Abstract:
A system for flushing ink residue from a fluid system is provided for use with a continuous ink jet print station. Ink is rapidly drained from the fluid system, and the fluid system is refilled with a flush fluid. The flow of flush fluid is directed through all fluid system components which normally contain ink. Subsequently, the flow of flush fluid can be diverted to a waste tank rather than re-circulated into the ink tank.

Description:
TECHNICAL FIELD 
     The present invention relates to the field of continuous ink jet printing and, more particularly, to the flushing of one ink from a fluid system when replacing it with one of a different color or chemistry. 
     BACKGROUND ART 
     Continuous ink jet printers are a substantial capital investment for a printing company. It is therefore desired to maximize the time available for such a system to print. A printer may have a variety of printing jobs, each requiring a different ink. Ink choice may be based on color, permanence or ease of operation. It is therefore desirable that the ink in a continuous ink jet printer may be easily changed, instead of dedicating a printer to each type of ink. 
     As ink chemistry, in addition to color, may be incompatible between inks, it is desirable to flush the system with a colorless fluid of low surface tension to remove and dilute the old ink, then introduce the new ink. 
     Existing art requires the operator to perform such tasks as draining the old ink and flush fluid by inserting a tube into a fitting while holding a bucket as the tank drains, disposing of these buckets of waste, and connecting a special manifold in place of the printhead to properly route the fluid. The flush fluid is then circulated and disposed. No provision is made to remove ink trapped in tubing by sending it directly to waste. The flush instead works by successive dilutions of the residual ink. 
     Another option is to attach a flush system, consisting of tanks of flush fluid, pumps and a waste tank. This involves extra expense for the customer in purchasing the flush system, and the disadvantage of only flushing one fluid system at a time with the flush system. 
     It is therefore an object of the present invention to provide a means of flushing and changing the ink in a continuous ink jet fluid system. 
     It is a further object of the present invention to have the flushing include the printhead(s) in a system. 
     It is yet another object of the present invention to accomplish the flushing with a minimum of auxiliary equipment. 
     SUMMARY OF THE INVENTION 
     These objects are met by the fluid system flush technique according to the present invention. 
     In accordance with one aspect of the present invention, the fluid flush system flushes residual ink from a fluid system to facilitate an ink change. The fluid system may be configured with one or more printheads. In accordance with the present invention, a common flush system is provided to serve all printheads in the multiple printhead configuration. The separate plumbing within each printhead interface controller (PIC) and printhead is, therefore, substantially identical. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawing and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a fluid schematic of a fluid system, with printhead interface controllers and printheads; 
     FIG. 2 illustrates the flush fluid supply connected to both the ink and replenisher fill ports; and 
     FIG. 3 illustrates the ink supply connected to both the ink and replenisher fill ports. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an ink jet print station comprises an external ink supply tank  1 , connected through a fill solenoid valve  11  and concentration sensor  12  to ink tank  13 . A similar external replenisher tank  2  is connected to a replenisher fill valve  15  and through it into the ink tank. Ink is supplied to the droplet generator  50 , by means of a pump  16 , through drain valve  17 , filter  18 , and printhead ink filter  51 . The ink which is not used for printing returns to the ink tank via the catcher return line  60 , bar outlet line  61 , or catch pan line  62 . The catcher and bar outlet lines have solenoid valves  63  and  64  which can divert the flow to the waste tank  30 . Solenoid valves  65  and  66  serve to start and stop the flow in the catch pan and catcher lines. 
     A system flush in accordance with the present invention comprises the following steps. Initially, ink is pumped out of ink tank  13  and into the external waste tank  4  by pump  16 , via drain control valve  17  and waste line  34 . As the intent of this step is to totally drain the ink tank, the float switch,  40  which during normal operation would turn off the ink pump when the ink level is too low, is disabled. Instead, the ink pump is turned on until the ink level is below the lowest float switch, then remains on for a defined time to totally drain the tank. Catcher and catch pan valves  66  and  65  are left open, allowing residual ink to drain into the tank, which is under vacuum. Prior to pumping out the ink tank, a float switch  5 , in the external waste tank, is checked to ensure adequate room for the waste ink. This occurs before every draining of the ink tank. If the tank is found to be full, the system displays a warning message to the operator and waits for the tank to be emptied or replaced. 
     Either before initiating the flush sequence or while draining the ink from the ink tank, the operator must disconnect the refill lines from the ink supply and replenishment supply vessels,  1  and  2 . These refill lines are tee&#39;d together and connected to the flush fluid supply vessel as shown in FIG.  2 . 
