Abstract:
In described embodiments, a portable image printing device is disclosed. The device is self-propelled and rolls over a substrate onto which the device imparts an image. The image is drawn from an electronic image file retained within or otherwise supplied to the device. The device can use a plurality of media, such as, for example, chalk or paint that is dispensed vertically onto the substrate. Alternatively, a cutting head can be used to cut an image into a grass-filled substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from U.S. Provisional Patent application 62/174,722, filed on Jun. 12, 2015, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    This invention relates to the field of image printing onto a substrate. More specifically, the invention provides a means for applying an image to a stationary and unmovable substrate such as paved ground, grass covered ground or similarly fixed surfaces. 
         [0004]    Description of the Related Art 
         [0005]    Many types of image printing devices exist that include a computer controlled printer whereby a movable substrate, normally paper, is fed through an arrangement of paper handling rollers into proximity with an effector that transfers ink to the substrate to apply a predetermined image to the substrate. Other types of printing machines consist of a table or platen onto which the substrate is fixed while an effector is moved about the perimeter of the printing area while ink is dispensed onto the fixed substrate. In this case the effector is moved about the substrate by a CNC Cartesian robot that straddles over the substrate platen. These examples, among others, are useful in the case where the substrate is able to be moved and fixed to the printing area of the machine and where the substrate is of a size that corresponds with the dimensional capabilities of the printing machine. If the substrate is not able to be moved to the printing machine or is larger than the capabilities of the machine, the image may not be able to be transferred onto that substrate or it may be printed by manual methods like stenciling or freehand drawing. 
         [0006]    It would be beneficial to provide an image printing device that can print on a substrate that is larger than the print area of the printing machine. 
       SUMMARY OF THE PRESENT INVENTION 
       [0007]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0008]    To address the shortcomings of the current technologies, the present invention provides a means for printing an image onto a large as well as permanently fixed substrate. More specifically, the device is a portable Cartesian robot gantry having a moveable x and y axis and a vertical axis whereby a printing effector, dispenser or other imaging apparatus will distribute a print medium that can be a variety of paint, ink or pigmented liquids or solid material, such as chalk or chalk dust, onto a fixed substrate to form a predetermined image onto the substrate. 
         [0009]    The invention also provides an alternative to the dispensing of pigmented liquids by adapting a commercially available chalk stick or other drawing implement to its perpendicular axis and moving the effector about the fixed substrate to draw the image onto the substrate. 
         [0010]    As another alternative to liquid dispensing, the effector may carry a powder such as chalk or dehydrated paint about the fixed surface while dispensing or dropping the powder onto the fixed surface to form as image on the surface. 
         [0011]    An inventive aspect of the invention is that one of the horizontal axis is movable over the surface of the substrate while the axis remains in full contact with said surface during the printing process. The first axis may be movable over the surface by means of wheels, track belt while the second axis is perpendicularly attached to the first axis and allowed to move in coordinated motion with each other as in a CNC automated process. 
         [0012]    Another aspect of the invention is that the invention may be programmed to draw an outline that allows for subsequent filling of the blank areas of the printed image such as in the example of a coloring book image that may be printed onto a paved surface to be “colored” by a child as one would in the case of a coloring book. The inventive device is also capable of dispensing a pigmented material onto a course or non-uniform surface such as grass on a sports playing field or golf course. The machine may be used to apply a mascot image to a grass or other type of field or sponsor logos and other images to a golfing surface. 
         [0013]    In any of the mentioned uses, it may be desired that the images are easily removed when the image is no longer wanted on the surface. In this case, the print medium can be a washable material and readily washed away. 
         [0014]    Another novel aspect of the invention is that the above mentioned effector may be a cutting or trimming device such as a string type weed trimmer that is moved about the image area of a grass surface while trimming the grass to a second height as compared to the grass surface resulting in a three dimensional predetermined image on the surface. 
         [0015]    Another aspect of the invention is that the device is capable of having a variety of the mentioned effectors available and readily interchangeable. 
         [0016]    While the first mentioned axis is in constant contact with the surface of the substrate and has wheels or tracks that give the axis the ability to move infinitely in a line with that axis, the second axis being fixed to the first axis limits the range by the length of the second axis beam. To overcome this shortcoming, the device may include provisions for readily exchanging the beam of the second axis with a beam of a suitable length. 
