Abstract:
A printing device includes a navigation unit for monitoring a cooperative navigation surface and provides data to a navigation engine for processing and generation of a positional signal representative of the position of a moving printer head.

Description:
TECHNICAL FIELD 
     The present invention relates to an optical navigation system for use in applications requiring accurate positioning of a toolpiece in relation to a workpiece. More particularly, the present invention relates to an optical navigation system for positioning a toolpiece in accordance with a known navigation surface. 
     BACKGROUND OF THE INVENTION 
     In devices which perform operations on a workpiece, it is often necessary to accurately position a toolpiece in relation to the workpiece in order to carryout the desired operations so as to achieve desired results. In operations wherein repeatability is important, the need to accurately control the position of the toolpiece throughout each successive interaction of the operation in relation to the workpiece is very important. 
     One example of a device that performs operations on a workpiece is a typical printing device, for example, but not limited to, a laser, ink jet, or dye-sublimation printer or the like is shown in FIG.  1 . FIG. 1 shows a printer cartridge  30 , a storage reservoir  35 , a print head  33 , and a print media  31 . These printers perform printing operations by distributing a dye, or pigment, onto a print media such as paper or resin coated substrate. 
     During the printing process carried out by a typical printing device it is common to move the print head about the surface of a print media in order to deliver pigment, or dyes, to the print media at predetermined locations thereon. In order to achieve desired and repeatably consistent results, it is necessary for the positioning of the printer head to be accurately controlled. 
     Known methods of controlling the positioning of the printer head include the use of rotary shaft encoders that monitor the rotation of shafts which feed the print media through the printing device during the printing process, glass etched optical encoders, as well as stepper motors. Unfortunately rotary encoders suffer from mechanical backlash which precludes consist and accurate control of print head navigation. Glass etched encoders are very expensive and not useful in cost sensitive applications where high resolution printing is desired. Finally, stepper motors suffer from inaccuracies due to loss of step count. Additionally, stepper motors are relatively expensive. 
     Optical navigation systems have been employed to determine the position of a toolpiece in relation to a work piece, however, because these systems have relied upon a the surface or feature of the print media itself, there were inconsistencies in results. Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies. 
     SUMMARY OF THE INVENTION 
     The present invention provides for a cooperative navigation surface, a navigation unit for optically monitoring the navigation surface, and a navigation engine for generating an output signal representative of the position of a toolpiece. The present invention provides for navigation of a print head for printing onto a print media based upon optical feedback derived from a known cooperative navigation surface, while printing onto a separate independent surface, or print media. Further, the present invention seeks to provide a navigation unit which tracks movement of the print head in the X direction and movement of the print media in the Y direction. By providing for optical navigation of a known navigation surface, the present invention seeks to avoid errors and inaccuracies that are common with typical optical navigation systems. 
