drive the drop generator of FIG. 2 .

FIG. 1 is a schematic block diagram of an embodiment of a drop-on-demand printing apparatus that includes a controller 10 and a printhead assembly 20 that can include a plurality of drop emitting drop generators. The controller 10 selectively energizes the drop generators by providing a respective drive signal to each drop generator. Each of the drop generators can employ a piezoelectric transducer. As other examples, each of the drop generators can employ a shear-mode transducer, an annular constrictive transducer, an electrostrictive transducer, an electromagnetic transducer, or a magnetorestrictive transducer. The printhead assembly 20 can be formed of a stack of laminated sheets or plates, such as of stainless steel.

FIG. 2 is a schematic block diagram of an embodiment of a drop generator 30 that can be employed in the printhead assembly 20 of the printing apparatus shown in FIG. 1 . The drop generator 30 includes an inlet channel 31 that receives ink 33 from a manifold, reservoir or other ink containing structure. The ink 33 flows into a pressure or pump chamber 35 that is bounded on one side, for example, by a flexible diaphragm 37 . An electromechanical transducer 39 is attached to the flexible diaphragm 37 and can overlie the pressure chamber 35 , for example. The electromechanical transducer 39 can be a piezoelectric transducer that includes a piezo element 41 disposed for example between electrodes 43 that receive drop firing and non-firing signals from the controller 10 . Actuation of the electromechanical transducer 39 causes ink to flow from the pressure chamber 35 to a drop forming outlet channel 45 , from which an ink drop 49 is emitted toward a receiver medium 48 that can be a transfer surface, for example. The outlet channel 45 can include a nozzle or orifice 47 .

The ink 33 can be melted or phase changed solid ink, and the electromechanical transducer 39 can be a piezoelectric transducer that is operated in a bending mode, for example.

FIGS. 3 and 4 are schematic diagrams of embodiments of a drive drop firing signal or waveform 51 that is provided to the printhead during a firing interval T to cause an ink drop to be emitted. The time varying drop firing waveform 51 is shaped or configured to actuate the electromechanical transducer such that the drop generator emits an ink drop. By way of illustrative example, the firing interval T can be in the range of about 56 microseconds to about 28 microseconds, such that the drop generator can be operated in the range of about 18 KHz to about 36 KHz. As another example, the firing interval T can be in the range of about 1000 microseconds to about 28 microseconds, such that the drop generator can be operated in a range of about 1 KHz to about 36 KHz.

By way of illustrative example, the drop firing waveform 51 can be a bi-polar voltage signal having in sequence a first negative pulse component 61 , a positive pulse component 71 , and a second negative pulse 62 component. The pulses are negative or positive relative to a reference such as zero volts. Each pulse is characterized by a pulse duration DN 1 , DP, DN 2 which for convenience is measured between the pulse transition times (i.e., the transition from the reference and the transition to the reference). Each pulse is also characterized by a peak pulse magnitude MN 1 , MP, and MN 2 which herein is a positive number.

The first negative pulse 61 can have a duration DN 1 in the range of about 5 microseconds to about 10 microseconds. The positive pulse 71 can have a duration DP in the range of about 7 microseconds to about 14 microseconds. The second negative pulse 62 can have a duration DN 2 in the range of about 3 microseconds to about 8 microseconds. In this manner, the positive pulse 71 can have a duration that is greater than the duration DN 1 of the first negative pulse 61 and greater than the duration DN 2 of the second negative pulse 62 . The duration DN 1 of the first negative pulse 61 can be less than or greater than the duration DN 2 of the second negative pulse 62 . The durations DN 1 , DN 2 of the first and second negative pulses 61 , 62 can be similar.

The first negative pulse 61 can have a peak magnitude MN 1 in the range of about 20 volts to about 35 volts. For example, the peak magnitude MN 1 of the first negative pulse 61 can be less than 30 volts. The positive pulse 71 can have a peak magnitude MP in the range of about 30 volts to about 45 volts. For example, the peak magnitude MP of the positive pulse 71 can be less than about 40 volts. The second negative pulse 62 can have a peak magnitude MN 2 that is in the range of about 30 volts to about 45 volts. For example, the peak magnitude MN 1 of the first negative pulse 61 can be less than 40 volts. The first negative pulse 61 can have a peak magnitude MN 1 that is less than the peak magnitude MP of the positive pulse 71 and is less than the peak magnitude MN 1 of the second negative pulse 62 .

By way of illustrative examples, the first negative pulse 61 can be generally trapezoidal ( FIG. 3 ) or generally triangular (FIG. 4 ). Other shapes can be employed.

The first negative pulse component is a pre-pulse that adds energy to the jet, which can reduce the peak magnitude MP of the positive pulse 71 and can reduce the peak magnitude MN 2 of the second negative pulse 62 . The portion of the positive pulse that has a non-negative slope causes the ink chamber to fill while the negative going portion of the positive pulse causes a drop to be emitted.

The first negative pulse can be timed so that its energy will add constructively with the positive pulse. The magnitude of the first negative pulse is preferably configured such that it does not cause a drop to be emitted. The magnitude of the first negative pulse can also be configured such that it does not cause air to be ingested into the jet.

The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.