Abstract:
The present invention is directed to a fiber optic media thickness sensor used in a print media or document processing device. The invention is further directed to a method for measuring media thickness in a media processing device using a fiber optic sensor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to printers and copiers and the like, and more particularly, relates to adjustments by such devices in response to variations in print media characteristics.  
           [0003]    2. State of the Art  
           [0004]    A myriad of document processing devices have been developed, including printers, photocopy machines, scanners, as well as other devices that either create images and patterns on print media (e.g., printers) or analyze images and patterns already resident on media (e.g., scanners). Complications arise in the use of these devices when media, having variations in media characteristics, are used. For example, printers may be presented with a myriad of print media, such as paper, which exhibit variations in thickness and stiffness and requires individualized image processing parameters in order to create an acceptable image on the specific print media. Without such image processing adaptation, the print quality may become unacceptable and may even result in damage to the processing device.  
           [0005]    Insight into the media characteristic of the media being acted upon by a document processing device enables the device to adapt and provide improved processing services to the media. For example, thicker media may require alternative handling such as alterations to forces associated with the “pick” or lifting forces for removing the media from a document processing device storage tray. Furthermore, document processing device attachments such as duplexers or output bins also have specifications including a range of media characteristics compatible with the attachment devices. Yet another concern of document processing devices, particularly printers and copiers, results from the variations in fuser temperature profiles as a function of the media thickness. Therefore, it would be advantageous to determine media characteristics such as thickness and stiffness of the media in order to more advantageously alter document processing device parameters.  
           [0006]    In yet another printing process, namely the application of toner to the print media, it should be appreciated that the thicker the print media, the more electrical charge must be applied to the media in order to attract an adequate amount of toner. Therefore, there is a need for providing an improved sensor capable of real or near real-time media evaluation to quantify the media characteristics allowing the document processing device to adjust the performance of the device&#39;s imaging processes.  
           [0007]    Mechanical media thickness measurement devices are known in the art. One type of mechanical thickness sensor uses a mechanical arm assembly coupled to a measurement circuit. The mechanical arm engages the surface of the media under evaluation. The measurement circuit measures the displacement of the media or the mechanical arm and generates a signal indicative of the media thickness. The present invention provides an alternative to mechanical techniques for detecting the thickness of print media.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a fiber optic media thickness sensor used in a print media or document processing device. The invention is further directed to a method for measuring media thickness in a media processing device using a fiber optic sensor. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]    In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:  
         [0010]    [0010]FIG. 1 is a simplified illustration of a thicker media passing through a media thickness sensor, in accordance with an embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is a simplified illustration of a thinner media passing through a media thickness sensor, in accordance with an embodiment of the present invention;  
         [0012]    [0012]FIG. 3 illustrates an alternate embodiment wherein media deflection is induced;  
         [0013]    [0013]FIG. 4 illustrates detection of media thickness by monitoring roller deflection, in accordance with another embodiment of the invention;  
         [0014]    [0014]FIG. 5 is a cross-sectional view of a sensing fiber within a thickness sensor, in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 6 is a cross-sectional view of a sensing fiber within a thickness sensor having an encapsulated resiliency coating, in accordance with an embodiment of the present invention; and  
         [0016]    [0016]FIG. 7 is a functional block diagram of a document processing device having a media thickness sensor therein, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 illustrates a simplified application of a media thickness sensor  10  as deployed within a document processing device, a portion of which is depicted as document processing device  12 . Those of skill in the art appreciate that document processing device  12  further comprises other subsystems, such as image processing and media storage aspects which, for clarity, are not illustrated in FIG. 1. A media processing path of document processing device  12  includes rollers or other guidance mechanism  14  directing a media  16  along a media processing path. Print media  16  traverses at least a portion of the media path before encountering media thickness sensor  10 . Media thickness sensor  10  provides a real time or near real time characterization of the thickness characteristic of media  16  within document processing device  12 . By way of illustration of the functional operation of media thickness sensor  10 , FIG. 1 illustrates a relatively thick media  16  deflecting a sensing fiber  18  of media thickness sensor  10 . Sensing fiber  18  includes a first or fixed end and a second or free end that extends into the media processing path for encountering the media and being deflected thereby.  
