Abstract:
A chambered doctor blade apparatus provides an automatic system for cleanup and replacement of coating substance, as well as operating a hydraulic head loading system that includes hydrostatic compensation, and integrates the head loading mechanism into the automated cleaning, flushing and replacement cycle. A programmable logic controller (PLC) is connected to a touch screen display that presents an interactive graphical user interface for control purposes. The PLC is programmed to carry out sequentially the required steps for cleaning, refilling, and running the chambered doctor blade assembly, and to alternate water-based and non-water-based coatings without necessitating removal of the doctor blade head from the transfer roller. Each coating run begins with a purge step in which a new coating material is pumped through the system to waste to remove any residual material from the previous coating run.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 09/444,666, filed Nov. 22, 1999, now U.S. Pat. No. 6,383,296, issued May 7, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     In the application of liquid substances to a moving web or successive sheets of material, it is considered well known in the art to apply the liquid using a rotating transfer roller, and to directly apply the liquid uniformly onto the roller by means of a doctor blade assembly. The doctor blade assembly generally includes a reservoir chamber extending the length of the transfer roller and in contact with the circumferential surface thereof, and a pair of doctor blades extending longitudinally on either side of the chamber. The doctor blades are angled obliquely toward the transfer roller surface, and serve both to seal the reservoir chamber to the roller and to form a uniform film of liquid on the roller transfer surface. The assembly also must include some means to seal the reservoir chamber at the ends of the roller, so that the liquid is not flung from the roller into the surroundings, and so that the liquid may be pumped through the reservoir during the transfer process. Such transfer systems are used in flexographic and gravure printing, adhesive applicators in the paper converting industry, coating applicators in many different industrial processes, and the like. An exemplary system is described in U.S. Pat. No. 4,821,672, issued to Nick Bruno on Apr. 18, 1989. 
     Chambered doctor blade devices are generally employed with large printing presses or paper converting machines, either of which comprising a substantial capital investment. The forces of economics dictate that these machines be used productively to the greatest extent possible. Any downtime is considered to be a diminishment of return on investment, to be avoided whenever possible. 
     It is often necessary to change the ink or coating compound that is applied by the chambered doctor blade apparatus, due to color change or alteration of the machine setup. Typically, the ink reservoir, supply lines, valves, and inking chamber must be drained, flushed, cleaned, and resupplied with a new ink or coating compound. The time spent in carrying out these tasks comprises machine downtime, a loss in productivity. Automated systems for supplying a doctor blade chamber are known in the prior art, and include some draining and flushing features. These systems also enable the transfer roller to be cleaned by the doctor blade assembly as it cleans itself, shrinking the labor requirement of the cleaning and refilling process. It is highly desirable for an automated system to drain, flush, and clean all of the supply lines and fittings, whereby contamination from a former machine setup is removed before a new setup is created. One such system, depicted in U.S. Pat. No. 5,683,508 describes a doctor blade coating system which purports to automate the wash and clean cycle in addition to supplying the coating chamber. However, this system typifies the prior art in that it does not route the washing and flushing liquids through the same lines and fittings that deliver the ink or coating substances. As a result, some components such as the supply pump and supply lines, and the associated connectors are not cleaned before a new ink color or coating is introduced into the system. 
     It is also known that chambered doctor blade devices rely on doctor blades impinging on a transfer (anilox) roller to form a smooth and uniform film of ink or coating substance on the roller. The doctor blades are required to present a highly linear edge that impinges on the transfer roller with a force that is very uniform along the entire length of the blades (which can extend over 170 inches). Due to vibration and wear, the doctor blade edges may develop areas where the contact force varies along the length thereof, causing uneven distribution of the ink or coating film on the transfer roller. 
     There is known in the prior art at least one system for urging the doctor blades toward the transfer roller that employs hydraulic cylinders spaced along the apparatus to distribute the loading force therealong. Moreover, the hydraulic system is energized by pneumatic pressure, which provides hydrostatic compensation in the hydraulic circuit that enables each hydraulic piston to advance or retract as necessary to maintain a constant loading pressure against the transfer roller. In addition, the system provides a restricted flow orifice at each hydraulic cylinder, so that each cylinder may resist rapid motion (vibration and the like) while enabling slower adjustability in response to wear conditions. Although this superior doctor blade loading system has been available in the prior art, it has not been integrated into an automatic cleanup and ink and coating replacement system. 
