Abstract:
A system and method are provided for detecting an adhesive label edge. The edge detection system employs two individually selectable light sources; one directed to providing transmissive mode detection while the second provides reflective mode detection of a label edge. The mode used is determined by the particular label media type used. The label edge detection system is dimensioned as either a subcomponent fabricated as part of any of a number of assemblies within a printer or as a stand-alone component positioned along a media path of the printer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to thermal demand printing, and more particularly, to detection of print area edges in label printing.  
         [0003]     2. Description of the Prior Art  
         [0004]     Thermal demand printing has been in use for years where speed is required. Such applications include printing receipts, facsimiles and adhesive shipping labels. Generally, a thermal demand printer uses media coated with a thermal-reactive layer, which darkens with exposure to heat above a threshold temperature. The printer is equipped with a print head having a heating element configured to apply direct heat at or above the threshold temperature to an area of the thermal media, which is usually dimensioned as a roll of media. The threshold temperature is usually set at a temperature high enough not to be encountered by the media accidentally in a typical storage environment but below the flashpoint of the media, i.e., the point at which the media would combust.  
         [0005]     In the specific case of adhesive label printing, the media used has a multitude of adhesive labels placed side-by-side on a substrate or backing and allows the labels to be readily peeled off individually. These labels come in a variety of sizes. The range of available label sizes and separation between labels gives rise to a significant printing issue.  
         [0006]     The problem encountered with label printing involves correctly aligning the individual label for printing. Since the printing area is not continuous throughout the roll, i.e., the printing area is defined by the dimensions of the individual label and not by the dimensions of the media roll, the printer must detect when one label ends and the next one begins so that the printer is able to render the print within the bounds of the printable area of each label.  
         [0007]     The criticality of this is best demonstrated by a hypothetical case wherein shipping labels are printed. In such a case, if the label is misaligned, the address may not be fully and clearly printed on the one label. In an automated shipping process, this inadequate shipping label may still end up on a package, but because the address is incomplete, the package cannot be efficiently delivered to its destination.  
         [0008]     Therefore, a need exists for techniques for detecting an edge of each label on a media roll. Preferably, such a detection means should detect the label edge of commonly used label rolls, regardless of the presence, or lack thereof, of an edge indicator on the media.  
       SUMMARY OF THE INVENTION  
       [0009]     The present disclosure provides a system and method for detecting an edge of a label on a media roll. The system includes a first light source positioned along a media feed path and a photodetector positioned opposite the first light source so that the media feed path is positioned between the photodetector and the first light source. A second light source is positioned adjacent and on the same side of the media feed path as the photodetector.  
         [0010]     Additionally, a controller is in electrical communication with the first and second light sources and the photodetector. The controller is configured for selectively activating the first light source and/or the second light source and for receiving feedback from the photodetector. A media feed mechanism is also provided for advancing media of a label roll, e.g., an adhesive label roll, along the media feed path. The media feed mechanism is controllable by the controller using the received feedback.  
         [0011]     Further, the present disclosure provides a method for detecting a label edge. In the disclosed method, a first light source is positioned along a media feed path, with a photodetector positioned opposite the first light source, on either side of the media feed path. A second light source is positioned adjacent and on the same side of the media feed path as the photodetector. One of either the first light source or the second light source is selected for illuminating a media roll supporting the label as the media moves along a point on the media feed path. At least a portion of the illumination is received by the photodetector, wherein the portion has previously impacted the media. It is determined that an edge of the adhesive label has been encountered based on at least one characteristic of the illumination received by the photodetector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings wherein:  
         [0013]      FIG. 1  is a schematic of an embodiment of a system for detecting an adhesive label edge in accordance with the present disclosure;  
         [0014]      FIG. 2  is a flow chart of the steps performed by a method for detecting an adhesive label edge in accordance with the present disclosure;  
         [0015]      FIGS. 3   a  and  3   b  illustrate two prior art label media types employed in accordance with the present disclosure; and  
         [0016]      FIGS. 4 and 5  illustrate perspective views of a modular printer. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring to  FIG. 1 , an embodiment of the present disclosure provides a system  100  for detecting an adhesive label edge during printing. The system  100  includes a first light source  102  with a lens  104  designed to provide illumination as either a narrow spot or line on an adhesive label sheet  107  moving through a media feed path  108 . The light source  102  may be an LED (light emitting diode) array arranged as a light bar. The lens may be a unitary body configured and dimensioned to slide within grooves of a support structure  118  of a thermal printer. The adhesive label sheet is fed through the media feed path  108  by a feed mechanism  112 , which may incorporate a conveyor, manual or motorized rollers or sprockets to advance the sheet  107 . A photodetector  106  is positioned across the media feed path  108  from the first light source  102  so that light transmitted through the media feed path  108  impacts the photodetector  106 . As light passes through a portion of the media having a label, e.g., label sheet  107 , the intensity of the transmitted light that impacts the photodetector  106  is diminished below a detection threshold, while light passing through portions of the media without a label impacts the photodetector  106  with intensity that is above the detection threshold. The system  100  may also incorporate a calibration component for calibrating the light output from the light source and the detection sensitivity of the photodetector as will be described below.  