         [0018]    Similarly, FIG. 2 illustrates the document processing device  12 , as introduced in FIG. 1, except with a thinner media  16 ′. In FIG. 2, thinner media  16 ′, likewise passes through guidance mechanisms  14  to encounter media thickness sensor  10  within document processing device  12 . As best seen by comparing FIGS. 1 and 2, the deflection of sensing fiber  18  by thinner media  16 ′ is smaller than that of thicker media  16 . Media thickness sensor  10 , therefore, detects a smaller thickness media and quantifies the thickness of the media for use by imagining processes within document processing device  12 .  
         [0019]    [0019]FIG. 3 illustrates an alternate embodiment of a document processing device wherein deflection of the print media is induced. In FIG. 3, document processing device  12 ′ includes a media deflector  50  positioned upstream in the media path from media thickness sensor  10 . Deflector  50  applies a known force and deflects media  16 . Media  16  then deflects sensing fiber  18  as it passes through media thickness sensor  10 . The amount the media  16  deflects sensing fiber  18  varies according to the amount of force that deflector  50  applies to media  16 . A larger deflection of media  16  by deflector  50 , for example, will cause a smaller deflection of sensing fiber  18  by media  16 . In the embodiment of FIG. 3, deflector  50  may also carry the load of deflecting media  16 , rather than sensing fiber  18 . Consequently, a sensing fiber  18  used with deflector  50  may be more flexible and, perhaps, more sensitive, that the stiffer sensing fiber  18  in the embodiment of FIGS. 1 and 2. Furthermore, deflector  50  also enhances the deflection of media  16  through application of a known load to media  16  thereby exaggerating the deflection of media  16  and providing additional deflection-resolution to the sensing fiber  18 . It should be appreciated that media deflector  50  may also be implemented to reduce deflection such as in the case where media deflector  50  attracts media  16 .  
         [0020]    In the embodiment of FIG. 4, media  16  passes through guidance mechanisms  14  which deflect, separate or otherwise move in response to the presence of media  16 . The deflection of media guidance mechanisms by media  16  is detected by locating media thickness sensor  10  in proximity to at least a portion of guidance mechanism  14  that deflects in response to the presence of media  16 . In FIG. 4, media thickness sensor  10  indirectly senses the media thickness by monitoring the deflection of components of guidance mechanisms  14 , an example of which is the monitoring of the deflection of a roller profile  52  illustrated in FIG. 4 as a roller axle. Various other tracking or monitoring profiles are contemplated within the scope of the present invention.  
         [0021]    [0021]FIG. 5 illustrates a cross-sectional view of a sensing fiber  18 . As illustrated, sensing fiber  18  operates as an optical fiber attached at a first end to a mounting housing  20  for providing a rigid base from which sensing fiber  18  may deflect when acted upon by the forces exerted by media  16 . Mounting housing  20 , while illustrated as a discrete housing, may also be adequately held rigid by a coupler or other assembly capable of receiving a sensing fiber  18  therein.  
         [0022]    Sensing fiber  18  is comprised of an optical fiber  22  which includes, on a second end, a mirror  24  or other reflective surface capable of reflecting light, originating from a light source at a first or fixed end of the flexible optical fiber, back again to the first or fixed end of the flexible optical fiber. Those of skill in the art appreciate that the occurrence of any deflection within optical fiber  22  results in an attenuation of light reflected back by mirror  24 .  
         [0023]    Sensing fiber  18  operates based upon the principle of light interference for obtaining originating and reflected light differences for correlating with media thickness. When propagating light is injected by light source  36  via coupler  34  into the first end of optical fiber  22  located on the mounting housing end of optical fiber  22 , it propagates down the core of the fiber and is reflected by mirror  24  back through the fiber to the detector  38 , also located on the first end of the optical fiber. The detector  38  measures the quantity of received reflected light and generates an electronic signal corresponding to the deflection of the optical fiber. Those of ordinary skill in the art appreciate that light losses occur when the bend radius of the optical fiber exceeds the critical angle necessary to confine the light to the core area of the fiber. When the fiber is flexed, the amount of light reflecting back to the detector is diminished accordingly and may be quantified to correlate to a media thickness.  
         [0024]    [0024]FIG. 6 illustrates another embodiment of a sensing fiber  18 ′ rigidly mounted in a mounting housing  20 . Sensing fiber  18 ′ includes a resiliency coating  26  which may be for protectively coating optical fiber  22  from abrasion associated with media  16 . Additionally, resiliency coating  26  may also be used to control the rigidity and flexibility of optical fiber  22 . It should be appreciated that resiliency coating  26  may be comprised of substances such as silicone, ABS, PCABS, or the like. Furthermore, resiliency coating  26  may be applied either by encapsulating optical fiber  22  or to selectively apply a coating to the optical fiber by other means compatible with processing and handling of optical fibers.  
