Patent GB-750908-A (GB)
Title: Improvements in or relating to methods and apparatus for recording electrical or mechanical vibrations
Inventor: DICKINSON FRANK CLIFFORD
IPC: G01H1/00
Filed: 1953-04-09
Abstract: 750,908. Recording-apparatus. ROTOL, Ltd. April 9, 1954 [April 9, 1953], No. 9706/53. Class 106 (4). [Also in Group XX] Apparatus for recording, in wave form, an image of a light source caused to move rectilinearly as a function of the amplitude of electrical or mechanical vibrations comprises a stationary optical system 27 arranged to form a real image of the light source, motive means for repeatedly passing a length of a strip of lightsensitive material through the image position and control means co-operating with the motive means to control the exposure of the strip to the light source so that any lengthwise portion of the length of the strip is recorded upon during only one of its passes through the image position. In the apparatus shown, a length of a strip of film is wrapped round a drum 10, enclosed in a casing and driven by an electric motor through a gear-box from which one of five ratios may be selected to give a drum periphery speed of 50, 100, 250, 500 or 1000 inches per second. An optical system 27 is arranged for forming at the drum periphery images of points of light which are formed on the screens of a group of cathode-ray tubes during the passage of a selected one of three portions of the length of strip under the control of two drumoperated switches. In these two switches, three pairs a, b, c, of contacts 125, 126, Fig. 6, normally closed by a contact ring 17 on a hub 29 of the drum 10, open when bridged by an insulated island 129, and three pairs a, b, c, of contacts 144, 145 normally open, close when bridged by a conductor 146 in an insulated ring 18 on the hub 29. In order to record on the first portion of the length of strip on the rotating drum 10, corresponding pairs of contacts, selected manually through switches 130, 143, are put into the anode and firing circuits respectively of a thyratron 128 and the latter circuit is prepared by charging a condenser 141 by manually closing and re-opening a switch 142. During the ensuing revolution of the drum, closing of the selected contacts 144, 145 fires the thyratron 128, allowing its anode current to flow through a resistance 118 to increase the negative potential on the grid of a self-excited oscillator 114 so that it stops producing the radio frequency current which, when passed through a heavily insulated transformer 115 and rectified, provides a sufficient voltage drop across a resistance 113 to extinguish the cathode-ray beams in tubes such as 110. Exposure starts and continues until, after approximately a third revolution of the drum, the opening of the selected contacts 125, 126 breaks the anode circuit of the thyratron to start the oscillator 114 and switch off the cathode-ray beams. Recording on the second and third portions follows upon operation of the selector switches 130, 143 and charging switch 142. A new length of strip is then wound into position on the drum 10 by manually operating a switch to start a motor 35 housed in a sleeve 34, Fig. 3, upstanding from the drum and receiving current through sliprings 13, 15 on the hub 29 co-operating with stationary brushes. The motor 35 drives a transverse shaft 40 from which drives are taken through different gear trains to drive supply and take-up spools and a toothed traction roller 53 engaging holes in the strip to draw it from a spool-box 42 round a toothed guide-roller 50, out of the drum 10 through a slot 51 and round its periphery back through the same or another slot, round a toothed guide-roller 52. The rollers 50, 52 are interconnected by gearing and roller 52 is manually set on its splined shaft to ensure a sufficient degree of slack to minimize friction between the strip and drum during winding. A cam 65 driven from the gearing actuates a switch 66 to stop the feed motor 35 when sufficient strip has been fed and also advances a counter one unit, the number registered being photographed on the length of strip, when a lamp circuit is completed through a slip-ring 16 on the hub 29. The roller 52 has two contacts on its upper flange co-operating with a spring-loaded copper-carbon brush connected to a slip-ring 14 on the hub 29 for transmitting two pulses each revolution to an indicator so that a fault due to breaking of the strip or tearing of the holes would be signified by inconsistency between the indicator and the length of strip which should have been fed. As the strip is transferred from one spool to the other, a counterweight 90 is driven along a leadscrew 92 and damage to the screw 92 due to over-running of the motor 35 is prevented by contacts 103 in the motor circuit being opened by the weight 90. The drum 10, inverted in Fig. 4, houses two ball-bearings whose inner races are carried by a hollow shaft 30 bolted to the casing, while the motor 35 is centralized by a bridge-piece 36 and carries a taper roller bearing 39 whose outer race is mounted in the cover of the casing. Three waveforms and a time base derived from a neon tube flashing at intervals may be recorded across a 70 mm. film using a single optical system or four waveforms and a time base using one wide-angle optical system for each pair of cathode-ray tubes and one narrower angle system for the neon tube.