Abstract: A hydraulic circuit and related method are provided for dynamically varying the pressure of ink supplied to an ink jet printer head to obtain consistent volume ejected ink drops despite differences in the time elapsing between successive drops. A dot rate command signal related to an actuation frequency and corresponding to the pressure of ink at the head necessary for producing an ejected drop having a desired volume is compared with the ink pressure at the head to produce a pressure control signal for varying the pressure of the ink in a variable volume fluid chamber to deliver ink to the head at the desired pressure. The pressure control signal is one chosen by experiment as that required to produce the desired ink drop volume for the specific ink supply and ink jet printer head employed.

Abstract: Image processing apparatus for increasing the gray scale resolution of a graphic generated by an ink jet printing system wherein the graphic is made up of pixel areas on a receiving surface and each pixel area is comprised of a fixed number of potential dot positions printed with substantially equal sized dots. A sequential series of image density signals representative of the gray scale color intensity is generated from an original graphic and converted to a dot level value for each pixel. A pixel's dot level value is compared to a set of integer and non-integer values and pixels having dot level values falling between the same two successive integer values are selected. A predetermined dot level value is alternately added to the identified adjacent pixels so that one is increased and the other is decreased by the predetermined dot value. The resulting values are rounded off to the nearest integer and each pixel is printed with its respective new value.

Abstract: An ink jet head for ejecting drops of ink in an ink jet printing system is designed for easy disassembly for cleaning and can readily be made in different sizes including one capable of ejecting relatively large volume drops of heavily pigmented and relatively viscous ink as may be used for printing outdoor billboards or other large scale graphics. The head also includes a means for reducing the size of or entirely eliminating any blob of ink which may form over the ejection port at low actuating frequencies, thereby making the velocity and other characteristics of the ejected drops more uniform over the full range of operating frequencies.

Abstract: A circuit and related method are provided for maintaining a desired spacing between an ink-jet printing means and a receiving surface along a line scanned by the printing means. An ultrasonic transducer transmits signals at timed intervals to the receiving surface from the printing means. A reflected signal from the receiving surface is sensed by the transducer during a receiving time window after the signal is transmitted. A reference position signal representative of the head to surface spacing at a printing location is compared to the desired head to surface spacing to produce a position error signal. A servomotor responds to the position error signal to move the printing means toward and away from the receiving surface to maintain the desired spacing.

Abstract: Ink jet printing apparatus is provided for vertically randomizing the flight paths of ink drops ejected from an ink jet printing head to print dots at positions randomly deviated vertically with respect to a line scanned by the printing head. Ejected ink drops are passed through an electric field having a randomly varying intensity and direction to randomly deflect the ink drop flight path with respect to a line scanned by the printing head.

Abstract: A circuit and related method are provided for driving an ink jet printer to achieve a consistent velocity of ejected ink drop despite differences in the time elapsing between successive drops. Timing pulses timing the ejection of drops each trigger the production of a fundamental waveform. This waveform is then multiplied by a multiplying factor selected from a look-up table in response to the time elapsing between the timing pulse causing the generation of the waveform and the preceding timing pulse, and the modified waveform so produced is used to drive the printing head through a power amplifier. The multiplying factor is one chosen by experiment as that required to produce the desired ink jet velocity. In a preferred embodiment both the fundamental waveform and the multiplying factor may each be obtained through the use of an associated PROM so that the waveform shape and multiplying factor versus dot frequency characteristic may be readily changed to suit the particular printer head in question.

Abstract: An ink jet printing system suited to the making of large scale graphics, such as outdoor billboards, includes an endless carrier for moving a plurality of rigid flat panels, onto which a graphic is to be printed in sections, repetitively past an ink jet printing station. At the printing station each panel moves in purely rectilinear fashion in a direction parallel to its ink drop receiving face so that such face remains essentially at a uniform spacing from the ink jet printing heads of the printing station as the printing occurs. A means for timing the operation of the ink jet heads takes into account irregularities or changes in the motion of the panels past the printing station so that the ink drops are correctly placed despite such irregularities or changes. The ink jet heads can eject relatively large drops of pigmented ink.