Abstract:
The invention relates to a mule ( 1, 201, 301, 401, 501 ) with at least one strap ( 3, 203, 303, 403, 503 ) detachably arranged on the mule. According to the invention, the strap ( 3, 203, 303, 403, 503 ) can be arranged on the main body optionally either by a form fit and/or force fit or by a force fit or by a form fit and is detachably connected. A fixation device ( 13, 213, 313,   413, 513 ) that cooperates at least indirectly with the free ends of the strap ( 3, 203, 303, 403, 503 ) is provided inside the main body ( 2, 2, 302, 402, 502 ) and means are provided that bring about a simultaneous detachment of the free ends of the strap ( 3, 203, 303,   403, 503 ).

Description:
BACKGROUND 
       [0001]    The invention relates to a mule with at least one strap for securing the foot on the mule. 
         [0002]    The word mule is to be understood as meaning a lady&#39;s shoe, a particularly fashionable shoe. The mule has a main body extending under the foot. This main body is generally made of plastic or wood. Similar materials are likewise provided. The main body thus comprises a seat for the foot, and a walking surface facing away from the foot. This walking surface serves as a sole and comes into contact with the ground on which the person wearing the mule is walking. The seat for the foot is adapted at least approximately to the contour of the foot, in such a way that the foot, including the toes, is received in its entirety by the planar design of the main body. The instep is covered only by a strap. The rest of the instep and also the heel are free. 
         [0003]    The walking surface of the main body is generally designed in three parts. The front part, directed toward the toes, is designed as a sole surface, and the part assigned to the heel area is designed as a heel surface. The area between the sole surface and the heel surface is designed in such a way that it does not touch the ground when the shoe is set down. 
         [0004]    The mule can be without a heel or can have a low or a high heel. 
         [0005]    As has already been stated above, the mule comprises at least one strap which extends, transversely with respect to the longitudinal extent, from one side of the main body of the mule to the other side of the main body of the mule. The mule can be decorated with ornamental elements. In particular the strap can be fashioned with beads, bows, leather bands or gems to give a simply stylish, plain or even grand appearance. 
         [0006]    Shaped like a strip or band extending across the instep of the foot, the strap holds the mule on the foot, so that no further holding device, for example a heel strap, is needed. The strap has a convex shape, such that it is able to bear, both longitudinally and also transversely, on the instep, which is likewise convex, and it thus provides a comfortable feel. 
         [0007]    The mule is distinguished especially by the comfort it provides. There are mules that are open at the toes and ones that are closed, while the heel is generally always free. The mule is preferably worn with summer clothing, short dresses or short trousers. 
         [0008]    Mules have been worn by women since the 15th century in Europe, mainly by housewives while doing housework. The end of the 20th century saw a fashion trend in which a large number of different forms of mules were developed, either with different materials or different colors and different creative designs. 
         [0009]    Along with the shape of the main body of the mule on which the foot is placed, another style feature is the strap. The latter is chosen such that it matches the clothes that are to be worn. 
         [0010]    The strap is either secured on the side faces of the main body by nails or screws or is adhesively bonded thereto. In order to ensure sufficient strength, the free end of the strap is inserted in a slit formation and secured there. Alternatively, the strap can also be secured directly on the side face of the main body. 
         [0011]    The consumer purchases a mule that is to her taste and that matches her clothing. Therefore, on account of the design of the strap and the design of the mule, it is necessary to own a number of different mules to ensure that they match the clothes. 
         [0012]    A further disadvantage is that, if the straps are provided with corresponding decorations and these decorations are damaged, the consumer has to purchase a new pair of mules. 
         [0013]    If the straps bursts, the consumer is forced either to get the mule repaired or to buy new mules. 
         [0014]    WO2006/020215 A2 discloses a sandal consisting of a main body, wherein exchangeable straps are arranged on the main body and, when the sandal is being worn, at least partially enclose the foot. The straps have hook-shaped elements, which engage in eyelet-like formations on the side of the main body. In order to detach the straps from the main body, the hook-like elements are moved in a direction such that they can disengage from the eyelets. 