     SUMMARY OF THE INVENTION 
     The present invention generally comprises a chambered doctor blade apparatus that provides automatic system for cleanup and replacement of ink or coating substance. The automatic system also operates a hydraulic head loading system that includes hydrostatic compensation, and integrates the head loading mechanism into the automated cleaning, flushing and replacement cycle. (Hereinafter, reference will be made to the use of ink in a printing process, but it is understood that any coating substance is encompassed by this discussion.) 
     In one aspect, the invention includes a chambered doctor blade assembly having a supply line connected to one end and a return line connected to the other end. A return pump has an intake connected to the return line, and an output connected through a return valve to a changeable ink reservoir. A supply pump has an output connected to the chamber supply line, and an intake connected through a supply valve to the ink reservoir. The supply pump intake line is also connected to a vent valve, and to a first wash valve that is connected to a first wash tank. The line from the supply valve at the ink reservoir is connected through a first pair of valves to a main water reservoir and a second wash tank. The line from the return valve at the ink reservoir is connected through a second pair of valves to the second wash tank and to a waste discharge outlet. Actuation of these valves and pumps in various combinations and sequences enables all of the valves, fittings, pumps, the doctor blade chamber, and the anilox roller to be drained, flushed, cleaned, flushed, and recharged with fresh ink. 
     In a further aspect of the invention, the system includes an automated system for controlling the valves and pumps enumerated above to carry out the cleaning and recharging functions also described above. The automated system includes a programmable logic controller (PLC) connected through a display driver to a touch screen display that depicts system conditions and presents an interactive graphical user interface for control purposes. The PLC is connected to a non-volatile memory that stores programming and values to carry out sequentially the required steps for cleaning, refilling, and running the chambered doctor blade assembly. The PLC is connected to each of the pumps and valves, and to the head loading valve of a hydrostatically compensated hydraulic head loading system. 
     The hydrostatically compensated hydraulic head loading system includes a hollow pivot tube extending parallel to the length of the doctor blade chamber and mounted on a coaxial pivot shaft. A plurality of hydraulic cylinders, each having a rolling diaphragm piston mounted therein, are spaced along the back panel of the doctor blade chamber, with each piston secured to the back panel. Each cylinder is rigidly secured to the pivot tube, whereby the pivot tube supports the hydraulic cylinders and the doctor blade assembly. A handle secured to the pivot tube permits the assembly to be rotated to bring the doctor blades into and out of engagement with the adjacent anilox roller. 
     The pivot tube also serves as a manifold to supply hydraulic fluid to the cylinders. An hydraulic supply reservoir includes a head space that is connected through a head loading valve to a source of selectively controlled pneumatic pressure, and the fluid is connected to supply the interior of the hollow pivot tube. An hydraulic supply line extends from each hydraulic cylinder to an adjacent fitting extending from the pivot tube to pressurize the cylinders whenever the head loading valve is activated. The pneumatic loading of the hydraulic fluid supplies a constant and uniform pressure to all the cylinders, and further enables the hydraulic fluid to flow bidirectionally and allows each hydraulic piston to advance or retract as necessary to maintain a constant loading pressure against the transfer roller. In addition, the system provides a restricted flow orifice at each hydraulic cylinder, so that each cylinder may resist rapid motion (vibration and the like) while enabling low velocity adjustability in response to wear conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a chambered doctor blade mounted on a hydrostatically compensated hydraulic head loading assembly and connected to an automatic cleaning and refilling system. 
     FIG. 2 is an enlarged partial plan elevation of the chambered doctor blade assembly as shown in FIG.  1 . 
     FIG. 3 is a schematic view of the hydrostatically compensated hydraulic head loading system combined with the automatic cleaning and recharging system of the invention. 
     FIG. 4 is a schematic representation of the active mechanical components of the automatic cleaning and recharging system of the invention. 
     FIG. 5 is a functional block diagram representation of the active electronic components of the automatic cleaning and recharging system of the invention. 
     FIG. 6 is a side elevation of the doctor blade assembly and the head loading system of the invention. 
     FIG. 7 is an enlarged cross-sectional detail of the doctor blade chamber connections to the return lines. 
     FIG. 8 is an enlarged top view of the drain reservoir valve of the automatic cleaning and recharging system of the invention. 
     FIG. 9 is a perspective view the console of the automatic cleaning and recharging system of the invention. 
     FIG. 10 is a chart depicting the operational status of each active mechanical component of the automated system in each step required for filling, running, and cleaning the chambered doctor blade assembly using non-water-based coatings. 
