Abstract:
A gripping element for gripping plastic containers with mouths, and in particular performs, includes a carrier on which there is arranged a gripping head which can be introduced at least partially into a mouth of the plastic container. Arranged on the gripping head is at least one holding element which is at least partially movable in a radial direction in relation to the gripping head to secure the container relative to the gripping head.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a gripping element for gripping plastic containers and in particular preforms. Such preforms are used in the prior art to be expanded during the production process to form plastic containers, such as PET bottles. During this production process, the plastic preforms are first heated and then expanded in a blowing machine. During this heating process, the preforms are transported by gripping elements. 
     It is known from the prior art to provide gripping elements which engage in a mouth of these preforms in order to hold the latter. However, different preforms or also different types of preforms sometimes have slightly different internal cross-sections or internal diameters of the mouths and/or bottle necks. But such different diameters can lead to the situation whereby gripping elements cannot pick up some containers since the mouth cross-sections thereof are too small, and other preforms slip off these gripping elements. The gripping elements known to date from the prior art are only able to handle diameter tolerances in the range of +/−0.2 mm. 
     The object of the present invention is therefore to provide a gripping element which can handle greater tolerances with regard to the performs and the mouth diameters thereof. 
     SUMMARY OF THE INVENTION 
     A gripping element according to the invention for gripping plastic containers, and in particular preforms, comprises a carrier on which there is arranged a gripping head which can be introduced at least partially into a mouth of the plastic container. 
     According to the invention, arranged on the gripping element is at least one holding element which is at least partially movable in a radial direction in relation to the gripping head and can preferably be pressed against the inner wall of the mouth to secure the container relative to the gripping head. An ability to move in a radial direction is understood to mean that at least one region of the holding element is movable at least also in the radial direction. This may be a movement which is inclined angle relative to the radial direction or else a pivoting movement in relation to a predefined axis. Furthermore, it is possible for the holding element to be movable in its entirety in a radial direction, but other movements such as, in particular but not exclusively, pivoting movements would also be conceivable. 
     This holding element which can move also in the radial direction allows a certain tolerance with regard to the containers to be gripped. In this way, it is possible to handle differences in diameter of the container mouths of up to +/−3 mm. 
     With preference, at least two and preferably at least three holding elements are arranged on the gripping head. By virtue of a plurality of such holding elements, on the one hand relatively large tolerances with regard to containers can be handled even with a relatively small radial movement, and on the other hand a more stable hold of the container on the gripping head or gripping element can be achieved by virtue of a plurality of holding elements. 
     In a further preferred embodiment, at least one section of the holding element can be pressed against the inner wall of the mouth of the container. In this way, a secure hold of the container can be achieved. However, it would also be possible for the holding element to act on a further element, for example an O-ring, and to press the latter against the inner wall of the mouth. 
     In a further advantageous embodiment, a plurality of holding elements are uniformly distributed on the gripping head around the circumference of the gripping head. In this way, too, a very stable hold of the containers on the gripping head is possible. In a further advantageous embodiment, the gripping element comprises five holding elements or seven holding elements. This number of holding elements, in particular five holding elements, has proven to be particularly advantageous for combining a stable hold with a favourable handling of different internal diameters of the containers. 
     Preferably, at least one holding element is arranged such as to be able to pivot about a predefined pivot axis. By virtue of this pivoting process, a region of the holding element is moved radially outwards to secure the container relative to the gripping head. 
     In a further advantageous embodiment, the gripping element comprises a piston body which is movable in a longitudinal direction of the carrier, wherein a movement of at least one holding element can be triggered by a movement of the piston body. The longitudinal direction of the carrier is also the longitudinal direction of the container which is arranged on the gripping element. More specifically, the movement of the holding element at least also in the radial direction of the gripping head is triggered by a movement of the piston body. Preferably, the piston body is arranged radially inside the holding elements. With particular preference, the piston body actuates a plurality of the holding elements and particularly preferably all the holding elements. 
     Preferably, the piston body has a first guide surface which is formed in the circumferential direction of the piston body and which cooperates with the holding elements in order to move the latter. These may be for example oblique surfaces which urge the holding elements radially outwards during the movement of the piston. 
     In a further advantageous embodiment, the gripping head comprises a covering body, inside which the holding elements are at least partially arranged. The covering body may be a cover which is arranged on the underside of the gripping head and which can be introduced fully into the mouth of the container. Thus an external circumference of this covering body is preferably adapted to the internal circumference of the preform and is particularly preferably slightly smaller than this internal circumference or internal cross-section. For example, it is possible for at least part of the holding elements to be arranged permanently inside the covering body, such as for example the pivot axle about which the holding elements can be pivoted. 
