Abstract:
The present teachings relate to a printhead maintenance station for an industrial printing apparatus which is used to prevent clogging of the printhead, particularly during periods in which the printheads are idle. The maintenance station includes a capping station which has sockets for keeping the printheads moist and a blotting station for cleaning any residual printing fluids prior to carrying out a print function.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Nos. 60/674,584, 60/674,585, 60/674,588, 60/674,589, 60/674,590, 60/674,591, and 60/674,592, filed on Apr. 25, 2005. The disclosures of the above applications are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present teachings relate to a printhead maintenance station for a piezoelectric microdeposition (PMD) apparatus. 
         [0004]    2. Background 
         [0005]    PMD processes are used to deposit droplets of fluid manufacturing materials on substrates without contamination of the substrates or the fluid manufacturing materials. Accordingly, the PMD processes are particularly useful in clean room environments where contamination is to be avoided such as, for example, when manufacturing polymer light-emitting diodes (PLED) display devices, printed circuit boards (PCBs), or liquid crystal displays (LCDs). 
         [0006]    PMD methods and systems generally incorporate the use of a PMD tool, which includes a head to deposit fluid manufacturing materials on a substrate and a nozzle assembly including multiple independent nozzles. The PMD head is coupled with computer numerically controlled system for patterning, i.e., precisely depositing droplets of the fluid manufacturing material onto predetermined locations of the substrate and for individually controlling each of the nozzles. In general, the PMD head may contain multiple printhead arrays and is configured to provide a high degree of precision and accuracy when used in combination with the various techniques and methods for forming microstructures on substrates. 
         [0007]    Due to extremely high droplet deposition, positional accuracy typically required in PMD applications, and the use of non-traditional ink jet fluids atypical of those used in graphics printers, maintenance methods previously employed in other fields of ink jet printing are often unsatisfactory for avoiding nozzle failure in PMD applications. Accordingly, there is a need for an improved device for maintaining the condition of the PMD heads. 
       SUMMARY OF THE INVENTION 
       [0008]    The present teachings include the use of a blotting station with precise dynamic control capability and single printhead interaction capability, a capping and priming station that offers several modes of nozzle maintenance operation and ink mist control, and a drop analysis system that sequentially interact with a printhead array in an automatic fashion. 
         [0009]    Another feature is the ability to configure a wiping action of the blotting station for different fluid and printhead types, as well as accommodating variables such as pressure, velocity, and vertical lift off during motion. The inclusion of a single blotting station apparatus within the blotting device to correct the failure of a single printhead is yet another aspect. A drop mist removal system integral to the capping station as part of waste removal to avoid contamination of the substrate being printed is also provided. Active Z movement of the printhead with respect to the maintenance system to optimize each of the functions used with respect to each fluid and printhead type is also considered to be unique. 
         [0010]    Still another feature is the dynamic tracking system and the elements thereof used to maintain flatness and integrity of the blotting and wiping station, as well as the dynamic motion capabilities of the various elements of the maintenance station in relation to various elements such as a drop analysis and a drop check assembly of the PMD system. 
         [0011]    Yet another feature of the present invention is the ability to fill localized fluid baths under each printhead with a solvent and bring the solvent to a precise distance from the nozzle plate of each printhead to cause a localized vapor-rich atmosphere to stop evaporation of the jetting fluid and density change within the PMD fluid. The use of an appropriate material for the localized fluid bath structure that a contact angle of the fluid to structure is less than 20 degrees is also possible. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    To further clarify the above and to demonstrate the advantages and features of the present teachings, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings are not to be considered limiting of the scope of the teachings. The teachings will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0013]      FIG. 1  is a perspective view of a piezoelectric microdeposition apparatus (PMD) incorporating the maintenance station of the present teachings; 
           [0014]      FIG. 2  illustrates a perspective view of one embodiment of the maintenance station of the PMD apparatus; 
           [0015]      FIG. 2A  illustrates a nozzle plate and a print head; 
           [0016]      FIG. 3  illustrates the drop analysis system as sub-assembly of the PMD apparatus that, by motions of a capping station and tray, allows for drop analysis in association with the maintenance station for the PMD appartus; 
           [0017]      FIG. 4A  is a perspective view of an embodiment of a capping station according to the present teachings; 
           [0018]      FIG. 4B  is an exploded perspective view of a tray used in an embodiment of the capping station according to the present teachings; 
           [0019]      FIG. 4C  is a top view of an embodiment of a tray used in an embodiment of the capping station according to the present teachings; 
           [0020]      FIG. 4D  is a cross-section view of the tray depicted in  FIG. 4B ; 
           [0021]      FIG. 5A  illustrates a perspective view of a blotting station according to the present teachings; 
           [0022]      FIG. 5B  is an exploded perspective view of the blotting station according to the present teachings; and 
           [0023]      FIG. 5C  is a perspective view of various elements of the blotting station according to the present teachings. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following description is merely exemplary in nature and is in no way intended to limit the teachings, its application, or uses. 
