Patent Application
20050248609
The present embodiments relate to an improved startup sequence for ink jet print stations when using low surface tension inks.
Prior art ink jet printing systems have steady state problems of “spitting” ink from the catcher when used with low surface tension inks. “Spitting” results from a poor two phase flow mixture in the catcher that periodically causes ink to ‘spit’ out. Over time, the ink ‘spit’ from the catcher builds up on the eyelid of the catcher assembly. The buildup, in turn, interferes with the printing drops causing print defects that force the operator to manually clean the eyelid. The solution of decreasing the vacuum supply to the printhead inadequately addresses the “spitting” problem.
The present methods have been designed to solve the steady state problems of “spitting” ink from the catcher.
The embodied methods relate to an automatic startup sequence for an ink jet print station using solvent based ink. The print station includes an orifice structure connected to the drop generator forming a jet array, a catcher assembly disposed opposite the jet array with a charge device, and an eyelid for engaging a catcher. The print station includes a catcher return line, a flushing fluid line connected to the drop generator, a flushing fluid pump and a flushing fluid valve disposed in the flushing fluid line. An anti-wicking return line, an ink pump, and an ink supply valve are disposed in the ink supply line.
The method entails introducing a flushing fluid to the drop generator using the flushing fluid pump at a drive level and at an initial flushing pressure that enables flushing fluid to flow through the jet array at a flow rate adequate to permit the catcher assembly to extract the flushing fluid. An operating voltage is applied to the charge device, and the ink pump is engaged using a drive level equivalent to the drive level of the flushing fluid pump to pressurize the ink supply line. The method continues by increasing the pressure of the flushing fluid from the initial flushing pressure while passing the flushing fluid through the jet array to an increased pressure. The increased pressure is between a pressure for stable drop formation and drop deflection from the jet array and at a second pressure sufficiently low enough to extract drops from the catcher assembly and to permit flushing fluid to flow freely through the catcher assembly and the anti-wicking return line. The method ends by simultaneously opening the ink supply valve and closing the flushing fluid valve permitting ink to flow into the drop generator. The flow of the flushing fluid is stopped concurrently with increasing pressure of the ink supply line to a stored operating value.
In the detailed description of the preferred embodiments presented below, reference is made to the accompanying drawings, in which:
The present embodiments are detailed below with reference to the listed Figures.
Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular descriptions and that it can be practiced or carried out in various ways.
These embodied methods are techniques for ink jet printer startup sequences where the print station uses solvent based inks.
The methods enable the use of a smaller catcher return line and a separate anti-wicking line, while still handling larger system fluid flow rates by carefully controlling the timing and amount of pressurization of the various fluid lines to the drop generator during start up.
The embodied methods successfully prevent ink from splattering during the transition from using flushing fluid to ink use during the ink jet print station start up. Specifically, the method keeps the eyelid of the catcher assembly clean during start up processes.
By preventing splatter during this transition, the charge device is kept clean during start up ensuring reliable operation.
The method stops spitting from the catcher assembly that causes print defects.
The methods provide an environmental advantage by reducing the presence of volatile fumes by reducing the amount of vacuum needed to return ink to the reservoir for ink.
With reference to the figures,
The print station has an ink supply line 10 that is pressurized with ink from a reservoir 11 with ink 42 or another supply source. The ink supply line 10 is pressurized using an ink pump 36. An ink supply valve 40 is connected to the ink supply line. 10 to control flow of ink from the reservoir for ink 11 to a drop generator 14. An example of an ink jet print station is a Kodak Versamark DT92 print station available from Kodak Versamark of Dayton, Ohio.
The drop generator 14 has an orifice structure 16 with a plurality of orifices to form a jet array with jets 18a, 18b, 18c and 18d. Orifice structures with 256 orifices from 256 jets are typically used in an exemplary ink jet print station according to one of the embodied methods. Other exemplary print stations have 120 jets per inch or 240 jets per inch.
Examples of solvent-based inks that can be used with the embodied ink jet print stations include Black Solvent Ink Model Number 7101, available from Kodak Versamark of Dayton, Ohio.
A catcher assembly 22 is disposed opposite the jet array. The catcher assembly includes a charge device 17 opposite the jets 18a, 18b, 18c, and 18d for providing a charge to the selected drops formed from the jet array. Drops selectively charged by the charge device are deflected so that the drops strike the catcher 23. The catcher 23 and, optionally, a catcher plate (not shown) are part of the catcher assembly 22. An eyelid 25 has a sealing engagement with the catcher assembly. A catcher return line 26 and an anti-wicking return line 34 are connected to the catcher 23. Either one or both of the catcher return line 26 and the anti-wicking return line 34 recycle fluid back to the reservoir.
To use the system, a flushing fluid pump 28 pumps flushing fluid 29 from a source of flushing fluid 31 through a flushing fluid valve 30 and a flushing fluid supply line 32 to the drop generator 14.
A controller, which includes a central processing unit, communicates with the valves and pumps to control the pressurization and the opening and closing of the valves.
Transducers, such as pressure transducers, can be located in the fluid lines and catcher assembly of the print station to provide sensor information on pressure and flow rates to the controller to regulate pressure and flow rates through the lines. Typical usable transducers are Kavlico transducers.
Next, a voltage is applied to the charge device 17 (Step 102). The charge device 17 can be a charge plate. The voltage is preferably the operating voltage of the charge device.
As the next step, the ink pump 35 is then engaged using a drive level equivalent to the drive level of the flushing fluid pump, and the ink supply line is pressurized (Step 104).
Once the ink pump raises the pressure of the ink, the pressure of the flushing fluid is increased while jetting the flushing fluid to a pressure between a first pressure for stable drop formation and drop deflection from the jet array, and a second pressure sufficiently low enough to extract drops from the catcher assembly and permit flushing fluid to flow freely through the catcher assembly into the catcher return line and the anti-wicking return line 34 (Step 106).
Simultaneously, the ink valve 40 is opened and the flushing fluid valve 30 is closed whereupon pressurized ink flows into the drop generator 14 (Step 108).
Finally, the flushing fluid is turned off while the pressure of the ink supply line increases (Step 110), forming stable ink jets with high image quality.
The method contemplates using a drive level that is a voltage level. The method can involve using a drive level that is a duty cycle level for pulse width modulation.
The method can include the step of stimulating the drop generator with a stimulating voltage prior to applying the operating voltage to the charge device. In a preferred embodiment, the stimulating voltage is up to three volts.
The pressures can be monitored with transducers disposed in the fluid lines. A controller can be used to monitor pressures, open and close the various valves, provide the appropriate voltages to the charge places, and operate the other equipment of the printhead.
In this embodiment, the operating voltage of the charge device can range between 115 volts and 180 volts.
In this embodiment, the flushing fluid pump can have an operating pressure between 5 psi and 7.5 psi.
The embodiments have been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the embodiments, especially to those skilled in the art.
