Ink Reconstitution System and Method for Ink Drop Printer

The problem of maintaining a proper consistency of the constituents in printing in ink drop printing systems, has been recognized in the art. Various schemes have been proposed and used for reconstituting the ink by adding solvents and the like, to compensate for loss of such solvents by evaporation in the printing ink which is collected and returned to the printing ink supply system. Most of the prior approaches either guess at or estimate the amount of solvent to be added from time to time, based upon an estimated exposure of the printing ink to the process of evaporation, or provide complex systems which depend for their operation upon the measurement of some parameter of the printing ink, such as by measuring the velocity of propagation of sound through the material, by measuring the specific gravity, or by measuring the conductivity. Inherently, the latter systems are necessarily complex.

The non-automatic systems, that is the systems which blindly add predetermined quantities of replenisher, have generally failed to take into account the fact that the system may need greater or lesser quantities of replenisher, depending upon the character of the material being printed. During the operation of an ink jet printer, it is known that the volume of ink in the principal supply system will gradually decrease as the ink drops are deposited on the printing receiving medium. Ideally, the volume lost in this matter is compensated for by the addition of fresh ink into the principal ink supply system. Further fluid loss results from evaporation of solvents from the ink. Since the fluid supply systems are generally closed, most of this evaporation occurs between the time that the drops leave the printhead and are caught by the catcher. If no printing were being accomplished, and all of the drops were being caught and returned to the ink system, the fluid loss would be entirely due to solvent evaporation, and the addition of a solvent or suitably constituted replenisher would be appropriate. On the other hand, if all of the drops produced by the printhead were being deposited on a print receiving medium, such as paper, none of the fluid would be lost as a result of evaporation and it would therefore be desirable to make this fluid loss up only by the addition of fresh ink. In actual operation, however, the fluid loss is a combination of both of these factors. Hitherto, blind or mechanical reconstituting systems have been incapable of distinguishing between conditions where the loss of fluid is primarily due to printing or primarily due to evaporation, and hence the more complex systems controlled by parameter measurements have come into being.

This invention is directed to a simplified system and method for replenishing or reconstituting printing ink in an ink jet printer, which operates only with ink withdrawn from the ink catcher and therefore only with ink which has been subject to essentially a single exposure to the atmosphere, and adds a predetermined amount of such replenisher to such exposed fluid prior to returning the exposed fluid plus replenisher to the principal source of printing ink in the system.

The method and apparatus of this application has the advantage of providing a uniform ink composition regardless of the amount of ink that is being caught by the catchers at any one time and returned to the system.

The present invention is an improvement over such prior systems which simply estimate the amount of solvent and the amount of fresh ink necessary for addition to the fluid system. In the present invention, the ink which is received from the catcher is delivered to a reconstitution reservoir or tank. Initially, the fluid level in the reservoir is low and is detected by a level sensor. A fixed or predetermined quantity of replenisher or solvent is then added to the reservoir. As the printer continues to operate, gradually additional ink from the catchers will accumulate in this reservoir until the fluid reaches a second or higher level which is detected by a second level sensor. Now the ink from the reconstitution reservoir, consisting solely of ink from the catcher which has been subject to evaporation and a fixed or measured quantity of replenisher, is returned to the principal ink supply reservoir and mixed with the fresh ink therein. This transfer or pumping action occurs until the fluid level in the reconstitution reservoir is lowered to the first or lower level. At this time, the cycle the repeats itself.

In the apparatus and method of this invention, since all of the ink from the catcher has been exposed to atmosphere, it can accurately be assumed that the only loss in fluid volume with respect to this portion of the ink, is a loss due to evaporation. Since this quantity between the low and high fluid level is a fixed quantity, and since the evaporation conditions are generally known, the amount of loss can be accurately predicted and made up by the application of solvent at this point.

It is accordingly an important object of the invention to provide a simplified yet effective apparatus and method for making up solvent losses in an ink supply system for an ink drop printer.

A further object of the invention is the provision of an ink supply system, as outlined above, where all of the ink from a collector is diverted to a reconstitution reservoir, in which predetermined or metered quantities of make-up fluid, such as solvent, are added in accordance with predetermined volumes of the returning ink, to provide a direct correlation between the volume of returning ink, and the volume of added solvent to compensate for evaporative loss.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

The drawing schematically represents an ink supply and reconstitution system in accordance with this invention.

Referring to the figure of the drawing which illustrates a preferred embodiment of the invention, an ink jet print head is diagrammatically illustrated generally at 10 as including an ink manifold or applicator bar 11 and a catcher 12. The catcher 12 will collect substantially all of the ink drops which are not deposited on a medium being printed by the printer. For details regarding the construction of print head 10 reference may be made to Paranjpe, U.S. Pat. No. 4,085,409.

