Patent Publication Number: US-9421802-B2

Title: Reference strip

Description:
BACKGROUND OF THE INVENTION 
     Print systems are oftentimes provided with scanning print heads. During a print operation, these print heads are moved (“scanned”) along a scan axis for firing ink onto the substrate in a number of swaths, to the end of printing an image onto the substrate. During a printing operation, after each one or multiple scanning movements along the scan axis, the substrate is moved with respect to the print head and subsequently a next swath of ink is printed onto the substrate. 
     The print head is mounted onto a print head carriage. The print head carriage is usually mounted onto a guide for guiding the print head along the scan axis. The print head may be mounted on the carriage so as to be exchanged, or the print head and the print head carriage may form an integral assembly. Furthermore, it is advantageous to detect the position and/or the speed of the print head carriage. For an accurate detection of the print head carriage speed and/or position, most print systems are provided with a print head carriage feedback system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustration, certain embodiments of the present invention will now be described with reference to the accompanying diagrammatic drawings, in which: 
         FIG. 1  shows a diagrammatic cross sectional front view of an embodiment of a print system with a print head carriage feedback system; 
         FIG. 2  shows a diagrammatic cross sectional side view of an embodiment of a print head carriage with a print head and a print head carriage feedback system; 
         FIG. 3  shows a detail of a fragment of an embodiment of a reference strip; 
         FIG. 4  shows and embodiment of two neighboring transmission windows in front view; 
         FIG. 5  shows a flow chart of an embodiment of a method of determining a position of a print head carriage; 
         FIG. 6  shows a flow chart of an embodiment of manufacturing a reference strip. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings. The embodiments in the description and drawings should be considered illustrative and are not to be considered as limiting to the specific embodiment of element described. Multiple embodiments may be derived from the following description and/or drawings through modification, combination or variation of certain elements. Furthermore, it may be understood that also embodiments or elements that are not literally disclosed may be derived from the description and drawings by a person skilled in the art. 
     It may be a challenge to detect the position of the print head in an environment where ink aerosol is dispersed during use, and wherein multiple parts may be replaced. It may be a challenge to provide a feedback system that is robust enough to allow operators to exchange, maintain and/or clean parts such as the print head with a relatively low risk of damaging the feedback system. At the same time the feedback system may be accurate to prevent possible misalignment of ink drops. 
     In  FIG. 1  a diagrammatic overview of a print system  1  is shown. The print system  1  may comprise a large format printer, for example for printing substrates  2  having a height or width of at least approximately 0.5 meter, for example at least approximately 1 meter. In certain embodiments, the print system  1  may be arranged to print maximum substrate sizes according to industry standards such as 42 inch (1.07 meter) or 60 inch (1.52 meter), or another large format standard. The print system  1  may comprise a inkjet printer, for example a thermal inkjet or a piezo inkjet printer. Accordingly, the print head  5  may comprise an inkjet print head, for example a thermal inkjet or a piezo inkjet print head. 
     The print system  1  may comprise a print head carriage  3 . The print head carriage  3  may comprise a print head  5 , as shown in  FIG. 2 . The print head  5  may be positioned in the print head carriage  3  so as to be removed. In such embodiment, the print head carriage  3  may comprise a print head holder  4 . In another embodiment, the print head  5  may be integrally fixed within the print head carriage  3 . 
     The print head carriage  3  may be arranged to scan along a scan axis  6  in opposite scanning directions M. The print head carriage  3  may be mounted onto a guide  7  to scan along the scan axis  6 . The guide  7  may comprise a rail or tube or the like. A drive system (not shown) may be provided to drive the print head carriage  3  along the guide  7 . The print head  5  may fire ink drops onto the substrate  2  while scanning in either one or both scanning directions M. 