     In a second step, the ink tank is refilled with flush fluid through both the ink and replenisher fill valves. During the refill with flush fluid, the float switches in the ink tank are ignored. As a result, the ink tank refill is allowed to continue filling until the ink tank overflows via the vacuum line  35  into internal waste tank  30 . The refilling is finally stopped when the lowest switch on the float switch assembly  31  of the internal waste tank  30  is tripped. Overfilling the ink tank ensures that dried residue on the tank walls, above the normal fill line, will wet out and dissolve. In filling the ink tank  13  with flush fluid, both ink refill and replenishment lines are used to speed the filling process. Refilling through the ink refill line alone is quite slow as the optical concentration sensor assembly  12 , as disclosed and claimed in co-pending, commonly assigned patent application Ser. No. 09,211,035 restricts its flow. Using both fill lines also ensures that both fill lines are appropriately flushed. 
     The third step of the system flush circulates the flush fluid to the printhead, while the bar out control valve  64  and catcher  63  waste valves divert the returning fluid to the internal waste tank  30 . The internal waste tank is pumped out to the external waste tank  4  as needed by waste pump  32 . The fluid is circulated with the drop generator in crossflush, returning flush fluid down the bar outlet line  61  and the catcher line  60 . The fluid is also circulated with ink jets formed by closing crossflush valve  80 , returning flush fluid down the catcher line when the eyelid is closed or the catch pan line  62 , when the eyelid is open. As ink residue may accumulate in the crevices of valves and o-rings, it is desirable to alternate the return fluid flow through these flow paths to ensure proper cleaning. The ink tank is refilled as needed, as controlled by the normal ink tank float switch, with fresh flush fluid to prevent the tank from emptying completely. This flushing of the printhead, while the alternating flush fluid return paths is done for approximately 3 minutes to remove the bulk of the ink remaining in the umbilical line  20 . 
     The bar out  64  and catcher  63  waste valves are then returned to their normal operating condition. This allows the flush fluid to circulate back to the ink tank for approximately 2 minutes, cleaning the other side of the bar outlet waste valves. The umbilical heater (not shown) is also turned on in this state to warm the flush fluid, aiding in redissolving deposits. While the flush fluid is circulated to the ink tank, the optical concentration sensor (OCS) supply pump  37  is turned on to flush out the OCS supply line and pump. 
     After this circulation step, the printhead purge pump  25  and valve  52  are activated to purge the air filter in the printhead. The filters are allowed to soak in the purge fluid for a few seconds, followed by another cycle of purge fluid. 
     In the next step, the tank is drained as in step  1 , and steps  2  through  6  are then repeated with clean flush fluid. The number of times the tank is drained and refilled with the flush fluid during the flush cycle may vary with the different ink changeovers. For example, ink with a higher degree of incompatibility may require more flushes. Similarly, lighter color inks, such as a yellow ink, may require additional fill and circulate cycles with flush fluid to dilute and remove traces of black ink. On the other hand, a black ink may only require one cycle of flush fluid as its dark color masks lighter inks. The number of flush cycles to employ is normally decided by the controlling software. The operator may however, elect to repeat the flush cycle if deemed necessary. Alternatively, during step  5  as described above, when the flush fluid is circulated through the OCS, the OCS can monitor the tint or color of the flush fluid to determine the necessary number of flush cycles. Typically, two draining and refilling flush cycles are sufficient. After the appropriate number of flush cycles are complete, the fluid system ink filters  18  are replaced with clean filters. The flush fluid supply is then disconnected from the ink and replenishment fill lines. 
     In the final step, both the ink and replenisher fill ports are connected to the ink supply tank, as shown in FIG.  3 . The system is now filled with ink and circulated as in steps  3  through  5 . The ink fill is controlled by the normal float switches in the ink tank. The ink is drained and refilled, and circulated again per steps  3  through  5 . The ink is drained from the system, the replenisher line is connected to the replenisher fill port, and the system is filled with ink a final time through the ink fill valve and OCS. 
     In a preferred embodiment of the present invention, the flush fluid used is a clear fluid, so as not to leave residue to tint light colored ink. It may also have a high pH to be compatible with the inks used in continuous ink jet systems. The flush fluid may also contain surfactants to lower the surface tension to aid in wetting out filters and other components. Finally, the flush fluid may or may not be the same as the cleaning fluid used in shutting down a printhead, such as is disclosed and claimed in co-pending, commonly assigned patent application Ser. No. 09,211,213, 
     The only additional component used to perform the flush according to the present invention is a “tee”, as shown in FIGS. 2 and 3, to connect flush fluid or ink supply vessels to both the ink refill and replenishment fill ports. The pumps and valves used in the flush perform other uses such as ink circulation and shutdown cleaning in the fluid system. The flushing feature does not require manually draining of the tanks, the use of printhead simulators, external flush systems or external vacuum systems. Control of this flushing sequence is carried out by the fluid system controller which controls the normal ink jet operation of the fluid system (not shown). 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention. Although this description has referenced the components for a single printhead in a multiple printhead fluid system, it should be understood that the flush system would concurrently flush the matching components for the second, or multiple, printhead(s). The invention is also applicable to single printhead fluid systems or fluid systems operating more than one printhead.