Abstract:
A cover for an alignment sensor that provides sensor output so as to align printer output from multiple print heads in an ink jet printer. The cover is preferably mounted for hinged movement between an open position and a closed position so that a sensing face of the alignment sensor is protected from ink mist during printing operations. A chassis of the printer may be provided with projections that engage with the cover when the carriage is moved to extreme rightward and leftward positions on the printer, so that the cover may be hinged to the open and closed position simply through movement of the printer carriage. Preferably, the cover is formed of an electrically conductive material with a tab that grounds the cover to a metallic portion of the printer chassis. Forming the cover from an electrically conductive material provides the additional benefit of protecting the alignment sensor from static discharge.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to ink jet printers having multiple print heads, and more particularly to a cover for an alignment sensor that facilitates alignment of one of the multiple heads to others of the multiple heads. 
     2. Description of the Related Art 
     Ink jet printers have become an extremely popular format for achieving high quality computer printout at low cost. Ink jet printers form a printed image by ejecting small ink droplets from a print head in predetermined patterns onto a recording medium. The print head is mounted on a moveable carriage which provides right and left reciprocal movement at high scanning speeds across the width of the recording medium, while the recording medium is slowly fed in the lengthwise direction. 
     Recently-introduced ink jet printers have multiple print heads, such as two or more print heads mounted on the reciprocating carriage. The print heads may be identical to each other, such as a dual black or dual color print heads which increase black and white or color printout speeds by up to a factor of two. Alternatively, the print heads may differ from each other, such as a black print head paired with a color print head which provides good color reproduction without sacrificing print speed for black and white documents. As a further example, some ink jet printers are equipped with one full color print head paired with a photographic-density color print head, so as to achieve high quality photographic-like printout. 
     One complication introduced by providing ink jet printers with multiple print heads is the need to align printout for one of the multiple print heads to all others of the multiple print heads. Without alignment, mechanical manufacturing tolerances would cause printout from one print head to be mismatched relative to printout from others of the print heads. 
     Some existing multiple head ink jet printers utilize a manual alignment technique in which predetermined patterns are printed and the computer user is asked to respond to questions concerning quality and appearance of the printout. Such techniques are not generally satisfactory, in that they cause needless user confusion, result in inconsistent alignment accuracy, and inevitably complicate the printer. 
     The assignee of the present application has recently described a technique for automatic alignment of multiple print heads in an ink jet printer, in which an alignment sensor is mounted on the carriage together with the multiple print heads. According to this technique, automatic alignment is achieved through printout of predetermined patterns, automatic sensing of printout results, and calculation of alignment parameters. See U.S. application Ser. No. 08/901,560, “Auto-Alignment System For A Printing Device”, the contents of which are incorporated herein by reference as if set forth in full. 
     One problem encountered in auto alignment techniques results from a back spray, or ink mist, that forms during the print process. Specifically, because the alignment sensor must be mounted in close proximity to the ink jet print heads, any ink mist that forms during the printing process tends to settle on the alignment sensor&#39;s face, obscuring light transmissivity and prevent accurate alignment. 
     SUMMARY OF THE INVENTION 
     It is an object the invention to address the foregoing difficulty by providing a cover for an alignment sensor that is mounted on the printer carriage. 
     In one aspect, a cover for an alignment sensor is mounted in hinged relation to a printer carriage that carries multiple print heads. The cover is hingedly moveable from an open position during auto alignment sensing operations, to a closed position during standard printing operations. Hinged movement of the cover is preferably obtained through movement of the printer carriage, so that the cover is hinged to the open position by movement of the carriage to one extreme edge of carriage reciprocation, and is hinged to the closed position by movement to the opposite extreme edge. Means are preferably provided on the cover, with complementary means provided on the carriage, to retain the cover in the open or closed position. 
     By virtue of the cover, ink mist formed during printing operations does not become deposited on the light receiving face of the alignment sensor. Accordingly, accurate alignment sensing is insured, without diminished operation over the life of the printer. In addition, the cover preferably is formed with an enclosing skirt, which during alignment sensing operation acts as a shield to shield the alignment sensor from any ambient light. The light shielding operation of the cover&#39;s skirt increases accuracy of alignment results. 
