Abstract:
An apparatus for forming a pouch for containing a product includes a pair of sealing bars configured to move toward each other along a first direction and to engage a web inserted therebetween, a linear cam configured to move along a second direction perpendicular to the first direction, and a coupling between the linear cam and the sealing bars for transforming motion along the second direction into motion along the first direction.

Description:
FIELD OF DISCLOSURE 
       [0001]    This disclosure relates to packaging machines, and in particular, to machines for packaging product into pouches. 
       BACKGROUND 
       [0002]    Known methods for packaging product include placing the product in cans, bottles, boxes, and pouches. In the case of pouches, packaging includes forming a pouch. Pouch formation includes passing a web having two panels through a pair of heat-sealing bars. The bars are periodically brought together to join the two panels along a line. The interval between two such lines determines the size of the pouch. 
         [0003]    Packaging machines for making pouches generally have a control system for causing the heat-sealing bars to be brought together at correct intervals. However, known control systems lack the ability to control pressure by recipe. As such, they lack the flexibility to easily switch between different size pouches. 
       SUMMARY 
       [0004]    In one aspect, the invention features an apparatus for forming a pouch for containing a product. Such an apparatus includes a pair of sealing bars configured to move toward each other along a first direction and to engage a web inserted therebetween, a linear cam configured to move along a second direction perpendicular to the first direction, and a coupling between the linear cam and the sealing bars for transforming motion along the second direction into motion along the first direction. 
         [0005]    In some embodiments, the coupling includes a cam follower. 
         [0006]    In other embodiments, the linear cam includes a curved guide-way extending along the linear cam, and the coupling includes a cam follower that engages the guide-way. Among these are those in which the guide-way includes walls forming a groove for receiving a cam follower and those in which the guide-way includes a rail for supporting the cam follower. 
         [0007]    Also among the embodiments are those in which the linear cam includes walls forming curved first and second guide-ways defining first and second path functions. Among these are the embodiments in which the coupling includes first and second followers engaging the curved first and second guide-ways, the embodiments in which each of the guide-ways includes an inner section and an outer section, wherein the first and second path functions in the inner section have a smaller derivative than the first and second path functions in the outer section, and those that further include a servo-motor for causing the linear cam to move along a longitudinal direction. 
         [0008]    In those embodiments that include a servo-motor, the servo-motor can be a programmable servo-motor. Among these are the embodiments in which the servo-motor is configured to move the linear cam such that the cam followers remain within the first section during formation of pouches, and to move the linear cam such that the cam followers remain within the second section during a retraction phase in which the sealing bars are fully retracted from the web. 
         [0009]    In another aspect, the invention features an apparatus for forming pouches for containing product. Such an apparatus includes means for heat-sealing a web, a linear cam, and means for coupling the linear cam to the means for heat-sealing a web. 
         [0010]    In some embodiments, the linear cam includes means for guiding a cam follower that causes motion of the means for heat-sealing a web. 
         [0011]    Other embodiments also include means for controlling motion of the linear cam, the means for controlling motion including means for implementing an operating mode of the linear cam and a retraction mode of the linear cam. 
         [0012]    In yet another aspect, the invention features a method for operating a machine for forming pouches for containing product. Such a method includes passing a web between heat sealing bars, translating a linear cam along a first direction, thereby causing the heat sealing bars to engage the web, and translating the linear cam along a second direction opposite the first direction thereby causing the sealing bars to release the web. 
         [0013]    In some practices, the method also includes translating the linear cam along the second direction to an extent sufficient to fully retract the heat sealing bars. 
