Recording styli and control circuits for styli

Claim 2

Recording apparatus comprising: a thermal stylus having an elongate electrically insulating core, an electrically resistive coating on the said core, and electrical connections attached to the ends of the coating for connecting the coating to a power source, the connections establishing a current path longitudinally through said coating; a record medium support having an edge of small radius; means for supporting said stylus so that it extends transversely across the said support edge and contacts a record medium passing around the said edge; and means responsive to an electrical signal for moving said stylus along said edge, whereby a heat-sensitive record medium in contact with said electrically resistive coating is marked in a pattern determined by movement of said stylus along said edge when a heating current flows through said coating.

Claim 3

Recording apparatus as defined in claim 1, in which said electrically insulating core is hollow and one of said electrical connections passes through the hollow core.

Claim 4

Apparatus as defined in claim 1, further comprising a servo amplifier connected to apply a common signal for controlling the movement of the stylus along a record medium passing over said edge and also for controlling the supply of current to the stylus, the control being such that the periods of increased heating of the stylus substantially correspond to the periods in which the stylus is moving.

Claim 5

Apparatus as defined in claim 1, in which the means for moving the stylus includes a coil to which the stylus is attached and which is arranged in a magnetic field, and means applying an alternating signal to said coil, the apparatus further comprising means including a coupling capacitance for applying the alternating signal to the stylus to provide a heating current for the stylus.

Claim 6

Apparatus as defined in claim 4, including means for applying a continuous DC potential across the stylus to provide a minimum standing level of heat.

Claim 7

Apparatus as defined in claim 4, including an adjustable resistance in series with the stylus to provide a manual control of trace intensity.

Claim 8

Apparatus as defined in claim 1, in which the stylus is pivoted to a supporting arm to permit free pivotal movement of the stylus in a plane perpendicular to the line of the edge.

Claim 9

Recording apparatus comprising a thermal stylus, the thermal stylus having an elongate electrically insulating hollow coRe, metallizing coatings on two end portions of the said core and an electrically resistive coating on the portion of the core between the said end portions, electrical connections attached to the two metallizing coatings for connecting the resistive coating to a power source and establishing a current path longitudinally through the resistive coating; a record medium support having an edge of small radius; means for supporting said stylus so that it extends transversely over the said support edge to contact a record medium passing around said edge; and means responsive to an electrical signal for moving said stylus along said edge; whereby a heat-sensitive record medium moving over the said edge and in contact with the said resistive coating when a current flows through the coating is marked, as a consequence of heat received from the said coating, in a pattern determined by the movement of the said stylus along said edge.

Claim 10

Recording apparatus comprising a thermal stylus, the thermal stylus having an elongate electrically insulating hollow coRe, metallizing coatings on two end portions of the said core and an electrically resistive coating on the portion of the core between the said end portions, electrical connections attached to the two metallizing coatings for connecting the resistive coating to a power source and establishing a current path longitudinally through the resistive coating; a record medium support having an edge of small radius; means for supporting said stylus so that it extends transversely over the said support edge to contact a record medium passing around said edge; and means responsive to an electrical signal for moving said stylus along said edge; whereby a heat-sensitive record medium moving over the said edge and in contact with the said resistive coating when a current flows through the coating is marked, as a consequence of heat received from the said coating, in a pattern determined by the movement of the said stylus along said edge.