Patent GB-648276-A (GB)
Title: Improvements in recording apparatus
IPC: G01K5/02
Filed: 1947-09-22
Abstract: 648,276. Recording-apparatus. YARNALLWARING CO. Sept. 22, 1947, No. 25734. Convention date, March 27. [Class 106 (iv)]. Recording-apparatus comprises a marker supported by a marker arm and co-operating with a chart, means being provided to vibrate the marker, the arm or a portion thereof being tuned to substantially the frequency of the vibrating means or to a harmonic thereof. A primary indicating shaft 37 carries an index 35 with counterweight 38 and a marker arm 44 comprising three parts namely an axially resilient reverse bend part 45 of non-magnetic spring material such as beryllium copper or phosphor bronze, a stiff part 55 preferably of thin-walled stainless steel tubing and a V-shaped spring support 56 for a marker. An electromagnet 68 is mounted on a bracket 64 and an armature 74 is mounted on the spring 45 so that when alternating current is fed to the electromagnet the marker arm 44 vibrates. The spring 56 is selected to have, with a particular marker suitably positioned, a natural period of vibration at or near that of the alternating current or a harmonic thereof. A chart plate 75 has a straight part 76 including the centre 77 and a part 78 curved to correspond with the path of the marker about the axis 37 and is rotated by a motor 81. A circular chart 86 rests against the chart-plate and is held against its curved part by a finger 87. The marker moves above the chart surface in accordance with the movements of the indicator shaft 37 and when current is fed to the electromagnet 68 and the marker is set in vibration it makes intermittent contact with the chart to mark a record thereon with a minimum of friction. The chart plate may be of sheet metal or of a transparent or translucent plastic material, when the chart may be illuminated from behind. A spring 88 is provided to hold the marker in inactive position when changing charts. The housing for the apparatus has windows through which the indicator and recording can be viewed. In a second embodiment, Fig. 8, the chart is flat and its axis of rotation is parallel to the shaft 37. The electromagnet is housed within the reverse bend of the spring 541 and the marker is mounted on a straight spring clip 56<SP>1</SP> which may be integral with the rigid tubular part 55<SP>1</SP> and may be formed by flattening the tube, varying its natural frequency according to the length of the part so flattened. The axially-resilient connection between the shaft 37 and the marker arm may take various forms including a spring loop, a double return bend, a bifurcated spring forming twin return bends and a rigid return bend connected to the rigid part of the arm by pins passing through holes with compression springs each side of the latter part of the arm held by nuts which can be adjusted to control the axial freedom of the arm. Excessive vibration may be damped by recessing or slotting the chart plate along the range of movement of the marker and also by tuning the marker slightly off resonance. By suitable adjustment the marker may be vibrated without breaking the ink film, thus obtaining a continuous line. When a metal chart disc is slotted the chart may be illuminated from behind in this region.