         [0017]    The first axis wheels or belt may be operated independently so that the device may be navigated remotely by the operator without removing the device from contact with the surface. By controlling the speed, proportion and direction of the first axis carriage wheels or belts in relation to the opposing wheels or tracks of the same axis, an operator may guide the device over the substrate as with a typical remote control toy vehicle and into a position on the surface where the user wishes to apply an image. In addition, the independent wheel movement allows the operator to print an image onto a substrate while maneuvering the device manually via remote control causing the image to print in an arched or wavy effect. Likewise, the operator may print an arched text or other image by varying the rotation ratio of one carriage wheel assembly relative to the other carriage wheel assembly to produce an arched text effect. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0018]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. 
           [0019]      FIG. 1  is a perspective view of a portable image printing device (“printing device”) according to a first exemplary embodiment of the present invention; 
           [0020]      FIG. 2  is a perspective view of a roller assembly of the printing device shown in  FIG. 1 ; 
           [0021]      FIG. 3  is a schematic view of the top of the printing device shown in  FIG. 1 ; 
           [0022]      FIG. 4  is a side elevational view of the printing device shown in  FIG. 1 , with the front of the beam removed; 
           [0023]      FIG. 5  is a front perspective view of the left hand portion of the printing device shown in  FIG. 1 ; 
           [0024]      FIG. 6  is a sectional view of a mounting plate slidably mounted on the rails on the front of the beam of the printing device shown in  FIG. 1 ; 
           [0025]      FIG. 7  is a top perspective view of the mounting plate shown in  FIG. 6 ; 
           [0026]      FIG. 8  is a perspective view of the mounting plate shown in  FIG. 6 , showing how the effector shown in  FIG. 1  is attached thereto; 
           [0027]      FIG. 9  is a perspective view showing the effector attached to the mounting plate shown  FIG. 8 ; 
           [0028]      FIG. 10  A bottom elevational view of the printing device shown  FIG. 1   
           [0029]      FIG. 11  is an exemplary electrical schematic for the printing device shown in  FIG. 1 ; 
           [0030]      FIG. 12  is a perspective view of the central portion of the top of the printing device shown  FIG. 1  showing the handle and controller; 
           [0031]      FIG. 13  is a schematic view of a printing device according to a second exemplary embodiment of the present invention; 
           [0032]      FIG. 14  is a perspective view of a printing device according to a third exemplary embodiment of the present invention with a beam having a first length; 
           [0033]      FIG. 15  is a perspective view of the printing device shown in  FIG. 14 , with the beam having a second length; 
           [0034]      FIG. 16  is a perspective view of a printing device according to an alternative exemplary embodiment of the present invention; 
           [0035]      FIG. 17  is an exploded view of the printing device shown in  FIG. 16 ; 
           [0036]      FIG. 18  is an exploded view of an exemplary drive mechanism used with the printing device shown in  FIG. 16 ; 
           [0037]      FIG. 19  is a perspective view of an exemplary beam and carriage used with the printing device shown in  FIG. 16 ; 
           [0038]      FIG. 20  is a bottom perspective view of the beam and carriage assembly shown in  FIG. 19 ; 
           [0039]      FIG. 21A  is a side elevational view of a paint can mounted in a first position on the beam and carriage assembly shown in  FIG. 19 ; 
           [0040]      FIG. 21B  is a side elevational view of a paint can mounted in a second position on the beam and carriage assembly shown in  FIG. 19 ; 
           [0041]      FIG. 21C  is a side elevational view of a paint can mounted in a third position on the beam and carriage assembly shown in  FIG. 19 ; 
           [0042]      FIG. 22A  is a side elevational view of a cam in a non-activating position on the device shown in  FIG. 16 ; 
           [0043]      FIG. 22B  is a side elevational view of a cam in a first activating position on the device shown in  FIG. 16 ; and 
           [0044]      FIG. 22C  is a side elevational view of a cam in a second activating position on the device shown in  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]    In the drawings, like numerals indicate like elements throughout. Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. The terminology includes the words specifically mentioned, derivatives thereof and words of similar import. As used herein, the term “longitudinal” is defined as a straight-line direction of the travel of the inventive printing device and the term “lateral” is defined as a straight-line direction perpendicular to the longitudinal direction, or straight-line direction between roller assemblies of the inventive printing device. The embodiments illustrated below are not intended to be exhaustive or to limit the invention to the precise form disclosed. These embodiments are chosen and described to best explain the principle of the invention and its application and practical use and to enable others skilled in the art to best utilize the invention. 
