Device for adjusting position for cutting bags and packaging machine incorporating same

#This invention relates to a packaging machine of the so-called form-fill-seal type adapted to concurrently form a bag from a film, to fill it with articles and to seal it to obtain individual packaged products. More particularly, this invention relates to a device for adjusting the position on the film at which it is cut (“cut-position”) to produce separated bags. The invention also relates to a packaging machine adapted to automatically adjust the cut-position according to an inputted size of the bags to be produced.

#Packaging machines adapted to concurrently bend a film into a tubular form, to fill it with articles to be packaged and to clamp it between a pair of sealing members (“seal jaws”) to simultaneously seal the top part of a filled bag and the bottom of the next bag to be filled have been known. If the bags are formed from a film with a design printed thereon corresponding to each bag to be formed, marks (hereinafter referred to as the “eye marks”) which are detectable by a light sensor are printed on the film at longitudinal intervals corresponding to the length of the bags to be made such that the film can be accurately sealed over and cut at boundary areas between portions of the film corresponding to two mutually adjacent bags as the packaging machine is operated to repeat a cyclic motion.

#Prior art methods of determining the cut-position of the bags or the clamping position by seal jaws can be roughly divided into those of adjusting the interval between the time when an eye mark on the film as a reference is detected and the time at which the film is cut (such as adjusting the dislocation of the cut-position while changing the time set on a timer by operating a dial) and those of displacing the position of the sensor for the eye marks (that is, to move the eye mark sensor by a distance corresponding to the displacement of the cut-position). The methods of the former kind are not desirable because repeated trials and errors tend to increase the wasted amount of the film. The methods of the latter kind are advantageous in that one has only to displace the eye mark sensor but it is a cumbersome operation to make the position adjustment while watching the markings of a dial.

#The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

#FIG. 1 is a schematic diagonal view of a part of a form-fill-seal packaging machine incorporating a device for cutting bags according to this invention;

#FIG. 2 is a schematic block diagram of a control system for the packaging machine of FIG. 1;

#For the purpose of reference, there is schematically shown in FIG. 1 a form-fill-seal packaging machine of the so-called vertical pillow type which may incorporate the present invention. For convenience, FIG. 1 shows only relevant parts of such a machine related to its forming, filling and sealing operations. U.S. Pat. No. 5,279,098 issued Jan. 18, 1994, for example, may be referenced for a detailed account of general structure and operations of such a machine. FIG. 2 shows schematically a control system including a computer 20 broadly described here only as having a data storing means (“memory” 21) and means for performing various operations (“operating means” 22), which may be used for such a packaging machine. A control system according to one particular embodiment of the invention is described next with reference to FIG. 3 showing its control circuit 10 more in detail. FIGS. 1, 2 and 3 will be referenced next to explain this embodiment of the invention generally.

#As shown in FIG. 1, an elongated web of flexible thermoplastic material (herein referred to as “the film”) 100 unwinds from a supply roll 90, being pulled by a pair of pull-down belts 81, and is guided by a plurality of guide rolls 91 towards a former 98 which serves to bend the film 100 into a tubular form. The pull-down belts 81 are operated by a belt-driving motor 83. A pulse generator 84 is attached to the drive shaft of this belt-driving motor 83, and the output pulse from this pulse generator 84 is adapted to be received by a film motion counter 11.

#After the mutually overlapping side edges of the tubularly formed film 100 is thermally sealed together by a longitudinal sealer 82 as the film 100 is pulled vertically downward along a specified film path, the tubular film 100 is sealed transversely (or horizontally) by a transverse sealer 50 Which is disposed below the pull-down belts 81 and includes a pair of seal jaws 51. The pair of seal jaws 51 of the transverse sealer 50 is disposed on mutually opposite sides of the film path and is adapted to move on generally D-shaped trajectories in mutually opposite directions so as to clamp the film 100 therebetween. Each of the seal jaws 51 is rotatably supported at one end of an elongated member (referred to as “the arm”) 52 adapted to rotate around an axis 59 at its other end such that both seal jaws 51 are always oriented in the same direction as they rotate around the axes 59 (for example, by means of a Schmidt coupling as illustrated in aforementioned U.S. Pat. No. 5,279,098).