This invention relates generally to equipment for handling sheet articles and, more particularly, to a vacuum-operated sheet pickup assembly for successively lifting the top sheet in a stack thereof from the stack and having hold-down structure associated therewith which mechanically prevents the vacuum assembly from picking up doubles.
Many of the structural properties and principles of operation of the sheet pickup assembly hereinafter described have been previously disclosed in prior U.S. Letters Patents Nos. 2,846,214 and 2,937,868 and, accordingly, such earlier patents are incororated herein by reference where needed for a full and complete understanding of the present invention.
As shown in the above patents, a vacuum pickup assembly is employed at each assembly station of a collating machine to successively lift the top sheet from a stack of sheet stock therebelow and successively place the sheets upon a series of trays moving continuously along the assembly line above the stack, whereby a package of sheets is progressively assembled as the trays advance past the stations. It has been found that static electricity tends to make the sheets adhere to one another and, especially where the sheet stock is thin and porous, that vacuum from the suckers of a pickup assembly tends to "bleed" through the top sheet in the stack, causing pickup of one or more of the next sheets in the stack. This introduces an extra, unwanted sheet to the assembled package which often consists of business forms having pages of carbon sheets interspersed between the forms.
Previous attempts at solving this problem have included the use of continuous air blasts directed at the edges of the sheets in the stack along the plane of the sheets in an effort to "float" the top sheet and flexible, spring steel stripper fingers to engage and carry back any extra sheet that has been picked up with the top sheet. While these efforts have been helpful to some extent, they have not totally solved the problem to date. Moreover, because paper characteristics such as curl, thickness, and sheet size often change in a single pile of stock, constant minor adjustments had to be made in the air blasts and stripper fingers to obtain good separation.
Accordingly, an important object of the present invention is to solve this problem by providing stationary hold-down fingers immediately behind the retractable suckers of the pickup assembly which operate to press against the sheet stock as the suckers attach themselves to a marginal edge of the top sheet and retract, thereby forcing the top sheet to flex or bend along a line through the stationary fingers such that the next sheet in the stack is prevented from adhering to the top sheet and moving therewith.
Another important object of the instant invention is the provision of means for mounting the hold-down fingers on the pickup assembly in such a manner as to permit adjustment of the fingers relative to the suckers to permit the feeding and pickup of sheets of various weights and thicknesses.
A further important object of the present invention is to provide simple, inexpensive hold-down structure as above set forth which may be readily incorporated into an existing pickup assembly without modification of the latter.
In the drawing:
FIG. 1 is a fragmentary, perspective view of a collating machine having a vacuum pickup assembly which utilizes the hold-down fingers of the present invention in association therewith;
FIG. 2 is a fragmentary, top plan view of the pickup assembly of FIG. 1 with the left end of the vacuum manifold partially broken away to reveal the mounting bar for the hold-down fingers therebelow;
FIG. 3 is a fragmentary, elevational view of the pick-up assembly and hold-down structure in FIG. 2 with the left end of the assembly and structure broken away and shown in cross section to reveal details of construction; and
FIG. 4 is an enlarged, fragmentary cross-sectional view of the assembly and structure taken along line 4--4 of FIG. 3, the retracted position of the sucker being illustrated in phantom with the attached marginal edge of the top sheet similarly shown.
Referring to the drawing, the pickup assembly 10 includes a rectangular, tubular vacuum manifold 12 which spans the width of the collating machine directly above a marginal edge portion of vertical stack 14 of sheet stock. Mounted on the manifold 12 at spaced intervals therealong are a number of sucker units 16, each comprising a generally U-shaped bracket 18 looped over manifold 12, a vertical vacuum tube 20, a hose 22 at the upper end of tube 20 which couples the unit 16 with manifold 12, a hollow cylinder 24 slidably carried on the opposite end of tube 20, and a coil spring 26 disposed about tube 20 between bracket 18 and the cylinder 24 to yieldably bias the latter to its extended, solid-line position of FIG. 4. Thus, as more completely described in detail in the earlier cited patents, the retractable cylinder 24 of each sucker unit 16 remains in its extended position through the action of spring 26 when vacuum pressure is communicated to the lowermost end of cylinder 24 until such time as material such as sheet paper comes into covering relationship with the lower end of cylinder 24, whereupon the latter immediately attaches itself to the sheet causing the vacuum pressure to retract cylinder 24 against bracket 18. This retraction causes initial separation of a marginal portion of the top sheet in the stack from the next sheet therebelow, whereupon raising of the entire assembly 10 through mechanism not shown causes the attached sheet to be completely lifted from the stack in preparation for depositing of the lifted sheet upon the next tray 28 moving into position beneath the raised sheet.