         [0046]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. 
         [0047]    As used in this application, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. 
         [0048]    Additionally, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. 
         [0049]    Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. 
         [0050]    The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. 
         [0051]    It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present invention. 
         [0052]    Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. 
         [0053]    Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements. 
         [0054]    Referring now to  FIGS. 1-12 , a portable image printing device  100  (“printing device”) according to a first exemplary embodiment of the present invention is shown. Printing device  100  rolls freely on top of a fixed substrate  50 , such as, for example, blacktop, concrete, grass, or other generally flat substrate, represented by the plane of the paper of  FIG. 1 . Substrate  50  is larger than the largest dimension of printing device  100  such that device  100  rolls on top of and over substrate  50  while printing device  100  is discharging a printing material onto substrate  50 . 
         [0055]    While it is desired the substrate  50  be generally flat, substrate  50  can have imperfections such that at least one part of substrate  50  may be vertically higher than another part of substrate  50 . Also, while it is desired substrate  50  is generally flat or horizontal, those skilled in the art will recognize that substrate  50  can be disposed at an angle relative to the horizontal, although such angle must be of a degree to allow printing device  100  to traverse substrate  50  without slippage. 
         [0056]    Printing device  100  travels in a longitudinal, or “x”, direction as indicated by arrows  52  shown in  FIG. 1 . Printing device  100  includes a first roller assembly  110 , a second roller assembly  140 , and a connecting beam  160  extending between first roller assembly  110  and second roller assembly  130 . Connecting beam  160  also includes an effector  180  that laterally traverses printing device  100  between first roller assembly  110  and second roller assembly  140 . In a first embodiment, as shown in  FIG. 1 , effector  180  is a paint sprayer that sprays a stream of paint or other liquid onto substrate  50 . In an alternative embodiment, effector  180  can be a printhead that dispenses ground particles, such as, for example, chalk dust, onto substrate  50 . 
         [0057]      FIG. 2  is a sectional view of first roller assembly  110 . Roller assembly  110  includes a frame  111  that supports a drive motor  112  (shown in  FIG. 1 ). Drive motor  112  is electrically powered by a power source  114  (shown in  FIG. 3 ) located within beam  160 . While an exemplary embodiment, a power source  114  can be a battery, those skilled in the art will recognize that other types of power sources, such as, for example, a solar cell mounted on top of beam  160 , can be used. 
         [0058]    A first drive wheel  116  is operatively connected to the output of drive motor  112 . A first drive belt  118  extends partially around first drive wheel  116  and is driven by drive wheel  116 . First drive belt  118  also extends partially around a second drive wheel  120  that is rotatably mounted onto frame  111  such that rotation of first drive wheel  116  rotates first drive belt  118 , which in turn rotates second drive wheel  120 . Second drive wheel  120  is coaxially connected to an upper wheel  122  via a connecting shaft  123  such that upper wheel  122  rotates with second drive wheel  120 . A second drive belt  124  extends partially around upper wheel  122 , as well as two lower wheels  126 ,  128  that are also rotatably mounted to frame  111  such that rotation of upper wheel  122  rotates second drive belt, which, in turn, rotates lower wheels  126 ,  128 . Wheels  126 ,  128  propel device  100  across substrate  50 . A front cover plate  129  is attached to frame  111  and protects drive motor  112 , drive belts  118 ,  124 , and wheels  116 ,  120 ,  126 ,  128 . As shown in  FIG. 2 , spacers  131  can be provided to space front cover plate  129  from frame  111 . 