     FIG. 11 is a chart depicting the operational status of each active mechanical component of the automated system in each step required for filling, running, and cleaning the chambered doctor blade assembly using water-based coatings. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention generally comprises a chambered doctor blade apparatus that includes an automatic system for cleanup and replacement of ink or coating substance. With regard to FIGS. 1,  2 , and  6 , the applicator portion of the invention includes a chambered doctor blade assembly  21  extending parallel to a transfer roller  22  (anilox or equivalent) that engages a printing press, coating applicator, or the like. The assembly  21  includes a longitudinally extending cavity, or chamber  24 , and a pair of doctor blades  23  that engage the surface of the transfer roller and form a uniform thin fluid film thereon. The chamber  24  is formed by a channel-like structure having a central web  26  and side walls extending therefrom in parallel, spaced apart relationship. 
     A hollow pivot tube  27  extends parallel to the central web  26  for substantially the entire length thereof, and is mounted on coaxial pivot shafts  28  which are rotatably supported at opposed ends. A plurality of hydraulic cylinders  31  are mounted rigidly on the pivot tube  27  and spaced longitudinally therealong. Each piston rod  32  of the cylinders  31  is secured to a mounting disk  33 , which in turn is slidably received in a receptacle in a bracket  30  secured to the back surface of the central web  26 . A lock-down screw  25  secures the disk  33  in the bracket  30 . Thus the entire structure  21  is supported by the piston rods  32 , which in turn are supported on the pivot tube  27 . A handle  34  is secured to the tube  27  to enable rotation of the tube to bring the chambered doctor blade assembly  21  into and out of engagement with the transfer roller  22 . At least one shaft lock  36  is also provided to lock the pivot tube  27  and pivot shafts  28  at a fixed angular orientation to secure the apparatus  21  in an engaged or disengaged disposition. 
     It may be appreciated that the entire head assembly  21  may be removed quickly and easily by loosening all of the screws  25 , and sliding the brackets  30  off of the disks  33 . Another head assembly  21  may be substituted by reversing this process. 
     The pivot tube  27  further serves as a manifold to supply low pressure hydraulic fluid to the cylinders  31 . An hydraulic supply reservoir  37  is disposed adjacent to the tube  27 , and includes a supply line  38  that delivers hydraulic fluid from the reservoir to the interior of the pivot tube  27 . The reservoir provides head space above the fluid charge therein, and a pneumatic line  39  connects the head space through a head loading valve to a pressurized gas source having a selectively adjustable pressure in a generally low pressure range. A plurality of supply lines  41  extend from a fitting on the pivot tube  27  to a respective one of the hydraulic cylinders  31 . Thus the hydraulic fluid supplied through the interior of the pivot tube  27  to each cylinder is under a constant and uniform pressure, and is free to flow bidirectionally between the reservoir, pivot tube, and cylinders. This feature enables all pistons to exert the same force on the central web of the doctor blade assembly, while each piston is able to extend a variable amount until it meets sufficient mechanical resistance that is equal and opposite to the hydraulic force of the piston. This attribute allows the doctor blade assembly to self-compensate for wear, expansion, and other physical variables in the relationship between the doctor blade assembly and the transfer roller. 
     With regard to FIG. 3, each cylinder  31  includes a piston  42  connected to the piston rod  32 , the piston  42  having a rolling diaphragm seal  43 . The driving chamber  44  of the cylinder  31  is connected through a restricted orifice  46  to the input of the supply line  41 . The restricted orifice  46  prevents the piston  42  from undergoing any high velocity translation, thereby minimizing any response to rapid motion of the doctor blade assembly, such as vibration and the like. On the other hand, the restricted orifice does not inhibit low velocity translation of the piston  42 , whereby the system provides self-compensating adjustment to wear and other long-term variables. 
     With regard to FIG. 4, the mechanical components  100  of the automated cleaning, filling, and operating system include an interchangeable coating supply reservoir  101 . A draw tube in the reservoir  101  feeds a coating substance (ink or UV coating or any other liquid) through a supply valve  102  to a supply line  131 . The supply line  131  extends to the intake port of supply pump  124 , the output of which is connected through line  132  to the doctor blade chamber. The system also includes a heated clean water reservoir  105  that is connected through supply valve  104  to the supply line  131 . The reservoir  105  is maintained at a fill level by a valve  110  connected to a clean water supply, using a level detector (as is known in the art) to operate the valve  108 . A heater  107  in the reservoir  105  heats and maintains the water at a preset temperature, and is thermostatically controlled. 
     In addition, the system includes a recirculation reservoir  109  that has an outlet connected through valve  103  to the supply line  131 . The inlet to reservoir  109  is connected through valve  106  to the return line  136 . A valve  107  connects the return line  136  to the inlet of coating supply reservoir  101 , and a valve  108  connects the return line  136  to a waste discharge receptor. 
