Abstract:
The present invention relates to a “poly” bag machine and, more particularly, to mechanisms for operating the seal bar component of such machines. The machine according to the invention includes a mechanism for reciprocatingly raising and lowering the sealing bar in which the movement and position of the sealing bar are controlled by the drive shaft and are selectively adjustable by one or two separate servo-drives. A main link is coupled to a seal bar drive shaft for movement in direct response to its rotation. A second link is movably coupled to the main link. A servo-drive system including a servo motor or servo valve is coupled to the second link for adjusting the position of the second link with respect to the main link while the main link is moving in response to the rotation of the drive shaft.

Description:
This application claims benefit to U.S. provisional application serial No. 60/128,897, filed Apr. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to “poly” bag making machines and, more particularly, to mechanisms for operating the seal bar component of such bag making machines. 
     Poly bag making machines are well known. Draw rolls pull a web of plastic film material from a supply. A transverse cutting and sealing bar (hereinafter referred to as a seal bar), is situated after the draw rolls and mounted for reciprocation to cut and seal the web after each web index movement to form individual bags. The bags are carried to a stacking station on a stacker conveyer by means of a rotating vacuum arm assembly. Bag machines of the type described are well known. For example, a typical bag making machine of this type is The Polystar 9000 available from Ro-An Industries Corp. of Maspeth, N.Y., U.S.A. 
     Generally, bag making machines of the type described are powered by a main drive motor that drives a main drive shaft which in turn drives the various components of the bag making machine, including the draw rolls, seal bar, vacuum arm assembly and stacker conveyer, through conventional mechanical linkages including, gears, pulleys, crank and rocker arms, clutch/brake systems, cams and cam followers and the like. 
     Recently, servo drives have been used to drive various components of bag making machines. For example, servo motors are used to drive the draw rolls and stacker conveyer components of bag making machines in a coordinated manner through a servo-controller in order to reduce the number of cycle interrupts required within which to index the stacker conveyer when a stacker station has been filled with bags. In this connection, reference is made to U.S. Pat. No. 5,338,281 to Terranova, the disclosure of which is incorporated herein in its entirety. 
     It has also been proposed to replace the conventional cam and cam follower mechanism for reciprocating the seal bar by a servo motor or servo valve to drive a linkage to raise and lower the seal bar of the bag making machine so that the position, and motion of the seal bar, including its dwell time in the fully down and sealing position, can be controlled independently of the machine speed and other components of the bag machine. In this connection, reference is made to U.S. Pat. No. 5,230,688, to Hatchell, et al., the disclosure of which is incorporated herein in its entirety. 
     However, reciprocatingly driving a seal bar by a servo motor or servo valve requires substantial modification of relevant components of the bag making machine. Moreover, any benefits obtained by the substantial modifications required to provide an independent operation of the seal bar are often outweighed by the substantial expense of the modifications which are required to accomplish this end. 
     Moreover, prior arrangements for reciprocating the seal bar in bag making machines are designed to raise and lower the seal bar in a uniform manner, i.e. so that the seal bar is lowered onto and contacts the plastic web uniformly over the entire width at the same time with a constant degree of penetration. While such operation is generally suitable, there are some applications,, e.g. in the sealing of certain multiple ply plastic webs, where it would be desirable to first lower one end of the seal bar onto the web and then gradually lower the other end so that the seal bar engages the web progressively from one edge of the web to the other. Other applications make it desirable to have different degrees of penetration of the web by the seal bar at respective end regions of the seal bar. However, it is not possible to accomplish these functions using conventional mechanical and servo controlled mechanisms for raising and lowering the seal bar. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide new and improved mechanisms for driving a seal bar in a bag machine. 
     Another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine which is controlled by the machine&#39;s drive shaft. 
     Still another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine which is controlled by the machine&#39;s drive shaft and which enables a selective adjustment of the dwell time of the seal bar. 
     Yet still another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine in which the raising and lowering of each respective end of the seal bar is independently adjustable. 
     Briefly, in accordance with the present invention, these and other objects are attained by providing an improvement in the mechanism for reciprocatingly raising and lowering the sealing bar in which the movement and position of the sealing bar are controlled by the drive shaft and are selectively adjustable by one or two separate servo-drives. 
