Media detection apparatus and method

Abstract

An apparatus and method for automatically calibrating a media sensor configured to detect advancing print media in a printing device. In some embodiments, the apparatus selects a first light intensity level and a second light intensity level greater than the first light intensity level. A light source unit, such as a light emitting diode or laser diode is activated to emit light at the second light intensity level. The light passes though print media, for example, a roll of self-adhesive labels, that is advanced along a print path of the printing device. The amount of light transmitted through the print media is measured as the print media advances. If the measured light increases decreases, the light source unit is reactivated to emit light at the first light intensity level. In some embodiments, the apparatus identifies whether print media has changed or an out-of-stock condition exists.

What is claimed is: 
     
       1. A method of automatically calibrating a media sensor configured to detect advancing print media, the method comprising:
 selecting a first light intensity level and a second light intensity level greater than the first light intensity level; 
 setting a light source unit to emit light at the second light intensity level; 
 measuring an amount of the emitted light that is transmitted through the print media; 
 advancing the print media; and; 
 setting the light source unit to emit light at the first light intensity level in response to a determination that the light transmitted through the print media is increasing decreasing. 
 
     
     
       2. The method in accordance with  claim 1 , further comprising recording a position of the print media. 
     
     
       3. The method in accordance with  claim 2 , wherein recording a position of the print media includes recording a position at which that the light transmitted through the print media increases or decreases. 
     
     
       4. The method in accordance with  claim 1 , further comprising recording a measured amount of light transmitted through the print media. 
     
     
       5. The method in accordance with  claim 1 , further comprising:
 determining whether a print media status has changed since a previous operation; 
 determining whether an out-of-stock condition exists in response to determination that print media status has changed; and 
 signaling a fault condition in response to a determination that an out-of-stock condition exists. 
 
     
     
       6. The method in accordance with  claim 5 , wherein determining whether a print media status has changed since a previous operation includes comparing a current measured amount of light transmitted through the print media with a previously measured amount of light transmitted through the print media. 
     
     
       7. The method in accordance with  claim 1 , wherein determining whether an out-of-stock condition exists includes comparing a measured amount of light transmitted through the print media to a predetermined out-of-stock value. 
     
     
       8. A label printer configured for automatic media calibration, the printer comprising:
 a media drive configured to advance label media from a media supply to a print head;   a setting unit in operable communication with the media drive;   a light source unit in operable communication with the setting unit;   a light detector unit in operable communication with the setting unit and configured to detect light emitted from the light source unit and transmitted at least in part through label media;   wherein the setting unit is configured to:
 select a first light intensity level and a second light intensity level greater than the first light intensity level; 
 cause the light source unit to emit light at the second light intensity level; 
 measure the amount of the emitted light transmitted through the print media into the light detector unit; 
 cause the media drive to advance the print media; and 
 set the light source unit to emit light at the first light intensity level in response to a determination that the light transmitted through the print media is decreasing. 
   
     
     
       9. The label printer in accordance with  claim 8 , further comprising a print head in operable communication with the setting unit and configured to imprint visible indicia upon a media label. 
     
     
       10. The label printer in accordance with  claim 8 , wherein the setting unit is further configured to record a position of the print media. 
     
     
       11. The label printer in accordance with  claim 10 , wherein a position of the print media is recorded by recording a position at which that the light transmitted through the print media increases or decreases. 
     
     
       12. The label printer in accordance with  claim 8 , wherein the setting unit is further configured to record a measured amount of light transmitted through the print media. 
     
     
       13. The label printer in accordance with  claim 8 , wherein the setting unit is further configured to:
 determine whether a print media status has changed since a previous operation;   determine whether an out-of-stock condition exists in response to determination that the print media status has changed; and   signal a fault condition in response to a determination that an out-of-stock condition exists.   
     
     
       14. The label printer in accordance with  claim 13 , wherein the determination whether a print media status has changed since a previous operation includes comparing a current measured amount of light transmitted through the print media with a previously measured amount of light transmitted through the print media. 
     
     
       15. The label printer in accordance with  claim 8 , wherein the determination of whether an out-of-stock condition exists includes comparing a measured amount of light transmitted through the print media to a predetermined out-of-stock value. 
     
     
       16. The label printer in accordance with  claim 8 , further comprising a communications interface operably coupled to the setting unit and configured to communicate via a protocol selected from the group consisting of a wired communication protocol or a wireless communication protocol. 
     
