Abstract:
An air vane directs air to cool the printhead of thermal inkjet printers having one or more movable carriages. A passive air vane is mounted on or molded to some portion of the carriage, printhead, ink tank or ink tank holder so that it moves with the movable carriage. Moving the air vane significantly increases the flow of air over the printhead, increasing the flow of heat away from the printhead and, consequently, improving the performance of the printer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates generally to thermal fluid ejectors with movable carriages. 
     2. Description of Related Art 
     Conventional thermal fluid ejectors with movable carriages have elements that are cooled through a physical connection to a heat sink and through natural heat convection from the heat sink to the ambient environment as the movable carriage moves over the guide rail. In some fluid ejector systems, this natural cooling becomes insufficient during times of high workload, such that the ejection elements tend to overheat. When the ejection elements start to overheat, some thermal fluid ejector systems are designed to automatically reduce the effective workload by decreasing the ejection rate, such that the natural cooling of the fluid ejectors again, becomes sufficient. 
     SUMMARY OF THE INVENTION 
     Improving the heat transfer away from the ejection elements would tend to solve this overheating problem. Such improvements would reduce the need for automatic reductions in the effective workload. 
     This invention provides systems and methods that improve the effective heat transfer rate from one or more thermal fluid ejectors of a fluid ejection system. 
     This invention separately provides systems and methods for increasing the effective heat transfer rate of heat generated by a thermal fluid ejector directly to the ambient atmosphere. 
     This invention separately provides systems and methods that increase effective flow rates of the ambient atmosphere over one or more thermal fluid ejectors of a fluid ejection system. 
     This invention separately provides one or more deflectors that direct a flow of ambient atmosphere across one or more printheads of a fluid ejector as a carriage on which the one or more thermal fluid ejectors are mounted moves during printing. 
     In various exemplary embodiments of the systems and methods according to this invention, a thermal fluid ejector cooling system improves the cooling of the thermal fluid ejector by taking advantage of the reciprocating motion of the movable carriage to increase the flow of the ambient atmosphere over the heat sink and/or one or more of the thermal fluid ejectors. The improved cooling obtained according to the systems and methods of this invention can be substantial and can decrease or even eliminate the need to automatically adjust the effective workload. 
     In various exemplary embodiments, the cooling systems according to this invention includes a passive structure, such as an air vane, that moves with the movable carriage and uses that movement to re-direct the ambient atmosphere to flow over the fluid ejector heads. The passive structure may be constructed of a variety of materials and may be an integral part of a thermal fluid ejection system or an add-on to an existing thermal fluid ejection system. 
     These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of this invention will be described in detail, with reference to the following figures, wherein: 
     FIG. 1 is a plan view of a conventional fluid ejection system; 
     FIG. 2 is a plan view of one exemplary embodiment of a fluid ejection system incorporating a first exemplary embodiment of the cooling systems according to this invention; 
     FIG. 3 is a side view of the fluid ejection system shown in FIG. 2; 
     FIG. 4 is a top plan view of the ejection system shown in FIG. 2; 
     FIG. 5 is a plan view of one exemplary embodiment of a fluid ejection system incorporating a second exemplary embodiment of the cooling systems according to this invention; 
     FIG. 6 is a plan view of a fluid ejection system incorporating a third exemplary embodiment of the cooling systems according to this invention; and 
     FIG. 7 is a plan view of one exemplary embodiment of a fluid ejection system incorporating a fourth exemplary embodiment of the cooling systems according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates one exemplary embodiment of a conventional thermal fluid ejection system  100 , such as for example a thermal inkjet printer, that includes one or more thermal fluid ejectors, one or more guide rails  101 , a movable carriage  102 , a number of fluid tanks  103 - 106 , and one or more heat sinks  110 , as are conventionally found in thermal inkjet printers with movable carriages. The one or more guide rails  101 , usually comprising at least one rectangular or cylindrical metallic bar, are rigidly fixed to a housing (not shown) of the thermal fluid ejection system. A fluid ejection head  115  includes one or more thermal fluid ejectors  108  and  109  and zero, one or more heat sinks  110 . A movable carriage assembly  116  includes the movable carriage  102  and those elements mounted on or supported by the movable carriage  102 . Elements mounted on or supported by the movable carriage may include but are not limited to at least one fluid ejection head  115  and at least one of the fluid tank  103 - 106 . 
     During operation, the movable carriage  102  is driven back and forth along the one or more guide rails  101  in a fast scan direction A. As shown in FIGS. 1 and 3, a fluid receiving medium  113  moves in a process direction B that is perpendicular to the fast scan direction A. As the movable carriage  102  moves back and forth along the one or more guide rails  101  along the fast scan direction A, the fluid ejector heads  108  and  109  expel fluid received from the fluid tanks  103 - 106  onto the exposed face of the fluid receiving medium  113  and generate a desired pattern of expelled fluid onto the fluid receiving medium  113 . 
     During fluid ejection operations of the thermal fluid ejection system  100 , the thermal fluid ejector heads  108  and  109  use thermal energy in methods well known in the industry to increase the temperature of the fluid to be expelled and to generate bubbles that cause droplets of the fluid to be expelled through nozzles of the fluid ejector heads  108  and  109 . This usually entails applying heat energy to keep the fluid ejector heads  108  and  109  within a predetermined operating temperature range. Additional heat energy is temporarily applied to generate fluid vapor bubbles in one or more ejector channels of the fluid ejector heads  108  and  109 . These fluid vapor bubbles eject droplets of the fluid through nozzles ending the ejector channels of the fluid ejector heads  108  and  109 . As a result, a desired pattern of fluid droplets is generated on the fluid receiving medium  113 . 