         [0025]    The terms “fluid manufacturing material” and “fluid material” as defined herein, are broadly construed to include any material that can assume a low viscosity form and which is suitable for being deposited, for example, from a PMD head onto a substrate for forming a microstructure. Fluid manufacturing materials may include, but are not limited to, light-emitting polymers (LEPs), which can be used to form polymer light-emitting diode display devices (PLEDs, and PolyLEDs). Fluid manufacturing materials may also include plastics, metals, waxes, solders, solder pastes, biomedical products, acids, photoresists, solvents, adhesives and epoxies. The term “fluid manufacturing material” is interchangeably referred to herein as “fluid material.” 
         [0026]    The term “deposition” as defined herein, generally refers to the process of depositing individual droplets of fluid materials on substrates. The terms ‘let,” “discharge,” “pattern,” and “deposit” are used interchangeably herein with specific reference the deposition of the fluid material from a PMD head for example. The terms “droplet” and “drop” are also used interchangeably. 
         [0027]    The term “substrate,” as defined herein, is broadly construed to include any material having a surface that is suitable for receiving a fluid material during a manufacturing process such as PMD. Substrates include, but are not limited to, glass plate, pipettes silicon wafers, ceramic tiles, rigid and flexible plastic and metal sheets and rolls. In certain embodiments, a deposited fluid material itself may form a substrate, in as much as the fluid material also includes surfaces suitable for receiving a fluid material during a manufacturing process, such as, for example, when forming three-dimensional microstructures. 
         [0028]    The term “microstructures,” as defined herein, generally refers to structures formed with a high degree of precision, and that are sized to fit on a substrate. Inasmuch as the sizes of different substrates may vary, the term “microstructures” should not be construed to be limited to any particular size and can be used interchangeably with the term “structure”. Microstructures may include a single droplet of a fluid material, any combination of droplets, or any structure formed by depositing the droplet(s) on a substrate, such as a two-dimensional layer, a three-dimensional architecture, and any other desired structure. 
         [0029]    The PMD systems referenced to herein perform processes by depositing fluid materials onto substrates according to user-defined computer-executable instructions. The term “computer-executable instructions,” which is also referred to herein as “program modules” or “modules,” generally includes routines, programs, objects, components, data structures, or the like that implement particular abstract data types or perform particular tasks such as, but not limited to, executing computer numerical controls for implementing PMD processes. Program modules may be stored on any computer-readable media, including, but not limited to RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing instructions or data structures and capable of being accessed by a general purpose or special purpose computer. 
         [0030]    Now referring to  FIG. 1 , a PMD apparatus including a maintenance station according to the present teachings is shown. The PMD apparatus  10  includes a pair of robots  12  that load and unload a substrate  14  onto a substrate stage  9  of the PMD apparatus  10 . The use of robots  12  further assists in maintaining the substrates  14  in a clean condition such that foreign materials do not obstruct or damage surfaces of the substrates  14  that will be deposited with the patterned inks. PMD apparatus  10  also includes an optics system that includes a pair of cameras  13  and  15  that assist in assuring that the substrates  14  are aligned in the PMD apparatus  10  properly. 