     In a further advantageous embodiment, the covering body has a plurality of openings arranged in the circumferential direction of the covering body, through which the holding elements extend. For example, it is possible that the holding elements extend radially outwards through the openings to grip the containers. 
     In a further advantageous embodiment, the covering body has wall sections with an external circumference shaped as a segment of a circle. 
     In a further advantageous embodiment, the gripping element has a spring device which prestresses the piston body relative to the gripping head. In this case, it is possible for the spring device to prestress the piston body in the upward direction, i.e. away from the container to be gripped. 
     In a further preferred embodiment, the holding elements have a first guide surface which cooperates with the piston body to move the holding elements radially outwards when the piston body is moved in a first direction, and a second guide surface which cooperates with the piston body to move the holding elements radially inwards when the piston body is moved in a second direction opposite to the first direction. In this embodiment, therefore, both the outward radial movement of the holding elements and also the inward radial movement is brought about by a movement of the piston body relative to the gripping head. This will be explained in more detail with reference to the figures. 
     In a further advantageous embodiment, the holding elements and/or the elements, respectively, which guide the holding elements are movable exclusively in a radial direction. Furthermore, it is possible that the holding elements are prestressed radially inwards by a flexible ring-shaped body. In addition, it is possible for example that use is made of a ring-shaped body which can be prestressed radially outwards by holding elements, for example pin-like bodies, arranged radially inside relative to this ring-shaped body, which in this case bears against an internal circumference of the thread. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and embodiments will emerge from the appended drawings: 
       In the drawings: 
         FIG. 1  shows a sectional view of a gripping element according to the invention; 
         FIG. 2  shows a perspective view of part of the gripping element of  FIG. 1 ; 
         FIG. 3   a  shows a perspective top view of a gripping element according to  FIG. 1  from below; 
         FIG. 3   b  shows a perspective top view of the gripping element of  FIG. 1  from below; 
         FIG. 3   c  shows a top view of the gripping element of  FIG. 1  from below; 
         FIG. 3   d  shows a perspective top view of the gripping element shown in  FIG. 3   a;    
         FIG. 4  shows a holding element for a gripping element according to the invention; 
         FIG. 5  shows a further embodiment of a gripping element according to the invention; 
         FIG. 6  shows a top view of the gripping element of  FIG. 5  from below; and 
         FIG. 7  shows a perspective view of the gripping element of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a gripping element  1  according to the invention. This gripping element  1  comprises a carrier  2 , on which a gripping head  4  is arranged. This gripping head  4  can be introduced into a mouth of a container (not shown) in order to grip the latter from inside. By means of this gripping element, the containers (not shown) can be transported, for example can be transported through a heating device which heats said containers prior to the actual expansion process. 
     The carrier  2  comprises a main body  10  and a sleeve body  12 . The gripping head  4  is screwed onto this main body  10  by means of an attachment device such as a screw device  18 . Just one screw means is shown in  FIG. 1 , but a plurality of screw means, for example three, may be provided. Reference  8  denotes a piston body which is movable within a bore or recess  20  in a longitudinal direction L of the gripping element. By virtue of this longitudinal movement of the piston body  8 , a holding element  6   a  shown in  FIG. 1  can be moved both outwards and inwards in the radial direction R. Reference  14  denotes a spring device which prestresses the piston body  8  in the upward direction in  FIG. 1 . This spring device is arranged in this case in a recess  15  of the piston body  8 . 
     The piston body  8  has two oblique surfaces or guide surfaces  82  and  84  which serve for moving the holding element  6   a  and also further holding elements (not shown). 
     Arranged within the main body  10  is a further recess  11 , within which a region of the piston body  8  can move. 
       FIG. 2  shows a perspective view of part of the gripping element according to the invention, more specifically of the gripping head  4  which is introduced into the mouth of the container. On its underside, the gripping element has a covering body  16  which has an insertion inclination  16   a  in the circumferential direction to facilitate insertion into the mouth of the container. 
     It is possible to see in  FIG. 2  two holding elements  6   a ,  6   b  which are pivotable. In this way, a region of these holding elements  6   a ,  6   b  can be moved radially outwards. Reference  22  denotes wall sections with an external circumference in the shape of a segment of a circle, between which in each case openings  23  are provided, through which the holding elements can extend and move. These wall sections  22  thus form part of the covering body  16 . 
       FIG. 3   a  shows a top view of a gripping element according to the invention from below. There can be seen here five openings  24  in the covering body  16  or the lower plate  26  of the covering body  16 , in which the holding elements  6   a - 6   e  are guided by means of pivot axles or shafts  66 . These openings  24  thus also define pivot axes S 1 -S 5 , about which the holding elements  6   a - 6   e  are guided. Furthermore, it is also possible to see the regions  29  in which the screw means shown in  FIG. 1  extend in the longitudinal direction L. 