     The present invention can also be viewed as providing a method for printing on a print media. In this regard, the method can be broadly summarized by the following steps: optically monitoring a cooperative navigation surface and generating an image output signal in accordance therewith; and delivering a pigment to a print media in accordance with said image output signal. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
     FIG. 1 is an illustration describing the prior art; 
     FIG. 2 is an illustration describing one embodiment of the present invention; 
     FIG. 3 is a diagram illustrating a navigation unit; 
     FIG. 4 is an illustration describing a navigation surface in relation to a print media; 
     FIG. 5 is an illustration describing cross-correlation between reference and comparison snapshots captured by a navigation unit; and 
     FIG. 6 is a flow chart describing the method of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
     With reference to FIG. 2 there is shown a printer cartridge  30 , which is arranged adjacent to a paper path (or work path) which receives a print media  31 . Printer cartridge  30  incorporates a printer head  33  and a navigation unit  32 . With reference to FIG. 3, navigation unit  32  can be seen to include an imager  61  and an optical system  62  for focusing light reflected from print media  31  on to imager  61 . Illumination of the print media  31  is provided by light source  64 . Imager  61  is preferably a complementary metallic-oxide semiconductor (CMOS) photo imager, however, other imaging devices such as a charge coupled-device (CCD), photo diode array or photo transistor array may also be used. Light from light source  64  is reflected from print media  31  and on to imager  61  via optical system  62 . Light source  64  as shown on FIG. 6 is a light emitting diode (LED). However, other light sources can also be utilized including, for example, incandescent or fluorescent light sources. Additionally, it is possible for ambient light sources external to navigation unit  32  to be utilized provided such light level is sufficient to meet the sensitivity threshold requirements of the Imager  61 . Imager  61  generates a signal  63 , or snapshot, at a predetermined rate, representative of that portion of the navigation surface  80  that is currently being monitored, or imaged by imager  61 . This output signal  63  is delivered to a navigation engine  73  and may be stored into memory  72 . The navigation engine converts raw image data into positional information that is delivered to the controller  71 . Navigation engine  73  generates positional signal  66  and outputs it to controller  71 . Controller  71  subsequently generates an output signal  65  that can be used to position the print head  33 . It should be noted that navigation engine  73 , and memory  72 , could be configured as an integral part of navigation unit  32 . Further navigation engine  73  could be implemented as, for example, but not limited, a dedicated digital signal processor (DSP); an application specific integrated circuit (ASIC) or a combination of logic gates. 
     FIG. 6 is a flow chart illustrating the method of the present invention. The print head  33  is positioned. A reference snap shot (REF) of navigation surface  80  is obtained via navigation unit  32  ( 201 ). The reference snap shot (REF) is stored into memory  72  ( 202 ). After a fixed period of time has elapsed ( 203 ), a comparison snap shot (CMP) of navigation surface  80  is obtained via navigation unit  32  ( 204 ). Navigation engine  73  calculates the position of print head  33  via cross correlating reference snap shot (REF) with comparison snapshot (CMP) ( 205 ). The position of print head  33  is then reported to the controller  71  in accordance with the calculations of  205  ( 206 ). A determination is made as to whether or not the print head  33  has moved more than a predetermined distance (or to a point where CMP and REF snapshots share less than a predetermined area of commonality) since the reference snapshot (REF) was obtained ( 207 ). If it is determined in  207  that the print head  33  has moved more than a predetermined distance (“out of bounds”), the comparison snapshot (CMP) obtained in  206  is stored to memory  72  and becomes the new REF snapshot ( 208 ). Print head  33  can then be re-positioned in accordance with the position reported to controller  71  at  206  ( 209 ). 
     Navigation surface  80  preferably has a cooperative texture, or pattern, along all surface areas that will be monitored by imager  61  of navigation unit  32 . It should be noted, however, that the surface texture of navigation surface  80  could also be of a random nature. 
     FIG. 5 shows a navigation surface  80 , which has a distinct surface characteristic, or pattern. In this example, the pattern is represented by alpha-numeric characters to ease explanation, as the alpha-numeric characters are more easily distinguishable for purposes of discussion. However, such alpha-numeric characters could in fact be used as an effective navigation surface pattern as contemplated by the present invention. 
     With reference to FIG. 4, it can be seen that one embodiment of the present invention requires that observation window  95 , be formed in navigation surface  80  so that navigation unit  32 , and more specifically imager  61 , can visually monitor the position of print media  31 . As the print media  31  is in a different plane than the navigation surface  80 , it may be desirable to provide for an optics systems, or lens, in the observation window  95  to compensate for this difference and allow imager  61  to accurately image the print media  31  and the navigation surface  80 . 
     With reference to FIG. 5, there is shown a first, or reference (REF) snapshot (REF)  41 ; a second, or comparison (CMP) snapshot (CMP)  42 ; and an area of commonality  45 . Each snapshot, REF  41  and CMP  42 , represents a predetermined area, for example, an area 1 mm 2 . 
