Abstract:
An upper jaw of the gripper is provided posteriorly to a fulcrum shaft, with opposed portions for a double effect cooperation with an eccentric element keyed on the shaft which controls the orientation of the gripper. The opening and closure movement of the gripper, in an appropriate phase of the distributor (D) of the film, is ensured by the cooperation of a roller of an action lever of the fulcrum shaft with a cam-function lever, horizontally fulcrumed with one end of a support fixed to the frame of the machine and provided on the other end with a trigger and hook device which, when actuated by the roller, deactivates and allows the lifting of the lever via an elastic return device. Subsequent to the lifting, the gripper closes and grasps the film from the distributor. During the opposite displacement run of the gripper from the distributor, a cam fixed to the carriage with the gripper, co-operates with a lateral arm of the lever with the function of cam, and causes the lowering of the latter in the original position, with re-loading of the relative trigger and hook device.

Description:
FIELD OF THE INVENTION 
   The present invention relates to functional and constructive improvements in a movable gripper for machines intended to package products with a stretchable film. 
   BACKGROUND OF THE INVENTION 
   Machines for packaging products with stretchable film include the one described in the Italian patent 1.262.267, belonging to the same applicant, herein incorporated by reference. In these type of machines, the packaging film is supplied by a fixed and horizontal distributor which is comb-shaped and usually placed under horizontal rollers which fold the last edge of the portion of the packaging film under the product previously retained by the distributor, while the same product is translated to the discharge portion of the machine by a pusher installed on the posterior folder. Under this posterior folder a comb-shaped gripper is installed, in an oscillating manner, parallel to the same folder, complementary to the combs of the distributor, which is oriented toward the distributor&#39;s comb, with its teeth and by suitable means, can be opened or closed and can be carried from a horizontal, raised position, to a lowered and downwardly inclined position, and vice-versa. When the carriage with the posterior folder performs its approach run to the distributor, the gripper is initially in a raised position and the gripper is closed. Then, the gripper is opened and downwardly inclined in such a manner to fit the teeth of the comb distributor which has left the last edge of the packaging film of the product being discharged and now is supporting the new head of the film which will envelope the following product. At the end of the run of the posterior folder, the gripper closes and grasps the head of the film supported and guided by the distributor. When the posterior folder performs the displacement run from the distributor, the gripper remains closed and initially in a low position to extract the film from the distributor. Subsequently, the gripper is raised horizontally to be pre-arranged for the repetition of a new packaging cycle. 
   In the gripper according to the prior art, the lower jaw is pushed upwardly by a flat spring which results in difficulty during pre-loading. Difficulties include undesired friction which may lead to possible poor reliability. 
   In the gripper according to the prior art, in all instances, the opening oscillation movement of the lower jaw, is ensured by the co-operation of a lever keyed on the fulcrum shaft of the jaw, with an oscillating cam pre-arranged on an axle parallel to the working run of the gripper and which is normally maintained in the vertical position by elastic means. When the lever arrives in the final portion of the profile of the cam, the lever comes up against a recess (step) which causes the gripper to close on the film distributor and the end of the same lever is positioned on a laterally inclined portion of the cam, so that when the gripper is moved away from the distributor, the lever causes the cam to oscillate or pivot around its own fulcrum. This action causes remarkable sliding friction between the pin of the lever arm and the cam, makes the active positioning of the same cam unstable and it is not well-suited for the speed and for the high working cycles of the packaging machine. 
   In all prior devices, the raising and lowering movement of the gripper is ensured by the co-operation of an extension beyond the fulcrum of the stem of the upper jaw of the same gripper, with a little and overhanging cam provided with two consecutive eccentricities, placed with an angular distance between them of about—30–45° and therefore with a steep and short fall between the two eccentricities. This configuration causes concentrated and quick wear of the cam and it is not suitable for the speed and the high working cycles of the packaging machine. Further, the gripper can freely upwardly oscillate. 
   SUMMARY OF THE INVENTION 
   One object of the present invention is to overcome the drawbacks of prior packaging machines with the use of a helical pin spring. 
   Another object of the present invention is the use of new cam which provides a more reliable packaging machine which does not have the sliding frictions of prior machines. 