Means for supplying ink under a positive and regulated head of pressure to the applicator bar 11 includes a main reservoir 15 of ink. The reservoir 15 may be maintained at a general predetermined level or volume by make-up additions from a principal ink supply 16. The reservoir 15 may, for example, consist of be a float controlled vacuum tank device which will automatically maintain a predetermined level of ink, and will draw its make-up needs from the principal supply 16 of fresh ink, with the transfer being vacuum assisted by means of the vacuum line 18. A fresh ink addition valve 19 may be interposed in the line between the ink supply 16 and the main reservoir or tank 15 which may be manually or automatically operated, or may be omitted in lieu of an automatic level maintenance system, such as a float operated vacuum tank reservoir as previously noted.

Means for supplying ink from the reservoir 15 to the printer 10 includes a pump 20, and means for maintaining pressure regulation includes a pressure regulator valve 22 between the outlet of the pump 20 and a return line 23. The ink application system shown is the constant flow type and therefore ink from the reservoir 15 under a predetermined head, as maintained by the regulator valve 22, is applied to the bar 11, and the ink not used flows through the bar and returns by a line 24 to the return line 23 for return to the reservoir 15.

In accordance with this invention, all of the ink collected by the catcher 12 is delivered to a temporary holding tank in the form of a reconstitution reservoir 25. The reservoir 25 incorporates means defining low and high liquid positions, and for this purpose preferably incorporates liquid level responsive switches which, for example, may be float operated. In any event, the reservoir incorporates a first switch 28 which defines a predetermined low fluid position and a second switch 29 which defines the high fluid position. Obviously the quantity of fluid between the respective low and high limit positions is a known and fixed quantity.

Means for withdrawing fluid from the reconstitution reservoir 25 for delivery to the main reservoir 15 includes an ink return pump 30, the output of which is connected by a line 32 to the return line 23. The pump 30 is controlled by the respective lower and limit switches 28 and 29 so that the occurrence of a liquid level at the upper limit 29 operates to start the pump 30, and the occurrence of a liquid level at or below the lower limit 25 operates to terminate the operation of the pump 30.

The invention includes means for adding a predetermined amount of reconstitution or replenisher fluid, primarily solvent, to the reservoir 25, in a cyclic manner, so that the quantity of such replenisher is volumetrically related to the working volume of fluid in the reservoir 25 between the upper and lower limits. For this purpose there is provided a source or supply 35 of such reconstitution fluid. A controlled metering or delivery valve 36 is connected in a line 38 between the source 35 and the tank 25. Each operation of the valve 36 permits a predetermined quantity of fluid from the source 35 to be added to the reservoir 25, which is under vacuum from a branch 39 of the line 18. Accordingly, the valve 36 may simply be a time controllable valve which opens for an adjustable or predetermined time to permit a predetermined quantity of replenisher to pass through or may consist of a single cycle position displacement diaphragm or piston pawl which operates in a cycle of operation to inject a fixed quantity of replenisher to pass therethrough. The valve 36 is operated in timed relation to the filling an emptying of the tank by the pump 30.

The operation of the apparatus and method of this invention is largely self-evident from the foregoing description. During the jetting or printing operation, the ink is applied to ink bar 11 by the pump 20, which pump also recirculates ink back to the main ink reservoir 15 to control the pressure at the bar.

During the jetting or printing process, solvents are lost to evaporation, which, depending upon the character of the material being printed, may result to as much as 10-20% of the fluid level. The ink which is not printed but is caught in the catcher 12, is pulled by vacuum to the reconstitution reservoir 25 by vacuum applied to the vacuum line 18. It will be understood that the quantity of ink in the tank 25 will gradually increase from the low limit position of the switch 28 to the high limit position defined by the switch 29. This defines a known volume, and when the switch 29 is activated, pump 30 delivers this quantity of fluid back to the main reservoir 15. It is understood that the reservoir 15 has sufficient capacity to accept this return ink at any given time. When the ink level is drawn down to the position of switch 28, the operation of this switch not only shuts off pump 30, but it also activates valve 36 to deliver a predetermined quantity of the reconstitution fluid from the source 35 through a line 40 to the reservoir 25. This insertion of reconstitution fluid is preferably at the low level of the receiver 25 in order that mixing of the same with the ink from the catcher 12 can be accomplished during the refilling operation.

It will thus be seen that the amount of replenisher from the source 35 is dependent only upon the amount of ink being returned to the system by the catcher, and therefore dependent only upon the amount of ink which has been subject to an evaporative process. Thus, by adding a fixed amount of replenisher to this quantity of recirculated ink, the overall consistency and quality of the ink may be maintained regardless of whether a substantial or insubstantial quantity of ink is actually being applied by the printer to the medium being printed. In a broader sense, the invention contemplates volumetrically measuring, in discrete quantities or increments, all of the ink gathered by the collector, and then inserting into the ink supply system predetermined or discrete amounts of a reconstituting liquid or replensiher corresponding to or concurrently with each such increment of collector ink being measured, and preferably inserting replenisher dirctly into the discrete quantity and mixing the same, so that when the collected ink is returned to the primary ink source it has already been fully constituted.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.