         [0059]    Referring to  FIG. 3 , a shaft  130  extends co-axially with connecting shaft  123  and extends through connecting beam  160  to drive second roller assembly  140 . Second roller assembly  140  is identical to first roller assembly  110 , with the exception of drive motor  112 , which is omitted from second roller assembly  140 . Wheels  126 ,  128  of second roller assembly  140  rotate in conjunction with wheels  126 ,  128  of first roller assembly  110  to propel device  100  along the x-axis  52 , as shown in  FIG. 1 . Wheels  126 ,  128  can be reversed such that device  100  can be propelled along the negative of x-axis  52 . 
         [0060]    Referring now to  FIG. 4 , a carriage motor  142  is mounted inside beam  160  and has an output drive wheel  144  that extends outwardly from a front face  162  of beam  160 . Operation of motor  142  rotates drive wheel  144  in a plane generally parallel to the front face  162  of beam  160 . Drive wheel  144  rotates an endless loop belt  150  that extends around idler wheels  152 - 157 . In an exemplary embodiment, belt  150  can be a strand of inextensible material, such as, for example, Kevlar. Alternatively, those skilled in the art will recognize that other types of belts, such as, for example, a chain, a timing belt, or other suitable endless loop belt, may be used. 
         [0061]    Idler wheels  152 ,  153  are mounted in first roller assembly  110  and idler wheels  154 ,  155  are mounted in second roller assembly  130 . Idler wheels  156 ,  157  are mounted on front face  162  of beam  160  generally below drive wheel  146  such that, as belt  150  winds around drive wheel  146  and idler wheels  152 - 157 , belt  150  engages drive wheel  146  over an arc of about  270  degrees around the outer perimeter of drive wheel  146 . A plate connector  158  is fixedly attached to belt  150 . A mounting plate  168  that is used to mount effector  180 , thereon is attachable to play connector  158 . 
         [0062]    A tensioning device  200  is shown in  FIGS. 2 and 4 . Tensioning device  200  can be used to tighten belt  150 . Tensioning device  200  is located between idler wheels  152  and  153  in order to pull belt  150  away from idler wheels  152  and  153  to reduce slack in belt  150 . 
         [0063]    Referring now to  FIG. 5 , an upper rail  164  and a lower rail  166  are mounted on front face  162  of beam  160  such that drive wheel  144  is between lower rail  166  and front face  162  of beam  160 . Each of upper rail  164  and lower rail  166  are electrified with electricity from power source  114  (shown  FIGS. 3 and 11 ) to provide electrical power to a pump  185  (shown schematically in  FIG. 11 ) on effector  180  from power source  114 . An exemplary electrical schematic for printing device  100 , shown in  FIG. 11 , shows the electrical circuit used to power effector  180 . 
         [0064]    Plate connector  158  extends below upper rail  164 . As shown in  FIG. 6 , a gap is formed between front face  162  and the front of each of rails  164 ,  166  such that mounting plate  168  having a generally “H” shaped cross-section fits between rails  164 ,  166 . Mounting plate  168  is attached to plate connector  158  such that, when drive wheel  146  drives belt  150  and plate connector  158 , mounting plate  168  traverses the length of beam  160 . Mounting plate  168  is constructed from an electrically insulating material such as, for example, a polymer. Optionally, although not shown, rollers can be attached to the top and bottom of mounting plate  168  to facilitate sliding of mounting plate  168 , between rails  164 ,  166 . Those skilled in the art will recognize that other types of mounting connections to reduce friction between mounting plate  168  and rails  164 ,  166  can be used instead. 
         [0065]      FIGS. 7 and 8  show front views of mounting plate  168 . Mounting plate  168  includes a plurality of magnets  170   a - d  that mate with magnetically attractive surfaces  188   a - d , respectively, on a non-electrically conducting mounting plate  169  four effector  180  to releasably secure effector  180  onto mounting plate  168 . Mounting plate  168  also includes a plurality of through openings  172 ,  174  through which Pogo pins  182 ,  184  extend to electrically engage rails  164 ,  166 , respectively. Each Pogo pin  182 ,  184  includes a biasing member, such as, for example, a spring  186  that biases the head of each Pogo pin  182 ,  184  against its respective rail  164 ,  166  to ensure electrical contact between rails  164 ,  166  and their respective Pogo pins  182 ,  184 . Pogo pins  182 ,  184  are electrically connected to effector  180 , shown in  FIG. 11 , to transmit electrical power from rails  164 ,  166  to effector  180 . Dashed lines  190  in  FIG. 8  show how Pogo pins  182 ,  184  are inserted through openings  172 ,  174 , respectively. 
