Abstract:
The preform conveying installation ( 2 ) comprises gripping members ( 6 ) and heads ( 7 ) for feeding them into the heating oven, and includes a detection system that selects preforms likely to cause incidents in said heating oven, and means for detaching each selected preform from its gripping head ( 7 ), which means apply pressure to the interior of the selected preform ( 2 ), on its base, and these consist of a nozzle ( 15 ) capable of directing a jet of pressurized fluid at said base. The gripping member ( 6 ) and the gripping head ( 7 ) comprise an orifice in the form of a bore ( 9 ) that enables the jet of pressurized fluid to be applied directly into the selected preform.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage of International Application No. PCT/FR2008/052074 filed Nov. 18, 2008, claiming priority based on French Patent Application No. 0708110, filed Nov. 19, 2007, the contents of all of which are incorporated herein by reference in their entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates in general to the field of manufacturing receptacles made of thermoplastic material obtained after heating and blow molding of a hollow body commonly called a preform, and it relates more particularly to a conveying system comprising a series of transport devices that are each furnished with at least one gripping member designed to carry a preform for the purpose of making it travel in a vertical position inside the installation. 
         [0003]    Therefore, the invention applies to the in-line processing installations for the manufacture or processing of preforms made of thermoplastic material such as PET, in which installations said preforms are moved individually one after the other with the aid of transport devices capable of holding them by their neck, so as to leave their body free for the purpose of heating. 
       DESCRIPTION OF THE PRIOR ART 
       [0004]    Routinely, a preform takes the general shape of a tubular cylindrical body closed at one of its axial ends and extended at its other open end by a neck already having the final shape of the neck of the final receptacle and a collar extending substantially radially. In the rest of the description, “receptacle provided with a neck” is understood to be any hollow body having a neck, namely preforms, from which receptacles are manufactured by blow molding or stretch-blow molding, that is to say receptacles having their final shape and having to undergo an additional process (such as a step of labeling or filling). 
         [0005]    In the particular case of the transport of preforms, in order to take them to temperature by heating prior to the blow molding step, it is necessary to provide a transfer device making it possible to take each preform by its neck (“gripping”) in order to move it into a heating zone, usually a heat-conditioning tunnel oven, in which zone the body of said preform is to be heated to the glass-transition temperature of the thermoplastic material, while remaining at a temperature below the crystallization temperature. 
         [0006]    To achieve this transfer, it is known practice to use transport devices furnished with gripping members which comprise a mandrel suitable for being engaged inside the neck of the preform (internal gripping) and which holds the latter simply by adhesion because of the presence of the forces of pressure and of friction. 
         [0007]    In document FR 2 706 876, in the name of the Applicant, a device for the internal gripping of preforms from a gripping head having a split-ring end is proposed. 
         [0008]    According to the same principle of internal gripping, it is known practice, as proposed in document FR 2 794 109 in the name of the Applicant, to produce a system for conveying preforms formed of a set of transport elements each comprising a gripping device furnished at its end with an annular split ring formed of several sectors; when the ring is engaged internally in the neck of a preform, the sectors that are forced radially outward by elastic means are capable of pressing on the inner cylindrical surface of the neck. 
         [0009]    Alternatively, it is also possible for the preform to be gripped on the outer face of its neck (external gripping) as described, for example, in document FR 2 882 963 in the name of the Applicant. 
         [0010]    When this preform enters the heat-conditioning oven, the preform undergoes a rotation on itself in order to allow an even heating over the whole outer surface of the preform. When a preform is loaded into the mold, both internally and externally, it is possible for the latter not to be axially aligned with the gripping head. 
         [0011]    In this case, because the preform is out of line and because of its rotary movement on itself, the body of the preform, and in particular its end, is capable of coming into contact with the heating lamps of the oven and of causing considerable damage by breaking them and also, sometimes, the preform can catch fire. 
         [0012]    Therefore, in order to prevent these incidents, such as the damaging of the oven heating lamps, it is necessary to provide, before they enter the oven, an operation of releasing of the preforms, that is to say an operation which consists in ejecting all the preforms that are capable of causing incidents when they pass into the heating oven. 
         [0013]    This releasing operation makes it possible, in a general manner, to prevent heating preforms which would have a design defect on entering the oven. 
         [0014]    Document FR 2 872 805 in the name of the Applicant describes a system for releasing preforms. 
         [0015]    Optical detection means are provided in order to determine which preforms are to be released and, under the effect of an appropriate command apparatus, such as a programmable controller, an ejection member intervenes in order to take away the preforms in question, which then fall into a recovery bin for example. 
         [0016]    This system, although giving full satisfaction, is nevertheless complex to apply and, above all, it hampers the production rates of the installation; specifically, the response time of the ejection member, for the purpose of the releasing, is relatively long. 
         [0017]    Moreover, because of the current production rates and therefore the speed of progress of the preforms, it is not possible to eject a single preform because, due to the response time of the pneumatic command means, several preforms are affected by the ejection member and, in general, routinely three successive preforms are on average ejected. 
         [0018]    Because of the cost of manufacturing the preforms, and in order to prevent the scrapping of preforms correctly placed on the gripping head or having no defect, it would be of particular value to produce a device for releasing preforms that allows the releasing of only the preform that is incorrectly secured or is incorrectly formed; said device being able to be applied at high rates of travel of the preforms. It would also be of particular value to produce a releasing system that could also be applied to the releasing of the preforms but and also to any type of hollow body. 
         [0019]    Moreover, because of this releasing of several preforms placed one beside the other, there are considerable free spaces in the preform-conveying chain (three successive gripping heads). These large spaces between the preforms, in the oven, disrupt the heating of the other preforms when they pass in front of the lamps of said oven; the result of this is defects in the evenness of heating of the preforms. 
         [0020]    Moreover, a current change in the context of the manufacture of preforms tends to reduce the dimensions of the collar, which becomes increasingly thin and increasingly wide, and hence more frequent gripping problems. 
         [0021]    Therefore, it would also be particularly advantageous to produce a releasing system that is not dependent on the size of a collar provided on the neck of the hollow body. 
       SUMMARY OF THE INVENTION 
       [0022]    The present invention therefore proposes to solve the various problems associated with the prior art with the aid of a system for releasing hollow bodies that makes it possible to release a single preform at high conveying rates, which system also does not depend on the dimensional characteristics of the collar of said preform. 
         [0023]    According to a first of its aspects, the present invention relates to an installation for conveying preforms to a processing unit such as a heating oven in which they are taken to an appropriate temperature in order subsequently to be formed by stretch-blow molding, which installation comprises:
       gripping members which are carried by an endless conveyor chain and which are each furnished with a gripping head in order to carry said preforms and in order to transfer them into said heating oven,   at least one detection system placed on the path of said preforms upstream of said heating oven, which detection system, such as a shape-recognition camera, selects the preforms that are likely to cause incidents in said heating oven, such as, for example, preforms the alignment of which does not correspond with that of the main axis of their gripping head,   means for detaching each selected preform from its gripping head,   an apparatus, such as a programmable controller, to command the ejection of the selected preform according to the information originating from said detection system,   means for retrieving the ejected preforms, and it comprises means for applying a pressure to the inside of the selected preform, on its bottom, and in particular a sufficient pressure to overcome the forces of adhesion between said selected preform and its gripping head, in order to detach them.       
 
         [0029]    Still according to the invention, the means capable of applying a pressure in the selected preform, on its bottom, consist:
       of a nozzle capable of spraying a jet of pressurized fluid at the bottom of said selected preform, and,   of an orifice in the shape of a bore arranged in the member and in the gripping head of said selected preform, said jet of pressurized fluid being administered when said bore passes in front of said nozzle.       
 
         [0032]    According to another stipulation of the invention, the bore, into which the pressurized fluid intended for the selected preform is injected, comprises an upstream aperture in the form of a funnel which has a narrowing of its cross section in the direction of the downstream aperture. 
         [0033]    Still according to the invention, the programmable controller used for commanding the injection of the pressurized fluid comprises a program arranged in order to establish an appropriate phase for the administration of said pressurized fluid to the selected preform, which phase extends for a period substantially greater than the time taken by said selected preform to pass in front of the spraying nozzle so as to ensure an injection time of said pressurized fluid into the bore that is long enough to ensure the ejection of said selected preform. 
         [0034]    The invention also relates to the method for releasing preforms while they are conveyed to the heating oven, in order to eliminate each preform capable of creating an incident during its passage in said heating oven, said method consisting:
       in monitoring the preforms which pass by, before they enter said heating oven, in order to detect, in said preforms, a flaw capable of causing incidents in said heating oven,   in detaching each preform recognized as undesirable from its gripping head, upstream of said heating oven, by applying an appropriate force to the inside of the undesirable preform, on its bottom, and in particular a sufficient force to overcome the forces of pressure and of friction that are applied between said undesirable preform and its gripping head,   in collecting the rejected preform in an appropriate container.       
 
         [0038]    Still according to the invention, the releasing method consists in separating the undesirable preform from its gripping head via an injection, in an appropriate bore of said gripping head, of a jet of pressurized fluid which penetrates the inner volume of said undesirable preform. 
         [0039]    According to another stipulation of the invention, the releasing method consists in anticipating the passage of the undesirable preform in order to trigger the injection of the pressurized fluid into said preform and it also consists in maintaining this injection of said pressurized fluid at least until the gripping head has passed in front of the nozzle for spraying said fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0040]    The present invention will now be described with the aid of an example that is only illustrative and in no way limiting of the scope of the present invention, and based on the following figure which represents a view in axial section of a device for transporting and gripping a hollow body according to the invention, which device, in cooperation with a blowing nozzle, makes it possible to carry out an operation of releasing of the preforms. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    In a simplified manner,  FIG. 1  represents a view in axial section of a device  1  for transporting a hollow body, such as a preform  2  made of thermoplastic material. The preform  2  has a body  3  extending in a substantially longitudinal manner and a neck  4  separated from the body  3  by a collar  5  extending in a substantially transverse direction. 
         [0042]    The transport device  1  comprises a gripping member  6  with a gripping head  7  capable of being secured to the preform  2 , and preferably, of being secured in a sealed manner to its neck  4 . 
         [0043]    Shown in  FIG. 1  is an “internal” gripping of the preform  2  and of the type described in the aforementioned document FR 2 794 109, that is to say that the gripping head  7  is inserted inside the neck  4  and therefore presses on the inner face of the neck  4 . 
         [0044]    However, it should be noted that the principle according to the invention applies equally to an “external” gripping of the preform  2 , that is to say when the gripping head  7  presses on the outer face of the neck  4 , in general pressing on the thread  8  of the neck  4 . 
         [0045]    According to the invention, the gripping member  6  has at least one bore  9  opening through the gripping head  7 . 
         [0046]    Therefore, according to a first application of the invention, the preform  2  is capable of being separated from the gripping head  7  by injection of a pressurized fluid (preferably compressed air at a pressure of the order of at least several bar, from 2 to 5 bar) in the bore  9  then opening into the closed volume  10  which is formed by the body  3  of the preform  2  secured to said head  7  and to do so whether the volume  10  is perfectly sealed or not. 
         [0047]    Alternatively, the inside of the preform  2  can be disinfected by injection of a disinfecting fluid into the bore  9  opening into the closed volume  10  which is formed by the hollow body  3  secured to said head  7 . 
         [0048]    In general, it is possible to inject any type of fluid through the bore  9  having an appropriate interaction and/or a desired processing action on the closed volume  10  which is formed by the hollow body  3  secured to the head  7 . 
         [0049]    The bore  9  is therefore designed passing through the gripping member  6 , in a substantially rectilinear manner inside said member  6 . This bore  9  is of generally cylindrical shape and is formed centrally in the member  6 , that is to say that considering the gripping member  6  defines a main gripping axis X-X, the axis X-X relative to which it is determined whether the preform  2  is correctly secured to the gripping head  7  and in line with the latter, then the bore  9  is substantially formed coaxially with the main gripping axis X-X. 
         [0050]    More precisely, the gripping member  6  comprises a mandrel  11  having said gripping head  7  and a gripping rod  12  to which said mandrel  11  is attached, preferably in a removable manner. 
         [0051]    The bore  9  is therefore formed and hollowed both in the gripping rod  12  and in the mandrel  11 . 
         [0052]    In order to limit the pressure losses during the injection of the pressurized fluid in the bore, said bore is designed to be substantially rectilinear inside the gripping member and it is advantageously of a general shape that is substantially cylindrical. 
         [0053]    More precisely, the bore  9  has an upstream aperture  13  for the injection of a fluid and a downstream aperture  14  in the gripping head  7 . The upstream aperture  13  has a narrowing of its cross section in the direction of the downstream aperture  14 . 
         [0054]    At the upstream aperture  13 , in order to allow a maximum quantity of fluid to be channeled, directed and to enter the bore  9 , it is therefore provided that the upstream aperture  13  has a larger cross section than the cross section of the majority of the bore  9 , and in particular larger than the cross section of the downstream aperture  14 . 
         [0055]    Even though what is shown in  FIG. 1  is a transport device  1  with a single central bore  9 , it is also possible to provide several bores  9 , for example placed concentrically with the main gripping axis X-X, or to provide a bore  9  that is divided into several secondary bores all opening into the gripping head  7 . 
         [0056]    The present invention also relates, according to a second of its aspects, and in a more general manner, to an installation for conveying hollow bodies  2  comprising a plurality of transport devices  1  which travel in line one after the other on an endless chain, not shown, of a type that is known per se, as can be seen, for example, in the aforementioned document FR 2 872 805. 
         [0057]    The conveying installation comprises means for injecting a jet of fluid such as a pressurized blowing fluid, for example at a pressure of between 2 and 5 bar, in the knowledge that, on this type of machine, a pressure is available of up to  40  bar, which means for injecting blowing fluid are directed toward a point of passage of at least one bore  9  formed internally in a transport device  1  when it travels on the endless chain. 
         [0058]    Preferably, the injection means take the form of a blowing nozzle  15  which is attached, secured to the chassis of the installation, not shown, which nozzle  15  is therefore directed toward a point of passage of the upstream aperture  13  of the bore  9  during the travel of the transport devices  1  associated with the endless chain. 
         [0059]    In order to prevent too great a loss of the fluid injected through the nozzle  15 , said nozzle  15  is situated facing a point of passage of the upstream aperture  13  of the bore of the transport devices  1  and it is only a very short distance from this upstream aperture  13 , for example of the order of a millimeter, or even a few millimeters. 
         [0060]    According to one application of the invention, the conveying installation may also comprise detection means such as a shape-recognition camera (not shown in the figure but of a type known per se), in order to reveal a defect of alignment of the body  3  of the preform  2  with the main gripping axis X-X and the axis of the gripping head  7 , whereby it is determined whether the preform  2  transported by said gripping head  7  must be separated from the latter by the injection of the pressurized blowing fluid. 
         [0061]    The command of this injection may be carried out via a programmable controller which receives and processes the information originating from the detection means mentioned above. 
         [0062]    This programmable controller comprises a program arranged to organize the command of the injection of the pressurized fluid into the preform that is recognized as having a defect that is likely to cause incidents in the oven for heating these preforms. 
         [0063]    The arrangement of the injection program comprises a phase that is appropriate for the administration of the pressurized fluid to the selected preform, which phase extends, for example, for a period that is substantially greater than the time taken by said selected preform to pass in front of the spraying nozzle so as to ensure an injection time of said pressurized fluid into the bore that is sufficiently long to ensure that said selected preform is ejected. 
         [0064]    This injection phase is also arranged to allow an anticipation of the triggering of the injection of the pressurized fluid into said undesirable preform facing the passage of said undesirable preform in front of the nozzle  15  for spraying said fluid and for maintaining this injection of said pressurized fluid at least until the gripping head  7  has completely passed in front of said nozzle  15  for spraying said fluid. 
         [0065]    The invention therefore makes it possible, in general, to produce a method for conveying a preform  2  secured to a transport device  1 , said method comprising a step of injection of a fluid through at least one bore  9  designed to pass through said transport device  1  and opening into the inner volume  10  of the body  3  of the preform  2  secured to said transport device  1 . 
         [0066]    According to another form of application of the invention, a disinfecting fluid is injected through the bore  9 . Alternatively, a pressurized fluid is injected, which makes it possible to separate the hollow body  2  from the gripping head  7 . 
         [0067]    Therefore, in summary, according to one application of the invention, it is detected, with the aid of the detection means, whether a preform  2  is out of alignment with the axis X-X or has a manufacturing defect. It is then determined, with the aid of the programmable controller and of appropriate programs and/or computing means, when the transport device  1  with this preform, and more precisely its bore  9 , will pass in front of the means  15  for injecting blowing fluid, in order then to command the injection of this fluid in order to release the preform (or any hollow body secured to a gripping head  7 ). 
         [0068]    The response time of the fluid injection means is markedly faster than the response times of the piston-based pneumatic means according to the aforementioned prior art, which makes it possible to release only one preform at a time. 
         [0069]    Therefore, according to a first application of the invention, the hollow body is capable of being separated from the gripping head by injection of a pressurized blowing fluid in the bore then opening into the closed volume that is formed by the hollow body secured to said head. 
         [0070]    Alternatively, the inside of the hollow body can be disinfected by injection of a disinfecting fluid into the bore opening into the closed volume that is formed by the hollow body secured to said head. 
         [0071]    More generally, the invention can find its place on an installation for transporting necked receptacles, where it is sometimes necessary to release the hollow bodies that have a defect, such as, for example, on leaving the preform blow molding unit.