Abstract:
Methods and apparatus include a handheld printer manipulated back and forth by an operator during use to print an image. An inkjet printhead of the printer has a plurality of fluid firing actuators arranged in a substantial column. A controller communicates with the printhead to identify active actuators given to fire at a particular time during use to print the image. However, to prevent unsightly print quality from occurring during overlapping adjacent print swaths, for example, certain of the identified actuators are prevented from firing. Especially, actuators in the column further from a center of the column fire less frequently than those closer to the center. A position sensor is also used to locate the printhead relative to the image. The controller correlates the position to the printhead and actuators and fires the active actuators or not.

Description:
FIELD OF THE INVENTION  
       [0001]     Generally, the present invention relates to handheld printers. Particularly, it relates to improving print quality in handheld printers of the type able to print in random motion patterns. In one aspect, stitching together overlapping print swaths is contemplated. In another, dithering per edges of columns of nozzles of an inkjet printhead is contemplated. Still other aspects relate to methods and structures for accomplishing same.  
       BACKGROUND OF THE INVENTION  
       [0002]     As is known, handheld printers afford mobile convenience to users. Unlike their immobile or stationary counterparts, however, users determine the path of a given swath of printing. In some instances, this includes random movement over a substrate. In others, it includes back-and-forth movement attempting to simulate a stationary printer.  
         [0003]     A common problem with handheld printers is poor alignment between adjacent swaths of print because position of the print element is often less accurate than with other types of printer. Alignment errors usually result in noticeable defects in the print. The most common print defects are called “print banding” and include both dark bands and white bands at the boundary between swaths where ink drops at the edge of a swath are printed too close or too far from drops in the adjacent print swath. Another category of print banding is a directional effect similar to the banded appearance of mowed glass when adjacent swaths are cut in different directions. These print banding defects may appear with other serial printers, but the defects can be minimized by printing a dithered image in multiple passes over the paper. With a handprinter, print banding is a problem because alignment errors are more likely, and requiring multiple passes is an unaccepted demand on the operator.  
         [0004]     Another common defect with handprinting is a gap or void in the print where the operator fails to pass the print element over that portion of the page. If detected, the operator can repair the void by moving the print element back over that area so the missing content can be printed. With a handprinter, positional errors accumulate during the page, so voids that are not repaired promptly may have significant print banding where the area printed in repair is misaligned with the adjacent areas.  
         [0005]     Accordingly, there exists a need in the art for robust, multi-directional and random printing handheld printers having improved print quality. Naturally, any improvements should further contemplate good engineering practices, such as relative inexpensiveness, stability, low complexity, ease of manufacturing, etc.  
       SUMMARY OF THE INVENTION  
       [0006]     The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described handheld printers that minimize printing defects. Specifically, methods and apparatus contemplate handheld printers manipulated randomly or predictably over a substrate on which an image is printed. In this regard, the printer examines which fluid firing actuators of an inkjet printhead in the printer are active to fire. From those, some are intentionally prevented from firing to create a dithered image having improved print quality, especially in contemplation of overlapped adjacent printing swaths.  
         [0007]     With a handheld printer, the operator must overlap swaths to avoid voids or print gaps. Since swaths must overlap to some extent, this invention takes advantage of that requirement to implement selective printing or dithering in the overlap zone. Doing so places no additional demands on the operator as might if (for example) full coverage multiple passes of the printer were required to reduce banding.  
         [0008]     In one aspect, the handheld printer includes a position sensor, a controller and a printhead. The sensor provides the location of the printhead and the controller correlates the actuators of the printhead to a to-be-printed image. In turn, the printhead has a plurality of fluid firing actuators arranged in a substantial column. The controller communicates with the printhead to identify active actuators given to fire during use to print the image. However, to prevent unsightly print quality from occurring during adjacent print swaths, for example, certain of the identified actuators are prevented from firing. Especially, actuators in the column further from a center of the column fire less frequently than those closer to the center.  