         [0031]    PMD apparatus  10  includes a system control/power module  11  which controls operation of the PMD apparatus  10 . In this regard, operating parameters such as ink patterns, discharge speed, etc. may be controlled by an operator. Further, module  11  also controls the variable ink jet array  16  and droplet inspection module of the PMD  10 . Ink jet array  16  includes various printheads (not shown) that deposit the inks onto the substrates  14 . 
         [0032]    Inks that are deposited by variable ink jet array  16  are supplied to the array  16  by ink supply modules  17 . As a plurality of modules  17  are provided, one skilled in the art will recognize and appreciate that various types of inks suitable for different applications may be stored simultaneously. Also included in PMD apparatus  10  is a solvent cleaning module  17 . Solvent cleaning module  17  supplies solvents used to clean the printheads  34  of the variable ink jet array  16  to a maintenance station  20  according to the present invention. 
         [0033]    The maintenance system  20  may be positioned relative to the printhead array  16  and the substrate stage  9  such that all maintenance functions can be executed (i.e., purging, soaking, priming, capping, blotting, wiping and drop inspection through the optical system) while the substrate loading, alignment, and unloading are being performed. System throughput may be enhanced as this arrangement allows identification and correction of a jetting problem in parallel with normal operations of the machine without affecting their sequence. 
         [0034]    Now referring to  FIG. 2 , the maintenance station  20  may be used to maintain proper printhead jetting and cleanliness of the printheads  34 . The maintenance station  20  generally includes a translation stage  22  for positioning various modules of the maintenance station  20  under the printhead array  16 . The modules of the maintenance station  20  include a blotting station  30  and a capping station  40 . Associated with the capping station  40 , as shown in  FIG. 2 , is a drop analysis system  60  which is described in co-pending U.S. Provisional Application No. 60/674,589, which is entitled “Drop Analysis System” and is hereby incorporated by reference. The drop analysis system  60  generally includes a vision system  62  movably mounted to a stage  64  having x-, y- and z-axis motion capabilities as shown in  FIG. 3 . The drop analysis stage  64  is in turn mounted to a frame member that is part of a larger substrate, camera system, and printhead translation stage system that has x- and y-axis movement capabilities. 
         [0035]    Capping station  40 , which provides for capping the printhead nozzle plate  36  ( FIG. 2A ) when not in use, idle, or when lowered sufficiently to allow for drop analysis or drop check to occur is generally operable in three positions. Namely, a vapor immersion position where printheads  34  can be positioned just above the solvent to provide a vapor rich atmosphere, a liquid immersion position where the printheads  34  are to be inserted into a solvent, and a fluid purging position where the capping station  40  is lowered slightly below the vapor immersion position. The head array z-axis can be used to control the vapor immersion and liquid immersion positions, while movement of a scissor-lift mechanism or movement the head array in combination with translation of the lower maintenance support stage  32  controls the third position, described below. 
         [0036]    By movement of the lower maintenance system support stage  32  relative to the printhead array  16 , the capping inserts  50  that can be refilled with clean-filtered solvent of the appropriate type can be positioned in a secondary taught position when purging old jetting fluid through the nozzle array so as not to contaminate the capping solvent. Movement of the printhead array  16  with the associated printheads  34  is described in more detail in co-pending U.S. Provisional Application No. 60/674,590 entitled “Printable Substrate Alignment System,” which is hereby incorporated by reference. Each of the three positions ensures that the nozzle plate  36  stays moist when not in use or idle which prevents clogging of the nozzle plate  36  and ensures better performance. 
         [0037]    Now referring to  FIG. 4A , it can be seen that the capping station  40  includes an insert  46  that is spaced away from the bottom plate  44  of tray  42  along at least one side  48  to provide a gap  51 . As shown in  FIG. 4A , the insert  46  includes a positioning track  43  that allows for the capping inserts, also known as solvent baths  50 , to be moved through various angles to correspond to positions relative to the printheads  34  of the printhead array  16 . The position of the solvent baths  50  is moved through the positioning track  43  by motor  47 . Motor  47  is controlled by system control/power module  11 . 