     With reference to FIG. 5, the invention further includes an automatic system  51  for operating the valves and pumps described above to carry out all steps required for filling, running, and cleaning the chambered doctor blade assembly. The automated system  51  includes a programmable logic controller (PLC)  52  connected through a display driver  54  to a touch screen display  56 . The display  56  serves as a graphical user interface by presenting system functions that are selectable by a user. The display  56  further acts as an input device by enabling the user to tap the portion of a screen display that corresponds to a chosen function, and the touch screen feeds the selection information back to the PLC  52 . In addition, a non-volatile memory  53  that stores programming instructions and data values is connected to the PLC  52  to provide the proper screen displays and carry out the functions and choices portrayed by the screen displays. 
     The PLC  52  is also connected to operate the system pumps  57  (corresponding to the supply pump  124  and return pump  126  of FIG.  4 ), and the system valves (corresponding to the valves  102 - 104 ,  106 - 108 ,  110 ,  123 , and  135 ). The PLC is also connected to operate the head loading valve  59  which, as described previously, controls the application of pneumatic pressure to the hydraulic fluid reservoir  37  that supplies the hydraulic cylinders  31  of the doctor blade mounting system. The PLC is further connected to the heater  107  and to appropriate sensors and limit switches that a prudent individual skilled in the art would include for safety and smooth operations. The stored programming of the PLC  52  is written to carry our the operating functions of the doctor blade system, including, but not limited to, the functions described in FIG. 10 (for UV cured coatings) and FIG. 11 (for water-based coatings). All of these functions may be carried out while the chambered doctor blade assembly  21  is engaged with the roller  22 , whereby the roller is cleaned, washed, and coated at the same time as the remainder of the system undergoes these processes. As a result, the head loading valve  59  is On for all of the procedures except the Stop and Unload condition. 
     The mechanical components depicted in FIG.  4  and the electronic system of FIG. 5 may be incorporated into a small, portable console  81 , as shown in FIG.  9 . The console  81  is supported on casters, and includes a tank  84  that comprises the heated water reservoir  105 , and a space for a removable container  86  that comprises the recirculation supply reservoir  109 . The coating supply reservoir  101  is maintained in separate tank  83  that is connected through removable lines to the console  81 . Note that the tank  83  is easily removed and replaced (swapped) to change the coating material that is applied by the system. A significant advantage of this system is that UV curable coatings (typically not compatible with water as a solvent) and water-based coatings may be alternated and are automatically accommodated, as described below. 
     The touch screen display  56  is supported in a handheld remote control  82  connected by cable to the console  81 , whereby the user may select a desired function for the system, and the function is carried out by the electronic system depicted in FIG.  5 . The desired function may include a plurality of the procedures listed in FIGS. 10 and 11, carried out sequentially to effect a complete job change for the transfer roller; i.e., coating purge and drain, recirculate wash and drain, and, thereafter, coating fill and run. 
     The apparatus may further include an ambient port  71 , as shown in FIGS. 1 and 2, that is disposed in a trough or channel  70  interposed between the return line  133  and the valve  127 . It has been observed that the chambered doctor blade assembly, when running against the transfer roller, may develop a suction adhesion to the transfer roller. When the system is switched to a function such as draining a liquid from the chamber  24 , the vacuum in the chamber may hamper complete pump-out of the liquid. To overcome this effect, the ambient port  71  includes a top opening  72  that is open to atmosphere, as shown in FIG. 9, to maintain the return line to atmospheric pressure and releases any vacuum suction effects. The return pump may be operated at a slightly greater rate than the supply pump to assure that the flow through channel does not overflow from opening  72 . Note that the trough  70  may extend substantially the entire length of the doctor blade chamber. 
     A significant advantage of this system is the capability to go from a water-based coating to a UV based coating and back again with little effort. This is successfully completed by the use of the coating purge step, followed by chamber filling of a different coating material. Thus, for example, a run of water based coating followed by a water based wash and drain routine could result in some residual water based fluids in the lines, valves, and fittings of the system. A subsequent run of UV coating could become contaminated by residual water based fluids in the system. To overcome this problem, a new coating run always begins with a coating purge step, in which the new coating is briefly pumped through the system and discharged to waste, thereby sweeping away the residual water based fluids. Thereafter, the coating fill and run routines are free of contamination. The same is true when switching from a UV coating to a water based coating. 
     The initial screen prompts the operator to select either water based coating or UV coating. When this selection is made the system selects the wash up procedure that is required. This is done due to the fact that water should not be used to wash UV coatings. Thus, as shown in FIG. 10, none of the wash steps for UV coatings involve opening the valve  104  to admit water to the system; rather, the recirc. supply tank  109  holds a solvent or the like that is fed through valve  103  to provide the fluid for the washing functions. 
