Abstract:
A printer comprising a carriage, a guide rail and a print surface, the carriage being movable along the guide rail and carrying a printhead that faces the print surface and is movable in a direction normal to the plane of the print surface, wherein a stop or brake mechanism responsive to a movement of the printhead in said direction normal to the plane of the print surface is provided and adapted to stop the movement of the carriage.

Description:
[0001]     This application claims the priority benefit of European Patent Application No. 05110956.9 filed Nov. 18, 2005 which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a printer comprising a carriage, a guide rail and a print surface, the carriage being movable along the guide rail and carrying a printhead that faces the print surface and is movable in a direction normal to the plane of the print surface.  
         [0003]     In a printer of this type, e.g., an ink jet printer, a sheet of paper or any other recording medium is advanced in a subscanning direction over the print surface. The printhead is arranged on the carriage in such a position that it faces the print surface, and a nozzle face of the printhead forms a narrow gap with the paper on the print surface. A drive mechanism causes the carriage to move back and forth in a main scanning direction along the guide rail, the position of the carriage in the main scanning direction being detected by means of a ruler or the like, and, on the basis of the detection result, the nozzles of the printhead are fired at appropriate timings, so that ink dots are printed in the intended positions on the paper. To this end, the position of the printhead on the carriage must be adjusted with high precision.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present invention to provide a printer in which the printhead is protected against damage or misadjustment that may result from a paper jam on the print surface.  
         [0005]     In order to achieve this object, the printer according to the present invention comprises a stop mechanism responsive to the movement of the printhead in said direction normal to the plane of the print surface and adapted to stop the movement of the carriage.  
         [0006]     When a paper jam occurs on the print surface, and the paper accumulates in the narrow gap between the print surface and the nozzle face of the printhead, which will impede or block the movement of the printhead in the main scanning direction, damage is likely to occur, if the drive mechanism continues to drive the carriage along the guide rail. However, the paper jam will also cause a slight upward movement of the printhead away from the print surface, typically 1-3 millimeters, and, according to the present invention, this movement will trigger the stop mechanism, so that damage is avoided by forcibly bringing the carriage to a stop. This can be at any position along the guide rail.  
         [0007]     In a preferred embodiment, the printhead is rigidly mounted to the carriage, and the upward movement of the printhead relative to the print surface is made possible by a tilting movement of the carriage, including the printhead, about a fulcrum on the guide rail. Then, the stop mechanism will also have the effect to protect the carriage against running out of the guidance.  
         [0008]     The guide rail and the carriage may be designed so as to provide an end stop which limits the tilting movement of the carriage and hence the lift movement of the printhead to a relatively small amount.  
         [0009]     In one embodiment, the co-operating end stops on the guide rail and on the carriage are configured as brake surfaces that will be brought into engagement with one another when the paper jam causes the lift movement of the printhead. Thus, the stop mechanism is embodied as a brake mechanism, and the force that is created by the paper and tends to lift the printhead away from the print surface is directly used as a brake actuating force for the brake mechanism.  
         [0010]     In another embodiment, one of the end stops, preferably the one on the carriage, is configured as a switch or contact sensor which issues an electronic signal to stop the drive mechanism as soon as the printhead has been lifted to such an extent that the sensor or switch is actuated.  
         [0011]     In other embodiments, the printhead may be mounted to be movable relative to the carriage in a direction normal to the plane of the print surface, and the brake and the sensor or switch, respectively, may be actuated by the relative movement between the printhead and the carriage. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Preferred embodiments of the invention will now be described in conjunction with the drawings wherein  
         [0013]      FIG. 1  is a front view of a printer according to the invention;  
         [0014]      FIG. 2  is a cross-section along the line II-II in  FIG. 1 , and  
         [0015]      FIGS. 3 and 4  are enlarged views of a carriage and a guide rail of the printer and show different embodiments of a stop mechanism. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     The printer shown in  FIG. 1  comprises a frame  10  having a lower support structure  12  formed by two uprights  14 , two cross-bars  16 , and two mounting plates  18  rising up from the cross-bars  16 . A plate-like function block  20  is attached to each of the mounting plates  18  and extends in parallel therewith. Two bearings  22  rotatably support a feed roller  24  between the two mounting plates  18 .  
         [0017]     A sheet support plate  26  is horizontally supported on the two function blocks  20  and forms a print surface  26 ′ which serves to support a sheet S of a recording medium which is advanced in an X-direction (normal to the plane of the drawing in  FIG. 1 ) by means of the feed roller  24 . A drive mechanism for the feed roller  24  has not been shown here for simplicity.  
