Abstract:
A locking device having a connection element ( 11 ) that is securely connected to the hook base ( 1 ) but can rotate is provided. On the connection element ( 11 ), a coil spring ( 17 ) is supported that is compressed after setting the bobbin case ( 5 ) on or in the hook base ( 1 ). Through a slight tilting movement, the bobbin case ( 5 ) or the bobbin ( 7 ) could be pushed and guided over the connection element ( 11 ) and then held by the force of the spring ( 17 ) in the locking position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Swiss Patent Application No. 00250/09, filed Feb. 17, 2009, which is incorporated herein by reference as if fully set forth. 
       BACKGROUND 
       [0002]    The invention is directed to a locking device for a bobbin case for a bottom thread bobbin. 
         [0003]    The bottom thread bobbin of sewing machines, especially household sewing machines, can be stored either directly in the hook base, wherein it is thus directly accessible, or it can also be inserted in a bobbin case that is designed specifically for this purpose and that is stored, for its part, in the hook base. The present invention relates to a bottom thread bobbin supported indirectly in a bobbin case in the hook base. The invention could also be applied to a bobbin that can be inserted directly in the hook base. From DE-A1 3819405 a bobbin case for rotary shuttles is known in which the bobbin is pushed on a cylindrical bobbin spindle that is part of the bobbin case and that is held by a securing lever. The securing lever that is constructed as a two-arm lever is held in two positions (open position and work position) by a spring-loaded plate. The locking system is released by the manual pivoting of the lever by 90° into an axis-parallel position. Then the bobbin can be lifted out from the hook base. In order to simplify the lifting of the bobbin from the hook base, in DE-A1 19510830 it is proposed to insert a coil spring between the bottom side of the bobbin, i.e., the bobbin flange at the bottom, and the hook base. After release of the bobbin by the lever, this spring presses the bobbin partially out of the hook base. At the same time, during sewing the spring exerts a braking moment on the bobbin, wherein this moment has a different magnitude according to the construction of the bobbin surface and cannot be influenced. This could impair the sewing process. 
         [0004]    From GB-A 2149433, a bobbin holder is known in which the bobbin is held by a spring-loaded holder spindle that can be guided through the bobbin. The holder spindle could be brought out from the holder in the removal position through a quarter rotation and releases completely from the hook base together with the bobbin. Consequently, when a full bobbin is inserted, the holder spindle must be inserted into this bobbin and then secured. From EP-B1 1541736 a locking device for a bottom thread bobbin is known in which, on the hook base, a locking device that can be guided through the central opening in the bobbin is held on a spring and the bobbin is automatically locked after pressing the bobbin down completely into the hook base. Through a radial shifting of the locking element relative to the rotational axis of the bobbin, the bobbin can be detached again from the locking device. It is then ejected by the spring carrying the locking element. 
       SUMMARY 
       [0005]    The present invention provides a locking device for a bobbin case for a bottom thread bobbin with which the bobbin case can be locked in the hook base and can be released without activating a catch means, which produces, in addition, an axial pushing of the bobbin or the bobbin case from the hook base after the release. Advantageous constructions of the invention are described in more detail below and in claims. 
         [0006]    Through slight eccentric pressure on the bobbin case or the bobbin, the holding position that holds the bobbin captured in the hook base can be released and simultaneously the partial ejection of the bobbin case or, if a bobbin is held without a bobbin case in the hook base, the ejection of the bobbin is initiated. The locking of a new bobbin case or a bobbin to be inserted in the hook base is realized through axial pushing of the bobbin or bobbin case into the hook base until this reaches the recess in the hook base and tilts over. Then no additional locking manipulations are needed. The bobbin held by the locking element is not braked in any way by the locking element, because this locking element does not contact the bobbin with a positive fit. 
         [0007]    The locking device according to the invention consequently manages without a bolt, slide, or flaps. The coil spring located in the bobbin or bobbin case represents the sole moving element, wherein this spring secures the locking position after the locking and causes the ejection of the bobbin or bobbin case during the unlocking. 
         [0008]    In contrast to known locking devices, according to the invention, no bobbin case hinge is needed and consequently there are no parts over the case or bobbin that could prevent a trouble-free passage of thread. By eliminating mechanical parts, such as hinges, there is more space on the bobbin case or bobbin and a bobbin with a larger quantity of thread can be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be explained in more detail with reference to an illustrated embodiment. Shown are: 
           [0010]      FIG. 1  is an axial section through a hook base with a bobbin case together with a bobbin inserted there lying above this carrier, 
           [0011]      FIG. 2  is an axial section through the hook base with an inserted bobbin case directly before the locking of the bobbin case (bobbin case still slightly inclined), 
           [0012]      FIG. 3  is an axial section through the hook base with locked bobbin case, 
           [0013]      FIG. 4  is an axial section through the hook base with bobbin case released again from the locking device, before ejection of the bobbin, 
           [0014]      FIG. 5  is an axial section through a bobbin with inserted sleeve, 
           [0015]      FIG. 6  is a horizontal section through the hook base and the bobbin case, 
           [0016]      FIG. 7  is a perspective view of the bobbin in  FIG. 5 , and 
           [0017]      FIG. 8  is an axial section through another embodiment of the connection element that is molded directly on the hook base. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    With the reference symbol  1 , a hook base of a hook assembly  3  is designated. In  FIG. 1 , a bobbin case  5  with a bobbin  7  inserted therein lies above the hook base  1 . The bobbin case  5  with the bobbin  7  is thus not yet inserted into the hook base  1 . This is a state after the replacement/filling of the bottom thread bobbin  7 . In the hook base  1 , a connection element  11  is placed on a spindle  9  constructed centrally. This element is connected rigidly to the spindle  9  but can rotate axially and can be made from plastic or metal. The periphery of the connection element  11  can have a cylindrical construction (no illustration) or, as shown in the figures, it can have a shoulder-shaped neck section in the upper region. The bobbin case  5  comprises, in the center, a borehole  13  that has a cylindrical profile in the upper part a and that has a cylindrical construction in the lower part b over a partial region of the periphery of the borehole  13 , e.g., over 180°, and the opposite region is formed by a cylindrical section whose axis lies at an angle to the axis of the other region (cf.  FIGS. 1-4 , in each, left side of the borehole  13 ). In the end region of the bobbin case  5 , the borehole  13  can have a closed construction or its cross section can have a smaller diameter than the cylindrical section a of the borehole  13  lying underneath. 
         [0019]    On a circular shoulder  15  or a flat end face on the upper end of the connection element  11 , a coaxially arranged coil spring  17  is supported. The spring  17  is attached with its upper end on the bobbin case  5 , e.g., clamped or bonded. When the bobbin case  5  is placed on top, the upper end ring  19  of the coil spring  17  therefore contacts the bobbin case  5 . Advantageously, the end ring  19  is larger in diameter than the rest of the windings. The coil spring  17  is dimensioned such that, in the case of a bobbin case  5  locked completely in the hook base  1 , the coil spring  17  is under compressive force and, when the bobbin case  5  is released, the coil spring  17  lifts or ejects the bobbin case  5  at least partially from the hook base  1 , in order to simplify the grasping of the bobbin case  5 . 
         [0020]    On the lower end of the connection element  11 , also called the case carrier, a circular groove  21  is countersunk. The axial height of the groove  21  is slightly greater than the axial height of a crescent-shaped flange section  23  directed inward and running over a partial region of the borehole  13  on the bobbin case  5 . The distance of the inner edge  25  of the flange section  23  relative to the opposite, non-parallel wall section b is slightly larger than the diameter of the connection element  11  (cf.  FIG. 6 ). 
         [0021]    Below, the functioning of the hook assembly  3  will be explained in greater detail. 
         [0022]    The bobbin case  5  equipped with a new bobbin  7 , i.e., a bobbin filled with thread, is pushed axially from the top over the connection element  11 . Here, the coil spring  17  comes into spring contact with the upper end of the connection element  11 . 
         [0023]    A marking  29  is formed eccentrically on the end face  27  of the bobbin case  5 . The marking  29  can be coloring or a region provided with grooves by means of, for example, a laser beam, or can consist of a recess. For engaging or locking the bobbin case  5 , the person sewing presses with one finger approximately in the center on the bobbin case  5  (arrow F 1 ); for further pressing, the bobbin case  5  becomes slightly tilted by the flange  23  provided only over a partial region (ca. 180°) on the lower end of the borehole  13 , as is visible in  FIG. 2 . Through this inclined position, it becomes possible that the crescent-shaped flange  23  on only part of the periphery can slide past the lateral surface of the connection element  11  and can then engage in the groove  21 , when the bobbin case  5  tilts back to the horizontal. 
         [0024]    For releasing the bobbin case  5  from the hook base  1 , the procedure is reversed, in that, a pressure according to arrow F 2  is exerted with a finger on the eccentrically formed marking  29  and thus the bobbin case  5  tilts and the edge  25  of the flange  23  moves out from the groove  21  and then the bobbin case  5  is lifted by the force of the coil spring  17  until it can be raised with two fingers from the hook base  1 . 
         [0025]    In  FIG. 5 , a bobbin  7  is shown in the axial section that is not supported in a bobbin case  5 . So that it can rotate within the hook base  1  during sewing, a sleeve  31  is inserted so that it can rotate in the center of the bobbin  7 . The sleeve  31  comprises, both at the top and also at the bottom, means, e.g., a raised edge or flange  33 , wherein these means hold the sleeve  31  in the bobbin  7  axially with play. The borehole  13  in the sleeve  31  is constructed analogous to the borehole  13  in the bobbin case  5  in the examples 1 to 4. In other words, the upper region a is cylindrical and approximately half of the lower region b has a profile of a cylinder-barrel surface inclined toward the axis of the bobbin case  5  (cf. also  FIG. 2 ). The upper end of the sleeve  31  is closed and is used as a contact for the coil spring  17  not shown in  FIG. 5 . 
         [0026]    In the ring-shaped flange of the sleeve  31  lying at the top, a marking  29  is formed eccentrically, as in the first embodiment, in order to indicate to the operator at which point he must apply a pressing force F 2  for unlocking. 
         [0027]    In another construction of the invention shown in  FIG. 8 , the connection element  11  is part of the spindle  9 , i.e., the periphery of the spindle  9  has the shape of the periphery of the connection element  11  in the first embodiment. The function of the insertion or ejection of the bobbin case  5  with the bobbin  7  takes place in the same way. 
       LEGEND 
       [0000]    
       
         
           
               1  Hook base 
               3  Shuttle arrangement 
               5  Bobbin case 
               7  Bobbin 
               9  Spindle 
               11  Connection element 
               13  Borehole 
               15  Shoulder 
               17  Coil spring 
               19  End ring 
               21  Groove 
               23  Flange 
               25  Edge 
               27  End face 
               29  Marking 
               31  Sleeve 
               33  Raised edge or flange