         [0038]    Although the solvent baths  50  of insert  46  may be designed to be movable through various angles, the insert  46  can also be designed such that solvent baths  50  are immovable. It should be understood that with this approach, either the head array can be pitched to the immovable, fixed positions of the solvent baths when the heads require maintenance or, in some PMD applications, a fixed print angle head array may be used. Regardless, referring to  FIGS. 4B to 4D , it can be seen that tray  42  may include a design where insert  46  is a plate that includes slots  37  that are engageable with solvent baths  50 . That is, the solvent baths  50  are configured to include tabs  39  that engage with slots  37 . In this design, solvent baths  50  and insert  46  are adapted to allow for drainage into tray  42 . In this manner, the solvent of solvent baths  50  may be frequently, or even continuously, drained and refreshed. To refresh the solvent, solvent baths  50  are fed by a solvent manifold  27  that is connected to solvent modules  17 . Further, to dispose of used solvent, tray  42  is equipped with a drain  49  (see  FIG. 4D ) and drain line (not shown) that leads back to solvent modules  17 . The drain  49  and drain line may be connected to a high flow vacuum pump to evacuate not only the liquid waste, but also the fumes above the capping station  40 , and to minimize possible side airflow during drop analysis. 
         [0039]    In either design, it should be understood that solvent baths  50  are designed to be a size that allows +/−1.5 mm head clearance to minimize solvent evaporation when the head is capped. Further, the gap  51  enables use of a vacuum mechanism  23 , which may evacuate vapors produced by the standing solvent pools to protect clean room integrity. A secondary and equally important function of the vacuum system  23  is to capture floating ink droplets from printheads  34  during halt and fire operations, discussed below. The solvent baths  50  also may include edges  33  which are chamfered ( FIG. 4D ) to reduce the effect of non-wetting of the trough material with solvent. Lastly, it should be understood that although only a pair of solvent baths  50  are shown in the drawings, any number of solvent baths  50  may be used as required. For example, depending on the number of printheads  34 , each printhead  34  may have a corresponding solvent bath  50  in capping station  40 . 
         [0040]    The capping station  40  is also equipped with a device to adjust the height and level of the module in the PMD apparatus  10 . As shown in  FIG. 4A , the height adjustment means  53  incorporates a scissor-lift system  54  to allow the module to raise and lower. The scissor lift  54  includes a pair of cross-bars  56 . One of the cross-bars  56  is fixed at one end to a base  55 , while the other of the cross-bars  56  is movably attached along another end to lift tracks  58 . 
         [0041]    By raising and lowering the capping station  40  as necessary, interference with the movement of other modules can be avoided. For example, the height adjustment device  53  enables the capping station  40  to be lowered to a position such that drop analysis system  60  is enabled to be moved along the translation stage  22  to be disposed over capping station  40 . That is, the capping station may be raised and lowered by the height adjustment device  53  to provide clearance for the vision system  62  of the drop analysis system. Further, such movement assists in the positioning of the capping station solvent baths  50  accurately in relation to the printheads  34 . For example, the capping station  40  can be positioned so that the printheads  34  are in a vapor immersion position, solvent immersion position, or waste removal position as described above. 
         [0042]    As stated above, the vapor immersion position of the capping station  40  positions the solvent baths  50  such that the printheads  34  are positioned directly above the solvent located in the baths  50 . In such a position, the print heads are suspended over the solvent baths  50  at a distance of 0.5 mm. It should be understood, however, that any distance that satisfactorily immerses the print heads in solvent vapor is acceptable. In this regard, the distance can be determined depending on the type of ink being used. For example, a more viscous ink may require the print head to be suspended more closely to the solvent baths  50  such that the print head is subjected to a higher concentration of solvent vapor. In contrast, a less viscous ink may enable the print head to be suspended further from the solvent bath  50  as a lower concentration of solvent vapor is needed to clean the nozzles in the print head. 