     A main link is coupled to a seal bar drive shaft for movement in direct response to its rotation. A second link is movably coupled to the main link. A servo-drive system including a servo motor or servo valve is coupled to the second link for adjusting the position of the second link with respect to the main link while the main link is moving in response to the rotation of the drive shaft. 
     Separate mechanisms may be provided for controlling and adjusting the position and movement of each one of the two ends of the sealing bar, independently of each other, in a coordinated fashion. Independent adjustment allows for variations of the sealing profile and seal bar penetration. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be obtained by reference to the following detailed description when considered in connection with the accompanying drawings in which: 
     FIG. 1 is a diagrammatic representation of a bag making machine incorporating a first embodiment of a seal bar mechanism in accordance with the present invention, including a block diagram of a servo control system for the machine; 
     FIG. 2 is a perspective view of a seal bar and a seal bar mechanism in accordance with the first embodiment; 
     FIG. 3 is a diagrammatic front view of a seal bar mechanism in accordance with the first embodiment; 
     FIG. 4 is a view similar to FIG. 3 showing the first embodiment of the seal bar mechanism at a subsequent stage of operation; 
     FIG. 5 is a diagrammatic side view of a seal bar mechanism in accordance with the first embodiment; 
     FIG. 6 is a diagrammatic front view of a seal bar mechanism in accordance with a second embodiment of the invention; and 
     FIG. 7 is a diagrammatic representation of a third embodiment of a seal bar mechanism in accordance with the present invention and showing a block diagram of part of a servo control system for the machine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1, a bag machine  10  for making “poly” bags from a web  12  of plastic material is shown. The web  12  is drawn from a supply roll (not shown) by a pair of draw rolls  14 . A seal bar  16  extends over the web  12  in the direction transverse to the running direction  18  of the machine and is mounted for reciprocation to cut and seal the web  12  after each web index movement to form individual bags  20 . A rotating vacuum arm assembly or wicketer  22  is arranged after the seal bar  16  in the running direction of the machine. The wickeder  22  has a plurality of pairs of arms  24  extending radially from a hub  26 . Each pair of arms  24  picks up a bag  20  that has been formed by seal bar  16  and carries it onto a stack of bags  20  being formed at a stacking station  28  of a stacking conveyer  30 . A plurality of stacking stands  32  comprising sets of wicket pins  34  are mounted on conveyer  30  for intermittent movement into the stacking station  28  to be filled with bags  20  by the vacuum arm assembly  22 . 
     The main drive shaft  37  of drive motor  36  drives the vacuum arm assembly  22  by belt or chain  38  and also drives the seal bar  16  in a manner according to the present invention as described below. 
     The draw rolls  14  are driven by a servo-motor  40  having a servo-amplifier  41  through a belt or chain  42 . The stacking conveyer  30  is driven by a servo-motor  44  having a servo amplifier  45  through a belt or chain  46 . An encoder or resolver  48  is coupled to the main drive shaft  37  and provides a zero marker signal  49  indicative of the position and movement of the main drive shaft. The resolver  48  directs the signal  49  to an encoder interface in the servo-controller  50  which also includes timing modules, command signal generators and profile generators for operating various components of the bag machine  10 . 
     In accordance with one mode of operation, the controller  50  through resolver  48  counts the number of bags  20  formed by seal bar  16  and when a predetermined number corresponding to a completed stack have been formed, a signal  52  is directed to servo-amplifier  41  which sends a signal  4  to servo-motor  40  to interrupt the operation of draw rolls  14  for a minimum number of interrupt cycles corresponding to a minimum number of wicket arm pairs which will thus be empty to provide sufficient time for the stacking conveyer  30  to index an empty stacking stand  32  into the stacking station  28 . After an interval of time sufficient to allow the last bag  20  formed prior to cycle interrupt to be carried to stacking station  28 , controller  50  sends a signal  56  to servo amplifier  45  which in turns sends a signal  58  to energize servo motor  44  to index the stacking conveyer  30  and move an empty stacking stand  32  into stacking station  28 . Each servo motor  40 ,  44  feeds back a respective encoder signal  60 ,  62  indicative of its position and movement to the servo-controller  50 . 
     The present invention concerns the mechanism for mounting the seal bar  16  to the bag machine  10  for reciprocatingly raising the seal bar  16  to allow the plastic web  12  to be drawn a pre-determined distance and then lowering the seal bar onto the stationary web to seal and cut the web into individual bags  20 . Referring to FIGS. 1-5, a first embodiment of a seal bar mechanism, designated  100 , is illustrated which comprises a pair of substantially identical mechanisms  100   a,    100   b  for controlling and adjusting the position and movement of respective ends  16   a,    16   b  of the seal bar  16 . 
     Each seal bar mechanism  100   a,    100   b  comprises a main link  102  coupled to the drive shaft  104  for movement in response to the rotation of drive shaft  104 . The drive shaft  104  is mounted on the frame of bag machine  10  with a fixed axis of rotation and is powered by the main drive shaft  37  through a belt or chain  106  (FIG.  1 .). In the illustrated embodiment, each main link  102  has an elongated lever portion  102   a  and is coupled to drive shaft  104  by means of an eccentric member  108  fitted into an enlarged body portion  102   b  of main link  102  at the lower end of lever portion  102   a.  Each mechanism  100   a,    100   b  includes a second L-shaped link  110  comprising a first leg  110   a  and a second leg  100   b.  The free end of first leg  110   a  of second link  110  is pivotally connected to the upper free end of the lever portion  102   a  of main link  102 . 
     Each mechanism  100   a,    100   b  includes a respective servo-drive in the form of a respective servo-motor  112  mounted on the machine frame  114 . The servo motor  112  includes a servo-drive shaft  116  having a fixed axis which drives an eccentric member  118  mounted in a follower member  120 . The follower member  120  in turn is fixed to a rail member  122  which is slidably received in a linear bearing  124  fixed to the second leg  110   b  of second link  110 . Each mechanism  100   a,    100   b  includes a respective connecting link  126  which is connected at one end to a respective end  16   a,    16   b  of seal bar  16  and at its other end pivotally to the second link  110  at the intersection of its first and second legs  110   a,    110   b.    
     As best seen in FIG. 2, separate but substantantially identical mechanisms  100   a,    100   b  having separate respective servo-motors  112 , are used to raise and lower the respective ends  16   a,    16   b  of seal bar  16 . As discussed below, while both mechanisms are driven and controlled by the rotation of the drive shaft  104  powered by main drive shaft  37 , the position and movement of each seal bar end can be independently adjusted utilizing the respective servo-motor  112  of the respective mechanism  100   a,    100   b.    
     The operation of mechanism  100   a  to adjust the dwell time of seal bar  16  will now be described. The end  16   a  of the seal bar  16  is in its bottom or dwell position is shown in FIG.  3 . Rotation of the drive shaft  104  from the position shown in FIG. 3 to the position shown in FIG. 4 results in the elevation of the pivot at the free end of lever portion  102   a  of main link  102  by means of the eccentric member  108 , from a level designated “ 1 ” in FIG. 3 to a level designated “ 2 ” in FIG.  4 . In conventional designs in which the seal bar is connected to the main link  102 , the elevation of the main link caused by the rotation of drive shaft  104  results in a comparable elevation of the seal bar  16 . However, by means of the present invention, the position and movement of the seal bar  16  can be adjusted, for example, to maintain the seal bar in the dwell position for a selected period. 
     As the drive shaft  104  rotates and the main link  102  is raised from the position illustrated in FIG. 3 to the position illustrated in FIG. 4, the servo-motor  112  is energized to rotate the servo drive shaft  116  to turn the eccentric member  118  and thereby rotate the follower member  120  as best seen in FIG.  4 . The rotation of the follower member  120  is accommodated by a linear sliding movement of the follower member  120  on the second leg  110   b  of second link  110  enabled by the rail and linear bearing arrangement. Rotation of follower member  120  adjusts the position of the second link by rotating counter-clockwise in FIG. 4 thereby causing the point on second link  110  at which the seal bar connecting link  126  is connected to remain essentially at the same level as that shown in FIG. 3, i.e., level “ 1 ”, despite the continued rotation of the drive shaft  104 . It will therefore be seen that the invention enables the drive shaft to control the position and operation of the seal bar while its position and movement can be adjusted by means of the servo-controlled mechanism. 
     Referring to FIG. 1, as discussed above, the position and movement of the main drive shaft  37  is input to servo-controller  50  by resolver  48 . This information also provides the position of the main link  102  of seal bar mechanism  100 . The desired profile for the reciprocation of seal bar  16  including a desired dwell time is input by an operator into and resides in a profile generator in servo-controller  50 . The positions of the second link  110  relative to the main link  102  which will result in the desired adjustments in the position and movement of the ends of the seal bar to obtain the desired profile are calculated and signals  128  are directed to servo amplifier  130  to send energize signals  132  to servo motor  112  to rotate second link  110 . Encoder feedback signals  134  are looped back to servo controller  50  to obtain the desired movement profile for seal bar  16 . 
     As explained above, a separate seal bar mechanism  100   a,    100   b  is provided at each end  16   a,    16   b  of seal bar  16 . When it is desired that the seal bar be raised and lowered in a uniform manner, i.e., so that the seal bar is lowered onto and contacts the plastic web uniformly over its entire width at the same time and with a constant degree of penetration, the identical desired profile will be set for the servo-drive of each of the two seal bar mechanisms. On the other hand, if it is desired to first lower one end of the seal bar onto the web and then gradually lower the other end so that the seal bar engages the web progressively from one edge to the other, or if it is desired to achieve different degrees of seal bar penetration at respective edge regions of the web, it is a simple matter to vary the profiles of the servo-drives of each of the two seal bar mechanisms independently of each other to achieve these objects. 
     Referring to FIG. 1, it will be seen that the servo-controller  50  comprises a 4-axis servo-controller for controlling the draw roll servo-motor  40 , the stacker conveyer servo-motor  44 , and the two seal bar servo-motors  112 . A suitable servo-controller is the model MSC850 available from Industrial Indexing Systems, Inc. of Victor, N.Y. 
     Referring to FIG. 6, another embodiment of a seal bar mechanism in accordance with the invention, designated  200 , is shown. Parts of seal bar mechanism  200  are similar or identical to parts of mechanism  100  and are designated by like numbers in the “ 200  ” series. Mechanism  200  includes a main link  202  coupled to a drive shaft  204  by an eccentric member  208 . A second L-shaped link  220  is pivotally mounted to the free end of main link  202 . A connecting link  226  connects the seal bar head  216  to the second link  210 . A servo-motor  212  having a servo-drive shaft  216  is mounted on the bag machine frame  214 . The servo-drive shaft  216  is coupled to the second link  210  by means of an articulated linkage comprising links  250  and  252  which are pivotally connected to each other and to servo-drive shaft  216  and second link  210 , respectively. The servo controller is programmed to cause energizing signals to be sent to servo motor  212  to rotate shaft  216  to turn second link  210  to obtain the desired profile for the reciprocation of the seal bar to which the mechanism  200  is coupled. 
     Referring to FIG. 7, a third embodiment of a seal bar mechanism in accordance with the invention, designated  300 , is shown. Parts of seal bar mechanism  300  that are similar or identical to parts of mechanism  100  are designated by like reference characters in the “ 300 ” series. Each mechanism  300  includes a main link  302  coupled to drive shaft  304  by an eccentric member,  308 . 
     A second link  310  is pivotally mounted to the free end of main link  302 . A connecting link  326  connects the seal bar head  316  to the second link  310 . The servo-drive of each of the seal bar mechanisms comprises a servo-controlled valve  350  and a fluid cylinder assembly  352  coupled to the servo-controlled valve for operation thereby. The assembly  352  in turn is coupled to the second link  310  to adjust its position with respect to the main link  301 . As in the case of the previously described embodiments, the profile generators in the servo-controller  50  are programmed to control the servo-valves to obtain the desired movement profiles. 
     Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the claims appended hereto, the invention may be practiced otherwise than as specifically disclosed herein.