       FIG. 3   b  shows a view of the gripping element from below, wherein here the lower plate  26  has been removed. It is possible to see a plurality of segments  22  which are rigidly arranged and have an external cross-section in the shape of a segment of a circle. Some of these segments  22  have openings  34  for arranging the covering plate  26  thereon. 
     It is also possible to see in the sectional view of  FIG. 3   b  the spring device  14  which prestresses the piston body in the upward direction. This spring device  14  is supported against the baseplate  26  (cf.  FIG. 3   a ). It is also possible to see in  FIG. 3   b  the design of the holding elements  6   a - 6   e,  which in each case cooperate with the piston body  8  to be urged outwards or inwards. 
       FIG. 3   c  shows a top view of a gripping element according to the invention from below. As mentioned above, the holding elements  6   a - 6   e  are pivotable about a predefined pivot axis and in this way an at least also radial movement of the section  68  of the holding elements in the radially outward or radially inward direction is brought about. 
       FIG. 3   d  shows a further view of a entire gripping element from below, wherein here the main body  2  is also illustrated. The holding elements  6   a  are in this case movable in the radial area r of the gripping element, and the radial tolerance of the containers to be gripped is also defined by this adjustment range. 
       FIG. 4  shows a perspective view of a holding element  6   a . Here, reference  66  denotes a pivot axle, about which the holding element can pivot. Reference  68  denotes a pressing section of the holding element  6   a,  which can be pressed against an inner wall of the container. Furthermore, the holding element has an oblique surface or guide surface  62  which cooperates with the section  82  of the piston body  8  shown in  FIG. 1 . When the piston body is moved downwards in the longitudinal direction of  FIG. 1 , the surface  62  makes contact with the surface  82  of the piston body and in this way the holding element  6   a  is pivoted about the pivot axle  66  and pushed outwards. 
     Reference  64  denotes a further oblique surface, which cooperates with the section  84  of the piston body  8  and therefore brings about a return movement of the holding element  6   a  when the piston body  8  is moved upwards in the longitudinal direction L of  FIG. 1 . In this way, both an outward movement of the holding elements  6   a - 6   e  and the return movement of the holding elements can be achieved by a cooperation of the oblique surfaces  62  and  64  with the surfaces  82  and  84  of the piston body  8 , depending on the direction of movement of the piston body  8 . Reference  65  denotes a further guide surface. 
       FIG. 5  shows a further embodiment of a gripping element according to the invention. Here too, as in the case discussed above, a carrier  2  is provided, on which a gripping head  4  is arranged. This embodiment also provides a piston body  8  which is displaceable in a longitudinal direction L of the gripping element  1  and is likewise prestressed in the upward direction here by a spring device  14 . In contrast to the embodiment shown in  FIG. 1 , however, here the spring device  14  is arranged further above, i.e. inside the carrier  2 . 
     More specifically, a cylindrical body  36  is provided, against which the spring device  14  is supported. At the other side, the spring device  14  is supported on a protrusion  8   a  of the piston body  8 . 
     At its lower end, the piston body  8  has a conical circumferential surface  82  which cooperates with the holding elements  6   a  to move the latter in the radial direction R. 
     The holding elements  6   a  have in this case a contact section  67  which cooperates with the piston body  8 , and also the region  68  which cooperates with the inner wall of the container (not shown). 
     Reference  32  denotes here once again to a screw device for arranging a plate  26  on the gripping head  4 . Reference  7  denotes a prestressing device such as an O-ring in this case, which extends in the circumferential direction around all the holding elements  6   a  and/or lies in a groove  63  formed by the holding elements. This O-ring prestresses the individual holding elements  6   a - 6   e  radially inwards and thus brings about a return movement of the individual holding elements  6   a - 6   e  if the piston body  8  is moved upwards in the longitudinal direction L. 
       FIG. 6  shows a top view from below of a gripping element according to the invention in the second embodiment. It is possible to see here once again the five holding elements  6   a - 6   e,  which are prestressed outwards in the situation shown in  FIG. 6 , i.e. in this case the piston body  6  is moved downwards. Furthermore, it is also possible to see in this view part of the O-ring  7  which returns the holding elements in the radial direction R. 
       FIG. 7  shows a perspective view of a gripping head  14 . Here, two holding elements  6   a ,  6   e  can be seen, which are in each case moved radially outwards. To prestress the holding elements inwards, the O-ring  7  is arranged in the above-described groove  63  which is formed both by the holding elements  6   a - 6   e  and by the sections  22  arranged therebetween. Reference  68  once again denotes the contact region which is pressed against the inner wall of the container or preform (not shown). 
     All of the features disclosed in the application documents are claimed as essential to the invention in so far as they are novel individually or in combination with respect to the prior art.