Patent GB-764506-A (GB)
Title: Self adjusting stylus
IPC: H04N1/032
Filed: 1954-11-26
Abstract: 764,506. Copying telegraphy. CREED & CO., Ltd. Nov. 26, 1954 [Dec. 3, 1953], No. 34333/54. Class 40 (3). In a facsimile recorder of the type in which an electrically energized stylus is employed for writing on electro-sensitive paper means are provided automatically to adjust periodically the extent of stylus protrusion so that its contact with the recording paper is maintained at a uniform and optimum pressure irrespective of stylus wear. Figs. 7 and 8 illustrate the application of the invention to a recorder in which a plate 61 carries four styli 6 for recording on a strip of paper 63 passing from a roll 71 through a curved shoot 64. Plate 61 is carried by a shaft 77 and is rotated by a motor (not shown) acting through gearing 81, 83. Each stylus is mounted in a chuck member 21 and is retained in a holder 4 by a spring 22 which exerts sufficient force to retain the stylus in position but permits axial adjustment. Located on the underside of plate 61, behind each stylus, and with its armature 67 protruding through a hole in the plate, is an electromagnet 92. The armatures are normally held away from the styli by springs 69, but by energizing an electromagnet the associated armatures may be displaced to strike the end of the chuck member and advance the stylus. This action takes place for each stylus when it comes opposite an anvil 68, which is so located as to stop the stylus at an extent of protrusion selected to provide optimum pressure in its subsequent sweep across record sheet 63. The energization of the electromagnets at the correct instants is effected by means of commutator 96 carrying segments 98 to which one side of the electromagnets are connected and which engages a brush 99 connected to a suitable power supply. In a modification, Fig. 10, a percussion displacement of the stylus is avoided and replaced by a gradual displacement resulting from the engagement of the chuck member 21 with an inclined surface 121 formed on the armature 118. In this case only a single electromagnet 116 and armature 118 is employed supported in a stationary position by a rod extending through a hollow drive shaft 77. The electromagnet is energized at the appropriate instants and the stylus is displaced against the anvil 68 as the chuck rides over surface 121. Stylus holders 4 are carried on pivoted arms 105 urged forwardly by springs 108 so as to allow the styli to yield to unevenness in the thickness of recording paper 63. The invention is also described as applied to a recorder in which the styli are carried by a flexible belt so as to transverse across a flat recording sheet, Figs. 1-6 (not shown). The stylus adjustment is effected by a spring-urged hammer released by an electromagnet and restored by a pin carried by one of the belt-drive pulleys. The electromagnet may be actuated by a switch tripped by a second pin on the belt-drive pulley, a commutator, a magneto, or by special signals sent from the transmitter. Reference is made to an arrangement in which phasing signals transmitted for a few seconds before the start of the actual transmission are employed to operate the electromagnet. The belt-drive pulley carries a brush for cleaning the stylus tip at each traverse of the pulley. Specifications 734,435, 739,594 and 739,595 are referred to.