         [0009]     These and other embodiments, aspects, advantages, and features of the present invention will be set forth in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:  
         [0011]      FIG. 1  is a diagrammatic view in accordance with the present invention of a handheld printer;  
         [0012]      FIG. 2  is a diagrammatic view in accordance with the present invention of a representative inkjet printhead for use in the handheld printer of  FIG. 1 ;  
         [0013]      FIG. 3  is a diagrammatic view in accordance with the present invention of a representative arrangement of a handheld printer for improving print quality;  
         [0014]      FIG. 4  is a diagrammatic view in accordance with the present invention of a representative handheld printer with printing swaths having dithered edges;  
         [0015]      FIG. 5  is a graph in accordance with the present invention representative of an embodiment for utilizing columns of nozzles in an inkjet printhead to effectuate printing coverage;  
         [0016]      FIGS. 6A and 6B  are diagrammatic views in accordance with the present invention of printing swaths of a handheld printer having improved print quality;  
         [0017]      FIGS. 7A-7C  are diagrammatic views in accordance with the present invention of representative columns of actuators in an inkjet printhead in a handheld printer;  
         [0018]      FIG. 8  is a flow chart in accordance with the present invention of a representative method for improving print quality in a handheld printer; and  
         [0019]      FIG. 9  is a flow chart in accordance with the present invention of an alternate embodiment of the flow chart of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention and like numerals represent like details in the various figures. Also, it is to be understood that other embodiments may be utilized and that process, mechanical, electrical and/or other changes may be made without departing from the scope of the present invention. In accordance with the present invention, a handheld printer that minimizes printing defects is hereafter described.  
         [0021]     With reference to  FIG. 1 , a handheld printer of the invention that minimizes printing defects is given as  10 . During use, an operator  12  maneuvers or manipulates a housing  14  of the printer back and forth over a substrate  16  in order to print an image  18 . In various embodiments, the image will be text, figures, combinations of text and figures or the like. They will be typified in color and/or black and white.  
         [0022]     In  FIG. 2 , an inkjet printhead of the printer internal to the housing is shown generally as  110 . It includes a housing  112  having a shape that depends upon the shape of the printer. The housing has at least one internal compartment  116  for holding an initial or refillable supply of ink. In one embodiment, the compartment contemplates a single chamber holding a supply of either black ink, cyan ink, magenta ink or yellow ink. In other embodiments, it contemplates multiple chambers containing multiple different colored inks. In one instance, it includes supplies of cyan, magenta and yellow ink. In still other embodiments, it includes plurals of black, cyan, magenta and/or yellow ink. It will be appreciated, however, that while the compartment  116  is shown as locally integrated within a housing  112  of the printhead, it may alternatively be separable from the housing  112  and/or printhead  110 , for example.  
         [0023]     Adhered to one surface  118  of the housing  112  is a portion  119  of a flexible circuit, especially a tape automated bond (TAB) circuit  120 . At  121 , another portion  121  is adhered to another surface  122 . In this embodiment, the two surfaces  118 ,  122  are arranged perpendicularly to one another about an edge  123  of the housing. Electrically, the TAB circuit  120  supports a plurality of input/output (I/O) connectors  124  for connecting an actuator chip  125 , also known as a heater chip, to the handheld printer during use. Pluralities of electrical conductors  126  exist on the TAB circuit to electrically connect and short the I/O connectors  124  to the input terminals (bond pads  128 ) of the actuator chip  125  and skilled artisans know various techniques for facilitating this. In an exemplary embodiment, the TAB circuit is a polyimide material and the electrical conductors and connectors are copper or aluminum-copper. For simplicity,  FIG. 2  shows eight I/O connectors  124 , eight electrical conductors  126  and eight bond pads  128  but present day printheads have larger quantities and any number is equally embraced herein. Also, skilled artisans will appreciate that the number of connectors, conductors and bond pads, while shown as equal to one another, may vary unequally in actual embodiments.  