     In further aspects of the invention, the cover provides static charge protection for the alignment sensor by forming the cover from an electroconductive material such as carbon-impregnated plastic. A grounding flap projects from an edge of the cover, with the grounding flap being in close but non-contacting proximity to a metallic element of the printer chassis. Preferably, the projecting flap projects from the rear of the cover so that it is adjacent a metallic carriage support rod upon which the carriage reciprocates from right to left to effect printout. 
     Because the cover is formed from electrically conductive material, the possibility of static damage to the alignment sensor is lessened, since any static charge will be dissipated to surrounding regions rather than damaging the alignment sensor. Moreover, because the projecting flap is in non-contacting close adjacency to the chassis, static charge can be dissipated to the chassis without impeding mechanical movement of the carriage. 
     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of preferred embodiments thereof in connection with the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a printer according to the invention. 
     FIG. 2 is a rear perspective view of a printer according to the invention. 
     FIG. 3 is a cutaway front perspective view of a printer according to the invention, showing a cover for an alignment sensor in a closed position. 
     FIGS. 4 and 5 are front and rear closeup views, respectively, of the cover mounted on a printer carriage. 
     FIGS. 6 and 7 are end perspective views of the cover shown in the closed and the open position, respectively. 
     FIG. 8 is a flow diagram explaining opening and closing operation of the cover. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 are perspective front and back views, respectively, of printer  30  incorporating an alignment cover according to the invention, and FIG. 3 is a cutaway perspective view thereof. With the exception of the alignment cover and related materials and processes, printer  30  is similar to that described in application Ser. No. 08/972,139, “Ejection Tray For A Printer”, the contents of which are incorporated herein by reference as if set forth in full. 
     As shown in FIGS. 1 and 2, printer  30  includes housing  31 , cover  32 , automatic feeder  34 , automatic feed width adjuster  36 , manual feeder  37  to accept wide-format or thick recording media, manual feed width adjuster  39 , media eject port  40 , ejection tray  41 , tray receptacle  42 , indicator light  43 , power button  44 , resume (on/off line) button  46 , power supply  47 , power cord  49  and parallel port connector  50  for connection of printer  30  to a host computer via a bi-directional communication interface. 
     Cover  32  is manually openable by a user so as to permit the user to access the interior of printer  30  such as when it is desired to service or replace print heads within printer  30 . Preferably, printer  30  senses when cover  32  has been opened, and in response moves the carriage carrying the print heads to a central position of the printer so as to facilitate access to the print heads. It is during such access and servicing operations that the print head is prone to static discharge damage. 
     Automatic feeder  34  defines a media feed position of printer  30  for up to standard-width print media. Automatic feeder  34  accommodates a stack of recording media and feeds individual sheets from the stack through printer  30  for printing on the medium during reciprocal left and right movement of the print carriage. 
     Manual feeder  37 , which also can feed individual sheets of standard width and weight print media, is provided to accommodate wide-width media or thick non-standard media, such as transparencies, fabric, card stock and the like. 
     Referring specifically to FIG. 3, which shows a perspective cutaway front view of printer  30 , printer  30  includes rollers  60  for feeding media from either automatic feeder  34  or manual feeder  37  through printer  30  to media ejection port  40 . Removable dual print heads  300   a  and  300   b  are mounted on carriage  64  at each of stations  64   a  and  64   b . Carriage  64  is mounted for reciprocal left and right movement on carriage guide rod  69 , and carriage  64  is reciprocally driven across guide rod  69  by belt  67  and an unshown carriage drive motor. Carriage  64  can be driven from an extreme leftward position generally indicated at  86 , which is outside of a carriage reciprocation area during normal (standard or wide width) print operations, to an extreme rightward position indicated generally by  87 , which is also outside of carriage reciprocation operation during normal printing. Position  87  is also referred to as the “home” position, and includes a pair of ink ejection stations  84   a  and  84   b , a pair of wiping blades  83   a  and  83   b  for wiping the face of the print heads to remove ink residue, and a pair of ink capping stations  88   a  and  88   b , each for respective ones of print heads  300   a  and  300   b.    
     Hingedly mounted on carriage  64  is alignment sensor cover  75 . In FIG. 3, cover  75  is shown in the closed position in which it protects an auto alignment sensor  82  (which is shown in FIG. 4) from ink mist and static discharge. Cover  75  is mounted by hinges  76  to carriage  64 , and includes a finger  77  that terminates in a button  78  (which is shown in FIG.  5 ). The button cooperates with complementary structure, such as a detent or a rib, on the rear of carriage  64 , so as to retain the cover in the open or closed positions, as appropriate. 
