Abstract:
A method of detecting the positions occupied on a pallet by stacks of blanks arranged on the pallet in a number of superimposed layers and, in each layer, in a number of side by side rows, to enable automatic pickup of each stack and supply of the stack to a cigarette packing machine; the method including the step of moving a sensor along each row to determine a lateral contour of the row close to a bases of the relative stacks.

Description:
[0001]    The present invention relates to a method of detecting the position of stacks of blanks for supply to a cigarette packing machine.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the packing of cigarettes, stacks of blanks, each comprising a number of superimposed blanks, are fed individually to the input of a packing machine.  
           [0003]    Normally, the stacks of blanks are originally arranged on a pallet in a number of superimposed layers separated by rigid boards, and in a number of side by side rows in each layer; the pallet so loaded is located in a given standard position close to the input; and the packing machine is normally equipped with an automatic transfer unit by which each stack is located, is removed from the relative row in the relative layer, and is fed to the input.  
           [0004]    Known automatic transfer units normally comprise a pickup head for removing each stack off the pallet, and which is associated with an at least four-axis operating machine for imparting to the pickup head the movements required to pick up the stack. Known automatic transfer units also comprise a sensor device, normally movable with the pickup head, for determining the position and orientation of the stack, and for enabling a central control unit to accurately control the pickup movements. In this connection, it should be pointed out that the location of each stack is a “final location”, seeing as how the central control unit already knows from the outset the shape and size of the blanks, a presumed (standard) position of the pallet with respect to the operating machine, a presumed distribution of the layers of stacks on the pallet, a presumed position and orientation of each row of stacks in the relative layer and of each stack in the relative row, and therefore a presumed position and orientation of each stack on the relative board.  
           [0005]    Before each stack is removed (obviously from the free top layer on the pallet), the sensor device takes a first reading to determine the height of the board supporting the layer containing the stack to be removed (this is normally done once for each layer, or may even be dispensed with if the operating machine is designed to move the pallet vertically so that the board supporting the stack to be removed is always set to a given fixed height), and then takes a second reading to determine the position and orientation of the stack on the board.  
           [0006]    Using known sensor devices, the second reading is made by moving the sensor device in an observation plane, parallel to the plane of the board supporting the stack and over the top of the stack, and about the presumed position of the projection of the stack in the observation plane, and by determining the position of at least two (but normally three) conspicuous points of the top blank in the stack.  
           [0007]    Taking the second reading as described above involves several drawbacks on account of the position and orientation of the stack being determined on the basis of the position and orientation of the top blank, i.e. without taking into consideration the possibility, as often occurs, of the stack being deformed, so that the horizontal position of the top blank no longer corresponds, when the stack is removed, to the position of the bottom blank, which is the one normally engaged by the pickup head to supply the stack to the packing machine.  
           [0008]    In other words, the method employed by known sensors of the type described above may result in mislocation of the stack, and also in possible damage to the stack by the pickup head.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a method of detecting the position of stacks of blanks for supply to a cigarette packing machine, designed to eliminate the aforementioned drawbacks.  
           [0010]    According to the present invention, there is provided a method of detecting the position of stacks of blanks for supply to a cigarette packing machine; said stacks having respective bases resting on a plane; and the method comprising the step of moving a sensor along a line parallel to said plane and extending alongside said stacks in a given direction to determine the position and orientation of each said base with respect to said line by determining a contour of a lateral edge of at least one given blank, in each said stack, located close to the relative said base. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 shows a plan view, with parts in section and parts removed for clarity, of a preferred embodiment of a unit implementing the method according to the present invention;  
         [0013]    [0013]FIG. 2 shows a larger-scale side view, with parts removed for clarity, of a detail in FIG. 1;  
         [0014]    [0014]FIG. 3 shows a larger-scale view of a FIG. 1 detail in two different positions; 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    With reference to FIGS. 1 and 2, number  1  indicates as a whole a unit for transferring stacks  2  of blanks  3 , and which constitutes a loading unit for loading a cigarette packing machine A.  
         [0016]    Stacks  2  comprise respective numbers of superimposed blanks  3 , and are arranged on a pallet  4  in a number of superimposed layers  5 —of which only the top layer  5  is shown—separated by respective substantially rectangular, horizontal boards  6  normally made of sheet material, and of which only the board  6  supporting the top layer  5  is shown for the sake of simplicity.  
         [0017]    Stacks  2  in each layer  5  are equioriented, and are arranged side by side on relative board  6  to define a first number of rows  7  and a second number of rows  8  perpendicular to rows  7 , so that each stack  2  is located on relative board  6  at the intersection of a relative row  7  and a relative row  8 . In actual use, pallet  4  is located as far as possible in a standard position within a given loading region Z beneath transfer unit  1 , and with rows  7  and  8  as parallel as possible to two given horizontal axes X and Y.  
         [0018]    Unit  1  comprises an articulated arm  9  in turn comprising an arm  10  fitted to a powered vertical shaft  11  to rotate about a fixed axis  12  coaxial with shaft  11  and close to the intersection of axes X and Y, and a further arm  13  hinged at one end to a free end of arm  10 , and rotated, with respect to arm  10  and by a known transmission not shown, about an axis  14  parallel to axis  12 . Arm  13  is the same length as arm  10  and is fitted on the free end with a powered swivel shaft  15  having an axis  16  parallel to axis  12 , and to which is suspended a pickup head  17 . Of this is only shown, for the sake of simplicity, a portion defined by a detecting device  18  comprising an optical sensor  19 , e.g. a laser sensor for emitting a beam  20  which, on encountering a point on a surface, is reflected back to cause sensor  19  to emit a signal of an intensity proportional to the distance between the point and sensor  19 .  
         [0019]    Pickup head  17  is of known type, may be fitted to articulated arm  9  at any point within loading region Z, and can be oriented by shaft  15  to selectively grip stacks  2  in top layer  5 , and feed stacks  2  successively to the input (not shown) of a packing unit (not shown) of packing machine A.  
         [0020]    As shown in FIG. 2, each blank  3  is positioned on pallet  4  with a longitudinal axis of symmetry  21  (FIG. 3) of the blank substantially parallel to relative row  7 ; and the peripheral edges of the blank, when observed laterally in any direction parallel to the plane of blank  3  and substantially parallel or substantially perpendicular to axis of symmetry  21 , have at least two singular points  22 .  
         [0021]    In actual use, and with reference to FIGS. 2 and 3, once pallet  4  is set in the standard position beneath transfer unit  1 , articulated arm  9  is activated to so position axis  16  as to pass through a point 0 at the intersection of two lines  23  and  24 , which are parallel to axes X and Y respectively, are located outwards of top layer  5  on pallet  4 , and are substantially parallel to and face respective lateral edges of a number of blanks  3   a , each forming part of a respective stack  2  in top layer  5 , and each lying in an observation plane P defined by lines  23  and  24  and located a given, relatively small distance from the bottom blanks  3   b  in stacks  2 .  
         [0022]    A relative vertical movement between articulated arm  9  and pallet  4  is then effected (by vertically moving pallet  4  and lines  23  and  24  with respect to articulated arm  9 , or articulated arm  9  with respect to pallet  4  and lines  23  and  24 ) to so position sensor  19  as to emit a beam  20  coplanar with observation plane P. And finally, pickup head  17  is rotated about axis  16  to orient beam  20  towards pallet  4  and in a direction parallel to line  23 .  
         [0023]    At this point, sensor  19  is moved along line  24  so that, of each blank  3   a  in stacks  2 , beam  20  sweeps an edge  25  oriented in a direction substantially parallel to line  24  and perpendicular to relative longitudinal axis of symmetry  21 .  
         [0024]    As a result of the sensor traveling along line  24 , a known central control unit (not shown), connected to sensor  19 , determines, along each edge  25  of each blank  3   a  in an outer row  8  facing sensor  19 , at least two singular points  22 , of which it comes to know the respective distances from line  24  and therefore, given the movement of sensor  19  along line  24 , the precise positions in observation plane P. By working out the difference between the distances of singular points  22  of each blank  3   a  from line  24 , the central control unit (not shown) is able to determine (FIG. 3 b ) any angle G (which will only be other than zero if the orientation of stacks  2  is other than the standard one shown in FIG. 3 a ) formed between the longitudinal axis  21  of each blank  3   a  and line  23 , and therefore the actual position and orientation in plane P of each blank  3   a  in the outer row  8 .  
         [0025]    Since, given the minimum distance between each blank  3   a  and relative blank  3   b , the position of each blank  3   a  with respect to relative blank  3   b , which is in a substantially fixed position on relative board  6 , is assumed to be unaffected by any deformation of relative stack  2 , the central control unit (not shown) is able, at this point, to guide pickup head extremely accurately to pick up the relative stack  2 .  
         [0026]    The above considerations also apply in the event sensor  19  is moved along line  23 , or along a line (not shown) parallel to line  24  and lying in observation plane P, but on the opposite side of pallet  4  to line  24 .  
         [0027]    In which two cases, the central control unit (not shown) will determine the positions of further singular points  22  along edges  26  and  27  of blanks  3   a  respectively.