         [0024]     At  132 , the actuator chip  125  contains at least one ink via (alternatively reference numeral  580  in  FIGS. 7A-7C ) that fluidly connects to the ink of the compartment  116 . During printhead manufacturing, the actuator chip  125  is attached to the housing with any of a variety of adhesives, epoxies, etc., as is well known in the art. Many processes are also known that cut or etch the heater chip through a thickness thereof to form the ink via. Some preferred processes include, but are not limited to, grit blasting or etching, such as wet, dry, reactive-ion-etching, deep reactive-ion-etching, or the like. To eject ink, the actuator chip contains columns (column A-column D) of fluid firing actuators, such as thermal heaters. In other actuator chips, the fluid firing actuators embody piezoelectric elements, MEMs devices, and the like. In either, this crowded figure simplifies the actuators as four columns of six dots or darkened circles but in practice the actuators might number several dozen, hundred or thousand. Also, vertically adjacent ones of the actuators may or may not have a lateral spacing gap or stagger there between as shown in  FIGS. 7A-7C . In general, however, the actuators have vertical pitch spacing, such as about 1/300 th , 1/600 th , 1/1200 th , or 1/2400 th  of an inch along the longitudinal extent of a via. Further, it is to be appreciated that the individual actuators are formed as a series of thin film layers made via growth, deposition, masking, patterning, photolithography and/or etching or other processing steps on a substrate, such as silicon. A nozzle member, such as a laser-ablated nozzle plate with pluralities of nozzles (which are sometimes referred to as nozzle holes), not shown, is adhered to or fabricated as another thin film layer on the actuator chip such that, in an exemplary embodiment, the nozzle holes generally align with and are positioned above the actuators to eject ink. In some embodiments, however, it may be advantageous to offset the actuator from the nozzle to minimize the adverse effects of cavitation from ink bubble collapse.  
         [0025]     With reference to  FIG. 3 , in a greatly exaggerated view, the handheld printer  10  further includes a position sensor  20  and a controller  22 . The position sensor, preferably of the optical type, includes a transmitter  24  and a receiver  26  that together shine light  28  and capture reflections  30  from the substrate  16 . In this manner, the position of the housing, especially printhead  110  is made known at the controller regardless of random or predictable movement of the housing  14  by an operator.  
         [0026]     Among other things, the controller  22  also includes a stored to-be-printed representation of an image  32 . In turn, it correlates the position of the printhead, especially individual actuators, to the image. It then prints the image with ink  35  on the substrate  16  according to the image pattern  36  in the pixels  38 . A has-been-printed image  34  may also be stored or accessed by the controller to keep track of future printing and to determine whether the image has been printed completely or not. In structure, the controller may embody an ASIC, discrete IC chips, firmware, software, a microprocessor, combinations thereof or the like.  
         [0027]     In an alternate implementation, the to-be-printed image representation  32  is dynamically updated to remove pixels that have been printed so that the has-been printed information  34  is merged with the to-be-printed information.  
         [0028]     To minimize print defects and improve print quality, the controller further identifies which fluid firing actuators of the printhead are active to fire in printing the image. From those, some are intentionally prevented from firing to create a dithered image having improved print quality, especially in contemplation of overlapped adjacent printing swaths. In one aspect, certain of the identified actuators are prevented from firing. Especially, actuators in the column of actuators further from a center of the column fire less frequently than those closer to the center.  
         [0029]     For example,  FIG. 4  teaches a handheld printer  10  that made adjacent printing swaths  40  and  41  overlapping one another in a lateral direction of the figure labeled as O. In accomplishing this, certain numbers of the actuators in the column  42  were fired less frequently than others, despite all actuators needing to be fired per the fully black image being printed. In this regard, a fairly thin or dithered printed image appears in regions such as  43 , but when overlapped printing swaths occur, the composite or resultant image at  46  occurs without any substantial printing defects. This improves print quality. In a representative embodiment, the column of actuators  42  is such that the terminally positioned actuators  51  fire less frequently than centrally positioned actuators closer to the center of the column such as actuators  53  and  54 .  