     After the initial type of coating is selected there are only two choices that need to be selected. Start Coat and Start Wash. All the functions happen automatically after these selections are made. When Start Coat is selected the following process steps occur: 
     Chamber Load: The chamber will load against the anilox roll and the coating purge process will start after a given amount of time. 
     Coating Purge: The supply pump pulls material from the supply container, pumps it up to the chamber and through the bottom of the chamber. It then flows into the trough or reservoir  70  and is pulled out of the trough  70  by means of the return pump which is then pumped to waste for the given amount of time. 
     Coating Fill: The chamber drain valve is then closed, allowing the chamber to fill. 
     Coating Run: The chamber drain valve remains closed and the pumps automatically slow down for the duration of the coating job, after which the operator will select the automatic wash up. The Run Speed can be adjusted at the console for different flow rates. 
     At this point the operator may select Start Wash and the following steps will automatically occur: 
     Coating Wash: The first step when Coating Wash is selected is Coating Drain. It stops the supply of coating to the chamber by means of opening a pump vent valve. It also opens the chamber drain valve allowing the coating to drain from the chamber into the trough or reservoir. It returns as much residual coating back to the coating supply container as is set as a timing function by the installer. 
     Warm Water Rinse: (This rinse is only enabled when ‘water based’ is selected on the touch screen) Water is drawn with the supply pump from the water reservoir up to the chamber, through the chamber with the chamber drain valve closed at first to fill the chamber then opened to flush the bottom of the chamber. All of this flows into the trough where the return pump draws the material and sends it to waste. 
     Water Drain: The supply pump vent valve opens, stopping the supply of water to the chamber and draining the system of the residual material. This mode is only enabled when water based is selected at the start of the process. 
     Recirculation Wash: This wash cycle is enabled with either water based selected or UV selected. It pulls recycled wash up material from the recirculation container by means of the supply pump, supplies it to the chamber with the chamber drain valve closed to fill the chamber then opens the valve to flush the bottom of the chamber, all of this flowing into the trough and returned to the recirculation container by means of the return pump. The difference between the Water based wash and the UV wash is the UV wash cycle uses only the recirculation container to supply cleaning material, as any fresh water would contaminate the UV material. 
     Recirculation Drain: This opens the supply pump vent valve stopping the supply of wash materials and allowing residual materials to be drained back into the recirculation tank. 
     Warm Water Rinse 2: This step pulls warm water from the warm water supply tank up to the chamber with the chamber drain valve closed at first and then opening. This mode is only enabled when water-based is selected at the start of the process. 
     Water Drain 2: This opens the supply pump vent valve which stops the flow of water to the chamber and drains the residual out of the systems and to waste. 
     Chamber Unload: At the end of the wash process the chamber is automatically unloaded. 
     It is significant to note that any residual wash fluid is purged from the system by the introduction of new coating material at the start of the subsequent coating run. The Coating Purge step uses the new coating material to sweep any residual wash fluid from the lines and valves, and this material all goes to waste. Thereafter, the coating fill and run stages are free of any wash fluid that may be solvent-incompatible. 
     With regard to FIGS. 1,  2 , and  7 , the return lines  133  and  134  are connected to a manifold  61  secured to the return end of the chamber  24  of the doctor blade assembly  21 . The connection of line  133  is used for circulating coating material during a system run cycle, as it provides the smoothest fluid flow through the chamber, and both the connections of lines  133  and  134  are used to drain liquid out of the chamber  24 , due to the fact that the connection of line  133  is at the bottom of the chamber when the system remains engaged with a transfer roller, as shown in FIGS. 1 and 2. On the other hand, the connection of line  134  is lowermost when the doctor blade assembly  21  is rotated about the pivot tube  27  to disengage and move away from the transfer roller  22 , and line  134  is used to drain the chamber in the disengaged disposition. In either case, liquid drained from the chamber first passes through the trough  70  at atmospheric pressure. 
     Thus the invention provides a system that automatically supplies coating material to a chambered doctor blade assembly, while also loading the doctor blade assembly against a transfer roller with a self-compensating, pressure balanced mounting apparatus. The system further carries out typical printer or industrial job changing tasks, such as draining, cleaning, and rinsing the doctor blade assembly and the transfer roller, and further refilling the system and supplying the system for a further production run, all automatically. 
     The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in light of the above teaching without deviating from the spirit and the scope of the invention. The embodiment described is selected to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular purpose contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.