         [0014]    In other practices, the method further includes causing a servo-motor to translate the linear cam according to a first movement profile and a second movement profile. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0015]      FIG. 1  shows a packaging machine; and 
           [0016]      FIG. 2  shows a linear cam from the packaging machine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A packaging machine  10 , shown in  FIG. 1 , includes first and second electrically heated sealing bars  12 A,  12 B mounted on corresponding first and second rails  14 A,  14 B that extend along a longitudinal direction  16 . These heated sealing bars  12 A,  12 B are movable back and forth along a transverse direction  18  perpendicular to the longitudinal direction  16 . The first sealing bar  12 A is mounted directly to the first rail  14 A, whereas the second sealing bar  12 B is mounted to a pair of springs  20 A,  20 B mounted to the second rail  14 B. As a result, to cause the sealing bars  12 A,  12 B to exert pressure against each other, it is necessary for the second rail  14 B to overcome the force of the springs  20 A,  20 B. 
         [0018]    In operation, a web having first and second opposed panels is fed through a narrow gap between the sealing bars  12 A,  12 B. The web is made of a material that melts in response to application of heat and pressure by the sealing bars  12 A,  12 B. At periodic intervals, the web stops moving so that the sealing bars  12 A,  12 B can be brought together at a pre-defined pressure to melt the panels together along a line. This creates a pouch  28 . 
         [0019]    The gap during operation is kept narrow, on the order of ⅜ inches, so that the sealing bars  12 A,  12 B do not have to move very far to create a seal. Because the sealing bars  12 A,  12 B are hot, it is important for the web to move fast enough so that melting occurs only when the sealing bars  12 A,  12 B are brought together, and not as a result of stray heat while the web is moving through the gap. 
         [0020]    During operation, there may be times when motion of the web stops. When this occurs, it is desirable for the sealing bars  12 A,  12 B to move further apart, so that stray heat does not melt the web that happens to be between the sealing bars  12 A,  12 B. A typical separation is 3 inches. 
         [0021]    Transverse motion of the rails  14 A,  14 B is controlled by a servo-motor  30  that moves a linear cam  32  along the longitudinal direction  16 . The linear cam  32 , better seen in  FIG. 2 , features curved first and second guide-ways  34 A,  34 B. At each point along the first guide-way  34 A, the direction of the first guide-way  34 A makes an angle relative to the longitudinal direction  16 . The value of this angle as a function of position along the first guide-way  34 A defines a first path function. Similarly, at each point along the second guide-way  34 B, the direction of the second guide-way  34 B makes an angle relative to the longitudinal direction  16 . The value of this angle defines a second path function. In general, the first and second path functions are symmetric. For a given coordinate along the transverse direction, the first and second path functions define equal angles of opposite sign. 
         [0022]    Each guide-way  34 A,  34 B has an outer section  35 A in which the absolute values of the path functions are within a first range and an inner section  35 B in which the absolute values of the path functions are within a second range. Except for the point at which the inner and outer sections meet, the values of a guide-way&#39;s path function within its inner section  35 B are smaller than the values of the path function within its outer section  35 A. In addition, except for the point at which the inner and outer sections meet, the derivative of a guide-way&#39;s path function within its outer section  35 A is greater than the derivative within its inner section  35 B. 
         [0023]    The first rail  14 A is coupled to a first cam follower  36 A such that transverse motion of the first cam follower  36 A results in transverse motion of the first rail  14 A. The first cam follower  36 A is set in the first guide-way  34 A of the linear cam  32  and thus moves transversely in accordance with the first guide-way&#39;s path function. Accordingly, as the servo-motor  30  causes the linear cam  32  to move in the longitudinal direction  16 , the first rail  14 A also moves transversely. 
         [0024]    If the linear cam  32  is moved inwardly along the longitudinal direction  16 , the first cam follower  36 A is pushed outwardly in the transverse direction  18  by the first guide-way  34 A, thus causing the first rail  14 A to move outwardly in the transverse direction  18 . Conversely, if the linear cam  32  is moved outwardly along the longitudinal direction  16 , the first cam follower  36 A is pushed inwardly along the transverse direction  18  by the first guide-way  34 A, thus causing the first rail  14 A to move inwardly along the transverse direction  18 . 