     The print system  1  may comprise a print head carriage feedback system for determining a position of the print head carriage  3  and providing feedback to a controller  8  about the position of the print head carriage  3 . The print head carriage feedback system may comprise a detector  9  for determining a position of the print head carriage  3  with respect to the scan axis. The detector  9  may send signals to the controller  8  for further processing. In the shown embodiment, the detector  9  is mounted onto the print head carriage  3 . The print head carriage feedback system may further comprise a reference strip  10  that is arranged along the scan axis. The reference strip  10  may extend parallel to the guide  7 . The detector  9  may be arranged to use the reference strip  10  as a reference for detecting the position of the print head carriage  3  with respect to the scan axis  6 . As shown in  FIG. 2 , the reference strip  10  may extend through the carriage  3 . As shown in the embodiment of  FIG. 3 , the reference strip  10  may comprise transmission windows  11 . 
     The print head carriage feedback system may further comprise a controller  8 . The controller  8  may comprise a processor  13  that is configured to process signals received from the detector  9  for determining the position of the print head carriage  3  with respect to the scan axis  7 , according to a predetermined algorithm. The controller  8  may further comprise a storage unit  12  comprising said algorithm for determining the position of the print head carriage  3  with respect to the scan axis  7 . 
     The detector  9  may comprise an emitter  14  and a receiver  15 , as illustrated by  FIG. 2 . In the shown embodiment, the detector  9  comprises multiple receivers  15  for detecting a signal from the emitter  14 . The detector  9  may comprise an optical detector. The emitter  14  may comprise a LED (light emitting diode), a laser, or other light emitting source. The receiver  15  may be arranged to receive the signal that is emitted by the emitter  14 , and transmitted by the transmission windows  11 . The receiver  15  may comprise a diode or transistor type light receiver, for example a photodiode, a LED, or laser diode. In the shown embodiment, the emitter  14  comprises a LED and the receiver  15  comprises multiple photodiodes. The emitter  14  and receiver  15  may both be mounted on the print head carriage  3 . The emitter  14  and the receiver  15  may extend on opposite sides of the reference strip  10 . The receiver  15  may have a diameter E of approximately 1 millimeter or less, for example approximately 0.275 millimeter or less. Herein, the diameter E may be understood as the largest straight cross sectional distance between two opposite sides of the circumference of the receiver  15 , and the receiver  15  may comprise a photodiode. 
     In other embodiments, the detector  9  may be arranged differently. For example, the emitter  14  may be mounted onto the print head carriage  3  and multiple receivers  15  may be mounted in the print system  1  so as to have a fixed position with respect to the reference strip  10  so that the print head carriage  3  moves with respect to the receivers  15 . In again another embodiment, the detector may be fixedly arranged within the print system  1  while the receivers may be mounted onto the print head carriage  3 . 
       FIG. 3  is a detailed front view of a portion of an embodiment of the reference strip  10 . The reference strip  10  may comprise a multiple transmission windows  11 . The transmission windows  11  may comprise windows for transmission of the light of the emitter  14 . The transmission windows  11  may comprise cut outs extending through the reference strip  10 . The emitter signal may pass between the emitter  14  and the receiver  15  without passing through a transparent layer. The signal may pass through air. 
     The transmission windows  11  may be arranged along a substantial part of the length L of the reference strip  10  in parallel to each other and also next to each other. The transmission windows  11  may have a substantially longitudinal shape, the longitudinal direction L being perpendicular to the scanning direction M. Each transmission window  11  may comprise one or more bridges  17 . Such bridges  17  may locally reinforce the reference strip  10 . The bridge  17  may extend across the width W of the respective transmission window  11 . In this description, reinforcing may be understood as stiffening, strengthening, and/or locally decreasing the flexibility of the strip  10 . 
     Each transmission window  11  may correspond to a position with respect to the scanning axis  7 . Each transmission window  11  may comprise multiple transmission window portions  16 . Transmission window portions  16  that correspond to the same transmission window  11  may be arranged on the same longitudinal axis A, having the same one dimensional position along the scanning axis  7 , with a bridge  17  in between. 
     The transmission windows  11  may have rounded edges  22  near the ends, as is more clearly illustrated in  FIG. 4 . Accordingly, the bridges  17  may have rounded sides. The shape of the round edges  22  may depend on the manufacturing method of the transmission window portions  16 . For example the transmission window portions  16  may be etched. In a further embodiment, the rounded edges  22  may have a reinforcing effect. 
