Patent Application
20140047802
This disclosure relates to packaging machines, and in particular, to machines for packaging product into pouches.
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.
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.
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.
In some embodiments, the coupling includes a cam follower.
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.
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.
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.
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.
In some embodiments, the linear cam includes means for guiding a cam follower that causes motion of the means for heat-sealing a web.
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.
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.
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.
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.
A packaging machine 10, shown in
In operation, a web having first and second opposed panels is fed through a narrow gap between the sealing bars 12A, 12B. The web is made of a material that melts in response to application of heat and pressure by the sealing bars 12A, 12B. At periodic intervals, the web stops moving so that the sealing bars 12A, 12B can be brought together at a pre-defined pressure to melt the panels together along a line. This creates a pouch 28.
The gap during operation is kept narrow, on the order of ⅜ inches, so that the sealing bars 12A, 12B do not have to move very far to create a seal. Because the sealing bars 12A, 12B are hot, it is important for the web to move fast enough so that melting occurs only when the sealing bars 12A, 12B are brought together, and not as a result of stray heat while the web is moving through the gap.
During operation, there may be times when motion of the web stops. When this occurs, it is desirable for the sealing bars 12A, 12B to move further apart, so that stray heat does not melt the web that happens to be between the sealing bars 12A, 12B. A typical separation is 3 inches.
Transverse motion of the rails 14A, 14B 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
Each guide-way 34A, 34B has an outer section 35A in which the absolute values of the path functions are within a first range and an inner section 35B 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's path function within its inner section 35B are smaller than the values of the path function within its outer section 35A. In addition, except for the point at which the inner and outer sections meet, the derivative of a guide-way's path function within its outer section 35A is greater than the derivative within its inner section 35B.
The first rail 14A is coupled to a first cam follower 36A such that transverse motion of the first cam follower 36A results in transverse motion of the first rail 14A. The first cam follower 36A is set in the first guide-way 34A of the linear cam 32 and thus moves transversely in accordance with the first guide-way's path function. Accordingly, as the servo-motor 30 causes the linear cam 32 to move in the longitudinal direction 16, the first rail 14A also moves transversely.
If the linear cam 32 is moved inwardly along the longitudinal direction 16, the first cam follower 36A is pushed outwardly in the transverse direction 18 by the first guide-way 34A, thus causing the first rail 14A 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 36A is pushed inwardly along the transverse direction 18 by the first guide-way 34A, thus causing the first rail 14A to move inwardly along the transverse direction 18.
The second rail 14B is coupled to a second cam follower 36B that is set in the second guide-way 34B. 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 14B moves outwardly along the transverse direction 18 in the same manner as described in connection with the first rail 14A.
Since the rails 14A, 14B are coupled to corresponding sealing bars 12A, 12B, motion of the linear cam 32 in the longitudinal direction 16 has the effect of opening and closing the sealing bars 12A, 12B, as well as applying pressure to the closed sealing bars 12A, 12B.
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 12A, 12B contact each other. The length of time that pressure is applied is the dwell time of the servo-motor 30 at that that position.
It is therefore a simple matter to vary the pressure applied by the sealing bars 12A, 12B, 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 20A, 20B having various spring constants.
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.
In operation, the servo-motor 30 generally moves the linear cam 32 so that the cam followers 36A, 36B remain within the inner section 35B. This ensures that in the open position, the sealing bars 12A, 12B remain fairly close together. This enables the sealing bars 12A, 12B to be quickly brought together.
On the other hand, when operation of the packaging machine is halted, it is desirable to move the sealing bars 12A, 12B further apart to prevent stray heat from the sealing bars 12A, 12B 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 36A, 36B enter the outer section 35A of the linear cam 32. Since the path functions at the outer section 35A have a greater derivative, the cam followers 36A, 36B are quickly forced further apart, thus opening the rails 14A, 14B further apart and providing increased clearance between the sealing bars 12A, 12B.
Guide-ways 34A, 34B can take on various forms. In one embodiment, illustrated in
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 34A, 34B. In conventional packaging machines, such changes are accompanied by changes to the rotary cam's geometry. Additionally, the use of a linear cam 32 enables the sealing bars 12A, 12B to be retracted quickly and easily, by simply causing the servo motor 30 to drive the cam followers 36A, 36B along the outer section 35A of the linear cam 32.