         [0018]     Additionally, a second light source  110  is positioned along side and at an angle to the photodetector  106 . The second light source  110  is angled so as to illuminate a spot on the media backing of the label sheet as it moves through the media feed path  108  in a manner in which the light reflected by portions of the media impacts the photodetector  106 . This reflection mode is appropriately used when the adhesive label roll separates individual labels with a black or absorptive marking or strip on a side of the media opposite the labels, e.g., the backing, thus light is reflected to the photodetector  106  by the underside of the labels but little or no light is reflected to the photodetector  106  by the portions of the media (or web as the label supporting media is known in the art) between the labels having the black or absorptive marking.  
         [0019]      FIGS. 3   a  and  3   b  illustrate two types of label media. Referring to  FIG. 3   a , labels  301   a  are supported on a web  302   a . The web may be formed from paper and have a waxy or non-adhesive film allowing the labels  301   a  to be easily peeled off of the web  302   a . Each label  301   a  is spaced apart on the web  302   a  by a predetermined distance, forming a gap  304 . The labels  301   b  in  FIG. 3   b  are supported on a web  302   b , as in  FIG. 3   a . However, the web  302   b  has a light absorpting strip  303  positioned between each label  301   b , preferably on a side opposite the side supporting the labels  301   b . Both types of label media are supported by the present disclosure.  
         [0020]     An enclosing protective shell  114  having a slot aperture  116  formed thereon may be positioned to encase the photodetector  106  and second light source  110 . The shell  114  provides two functions, the first being to protect the photodetector  106  and second light source  110  from damage, while also providing an increased sensitivity to smaller gap widths between labels by the use of the slot aperture  116  above the photodetector  106 , which reduces the area of the focal plane normal to the relative motion of the gap between labels as it moves past the sensor.  
         [0021]     The various components of the present embodiment, e.g., the first light source  102 , second light source  110 , and photodetector  106  are in electronic communication with a controller (not shown). The controller provides the activation inputs to the two light sources  102  and  110  and receives an output signal from the photodetector  106 .  
         [0022]     The controller also controls calibration components and the media feed mechanism using the output signal from the photodetector  106  as the control signal. The controller may analyze the control signal to determine the intensity of the light produced by the light sources  102  and  110 , and increase or decrease the output power of the light sources, adjusting the edge detection sensitivity. For example, a typical calibration sequence may include removing media from the paper feed path, adjusting the light source (e.g., LED) current in steps from minimum to maximum and recording the sensor reading for each step; next, inserting the backing, i.e., with no label, into the feed path, adjusting LED current in steps from minimum to maximum and recording the sensor reading for each step; and lastly, inserting the backing with at least one label into the feed path, adjusting LED current in steps from minimum to maximum and recording the sensor reading for each step. The recorded data may then be used to determine a current setting for the LED that yields the best separation for label/backing to backing to media out conditions. Additionally, the data may be used to select edge detection thresholds based on the determined current setting. Alternatively, voltage levels of the light sources may be adjusted to calibrate the system.  