     
       17. The label printer in accordance with  claim 8 , wherein the media drive includes a stepper motor. 
     
     
       18. A method of automatically calibrating a media sensor configured to detect advancing print media, the method comprising:
 selecting a first light intensity level for a light source unit corresponding to gap or liner portions of a print media, the first light intensity level selected to allow a light detecting unit to detect a first predetermined value of light when transmitted through the gap or liner portions of a print media;   selecting a second light intensity level for the light source unit corresponding to label portions of the print media, the second light intensity level selected to allow the light detecting unit to detect a second predetermined value of light when transmitted through the label portions of the print media, the second light intensity level greater than the first light intensity level;   setting the light source unit to emit light at the second light intensity level, based at least in part on an assumption that initially a label portion of the print media will be located between the light source unit and the light detecting unit;   advancing the print media and detecting a transition in light intensity from one of the first and second predetermined values of light to a detected value of light transmitted through the print media; and   ascertaining that initially a label portion of the print media was located between the light source unit and the light detecting unit if the transition from the predetermined value to the detected value reflects an increase in the light transmitted through the print media, and/or ascertaining that that, rather than a label portion, initially a gap or a liner portion of the print media was located between the light source unit and the light detecting unit if the transition from the first predetermined value corresponding to the second light intensity level to the detected value reflects a decrease in the light transmitted through the print media.   
     
     
       19. The method of claim 18, further comprising:
 setting the light source unit to emit light at the first light intensity level if the transition from the first predetermined value to the detected value reflects a decrease in the light transmitted through the print media, the decrease indicating that, rather than a label portion, initially a gap or a liner portion of the print media was located between the light source unit and the light detecting unit.   
     
     
       20. The method of claim 18, further comprising:
 recording a position of the print media corresponding to the transition from the first predetermined value to the detected value, the position representing a label edge;   performing a first print command or feed command;   advancing the print media until light detected by the light detecting unit corresponds to the first predetermined value of light transmitted through the gap or liner portions of the print media.   
     
     
       21. The method of claim 20, further comprising recording a measured amount of light detected by the light detecting unit at the conclusion of the first print command or feed command. 
     
     
       22. The method of claim 21, further comprising: ascertaining whether the print media has been changed prior to performing a second print command or feed command, at least in part by comparing a measured amount of light detected by the light detecting unit upon receiving the second print command or feed command to the measured amount of light detected by the light detecting unit at the conclusion of the first print command or feed command. 
     
     
       23. The method of claim 22, further comprising:
 upon ascertaining that the print media has been changed, prior to performing the second print command or feed command:   setting the light source unit to emit light at the second light intensity level, based at least in part on an assumption that initially a label portion of the print media will be located between the light source unit and the light detecting unit;   advancing the print media and detecting a transition in light intensity from the second predetermined value corresponding to the second light intensity level to a detected value of light transmitted through the print media; and   ascertaining that initially a label portion of the print media was located between the light source unit and the light detecting unit if the transition from the second predetermined value to the detected value reflects an increase in the light transmitted through the print media, and/or ascertaining that that, rather than a label portion, initially a gap or a liner portion of the print media was located between the light source unit and the light detecting unit if the transition from the first predetermined value to the detected value reflects a decrease in the light transmitted through the print media.   
     
     
       24. A method of automatically calibrating a media sensor configured to detect advancing print media, the method comprising:
 selecting a first light intensity level for a light source unit corresponding to gap or liner portions of a print media, the first light intensity level selected to allow a light detecting unit to detect a first predetermined value of light when transmitted through the gap or liner portions of a print media;   selecting a second light intensity level for the light source unit corresponding to label portions of the print media, the second light intensity level selected to allow the light detecting unit to detect a second predetermined value of light when transmitted through the label portions of the print media, the second light intensity level greater than the first light intensity level;   setting the light source unit to emit light at the second light intensity level, based at least in part on an assumption that initially a label portion of the print media will be located between the light source unit and the light detecting unit;   advancing the print media and detecting a transition in light intensity from one of the first and second predetermined values of light to a detected value of light transmitted through the print media; recording a position of the print media corresponding to the transition from the first predetermined value to the detected value, the position representing a label edge;   performing a first print command or feed command;   advancing the print media until light detected by the light detecting unit corresponds to the first predetermined value of light transmitted through the gap or liner portions of the print media; and   ascertaining that initially a label portion of the print media was located between the light source unit and the light detecting unit if the transition from the predetermined value to the detected value reflects an increase in the light transmitted through the print media, and/or ascertaining that that, rather than a label portion, initially a gap or a liner portion of the print media was located between the light source unit and the light detecting unit if the transition from the first predetermined value corresponding to the second light intensity level to the detected value reflects a decrease in the light transmitted through the print media.