         [0043]    Regardless of the distance away from the solvent bath  50 , the nozzles of the print head may be spot fired at any frequency from 1 Hz to 1000 Hz by software control that is selected and stored by the user to occur when substrate printing is not active to further eliminate drying of the ink in the printhead  34 . At such a frequency, a minimal amount of ink is discharged in a manner that prevents aggolmeration of particles within the printhead  34  for some ink types and deters air bubbles from developing in the nozzle, while still allowing the solvent vapor to inhibit drying of the inks on the face of the nozzle plate  36  to a point where normal blotting and wiping cannot remove the material. 
         [0044]    In contrast to the vapor immersion position of the capping station  40 , the liquid immersion position of the capping station  40  fully immerses the nozzles of the print head into the solvent located in the solvent baths  50 . By immersing the print head into the solvent, the print heads do not need to be spot fired to reduce the risk of air bubbles developing in the nozzles of the print head and deposits that may have built up on the nozzle surface from ink mist can naturally dissolve or soften from extended immersion, followed by a routine wiping action to renew the nozzle plate surface. 
         [0045]    In the fluid purging position, the capping station  40  is lowered to using the scissor-lift mechanism  54  to a position that is slightly lower than the vapor immersion position. In combination with movement of the lower maintenance support stage  32 , up to a 15 mm horizontal movement of the capping station  40  relative to the head array may be effectuated. In this manner, the nozzles may be positioned over a waste trough  31  that runs substantially parallel to the solvent baths  50  such that waste ink discharged by the nozzles will not be deposited into the solvent baths  50  that is filled with clean solvent. At this position, the nozzles may be spot-fired in the same manner as the vapor immersion position to discharge a minimal amount of ink, while still being cleaned in a vapor-rich atmosphere. In this position, however, the ink is discharged into the waste troughs  31  and insert  46  which includes slots  29 . Because the capping station may be connected to a vacuum mechanism  23  that runs continuously, the waste ink may be drawn into tray  42  and through the drain  49  as shown in  FIG. 4D . 
         [0046]    Another embodiment of capping station  40  uses a four bar lift mechanism to raise and lower the station  40 . This design uses a series of solvent baths  50  which are fixed, for fixed pitch print head arrays. 
         [0047]    Now referring to  FIG. 5A , the blotting station  30  absorbs excess solvent or printing fluid from the print nozzle plates  36  of the printheads  34  by contacting the printheads  34  with a blotting material  74 . Blotting is used for both recovery of blocked nozzles, and routine maintenance of nozzle plates  36 . The blotting station  30  generally includes a base  70  which is mounted to the platform  32 , as shown in  FIG. 2 . 
         [0048]    Base  70  is comprised of a base plate  90  (see  FIG. 5B ) and housing  92 . Extending from the top of the base  70  is a supporting plate  72  over which the blotting material  74  is fed via servo controlled feed motors  71 . A pop-up section  84  in the supporting plate  72  may be incorporated to allow blotting of a single printhead  34 . Supporting plate  72  may be formed of aluminum, or any material known to one skilled in the art. Further, supporting plate  72  is covered by a padding  73  and thin sheet  75  of polytetrafluoroethylene (PTFE) to protect the padding  73  and to allow for the blotting material  74  in concert with dried or drying jetting fluids to release from the surface of supporting plate  72  after periods of non-use. 
         [0049]    The blotting material  74  may be supplied as a roll that is held by support roller assemblies  76  that include brackets  78  and rollers  81 . The blotting material  74  is held at a constant tension force by supply and take-up roller assemblies  94  and  96 . Supply roller assembly  94  is attached to supporting plate  72  via bearing assemblies  98 . Take-up roller  96  assembly is supported by a support bracket  100  that is attached to bracket  78  of one of the support roller assemblies  76 . 
         [0050]    The blotting material  74  is preferably held at a constant tension force, even when the material  74  is advancing during a wiping function. The required tension is a function of the particular material and size thereof and can be set and stored through the control/power module  11 . The desired tension is achieved by pulling with the take-up roller assembly  96  and holding back with the supply roller assembly  94  until an error of a sufficient magnitude that is equal to the desired tension of the web is sensed by a motion controller system that includes a supply roller motor/encoder  102 . 