         [0018]     A guide rail  28  rests on the top ends of the function blocks  20  and extends in parallel with the axial direction Y of the feed roller  24 . A carriage  30  is guided on the guide rail  28  and is driven to move back and forth along the guide rail by means a drive mechanism formed by a belt  32 , for example. The carriage  30  has a portion extending over the sheet support plate  26 , and a printhead  34  is mounted on the bottom side of this carriage portion so as to face the sheet S that is advanced over the print surface  26 ′. The printhead  34  may be, for example, a hot melt ink jet printhead.  
         [0019]     A detection and control system, which may have a conventional design and has not been shown here, detects the Y-position of the carriage  30  and determines the timings at which the print units or nozzles of the printhead  34  are energized while the carriage moves across the recording medium.  
         [0020]     As is shown in  FIG. 2 , the guide rail  28  is formed by a profile member which supports two cylindrical rods  36 ,  38  on which the carriage  30  is supported and guided with roller bearings. The guide rail  28  rests on V-shaped top surfaces of the function blocks  20  and is thereby accurately positioned in the X-direction, i.e., the direction, in which the recording medium advances, and in the vertical Z-direction normal to the print surface  26 ′.  
         [0021]     When the printhead  34  is subject to an upwardly directed force, it may be lifted away from the print surface  26 ′ in the direction Z, because the carriage  30 , to which the printhead is rigidly connected, is capable of tilting about the cylindrical rod  36 . This tilting movement, however, is limited by an end stop  40  that projects from the carriage  30  and forms a little clearance with the bottom side of a flange  42  of the guide rail  28 .  
         [0022]     As is shown in  FIG. 1 , the belt  32  is trained around a pulley  44  that is driven by a motor  46 . When the printer is operating, the motor  46  is speed-controlled, so that the carriage  30  is moved along the guide rail  28  with uniform velocity. Print signals are transmitted to nozzle actuators of the printhead  34  through a flexible cable  48 .  
         [0023]     The feed roller  24  and the sheet support plate  26  are capable of handling sheets S or webs of paper of varying width, corresponding to sheet sizes from A4-A0, for example. In  FIG. 1 , a sheet S of relatively small size is advanced over the print surface  26 ′, and, as has been shown exaggeratedly in the drawing, the edges of the sheet S are curled upwardly, so that they will be hit by the printhead  34  when the carriage  30  moves along the guide rail. In the case of such an event, the sheet S will crumple in the gap between the nozzle face of the printhead and the print surface, so that a severe paper jam may occur, which involves the risk that the printhead  34  or parts of the mounting structure thereof are damaged or distorted. This risk is not eliminated by the fact that the printhead  34  is capable of being lifted away from the print surface  26 ′ within certain limits, as has been described above, because, as long as the carriage  30  moves on, the paper will tend to accumulate further in the gap between the print surface and the printhead.  
         [0024]     In order to avoid this risk, the end stop  40  and the flange  42  are configured to provide a stop mechanism for the carriage  30 , as has been shown in  FIG. 3 . This figure illustrates a situation where the sheet S has jammed between the print surface  26 ′ and the nozzle face on the bottom side of the printhead  34 , so that the carriage  30  has been tilted about the central axis of the cylindrical rod  36 . The end stop  40  on the carriage  30  and the flange  42  of the guide rail  28  are formed with brake surfaces  50  and  52 , respectively, which provide a relatively high friction coefficient and are so inclined that they are brought into mating engagement with one another by the tilting movement of the carriage  30 . Thus, as soon as the paper jam causes the brake surfaces  50  and  52  to be pressed against one another, the movement of the carriage  30  along the guide rail  28  will be braked. The motor  46  may continue to rotate, but a slip coupling  54  between the output shaft of the motor and the pulley  44  prevents the belt  32  from being moved further and from overcoming the braking force of the brake surfaces  50 ,  52 . Thus, the brake surfaces  50 ,  52  form a simple and yet efficient and sensitive stop mechanism which will bring the carriage  30  to a stop before the paper jam becomes worse and causes damage to the printhead  34 . As an alternative for the slip-type coupling, the motor  26  can be provided with an overload switch that stops the motor when the resistance caused by the brake surfaces becomes larger.  
         [0025]     When the paper jam has been removed, the carriage  30  will tilt back into its original position in which it is supported on the rod  38 , and the print process may be resumed.  
         [0026]      FIG. 4  illustrates a modified embodiment, wherein the brake mechanism is formed by a sensor  56  or a switch that is mounted on the end stop  40  in such a position that is faces the bottom side of the flange  42  and delivers an electronic signal as soon as the sensor  56  contacts the flange  42 . This signal is transmitted to the drive circuit for the motor  46  via the cable  48  and causes the motor  46  to stop. The motor  46  may be a step-motor or, more generally, a motor that is capable of creating a high braking force, so that the carriage  30  will be stopped instantaneously as soon as a paper jam occurs.  
         [0027]     It will be understood that the two types of stop mechanism described above may also be combined with one another.  
         [0028]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.