This invention relates to web handling apparatus of the type comprising a pair of sprocket wheels spaced on opposite sides of the machine and which have a plurality pins of projecting therefrom and equispaced around the periphery of each sprocket wheel for engaging with a line of equispaced holes down each side of the web of material which is to be fed through the machine by the drive to the sprocket wheels. More particularly, this invention relates to a web of material, usually but not necessarily a web of sign making stock, for use with such apparatus having a line of sprocket holes down each side of engagement by the sprocket wheel of the web handling apparatus.
In the loading of such webs into the web handling apparatus, a problem of alignment can arise, particularly with web handling apparatus of considerable width. In these cases it is often quite easy to feed a new web of material into such a machine in a skew position, i.e. with the two sides of the web out of exact alignment, or out of registration by the spacing of one or two pins.
Various designs have been proposed in the past for obtaining the proper initial alignment of the web in the machine by the position of various registration marks or extra registration holes on opposite sides of the web, possibly engaging with extra registration pins on each sprocket wheel, thus ensuring the correct alignment as the web is loaded into the apparatus.
One such proposal has recently been put forth in EP-B-0134064 by Gerber Scientific Products Inc. The solution to the problem proposed by Gerber involves providing each sprocket wheel with an extra registration pin, or possibly two extra registration pins between an adjacent pair or adjacent pairs of drive pins, thus providing a visually distinct group of three or five pins, distinguished from the other pins around the sprocket wheel, by virtue of a different spacing therebetween. Preferably, the extra registration pins are located at the midpoint between two adjacent drive pins, so that the visually distinct group of three (two drive and one registration) pins or five (three drive and two registration) pins is distinguishing by an interpin spacing of D/2 where D is the normal pin spacing, i.e. the normal spacing of all drive pins around the periphery of the sprocket wheel.
Correspondingly, the web for use in the Gerber apparatus has at intervals along the length of the web equal to the circumference of the sprocket wheels an extra registration hole, or as the case may be, two extra registration holes, on the same line as the line sprocket drive holes down each side of the web, and located between an adjacent pair, or two immediately adjacent pairs of drive holes, and again preferably at a spacing of D/2. The web thus has, down each side, at the appropriate intervals corresponding to the circumference of the sprocket wheels, a visually distinct group of three or five holes aligned with each other across the width of the web. Because of the different pin/hole spacing, it is impossible for the loader to load the web into the web handling apparatus in anything other than the correct registration, since this is the only position in which the web will fit onto the sprocket wheels, i.e. with the extra registration pin(s) engaging the extra registration holes on the opposite sides of the sheet.
At various times in the past, webs having differently configured sprocket pin drive holes have been proposed, including extra holes in the web, either in line with the sprocket pin drive holes or to one side thereof (US-A-4802692), and for a variety of different purposes, but mainly to accommodate misaligned pins on the drive sprockets. For example, it is known from DE-A-1964643 to provide either enlarged holes of elongate, round ended elongate slots between each adjacent pair of drive holes (see in particular Fig. 3). Also, in EP-A-382574 (published 16.08.90), a web is shown having additional in-line sprocket holes at half pitch spacing between the normal drive holes, those additional sprocket holes being associated with radially extending cuts or lines of weakness, which enable the web to deform and be deflected if the web should encounter a misaligned drive pin. Webs having that type of hole configuration, i.e. with extra in-line holes at half pitch, will, of course, be useable on apparatus of the Gerber type, i.e. with the extra in-line registration pin on each sprocket drive, but were not specifically designed to do so. In contrast, the present invention seeks to provide a web configuration which will fit equally well onto the apparatus of the Gerber type, i.e. having an extra registration pin, or possibly two, on each sprocket wheel, in line with and spaced between an adjacent pair, or between two immediately adjacent pairs, preferably at a spacing D/2, although that is quite immaterial as far as the present invention is concerned, or on apparatus with the more usual form of sprocket drive.
The web configuration of this invention is shown in the accompanying drawing, which is a plan view of a web (1), e.g. a web sign making stock, although the material from which the web is constructed is wholly immaterial to the present invention, of indefinite width, i.e. whatever width is appropriate to fit a particular apparatus, and indefinite length, and having a line of equispaced sprocket drive pin holes (2,2') down each side and spaced inwardly in distance "d" from the edge of the web. Again the value of "d" is immaterial and will depend on the intersprocket spacing of the apparatus concerned and the overall width of the web. Usually, "d" will be of the order of 1-2 cms.
On the same line as each line of sprocket pin holes (2,2'), and down each side of the web, are elongated slots (3,3') equispaced between each adjacent pair of sprocket pin holes (2,2') having a length "1" (see the enlargement) that is equal to or less than D-2r, where D is the interhole spacing and "r" is the radius of the sprocket pin holes, and a width "2r", i.e. a width that is equal to the diameter of the sprocket drive holes.
When considered along the length of the web, the opposite ends of each slot (3,3') are inwardly arcuate at a radius r' that is preferably equal to r. Thus each of the slots (3,3') is separated from its adjacent sprocket pin holes (2,2') by an arcuate web of material (4,4') having a uniform width "w", measured in the longitudinal direction of the web that is equal to at least 2mm, thereby to give the web adequate longitudinal strength.
As will be apparent, such a web will fit apparatus of the Gerber type incorporating an extra registration pin or pins on the sprockets in line with and between adjacent sprocket pins.
When loaded with a web according to the present invention, the elongated slots (3,3') will permit the web to be driven quite smoothly through the apparatus in the normal, conventional manner, i.e. by the equispaced drive pins on each sprocket engaging the drive holes (2,2') on the web. The elongated slots (3,3') are simply there to permit the web to run over the extra registration pins(s) on each sprocket wheel, but serve no other purpose. In particular they do not serve the purpose nor the function of the extra registration holes as taught by the Gerber patent, since the slots (3,3') are incapable of distinguishing adjacent pairs of sprocket holes anywhere along the length of the web. The slots (3,3') therefore do not serve any registration purpose or function.
If desired, a registration function can be provided in known manner, by providing an indicator mark at equal intervals along each edge of the web adjacent opposite pairs of drive holes (2,2'). Such an indicator is shown at (5,5') comprising an extra hole at intervals along each edge of the web at a longitudinal spacing equal to the circumference of the sprockets, and at a distance d' from the edge of the web where d' is greater (or less) than d by an amount greater than r + ri, where ri is the radius of the indicator hole. Preferably d' is greater than