         [0051]    As the diameter of the two rolls changes, the magnitude of the error is adjusted on the supply roller assembly  94  to reflect that a decrease in the applied torque by the servo motor  71  on the supply roller assembly  94  side of the blotting station  30  is needed to sustain the constant tension as the roll size increases on the take-up roller  96  side of the blotting station  40 . The roll size is determined by a relationship between an encoder (not shown) that is provided in the servo motor  71  on the supply roller assembly  94  side of the blotting station  30  and the encoder  102  on the fixed diameter linear feed encoder shaft  104  of the supply roller assembly  94 . 
         [0052]    Shaft  104  is preferably formed of aluminum, sandblasted, and then anodized to provided a sufficiently roughened surface that prohibits slip of the blotting material  74  against its surface, such that linear motion of the blotting material  74  always has a constant relationship to the number of encoder counts that are generated by the rotary optical encoder  102  attached to this shaft  104 . If the supply roll is new and at its largest diameter, very few encoder counts will be generated by the encoder in the servo motor  71  on the supply roller assembly  94  side of the blotting station  30  relative to the linear feed encoder roller optical encoder  102 . If the supply roll is almost depleted, representing a much smaller diameter, the number of encoder counts on the encoder in the motor  71  will be proportionately larger based on the ratio of diameters. As such, it should be understood that the linear feed encoder roller encoder  102  output is important to the function of the system in maintaining constant web tension leading to the correct compliance of the blotting material  74  cloth relative to the nozzle plate  36  and elimination of wrinkles in the cloth due to extreme tension. 
         [0053]    An edge sensor  106 , shown in  FIG. 5C , may be incorporated to monitor cloth tracking errors and provide feedback to an angular adjustment actuator  108 . The angular adjustment actuator  108 , in proportion to the tracking error indicated by the edge sensor  106 , introduces a slight distortion in the tension across the blotting material web  74  by rotation of the take-up roller assembly  96  and the linear feed encoder roller  104 . This distortion causes a reaction force in the web  74  that tracks the material in a direction opposed to the error detected. The edge sensor  106  has a range of 10 mm to sense movement, and a dead band of 1 mm is established in the center of this range. No corrections will be made as long as the blotting material  74  is in the dead band region. Should it go outside the deadband region, an angular correction is made by using a steering motor  110  to drive the angular adjustment actuator  108  and the blotting material  74  is returned to its home position within 100 ms of the cloth re-entering the dead band. The amount of angular correction is also determined by the velocity of the tracking error as the blotting material  74  leaves the dead band area. 
         [0054]    The design of the blotting station module  30  also allows a vacuum hood (not shown) to be implemented because it may be required to have fume evacuation from near the blotting material rolls and table. Further, the blotting station may be positioned in a secondary containment tray that protects other modules from accidental fluid spills. 
         [0055]    As stated above, pop-up section  84  allows for the cleaning of a single print head. The pop-up section  84  may be a through-hole formed in support plate  72  that is in fluid communication with an air cylinder (not shown). Pop-up section  84  is covered by the padding and PTFE sheet that covers plate  72 . 
         [0056]    As the pop-up section  84  is in fluid communication with an air cylinder, when air is blown through pop-up section  84  the padding and PTFE sheet “pops up” to a height of 0.5 to 1.0 mm above the surrounding surface such that only a single head of interest will contact the blotting material in this area. The printhead array  16  will then move to a second taught Z position that allows precise contact of the target printhead with the popped-up section of blotting material  74 . This Z position is set to accommodate the exact pop-up height mentioned above. 
         [0057]    The printhead  34  may penetrate against the blotting assembly no more then 0.2 mm+/−0.05 mm to achieve intimate contact without causing undue wear on the nozzle plate surface  36  during wiping. The maintenance translation stage  22  in concert with the printhead array motion controller can locate any printhead  34  from a large array of heads at this singular location. Thus, while only the defective printhead is serviced, thereby reducing use of blotting material  74  and ink, no negative effects are experienced by printheads that are functioning within specified parameters. In this manner, a single print head may be cleaned independently of the other printhead ink jet array  16 . 
         [0058]    The description is merely exemplary in nature and, thus, variations are not to be regarded as a departure from the spirit and scope of the teachings.