Non-sequential Symbol Generation System For Fluid Jet Printer

Abstract

A fluid jet printing system includes a vibrating nozzle for emitting a stream of fluid which is broken into a series of uniform drops. The drops are charged by a voltage which is generated from a symbol code input by a symbol generator which produces a charging voltage representation for each drop of each symbol to be printed. The symbol generator includes a symbol storage means having stored in each location a representation of the charging voltage to be applied to each fluid drop. Deflection electrodes which supply an electric field for the purpose of deflecting charged fluid drops are positioned at an angle with respect to a base line for a row of symbols to provide greater flexibility and more accurate placement of fluid drops on a record media surface.

Description

BACKGROUND OF THE INVENTION

The present invention relates to apparatus for controlling a fluid jet printer and more particularly to apparatus for generating symbols to be printed by a fluid jet printer.

In the prior art, symbol generators for fluid jet printers have included symbol matrices which were scanned sequentially to produce a video signal used to control the charging of fluid drops in the printing apparatus. The information stored in the sequentially scanned matrix was a binary value which indicated whether a particular spot in the symbol matrix was to be printed (unblanked) or not (blanked). The sequential binary video signal produced from the prior art symbol generators was combined with a ramp voltage signal in such a manner that a charging voltage was produced for each video print signal with a charging voltage magnitude determined by the instantaneous value of the ramp voltage signal.

The sequential scanning of the symbol matrix of prior art systems limits the flexibility of print drop placement to a small, fixed number of locations in a normally rectangular matrix. This limitation results in unsatisfactory printing of symbols employing diagonal lines or graphics.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to efficiently control the printing of symbols.

It is another object of the present invention to increase printing speed in a fluid jet printer including a non-sequential symbol generator.

It is yet another object of the present invention to increase fluid drop utilization in a fluid jet printer.

A still further object of the present invention is to increase the number of possible fluid drop positions on a record medium in a fluid jet printer having a non-sequential matrix symbol generator and having a pair of deflection electrodes precisely positioned.

To achieve the foregoing objects, a fluid jet printing system includes a fluid drop emitting subsystem including fluid supply, pump, nozzle, and means for vibrating the nozzle to form uniform fluid drops; a non-sequential symbol generation means for converting a symbol code input into a series of voltage signals to be applied to an electrode to charge individual fluid drops to a potential representative of the print position in a given symbol; and a deflection means positioned at an angle so as to provide a greatly increased number of possible print positions for a given symbol.

It is an advantage of the present invention that possible drop locations are increased by a factor of 10 to 1 over prior art fluid jet printers.

Another advantage of the present invention over the prior art is that the record medium may be transported at a speed twice as fast as the prior art.

A still further advantage of the present invention is that greater precision can be obtained in printed symbols since separation between available print positions is decreased.

Yet another advantage of the present invention over the prior art is the elimination of "guard drops" used to compensate for drop interaction.

Still another advantage of the present invention is the capability of printing a wide variety of symbols, character sets and limited graphics.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

FIG. 1 is an isometric diagram of a fluid jet printing apparatus with deflection electrodes positioned according to the present invention.

FIG. 2A is a block diagram of apparatus for converting an input symbol code to a charging electrode potential.

FIG. 2B is a block diagram showing the logic elements of a non-sequential symbol generator according to the present invention.

FIG. 2C is a chart showing the magnitude in decimal and binary notation for the charging voltage to be applied to each fluid drop necessary to form the symbol 8.

FIG. 3A is a representation of a simbol 8 showing the placement of each fluid drop.

FIG. 3B is a diagram showing the relative displacement of each drop necessary to form the symbol 8 as a function of the binary coded voltage representation.

FIG. 3C is a schematic representation showing the positioning of a symbol 8 on a record medium relative to the angle of the deflection electrodes.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a fluid jet printing system is shown including the present invention. In fluid jet printing system 100, fluid from reservoir and pump 114 is transmitted under pressure through tube 112 to nozzle 110. A nozzle actuator transducer 120 which is driven by a transducer driver 122 vibrates nozzle 110 causing the fluid stream 102 to be broken into a uniform series of droplets 104. A charging electrode 130 surrounds the fluid stream at about the point of droplet separation. The charging electrode charges each droplet to a potential determined by data source 132 which drives the charging electrode 130. The charged droplets pass through an electric field which is created between deflection electrodes 140. The deflection electrodes generate a constant electric field due to an applied potential. The fluid droplets are deflected while moving through the electric field formed by deflection electrodes 140 an amount dependant upon the applied charge for each droplet. For those droplets which are not to be printed, a charge is applied which will cause them to strike gutter 150 which returns the fluid to reservoir 114.

Referring also to FIG. 3C, it should be especially noted that deflection electrodes 140 are mounted at an angle to the direction of record medium motion as shown by the arrow in FIG. 1. The selected angle .PHI. (FIG. 3C) is adjusted to allow the maximum usage of fluid droplets for printing and avoid the need for guard drops or other means of compensation. In a preferred embodiment, the angle .PHI. may be in the range of 20.degree. to 30.degree. depending primarily on paper speed, drop separation and drop size.

Referring now to FIGS. 2A and 2B, the data source and symbol generation means will be described. A symbol code input representing a symbol to be printed is presented to symbol code buffer 310. Symbol code buffer 310 provides temporary storage for the symbol code to enable synchronization of the input symbol code data with a drop formation clock (not shown).