     Hinges  76  permit cover  75  to be hinged between an open position or a closed position. To hinge the cover to the open position, upstanding tab  70  is provided at area  86 . When carriage  64  is moved to extreme area  86 , tab  70  engages with a lower surface of cover  75  so as to hinge the cover outwardly to the open position. Thereafter, to hinge the cover inwardly to a closed position, carriage  64  is moved to area  87  where a corner  71  of the printer chassis hinges the cover back to a closed position. 
     FIG. 4 is a closeup front view showing cover  75  hinged in an open position relative to carriage  64 . In the open position, alignment sensor  82  is able to sense predetermined printing patterns on a recording medium so as to perform automatic alignment of print heads  300   a  and  300   b , as described in the aforementioned Ser. No. 08/901,560. Preferably, a small light source such as an LED operating in the visible light region is provided adjacent alignment sensor  82 , so as to illuminate the predetermined alignment pattern printed on the recording medium, thereby to facilitate the alignment process. Alignment sensor  82  includes a sensing face that is mounted in the downward direction so that the alignment sensor can sense the predetermined printed alignment pattern printed by the multiple print heads. Cover  75  includes a lower lid  83   a  (shown in FIG. 7) that in the closed position of the cover protects the sensor face, and that in the open position is moved away from the sensor face so that alignment sensor  82  can perform a sensing operation. 
     FIG. 5 is a rearward closeup view of cover  75  shown in solid lines in a closed position and in dotted lines in an open position. As mentioned in connection with FIG. 3, finger  77  terminates in button  78 , which cooperates with rib  79  projecting outwardly from the rear of carriage  64 . Finger  77  is preferably somewhat flexible, so as to allow button  78  to flex outwardly and inwardly over rib  79  as cover  75  hinges between the open and closed position. Cooperation between button  78  and rib  79  retains the cover in the open or closed position until hinging action is forcibly performed through movement of carriage  64  to extreme positions  86  or  87 . 
     Preferably, cover  75  is formed of an electrically conductive material such as carbon-impregnated plastic, so as to dissipate a static charge and to protect alignment sensor  82  from static damage. FIGS. 6 and 7 show this arrangement, and further show a projecting tab that cooperates to ground any static charge to the chassis of printer  30 . 
     Specifically, FIGS. 6 and 7 are end views of cover  75  in the closed and opened position, respectively. As shown in the closed position of FIG. 6, cover  75  includes projecting tab  80  which projects in non-contacting adjacency to carriage guide rod  69 . Carriage guide rod  69  is metallic, and provides a ground path to the printer chassis. A gap  81  exists between tab  80  and guide rod  69 . The size of gap  81  is selected to be small relative to the distance across which a static spark can jump, and preferably is on the order of 1 (one) mm. When gap  81  is so sized, it is smaller than the gap between an operator&#39;s finger and cover  75  when a potentially damaging static charge jumps from the finger to the cover (or jumps from the operator&#39;s finger to whatever structure of printer  30  that the finger is approaching). With a small gap  81 , the static charge can jump across gap  81 , thereby grounding the static charge and avoiding damage to alignment sensor  82  or to its leads. 
     In FIG. 7, cover  75  is shown in the open position. Because of hinging action around hinge  76 , tab  80  is somewhat closer to carriage guide rod  69 . However, gap  81  is sized sufficiently large so that even in the open position a gap  81   a  is maintained between tab  80  and guide rod  69 , so that tab  80  is in non-contacting close adjacency to guide rod  69 . 
     As further shown in FIG. 7, cover  75  includes a skirt  83  which completely surrounds sensor  82  even when the cover is hinged to the open position. Skirt  83  shields sensor  82  from ambient light conditions, thereby facilitating a more accurate sensing operation, and improving alignment results. 
