Patent Publication Number: US-8118390-B2

Title: Media identification system with moving optoelectronic device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, co-pending U.S. Patent Applications: 
     U.S. patent application Ser. No. 12/332,722, filed herewith, entitled: “MOVABLE MEDIA TRAY WITH POSITION REFERENCE MARKS”, by D. V. Brumbaugh et al., the disclosure(s) of which are incorporated herein by reference in their entirety; U.S. patent application Ser. No. 12/332,648, filed herewith, entitled: “MEDIA IDENTIFICATION SYSTEM WITH SENSOR ARRAY”, by T. D. Pawlik et al., the disclosure(s) of which are incorporated herein by reference in their entirety; and 
     U.S. patent application Ser. No. 12/332,616, filed herewith, entitled: “MEDIA MEASUREMENT WITH SENSOR ARRAY”, by J. J. Haflinger et al.; the disclosures of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of printers, and in particular to identifying a type of recording medium that has been loaded into a printer. 
     BACKGROUND OF THE INVENTION 
     In order for a printing system (e.g. inkjet, electrophotographic, thermal, etc.) to print high quality images on a recording medium it is important to know what kind of media is about to be printed. In the case of inkjet, for instance, preferred recording conditions differ for different types of media, partly because different media interact differently with ink. An example of this is that ink is able to wick along the paper fibers in plain paper, so that the spot of ink on the paper is enlarged and irregularly shaped relative to the drop of ink that strikes the paper. Media, which are specially formulated for high quality images, such as photographs, typically have an ink-receiving layer that absorbs the ink in a more controllable fashion, so that the spot size and shape are more regular. Because the colorants are trapped closer to the paper surface, and because a larger quantity of ink can be printed, (the associated carrier fluids being absorbed), an image printed on photographic print media has more vibrant colors than the same image printed on plain paper. 
     The appropriate amount of ink to use for printing an image on one type of medium is different than printing on another type of medium. If plain paper receives the same quantity of ink, more appropriately deposited in order to print a high-density image such as a photo that would be used for that same image on photographic print medium, the plain paper may not be able to dry quickly enough. Even worse, the plain paper may cockle or buckle in the presence of excess ink, so that the printhead crashes into the printed image, thus smearing the image, and possibly damaging the printhead as well. Even for two different types or grades of photographic print media, the amount of ink or number of passes to lay down an image for good tradeoffs in printing quality and printing throughput will be different. It is, therefore, important when receiving image-related data on a specific image to be printed, that the specific image be rendered appropriately for a specific media type that the image will be printed on. Image rendering is defined herein as determining data corresponding to: a) the appropriate amount of ink to deposit at particular pixel locations of the image; b) the number of multiple passes needed to lay the ink down on the medium in light of ink-to-ink and ink-to-medium interactions; and c) the type of pattern needed to produce the image. 
     Various means are known in the art for providing information to the printer or to an associated host computer regarding the type of medium (e.g. glossy media or matte media of various grades, or plain paper), that is in the input tray of the printer. For example, the user may enter information on media type. Alternatively, there can be a barcode or other type of code pattern printed on the backside of the medium that is read to provide information on media type as a sheet of medium is picked from the input tray and fed toward the printing mechanism. Alternatively, media characteristics such as optical reflectance can be used to distinguish among media types. Generally, the processes for automatic media type detection require several seconds to provide accurate media-related information on media type. For competitive printers today, it is important to achieve excellent print quality at fast printing throughput. In particular, a user may be dissatisfied if the time required to print the first page of a print job is excessive. 
     U.S. Pat. No. 6,830,398 discloses one method providing faster printing throughput while enabling automatic media type detection prior to controlling conditions in the printing operation. In U.S. Pat. No. 6,830,398, a load detector is provided for detecting that recording medium has been loaded into the printer. In addition, there is provided a sensor, such as a reflective optical sensor, that can discriminate the type of media type after the medium has been loaded into the recording medium loading section, but before paper feeding starts. In U.S. Pat. No. 6,830,398, when the printer is turned on, or after medium loading has been detected, the sensor obtains information about the medium type, even before the first page of medium is picked for feeding to print a print job. However, conventional printers do not have a sensor capable of reliably discriminating paper type as described in U.S. Pat. No. 6,830,398. For example, the sensor in U.S. Pat. No. 6,830,398 would have difficulty discriminating between matte paper versus plain paper. To date, it has been found that improved reliability of media type detection is provided when the sensor (such as an optical reflective sensor) provides information regarding a plurality of regions of the recording medium. 
     U.S. Pat. No. 7,120,272; includes a sensor that makes sequential spatial measurements of a recording medium moving relatively to the sensor, where the recording medium contains repeated indicia to determine a repeat frequency and repeat distance of the indicia. The repeat distance is then compared against known values to determine the type of recording medium present. 