The symbol code data is presented to symbol generator 320 which is shown in greater detail in FIG. 2B.

The symbol code contains n parallel bits, which for example, in a symbol font having less than 64 symbols might be a six bit parallel data path. The symbol code is decoded by symbol decode means 322 which has as a first output an address of a location in symbol storage means 326 in which is stored the binary representation of the charging voltage to be applied to the first fluid drop to be printed for the symbol decoded. This address is loaded into address counter 324 which controls the addressing of symbol storage means 326 via lines 323.

A second output of symbol decode means 322 is connected to symbol drop count decode means 327 to set the symbol drop count to the number of fluid drops to be printed for the particular symbol decoded.

It should be noted that different symbols of the same symbol font will be formed of a different number of fluid drops. For example, referring to FIG. 2C it can be seen that the symbol 8 is formed of 14 drops. Some symbols may require less than 14 drops and some symbols may require many more than 14 drops. Therefore, for most efficient use of the symbol storage matrix 326 the drop count is used to control the resetting of address counter 324 to eliminate unnecessary storage access cycles.

It should be noted, referring to FIG. 2B that symbol storage means 326 is a three-dimensional matrix having K symbol locations where K is the number of symbols in a particular font, each of which contain L fluid drops to be printed where L is variable depending upon the symbol to be printed, with m bits for each storage location representing the charging potential to be applied to a particular drop in a symbol.

The output of symbol storage means 326 which is m bits in parallel is applied to symbol video code buffer 328 which provides a temporary storage of the charging voltage representation for a particular drop to be printed.

Referring again to FIG. 2A, the output of symbol generator 320 which is also the output of symbol video code buffer 328 is connected to video decoder 330 which converts the binary digital charging voltage representation into an analog voltage signal which is amplified by video amplifier 340 which in turn is connected to charging electrode 130 (see FIG. 1).

It should be especially noted that the symbol storage means 326 (FIGS. 2B) contains information regarding the exact charging potential for each of the L drops for each of K symbols.

Referring now to FIGS. 2C, 3A, 3B and 3C, the printing of a representative symbol 8 will be described.

FIG. 2C shows the decimal and binary code representations of the charging voltage to be applied to each of the 14 drops to be printed for the symbol 8. For example, drop L1 has a decimal code voltage representation of 2 and a binary code voltage representation of 010. Referring now to FIG. 3B, it can be seen that drop L1 is positioned 2 voltage units above a base line. The other drops required to form the symbol 8 are similarly positioned a number of voltage units above a base line determined by the binary code representation as shown in FIG. 2C. Referring now to FIGS. 3A and 3C, the purpose and function of positioning deflection electrodes 140 at angle .PHI. will be explained.

Deflection electrodes 140 are positioned at an angle of approximately 26.5.degree. relative to the motion of the record medium. In FIG. 3A, it can be seen that each fluid drop follows a path which is along a line of (90 - .PHI.).degree. from a base line. Each fluid drop may be positioned at any location along the dotted line indicated in FIG. 3A as determined by the binary voltage representation. Thus, taking drop L8 as an example, that fluid drop could be positioned at any one of 7 positions along that dotted line as determined by the binary code which was contained in the appropriate location of symbol storage means 326. This is in contrast to the prior art symbol generation techniques in which the only information stored in a symbol storage matrix was the presence or absence of a drop to be printed in a line scan sequential manner.

It can be seen, therefore, that the present invention enables a greater flexibility in the printing of symbols than does the prior art. Further, no drop interaction compensation is required since the effects of drop interaction can be considered in assigning the binary representation for the charging voltage to be applied to each fluid droplet to be printed. Therefore, guard drops can be eliminated and every drop emanating from nozzle 110 (see FIG. 1) can be utilized for printing.

The net result of the improvements due to the present invention are that although the storage requirement is increased by a factor of slightly more than 2.0, the number of possible drop locations on the printing surface has increased by greater than 10 times and the paper speed may be increased by a factor of two.

While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. In a fluid jet printer having fluid reservoir means, fluid jet means, transducer means for vibrating said fluid jet to produce a stream of fluid droplets, means for applying a charging voltage to individual ones of said droplets, and record means for receiving the droplets thereon, in combination therewith;

means for generating a charging voltage signal representative of the print position for each fluid droplet of each symbol, said means comprising:

storage means having prestored therein individual droplet charging voltages represented as digital values, the magnitude of said digital values being time-independent values with respect to each of a plurality of droplets for each symbol in a set of symbols;

decode means connected to said storage means and responsive to a symbol code input signal for addressing said storage means to read out in sequence said stored digital values for each droplet of one of said pluralities for said symbol code; and

converting means connected to the output of said storage means for converting each said digital value in said sequence into an analog charging voltage signal for an ink droplet, with each charging voltage signal being independent of charging voltage signals applied to a preceding or succeeding droplet in said stream of fluid droplets; and

means for deflecting each said droplet according to the charge thereon, said deflection means being arranged so that said droplets are deflected along a path angularly disposed with respect to the relative motion of said record means and fluid jet means an amount determined in part by the maximum number of drops used in a symbol of said set.

2. Apparatus according to claim 1 further comprising means for counting the number of drops to be printed for each symbol to achieve maximum utilization of said storage means.

3. Apparatus according to claim 1 further comprising oscillator means, connected to said means for generating a charging voltage signal, for synchronizing generation of said charging voltage signals with emission of fluid droplets from said fluid jet to insure that the correct charge is applied to each fluid droplet.