         [0066]    An exemplary effector  180  mounted on mounting plate  168  is shown  FIG. 9 . In this embodiment, effector  180  may include a commercially available liquid reservoir  182  operatively connected to a dispenser nozzle  184  for dispensing liquid within liquid reservoir  182  onto substrate  50 , such as, for example, to draw a picture. While effector  180  is shown in  FIG. 9  as a liquid dispenser, those skilled in the art will recognize that effector  180  can be other units, such as, for example, a solid (granular or powder) dispenser, a drawing stick (chalk stick) that physically engages substrate  50 , a rotating filament (Weed Wacker) or other electrically operated unit that can leave a mark on or otherwise modify substrate  50 . Further, while reservoir  182  is a single reservoir for containing a single color liquid, those skilled in the art will recognize that, alternatively, multiple reservoirs (not shown), with different colored liquids can be incorporated into effector  180 . 
         [0067]    An underside portion  210  of beam  160  is shown in  FIG. 10 . Hardwire electrical connections, such as, for example, a USB port  212 , a serial RS-232 port  214  and a parallel port  216  are shown. USB port  212  can be used to recharge power source  114  while hardwire connections to  14 ,  16 , such as, for example, RS-232 port  214  and/or parallel port  216 , can be used to provide electronic information to controller  183  for controlling the operation of effector  180 . While removable hardwire connections  214 ,  216  for transmitting an image file to bring device  100  are shown, those skilled in the art will recognize that wireless connections to a controller  220  (shown in  FIG. 11 ) from an outside source, such as a remote device  60  (also shown in  FIG. 11 ), can be provided instead. 
         [0068]    Additionally, a power switch  218  to provide electrical power from power source  114  can be provided on beam  160 . Power switch  218  can be electrically coupled to control board  220  and/or effector power controller  224  While  FIG. 10  shows hardwire connections  214 ,  216  and power switch  218  on the underside portion  210  of beam  160 , those skilled in the art will recognize that hardwire connections  214 ,  216  and power switch  218  can be located other places on device  100 . While, in  FIG. 1 , drive motor  112  that is used to power roller assemblies  110 ,  140  is shown as extending outwardly from  110 , alternatively, as shown in  FIG. 10 , drive motor  112  can alternatively be mounted within beam  160 . 
         [0069]    An exemplary electrical schematic drawing for device  100  is shown in  FIG. 11 . As shown in the Figure, a remote device  60 , such as, for example, a laptop computer  60 , can be provided to generate an image that will be printed by printing device  100 . A file containing the image is transmitted from remote device  60 , via connections  214 ,  216 , or wirelessly to controller  220 . Printing device  100  may be configured to a print raster type image onto substrate  50 . In such an arrangement, effector  180  will traverse (in a scanning motion) the entire image area of substrate  50  while placing dots of the printing material (paint) onto the locations that need to be covered by the material to form the image. After each pass over the length of beam  160 , drive motor  112  will advance printing device  100  a predetermined distance, and effector  180  will then traverse across beam  160  along the opposite direction (parallel to the y-axis). This process is similar to the method commonly used in a desktop printer, such as an inkjet or a laserjet printer. 
         [0070]    Alternatively, an alternative exemplary embodiment of printing device  100  may be configured to dispense the paint product by drawing lines and arcs from point to point as a person would commonly do while drawing the image with pencil or other handheld implement in a process known as a vector type drawing. In this embodiment, drive motor  112  can be moving printing device  100  along the X-axis while, simultaneously, effector  180  is traversing along the length of beam  160  and discharging printing medium onto substrate  50 . 
         [0071]    The control system for printing device  100  also includes a drive motor controller  222  that receives electronic signals from controller  220 . Controller  222  is operatively connected to drive motor  112  as well as to carriage motor  142 . Additionally, drive motor controller  222  is also electronically connected to an effector power controller  224  that provides electrical power to effector  180  via rails  164 ,  166 . The electricity from rails  164 ,  166  is used to power pump  185  on effector to dispense the printing material onto substrate  50 . 
         [0072]    In an exemplary embodiment, as illustrated in  FIG. 3 , power source  114  is generally centrally located within beam  160 , generally underneath handle  230 , in order to centrally balance the weight of power source  114  within beam  160 . Additionally, an operator control interface  190  is located beneath handle  181  and is operatively coupled to controller  220 . Operator control interface  190  includes a display panel  192  that displays operating parameters, such as, for example, the speed of printing device  100 . A first button  194  can be pressed to increase the speed of printing device  100  and a second button  196  can be pressed to decrease the speed of printing device  100 . In an exemplary embodiment, printing device  100  can be programmed to traverse over substrate 50 at speeds of 4 in./second, 8 in./second, 12 in./second, or 16 in./second, although those skilled in the art will recognize that printing device  100  can be programmed to operate at different speeds as well. 
         [0073]    Additionally, a “Clear” button  198  can be pressed to clear the memory in controller  220  so that a new program can be transmitted to controller  220  for printing by printing device  100 . 
         [0074]    In an alternative exemplary embodiment of a printing device  250 , shown in  FIG. 13 , roller assembly  110  is de-coupled from roller assembly  140  such that roller assembly  140  is independently operable from roller assembly  110 . As a result, drive assemblies  110 ,  140  can be operated by drive motor controller  222  at different speeds, resulting in printing device  250  being able to turn. Still alternatively, drive assemblies  110 ,  140  can be operated in different directions (roller assembly  140  can be reversed relative to roller assembly  110 ), resulting in printing device  250  in place. Drive assembly  140  is operated by a separate drive motor  252  that is separately controlled by controller  220 , as shown by the dashed lines in  FIG. 11 . 
         [0075]    In the exemplary embodiments described above, connecting beam  160  is fixedly connected to each of first roller assembly  110  and second roller assembly  140 . 
         [0076]    In an alternative exemplary embodiment of a printing device  300  according to the present invention, however, as shown in  FIGS. 14 and 15 , a connecting beam  350  is removably connected to each of a first roller assembly  310  and a second roller assembly  330  so that connecting beam  350  can be removed from printing device  300  and replaced with a connecting beam  350 ′ (shown in  FIG. 15 ), that has a length different than connecting beam  350  to form printing device  300 ′. The interchangeability of connecting beam  350  and connecting beam  350 ′ allows printing devices  300 ,  300 ′ of different lateral length to be able to print different sized output onto substrate  50 . 
         [0077]    Optionally, substrate  50  can be coated with a sealant (not shown) after printing with effector  180  in order to retain the image generated onto substrate  50  for extended period of time. 
         [0078]    An alternative embodiment of a printing device  400  is shown in  FIGS. 16-22C . Device  400  is similar to the previously described embodiments, with alternative features regarding translation and dispensing of a print medium from an effector assembly  480 . Device  400  rolls freely on top of a fixed substrate  50 , such as, for example, blacktop, concrete, grass, or other generally flat substrate, represented by the plane of the paper of  FIG. 16 . Substrate  50  is larger than the largest dimension of printing device  400  such that device  400  rolls on top of and over substrate  50  while printing device  400  is discharging a printing material onto substrate  50 . 
         [0079]    Referring to  FIG. 17 , device  400  includes a frame in the form of a generally hollow beam  402  on which other elements of device  400  are connected. Beam  402  can be hollow so that some components, such as, for example, a controller  404 , can be stored therein. Beam  402  includes a first end  406  to which a first drive assembly  410  is connected, and a second end  412 , distal from first end  406 , on which a second drive assembly  420  is connected. Each of first and second drive assemblies  410 ,  420  can be removably connected to beam  402 , such as by screws, to allow beam  402  to be replaced by a beam of a different length, or to repair/replace controller  404 , if required. 
         [0080]    An effector assembly  480  rides on beam  402  between first drive assembly  410  and second drive assembly  420 . Effector assembly  480  prints an image onto a substrate  50 , such as, for example, asphalt, concrete, grass, or any other surface over which drive assemblies  410 ,  420  can travel. 
