US PATENT SUBCLASS 400 / 55
INCLUDING ADJUSTMENT FOR OPTIMUM PRINTING PLANE

Current as of: June, 1999
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400 /   HD   TYPEWRITING MACHINES

55INCLUDING ADJUSTMENT FOR OPTIMUM PRINTING PLANE {4}
56  DF  .~> Responsive to thickness of record-medium
57  DF  .~> In accordance with the number of sheets of record-medium
58  DF  .~> By adjustment of platen relative to carriage
59  DF  .~> By adjustment of carriage (e.g, carriage-guide rollers) {1}

DEFINITION

Classification: 400/55

INCLUDING ADJUSTMENT FOR OPTIMUM PRINTING PLANE:

(under the class definition) Subject matter wherein significance is attributed to adjustment of the optimum printing plane of a typewriter as that term is discussed and defined in (1) Note below.

(1) Note. In over simplified terms, a typewriter requires at least two elements for a typing operation. One of these elements is a type-member* that impacts against a record-medium* at a print-point*; another of these elements is a platen* that serves to prevent movement of the record-medium away from the type-member during impact. (Obviously, other structures and mechanisms are also required for operation, but discussion of these may be deferred.) The type-member includes a type-face* that lies in a plane; the platen includes a surface that lies in a plane. In the instance of a cylindrical platen, the platen plane is theoretically tangent to the peripheral surface of the platen, whereas the surface itself is arcuate, therefore not

planar, but considering the small area of a character* compared to the area of a cylindrical platen, the difference between the arcuate surface and the tangent plane is minimal; the platen plane can be considered as planar. Theoretically, the platen plane should coincide with the type-face plane when the type-face is at the print-point to ensure an imprinted character that is uniformly legible at any point on its area. Actually, the two planes cannot coincide because of the thickness of the record-medium and the thickness of a ribbon*, both of which lie between the two planes in most typewriters, but at the very minimum the two planes should be parallel, one to the other. Because in an actual typewriter the planes may become out of parallelism with each other, it is necessary to provide means to adjust either the platen plane or the type-face plane, or both, to correct the possible misalignment. Moreover, in an actual typewriter the number or thickness of record-medium sheets may vary. If the record-medium of greater than usual thickness is used, the type-face will impact the surface of the record-medium at a print-point that is further from the axis of the platen than is usual. The type-face plane would not be parallel to the plane of the record-medium at the new print-point. To summarize, the "optimum printing plane" is the plane at which the type-face and the record-medium best meet to form an imprinted character that is uniformly legible at any point on its area, and is the result of adjustments to the typewriter to ensure the coincidence and parallelism of the record-medium with the type-face at the print-point.