     In a carriage printer, such as an inkjet carriage printer, a printhead is mounted in a carriage that is moved back and forth across the region of printing. To print an image on a sheet of paper or other recording medium (also interchangeably referred to as paper or media herein), the recording medium is advanced a given distance along a recording medium advance direction and then stopped. While the recording medium is stopped and supported on a platen in a print zone relative to the printhead carriage, the printhead carriage is moved in a direction that is substantially perpendicular to the recording medium advance direction as marks are controllably made by marking elements on the recording medium, for example, by ejecting drops from an inkjet printhead. After the carriage has printed a swath of the image, while traversing the recording medium; the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath. 
     Commonly assigned co-pending U.S. patent application Ser. Nos. 12/037,970 and 12/250,717, disclose methods for identifying a general type of recording medium (e.g. photo paper versus plain paper) by analyzing a signal from a photosensor that is mounted on the printhead carriage. However, these co-pending patent applications disclose waiting until the recording medium is advanced into the print zone to scan the recording medium with the photosensor. This can increase the time required before the first print is available. 
     U.S. patent application Ser. No. 12/047,359, discloses a method for identifying a type of recording medium by using identification marks provided on the recording medium, for example on its backside. An embodiment described therein uses the motion of the recording medium as it is being picked from the media input tray in order to move the identification marks past a sensor. In other words, this U.S. Patent Application discloses waiting until a print job is initiated and the recording medium is being picked. This can increase the time required before the first print is available. Special methods for identifying locations of marks are also disclosed in U.S. patent application Ser. No. 12/047,359, in order to compensate for errors in measuring spacings between marks that are due, for example, to media slippage during advance of the recording medium. 
     What is needed, is a way to reliably identify a type of recording medium at a media input location in a printing system before a print job is initiated. 
     SUMMARY OF THE INVENTION 
     The aforementioned need is met by providing a printing system that includes a carriage movable along a carriage scan direction with an optoelectronic device mounted on the carriage. A media input location, for storing a recording medium, is included along with at least one unobstructed optical path between the optoelectronic device and a plurality of regions of the media input location as the carriage is moved along the carriage scan direction. 
     Another aspect of the present invention provides a method for identifying a type of recording medium that is stored in a media input location of a printing system, the method includes the following steps: 
     providing a carriage that is movable along a carriage scan direction; 
     providing an optoelectronic device that is mounted on the carriage; 
     providing at least one unobstructed optical path between the optoelectronic device and a plurality of regions of the media input location as the carriage is moved along the carriage scan direction; 
     providing a printing system controller including a table of characteristics of a plurality of recording media types; 
     activating the optoelectronic device while the carriage is moving along the carriage scan direction in order to provide a time-varying electronic signal corresponding to a plurality of regions of the input location; 
     transmitting the time-varying electronic signal to the printing system controller; and 
     comparing the time-varying electronic signal to the table of characteristics for identifying the type of recording medium that is stored in the media input location of the printing system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an inkjet printer system; 
         FIG. 2  is a perspective view of a portion of a printhead chassis; 
         FIG. 3  is a perspective view of a portion of a carriage printer; 
         FIG. 4  is a schematic side view of a paper path in a carriage printer; 
         FIGS. 5 ,  6 , and  7  are schematic side views of embodiments of media identification using a photosensor that is mounted on the carriage; 
         FIG. 8  is a schematic side view of an embodiment of media identification using a light emitter and photosensor that are mounted on the carriage; 
         FIG. 9  is a perspective view of a carriage mounted sensor including both a light source and a photosensor; 
         FIGS. 10   a  and  10   b  show schematic representation of markings on the backside of a first type of recording medium and a second type of recording medium respectively; and 
         FIG. 11  is a schematic side view of an embodiment of media identification using a light emitter that is mounted on the carriage. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a schematic representation of an inkjet printer system  10  is shown, as described in U.S. Pat. No. 7,350,902, and incorporated by reference herein in its entirety. Inkjet printer system  10  includes an image data source  12 , which provides data signals that are interpreted by a controller  14  as being commands to eject drops. Controller  14  includes an image processing unit  15  for rendering images for printing, and outputs signals to an electrical pulse source  16  of electrical energy pulses that are inputted to an inkjet printhead  100 , which includes at least one inkjet printhead die  110 . 
     In the example shown in  FIG. 1 , there are two nozzle arrays. Nozzles in the first array  121 , in the first nozzle array  120 , have a larger opening area than nozzles in the second array  131 , in the second nozzle array  130 . In this example, each of the two nozzle arrays ( 120  and  130 ) has two staggered rows of nozzles, each row having a nozzle density of 600 per inch. The effective nozzle density then in each array is 1200 per inch. If pixels on the recording medium  20  were sequentially numbered along the media advance direction  304 , the nozzles from one row of an array would print the odd numbered pixels, while the nozzles from the other row of the array would print the even numbered pixels. 