         [0030]     Graphically, the actuator or nozzle number, from number 1 to some number n per a given column of fluid firing actuators  42 , is laid adjacent the printing swath  41  to show image printing coverage in percent. As is seen, nozzle numbers further away from a center C yield lower coverage percent than do nozzle numbers closer to the center. In a preferred embodiment, this results because the terminally positioned actuators are fired less frequently than centrally positioned actuators. For instance, one embodiment contemplates that actuators with nozzle numbers  1  and n (e.g., actuators  51 ) fire only 1 out of 10 fire times per a given printing swath. In turn, actuators  2  and n−1 fire 2 out of 10 times, while actuators  3  and n−3 fire 3 out of 10 times and so on until nozzle numbers  10  and n−10 fire 10 out of 10 times. With reference to  FIG. 5 , a further detailed embodiment  50  is given per a column of actuators labeled with nozzle numbers  0  to  128 . In this embodiment, full percent printing coverage is obtained for nozzles  20  through  108  while those outside the range produce less percent printing coverage. Of course, skilled artisans can contemplate other embodiments.  
         [0031]     With reference to  FIGS. 6A and 6B , two overlapping and adjacent printing swaths of the handheld printer are given as  52  and  54  in the direction of the arrows. As seen, both swaths are fully printed in the region  56  between the hash marks  57  and  58 . Also, both are less than fully printed or dithered in the regions  59  and  61  given between the hash mark and the solid lines  60  and  62 . In the inset  63 , this then produces variously printed regions. In the regions labeled  64 , the image is fully printed by either the first or second swaths  52 ,  54  of the printer having its actuators printing in a position of the column of fluid firing elements yielding 100% coverage. Conversely, region  66  has no printing because neither swath  52  or  54  ever passed over it. Regions  67 , however, remain dithered, such as region  43  in  FIG. 4 , because only a single printing swath has covered it and done so with actuator(s) in a position of the column of fluid firing elements yielding less than 100% coverage. In the last region  65 , coverage here is accomplished to an extent greater than dithered regions  67  but lesser than regions  64  because it has occurred with actuators within a position of the column of fluid firing elements yielding less than 100% coverage and more than one printing swath has been effectuated. Of course, still other coverage schemes are contemplated. For example, region  65  might be printed to 100% coverage in the second swath.  
         [0032]     With reference to  FIGS. 7A-7C , a column of fluid firing actuators could have designs alternate to those previously shown and still be embraced within the scope of the invention. For example,  FIG. 7A  shows actuators  1  through n of a given column  534  existing exclusively along one side  584  of an ink via  580 . As seen, a slight horizontal spacing gap S exists between vertically adjacent ones of the actuators and such is on the order of about 3/1200 th  of an inch. On the other hand, a vertical distance or pitch P exists between vertically adjacent actuators and such is on the order of about 1/300 th , 1/600 th , 1/1200 th , or 1/2400 th  of an inch. In  FIG. 7B , vertically adjacent ones of actuators in column  534  are substantially linearly aligned with one another along an entirety of the length of the ink via  580 . Although the actuators of  FIGS. 7A, 7B  have been shown exclusively on a left side of the ink via, alternate embodiments of the invention contemplate their location on the right side or on both sides. In  FIG. 7C , a representative embodiment of actuators on both sides of the ink via includes those in columns  534 -L and  534 -R. In this instance, each column has a spacing gap S 1  and S 2  between vertically adjacent ones of actuators and both are substantially equal. Also, pitch P is given between sequentially numbered actuators such that a twice pitch (2P) vertical spacing exists between sequential odd or even numbered actuators. Of course, all embodiments contemplate more or the same number of ink vias shown.  