         [0081]    Effector assembly  480  cooperates with drive assemblies  410 ,  420  to print an image onto substrate  50  that is provided through controller  404  in the form of an electronic file, such as, for example, a JPEG, GIF, PDF, raster, or other type of electronic image. Referring specifically to  FIG. 16 , drive assemblies  410 ,  420  drive device  400  in a direction identified by double arrows X, while effector assembly  480  travels in a direction identified by double arrow Y and discharges a print matter (paint, chalk, etc.) onto substrate  50 . The image can be downloaded to controller  404  via a wireless connection or a hardwired connection, such as via a USB or other type of connection  408  located on device  400 . While USB port  408  is shown in  FIG. 17  as being located on beam  402 , those skilled in the art will recognize that USB port  408  can be located in other places on device  400 . 
         [0082]    Referring to  FIG. 17 , a power supply  422 , such as a rechargeable battery, is releasably attached to first drive assembly  410  via a generally U-shaped retainer  424 . Power supply  422  can be recharged while attached to retainer  424  or, alternatively, power supply  422  can be removed from retainer  424  and recharged at a separate location. Power supply  422  provides electrical power to operate first and second drive assemblies  410 ,  420 , effector assembly  480  and controller  404  via electrical connections (not shown). 
         [0083]    Instead of, or in addition to, power supply  422  mounted on first drive assembly  410 , a power supply  423  can be located inside beam  402 . Power supply can be rechargeable via USB port  408 . 
         [0084]      FIG. 18  shows drive assembly  420 . Drive assembly  410  is a mirror image of drive assembly  410  with the addition of power supply  422  and retainer  424 , although those skilled in the art will recognize that and additional power supply (not shown) can be attached to drive assembly  420  to provide additional power and/or longer operating life. 
         [0085]    Drive assembly  420  includes an inner frame  430  and an electric motor  432  attached to inner frame  430 . Motor  432  is electrically connected to and driven by power supply  422  through controller  404 . An output of motor  432  is connected to and drives a first idler wheel  434 . Idler wheel  434  is operatively connected to a drive wheel  436  via a belt  438 . Drive wheel  436  rotates on a support shaft  439  and is connected to a wheel driver  440  such that rotation of drive wheel  436  rotates wheel driver  440 . 
         [0086]    Wheel driver  440  is operatively connected to a first drive wheel  442  via a first drive belt  444  connected to a first pinion  446 , and wheel driver is also operatively connected to a second drive wheel  450  via a second drive belt  452  connected to a second pinion  454 . Pinions  446 ,  454  are connected to wheel driver  440  such that pinions  446 ,  454  and wheel driver  440  all rotate together. 
         [0087]    First wheel drive  442  is rotatably supported on a shaft  458  and second wheel drive  450  is supported on a shaft  460 . In addition to supporting their respective wheels, shafts  439 ,  458 ,  460 , as well as a spacer  464 , act as spacers to space inner frame  430  from an outer frame  464 . 
         [0088]    Referring now to  FIG. 19 , effector assembly  480  includes a first frame mount  482  with a drive motor  484  mounted on an outer portion of frame mount  482 . Drive motor  484  is electrically connected to power supply  422  through controller  404  and drives an output wheel assembly  484  that rides along the top surface of beam  402 . Output wheel assembly  484  includes a first wheel  486  and a second wheel  488 , connected to each other by a shaft  490 . Each wheel  486 ,  488  rides on a respective track  490 ,  494  mounted on the top of beam  402 . Although not shown, each track can be a toothed track and each wheel  486 ,  488  can have corresponding teeth that engage the teeth on tracks  490 ,  492  to prevent slippage of wheels  486 ,  488  with respect to tracks  490 ,  492 . 
         [0089]    Wheel  488  is rotatably connected to a second frame mount  500  that is used to receive and retain an effector, such as a spray paint can  70 . Each of first frame mount  482  and second frame mount  500  includes a pair of upper rollers  502 ,  504 ,  506  (second upper roller on second frame mount  500  not shown) and, as shown in  FIG. 20 , a pair of lower rollers  508 ,  510 ,  512 ,  514 . Upper rollers  502 - 506  and lower rollers  508 - 514  are used to secure effector assembly  480  onto beam  402  and stabilize effector assembly  480  as effector assembly rolls along the top of beam  402 . 