     In fluid communication with each nozzle array is a corresponding ink delivery pathway  132 . Ink delivery pathway  122  is in fluid communication with first nozzle array  120 , and ink delivery pathway  132  is in fluid communication with second nozzle array  130 . Portions of ink delivery pathways  122  and  132  are shown in  FIG. 1  as openings through printhead die substrate  111 . One or more inkjet printhead die  110  will be included in inkjet printhead  100 , but only one inkjet printhead die  110  is shown in  FIG. 1 . The inkjet printhead die  110  are arranged on a support member as discussed below relative to  FIG. 2 . In  FIG. 1 , first fluid source  18  supplies ink to first nozzle array  120  via ink delivery pathway  122 , and second fluid source  19  supplies ink to second nozzle array  130  via ink delivery pathway  132 . Although distinct fluid sources  18  and  19  (first and second, respectively) are shown, in some applications, it may be beneficial to have a single ink source supplying ink to nozzle arrays  120  and  130  via ink delivery pathways  122  and  132  (first and second, respectively). Also, in some embodiments, fewer than two or more than two nozzle arrays may be included on inkjet printhead die  110 . In some embodiments, all nozzles on an inkjet printhead die  110  may be the same size, rather than having multiple sized nozzles on an inkjet printhead die  110 . 
     Not shown in  FIG. 1 , are the drop forming mechanisms associated with the nozzles. Drop-forming mechanisms can be of a variety of types, some of which include a heating element to vaporize a portion of ink and thereby cause ejection of a droplet, or a piezoelectric transducer to constrict the volume of a fluid chamber and thereby cause ejection of a droplet, or an actuator which is made to move (for example, by heating a bi-layer element) and thereby cause ejection of a droplet. In any case, electrical pulses from electrical pulse source  16  are sent to the various drop ejectors according to the desired deposition pattern. In the example of  FIG. 1 , droplets ejected from first nozzle array  181 , ejected from first nozzle array  120  are larger than droplets ejected from the second nozzle array  182 , ejected from second nozzle array  130 ; due to the larger nozzle opening area. Typically, other aspects of the drop-forming mechanisms (not shown) associated respectively with nozzle arrays  120  and  130  (first and second, respectively) are also sized differently, in order to optimize the drop ejection process for the different sized droplets. During operation, droplets of ink are deposited on a recording medium  20 . 
       FIG. 2  shows a perspective view of a portion of a printhead chassis  250 , which is an example of an inkjet printhead  100 . Printhead chassis  250  includes three printhead die  251  (similar to inkjet printhead die  110 ), each printhead die  251  containing two nozzle arrays  253 , so that printhead chassis  250 , contains six nozzle arrays  253 , altogether. The six nozzle arrays  253 , in this example, may each be connected to separate ink sources (not shown in  FIG. 2 ), such as: cyan, magenta, yellow, text black, photo black, and a colorless protective printing fluid. Each of the six nozzle arrays  253  is disposed along direction  254 , and the length of each nozzle array  253  along direction  254  is typically on the order of 1 inch or less. Typical lengths of recording media are 6 inches for photographic prints (4 inches by 6 inches), or 11 inches for paper (8.5 inches by 11 inches). Thus, in order to print the full image, a number of swaths are successively printed while moving printhead chassis  250  across the recording medium  20 . Following the printing of a swath, the recording medium  20  is advanced along a media advance direction  304  that is substantially parallel to nozzle array direction  254 . 
     Also shown in  FIG. 2  is a flex circuit  257 , to which the printhead die  251  are electrically interconnected, for example, by wire bonding or TAB bonding. The interconnections are covered by an encapsulant  256  to protect them. Flex circuit  257  bends around the side of printhead chassis  250  and connects to connector board  258 . When printhead chassis  250  is mounted into the carriage  200  (see  FIG. 3 ), connector board  258  is electrically connected to a connector (not shown) on the carriage  200 , so that electrical signals may be transmitted to the printhead die  251 . 
       FIG. 3  shows a portion of a desktop carriage printer. Some of the parts of the printer have been hidden in the view shown in  FIG. 3  so that other parts may be more clearly seen. Printer chassis  300  has a print region  303  across which carriage  200  is moved back and forth in carriage scan direction  305  along the X axis, between the right side  306  and the left side  307  of printer chassis  300 , while drops are ejected from printhead die  251  on printhead chassis  250  that is mounted on carriage  200 . Carriage motor  380  moves belt  384  to move carriage  200  along carriage guide rail  382 . An encoder sensor (not shown) is mounted on carriage  200  and indicates carriage location relative to an encoder fence  383 . 
     Also mounted on carriage  200  is a carriage-mounted optoelectronic device  210 , as shown schematically in  FIG. 4 . Carriage-mounted optoelectronic device  210  includes at least one device that either converts an electronic signal to emitted light or converts light impingent on the optoelectronic device into an electronic signal. Examples of such optoelectronic devices include LED&#39;s and photosensors, respectively. In some embodiments, carriage-mounted optoelectronic device  210  includes both a light emitter such as an LED that shines light onto the recording medium  20 , and a photosensor  212  that receives light reflected from the recording medium  20 . 
     Printhead chassis  250  is mounted in carriage  200 , and ink supplies  262  and  264  are mounted in the printhead chassis  250 . The mounting orientation of printhead chassis  250  is rotated relative to the view in  FIG. 2 , so that the printhead die  251  are located at the bottom side of printhead chassis  250 ; the droplets of ink being ejected downward onto the recording medium  20  in print region  303  in the view of  FIG. 3 . Multi-chamber ink supply  262 , in this example, contains five ink sources: cyan, magenta, yellow, photo black, and colorless protective fluid; while single-chamber ink supply  264  contains the ink source for text black. Paper or other recording media (sometimes generically referred to as paper or media herein), is loaded along paper load entry direction  302  toward the front  308  of printer chassis  300 . 
     A variety of rollers are used to advance the medium through the printer, as shown schematically in the side view of  FIG. 4 . In this example, a pick-up roller  320  moves the top sheet of medium  371  of a stack of recording media  370  of paper or other recording media from the media input location  372  in the direction of arrow  302 . The media input location can be an input tray, for example. A turn roller  322  acts to move the paper around a C-shaped path (in cooperation with a curved rear wall surface) so that the paper continues to advance along media advance direction  304  from the rear  309  of the printer (with reference also to  FIG. 3 ). The paper is then moved by feed roller  312  and idler roller(s)  323  to advance along the Y axis across print region  303 , and from there to a discharge roller  324  and star wheel(s)  325  so that printed paper exits along media advance direction  304 . Feed roller  312  includes a feed roller shaft along its axis, and feed roller gear  311  is mounted on the feed roller shaft. Feed roller  312  may consist of a separate roller mounted on the feed roller shaft, or may consist of a thin, high-friction coating on the feed roller shaft. 
     The motor that powers the paper advance rollers is not shown in  FIG. 1 , but the hole  310  at the right side of the printer chassis  306 , is where the motor gear (not shown) protrudes through in order to engage feed roller gear  311 , as well as the gear for the discharge roller (not shown). For normal paper pick-up and feeding, it is desired that all rollers rotate in forward rotation direction  313 , toward the left side  307 , in the example of  FIG. 3 , is the maintenance station  330 . 
     Toward the rear  309  of the printer in this example is located the printer electronics board  390 , which contains cable connectors  392  for communicating via cables (not shown) to the printhead carriage  200  and from there to the printhead. Also, on the printer electronics board  390  are typically mounted motor controllers for the carriage motor  380 ; and for the paper advance motor, a processor and/or other control electronics (shown schematically as controller  14  and image processing unit  15  in  FIG. 1 ), for controlling the printing process, and an optional connector for a cable to a host computer. 
     For the C-shaped paper path shown in  FIG. 4 , the stack of recording media  370  is loaded backside, facing up at media input location  372 . The backside of a sheet of medium is defined as the side of the sheet that is not intended for printing. Specialty media such as those having glossy, luster, or matte finishes for different quality media, may be marked on the backside by the medium manufacturer to identify the media type. In addition to information on printing surface finishes, marking code patterns can provide information in regards to the thickness, length, width, orientation, etc., of the recording medium  20 . 
     Unlike examples disclosed in U.S. patent application Ser. No. 12/047,359, where the media manufacturer&#39;s markings are detected by a backside media sensor located near the media input location  372 ; embodiments of the present application use the one or more optoelectronic devices in carriage-mounted optoelectronic device  210  to provide a time-varying electronic signal corresponding to a plurality of regions of a sheet of medium (e.g. top sheet of medium  371 ) in the media input location  372 . Although examples disclosed in U.S. patent application Ser. No. 12/047,359, rely on the motion of top sheet of medium  371  as it is being picked from stack of recording media  370  at media input location  372  in order to bring a plurality of regions of the top sheet of medium  371  past the field of view of the backside media sensor, embodiments of the present invention rely on motion of carriage-mounted optoelectronic device  210  to bring a plurality of regions of top sheet of medium  371  past a field of view of a photosensor  212  to provide a time-varying electronic signal. 
       FIG. 5  shows the same view as in  FIG. 4  however, the top sheet of medium  371  is still at media input location  372 . A light source  360  illuminates a portion of the top sheet of medium  371 . (While the word “light” is used herein, the term is not meant to exclude wavelengths outside the visible spectrum.) Although, in some exemplary embodiments ( FIGS. 5 through 7 ), the light source  360  can be separate from carriage-mounted optoelectronic device  210 . In other embodiments, such as the one shown in  FIG. 8 , light source  360  can be mounted on carriage  200 , as a LED or laser diode for example. In  FIGS. 5 through 8 , optoelectronic device  210  includes a photosensor(s)  212 . 
       FIGS. 5 through 8 , show light paths (also called optical paths) indicated by arrows from light source  360  to the top sheet of medium  371  at a media input location  372  to the photosensor(s)  212  that is mounted on the carriage-mounted optoelectronic device  210 . The light paths shown in  FIGS. 5 through 8  are only meant to be schematic representations and are not directionally or dimensionally precise. The optical path can include optical elements such as a lens  350 , and/or a mirror(s)  362  (as in  FIG. 6 ), and/or a beam splitter  364  (as in  FIG. 7 ), and/or an aperture  214  (as in  FIG. 9 ); to properly direct light from the light source  360  to the media input location  372  and from there to the photosensor(s)  212 , such that an unobstructed optical path is provided and stray light is shielded from the photosensor(s)  212 . In other words, a region of the top sheet of medium  371  is within the field of view of the photosensor(s)  212 , and that field of view is not blocked substantially. After the top sheet of medium  371  has been advanced into the printing region  303  (as in  FIG. 4 ), the optical path between the light source  360 , the media input location  372 , and the photosensor(s)  212 ; it may be blocked by the top sheet of medium  371 , but prior to advancing of the top sheet into the printing zone, where the optical path is unobstructed (as in  FIGS. 5 through 8 ). 
     As the carriage  200  moves along the carriage scan direction  305  (into and out of the plane of  FIGS. 5 through 8 ), a plurality of unobstructed optical paths between the photosensor(s)  212  and the media input location  372  allow identification of the type of recording medium by spatially-varying characteristics on its surface, such as manufacturer&#39;s code markings. Photosensor(s)  212  is activated by receiving light to provide an electronic signal. The photosensor signal is larger when more light is received, so that as the carriage  200  is moved along the scan direction and different regions of the recording medium enter the field of view of photosensor(s)  212 , a time-varying electronic signal is provided. For the case where the anchor bars and identification marks absorb light to a greater extent than the backside media surface, when the backside surface of the media is in the field of view (without other markings), the photosensor signal will be approximately at a high, background level. When anchor bars, identification marks, logos, or other markings enter the field of view of the photosensor, the photosensor signal decreases. When a mark is fully in the field of view of the photosensor, the photosensor signal is at a relative low point. (Note: Subsequent signal processing can result in such low points being peaks rather than valleys in the signal, and they will generally be referred to as peaks herein.) A characteristic, spatially-varying set of manufacturer&#39;s markings, provide a characteristic time-varying output signal from photosensor(s)  212 , where the time variation of the signal is related to the spatial variation of the markings through the velocity of the carriage. 
     For embodiments including a lens  350  in the optical path, the lens  350  can also be attached to the carriage  200  such that it moves along with optoelectronic device  210 . For embodiments where the attached lens  350  or portions of optoelectronic device  210  prevent the free movement of carriage  200 , the lens  350  or other motion-obstructing portions, can be pivotally mounted on carriage  200 , so that they can be moved out of the way during printing. Alternatively, lens  350  can be a cylindrical lens that is stationarily mounted above media input location  372  with the cylinder axis being substantially parallel to the carriage scan direction  305 . 
       FIG. 9  is a perspective view of carriage-mounted optoelectronic device  210  that can be used in embodiments of the present invention such as the example shown in  FIG. 8 , where the light source  360  and the photosensor(s)  212  are both mounted on carriage  200 . Such a carriage sensor and its associated uses are described more completely in U.S. patent application Ser. No. 12/037,966.  FIG. 9  shows a perspective view of the carriage-mounted optoelectronic device  210 , the frame  211 , of which may be attached to carriage  200  by bolt  213 , for example. Also shown in carriage-mounted optoelectronic device  210 , are photosensor  212 , aperture  214 , first LED  216 , and second LED  218 . The photosensor  212  and the two LED&#39;s  216  and  218  are semiconductor devices (not shown), that are encapsulated in optically clear materials (transmissive to light at the wavelength of interest) that form lenses  215 ,  217 , and  219 , respectively. Photosensor lens  215  helps to focus light received through aperture  214  onto the photosensor device, while lenses  217  and  219  help to direct the emitted light toward the plane of the recording medium. Photosensor  212  is a particular example of photosensor(s)  212 , and LED&#39;s  216  and  218  are particular examples of light source  360  (as shown in earlier figures). 
       FIG. 9  shows an orientation of carriage-mounted optoelectronic device  210  that is appropriate for an embodiment in which recording medium either in the print region  303  or in the media input location  372  is located horizontally below the printhead  250  and the carriage-mounted optoelectronic device  210 , which are mounted on carriage  200 . First LED  216  is oriented to emit light vertically downward, i.e. substantially normal to the plane of the recording medium in both the print region  303  and in the media input location  372 . Photosensor  212  is configured to be on one side of first LED  216 , and photosensor  212  is oriented to receive light along a direction that is at an angle of about 45 degrees with respect to the normal to the plane of the recording medium (and pointing toward the back of the printer so that it does not receive external stray light) in this example. Second LED  218  is configured to be on the other side of first LED  216 , and second LED  218  is oriented to emit light at substantially the same angle with respect to the normal, as the photo sensor  212 , but on the other side of the normal. In this example, second LED  218  is oriented to emit light along a direction that is around 45 degrees from the normal to the plane of the recording medium in the print zone. In other examples, the angle between the normal and the photosensor  212  on one side and second LED  218  on the other side can range between 30 degrees and 60 degrees, but the angle for each should be the same. Thus, in this example, the two LED&#39;s ( 216  and  218 , respectively) are aligned, by the optoelectronic device package, relative to the photosensor  212  such that the photosensor  212  receives specular reflections of light incident on the recording medium from second LED  218 ; and photosensor  212  receives diffuse reflections of light incident on the recording medium from first LED  216 . Photosensor  212  provides an output signal (typically an output current) corresponding to the amount of light that strikes the photosensor  212 . In various embodiments, either specular reflection or diffuse reflection of light can be used to identify the type of recording medium. 
     Aperture  214  allows light that is incident within a range of angles to enter the photosensor  212 , thus providing a field of view of the backside of the medium in the media input location  372 . The aperture  214  helps to shield the optical path to the photosensor in order to block stray light that has not been reflected from the medium at the media input location  372 , and also limits the field of view to a small region on the order of several tenths of a millimeter to several millimeters in extent. 
     The light signal reflected from the manufacturer&#39;s marking is different from the light signal on the rest of the backside of the medium, so that different spacings of identification bars, for example, may be detected as different spacings of peaks or valleys of the photosensor signal. In some examples, the markings may be made using an IR absorbing material, and the light source  360  can be an infrared light source, so that light reflected from the manufacturer&#39;s markings produces a lower amplitude signal in photosensor(s)  212  than if the field of view only includes unmarked portions of medium. In other examples, fluorescent materials can be used to provide the marking information rather than light absorbing materials. In such examples, relative interaction between the light emitted from the LED and the markings or the rest of the backside of the medium, can be different. Rather than absorbing light to a greater extent than the rest of the medium, the fluorescing information markings can provide greater light to the photosensor than the rest of the medium. In general, the photosensor signal corresponding to the information markings is different from the photosensor signal corresponding to the rest of the backside surface of the medium. Embodiments for using fluorescence detection typically include an optical filter (not shown) in the reflected light path to exclude the excitation light. 
       FIGS. 10   a  and  10   b  show schematic representation of markings on the backside of a first type of recording medium and a second type of recording medium, respectively. In this embodiment, each of the various types of recording media has a reference marking consisting of a pair of “anchor bars”  225  and  226 , which are located at a fixed distance with respect to one another for all media types. In addition, there is a first identification mark  228  on the first media type  221  in  FIG. 10   a , and there is a second identification mark  229  on the second media type  222  in  FIG. 10   b . In this example, first identification mark  228  is spaced a distance s 1  away from second bar of anchor bar pairs  226  on first media type  221 , and second identification mark  229  is spaced a distance s 2  away from second bar of anchor bar pairs  226  on second media type  229 , such that s 1  does not equal s 2 . Thus, in this example, it is the spacing of the identification mark from one of the anchor bars that identifies the particular type of recording medium. 
     Ovals  240  in  FIG. 10   a , schematically represent the field of view of previously described photosensor(s)  212  in optoelectronic device  210  as the carriage  200  is scanned relative to first type recording medium  221  in media input location  372 . Because the field of view  240 , of the photosensor(s)  212 , moves along the carriage scan direction  305  as the carriage  200  moves, it is actually the projections of marking spacings s 1  and s 2  along carriage scan direction  305  that are measured. Photosensor data is actually sampled much more frequently than the ovals  240 , shown in  FIG. 10   a , but only a few samples are shown for clarity. In addition, the actual field of view can be a different size or shape than the ovals  240 , shown in  FIG. 10   a , as determined; for example, by aperture  214  shape, the angle of the aperture plane relative to the plane of the recording medium, optical elements such as lenses, and optical path lengths. 
     The photosensor output signal can be amplified and filtered to reduce background noise and then digitized in an analog to digital converter. Once the amplified photosensor signal has been digitized, digital signal processing can be used to further enhance the signal relative to high frequency background noise. In addition, the time-varying signal can be converted into spatial distances to find peak widths or distances between peaks corresponding to the code pattern markings. 
     With reference to  FIGS. 10   a  and  10   b , suppose the spacings s 1  and s 2 , as projected along carriage scan direction  305 , are 0.4 inch and 0.2 inch, respectively. If the carriage sensor assembly is scanned at a speed of 10 inches per second, then the interval of time corresponding to those projected spacings would be 0.04 second and 0.02 second, respectively, giving rise to signal peaks at those intervals. 
     The same linear encoder fence  383  (as in  FIG. 3 ) that is used by the carriage printer to let the controller  14  know the location of the printhead during printing can be used to interpret the position of the carriage sensor during scanning. A typical linear encoder has a resolution of R=600 transitions per inch (0.0017 inch). This resolution is sufficient to distinguish media marking spacings such as 0.2 inch and 0.4 inch. In addition, because the recording medium is not being moved during media type identification, and because the carriage location can be precisely located by the linear encoder fence  383 , embodiments of the present invention are not susceptible to motion inaccuracies such as media slippage. 
     A table of media surface characteristics is stored in printer memory in printing system controller  14  for comparison with the photosensor data. For identifying media type by manufacturer&#39;s markings, the time-varying photosensor data peaks can be used if a standard carriage velocity, corresponding to the velocity used in preparing the table is used for scanning the photosensor(s)  212 . Alternatively, the data can be compared in terms of spatial distances, by use of the linear encoder as described above. In any case, the table includes characteristics corresponding to a plurality of media types, and the electronic signal from the photosensor(s)  212  is compared to the characteristics in the table, in order to identify the type of recording medium that is stored in the media input location  372 . 
     As sheets of medium are removed from or added to stack of recording media  370  as shown in  FIGS. 5 through 8 , in some embodiments, the distance between top sheet of medium  371 , the lens  350 , and photosensor(s)  212  is held constant; for example, by moving a media tray up and down. However, in other embodiments, removing or adding media causes the distance between top sheet of medium  371 , the lens  350 , and photosensor(s)  212  to change. In such embodiments, the depth of field of the optical imaging path to the photosensor should be designed such that whether stack of recording media  370  is full, or only has one sheet, the surface of the top sheet of medium  371  is still sufficiently in focus for providing photosensor data that can be meaningfully compared to the table of values stored in printer memory. Depth of field can be increased, for example, by decreasing the size of aperture  214 . If the manufacturer&#39;s markings are slightly out of focus, the peaks corresponding to markings can be broadened; but the centers of two peaks should remain at the same spacing, so a measurement of center-to-center peak spacings can provide data that is less sensitive to media stack height than a measurement of peak widths, for example. 
     An example of the embodiment shown in  FIG. 5 , was built using an infrared LED (880 nm) as light source  360 . Carriage mounted photosensor(s)  212  was a 0.5 mm 2  photodiode with an integrated amplifier and a visible light exclusion filter. Lens  350  had a focal length of 20 mm. For manufacturer&#39;s markings consisting of an IR absorbing barcode, it was found that the photodetector output voltage decreased by 15 percent at the peak. 
     For the C-shaped paper path, shown in  FIGS. 4 through 8 , the recording medium at the media input location  372  is stacked printing-side down so that the backside of the recording medium is visible. Thus, in the above embodiments, the recording medium type is identified by characteristics (e.g. code markings) on the backside of the recording medium. For a printing system having a paper path where the paper is moved directly to the printing process without turning the paper over, the recording medium is stacked printing-side up at the media input location  372 . Embodiments of the present invention in such cases include using printing surface optical reflection characteristics for different types of recording media (e.g. glossy paper versus plain paper), as described in U.S. patent application Ser. Nos. 12/037,970 and 12/250,717; but using the carriage mounted photosensor to detect reflection characteristics while the recording medium is at the media input location  372  rather than at the printing zone. 
     In some embodiments, even if the recording medium at the media input location  372  is stacked printing side down, it may be possible to detect manufacturer&#39;s code markings on the printing side. Such embodiments can be implemented if the recording medium is sufficiently transmissive, the light source  360  is sufficiently intense, and/or the contrast provided between the markings and the background is sufficiently high. Furthermore, if markings are used that are invisible to the human eye, such as IR absorptive or UV fluorescent markers, the embodiment of the present invention could detect manufacturer&#39;s code markings on both sides of the media. This is particularly useful for identifying double-sided media. 
     Embodiments of the present invention have one or more optoelectronic devices (a light-emitting device and/or a light-sensing device), mounted on a carriage in a printing system, such that there is an unobstructed optical path between the optoelectronic device and a plurality of regions of the media input location  372  as the carriage is moved along the carriage scan direction  305 .  FIGS. 5 through 7  show the embodiment of the carriage-mounted optoelectronic device  210  being a photosensor(s)  212  (with the light source  360  stationarily mounted separately from the carriage  200 ).  FIG. 8  shows the embodiment of the carriage-mounted optoelectronic device  210 , including both a light source  360  and a photosensor(s)  212 . 
     Another embodiment has the light source  360  mounted on the carriage  200 , and a photosensor array  366  is stationarily mounted separately from the carriage  200 . A schematic side view is shown in  FIG. 11 , where the photosensor array  366  extends into the plane of  FIG. 11 , as does the carriage scan direction  305 . Light source  360  is activated to provide a narrow impingent beam of light (as indicated by the longer arrow) to the media input location  372 , and the narrow beam is reflected from the top sheet of medium  371  (as indicated by the shorter arrow) to one or more photosites on the photosensor array  366 . As the carriage  200  moves along the carriage scan direction  305 , the reflected light is received at a different set of photosites. The time-varying photosensor signals from the photosensor array  366  are then digitally processed and correlated to impingent beam location through the carriage location provided by encoder fence  383 . Variations in the amplitude of the photosensor signal at the different photosites corresponding to different locations of the impingent beam and due to variations of manufacturer&#39;s markings in different regions of the recording medium, for example, are then compared to a table of photosensor array signals that correspond to multiple media types in order to identify the type of recording medium in media input location  372 . The narrow impingent beam can be provided by collimating the light from light source  360  using optical elements such as lenses, or a laser diode can be used for the light source  360  in this embodiment. 
     Commonly assigned co-pending U.S. patent application Ser. Nos. 12/332,648, and 12/332,616, disclose different aspects of media sensing at the media input location  372  using photosensor arrays. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           10  Inkjet printer system 
           12  Image data source 
           14  Controller 
           15  Image processing unit 
           16  Electrical pulse source 
           18  First fluid source 
           19  Second fluid source 
           20  Recording medium 
           100  Inkjet printhead 
           110  Inkjet printhead die 
           111  Substrate 
           120  First nozzle array 
           121  Nozzles in first nozzle array 
           122  Ink delivery pathway (for first nozzle array) 
           130  Second nozzle array 
           131  Nozzles in second nozzle array 
           132  Ink delivery pathway (for second nozzle array) 
           181  Droplet(s) ejected from first nozzle array 
           182  Droplet(s) ejected from second nozzle array 
           200  Carriage 
           210  Carriage-mounted optoelectronic device (carriage sensor) 
           211  Frame of carriage sensor assembly 
           212  Photosensor(s) 
           213  Bolt 
           214  Aperture 
           215  Photosensor lens 
           216  LED (mounted for diffuse reflections) 
           217  LED lens 
           218  LED (mounted for specular reflections) 
           219  LED lens 
           221  First type recording medium (first media type) 
           222  Second type recording medium (second media type) 
           225  First bar of anchor bar pairs 
           226  Second bar of anchor bar pairs 
           228  First identification marks (for first type recording medium) 
           229  Second identification marks (for second type recording medium) 
           240  Field of view (ovals) 
           250  Printhead chassis 
           251  Printhead die 
           253  Nozzle array(s) 
           254  Nozzle array direction 
           256  Encapsulant 
           257  Flex circuit 
           258  Connector board 
           262  Multi-chamber ink supply 
           264  Single-chamber ink supply 
           300  Printer chassis 
           302  Paper load entry direction 
           303  Print region 
           304  Media advance direction 
           305  Carriage scan direction 
           306  Right side of printer chassis 
           307  Left side of printer chassis 
           308  Front of printer chassis 
           309  Rear of printer chassis 
           310  Hole (for paper advance motor drive gear) 
           311  Feed roller gear 
           312  Feed roller 
           313  Forward rotation direction 
           320  Pick-up roller 
           322  Turn roller 
           323  Idler roller(s) 
           324  Discharge roller 
           325  Star wheel(s) 
           330  Maintenance station 
           350  Lens 
           360  Light source 
           362  Mirror(s) 
           364  Beam splitter 
           366  Photosensor array 
           370  Stack of recording media 
           371  Top sheet of medium 
           372  Media input location 
           380  Carriage motor 
           382  Carriage guide rail 
           383  Encoder fence 
           384  Belt 
           390  Printer electronics board 
           392  Cable connectors