     Heat is conducted away from the fluid ejector heads  108  and  109  through the one or more heat sinks  110 , if provided, that are in physical contact with the fluid ejector heads  108  and  109 . Heat is convected away along the surface of the heat sinks  110 , if provided, and, to a lesser extent is some exemplary embodiments, along the surface of the fluid ejector heads  108  and  109 , as heated gases in the ambient atmosphere naturally rise and as the ambient atmosphere flows past the one or more heat sinks  110 , and/or the fluid ejector heads  108  and  109 , with each movement of the movable carriage  102  along the one or more guide rails  101 . During normal use of such conventional thermal fluid ejection systems  100 , this arrangement is sufficient to keep the operating temperature within the temperature limits predetermined for optimal fluid ejection functions and acceptable life of the fluid ejector heads  108  and  109 . 
     However, in some fluid ejection systems  100 , for example during periods of sustained and/or heavy use, the actual operating temperature tends to increase beyond the predetermined operating temperature range. When this happens, fluid ejection functions tend to degenerate, as the size of the fluid droplets to be expelled is highly dependent upon temperature. The useful life of the fluid ejection heads  108  and  109  also tends to be negatively affected, as the electronic elements contained in the ejection head  115  can be sensitive to sustained elevated temperatures. Some fluid ejection systems  100  are designed to lower the effective workload during periods of overheating by reducing ejection speeds, so that the cooling system is again able to effectively cool the fluid ejection heads  108  and  109 . Although this solution is to be desired over the problem, such an arrangement trades one negative performance characteristic for another negative performance characteristic. 
     The various exemplary embodiments of the cooling systems according to this invention increase the flow of the ambient atmosphere over the ejection head  115  as the movable carriage  102  moves back and forth along the one or more guide rails  101  in the fast scan direction A. FIGS. 2-4 illustrate one embodiment of the fluid ejection system  100  that incorporates a first exemplary embodiment of a cooling system  200  according to this invention. 
     As shown in FIGS. 2-4, in this exemplary embodiment, the movable carriage assembly  116  is equipped with a multi-curved vane  200  that is attached to a portion of the movable carriage  102 . The multi-curved vane  200  may be of any shape that is suitable to increase the flow of the ambient atmosphere to the ejection head  115  as the movable carriage  102  moves back and forth along the one or more guide rails  101  in the fast scan direction A. In various exemplary embodiments, the multi-curved vane  200  may be made of any suitably light and/or durable material. In various exemplary embodiments, the improved cooling provided by the multi-curved vane  200  reduces the operating temperature of the ejection head  115  relative to the exemplary embodiment shown in FIG. 1 for any given rate of movement of the movable carriage assembly  116  along the guide rails  101  and reduces or eliminates the need to reduce the effective level of use. 
     It should be appreciated that the shape of the multi-curved vane  200  can vary as well as the as the manner and location of its attachment. FIG. 5 is a plan view of one exemplary embodiment of a fluid ejection system incorporating a second exemplary embodiment of the cooling systems according to this invention. As shown in FIG. 5, instead of the multi-curved vane  200  shown in FIGS. 2-4, the cooling system according to this invention is implemented using a single, straight vane  201 . The straight vane  201 , like the multi-curved vane  200 , redirects the ambient atmosphere to improve the cooling of the ejection head  115 . 
     FIGS. 6 and 7 are plan views of one exemplary embodiment of a fluid ejection system incorporating third and fourth exemplary embodiments of the cooling systems according to this invention. As shown in FIGS. 6 and 7, the second and third exemplary embodiments of the cooling systems according to this invention include a plurality of vanes  202  and  203 , respectively. In particular, in FIG. 6, the plurality of vanes, or more generally, passive structures,  202  are straight structures that are set at an angle α and relative to the direction of travels along the fast scan direction A. Of course, the flow of ambient atmosphere across the fluid ejection head is increased or decreased in accordance with the shape of each passive structure and the angle α at which it is attached. 
     However, the invention is not limited to the exemplary embodiments portrayed in FIGS. 6 and 7. Neither the size, shape or number of passive structures nor the manner of attachment is limited to that discussed above. Further, the angles of attachment for each passive structure may be the same, as portrayed in FIGS. 6 and 7 or each passives structure may be located at a different angle α to the fast scan direction A. Multiple passive structures, such as those described above, allow improved redirection of the ambient atmosphere regardless of the direction of the movable carriage  102 . 
     The passive structure  200 - 203  could be formed as a molded portion of the movable carriage  102  of a fluid ejection system as manufactured, or could be implemented as separate structures attached to the movable carriage  102  of an existing fluid ejection system. Such separate structures could be attached using any number of well known attaching materials, structures and/or devices, such as glue, screws and/or velcro. Also, it should be appreciated that the attachment location for the passive structures  200 - 203  is not limited to the portion of the movable carriage  102  depicted in FIGS. 2-7. It should be appreciated that the passive structures  200 - 203  can be located on another portion of the movable carriage  102 , as well as any part supported by the movable carriage  102 . Finally, it should be appreciated that the passive structures  200 - 203  are not limited to single passive structures. Obviously, the passive structures  200 - 203  can include any number of similar passive structures arranged to increase air flow over the fluid ejection head  115 . 
     While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.