     During the printing process, navigation unit  32  obtains a first snap shot (image) of the navigation surface  80  as a reference snapshot (REF). This reference-snapshot data (REF) is stored into memory  72 . After a fixed amount of time, a second snapshot of the navigation surface  80  is obtained by the navigation unit  32  as comparison (CMP) snapshot  42 . Data representing CMP  42  is then compared by navigation engine  73  with data representing REF  41 , which is stored in memory  72  to determine the present position of print head  33 . More particularly, CMP data is mathematically cross-correlated with REF image data stored in memory  72  so as to determine the offset, in both the X and Y direction, between the first (REF) snapshot  41  and the second (CMP) snapshot  42 . Cross correlation calculations may be carried out as follows:          C     i   ,   j       =         ∑     m   =   1     M            ∑     n   =   1     N          1        r     m   ,   n             -       c       m   -   i     ,     n   -   j            1                              
     where r m,n  and c m,n  represent REF and CMP snapshots at point {m,n} and i and j represent the offset between REF and CMP snapshots. 
     The area of the navigation surface  80  that is the subject of each snapshot is typically substantially less than the overall size (area) of the navigation surface  80 . As the print head  33  moves, so does the navigation unit  32  in relation to the navigation surface  80 . In order for cross-correlation calculations to be effectively carried out, it is important that details of the navigation surface  80  contained in the REF snapshot have some commonality (area of commonality  45 ) with details of the navigation surface  80  contained in the second CMP snapshot. In other words, the distance traveled by navigation unit  32  between the point at which the REF snapshot is obtained and the point at which the CMP snapshot is obtained cannot be so great that the details contained in the CMP snapshot totally lack commonality with the REF snapshot. If this condition occurs, the print head  33  will become “lost” or “out of bounds.” In order for navigation to function smoothly it is necessary for the CMP snapshot of the navigation surface to be taken so as to include at least some portion of the navigation surface details that also appear in the first REF snapshot image. 
     As movement of the print head/navigation unit progresses, the overlap (or area of commonality) between the CMP and REF snapshots decreases. In the extreme case, there would be no overlap (area of commonality) between the CMP and REF images, as is exemplified in FIG. 5 by REF snapshot  41  and snapshot  48 . In this case, the navigation unit  32  would become “lost” and be unable to properly report the position the print head  33 . However, in the present invention as the area of commonality between the CMP snapshot and the REF snapshot decreases to a predetermined area, or percentage, of commonality (overlap), the CMP snapshot is copied into storage memory  72  to thus become the new REF snapshot. This procedure is called a re-referencing procedure or REREF. Immediately, subsequent to a REREF, the CMP snapshot and REF snapshot are the same, meaning that there is complete or total overlap (commonality) for cross-correlation purposes. 
     An alternate to the above procedure involves obtaining a cumulative snapshot of the entire navigation surface  80  via taking a series of snapshots of the navigation surface at various points along the navigation surface and storing the data into memory  72 . This stored data cumulatively represents the entire navigation surface (cumulative snapshot), or a selected portion thereof. Subsequently, as print head  33  is positioned, and repositioned during the printing process, comparison snapshots (CMP) are taken of the navigation surface and compared with the cumulative snapshot data stored in memory  72 . This alternative does require increased hardware, specifically memory. To accommodate the increased snapshot data size. However, it eliminates the possibility that cross-correlation calculations cannot be carried out where the CMP snapshot shares no commonality of details with the REF snapshot (where the print head  33  gets lost), since all details of the navigation surface  80  are stored in memory  72 . 
     The present invention is described herein via the example of a printing device. It will be recognized by persons skilled in the art that the present invention is equally applicable to scanning devices such as a photographic or flat-bed paper scanners. Further the present invention can be implemented in automated factory or manufacturing equipment and the like wherein assembly operations are carried out. Additionally, the present invention is also applicable to medical applications, such as diagnostic imaging, or control of surgical instrumentation. 
     The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. Obvious modifications or variations are possible in light of the above teachings. The embodiment or embodiments discussed herein were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.