   A third object of the present invention is to overcome the drawbacks of prior machines by pre-arranging the gripper for a double-effect co-operation with opposite points of a single-eccentricity cam, where this cam acts by means of rolling friction and where this cam can be actuated with oscillations up to about 120–180°, with a gradual progression, all not obtainable with the prior art machines. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the improvements which are referred to and the advantages deriving therefrom, will appear better evident from the following description of a preferred embodiment of the same, made by way of a non-limiting example, with reference to the figures of the attached sheets of drawings, in which: 
       FIG. 1  is a plan view from the top and with portion in section of the gripper which is referred to, taken in the stretching end run position of the film in the packaging station; 
       FIG. 2  is a top view of the posterior and middle portion of the gripper connected to the opening-closing and lifting-lowering shafts of the same gripper; and 
       FIGS. 3 and 4  are lateral views and with portions in section of the gripper respectively in the upper and closed position, when it arrives at the level of the opening means and at the end of the co-operation run with the opening means, when it stops to grip the film from the distributor and to begin the reverse translation run, to stretch a new portion of film in the packaging station. 
   

   DETAILED DESCRIPTION 
   In  FIGS. 1 and 3 , carriage  1  carries the posterior folder, the pusher and the mobile gripper for the clamping of the film. The carriage  1  has, for example, a flat conformation, which has a lower ribbed portion, and substantially rectangular shape. Small wheels  2  are provided at the ends of the carriage  1 , which run in corresponding horizontal slots, (not shown), fixed to the frame of the machine and parallel to the rectilinear actuator  3  visible in  FIG. 3 , driven by a step motor controlled by a computer of the machine and to the movable element of which is connected in a known manner. With numeral references  4 ,  4 ′ there are shown the pairs of slide cams which run in corresponding horizontal guides, of known type, which act on the lateral grippers of the packaging machines and which are not further described as such a description is unrelated to the understanding of the present invention. 
   The front of the carriage  1 , which is turned in the discharging direction of the packaged product, is provided with a wide symmetrical recess  5  which is occupied by the flat and posterior folder  6 , shown with dash and dot line of  FIG. 1 , fixed with screws  7  and made with any suitable and/or, if required, treated material in such a manner to have a low coefficient of friction with respect to the packaging film and whose anterior edge  106 , which is conveniently projecting from the carriage  1  and which is parallel to this one, is suitably bevelled. The carriage  1  carries integral, under the folder  6  and in median position, a small raised wall  101  which has a ribbed surface, provided with a pair of through holes to which may be pressure coupled the connection appendices of a little rubber cap, downwardly open, which is partially surmounting the folder  6  and which acts like a yielding hold up or contrast means to posteriorly push the product during the finishing phase of the packaging and during the translation toward the discharging station of the machine. 
   The carriage  1  carries integrally, in middle position and projecting in a direction which is opposite to the folder  6 , a small horizontal and annular appendix  201 . Lateral of the appendix  201  rotatably support a first shaft  10  with small bushings  9 . The first shaft  10  is horizontal and parallel to the anterior edge  106  of the folder. On the portion of the shaft  10  which is placed inside of the support ring  201 , there are rotatably assembled, with small bushes  11 , the lateral walls of the forked terminal end  112  of the stem  212  of the upper, ribbed and flat jaw  12  of the gripper P. The flat jaw  12  has, in plan view, a substantially rectangular shape. The flat jaw  12  is posteriorly connected to the stem  212  with a symmetrically tapered conformation and jaw  12  is provided with a rectilinear anterior edge  312 , having a rounded shape and which incorporates the anterior edge of the folder  6  when the gripper is raised. 
   The fork terminal end  112  of the upper jaw  12  of the gripper P supports, with the interposition of eccentric bushes  13 , the ends of a pivot  14  which is parallel to the shaft  10  and upon which there is rotatably assembled a bearing  15 . An end portion of the shaft  17  is rotatably supported in a position parallel to the same shaft  10  by the interposition of bushes  16 . An eccentric element  19  made of suitable material is keyed by means of a grub screw  18 . The eccentric element  19  has a cylindrical shape, which co-operates, on one side with an upper bar  112 ′ of the fork terminal end  112  and which, with another portion, which forms substantially an angle of 180° with respect to the bar, co-operates with the above mentioned bearing  15 . The cooperation of both parts of eccentric element  19  is such that rotating the shaft  17  results in the eccentric element  19  causing the lowering or the raising of the upper jaw of the gripper P, with a double control effect. The eccentric bushings  13  are provided with fixing radial grub screws  20 , through which it is possible to ensure a better contact position of the bearing  15  with the eccentric element  19 , as well as accommodate the presence of possible working tolerances of the various portions which compose the gripper P. The fork terminal end  112  is provided between the bar  112 ′ and the small support portion of the pin  14 , and with wide side grooves avoid interference between the same fork terminal end  112  and the shaft  17 . As shown in  FIGS. 1 and 3 , the shaft  17  has a length which is sufficient to rotatably traverse one of the lateral cams  4 ′ of the carriage  1 . A small support  21  is placed under the fix cam and is fixed to the carriage  1 . A small lever  22  is square keyed on the end of the same shaft  17 . The small level  22  is oriented high and in the direction of the folder  6 . A lateral roller  23  is attached to the lever  22  on an end opposite the shaft  17 . The lateral roller  23  has an axis of which is parallel to the shaft  17 . On the portion of the shaft  17  which runs between the cam  4 ′ and the support ring  201 , there is wound a needle spring  24 . The needle spring  24  is anchored to a wall of the ring  201  of the carriage  1  via end  124 . The other end of spring  24  is anchored to a bush  25 . Bush  25  is fixed with a grub  26  on the same shaft  17 . The spring  24  is pre-loaded in such a manner to maintain the lever  22  against a lower retainer  121 , integral with the support  21 . In these conditions, the eccentric element  19  is in the position of  FIG. 3  and maintains the upper jaw of the gripper P raised against the folder  6 . 
   From  FIGS. 1 ,  2 , and  3 , it is noted that on the portion of the shaft  10  which is between the lateral walls of the posterior fork  112  of the stem of the upper jaw  12 , the stem  227  of the lower jaw  27  of the gripper P, is fixed with its structural clamp end  127 . The comb-shaped gripper P, when it is in the closing position, touches, with its teeth, a strip  28  of material with a high coefficient of friction, for example rubber, fixed on the lower face of the upper jaw  12  of the same gripper P. The lower gripper  27  is normally urged in closure by a couple of needle springs  29 ,  29 ′ which wind around portions of the shaft  10  which are laterally projecting from the ring  201  of the carriage  1 . These externally projecting portions are anchored with respective external ends to bushings  30 ,  30 ′. Bushing  30 ,  30 ′ are fixed with grubs to the same shaft  10 . The opposite end of the springs  29 ,  29 ′ are anchored to the posterior fork  112  of the stem of the upper jaw using screws  31 ,  31 ′, with lateral ledges  412 ,  412 ′. The springs  29 ,  29 ′ are advantageously pre-loaded to urge the two jaws of the gripper P against one another with an appropriate thrust. 
     FIG. 2  shows how the posterior fork  112  is superiorly provided with a window  32  through which it is possible to act on the screw of the clamp  127 , which fixes to the shaft  10 , the stem of the lower jaw  27  of the gripper P. Through this window, there projects an appendix  327  which is bent upwards, onto which the operator can act to lower the inferior jaw  27  each time that this operation is required. 
   The shaft  10  passes, in a rotatable manner, through one of the internal cams  4  which is integral with the carriage  1 . Shaft  10  includes a lever  33  at one end which is keyed and oriented in the same direction as the lever  22 . A lateral roller  34  is provided at the end of lever  33 . The axis of the lateral roller  34  is parallel to the shaft  10 . A cam  35  is fixed on carriage  1 , laterally to the roller and upwardly oriented. 
   The actuator  3  is placed on the side of the carriage  1  which carries the lever  33 . Taking advantage of the lateral grooves  103  of the body of the actuator, upon this is laterally fixed a base  36  which carries the mechanisms (described below) to actuate the opening and then the closure of the described gripper when the carriage  1  reaches the expulsion end run of a packaged product and when the same gripper P arrives to co-operate with the known type distributor D, to clamp from this the new head of the film which must be stretched in the packaging station of the machine during the next return run of the same carriage  1 . 
   From  FIG. 3  it is noted that, when the carriage  1  reaches the position where gripper P begins to open, the roller  34  of the lever  33  begins to co-operate with the lower side of a lever  37  downwardly inclined, placed with its longitudinal axis on an ideal vertical plane which is parallel to the run of the carriage  1  and articulated with one end on a pin  38  fixed to the plate  36  and parallel to the shaft  10 . On the same end of the fulcrum, the lever  37  carries laterally fixed, by means of the screws  39 , a lever arm  40  downwardly oriented, in the opposite direction with respect to the lever  37  and which terminates with a rounded end  104  placed on the sliding path of the cam  35  fix to the carriage  1 . When the lever  37  is in the active position shown in  FIG. 3 , the end  140  of the lever arm  40  is raised and does not interfere with the cam  35 . The lever  37  includes a laterally flattened portion  137 , on an end of the lever  37 , opposite to the end  140 . Flattened end portion  137  is parallel to the fulcrum fulcrumed at  41 . A short lever  42  is parallel to the fulcrum  38 . Short lever  42  has a lower portion  142  which projects downwardly from the lever  37  to act as a trigger. An upper portion projects upwardly from the lever  37  to act as a trigger or hook. An upper end of the lever  42  has a horizontal pin  43  which engages a lateral recess  44  of a small vertical guide  45  fixed upon a small plate  36 . 
   A return spring  46  is housed in a seat formed on the base of the recess  137  of the lever  37 . The return spring  46  acts on the upper arm of the lever  42 , to maintain the small pin  43  inside of the recess  44 . A second return spring  47  is laterally anchored at  48  to the lever  37  on one end, and anchored to an appendix  49 , of the upper portion of the guide  45 , at the other end the level of which the same guide is provided with a projecting step  50 . The anchoring is achieved, partially realized with an elastic-yielding material. 
   When the roller  34  of the lever  33  runs along the lower and descending side of the lever  37 , the shaft  10  of the gripper oscillates or pivots in a counterclockwise direction, as shown in  FIGS. 1 and 3 , and the lower jaw  27  of the gripper P oscillates or pivots downwardly and moves away from the upper jaw  12 , opening the same gripper. 
   In a correct phase with the above mentioned opening phase, the gripper P oscillates or pivots downwardly to reach the same level of the complementary gripper PD of the distributor D which retains the new head of the packaging film F. To accomplish this function, a cam  51  is fixed to the frame of the machine, against a vertical edge. The cam  51  co-operates with the roller  23  of the lever  22 , in such a manner that the translation of the carriage  1  causes the roller to first goes up on the front  151  of the cam, then to go down, then to run along the rounded corner zone  251  of the same cam and finally to run along the lower (inferior) and horizontal side of the same cam  51 . As a consequence of this wide movement of the lever  22  and of the relative shaft  17 , the eccentric element  19  rotates in a clockwise direction (as shown in  FIGS. 1 and 4 ) and the whole gripper P is lowered while remaining opened and disposes with the upper jaw  12  and with the lower jaw  27 , respectively, over and under the gripper PD of the distributor D. When the carriage  1  is about to traverse the last portion of its run (e.g. a few millimeters) towards the distributor D, the roller  34  of the lever  33  touches the lower trigger  142  of the lever  42  and urges the lever to rotate in a clockwise direction (as shown in  FIG. 3 ), resulting in the disengagement of the pin  43  from the recess  44 , in contrast with the spring  46 , so that by effect of the traction performed by the spring  47 , the lever  37  oscillates rapidly upwardly (as shown in  FIG. 4 ), causing the rising of the lower jaw  27  of the gripper P. The teeth of the lower jaw  27  pass through the empty spaces of the comb PD of the distributor and raise the head of the film F, clamping the same firmly against the rubber strip  28  of the upper jaw  12 . The pin  43  runs on the side of the guide  45  and arrives against the elastic rubber bumper  50 . With the raising of the lever  37 , the lower (inferior) side of the lever has been moved over the roller  34  of the lever  33 , while the lever arm  40  has been lowered and its end  140  has been carried to the level of future co-operation with the cam  35 . 
   When the run of the carriage  1  is reversed and the gripper P moves away from the distributor, with a movement toward the right (as shown in  FIG. 4 ), the same gripper P remains closed and remains low to be withdrawn from the gripper PD of the distributor D. When the roller  23  of the lever  22  is moving backwards passing the lower (inferior) side  351 , the corner zone  251  and then the front  151  of the cam  51 , the gripper P will come out from the distributor D and gradually returns in the high position of  FIG. 3 , with the conclusion of its lifting when the roller  34  has gone beyond the fulcrum zone  38  of the lever  37 , in such a manner that the gripper must change its position while the gripper always remains closed. When the cam  35  passes under the end  140  of the lever  40 , the lever is raised, causing the lowering of the lever  37 , while the lever  42 , with the functions of hook and trigger, is reloaded as from  FIG. 3 , preparing the whole mechanism for the repetition of a new working cycle. 
   It is to be understood that the end  140  of the lever  40  may be provided with a roller for the co-operation with rolling friction with the cam  35 . For the same objects, also the upper bar  112 ′ of the posterior fork  112  of the upper gripper, may be provided with a roller for the co-operation with rolling friction with the eccentric element  19 , even if the eccentric element works preferably in contact with the lower bearing  15 .