         [0015]    In order to bring about this detachment, an actuation element is provided on the heel side or rear side of the sandal and is coupled to the eyelet-like formations. In this way, the eyelet-like element can be separated from the hook-like element by a kind of cable pull. 
         [0016]    US 2006/0080813 A1 likewise discloses a mule that has exchangeable straps. At their free ends, the straps have fixing elements which, on the side facing the foot, engage in corresponding recesses and latch therein. In order to remove a strap, it is necessary to operate the respective free end of the straps via an actuation element, so as to release the snap-fit connection between the fixing element and the fixing device. 
         [0017]    The design is very complex, since the device has to be arranged at each free end of the straps. For this purpose, it is necessary to work the main body, both on the side facing the foot and also on the front face, in order to introduce the fixing device into the main body. The actuation element is very small, such that it can only be operated using an additional object. 
         [0018]    WO 2008/030479 likewise discloses a sandal that has exchangeable straps. The free ends of the exchangeable straps have fixing elements which can be preferably screwed into the respective fixing device in the area of the main body. Alternatively, provision is also made for magnetic elements to be arranged in the respective fixing devices, which magnetic elements provide a force-fit connection between the fixing device and the fixing elements. 
         [0019]    This design is also very complex, since the fixing devices have to be formed exactly at the corresponding locations inside the main body. To do this, it is necessary for the main body to be worked very precisely on the side facing toward the foot. Moreover, very high forces act in the area of the foot, such that a magnetic closure alone is not sufficient. In order to counteract this, provision is additionally made to form a bayonet catch. However, this bayonet catch has the disadvantage that the strap first has to be turned through at least 45 degrees before it reaches the correct position. 
         [0020]    A sandal designed in the manner of a flip-flop is known from US 2010/0132223 A1. The free ends of the respective straps have, as fixing elements, clip-like connection elements that cooperate with fixing devices, which are also designed like clips and are present in the main body. In order to detach the strap, each free end has to be suitably operated. To ensure that the clip-like connections do not adversely affect the wearing comfort, they are made very small. This in turn has the disadvantage that they are extremely difficult to operate. In addition, the link to the respective clip elements offers a predetermined breaking point, such that increased wear is present. 
         [0021]    U.S. Pat. No. 6,430,846 discloses a sandal that likewise has exchangeable straps, of which the free ends are designed with fixing elements. These fixing elements are very broad, such that they interact with fixing devices arranged inside the main body. The interaction is obtained by providing openings on the side facing toward the foot, into which openings the fixing elements can be inserted. Latching elements of the fixing device ensure that the straps are held firmly on the main body. Actuation elements are provided at the end face which disengage the latch. The actuation for this design of sandals with detachable straps is designed like a push button at the end face. Here too, however, there is the disadvantage that it is complicated to operate each free end with the actuation. There is a danger that if one side is suitably detached and one turns to the other side, the one side latches again. In addition, the openings directed toward the foot, for the purpose of receiving the fixing elements, offer a very large space for dirt. Moreover, they are arranged in the visible area, and this therefore already represents a disadvantage for esthetic reasons. 
         [0022]    DE 10 150 792 A1 counters this disadvantage. Here, a shoe is provided with a main body that likewise has exchangeable straps. However, the straps are not insertable on the top of the main body facing toward the foot, but instead at the front. For this purpose, a recess is provided on each side, in which recess a pin element is arranged which extends in the longitudinal direction of the shoe and of which the free ends are designed like springs and can be brought into engagement with fixing elements. The spring pin designs, of the kind also known for fastening watch straps for example, are intended to serve to fix the straps. However, this design has the disadvantage that the forces that act in mules of this kind cannot be taken up by the pin-like designs. Moreover, detaching the straps proves very difficult, since a very small tool is also needed in order to disengage the pins from the fixing aids. 
         [0023]    The problem addressed by the invention is to make available a mule having detachable straps, of which the stylish appearance can be adapted by the consumer to the corresponding needs of the consumer, wherein handling is intended to be simple, such that the straps can be detached by simple operation. 
       SUMMARY 
       [0024]    The problem is solved by the features of claim  1 . 