         [0025]    The optical fiber may be manufactured in accordance with typical fiber optic principles including composition and size. Additionally, the fiber may be mirror-coated on the end as mirror  24  and may optionally additionally include mirror-coating on the sidewalls. Such an implementation may be manufactured by cladding the side and end walls with a higher index of refraction material so that light transmitted through the fixed-end toward the free-end will experience significant internal reflection losses when the resilient fiber is deflected by the presence of the print media.  
         [0026]    [0026]FIG. 7 illustrates a functional block diagram of a document processing device  12 , in accordance with a preferred embodiment of the present invention. Document processing device  12  includes, among other things, image processing apparatus  28  and a media processing adjustment assembly  30 . Image processing apparatus  28  performs conventional imaging processes and may include a controller/formatter and a print engine, and a scanner in the case of copy and facsimile machines. The functionality of these imaging processes are known in the art and their intricacies are not described herein.  
         [0027]    Media processing adjustment assembly  30  is comprised of a media thickness sensor  10  and an engine adjuster  32 . Media thickness sensor  10  is comprised of various functional elements that are coupled with sensing fiber  18 . Such functional elements include an optical coupler  34  for coupling a light source  36  to sensing optical fiber  18  while further allowing reflected light to be detected at the same end of sensing optical fiber  18  by a light reflection detector  38 . The process and methods for coupling one end of an optical fiber to an optical coupler for further coupling with both a light source and a detector is appreciated by those of ordinary skill in the art. One embodiment of the coupler and light source/detector is governed by the principles of the operation of the fiber optic Fabry-Perot interferometer. The mathematical equations governing the deflection correlation to reflected light in addition to the mechanical coupling and identification of suitable parts are known and readily discernable by those of ordinary skill in the art.  
         [0028]    Media thickness sensor  10  is further comprised of a media thickness estimator  40  coupled to light reflection detector  38  and optionally coupled to light source  36  for quantifying differences in the reflected light so as to create a gradient of media thicknesses for use by document processing device  12 . Media thickness estimator  40 , as part of media thickness sensor  10 , transfers a paper thickness identifier or gradient value to engine adjuster  32  for use in both status and control applications of components of document processing device  12 . Engine adjustor  32  may be implemented as a look-up table of adjustment values comprising calculated or empirical values such as adjustment identifiers that are forwarded to a controller of the document processing device for use in modifying or adapting the image processing apparatus  28 . Image processing apparatus  28  may include functionality (not shown) such as a controller that is responsive to signals or commands from engine adjustor  32  and further capable of modifying commands to image processes such as printing and scanning. By way of example and not limitation, exemplary status and control signals for use by document processing device  12  may include a signal for adjusting the roller spacing speed or other interpage gaps illustrated as control signal  42 . For example, adjustment of the interpage gap is desirable due to the processing of a thicker media wherein a thicker media requires more energy to be transferred from the fuser thus requiring a longer recovery time for the fuser. Therefore, an adjustment in the interpage gap would allow the fuser to recover without requiring additional energy to be pumped into the fuser.  
         [0029]    An additional control signal, illustrated as control signal  44 , may adjust the temperature profile for the fuser in the print engine of a laser printer due to variations in media thickness. For example, thicker media requires a different fuser temperature profile for fusing the toner onto the print media. Yet another control signal, depicted as transfer voltage control signal  46 , is a voltage that is applied to pull the toner down onto the page, for example, as a media thickness increases, the amount of voltage required to pull or transfer the toner from, for example, a photosensitive drum, increases. Likewise, for thinner print media, the amount of transfer voltage is lessened. Therefore, there are advantages to being able to determine to a relative degree of certainty the specific thickness of the current media in order to optimize the transfer process.  
         [0030]    Yet another advantageous control signal that may result from the determination of the media thickness is illustrated as control signal  48  in which the pick force, the force required for retrieving a sheet of media from a tray, may be adjusted according to the media thickness. An example of various pick force mechanisms includes friction rollers as well as vacuum-based media picking techniques. As mentioned above, in addition to control signals, status or monitoring data  50  may also be present for providing statistical or other feedback information to other portions of document processing device  12 .  
         [0031]    The media thickness sensor described herein provides the ability to detect media thickness in real-time to perform processing adjustments on the current page in process rather than on a processing batch (e.g., print batch) configuration basis. Although the present invention has been described with reference to specific example embodiments, it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims.