Patent Publication Number: US-10322904-B2

Title: Media detection

Description:
BACKGROUND 
     In printing apparatus such as for example some large format printers, a print medium may advance on a flat platen past a print zone, where printing fluid is deposited on print media, for example by inkjet printheads. In some apparatus print media may be maintained flat on the platen during advance by a hold-down system, such as a vacuum hold-down system. 
     Under some circumstances, the print medium during advance may touch or crash with a part of the printing apparatus such as the printheads, causing a jam which may damage the printheads themselves or other parts of the printer. 
    
    
     
       BRIEF DESCRIPTION 
       Some non-limiting examples of the present disclosure will be described in the following with reference to the appended drawings, in which: 
         FIG. 1  is a schematic drawing showing examples of printing apparatus as disclosed herein; 
         FIGS. 2 a , 2 b  and 3 a , 3 b    are schematic drawings of examples of printing apparatus with print media detection systems according to implementations as disclosed herein; 
         FIG. 4  is a schematic view in elevation showing part of a printing apparatus according to examples disclosed herein; 
         FIG. 5  is a flowchart illustrating example methods for detecting print media according to implementations disclosed herein; 
         FIG. 6  is a diagram illustrating the pressures measured by a pressure sensor in apparatus according to some examples disclosed herein; and 
         FIGS. 7 and 8  are flowcharts illustrating example methods for detecting print media and determining print media jam situations according to implementations disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Some implementations of printing apparatus such as large format printers may comprise a horizontal, substantially flat platen for supporting print media. Print media, for example web print media or sheets of different length, may be advanced on the platen by a driving mechanism, past a print zone where printing fluid is deposited on the print media. The printing fluid may for example be ejected by inkjet printheads that are above the platen. 
     Printheads may for example be mounted on a carriage that prints a swath while travelling along a scan axis that is perpendicular to the print media advance direction, and the print media may be advanced a predetermined length between swaths. In page-wide array printers, a plurality of stationary printheads, or a wide printhead, spanning all the width of the printer, deposit printing fluid on a print medium that advances continuously on the platen. 
     In some circumstances, when a print medium advances in the apparatus during a printing operation it may happen that it crashes against one of the parts of the apparatus: for example, the leading edge of the print medium may crash against the printheads, for example because it is curled. 
     This situation may cause a print media jam in the apparatus, with the risk of potential damage to the printheads or to the print media advance mechanism. 
     It may therefore be useful to detect a print media jam as soon as possible, to reduce the associated risks. In some printing apparatus it is known to detect such a situation by algorithms based on several inputs and conditions, including information provided by a sensor to detect the presence of print media at specific positions in the apparatus. Detecting the presence of print media may also be useful in other circumstances during printing operation. 
     It is known to detect the presence of print media, for example with optical sensors, at the print media input of the printing apparatus. 
     However, optical sensors may not be easily placed near the print zone in printing apparatus that employ a vacuum hold-down system to maintain the print media flat on the platen, because their installation may cause vacuum leaks and affect the vacuum system. 
     On the other hand, sensors that contact the print media for detecting the presence may not be a satisfactory solution in the print zone or after the print zone in an inkjet printing apparatus, because contact may damage the printed image. 
     The present disclosure provides implementations of methods and systems for detecting print media on the platen of a printing apparatus. 
     In implementations of a printing apparatus as shown in  FIG. 1 , the apparatus may comprise a platen  10  having a print media advance surface  11 , on which print media may be supported and may advance. The printing apparatus may also comprise a vacuum source  40  and a pressure sensor  50 . 
     The platen  10  may be substantially horizontal, i.e. horizontal or with a small incline, and/or it may be substantially planar or flat, even though it may comprise channels or recessed portions. 
     The platen  10  may comprise a hole  20 , that may be open towards the print media advance surface  11  of the platen  10 . The hole  20  may also be connected with the vacuum source  40  and with the pressure sensor  50  of the apparatus, such as to be in fluid communication with them, as shown schematically in  FIG. 1  and as will be described in more detail later on. 
     Examples of printing apparatus according to implementations disclosed herein may comprise a control unit  60 , as shown in  FIG. 1 . The control unit  60  may receive an output of the pressure sensor  50  and it may determine that a print medium is present on the platen at the hole  20  if the pressure sensor  50  measures an air pressure below a predetermined threshold. 
     The hole in fluid communication with the pressure sensor may be located at a suitable position on the platen, where it may be convenient to detect the presence of print media. For example it is possible to place it in the proximity of the print zone in an apparatus with a vacuum print media hold-down system, and indeed it may be provided in combination with such a hold-down system. 
     Furthermore, in implementations of such a printing apparatus some of the elements of the print media detection system may be part of the vacuum hold-down system, for example the pressure sensor, and therefore an apparatus may be provided with a print media detection system at a relatively low cost. 
     Implementations of the detection system may be robust and reliable, as they may be unaffected by aerosol, printing fluid, print media particles or the like, and may allow fast detection of print media at predetermined positions on the platen. For example this may be useful, amongst others, in page-wide printing apparatus, where the speed of print media advance is high and therefore it is useful to detect malfunctions as early as possible. 
     According to some implementations or examples of a printing apparatus, the hole  20  in the platen  10  is after or downstream the print zone, in the direction of print media advance, such that it allows detecting that the print medium has advanced along the print zone. 
     In some implementations, the control unit  60  may determine that a potential print media jam situation has arisen if the presence of a print medium is not detected at the hole  20  within a predetermined time period after a triggering event has occurred: for example, after the print medium PM is detected at the print media input of the printing apparatus. 
     In some implementations, the control unit  60  may determine that a print media jam situation has arisen if the presence of a print medium is not detected at the hole  20  after the print medium PM has advanced a predetermined length from the moment the triggering event has occurred. 
     In other words, the control unit  60  may determine that a potential print media jam situation has arisen if the print medium has entered the printing apparatus and advanced, but has not reached the position of the hole when it should have. If the hole for example is after the print zone, then a potential print media jam situation in the print zone may be detected. 
       FIGS. 2 a  and 2 b    show implementations of a printing apparatus as disclosed above, comprising a print media detection system, in two different conditions.  FIGS. 2 a  and 2 b    show partial views of the platen  10  of a printing apparatus, on which a print medium PM ( FIG. 1 b   ) may be supported and may advance. 
     In some examples such as illustrated in  FIGS. 2 a  and 2 b    the platen  10  may have a recessed portion  12 , and the hole  20  may be provided in this portion of the platen. The hole  20  is open towards the print media advance surface  11  and may be in fluid communication with the pressure sensor  50  through a conduit  70 . 
     In the recessed portion  12  of the platen  10  there may be a vacuum opening  30 , in fluid communication with the vacuum source  40 . The hole  20  may therefore also be in fluid communication with the vacuum source  40 , through the recessed portion  12  and the vacuum opening  30 . 
     In some implementations the recessed portion  12 , the vacuum opening  30  and the vacuum source  40  may be part of a vacuum hold-down system. 
     In the situation of  FIG. 2 a   , wherein no print media is present over the recess  12  in the platen, the air pressure in correspondence with the hole  20 , which may be measured by the pressure sensor  50 , is atmospheric pressure or close to atmospheric pressure. 
     When a print medium PM advances on the platen  10  and covers the recessed portion  12 , as shown in  FIG. 2 b   , it is drawn downwards by the negative pressure caused by the vacuum source  40 , substantially closing the recessed portion  12 , and a level of vacuum is established in the vacuum opening  30 , the recessed portion  12 , and the hole  20 . In this situation, the air pressure in correspondence with the hole  20 , which may be measured by the pressure sensor  50 , is lower than atmospheric pressure. It may be equal or close to the level of vacuum provided by the vacuum source  40  if there are no other losses in the vacuum system. 
       FIGS. 3 a  and 3 b    show implementations of a printing apparatus, comprising a print media detection system, in two different conditions. In some examples such as illustrated in  FIGS. 3 a  and 3 b    the hole  20  may be provided in a substantially flat portion of the platen  10 . The hole  20  is open towards the print media advance surface  11 . 
     In examples according to  FIGS. 3 a  and 3 b   , a conduit  80  may be provided for fluid communication of the hole  20  with the vacuum source  40 , and the conduit  80  may comprise a tee branch  90 , connected to the pressure sensor  50 . The hole  20  may therefore be in fluid communication with the vacuum source  40  and with the pressure sensor  50 . 
     In the situation of  FIG. 3 a   , wherein no print media is present over the hole  20  in the platen  10 , the air pressure in a position  21  which is associated with the hole  20 , depends on the geometry of conduit  80  and tee branch  90  and on the negative pressure exerted by the vacuum source  40 . It is a pressure below atmospheric pressure, but above the pressure of the vacuum source  40 . The pressure in position  21  associated with the hole  20  may be measured by the pressure sensor  50 . 
     When a print medium PM advances on the platen  10  and covers the hole  20 , as shown in  FIG. 3 b   , it is drawn downwards by the negative pressure caused by the vacuum source  40  in the hole  20 , substantially closing the hole  20  to the environment, and a level of vacuum is established in the hole  20 , the conduit  80  and the tee branch  90 . In this situation, the air pressure in the position  21  associated with the hole  20 , which may be measured by the pressure sensor  50 , is below the pressure measured in the situation of  FIG. 3 b   . It may be equal or close to the level of vacuum provided by the vacuum source  40  if there are no other losses in the vacuum system. 
     In some implementations of a printing apparatus, comprising a conduit  80  for providing fluid communication of the hole  20  with the vacuum source  40  and with a tee branch  90  connected to the pressure sensor  50 , the hole  20  and associated conduits may also be provided in a recessed portion of the platen  10 . For example, in some implementations comprising a platen  10  with a recessed portion  12  such as shown in  FIGS. 2 a  and 2 b   , a single hole  20  may be provided instead of a hole  20  and a vacuum opening  30 , and the single hole  20  may be connected via a conduit and tee branch both to the vacuum source  40  and to the pressure sensor  50 . 
     In implementations of a printing apparatus the platen may comprises a recessed portion, the hole may be in a recessed portion, and the apparatus may comprise a vacuum chamber between the platen and the vacuum source, in correspondence with the recessed portion and in fluid communication with the hole. 
     For example,  FIG. 4  shows in a schematic elevation view implementations of a printing apparatus with such a vacuum chamber. The apparatus may comprise a platen  10  with recessed portions  12  and a vacuum chamber  41 , under the platen  10 , such as to be in correspondence with the recessed portions  12 , and connected to a vacuum source  40 , such as a vacuum fan, by a vacuum pipe  42 . A pressure sensor  50  may be provided. 
     The recessed portions  12  may comprise vacuum openings  30 , for example as shown in the enlarged detail on the right of  FIG. 4 , that may illustrate a detail of the platen  10 , and the assembly may provide a hold-down system for print media on the platen  10 . 
     In implementations such as shown in  FIG. 4 , a hole  20  may be provided in one of the recessed portions  12 , as shown in the enlarged detail on the left of  FIG. 4 , and may be in fluid communication with the pressure sensor  50 , as shown by the dotted line in  FIG. 4 . The pressure sensor  50  may therefore measure the air pressure in a position associated with the hole  20 . 
     In some examples the fluid communication between the hole  20  and the pressure sensor  50  may be for example through a tube  22  that may isolate the hole  20  from the vacuum chamber  41  on the underside of the platen  10 , as shown in the enlarged detail on the left of  FIG. 4 , although the hole  20  may still be in fluid communication with the vacuum chamber  41  via the recessed portion  12  of the platen and the vacuum opening  30 . 
     In some implementations the hole  20  may be provided for example in a recessed portion  12  that is near a print zone PZ where printing fluid is deposited on the print media. For example, the hole  20  may be provided after the print zone PZ in the direction of print media advance, which is shown by arrow A. 
     The pressure sensor  50  may also be employed for calibrating the vacuum system during installation of the printing apparatus. 
     Also disclosed herein are implementations of a print media detection system for a printing apparatus, such as shown in  FIG. 1 . 
     According to some implementations, a print media detection system may comprise a platen  10  with a print media advance surface  11 , and a hole  20  in the platen that is open towards the print media advance surface  11 . The hole  20  may be put in fluid communication with a vacuum source  40  of a printing apparatus. The system may comprise a conduit, such as for example conduit  70  in  FIG. 2 a   , or for example conduit  90  in  FIG. 3 a   , for putting the hole  20  in fluid communication with a pressure sensor  50  of the printing apparatus. 
     In some implementations, the hole  20  may be foreseen in the central zone of the platen  10  in the print media width direction, i.e. in a direction perpendicular to the print media advance direction, so that print media of any width may pass over the hole during printing. 
       FIG. 5  illustrates example methods for detecting the presence of print media in a printing apparatus which comprises a platen on which print media may advance, according to implementations disclosed herein. 
     As shown in  FIG. 5 , implementations of a method for detecting the presence of print media on a platen of a printing apparatus may comprise:
         in block  100 , measuring the air pressure in a position associated with a hole in the platen, the hole being in fluid communication with a vacuum source and being open towards the print media advance surface of the platen;   in block  110 , verifying if the measured air pressure is below a predetermined threshold; and   in case the measured air pressure is below the threshold, determining in block  120  that a print medium is present at the hole in the platen.       

     In case the measured air pressure is not below the threshold in the verification in block  110 , the method returns to block  100 . 
     In implementations of a printing apparatus such as illustrated in  FIGS. 1 to 4 , the measured air pressure when a print medium is present on the platen  10  at the hole  20  may be equal to or close to the vacuum pressure provided by the vacuum source  40 , if there are no other losses in the vacuum system. When no print medium is present at the hole  20  on the platen, the air pressure measured by the pressure sensor  50  is higher: it may be equal or close to atmospheric pressure in the cases such as those illustrated in  FIG. 2 a    or  FIG. 4 , for example, and it may be an intermediate value between the atmospheric pressure and the vacuum pressure in cases such as those illustrated in  FIG. 3   a.    
     A predetermined threshold that may be employed in implementations of methods disclosed herein may be for example a percentage of the vacuum pressure that is provided by the vacuum source  40  and measured by the pressure sensor  50  when a print medium is present: it may be for example a value of about 20% of the vacuum pressure. 
     In some implementations of the method, the predetermined threshold may be for example a value based on the atmospheric pressure, for example a value of about 80% of the atmospheric pressure. 
     Selecting values of the predetermined threshold closer to the atmospheric pressure allows faster detection of the print media, and therefore also faster detection of a situation in which a print medium should have reached the hole  20  but has not. 
       FIG. 6  is a diagram that illustrates the variation of the pressure measured by the pressure sensor  50  in implementations of the method, for example a method applied to a printing apparatus as shown in  FIG. 4 , comprising a vacuum hold-down system with a plurality of recessed portions  12  and vacuum openings  30  connected to a vacuum chamber  41 . 
     In this example the recessed portion  12  with the hole  20  is placed at about 90 mm from the beginning of the print platen  10  where the print media enter. The vacuum source provides a vacuum pressure of about −85 mm H 2 O, and the speed of advance of print media is 15 inches per second (37.5 cm/s). 
     In  FIG. 6 , the relative pressure measured by the pressure sensor  50  (relative pressure) is plotted against the position of the leading edge of a print medium that is advancing on the platen. The vertical line in the diagram indicates the position on the platen of the recessed portion  12  with the hole  20 ; the beginning of the platen is indicated by position  0 . 
     From left to right, the diagram illustrates that when the print medium starts advancing on the platen, and its leading edge has not reached the position of the hole  20 , the pressure measured by the sensor  50  generally oscillates around a value of 0 mm H 2 O, i.e. atmospheric pressure. 
     When the leading edge reaches the position of the recessed portion  12  of the platen where the hole  20  is located, and advances covering this recessed portion  12 , the air pressure in hole  20  may descend abruptly as shown to the right of the vertical line, because the hole  20  is then subject to the negative pressure originating from the vacuum source  40 , through the vacuum opening  30 . The level or value of the negative pressure is not yet the maximum negative pressure provided by the vacuum source  40 , because part of the platen  10  is not yet covered by the print medium and therefore there are air losses through the vacuum openings  30  of the platen downstream or after the position of the hole  20 . 
     As the leading edge of the print medium advances further downstream of the hole  20 , and covers a larger proportion of the vacuum openings  30  of the platen, the pressure of the whole vacuum system decreases, and therefor the pressure measured by the pressure sensor  50  also decreases, until it reaches the negative pressure provided by the vacuum source once all the platen is covered by the print medium. 
     As shown in the diagram, in this example the pressure measured by the sensor is down to about −15 mm H 2 O after a print medium advance of about 8 mm from the moment the leading edge of the print medium reaches the hole  20 . This shows that in implementations of the apparatus and methods disclosed herein it is possible to detect a situation of absence of a print medium (that was expected to reach the hole  20 ), which may indicate that a print media jam has occurred, when just a short length of print medium may be involved in the print media jam. 
     Implementations of methods disclosed herein for detecting the presence of print medium on the platen of a printing apparatus may be applied in printing apparatus such as disclosed above with reference to  FIGS. 2 a   / 2   b  and/or  FIG. 4 . Implementations of methods disclosed herein may also be applied in printing apparatus such as disclosed above with reference to  FIGS. 3 a   / 3   b.    
       FIG. 7  is a flowchart illustrating implementations of a method for detecting print media and for determining if a print media jam situation may have occurred. In an example, the hole  20  may be after a print zone of the printing apparatus, in a direction of print media advance. 
     In such cases, and as shown in  FIG. 7 , implementations of the method may comprise, in block  200 , detecting that a triggering event has occurred. The triggering event may be, for example, the entry of the leading edge of a print medium on the platen, the presence of the print medium in a position upstream or before the position of the hole  20 , the activation of the print medium advance system, etc., 
     When the triggering event has been detected, the method may comprise measuring the air pressure at the hole  20 , in block  210 . 
     In block  220  the measured pressure is compared with a predetermined threshold: if the measured pressure is below this threshold, it is determined in block  230  that a print medium is present at the hole in the platen. 
     If in block  220  it is found that the measured pressure is not below the predetermined threshold, which would indicate that no print medium is present at the hole  20 , then the method may comprise, in block  240 , verifying if a predetermined time period has lapsed, or if a predetermined length of print medium has advanced, after the triggering event, for example after the leading edge of the print medium has been detected at the beginning of the platen. 
     The predetermined time period or print media advance length are selected depending on the triggering event used, on the speed of advance of the print medium, on the desired level of security, etc. 
     In case of a positive determination in block  240 , then it may be determined in block  250  that a print media jam has occurred. For example, the print medium may have crashed with the printheads in the print zone. Suitable actions may then be taken, such as issuing an alarm signal, stopping the advance of the print medium, or the like. 
     In case of a negative determination in block  240 , then the method may return to block  210 . 
       FIG. 8  is a flowchart illustrating implementations of a method for detecting print media on the platen and for determining if a print media jam situation may have occurred downstream or after the position of the hole  20  in the direction of print media advance, for example at the outlet of the platen. 
     If a print medium crashes at the outlet of the platen, and since the print medium continues entering and advancing on the platen, the print medium tends to rise from the platen forming a bubble and therefore uncovering at least some of the vacuum openings  30  of the platen. As a consequence, the vacuum level in the vacuum system, and therefore the air pressure measured by the pressure sensor  50  connected to the hole  20  in the platen  10 , may increase. 
     Implementations of a method disclosed herein that allows detecting a print media jam downstream or after the position of the hole  20  may comprise detecting the presence of print media at the hole  20 , and then continuing measuring the air pressure at the hole  20  and determining that a print media jam has occurred if, within a predetermined time period or a predetermined print media advance length after a triggering event, the measured pressure raises above a predetermined threshold. 
     Implementations of such a method allow detecting print media jams at the exit of the printing apparatus shortly after they occur, even in the case of relatively long sheets of print media, for which the detection of the trailing edge of the print medium takes a longer time. 
     As shown in  FIG. 8 , implementations of such a method may comprise, in block  300 , detecting the presence of a print medium at the hole, for example as described in relation to  FIG. 5 , and then, in block  310 , detecting that a triggering event has occurred. 
     The triggering event may be, for example, the presence of the print medium at a predetermined position downstream or after the hole in the direction of print media advance, for example at the outlet of the platen. This may be detected for example by suitable sensors, or by the detection of an air pressure at the hole  20  that is equal or close to the vacuum level provided by the vacuum source  40 , which may indicate that the print medium has covered all the platen. 
     Once the triggering event has been detected, the method may comprise continuing measuring the air pressure at the hole  20 , in block  320 . 
     In block  330  the measured pressure is compared with a predetermined threshold: if the measured pressure is below the threshold, it is determined in block  340  that a print medium is still present at the hole  20  in the platen, and the method may return to block  320 . 
     If in block  330  it is found that the measured pressure is not below the predetermined threshold, which would indicate that the air pressure has risen and no print medium is present at the hole  20 , then the method may comprise, in block  350 , verifying if a predetermined time period has lapsed, or if a predetermined length of print media has advanced, after the triggering event. 
     In case of a negative determination in block  350 , then it may be determined in block  360  that a print media jam has occurred. Suitable actions may then be taken, such as issuing an alarm signal, stopping the advance of the print medium, or the like. 
     In case of a positive determination in block  350 , indicating that the trailing edge of the print medium has reached the hole  20  and therefore the rise in pressure at the hole does not indicate a malfunctioning, the method may return to block  300 . 
     In implementations of methods as illustrated by  FIG. 8  the hole  20  may be placed at or after a print zone of the printing apparatus, in a direction of print media advance. The predetermined time period or predetermined print media advance length used in block  350  may be the time that the trailing edge of the print medium takes to reach the position of the hole  20  on the platen, and may therefore depend on the length of the sheet being printed, as well as on the speed of advance, the desired level of security, etc. 
     In some implementations of a method as disclosed herein, the method may comprise using the same print media detecting system, such as disclosed with reference to  FIGS. 1 to 4 , for detecting a potential print media jam at the print zone, for example as disclosed in  FIG. 7 , and for detecting a potential print media jam downstream of the print zone, as disclosed in  FIG. 8 . 
     Although a number of particular implementations and examples have been disclosed herein, further variants and modifications of the disclosed devices and methods are possible. For example, not all the features disclosed herein are included in all the implementations, and implementations comprising other combinations of the features described are also possible.