High speed printing machines have been developed in recent years for printing data on computer paper, business forms and the like. The paper supplied to such printers is provided in webs of indeterminate length formed with longitudinally spaced, transversely oriented perforations. The paper is fed at high speeds from the web to the printer which prints the desired information on the individual sheets formed between adjacent perforations, and then discharges the printed sheets for further handling.
In order to convert the continuous length of paper from the printer into a form which can be handled and shipped, the paper must be folded along its perforations as it is discharged from the printer. One type of folding apparatus intended for use with high-speed printers is a spiral, zig-zag folder.
Spiral zig-zag folders include a series of rollers which receive the paper from the printer and guide it to a reciprocating swing chute mechanism. The swing chute is driven forwardly and rearwardly relative to the frame of the folder through a distance or throw which is equal to the distance between the longitudinally spaced, transverse perforations in the paper. At both the forward and rearward limit of the throw of the swing chute, a set of beaters or fingers engages the paper in the area of its perforations and forces it into contact with one or more rotating spirals. The spirals resemble a screw having threads which are spaced progressively closer together from top to bottom. The paper is forced by the beaters or fingers between the threads of the spirals which crease the paper along its perforations. The paper is then discharged from the spirals onto a ramp or shelf for stacking.
In addition to operating at high speeds, present day printers are also capable of accommodating different webs of paper each having a different spacing between the transverse perforations. Depending upon the particular business form or computer sheet involved, the spacing between adjacent transverse perforations along the length of the web may vary from about 71/2 inches to 18 inches or more. The folding apparatus associated with the printers must therefore also be capable of accommodating different spacings between the transverse perforations of the web. This requires adjustment of the spacing between the fingers and spirals on both the forward and rearward ends of the machine, and also an adjustment of the length of the throw, i.e., the forward and rearward reciprocating movement, of the swing chute.
In some zig-zag folding apparatus, the swing chute comprises a single pair of plates or blades which are spaced from one another to form a gap therebetween through which the paper is fed for delivery to the spiral folders. See, for example, U.S. Pat. Nos. 4,512,561 to Ury, 3,912,252 to Stephens, and 2,098,427 to Menschner. Each of the blades is pivotally mounted at opposite ends to a bracket carried by the frame of the folding apparatus such that the top of the blades is laterally fixed and the bottom swings or pivots relative to the top along an arc having a radius equal to the length of the blades.
In order for the fingers of such prior art folding apparatus with a single pair of swing chute blades to engage the paper and force it into contact with the spiral folders, the bottom of the swing chute blades must deliver the paper within a predetermined area at the end of its forward and rearward stroke. If the bottom of the swing chute blades falls short of the fingers, or delivers the paper above or below the folding area within which the fingers can engage the paper and direct it into contact with the spirals, folding of the paper is difficult if not impossible. Fixed length swing chutes are capable of only limited adjustment in the length of movement or stroke before the bottom of their blades swing to a position short of, or above or below, the folding area of the fingers at the forward and rearward end of the machine.
The problem of limited swing chute adjustment has been solved, to some extent, by the structure disclosed in U.S. Pat. Nos. 3,889,940 to Jakob; 4,045,012 to Jakob; and 4,401,428 to Thomas et al. The swing chute assembly disclosed in each of these patents comprises an upper chute and a lower chute each having a pair of spaced plates or blades. As described in detail in such patents, opposite sides of the upper chute are pivotally mounted to the frame of the folder, and the lower chute is pivotally mounted to the upper chute. A drive mechanism is provided which comprises two pairs of drive arms, one pair mounted on each side of the frame. One of the drive arms of each pair is connected at approximately the midpoint of the upper swing chute and the second drive arm of each pair is mounted to the upper end of the lower swing chute. Each pair of drive arms is mounted upon and driven by eccentric cam surfaces of a common cam which is adjustable to vary the stroke or throw of the drive arm pairs depending upon the distance between adjacent perforations formed in the paper to be folded.
A swing chute assembly having both an upper chute and a lower chute substantially increases the distance or stroke through which the paper can be moved compared to those having a single pair of swing chute blades. This is because the reciprocating movement is obtained not only by the pivoting motion of the upper chute with respect to the frame, but also by pivotal movement of the lower chute with respect to the upper chute.
Although an improvement, the swing chute assemblies disclosed in the above identified patents to Jakob and Thomas et al are relatively complicated, cumbersome and difficult to adjust. The upper and lower swing chutes described in such patents are driven by two pairs of drive arms with one pair being mounted on each side of the machine frame. In order to adjust the length of throw of the swing chute assembly, each pair of drive arms must be adjusted. Furthermore, because both arms of a pair of arms are mounted upon a common eccentric cam, adjustment of its throw of one arm changes the throw of the other arm. The structure required to make such adjustment, and the provision of multiple drive arms for moving the swing chute, adds to the expense of the apparatus and complicates its operation.
Another difficulty with the swing chute assemblies of the type disclosed in the patents to Jakob and Thomas et al is that of buckling or bending of the blades which form both the upper and lower swing chutes. Such blades are formed of aluminum and at high operating speeds aluminum blades tend to buckle as they are rapidly reciprocated between the opposed sets of fingers and spiral folders. Buckling of the blades can cause them to contact and damage the fingers at both the forward and rearward end of the frame. As a result, prior art folding machines may have to be operated at speeds lower than that of the associated printers.