         [0025]    The second rail  14 B is coupled to a second cam follower  36 B that is set in the second guide-way  34 B. Accordingly, the second cam moves either inwardly or outwardly along the transverse direction  18  as defined by the second path function. Thus, when the linear cam  32  moves inwardly along the longitudinal direction  16 , the second rail  14 B moves outwardly along the transverse direction  18  in the same manner as described in connection with the first rail  14 A. 
         [0026]    Since the rails  14 A,  14 B are coupled to corresponding sealing bars  12 A,  12 B, motion of the linear cam  32  in the longitudinal direction  16  has the effect of opening and closing the sealing bars  12 A,  12 B, as well as applying pressure to the closed sealing bars  12 A,  12 B. 
         [0027]    The extent of the applied pressure is controlled by the extent to which the linear cam  32  is moved outwardly beyond the point at which the sealing bars  12 A,  12 B contact each other. The length of time that pressure is applied is the dwell time of the servo-motor  30  at that that position. 
         [0028]    It is therefore a simple matter to vary the pressure applied by the sealing bars  12 A,  12 B, simply by varying the extent to which the servo-motor  30  moves the cam in a longitudinal direction  16 . To apply high pressure, the servo-motor  30  simply moves the linear cam  32  outward by a greater amount. Conversely, to apply lower pressure, the servo-motor  30  simply moves the linear cam  32  inward by a lesser amount. The ability to apply variable amounts of pressure enables the servo-motor  30  to easily accommodate springs  20 A,  20 B having various spring constants. 
         [0029]    The servo-motor  30  can also be programmed to apply a time varying pressure. For example, if one wishes to smoothly increase the applied pressure from a first value to a second value, it is only necessary to program the servo-motor  30  to gradually move the linear cam  32  outwards from a corresponding first position to a second position. 
         [0030]    In operation, the servo-motor  30  generally moves the linear cam  32  so that the cam followers  36 A,  36 B remain within the inner section  35 B. This ensures that in the open position, the sealing bars  12 A,  12 B remain fairly close together. This enables the sealing bars  12 A,  12 B to be quickly brought together. 
         [0031]    On the other hand, when operation of the packaging machine is halted, it is desirable to move the sealing bars  12 A,  12 B further apart to prevent stray heat from the sealing bars  12 A,  12 B from melting the web in an uncontrolled manner. To do this, the servo-motor  30  drives the linear cam  32  inward far enough so that the cam followers  36 A,  36 B enter the outer section  35 A of the linear cam  32 . Since the path functions at the outer section  35 A have a greater derivative, the cam followers  36 A,  36 B are quickly forced further apart, thus opening the rails  14 A,  14 B further apart and providing increased clearance between the sealing bars  12 A,  12 B. 
         [0032]    Guide-ways  34 A,  34 B can take on various forms. In one embodiment, illustrated in  FIG. 1 , the guide-way includes walls forming a groove, in which case the cam followers  36 A,  36 B are protrusions extending from rails  14 A,  14 B. However, a guide-way  34 A could be a mono-rail, in which case the cam follower  36 A would have a groove to receive the rail and perhaps wheels to roll along the mono-rail. Or the guide-way  34 A could be embodied as a track having two rails, in which case the cam follower  36 A would be a truck with flanged wheels for engaging the rails. 
         [0033]    The use of a linear cam  32  in a packaging machine  10  as described herein offers numerous advantages over the use of a rotary cam in conventional machines. First, the resulting packaging machine  10  can more readily accommodate different performance requirements, such as varying pressures and varying intervals between heat sealing events. This is because the servo motor  30  that drives the linear cam  32  can easily be re-programmed to translate the linear cam  32  by different amounts and at different speeds along different sections of the guide-way  34 A,  34 B. In conventional packaging machines, such changes are accompanied by changes to the rotary cam&#39;s geometry. Additionally, the use of a linear cam  32  enables the sealing bars  12 A,  12 B to be retracted quickly and easily, by simply causing the servo motor  30  to drive the cam followers  36 A,  36 B along the outer section  35 A of the linear cam  32 .