Variable bottom-edge margin indicator and method for typewriter paper and the like

Claim 1

A variable bottom-edge margin indicator for typewriter paper and the like having, in combination with a typewriter of the type having a ball printing head, a cylindrical typewriter platen rotatable about its axis, immobile along its axis, and around the cylindrical surface of which the paper is advanced in a transverse path during typewriting, and a cylindrical-section paper shield beneath the platen; sensor means mounted beneath the platen inwardly of and adjacent to one end of the platen in the region of the paper shield and the path of advancement of the adjacent-side margin of the paper and disposed to receive said side margin of the paper between the sensor means and the platen at said region, said sensor means having means for discriminating between the presence and absence of said paper at said region and producing an electrical signal indicative of the advent of said absence corresponding to the advancement of the bottom edge of the side margin of the paper out of said region, said discriminating means comprising a pair of insulated electrical contacts closely separated at substantially the same circumferential region of said platen and cooperative with juxtaposed conductive band means circumferentially carried by the platen; indicator means connected to said sensor means and responsive to said signal and comprising audible signal means; means for adjusting the position of said sensor means transversely circumferentially about the platen correspondingly to vary the location of said region, said adjusting means comprising insulating band means carrying said contacts at its forward end, housing therein conductors for connecting said contacts to a power source, and adjustably disposed transversely within guide means provided under and adjacent said platen and upon said paper shield, said band means extending rearwardly of said paper shield to provide exposed tab means for enabling the circumferential adjustment of the band means within said guide means and along said paper shield and to provide an exposed region at which said conductors housed in said band means are connected to further conductors leading to said power source, and calibration setting means cooperative with said adjusting means and disposed external to said platen and sensor means to enable viewing of said calibration setting means by the operator for controlling the tab means of said adjusting means in order to vary the region, correspondingly to set different-dimensional desired bottom-edge margins of the paper.