         [0025]    The basic concept of the invention is that the strap is connected to the main body of the mule by a detachable form fit and/or force fit or only by a detachable force fit. 
         [0026]    To provide such a force fit, a fixing device that detachably fixes the free ends of the strap at least indirectly on or in the main body is arranged inside the main body or on the main body. By actuation of an actuation element, which is part of the fixing device, the force fit is canceled, and the strap fixed per se on the main body can be removed from the main body and can be replaced by a new strap which, for example, meets the fashion style of the user. 
         [0027]    In one development, a form fit is also provided in addition to the force fit. The forces that occur in the area of the instep, held by the strap, while walking and running are great, and therefore a form fit is additionally provided for a preferably optimal design of the force fit. For this purpose, provision is made that fixing elements are arranged on the free ends of the strap, in such a way that these engage recesses provided in the main body and thus establish a form fit at least indirectly between the strap and the main body. The force-fit means or fixing means hold the fixing element detachably on the main body. 
         [0028]    Different configurations may be proposed for the above-described force fit. 
         [0029]    Firstly, provision is made that the detachable force fit is made available, regardless of whether a form fit is provided or not, by laterally arranged means, for example push buttons, magnets or similarly or identically acting means. Secondly, provision can be made that the fixing device is arranged inside the main body and can thus be designed in various ways. This has the basic function of receiving a fixing element, which is arranged on the strap, with a force fit but also detachably. By actuating an actuation element, for example a button, a rotary knob or the like, the force-fit connection can be released, such that the strap can be exchanged after it has been guided by hand out of the connection. A combination of force fit and form fit supports the holding force of the strap on the main body. 
         [0030]    The force fit itself can be effected through one or more clamp elements. These clamp elements can be spring-loaded such that, when the force-fit means arranged on the free ends of the strap is pressed in, an independent locking takes place inside the main body. By actuating a trigger mechanism, the lock is freed again. This trigger mechanism can be arranged both on the underside and also on the top of the main body. A lateral arrangement is likewise conceivable. Provision is preferably made that this trigger mechanism is arranged on the underside of the main body between the sole surface and the heel surface of the mule. Triggering can be effected by a rotation of an adjustment element, wherein the rotation movement is either to be carried out using a special key, or the adjustment element has a slit, such that the rotation movement can be effected by an inserted coin (in place of a screwdriver). 
         [0031]    The release can also take place only indirectly. For this purpose, provision is preferably made that by means of a magnet, which is held on the underside the sole side of the mule facing toward the street, the force-fit connection between the fixing elements and the fixing device is releasable. For this purpose, provision is made that the locking or also the undercut or engagement behind of fixing elements and fixing device can be released by a single for example lifting movement, in such a way that both parts are disengaged. On account of the pretensioning that results from the material of the strap, the two fixing elements migrate away from the main body and are thus released in a very simple manner from the main body. 
         [0032]    In a particular development, provision can be made that the fixing device is made available as a subassembly, such that it can be arranged in a simple way as a unit on a specially designed main body which provides the corresponding recess. In this way, the main body can be produced and made available separately from the means for establishing the force fit or form fit. When the two components are made ready, they can be simply joined together by adhesive bonding or screwing. It is also conceivable that the subassembly is made of plastic and the main body is made of wood. Other materials are also provided. The formations which in particular effect the operation of the release of the strap from the main body on the underside, that is to say the side of the main body of the mule directed away from the foot, can also be designed in such a way that an actuation element is no longer visible at all. This can be achieved particularly by the design as a magnet. For this purpose, for example, provision is made that a lipstick, for example, is present as a counter-magnet in an accessory of the user. This counter-magnet is simply held on the underside of the mule, that is to say on the sole in a certain area. In this way, the magnet arranged inside the main body is attracted and the existing lock between the strap and the main body is freed. 
         [0033]    In another solution, provision is made to incorporate the actuation element into the sole of the mule. For example, the actuation element can be covered by a suitable flap. To release the straps, the flap first of all has to be opened in order to access the actuation element, in such a way that the lock between the free ends of the strap and the main body is freed. 
