Abstract:
A mounting structure for a printhead having a contact surface and a coupling member for connection to an ink supply line, the mounting structure including a casing which defines a bay for accommodating the printhead therein, and a biasing mechanism for biasing the printhead into engagement with the internal walls of the bay, the biasing mechanism containing a latch member mounted on the casing and movable relative thereto between an open position which permits the printhead to be inserted into the bay, and a latched position where it secures the printhead in the bay, and a contact member adapted to exert a force against the contact surface of the printhead in the latched position. A mating coupling member of an ink supply line is mounted on the latch member so as to be brought into engagement with the coupling member of the printhead when the latch member is moved into the latched position.

Description:
[0001]     This application claims the priority benefits of European Patent Application No. 05109848.1 filed on Oct. 21, 2005 which is hereby incorporated by reference.  
         [0002]     The present invention relates to a mounting structure for a printhead having a contact surface and a coupling member for connection to an ink supply line, the mounting structure comprising a casing which defines a bay for accommodating the printhead therein, and a biasing mechanism for biasing the printhead into engagement with the internal walls of the bay, the biasing mechanism comprising a latch member mounted on the casing and movable relative thereto between an open position where it permits insertion of the printhead into the bay, and a latched position where it secures the printhead in the bay, and a contact member adapted to exert a force against the contact surface of the printhead in the latched position. The present invention also relates to a combination of a printhead with such a mounting structure and to a carriage for an ink jet printer having such a mounting structure.  
         [0003]     U.S. Pat. No. B1-6,481,829 discloses a mounting structure of the type indicated above, which comprises a mating, coupling member which is brought into engagement with the coupling member of the printhead. The mating coupling member is mounted on a first lever, and the latch member is formed by a second lever which is adapted to lock the first lever in a position in which the coupling members are engaged.  
         [0004]     EP-A-1,389,530 discloses a mounting structure for an ink jet printhead, wherein coupling members that are mounted on the printhead and on the casing, respectively, for establishing an ink supply line, are automatically brought into engagement with one another when the printhead is inserted in the bay. In this mounting structure, the printhead is brought into its final position by a tilting movement within the bay, and this tilting movement brings the coupling members into engagement with one another.  
         [0005]     Another mounting structure for an ink jet printhead with an integrated ink cartridge is disclosed in U.S. Pat. No. 5,646,665. The printhead has a nozzle face formed on a projecting portion that projects through an opening formed in the walls of the bay so as to face the print medium. The printhead further has a contact surface engaged by an elastically biased contact member for establishing electrical contacts between a control circuit and actuators that are associated with the nozzles of the printhead. In this mounting structure, the biasing mechanism for the printhead comprises a low-friction cam on the free end of a spring that projects from a wall of the bay. When the printhead is inserted, the cam snaps-in at the ramp surface to secure the printhead in its final position within the bay.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of the present invention to provide a mounting structure which is easy to handle and ensures a reliable engagement and disengagement of the coupling member when the printhead is respectively inserted into and removed from the bay.  
         [0007]     According to the present invention, the mating coupling member of the ink supply line is mounted on the latch member so as to be brought into engagement with the coupling member of the printhead when the latch member is moved into the latched position.  
         [0008]     Thus, the movement of the latch is also used for bringing the coupling members of the ink supply line into engagement with one another. As a result, a single operation is sufficient for locking the printhead in position and connecting the coupling member thereof to the in supply line. Conversely, when the printhead is to be removed, the unlocking movement of the latch member will automatically disengage the coupling members before the printhead can be withdrawn from the bay. This has the particular advantage that inadvertent damage of the coupling members can be reliably prevented when a user removes the printhead from the bay.  
         [0009]     Preferably, to position and secure the printhead within the bay with improved accuracy and reliability, the biasing mechanism comprises a roller mounted on an axis that is elastically supported on the latch member to bias the roller against a ramp surface formed on the printhead, when the latch member is in the latched position. The ramp surface has a normal that extends in a plane spanned by two mutually orthogonal directions and is inclined relative to both of said directions. In this way, the printhead is simultaneously biased in the two mutually orthogonal directions against the walls of the bay.  
         [0010]     The use of a roller instead of a cam for engaging the ramp surface of the printhead reduces the frictional forces that have to be overcome when the printhead is brought into its final position, and thereby assures that the printhead will reach its intended position with improved reliability. Moreover, since the biasing mechanism comprises a movable latch member, the movement of this latch member may be utilized to optimise the direction in which the roller presses against the ramp surface, so that the printhead is brought into engagement with the support points in a well defined manner, and the frictional resistance occurring at the support points can safely be overcome.  
         [0011]     Preferably, the latch member is a lever that is pivotally supported at the casing and snaps-in at a catch of the casing when it reaches the latched position. In order to assure that the coupling members are brought into engagement in a linear movement, the coupling member on the side of the casing is preferably guided in a stationary guide and is suspended at the lever by means of a rig which transforms the pivotal movement of the lever into a linear movement of the coupling member along the guide.  
         [0012]     The axis of roller is preferably mounted at a first arm of a two-armed auxiliary lever that is pivotable about a fulcrum defined by the latch member. A spring for biasing the roller against the ramp surface is supported between a second arm of the auxiliary lever and the portion of the latch member. Preferably, the arrangement is such that when the latch member is brought into the latched position, the roller is pressed against the ramp surface in a direction that is approximately normal to the ramp surface. As a consequence, the force exerted onto the ramp surface by the roller has components that press the printhead against the support points in both of said mutually orthogonal directions.  
         [0013]     A contact member is arranged to be elastically biased against a contact surface of the printhead in one of said directions, so that the biasing force will reliably be overcome by one of the components of the force exerted by the roller.  
         [0014]     Preferably, a straight imaginary line that passes through the axis of the roller and through the fulcrum of the auxiliary lever extends approximately but not exactly normal to the ramp surface. Thus, when the latch member is brought into the latched position, a comparatively large component of the force that is transmitted through the auxiliary lever will firmly press the roller against the ramp surface, while a smaller component of that force will cause the roller to roll along the ramp surface and to pivot the auxiliary lever about its fulcrum against the force of the spring. Then, when the latch member is in the latched position, the spring will continue to bias the roller against the ramp surface, and the wedge action of the ramp surface assures that the printhead is pressed against the support points with an increased force. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     A preferred embodiment of the present invention will now be described in conjunction with the following drawings, wherein:  
         [0016]      FIG. 1  is a sectional view of a mounting structure for an ink jet printhead,  
         [0017]      FIG. 2  is a separate view of the printhead;  
         [0018]      FIG. 3  shows the mounting structure of  FIG. 1  during a process of insertion of the printhead;  
         [0019]      FIG. 4  is a top plan view of the mounting structure;  
         [0020]      FIGS. 5 and 6  are sectional views of coupling members in an uncoupled and coupled state, respectively;  
         [0021]      FIG. 7  is a sectional view of a suspension and guide mechanism for one of the coupling members shown in  FIG. 5 ;  
         [0022]      FIG. 8  is a sectional view taken along the line VIII-VIII of  FIG. 7 ; and  
         [0023]      FIGS. 9 and 10  are schematic views illustrating the position of the suspension and guide mechanism in different conditions. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     As is shown in  FIG. 1 , a casing  10 , which may form part of a carriage of an ink jet printer, defines a bay  12  which accommodates a printhead  14 .  
         [0025]     The printhead  14 , which has been shown separately in  FIG. 2 , has an essentially rectangular box-like shape with a projection  16  which projects downwardly through an opening in a bottom wall near the left corner of the bay  12  and defines a nozzle face  18 . On the top side, the printhead is provided with a handle  20  which permits gripping the printhead and inserting it into the bay  12 , a ramp surface  22 , and a coupling member  24  for connecting the printhead to an ink supply line. In the top left corner of  FIG. 2 , the printhead has a laterally and downwardly projecting nose  26 .  
         [0026]     The print elements of the printhead are formed by a number of nozzles that are formed in the nozzle face  18  and are not visible in the drawing. These nozzles must be positioned with very high accuracy relative to the casing  10 . To this end, the printhead  14  is supported in the bay  12  at three support points  28 ,  30  and  32  which define small, practically point-like, contact areas between the printhead and the walls of the bay  12 . The support point  28  is formed by a horizontal wall of the casing which is engaged by the nose  26  of the printhead. The support point  30  is formed by a small boss in a corner of the printhead diagonally opposite to the nose  26 . The boss may be formed either on the printhead or on the casing. The support points  28  and  30  define the position of the printhead in the vertical Y-direction (which, by definition, is the direction from the open side towards the bottom of the bay) and also the angular position of the printhead about a Z-axis normal to the plane of the drawing in  FIG. 1 . The third support point  32  is formed on an end face of the casing wall which defines also the support point  28 . The support point  32  defines the position of the printhead in the horizontal X-direction.  
         [0027]     Internally, the printhead  14  is provided with a number of actuators (not shown) that are associated with the individual nozzles. These actuators are controlled by a control circuit (not shown) that is provided outside of the printhead. Electrical connections between the control circuit and the actuators are provided by electrical contacts arranged in a contact face  34  of the printhead and by a contact member  36  that is elastically biased against the contact face  34 . The contact face  34  is formed in an end wall of the printhead below the contact points  28  and  32 . Thus, the biasing force of the contact member  36  tends to push the printhead away from the support point  32  in (negative) X-direction.  
         [0028]     A biasing mechanism  38  is provided to hold the printhead in firm engagement with all three support points  28 ,  30  and  32  against the force of the contact member  36 . The biasing mechanism comprises a latch member  40  that is pivotally connected to the casing  10  and is pivotable about an axis  42 . The axis  42  is arranged approximately at the height of the support points  28  and  32  on the side of the printhead opposite to these support points. The free end of the latch member  40  forms an elastic claw  44  which, in the condition shown in  FIG. 1 , secures the latch member in the latched position by snapping-in at a catch  46 .  
         [0029]     A two-armed auxiliary lever  48  is arranged inside of the latch member  40  and is pivotable about a fulcrum  50  that is defined by the latch member. A first arm of the auxiliary lever  48  supports a roller  52  which engages the ramp surface  22  of the printhead. A compression spring  54  is supported at the latch member  40  and tends to tilt the auxiliary lever  48  in clock-wise direction in  FIG. 1  about the fulcrum  50 , thereby urging the roller  52  against the ramp surface. Since the normal of the ramp surface  22  is inclined relative to the X-direction and also relative to the Y-direction in the plane (X, Y), the force which the roller  52  exerts onto the ramp surface  22  has two components which urge the printhead  14  in X-direction against the support point  32  and in Y-direction against the support points  28  and  30 .  
         [0030]      FIG. 3  shows the latch member  40  in an open position permitting the insertion of the printhead  14  into the bay  12 . The spring  54  urges the second arm of the auxiliary lever  48  against a stop  56 .  
         [0031]     A rear wall of the bay  12 , which is covered by the printhead  14  in  FIG. 3 , is provided with three additional support points  58  which are shown in phantom lines in  FIG. 3  and two of which are also visible in  FIG. 4 . These support points  58  define the position of the printhead  14  in the Z-direction or, more exactly, the plane in which the printhead is movable in the X- and Y-directions. A leaf spring  60  is arranged on the internal wall of the bay  12  opposite to the support points  58  and urges the printhead against these support points. Thus, when the printhead is inserted into the bay, the frictional forces caused by the leaf spring  60  and the support points  58  has to be overcome.  
         [0032]     In  FIG. 3 , the printhead is inserted into the bay, until the nose  26  engages the support point  28 . However, the contact member  36  pushes the printhead away from the support point  32  and has slightly tilted it, so that it does not contact the support point  30 , neither. When the latch member  40  is now pivoted counterclock-wise about the axis  42  towards the latched position shown in  FIG. 1 , the roller  52  will impinge on the ramp surface  22  and will push the printhead in both the X- and Y-directions.  
         [0033]     It should be noted that the ramp surface  22  is located at a higher level than the axis  42  and slopes toward that axis. Thus, the direction of arcuate movement of the roller  52 , when it hits the ramp surface  22 , is almost perpendicular to this ramp surface. More specificly, the angle between the path of the roller  52  and the ramp surface  22  is larger than 45° and preferably larger than 80°.  
         [0034]     Likewise, the angle formed between the ramp surface  22  and an imaginary straight line through the fulcrum  50  and the axis of the roller  52  is significantly larger than 45°. Thus, the force which the fulcrum  50  exerts upon the roller  52  via the auxiliary lever  48  has a major component in a direction perpendicular to the ramp surface  22  and only a small component in a direction parallel to the ramp surface. As a result, when the latch member  40  is finally locked in the latched position, the roller  52  exerts a relatively large force which reliably presses the printhead into engagement with all three support points  28 ,  30  and  32 .  
         [0035]     The relatively small force component which is directed in parallel with the ramp surface  22  and is thus not compensated by the reaction force of the ramp surface causes the roller  52  to roll along the ramp surface  22  with low friction, thereby tilting the auxiliary lever  48  about the fulcrum  50 , with the compression of the spring  54 . The force of the spring  54  will then safely hold the printhead in the intended position.  
         [0036]     As is indicated in  FIG. 4 , the casing  10  may form a plurality of compartments  62  each of which accommodates a printhead and is provided with a mounting structure identical to the one described above. These mounting structures assure that all the printheads are accurately positioned relative to the casing  10  and, as a consequence, relative to one another.  
         [0037]     When, in the condition shown in  FIG. 1 , the printhead  14  is to be removed, it is sufficient to press the claw  44  away from the catch  46  and then to tilt the latch member  40  into the open position shown in  FIG. 3 .  
         [0038]     As is shown in  FIGS. 1 and 3 , the coupling member  24  of the printhead can be connected with and deconnected from a mating coupling member  64  that is itself connectable to an ink supply line (not shown). The coupling member  64  is guided in a guide rail  66  that is snap-fastened on the axis  42  and is held stationary in the casing  10 , so that, when the printhead  14  is inserted, the coupling members  24  and  64  are aligned with one another.  
         [0039]      FIGS. 5 and 6  are longitudinal sections of the coupling members  24  and  64  in the uncoupled and the coupled state, respectively.  
         [0040]     The coupling member  24  has a body  68  which defines a passage  70  that communicates with the interior of the printhead  14 . In  FIG. 5 , the end of the passage  70  is closed by an annular seal member  72  made of a rubber-elastic material. The seal member  72  is locked in position by a cap  74 .  
         [0041]     The mating coupling member  64  has a cylindrical body  76  which defines a connector  78  for connection to a flexible ink supply tube (not shown). A piston  80  is slidingly guided in the body  76  and surrounds an annular sleeve  82 . A needle  84  passes through the sleeve  82  and extends into the connector  78  with its rear end. In  FIG. 5 a  spring  86  biases the piston  80  into an end position defined by keys (not shown) that are formed on the internal wall of the body  76  and engage into grooves of the piston  80 . The needle  84  has a closed front end and a lateral opening  88  which, in the end position of the piston  80 , is located inside of the sleeve  82 . The sleeve  82  is slidable on the needle  84  and defines two seal portions on both sides of the opening  88 , so that the sleeve forms a valve which closes the ink supply line.  
         [0042]     When the coupling members  24  and  64  are engaged with one another, as shown in  FIG. 6 , the cap  74  pushes the sleeve  82  and the piston  80  back into the cylindrical body  76  against the force of the spring  84 . As a result, the front end of the needle  84  penetrates the seal member  72 , so that its opening  88  communicates with the passage  70 , thereby connecting the printhead to the ink supply line. When the coupling member  64  is drawn away from the coupling member  24 , the condition shown in  FIG. 5  is automatically restored by the spring  86 .  
         [0043]     The latch member  40  is a U-shaped member with two parallel side walls  90 , parts of which are shown in cross-section in  FIG. 7 . An arcuate rig  92  is suspended in the latch member  40  with two coaxial pivot pins  94  which engage elongated holes  96  in the side walls  90 . The body of the coupling member  64  is suspended in the rig  92  by means of an axle  98  which is rotatably supported in the rig in a position offset from the pivot pins  94 . A guide plate  100  is formed integrally with the body of the coupling member  64  and is guided in the guide rail  66 .  FIG. 8  is a side elevation showing the detailed configuration of the rig  92 .  
         [0044]      FIGS. 9 and 10  schematically illustrate the movement of the coupling member  64  when the latch member  40  is moved between the open position ( FIG. 9 ) and the latched position ( FIG. 10 ). In  FIG. 9 , the movement of the pivot pins  94  in the elongated holes  96  permits opening the latch member  40  sufficiently wide so that the printhead  14  can be inserted, as shown in  FIG. 3 . When the latch member is rotated counterclock-wise, the pivot pins  92  move to the opposite ends of the elongated holes  96 , as is shown in  FIG. 10 . Then, during the continued pivotal movement of the latch member  40  about the axis  42 , the pivot pins  96  are pushed forward by the latch member, and a tilting movement of the rig  92  transforms the arcuate movement of the pivot pins  96  about the axis  42  into a linear movement of the coupling member  64  along the guide rail  66 , until the latch member  40  has reached its latched position and the coupling member  64  is coupled to the coupling member  24  of the printhead, as shown in  FIGS. 1 and 6 .  
         [0045]     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.