Patent Publication Number: US-6655678-B2

Title: Suction gripping unit

Description:
This application is a continuation-in-part of Ser. No. 09/264,933 filed Mar. 9, 1999 abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a suction gripping unit. 
     In the following description, specific reference is made purely by way of example to the cigarette packing sector, and in particular to a suction gripping unit for supplying blanks on a cigarette packing machine. 
     Cigarette packing machines are known to employ a suction gripping unit for feeding blanks successively between a blank pickup station, located at a blank store, and a supply station where the blanks are transferred to respective seats on a packing wheel. 
     Known suction gripping units such as those described in U.S. Pat. Nos. 4,513,957, 3,649,002 and 5,511,772 comprise a gripping head having a cavity connected through a conduit to a vacuum source and a valve for selectively interrupting the communication between the cavity and vacuum source. Some of the known units are also provided with venting holes for venting the cavity when the gripping head has to release the blank. The known units are not satisfactory when the blanks have to be transferred to a cigarette packing machine with an output close to twenty packets per second. For achieving that output the unit should permit a rapid alternation of vacuum and atmospheric pressure inside the cavity. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a suction gripping unit designed to eliminate the aforementioned drawbacks, and which in particular is cheap and easy to produce. 
     According to the present invention there is provided a suction gripping unit comprising at least a gripping head rotating about an axis and having at least one cavity defined in said suction head; suction means for creating a vacuum inside said cavity, said suction means comprising a conduit communicating with said cavity, a suction connected to said conduit and a control valve located between said pump and said cavity movable between an open position in which said cavity is in communication with the pump and in a closed position in which said valve interrupts the communication between the cavity and the pump; wherein the suction gripping unit comprises at least a venting hole in close proximity to the valve for automatically venting said cavity when said valve is in the closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a cross section, with parts removed for clarity, of a preferred embodiment of the unit according to the present invention; 
     FIG. 2 shows a larger-scale section along line II—II in FIG. 1 of a FIG. 1 detail in two different operating positions; 
     FIG. 3 shows a section along line III—III in FIG. 2; 
     FIG. 4 is similar to FIG.  2  and shows a FIG. 2 detail in a further operating position; 
     FIG. 5 shows a cross section of a portion of a further preferred embodiment of the gripping unit according to the present invention in a first operating position; and 
     FIG. 6 shows a cross section of the gripping unit of FIG. 5 in a second operating position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a continuous packing machine comprising a powered packing wheel  2 , which rotates continuously (anticlockwise in FIG. 1) about a respective axis (not shown) perpendicular to the FIG. 1 plane, and in turn comprises a number of hollow, equally spaced, peripheral seats  3  (only one shown) for successively receiving respective prefolded blanks  4  of cardboard or similar material Machine  1  also comprises a store  5  for a stack  6  of blanks  4 ; and a suction gripping unit  7  interposed between a pickup station S 1  at the open end  8  of store  5  and a supply station S 2  at packing wheel  2 , and for extracting blanks  4  from end  8  and feeding them successively to respective seats  3 . 
     Gripping unit  7  comprises a powered roller  9  rotating continuously clockwise in FIG. 1 about a respective fixed central axis  10  parallel to the axis (not shown) of wheel  2  and perpendicular to a longitudinal axis  11  of store  5 . Roller  9  comprises an inner chamber  12  connected by a conduit  13  to a suction pump  14 , preferably a so-called “side-channel” pump, for creating in chamber  12  a vacuum with respect to the atmospheric pressure outside. 
     Roller  9  supports a number of pneumatic gripping heads  15  distributed about axis  10  and connected to roller  9  via the interposition of respective arms  16 . As shown more clearly in FIG. 2, each head  15  is substantially in the form of a plate, which is connected on one side to respective arm  16 , and is defined on the other side by a gripping surface  17  in which a cavity  18  is defined by an annular edge  19  and connected to chamber  12  by a respective conduit  20  formed along respective arm 
     In the embodiment shown, gripping surface  17  is substantially defined by the top surface of edge  19 . 
     At a joint  21  connecting conduit  20  to respective head  15 , each conduit  20  houses a valve  22  for controlling conduit  20 , i.e. for opening or closing conduit  20  to connect or disconnect it from respective cavity  18 . A through hole  23  is formed in each head  15  so that respective cavity  18  communicates permanently with the outside atmosphere. 
     Each valve  22  is a known mechanical valve, and comprises a head  24 ; an annular seat  25  engaged by head  24  and formed at respective joint  21 ; and a control rod  26 , which is fitted in axially-sliding manner to two perforated supporting walls  27  (FIG. 3) housed inside conduit  20 , and is moved axially, by an actuating device  28  and in a radial direction with respect to axis  10 , between an open position (FIG. 2 a ) in which cavity  18  is connected pneumatically to conduit  20  and therefore to chamber  12 , and a closed position (FIG. 2 b ) in which cavity  18  is isolated pneumatically from conduit  20  and therefore from chamber  12 . 
     Actuating device  28  comprises a body  29 , which is fitted to the end of respective rod  26  opposite the end connected to respective head  24 , and is fitted to roller  9  so as to slide, together with rod  26 , in a radial direction with respect to axis  10  and so move rod  26  between said open and closed positions. Actuating device  28  comprises a spring  30 , which is located radially with respect to a wall  31  defining chamber  12  and coaxially with respect to respective rod  26 , and is compressed between a respective wall  27  and body  29  to normally maintain rod  26  in said closed position. 
     Actuating device  28  also comprises a cylindrical rod  32 , which is fitted to body  29  so as to slide longitudinally, with respect to body  29 , along a respective axis  33  parallel to axis  10 , and is fitted in rotary manner at one end with a tappet roller  34  cooperating with a fixed cam  35 . Cam  35  is so formed that, as roller  9  rotates about axis  10 , body  29 , and therefore respective rod  26 , of each head is is moved, in a radial direction with respect to axis  10 , between said open position and said closed position. 
     The movement of rod  32  along axis  33  is controlled by an actuating device  36  for cutting off control of respective valve  22 , and which moves rod  32  between a work position (FIG. 2) in which roller  34  engages cam  35 , and a rest position (FIG. 4) in which roller  34  is detached from cam  35 . Actuating device  36  comprises a known magnetic actuator  37  which, when energized, moves rod  32  along axis  33  from said work position to said rest position; and a spring  38  located coaxially with rod  32  between body  29  and roller  34  to normally maintain rod  32  in said work position. 
     As shown in FIG. 1, each seat  3  is formed in an outer surface  39  of a respective head  40  opposite an inner portion of head  40  connected to wheel  2  so as to oscillate, with respect to wheel  2 , about a respective axis  41  parallel to axis  10  under the control of a known cam-rocker arm control device not shown. Each seat  3  comprises two lateral surfaces  42  sloping towards each other and towards a bottom surface  43  through which are formed a number of holes  44  by which a known suction device (not shown) communicates externally. 
     The operation of one gripping head  15  will be described with reference to FIG.  2 . 
     To retain a blank  4  on gripping surface  17  of head  15 , surface  17  is brought into substantial contact with blank  4 , which closes respective cavity  18  to define, with cavity  18 , a suction chamber in which a vacuum (with respect to atmospheric pressure) is formed by closing respective valve  22  and so connecting said suction chamber to chamber  12  in which pump  14  maintains a constant vacuum. 
     The load losses caused by through hole  23  connected permanently to the outside pose no serious problems, by pump  14  being capable of compensating even relatively high load losses, such as those induced by hole  23 . 
     To release blank  4 , atmospheric pressure is restored inside said suction chamber automatically, by virtue of hole  23 , by simply closing valve  22 . 
     The relatively small volume of the suction chamber provides for achieving extremely rapid response of gripping head  15 , which at the same time is cheap and easy to produce by comprising only one valve  22 . 
     Operation of gripping unit  7  will be described with reference to FIG. 1, with reference to one gripping head  15 , and as of the instant in which head  15 , having released a blank  4  inside a respective seat  3  at supply station S 2 , is moved by the rotation of roller  9  towards pickup station S 1  to withdraw another blank  4 . 
     Between supply station S 2  and pickup station S 1 , valve  22  of head  15  is maintained in said closed position. 
     As it is fed through station S 1 , gripping head  15  withdraws the blank  4  contacting end  8  of store  5  and retains it by suction on gripping surface  17 . More specifically, at a given point in its movement, gripping head  15  is positioned with gripping surface  17  substantially contacting the blank  4  contacting end  8 ; and, just before said position is reached, actuating device  28  moves valve  22  into said open position to connect cavity  18  to chamber  12  and, via cavity  18 , activate the suction force causing the blank  4  contacting end  8  to adhere to gripping surface  17 . 
     As roller  9  rotates, head  15  leaves pickup station S 1  in which blank  4  has been withdrawn, and is fed to supply station S 2  where blank  4  is fed to a respective seat  3  on a respective head  40 . 
     At station S 2 , head  40  is oscillated in known manner about respective axis  41  by said known cam-rocker arm device (not Shown) so as to remain a given length of time facing gripping surface  17  of head  15 . During this time, head  15  is inserted inside seat  3  so that gripping surface  17  is positioned substantially contacting surface  43 ; and, just before said position is reached, actuating device  28  moves valve  22  into said closed position to cut off the suction through cavity  18 , and the suction through holes  44  in surface  43  is activated to release blank  4  inside and adhering by suction to seat  3 . 
     As shown in FIG. 1, the insertion of head  15  inside respective seat  3  provides for folding blank  4  into a U along respective known preformed bend lines (not shown) as blank  4  is fed into seat  3 . 
     The above operations are repeated cyclically. 
     To prevent a blank  4  from being fed into a seat  3 , the respective head  15  must be prevented from withdrawing a blank  4  as it travels through station S 1 , which function is provided for by actuating device  36  of head  15 . More specifically, throughout the passage of head  15  through station S 1 , respective magnetic actuator  37  is maintained energized to detach roller  34  from cam  35  and so prevent respective valve  22  from being opened, so that, in the absence of suction, gripping surface  17 , as it travels through station S 1 , is brought into contact with, but fails to withdraw, the blank  4  at end  8 . 
     In a further embodiment not shown, cavity  18  is divided into a number of elementary cavities separated and maintained pneumatically connected to one another by perforated sections; and surface  17  is defined by the top surface of edge  19  and by the top surfaces of said sections to provide a larger supporting surface for blank  4 . 
     In yet a further embodiment not shown, cavity  18  communicates permanently with the outside atmosphere via a number of small-diameter through holes  23 . 
     With reference to FIGS. 5 and 6, with reference numeral  107  is shown a gripping unit, wherein all such parts of the gripping unit  107 , which are identical with or clearly analogous to the parts of the previous embodiment will be designated by the same reference numeral plus 100. 
     The gripping unit  107  of FIGS. 5 and 6 has a plurality of gripping heads  115  arranged about a roller  109  rotating about an axis  110 . Each gripping head is supported by a radial arm  116  and connected to the chamber  112  by a conduit  120 , which extends partially inside the arm  116  and partially between a front wall  145  of the powered roller  109  and a wall  146  located in the chamber  112 . Conduit  120  houses a valve  122  for controlling conduit  120 , i.e. for opening or closing conduit  120  to connect or disconnect the cavity  118  from the chamber  112 . 
     Each valve  122  comprises a head  124 , an annular seat  125  supported by walls  145  and  146 , an O-ring  147  fitted to the annular seat  125 , and a control rod  126 , which extends along an axis  148  parallel to axis  10  and reciprocated along axis  148  by an actuating device  128 . Control rod  126  is supported by a passage in the wall  146 , and supports an annular ring  149  and the head  124 . 
     Actuating device  128  comprises a spring  130  arranged between wall  146  and ring  149  for keeping the valve  122  in the open position, and a tappet roller  134  at one distal end of the rod  126  and a fixed cam  135  located inside the chamber  112  and cooperating with the tapped roller  134  for closing the valve  122  as shown in FIG.  6 . 
     The gripping unit  107  comprises a venting hole  123  located along conduit  120  in front of the valve  122  and substantially coaxial with the seat  125 . The venting hole  123  is made through the front wall  145 , is enclosed by an annular projection  150  of the front wall  145  supporting an O-ring.  151 , and is closed by a leaf spring  152  mounted on to the external surface of front wall  145  and urged against the O-ring  151 . Control rod  126  has a distal end  153  opposite to the end provided with the tappet roller  134  and cooperating with the leaf spring  152  in order to push away the leaf spring  152  from the conduit  120  in order to open the venting hole  123  as soon as the rod  126  moves the valve head  124  toward the closed position. In the open position of the valve  122 , the distal end  153  is located in closed proximity to the leaf spring  152  so as to the control rod  126  when pushed in the right direction in FIG. 5 first open the venting hole  123  and then closes valve  122 . Such a sequence permits re-establishing the atmospheric pressure in the cavity  118  as soon as the venting hole is open because the venting hole  123  neutralizes the vacuum generated through the valve  122  still partially open.