         [0034]    Both of the last-mentioned embodiments have the advantage that, to an observer, it is not in any way apparent from the outside that these shoes are sandals or mules of which the straps are exchangeable. 
         [0035]    In a further embodiment, provision is made that, in the area of the seat for the foot, the main body has a recess, an inlay stylishly matching the respective inserted strap being introduced into the recess. The inlay is fixed either by a Velcro fastener, a magnet or another type of force fit or form fit. 
         [0036]    The inlay preferably extends from the heel area of the main body of the mule as far as the metatarsal region or even the toe region. The inlay can be made from the same material as the strap, can at least have the same color or present similar structures. In one embodiment, provision is made that the aid for actuating the fixing device for the strap is provided under the inlay. The aid can be fitted in a cavity, which is closed off from the outside by the inlay. Since the inlay is arranged releasably on the main body, the aid can also be very easily removed as and when required. It is then almost impossible for the aid to be mislaid or lost. 
         [0037]    In order to permit simple production of such a mule according to the invention, a recess is advantageously provided in the main body on the side facing away from the foot, starting from the sole, and pointing toward the walking surface with the ground. The recess is designed in such a way that it preferably extends in the shape of a rectangle and has connection paths to the respective front faces. The front faces likewise have recesses and are designed in such a way that at least one connection exists between the front-face recesses and the recess on the sole side. 
         [0038]    The fixing device is arranged in a housing. This affords the advantage that it can be inserted as a finished subassembly into this recess. The recess is designed in such a way that the housing fits into this recess in such a way that only minor fixing elements are still provided. If the embodiment that can be operated with a magnet is chosen, it suffices to close the recess with the sole of the mule. The fixing device is then arranged securely inside the recess. It can then still be reached only via the respective front-face recesses or the bores associated with these. In this way, very simple production is possible, without the need for elaborate working of the main body of the mule. Moreover, no mechanical working is needed that cannot be done by a shoe manufacturer, since the fixing device can already be supplied as a prefabricated subassembly. 
         [0039]    Further advantageous embodiments will become clear from the attached drawings, the description and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  shows a perspective view of the mule according to the invention, consisting of a main body and a strap connected to the main body; 
           [0041]      FIG. 2  shows a perspective view of the mule according to  FIG. 1 , but in a perspective view from underneath; 
           [0042]      FIG. 3  shows a perspective view of a first illustrative embodiment of the device according to the invention, wherein the strap can be fixed on the main body by means of a fixing device arranged inside the main body; 
           [0043]      FIG. 4  shows a perspective view of the mule according to  FIG. 3 , but partially in a cut away view; 
           [0044]      FIG. 5  shows a further view of the mule according to  FIG. 4 ; 
           [0045]      FIG. 6  shows a detailed view of the fixing device according to the first illustrative embodiment shown in  FIGS. 3 to 5 ; 
           [0046]      FIG. 7  shows a perspective view of a mule in a second illustrative embodiment according to the invention; 
           [0047]      FIG. 8  shows a perspective view of the mule according to the invention, but in an exploded depiction with a corresponding fixing device; 
           [0048]      FIG. 9  shows a view of a modified form of a fixing device shown in  FIGS. 7 and 8 , namely a design as an independent subassembly; 
           [0049]      FIG. 10  shows a perspective view of a fourth illustrative embodiment, in which the fixing device can be operated by means of a magnet; 
           [0050]      FIG. 11  shows an exploded view of the embodiment according to  FIG. 10 ; 
           [0051]      FIG. 12  shows an enlarged view of the fixing device of the illustrative embodiment according to  FIGS. 10 and 11 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0052]    The basic concept of the mule  1  according to the invention is shown in  FIGS. 1 and 2 . 
         [0053]    The mule  1  according to the invention consists of a main body  2  and of a strap  3 . The main body  2  has a top  4  and an underside  5 . Side faces  6  are also provided. 
         [0054]    The top  4  of the main body  2  serves as a seat  7  for the foot. This seat  7  is dimensioned in such a way that a foot can be arranged in its entirety on this seat. The underside  5  is divided into three areas, namely into a first area of the sole surface  8  and into a second area of the heel surface  9 . Between the sole surface  8  and the heel surface  9 , a third area  10  is provided which generally does not come into contact with the ground. 
         [0055]    The strap  3  extends from one side face  6  of the main body to the opposite side  6  and is dimensioned in such a way that it can enclose the back of the foot (instep), such that the mule holds on the foot. The length of the strap can be adjusted by means of a width control (not shown in the drawings) which, for example, can be designed like a belt buckle. In this way, the strap  3  can be adapted to the specific circumference of the instep. 
         [0056]    Fixing elements  12  are arranged at the free ends  11  of the strap  3  and interact with a fixing device  13  arranged inside the main body. This interaction between the respective fixing element  12  and the fixing device is described in more detail in the further illustrative embodiments and can be effected in different ways. This design difference is such that there is either a form fit or a force fit, or a combination of form fit and force fit, between the fixing element  12  and the fixing device  13 . 
         [0057]    The fixing device  13  is arranged in or on the main body and is used to fix the strap  3  firmly on the main body  2 , but also to release the strap upon actuation of a corresponding actuation element (also not shown in the drawings) when this is desired by the user. This may be desired when the user seeks to exchange the strap  3  and, for example, replace said strap with another one. 
         [0058]    A further purpose of the fixing device  13  and of the interaction with the fixing element  12  is that, at least while the mule  1  is being worn on the foot, it is not apparent to the consumer that the strap  3  is in any way exchangeable. 
         [0059]    The seat  7  of the main body  2  for receiving the foot has an inlay E. This inlay E is detachably connectable to the main body  2  and preferably forms a plane with the seat  2  of the main body  2 , such that the user feels a difference at best on account of different material but not because of an edge being present. This inlay E is designed as an optical element and is provided such that, at least for optical reasons, it forms an optical unit with the strap  3  and its configuration. 
         [0060]    This basic concept of the invention, along with the features associated therewith, is described by way of example in the illustrative embodiments below. 
         [0061]    The above-described features can be used singly or in combination in the examples below. 
         [0062]    However, the invention is not limited to the illustrative embodiments. Instead, all configurations are claimed that follow the basic concept, namely that of making it easy for the user to secure the strap of a mule detachably on the main body. 
       FIRST ILLUSTRATIVE EMBODIMENT 
       [0063]      FIGS. 3 to 6  show a first illustrative embodiment of a mule  201 . The mule  201  comprises a main body  202  with a strap  203  detachable from the latter. The free ends  211  of the strap  203  can be arranged detachably on the side faces  206  of the main body  202  of the mule  201 . 
         [0064]    As can be seen from  FIGS. 4 and 5  in particular, the free ends have fixing elements  212  shown with a fixing device  213 , which is outlined in the figure. 
         [0065]    The fixing device  213  is arranged inside the main body  202  and serves to arrange the strap  203  detachably on the main body  202 . An actuation element  214 , as shown in  FIGS. 4 and 5 , is preferably arranged in the third area  210  on the underside  205  of the mule  201  and serves to release the fixing elements  212  from the at least force fit, such that the strap  203  is removable from the fixing device  213 . 
         [0066]    The fixing device  213  is shown in an enlarged view in  FIG. 6 . Fixing elements  212 , in which pins  212   c  comprise a groove  212   b,  are received with a force fit by the fixing device  213 . For the force-fit engagement, the fixing device  213  has a force-fit element  213   a  with an area  213   b  that engages in the groove  212   b  of the fixing element  212 . 
         [0067]    The fixing device  213  or force-fit element  213   a  shown in the illustrative embodiment is movable in and counter to arrow direction  215  by actuation of the actuation element  214 . The movement is spring-loaded by means of a spring  216 , such that, when the fixing elements  212  are pressed inward in arrow direction  217 , an automatic latching of the fixing elements  212  in the fixing device  213  is obtained. The easier insertion is simplified by the pin-like formation  212   c  being cone-shaped and thus being able to more easily pass through the area  213   b.  For release, the actuation element  214  is actuated, and the force-fit element  213   a  moves in arrow direction  215 . The fixing elements  212  snap out of the force-fit element  213   a  and are released. The strap  203  can now be suitably exchanged. 
         [0068]    To form the fixing device  213 , a cavity  218  ( FIG. 3 ) in which the fixing device  213  can be fitted is provided inside the main body  202 . This cavity  218  is preferably arranged in the area of the sole surface  208  ( FIG. 4 ) of the mule  201 . The actuation element itself can be provided both by a cover element in the area of the sole surface  208  and also, as shown in  FIGS. 4 to 7 , in the third area  210 . 
       SECOND ILLUSTRATIVE EMBODIMENT 
       [0069]      FIGS. 7 and 8  show a second illustrative embodiment of a mule  301 . This mule  301  consists of a main body  302  and a strap  303  to be arranged on the main body and to be detachable from the latter. The main body  302  is designed in a manner comparable to the main bodies described above. Under the sole surface  308 , it has a fixing device  313  (shown by broken lines in  FIG. 8 ), which receives the fixing elements  312  (not shown in detail) with a form fit and force fit. 
         [0070]    The fixing device  313  is arranged as a subassembly in the cavity provided in the main body  302 . By means of an actuation element, which is arranged inside the sole surface  308  and can be covered by a cover element (not shown in detail), a rotation movement  314  can be generated, as is indicated symbolically in  FIG. 8 . By means of the rotation movement, the force-fit elements  313   a  of the fixing device  313  are disengaged from the fixing elements  312  or from the pin-like formation thereof, such that the strap  303  can be removed from the main body  302  of the mule  301 . 
       THIRD ILLUSTRATIVE EMBODIMENT 
       [0071]      FIG. 9  shows another preferred embodiment in accordance with the basic concept of the invention. 
         [0072]    In principle, the device according to the invention is such that a mule is made available which has a strap  403  that the user is able to detach without an aid or with a small aid. At each of its free ends, the strap  403  has fixing elements  412 , which can be fitted detachably on a main body by means of a fixing device  413 . This therefore affords the user the possibility of removing the strap  403  as and when required and of exchanging it or adapting it to the clothing. The preceding examples show that a main body is made available that has a corresponding cavity into which the fixing device  413  can be installed. 
         [0073]    It differs mainly in that the fixing device  413  according to  FIG. 9  is designed as a finished subassembly for mounting on a main body  402  of a mule. This means that the fixing device  413  is arranged in a housing  430 , in such a way that the latter can be supplied as a delivery part for a shoe manufacturer. The problem arises that shoe manufacturers do not have the necessary machinery to provide such fixing devices with the corresponding fixing elements. It is therefore a considerable advantage if the fixing devices  413  can be supplied ready to function in a housing  430 , in such a way that it can be fixed in a corresponding recess in the area of the sole surface of the main body  402  of the mule  401 . 
         [0074]    Alternatively, provision can also be made that the above-described housing  430  is a constituent part of the shoe, such that only the fixing device  413  has to be fitted. It suffices to make available a cavity having the size of the illustrated housing into which the fixing device  413  can be fitted. 
         [0075]    The housing  430  can be arranged in its dimensions in the area of the sole surface (for example reference sign  8  in  FIG. 1  or  FIG. 2 ) of the mule, wherein the housing  430  already has the necessary recesses  413   a  for receiving the fixing elements  412 . The fixing elements  412  can be arranged on the free ends of the straps; they are therefore only shown in this  FIG. 11  in order to illustrate the function of the fixing device  413 . 
         [0076]    Moreover, the actual force-fit element  413   b  is arranged rotatably on a bearing device  413   c  in the housing  430 . Spring elements (not shown in detail) press the force-fit element  413   b  into the position in which a locking with the fixing elements  412  is to be effected when these are each fully inserted into the recesses  413   a.    
         [0077]    The force-fit element  413   b  is preferably of symmetrical construction and is mounted centrally. At its free ends, it has means  413   d  that interact with the fixing elements  412 . The interaction is such that the means  413   d  have u-shaped formations which, by pivoting of the force-fit element  413   d,  engage in the grooves  412   b  provided by the fixing elements  412 . A force fit is achieved by the engagement of these u-shaped formations. Since the free ends of the fixing elements  412  have pin-like formations  412   a,  which engage in bores  413   e,  a correct positioning of the fixing elements  412  is achieved, such that a reliable locking of force-fit element  413   b  with the fixing element  412  is achieved. The free ends of the pin-like formations  412   a  are preferably cone-shaped, such that, when the fixing elements  412  are pressed into the recesses  413   a  of the housing  430 , the bores  413   e  are penetrated, and then the cone-like free ends effect a slight rotation of the force-fit element  413   b  until it automatically snaps back, such that the locking is brought about. 
         [0078]    In order to exert the corresponding rotation in or counter to arrow direction  416 , an aid  415  is provided that engages in an actuation element  414 . The actuation element  414  is rotatably connected at least indirectly to the force-fit element  413   a  via a slide element  417 . 
         [0079]    With the aid  415 , the user can disengage the force-fit element  413   a  from the fixing elements  412  by rotation in or counter to arrow direction  416 . Since provision is made for automatic locking to take place when the fixing elements  412  are pressed into the force-fit element  413   b,  active rotation via the actuation element  414  is only necessary when the user wishes to release the fixing elements and exchange the strap. 
         [0080]    The subassembly can be joined together with a small number of fastening elements. Clip connections or screw connections are preferably used in order to ensure simple and inexpensive production of this subassembly. 
         [0081]    Instead of the housing  430  in  FIG. 9 , the subassembly, when joined together as shown here, can also be fitted into a cavity provided in a main body of a mule. The subassembly is in this case reduced to the fixing element. 
       FOURTH ILLUSTRATIVE EMBODIMENT 
       [0082]      FIGS. 10 to 12  show a fourth preferred illustrative embodiment in accordance with the basic principle of the invention. In principle, the device according to the invention is such that a mule is made available with a strap  503  in that way that the user is able to detach it with small auxiliary means. At its free ends, the strap  503  has fixing elements  512 , which can be fitted detachably on a main body  502  by means of a fixing device  513 . This therefore affords the user the possibility of removing the strap  503  as and when required and of exchanging it or adapting it to the clothing. The preceding examples show that a main body is made available that has a corresponding cavity into which the fixing device  413  can likewise be installed. 
         [0083]    The fixing device  513  differs from those according to the first and second illustrative embodiments in that, as in the third illustrative embodiment, it is designed as a finished subassembly for mounting on a main body  502  of a mule. This means that the fixing device  513  is preferably arranged in a housing  530 , in such a way that the latter can be supplied as a delivery part for a shoe manufacturer. The problem arises that shoe manufacturers do not have the necessary machinery to provide such fixing devices with the corresponding fixing elements. It is therefore a considerable advantage if, as in the third illustrative embodiment too, the fixing device  513  can be supplied ready to function in a housing  530 , in such a way that it can be fixed in a corresponding recessed area of the sole surface of the main body  502  of the mule  501 . 
         [0084]    The housing  530  can be arranged in its dimensions in the area of the sole surface of the mule, wherein the housing  530  is designed with a box shape. A force-fit element  513   b  is arranged inside the box shape, as is shown in  FIG. 12  for example, and engages like a bracket in the grooves  512   b  provided by the fixing elements  512 . The grooves  512   b  are again arranged on pin-like formations  512   a  of the fixing element  512 . The fixing elements  512  are adjoined, as is indicated in  FIG. 10 , by the strap  503 . 
         [0085]    The force-fit element  513   b  is of symmetrical construction and is mounted movably on bearing elements  513   f  in and counter to arrow direction  513   g.  Spring elements  513   h  serve to effect the spring-loaded movement according to arrow direction  513   g.    
         [0086]    A plate element  513   i  limits the height movement in arrow direction  513   g  ( FIG. 12 ). 
         [0087]    To provide a locking action, the fixing elements  512  are inserted into the recesses  513   a  of the main body  502  of the mule  501 . By means of the insertion, a corresponding form fit is obtained firstly with the outer contour of the fixing element  512 . The pin-like formation  512   a  moves through a bore provided in the main body in the recess  513 , and then through an opening  513   e,  which is arranged on the main body  530 . On account of the bracket-like design of the force-fit elements  513   d,  the locking action is brought about when force is exerted on the fixing elements in arrow direction  512   c,  in such a way that the free ends of the force-fit element  513   b  engage in the groove  512   b  of the fixing element  512 . The locking action is thus brought about. 
         [0088]    To cancel the locking action, a magnetic element  515  is now held, as shown in  FIG. 10 , on the sole surface, that is to say on the underside of the mule. In this way, a magnet  516 , which interacts with the housing cover  513   i  of the subassembly, is moved in arrow direction  517  ( FIG. 11 ). Since the plate element  513   i  is spring-loaded, it likewise moves in the arrow direction, in such a way that the force-fit element  513   b  likewise moves in this arrow direction. In this way, the free ends  513   b  of the force-fit element disengage from the grooves  512   b  of the fixing elements  512  and thus release the force-fit connection. Depending on the choice of material of the strap, the form-fit connection between the fixing element  512  and the recess  513   a  is maintained or, because of the corresponding pretensioning, it is also accordingly canceled. 
         [0089]    When the magnetic element  515  is spatially removed from the sole, the plate element  513   i  recovers its original position. This is again achieved by the spring action. The force-fit elements  513   d  thus return to their original rest position, such that they are ready to receive the fixing elements  512 . 
         [0090]    Alternatively, provision is also made that the magnetic element  516  interacts with a further component part  518 , which is in form-fit and force-fit connection with the force-fit element  513   b.  If the magnet  515  is held on the outside of the sole as has already been described above and as is shown in  FIG. 10 , it is thus possible that the magnet  516  is moved together with the component part  518  in arrow direction  517 , specifically counter to the spring force provided by the springs  513   h.  As has likewise been described above, the fixing element is thus also disengaged from the fixing device. 
         [0091]    Instead of the housing  530  described in  FIG. 11 , the subassembly, when joined together as shown here, can also be fitted into a cavity provided in a main body of a mule. The subassembly is in this case reduced to the fixing element. A housing is then not necessary. 
         [0092]    The basic concept of the invention is thus to make available a mule that has exchangeable straps. These straps can be secured on the main body in different ways. They can be secured using force-fit and also form-fit connections and also combinations thereof. The basic concept is also such that, when the shaped elements arranged at the free ends are simply pressed in, an at least form-fit but also preferably force-fit connection is established between the strap and the main body. Provision is made for an actuation element to be activated only in order to detach the strap from the main body. The activation can be effected either using a coin, by inserting the latter into a slot (comparable with a screwdriver or an auxiliary element such as a key). The generally tensioned shaped elements are then released by a simple rotation. They are tensioned because the material from which the strap is made does not assume the shape and it is therefore sought to resume an elongate shape as soon as a force fit is canceled. 
         [0093]    As an alternative to the above-described actuation element, provision can also be made that the fixing device, or the locking of fixing element and fixing device, is released without a force-fit and form-fit connection. By means of a magnet, the locking action can be canceled without any outward sign that any such thing is present. This has an extremely high esthetic value and, moreover, this device can be operated very easily by anyone. 
         [0094]    An accessory, for example lipstick, a comb, a mirror or the like, can be installed in the magnetic element that can serve to cancel the locking action. It is then only necessary for the user to hold this accessory on the sole area until a suitable sound clearly indicates that the locking action is now canceled. Depending on the pretensioning of the straps, this can already be observed visually, or a small slight movement has to be performed in order to likewise cancel the form fit that is still present between the fixing elements and the recess. 
         [0095]    In one particular embodiment, the fixing device is designed as a subassembly that can be arranged as a finished unit on a main body of a mule, in order to easily implement the basic concept of the invention. 
         [0096]    For this purpose, a cutout is provided inside the mule on the underside, wherein recesses are to be made on the sides that are designed for the fixing elements. 
         [0097]    The subassembly is also very easily fitted into the cutout itself. The corresponding cutout can then be covered exclusively by the fitted sole, without additional effort to further design the fixing device. The fitting is thus very simple and can be carried out by anyone without further tools.