       FIG. 4  shows an embodiment of two neighboring transmission windows  11  in a more detailed view. Each transmission window  11  may comprise one or more bridges  17 , for example one, two, three, four, five or more bridges  17 . 
     As can be seen from the embodiment of  FIG. 3 , the bridges  17  corresponding to certain transmission windows  11  may extend at a different location with respect to the bridges  17  of the neighboring transmission window  11 . For example, as can be seen in  FIG. 3 , a first lowermost bridge  17 A of a first transmission window  11  may extend at a different distance from a respective edge zone  18 ,  19  as compared to a neighboring lowermost bridge  17 B,  17 C of a second neighboring transmission window  11 . 
     The reference strip  10  may comprise two edge zones  18 ,  19  and a transmission zone  20 . The reference strip  10  may comprise a top edge zone  18  and a bottom edge zone  19 . The transmission zone  20  may be formed by the transmission windows  11 . 
     The transmission zone  20  may comprise a repetitive pattern of bridges  17  and transmission window portions  16 . In an embodiment the repetitive pattern may comprise three different transmission windows  11  having different locations and/or different numbers of bridges  17 , as can be seen from in  FIG. 3 . For example, a first transmission window  11  may comprise two bridges  17 , a second transmission window  11  neighboring the first transmission window  11  may comprise three bridges  17 , and a third transmission window  11  neighboring the second transmission window  11  may also comprise three bridges  17 , wherein said bridges  17  may have different heights within the transmission zone  20 . In other embodiments, the repetitive patterns may comprise two, four, five or more different bridge arrangements, or all transmission windows  11  may have the same bridge locations. 
     Spaces  21  may be provided between the transmission windows  11 . The spaces  21  may form transmission window frames. A function of the bridges  17  may be to reinforce these transmission window frames, to prevent deformation of the transmission window frame. The bridges  17  may affect signal reception by the detector  9  because they may block a signal. Hence, the transmission windows  11  and its bridges pattern may be determined according to a balance between signal reception and a relatively robust print head carriage feedback system. 
     In an embodiment, the reference strip  10  may have a length L of approximately 1 meter or more. In further embodiments the length of the reference strip  10  is approximately 1.9 meters or more, or approximately 2.4 meters or more, for example corresponding to the scan length of the respective print system  1 . The reference strip  10  may have a thickness T (see  FIG. 2 ) of between approximately 0.01 and approximately 1 millimeter, for example around approximately 0.05 millimeter. The reference strip  10  may comprise metal. 
     The reference strip  10  may have a height H of between approximately 2 and approximately 50 millimeters, or for example between approximately 5 and approximately 30 millimeters. In an embodiment, the height H of the reference strip  10  is approximately 13.5 millimeters. The transmission zone  20  may be between approximately 1 and approximately 20 millimeters, for example approximately 6 millimeter. 
     In an embodiment, the transmission windows  11  may have a width W of between approximately 0.01 and approximately 0.4 millimeters, for example between approximately 0.03 and approximately 0.2 millimeters. In an embodiment the width W of the transmission windows  11  is approximately 0.0847 millimeters. In an embodiment, a Space S between neighboring transmission windows  11  may be between approximately 0.04 and approximately 0.4 millimeter, for example between approximately 0.03 and approximately 0.2 millimeters. In an embodiment the said space S is approximately 0.0847 millimeters. The space S between subsequent transmission windows  11  may be approximately the same as the width W of the transmission windows  11 . The pitch of the transmission windows  11  may be approximately 0.17 millimeters. 
     The bridges  17  may have a width B of between approximately 0.01 and approximately 0.5 millimeters, the width B being determined by the distance between two transmission window portions  16  of the same transmission window  11 , as can be seen from  FIG. 4 . The width B of the bridge may be between approximately 0.01 and approximately 0.25 millimeters, for example approximately 0.135 millimeters, or at least approximately 0.05 millimeters. 
     In the shown embodiments, the transmission windows  11  may comprise through holes in the reference strip  10 , which may prevent that aerosol sticks to the transmission windows  11  and facilitates better transmission. The dimensions of the transmission windows  11  may prevent that aerosol passes through the transmission windows  11 , onto the receivers  15 . In another embodiment (not shown), the reference strip  10  may comprise a transparent film or layer covering the transmission windows  11 . 
       FIG. 5  shows an embodiment of a method  500  of determining a position of a print head carriage  3 . In a step  510 , the print head carriage  3  may be moved along the reference strip  10 . In an embodiment, the reference strip  10  may extend through the print head carriage  3 . In a further step  520 , a signal may be emitted by the emitter  14 , onto the reference strip  10 . The signal may comprise an optical signal. The signal may be transmitted by the transmission windows  11 . The signal may be received by the receivers  15 , in a further step  530 . The signal may be interrupted by the spaces  21  between the transmission windows  11  and by the bridges  17 . The signal interruption caused by the spaces  21  between the transmission windows  11  may be received by the receivers  15  and processed by the processor  13  for determination of a position of the print head carriage  3 . The signal interruptions caused by the bridges  17  may be such that they have a reduced effect on the signal received by the respective receivers  15 , or may be such that the position of the print head carriage  3  can still be derived with sufficient accuracy. The position of the print head carriage  3  with respect to the scan axis  6  may be determined, in a further step  540 , for example by deriving from the total interrupted signal the interruptions caused by said spaces  21 . If the determined position of the print head carriage  3  is determined to be different than the desired position, than the processor  13  may provide feedback to the drive system to adjust a speed and/or position of the print head carriage  3 , as indicated by calibration step  550 . The steps  510 - 550  may be performed approximately simultaneously and/or in any order. Multiple algorithms, as stored by the storage unit  12 , may be suitable to derive the print head carriage position from the received signals. 
       FIG. 6  shows an embodiment of a method  600  of manufacturing a reference strip  10  for a print head carriage feedback system. In a first step  610 , the method  600  may comprise placing a reference strip  10  so as to be etched by an etch process. Multiple etch process may be suitable for etching the transmission windows  11  in the reference strip  10 . In a second step  620 , a transmission window pattern may be applied to the reference strip  10 . For example, a mask may be applied to the reference strip  10 . The mask may comprise the transmission window pattern. In a third step  630 , the transmission windows  11  may be etched in the reference strip  10 . A negative or positive of the mask may be etched in the reference strip  10 , which may for example comprise a suitable metal, for formation of the desired transmission window pattern. The transmission windows  11  may be etched so as to be arranged in parallel and/or approximately perpendicular to a longitudinal direction L of the reference strip  10 . The transmission windows  11  may be etched having a width W of approximately 0.4 millimeter or less. The transmission windows may be arranged in a pattern having a pitch of approximately 0.8 millimeter or less, for example approximately 0.17 millimeters. For each transmission window  11 , the etch operation may etch multiple through holes with at least one interruption in between. The interruption may form a bridge  17 , as discussed above. Each through hole may be arranged to transmit a detection signal and to prevent undesirable quantities of aerosol from passing through. The through holes may form the transmission window portions  16 . In a last step  640 , the reference strip  10  may be mounted onto a print system  1 . 
     The measures discussed in this disclosure may prevent aerosol from affecting the detector  9 . The measures discussed in this disclosure may prevent that the reference strip  10  may be deformed during usage and/or during replacement and/or inspection of parts of the print system  1 . Furthermore, the measures discussed in this disclosure may be manufactured relatively efficiently. 
     The above description is not intended to be exhaustive or to limit the invention to the embodiments disclosed. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The indefinite article “a” or “an” does not exclude a plurality, while a reference to a certain number of elements does not exclude the possibility of having more elements. A single unit may fulfil the functions of several items recited in the disclosure, and vice versa several items may fulfil the function of one unit. 
     In the following claims, the mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Multiple alternatives, equivalents, variations and combinations may be made without departing from the scope of the invention.