         [0023]     As shown in  FIG. 2 , the present embodiment provides a procedure for detecting adhesive label edges during printing. The detection procedure begins with a determination of the label roll type in step  201 . The determination may be either manual or automatic in nature and directed towards identifying whether the label roll has an optically absorptive strip between each label or not. Upon completion of the roll type determination, step  202  provides for the selection of an appropriate operation mode, e.g., transmissive or reflective mode. The media roll type determines the mode selected: reflective mode is appropriate for use on rolls having the absorptive strip while transmissive mode is used on all other supported rolls. The selected light source is selected and activated in step  203   a  or  203   b  either in short duration pulses or continuously. If the operation mode is transmissive, the first light source  102  is selected in step  203   a ; in reflective mode, the second light source  110  is selected in step  203   b . A photodetector  106  or other such device is used in step  204   a  or  204   b  to detect light emanating from the selected light source after having interacted with the media roll.  
         [0024]     In transmissive mode light detection step  204   a , the detected light intensity needs to be above a predetermined intensity threshold in order for the determination of edge detection to have occur at which point, printing begins in step  206 ; less then the threshold intensity value results in a ‘no edge detected’ determination and the media is advanced in step  205 . Upon completion of step  205 , the process loops back to step  204   a  until an edge is detected.  
         [0025]     Alternatively in the reflective mode light detection step  204   b , the detected light intensity needs to be below a predetermined intensity threshold in order for the determination of edge detection to have occur at which point, printing begins in step  206 ; detected light intensity greater then the threshold intensity value results in a ‘no edge detected’ determination and the media is advanced in step  205 . Upon completion of step  205 , the process loops back to step  204   b  until an edge is detected.  
         [0026]     The present disclosure is dimensioned as a component installable, either during manufacture or as an after-market option, on commercially available label printers such as the modular printer disclosed in U.S. Pat. No. 6,616,362 issued on Sep. 9, 2003 and incorporated herein by reference in its entirety.  
         [0027]      FIGS. 4 and 5  illustrate perspective views of a modular printer, with parts separated, shown generally as  10 . More specifically,  FIG. 4  illustrates the printing components of the modular printer and  FIG. 5  illustrates the electrical and drive components of the modular printer.  
         [0028]     Briefly, modular printer  10  includes a media take-up assembly  12  including a hub assembly  14  configured to support a media take-up roll (not shown), a support block assembly  16 , a printhead assembly  18 , a stepper motor assembly  20 , a media sensor assembly  24  (see  FIG. 5 ), a cover assembly  30  and a display assembly  32 . The label edge detection system of the present disclosure as exemplified in  FIG. 1 , preferably, is a component part of the media sensor assembly  24 , printhead assembly  18 , or media take-up assembly  12 , however the label edge detection system may also be dimensioned as a separate assembly positioned along a media path of the printer  10 . When printer  10  is operated as a ribbon ink printer, a ribbon spool take-up assembly  28  may also be provided in conjunction with the media take-up assembly. Each of the above-identified assemblies is removably supported on a support body  34 . The support body defines an internal support wall of the modular printer and is configured to properly align each of the assemblies with respect to each of the other assemblies within the printer. Support body  34  is preferably formed from a heat conductive material, such as an aluminum support body, to facilitate the removal of heat from printer  10 . However, other materials may also be used to form housing  34  including ceramics, plastics, sheet metal etc.  
         [0029]     As discussed above, printer  10  has a display assembly  32 . Display assembly  32  includes a module  150  having an LED display and a casing  152 . Module  150  is positioned between diametrically opposed guide brackets  154  formed on support body  34 . Opposite corners of module  150  are subsequently secured to support body  34  by screws. Casing  152  includes a plurality of flexible brackets  156 , which can be snap fit to support body  34  over module  150 . Support body  34  includes receiving structure  158  formed therein. Alternately, other known fastening devices may be used to secure module  150  and casing  152  to support body  34 .  
         [0030]     Referring again to  FIG. 5 , the electrical and drive components of the ink printer  10  are secured to the opposite side of support body  34  than are the printing components of the printer  10 . As discussed above, stepper motor assembly  20  is secured to support body  34  on the side opposite the printing components. Electronic circuitry  160  and electric drive assembly  162  to operate printer  10  are secured to the support body  34  on the side opposite the printing components. Electronic circuitry  160  is in the form of circuit boards  164 , which can be installed in printer  10  by sliding the circuit boards through an opening  166  formed in support body  34 . The circuit boards can be chosen to suit the particular printing operation to be performed. For example, the circuitry  160  can be changed for different communications interfaces. Alternatively, software can be downloaded via a communication port to control a particular printing application.  
         [0031]     The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.