         [0033]     With reference to  FIG. 8 , a method for printing with a handheld printer to minimize printing defects is given as  300 . At step  302 , the printhead position of the printer is determined. As before, this is preferably done via the assistance of a position sensor in communication with a controller. At step  304 , the printhead position is then correlated to the to-be-printed image. Again, preferably a controller of the printer effectuates this process. Then, per each of the actuators available to a printhead of the printer, it is determined whether the actuator is to be fired or not at that particular position in order to print the image, step  306 . If it is not to be fired, e.g., because the actuator would avoid yielding an ink drop at a location commensurate with the to-be-printed image, the actuator is simply not fired at step  308 . On the other hand, if the actuator is to be fired to create the image at hand, it can be considered an active actuator and a further inquiry is made. That is, at step  310 , per each of the active or to be fired actuators, is the actuator in a dithering or stitching zone. In this regard, those actuators in a column of fluid firing actuators furthest away from a center of the column are in the zone whilst those closest to the center are not.  FIG. 5 , for example, shows a representative grouping of this concept for  128  actuators. Then, at step  312 , if the actuator is not in the stitching zone (stated differently: if the actuator is in the 100% coverage zone), the actuator is simply fired and ink from the actuator is compiled on the substrate and serves to create the to-be-printed image. As an example, this corresponds to the region labeled  56  in  FIGS. 6A and 6B . Conversely, those actuators indeed in the stitching zone, e.g., regions  43 ,  47 ,  59  in  FIGS. 4, 6A  and  6 B, respectively, then need application of a stitching algorithm to fire them or not, step  314 . As before, this could correspond to firing those actuators furthest from a center of the column of actuators less frequently than those nearest the center.  
         [0034]     Finally, if the to-be-printed image is completely printed at step  316 , the process ends. If not, the printer is moved at step  318  and repeated until eventually the entire to-be-printed image is rendered on the substrate. To ascertain this, it is preferred the controller  22  ( FIG. 4 ) compares the to-be-printed image  32  to the has-been-printed image  34 . In the event the images are the same, then printing is complete. Conversely, if they are different, printing is incomplete. Of course, certain de minimus exceptions could be programmed such that the controller would conclude complete printing even though an exact 100% percent comparison did not exist. Also, various noise could be introduced into the has-been-printed image to afford even better print quality. In this regard, certain random or predictable pixels  37  ( FIG. 4 ) could be removed from a bitmap of pixels. Noise, as is well known, is common to stationary printing and not further described herein.  
         [0035]     In still another embodiment,  FIG. 9  explores the concept that certain instances of printing might not require the notion of dithering or stitching despite an actuator being located in a stitching zone. That is, step  320  is introduced at nodes A and B between steps  310  and  314  of  FIG. 8  to further inquire whether the to-be-printed image is at an object edge, such as edge  21  in  FIG. 1 . If not, the actuator under consideration progresses as normal to the stitching algorithm of step  314  to minimize print defects. If so, the actuator under consideration progresses to being fired at step  312  regardless of its position in a column of fluid firing actuators. In this manner, it is contemplated that further printing swaths over the object edge would fairly unlikely require stitching. It is expected that banded ink from the printhead would not appear at an object edge because no future ink firing commands would be given to any actuators once the pixel of the to-be-printed image at the edge has been considered fired or printed.  
         [0036]     In any embodiment, certain advantages of the invention over the prior art are readily apparent. For example, the invention at hand minimizes print banding and improves print quality. Less intuitively, whenever an operator using the handheld printer of the invention traverses visible voids in the image, the dithering of printing produces better quality. Also, because of simple logic in the apportioning of which active or to-be-fired actuators are prevented from being fired in a column of actuators, printing robustness is added while manufacturing costs are minimized.  
         [0037]     Finally, one of ordinary skill in the art will recognize that additional embodiments are also possible without departing from the teachings of the present invention. This detailed description, and particularly the specific details of the exemplary embodiments disclosed herein, is given primarily for clarity of understanding, and no unnecessary limitations are to be imported, for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit or scope of the invention. Relatively apparent modifications, of course, include combining the various features of one or more figures with the features of one or more of other figures.