Also carried by manifold 12 of assembly 10 is hold-down structure broadly denoted 30 which includes a series of finger elements 32, there being a finger 32 for each sucker unit 16. Each of the fingers 32 includes a rigid core 34 affixed to a common, elongated mounting bar 36, the core 34 optionally having a resilient covering tube 37 of a suitable plastic material projecting downwardly therebeyond to present the sheet-engaging end of the finger 32.
The fingers 32 are spaced along bar 36 identically with the spacing of sucker units 16 along manifold 12, and the bar 36 is mounted on manifold 12 by means of a bracket assembly 38 which holds the bar 36 and hence fingers 32 in parallelism with the line of sucker cylinders 24. Moreover, each finger 32 is disposed directly behind a corresponding sucker cylinder 24 in juxtaposed relationship therewith such that each sucker cylinder 24 and finger 32 are disposed in a common vertical plane perpendicular to the line of fingers 32.
The bar 36 is provided with a pair of the bracket assemblies 38, each of which includes an inverted L-shaped member 40 having the vertical leg thereof secured to bar 36 on one side of manifold 12 and the horizontal leg thereof extending across the top of manifold 12, and a vertical member 42 also secured to bar 36 but on the opposite side of manifold 12 to capture the latter. Each of the members 40 and 42 slidingly engages a proximal face of manifold 12, and an adjusting screw 44 threadably received by the horizontal leg of member 40 bears against the upper face of manifold 12 to permit vertical adjustment of the bar 36 and hence fingers 32 with respect to the sucker units 16. A locking nut 46 selectively limits the extent of vertical travel of the horizontal leg member 40 from manifold 12, while a plurality of coil springs 48 disposed between the lower face of manifold 12 and bar 36 along the length of the latter serve to yieldably bias bar 36 away from manifold 12.
Prior to operation of the machine the fingers 32 should be adjusted with respect to sucker cylinders 24 by means of adjusting screw 44 so that the desired positioning of the lowermost end of fingers 32 with respect to the corresponding lowermost end of cylinders 24 is obtained. In this respect, it should be appreciated that thick, heavy sheet stock cannot and need not flex to the extent of relatively thin, lightweight sheets. Therefore, when heavier stock is to be handled, the differential between the lower end of each finger 32 and the lower end of the corresponding cylinder 24 when the latter is in its retracted position should not be as great as that when lighter weight material is to be handled. For the sake of clarity and convenience, the lowermost ends of the finger 32 and sucker cylinder 24 in FIG. 4 have been shown at the same level with respect to the paper stock. incorporated
As the pickup assembly 10 is lowered to stack 14, the fingers 32 and sucker cylinders 24 engage a marginal, pickup edge portion of the top sheet 14a with the fingers 32 exerting light, downward pressure against sheet 14a and the sheets immediately therebelow in an area adjacent the pickup edge. Then, when the sucker cylinders 24 attach to the pickup edge, the vacuum pressure in cylinders 24 causes the latter to retract with the pickup edge to the phantom position shown in FIG. 4, while the fingers 32 and the area engaged thereby remain in a stationary condition. Thus, the sheet 14a is caused to bend or flex about a line extending between the fingers 32 which greatly decreases the likelihood that the next sheet in the stack will be lifted along with sheet 14a. This appears to be due to the fact that in order for the next sheet or sheets to be lifted along with sheet 14a, they would also have to bend about the same point as top sheet 14a, which they cannot readily do in the absence of exceptionally strong vacuum pressure from cylinder 24.
Thereafter, the pickup assembly 10 and hold-down structure 30 are raised as a unit above the level of the next tray 28 and subsequently placed beneath retaining clips thereon, as shown by the clips 50 on the previous tray 52 downstream from stack 14. After depositing the removed sheet upon the collecting tray 28, the pickup assembly 10 is then returned to stack 14 for completing another cycle.
In practice it has been found that increased efficiency may often be obtained by slightly tilting the pickup assembly 10 and hold-down structure 30 as a unit in either direction from the vertical position of FIG. 4 in order to compensate for curl-up or curl-down of the edges of the sheet stock. This is accomplished by supporting apparatus (not shown) for the manifold 12 and the hold-down fingers 32 are equally effective in this condition. More importantly, because of the fact that the hold-down fingers 32 are mounted on manifold 12 as opposed to some external support means and because of the readily adjustable nature of the fingers 32, the manifold 12 can be easily rotated to its desired position without interference from the fingers 32 or extensive time-consuming readjustment thereof.
In many instances, the hold-down fingers 32 have proven so effective that the need for air blast separation devices and stripper fingers has been completely eliminated. Even in those situations which do require the additional, traditional separation means, however, it has been found that adjustment of all of the separation components is not as critical to good operation as in the past. Moreover, improved separation of sheets that tend to adhere to each other because of static electricity has been obtained along with dramatic improvements in increasing operating speeds and reducing set-up refinements.