     FIG. 8 is a flow diagram used for explaining operation of openings and closings for cover  75 . Generally speaking, the process steps shown in FIG. 8 illustrate operation by which cover  75  is hinged between open and closed positions in response to reciprocal movement of printer carriage  64  to extreme positions  86  and  87 . In particular, cover  75  is hinged to its open position at the first opportunity following receipt by printer  30  of a command to obtain alignment sensor data, even though potentially contaminating printout is still underway. Such printout may include printout of a predetermined alignment pattern; and in this case, hinging to an open position at the first opportunity following receipt of a command to obtain alignment data speeds overall operation, since there is no need to wait for the cover to be opened following completion of printout of the alignment pattern. 
     In addition, the process steps shown in FIG. 8 generally depict process steps by which the cover is deliberately closed in anticipation of other printer maintenance operations that potentially could damage the auto alignment sensor  82 . In the situation described here, one potentially damaging operation is a wiping operation by wiping blades  83   a  and  83   b . Wiping operations can occur at predetermined intervals that are independent of other operations of printer  30 , and therefore might occur at a time when cover  75  is open. If cover  75  were open during a wiping operation, then wiping blades  83   a  and  83   b  might brush the surface of alignment sensor  82  or might otherwise cause significant quantities of ink to be deposited on the face of sensor  82 . Consequently, cover  75  is deliberately closed in anticipation of a wiping operation, as well as in anticipation of any other operation such as ink pre-firing so as to clear nozzles that have the potential to damage sensor  82 . 
     Generally speaking, and as described in the aforementioned application Ser. No. 08/972,139, printer  30  prints data such as predetermined alignment patterns and obtains alignment sensor information in response to commands from an unshown host computer. A [DATA] command includes print data that is stored by printer  30  in anticipation of printout. A [PRINT] command signifies that printer  30  should commence printout operations of the stored print data. A [STATUS REQUEST] command signifies that printer  30  should obtain alignment sensor data and transmit the sensor data to the host computer, so that the host computer can process the alignment data into alignment calibration parameters. 
     Thus, reverting to step S 801  of FIG. 8, it is assumed that a [DATA] command has issued from the host computer, and that printer  30  continues to receive print data. In response to a [PRINT] command, step S 802  advances flow to step S 804  in which printer  30  commences printout of the received print data. It should be noted that printer  30  can continue to receive print data even after receipt of a print command. 
     Step S 805  tests whether a [STATUS REQUEST] command has issued. Until a [STATUS REQUEST] command has issued, printer  30  simply continues printout (step S 806 ). 
     In response to receipt of a [STATUS REQUEST] command, flow advances to step S 807 , in which printer  30  determines whether cover  75  is open or closed. Such a determination can be made by reference to an internally-maintained flag that stores the current state of the cover. If the cover is not open, then flow branches to step S 809  in which printer  30  opens cover  75  at the next opportunity for doing so. Preferably, the next opportunity for doing so would include a situation in which carriage  64  is already close to an extreme leftward position of the print mediums, so that opening of cover  75  can be accomplished by simply extending movement of carriage  64  to the extreme position  86 , for engagement of tab  70  with cover  75 . In this situation, opening of cover  75  can be accomplished quickly and efficiently. In any event, flow proceeds with step S 810  in which printer  30  continues printout of print data. During any printout printout in which cover  75  is open, however, if printer  30  undertakes an operation that is potentially damaging to alignment sensor  82 , then step S 811  and steps S 13  through S 815  operate to deliberately close cover  75  in anticipation of the operation, and re-open the cover when the operation has been completed. In the example given here, the potentially damaging operation is a wiping operation of the print heads by wiping blades  83   a  and  83   b.    
     Thus, if in step S 811  the printer  30  is undertaking a wiping operation, then flow branches to step S 813  in which printer  30  deliberately closes cover  75 . Closing of cover  75  is accomplished by moving carriage  64  to the extreme position  86 , so that cover  75  engages with plate  71 . Thereafter, following deliberate closure of cover  75 , the wiping operation is accomplished in step S 814 . Following completion of the wiping operation, cover  75  is re-opened in step S 815  by moving carriage  64  to extreme position  86  so that tab  70  can engage cover  75 . 
     Flow advances to step S 816  which returns flow to step S 807  until printout is finished. When printout is finished, flow advances to step S 817  in which printer  30  performs a sensing operation by moving carriage  64  with cover  75  in its open position, past the printed alignment pattern. Step S 819  returns the alignment sensor results to the host computer, and step S 820  closes the cover. 
     The invention has been described with respect to particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention.