Abstract:
Assembly for supporting and retaining sheets of glass, particularly in a machine for machining the sheets of glass; the assembly possesses a support structure, a plurality of suckers carried by the support structure to hold the sheet of glass in an unambiguous reference position on a horizontal plane and, for each sucker, a corresponding actuator for vertically displacing the suckers between a raised position and a lowered position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Italian Patent Application TO2000A 000663 titled “Metodo e Macchina di Molatura per la Lavorazione di Lastre di Vetro,” filed Jun. 30, 2000; the contents of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     In machines for machining sheets of glass, particularly in grinding machines, it is known practice to hold the sheets of glass in an unambiguous reference position during machining using a retention assembly comprising a plurality of sucker bodies which are arranged manually on a support surface defined by the machine base, their positions being modified whenever required as a function of the dimensions and type of the glass sheets to be machined. 
     Retention assemblies of the known type described above are not very satisfactory when it is necessary to machine a succession of sheets of glass whose dimensions differ from each other, not only because it takes a relatively long time to arrange the sucker bodies manually each time in the appropriate positions, but more importantly because of the obvious need to ensure that the machining tools do not interfere with the base or with the members used to support, position and retain the sheets of glass, independently of the dimensions and shape of the sheets. 
     SUMMARY 
     It is an object of the present invention to provide an assembly for supporting and retaining sheets of glass, particularly in a machine for machining the sheets of glass, by which the problems described above can be solved in a simple and economical manner. 
     The present invention provides an assembly for supporting and retaining sheets of glass, particularly in a machine for machining the sheets of glass. The assembly comprises a support structure and retention means carried by the support structure to keep the sheet of glass in an unambiguous reference position with respect to the support structure on a plane. The assembly also comprises actuator means for displacing the retention means between a raised position and a lowered position perpendicularly to the plane. 
    
    
     FIGURES 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying figures where: 
     FIG. 1 illustrates in perspective and schematically a preferred embodiment of the assembly for supporting and retaining sheets of glass, particularly in a machine for machining the sheets of glass, produced in accordance with the present invention; and 
     FIG. 2 is a plan view, with parts removed for the sake of clarity, of a detail of the supporting and retaining assembly shown in FIG.  1 . 
    
    
     DESCRIPTION 
     In FIG. 1,  1  indicates a grinding machine for machining sheets  2  of glass (partially illustrated), comprising respective rectangular perimeter edges  5  to be ground, which have dimensions which can optionally be different from one another. 
     The machine  1  comprises a base  8 , which supports a conveyor unit  9 , which, in particular, comprises a plurality of drive belts  10 , in order to transfer the sheets  2  in succession one after another, along a horizontal plane  11 , in a longitudinal horizontal straight direction A, from a loading station  12 , towards an unloading station  13 , through a work station  14 . 
     With reference to FIG. 2, the station  14  contains two straight longitudinal guides  15 , which are disposed on opposite sides relative to the direction A, and are integral with the base  8 , and four beams  20 ,  21 ,  22 ,  23 , which extend in a horizontal direction B, which is at right-angles to the direction A, in positions which are adjacent to one another. The beam  20  is connected integrally to the base  8 , in a position adjacent to the station  13 , whereas the beams  21 ,  22 ,  23  are connected to the guides  15 , such as to slide in the direction A, between the beam  20  and the station  12 , and are actuated by a movement unit  24 , which is controlled by an electronic command and control unit  25  (illustrated schematically). 
     The unit  24  comprises a motorized shaft  26  and an idle shaft  27 , each of which can rotate around its own axis, parallel to the direction B, and at its ends supports two sets of three wheels  30 ,  31 ,  32 , which are keyed in fixed positions, coaxially relative to one another, on the corresponding shaft  26 ,  27 , and have respective radii which increase from the wheel  30  to the wheel  32 , in order to define ratios of transmission which are different from one another. The unit  24  also includes two sets of three belts  34 ,  35 ,  36 , which extend in the lateral portions  37  of the base  8 , are each wound around a pair of wheels  30 ,  31 ,  32 , and comprise respective sections  38 ,  39 ,  40 , which are each connected integrally to the corresponding beam  21 ,  22 ,  23 . 
     Each of the beams  20 ,  21 ,  23 ,  23  supports a row of suckers  45 , which have an upper surface  46  to support the sheet  2  to be ground, constitute part of a retention unit  44 , which is controlled by the unit  25 , in order to retain the sheet  2  itself on the surface  46  during grinding, and are connected to a suction pump (not illustrated) by means of respective pneumatic control valves (not illustrated). Each sucker  45  supports a lower rod, which is connected to a pneumatic cylinder, which is integral with the corresponding beam  20 ,  21 ,  22 ,  23 , and defines together with the corresponding rod an actuator  47  (illustrated schematically), which is controlled by the unit  25 , in order to displace the suckers  45  between a raised position, in which the sheet  2  is disposed in a position spaced from the belts  10  in order to be ground, and a lowered rest position, in which the sheet  2  is disposed on the belts  10 , in order to be transferred from and to the station  14  on the plane  11 . 
     The station  14  accommodates a positioning unit  50 , which is controlled by the unit  25 , in order to dispose each sheet  2  to be processed in a reference position on the plane  11 , relative to the base  8 , and comprises a retractable reference stop (not illustrated) of a known type, which is supported by the base  8 , and an alignment device  51 , which is supported by the lateral portion  37 . In particular, the device  51  comprises a thrust unit  52 , which is delimited by a surface  53 , parallel to the direction A, and is actuated by an actuator  54 , by means of interposition of a four-bar chain lever system  55 , in order to displace the surface  53  parallel to itself in the direction B, against one side  5   b  of the sheet  2 , thus aligning the side  5   b  itself in the direction A. 
     As illustrated in FIG. 1, the station  14  contains a frame  56 , which supports four grinding heads  74 ,  75 ,  76 ,  77 . 
     The grinding heads  74 ,  75 ,  76 ,  77  are actuated by respective motors (not illustrated), which are independent from one another, are accommodated in the frame  56 , and are controlled by the unit  25 , in order to displace the heads  74 ,  75 ,  76 ,  77  themselves simultaneously along respective transverse paths which are incident relative to one another, defined by respective guides, such as to grind respective sides  5   a,    5   b,    5   c,    5   d  of the edge  5 , which are transverse relative to one another, and consecutive. 
     In use, the sheets  2  are loaded one after another on the station  12 , by setting on the unit  25  the parameters relative to the perimeter dimensions to be obtained for the sheets  2  to be processed. The parameters can be set manually for each of the sheets  2 , or they can be entered together with the number of consecutive sheets  2  which have the same dimensions, or they can be taken from a data base which is stored and resident in the unit  25 , or in a remote computer (not illustrated), which is connected to the unit  25  itself. It is understood that the machine  1  comprises sensors (not illustrated), which allow the unit  25  to detect the type of sheet  2  present on the station  14 , and check the accuracy of the parameters set. 
     During transfer of the sheet  2  to be processed, towards the station  14 , the unit  25  controls actuation of the shaft  26 , in order to make the belts  34 ,  35 ,  36  run at different linear speeds from one another, and such as to move the beams  21 ,  22 ,  23  apart from one another progressively, on the basis of the dimensions of the sheet  2 , keeping the beams  20 ,  21 ,  22 ,  23  equally spaced. 
     When the sheet  2  reaches the station  14 , the unit  25  firstly controls the unit  50 , in order to position the sheet  2  in an unambiguous reference position, and then the unit  44 , in order to actuate only the suckers  45  covered by the sheet  2 . Subsequently, the unit  25  actuates the actuators  47  associated with the suckers  45  which are retaining the sheet  2 , such as to bring the sheet  2  itself into the raised machining position. 
     While these operations are being carried out on the sheet  2 , the unit  25  commands positioning of the head  75 ,  74 ,  76 ,  77  with respect to the base  8  in respective corresponding points for commencement of machining, each at a vertex of the edge  5 , in order to adapt the grinding cycle to the dimensions of the sheet  2 . Simultaneously, the configuration of the grinding wheels of each head  74 ,  75 ,  76 ,  77  is regulated by the unit  25 , on the basis of the thickness of the sheet of glass  2  to be ground. 
     During the grinding operations, the heads  74 ,  75 ,  76 ,  77  are displaced in an unambiguous direction of travel or advance of the edge  5 , following one another without interfering with one another. The point or vertex of completion of machining of each head  74 ,  75 ,  76 ,  77  coincides with the point or vertex of commencement of machining of the following side  5   a,    5   b,    5   c,    5   d.  When the grinding has been completed, the actuators  47  are controlled such as to take the suckers  45  into their lowered position, and the suckers  45  themselves are deactivated in order to release the sheet  2 , which is then transferred towards the station  13 . The subsequent sheet  2  is already on the station  14 , in particular in the case in which the sheet  2  which is being processed is smaller than the station  14  itself, and is transferred such as to initiate a new cycle on the basis of the parameters entered in the unit  25 . 
     It will be clear from the above that the base  8 , the suckers  45 , the actuators  47  and the units  24 ,  25  and  50  are part of a supporting and retaining assembly  80  that is extremely flexible since it is capable of holding sheets  2  of dissimilar dimensions firmly and precisely and machining the sheets  2  without difficulties, independently of their dimensions. 
     This is due to the fact that the raising, by the suckers  45 , of the sheet  2  to be ground prevents interference of the heads  74 ,  75 ,  76 ,  77  against the base  8  and with any suckers  45 , or with other devices for positioning the sheets  2 , which are positioned outside of the projection of the edge  5  onto the plane  11 . 
     Moreover, the unit  24  makes it possible to adapt the position of the suckers  45 , and to render stable the positioning and retention of sheets  2  which have dimensions different from 
     Moreover, the unit  24  makes it possible to adapt the position of the suckers  45 , and to render stable the positioning and retention of sheets  2  which have dimensions different from one another. 
     Lastly, owing to the features of its construction, the assembly  80  is extremely simple and compact. 
     Finally, it is apparent from the foregoing that modifications and variants can be made to the assembly  80  described, which do not depart from the field of protection of the present invention. 
     In particular, the units  24  and  50  could be different from those illustrated and described, and the assembly  80  could be used in a glass-sheet machining machine different from the machine  1  described and illustrated by way of example. 
     Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained in this disclosure.