The present invention relates to carton erecting machines, and, more particularly, to such machines which employ vacuum devices for gripping both surfaces of the folded carton and a mechanism for moving one of the vacuum devices with respect to the other to pull the carton into an opened condition.
Folded cartons are formed from flat carton blanks having score lines defining the individual panels of the carton and having a narrow tapered strip or edge on one end for glueing. The blank is bent at each of score lines defining the side edges of the panels, and the tapered strip is glued to the edge of the panel on the opposite end of the blank. The folded carton, when properly formed, is a tubular parallelogram which flattens out under the weight of a stack of cartons but tends to spring open again when pressure is removed. Such cartons are easy to open, and if made of board of uniform thickness and stiffness, can be erected by the conventional prior art machines without incident.
In actual practice, a significant percentage of folded cartons are not properly and uniformly made and the prior art machines are not capable of effectively erecting such imperfect cartons. The machine therefore malfunctions causing a temporary shut down of the line while the machine is cleared of faulty cartons or readjusted to accomodate cartons made of different board.
One common fault in carton construction is failure to bend the blank along all appropriate score lines as it is formed. This makes the carton difficult to open since the opening mechanism must supply enough force to bend the carton along that score line. A second common fault is the partial glueing together of the internal surfaces of the carton caused by misalignment of the glueing mechanism or the application of an excessive amount of glue. In order to open these cartons, this glue bond must be broken by the erecting mechanism. A third common problem is warpage of the cartons due to improper storage or construction. Warpage has two adverse effects. When it bends the carton transversely to the score lines, it makes opening of the carton difficult, and it changes the position of the surface of the end carton in the magazine causing problems in removing the carton from the magazine.
Another factor which causes many prior art carton erecting machines to malfunction is a variation in the stiffness of the cartons due to a change in the board from which they are formed. Where the carton at the open end of a magazine is held in by lips which engage opposite edges of the carton, and where the magazine is oriented so that the weight of the cartons act against the end carton, the end carton bends in an outward arc between the two retaining lips. The extent of this deflection is dependent upon the stiffness of the board from which the cartons are made. The prior art erecting machines using this type of magazine must be adjusted according to the extent of the deflection and therefore a variation in the stiffness of the cartons causes the machine to malfunction and requires readjustment.