         [0090]    Second frame mount  500  includes a generally flat face  516  with a vertical slot  518  extending the length thereof. An effector receiver  520  includes a corresponding flat face  522  that engages flat face  516  of second frame mount  500 . Receiver  520  also includes a rib  524  that engages slot  518 . At least one of face  56 , slot  518 , face  522 , and rib  524  is magnetic, while an engaging member is magnetically attractive so that receiver  520  is magnetically connected to second frame mount  500 . 
         [0091]    Effector receiver  520  includes a flat lower receiver plate  526  with a beveled central through-opening  528  and a generally arcuate upper receiver  530 . Both central through-opening  528  and upper receiver  530  are sized to accommodate the dimensions of paint can  70  so that paint can  70  can be inserted into receiver  520  and frictionally secured to receiver  520  so that can  70  does not fall out of receiver  520 . 
         [0092]    Referring to  FIGS. 20 and 21A-21C , a paint discharge assembly  531  is attached to a bottom of effector receiver  520 . Paint discharge assembly  531  includes an electric motor  532  having a cam  534  connected to its output. Motor  532  receives electrical power from power supply  422  through controller  404 . When controlled by controller  404 , motor  532  operates to rotate cam  534  sufficiently to bias a nozzle  72  on can  70  away from a longitudinal axis  74  of can  70 , opening nozzle  72  and allowing paint inside can  70  to be discharged onto substrate  50 . 
         [0093]    As shown in a comparison of  FIGS. 21A-C , different height locations of effector receiver  520  relative to second frame mount  500  (provided by the magnetic connection between effector receiver  520  and second frame mount  500  discussed above) result in paint spray cones of different sizes, allowing a user to adjust the thickness of lines generated by device  400 .  FIG. 21A  shows effector receiver  520  mounted relatively high on second frame mount  500 , resulting in a line thickness “A”;  FIG. 21B  shows effector receiver  520  mounted approximately mid-range on second frame mount  500 , resulting in a thinner line thickness “B”; and  FIG. 21C  shows effector receiver  520  mounted relatively low on second frame mount  500 , resulting in an even thinner line thickness “C”. 
         [0094]      FIGS. 22A-22C  show a technique for adjusting a volume of print medium dispensed from paint can  70 .  FIG. 22A  shows cam  534  in an “OFF” position such that nozzle  72  is not activated and no paint is being discharged from can  70 .  FIG. 22B  shows cam  534  having been rotated by motor  532  about 22½ degrees, generating a relatively small volume of paint being discharged from nozzle  72 .  FIG. 22C  shows cam  534  having been rotated by motor  532  about  45  degrees, generating a relatively larger volume of paint being discharged from nozzle  72 . Those skilled in the art will recognize that cam  534  can be rotated between about zero degrees and about  180  degrees to generate different thicknesses of lines, as desired. 
         [0095]    Therefore, by adjusting both the height of paint can  70  relative to frame  402  and the volume of paint dispensed from paint can  70 , a user can vary both line thickness and volume or density of paint to be applied to substrate  50 . 
         [0096]    To operate device  400 , an electronic data file of a drawing or figure is transmitted from a remote device  60  (shown in  FIG. 11 ) to controller  404 , either wirelessly (such as by Bluetooth®) or by connecting to hardwire connection  408 . 
         [0097]    Controller  404  transmits electrical signals to motors  432  on each of first and second drive assemblies  410 ,  420  to drive device  400  along the “X” direction (identified in  FIG. 16 ) on top of substrate  50 . First and second drive assemblies  410 ,  420 , although separate from each other, are operated in tandem to maintain the “X” direction. 
         [0098]    Controller  404  also transmits electrical signals to effector motor  484  to rotate wheels  486 ,  488  on output wheel assembly  484  to traverse effector assembly  480  along beam  402  along the “Y” direction (identified in  FIG. 16 ), generally orthogonal to the “X” direction. Further, controller  404  also transmits electrical signals to electric motor  532  to rotate cam  534  to move nozzle  72  for dispensing paint from can  70 , drawing the figure onto substrate  50 . 
         [0099]    It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.