Patent GB-1336680-A (GB)
Title: Photo-electric information carrier scanning apparatus
IPC: D04B15/66
Filed: 1971-08-23
Abstract: 1336680 Photo-electric reader FRANZ MORAT GmbH 23 Aug 1971 [22 Aug 1970] 39450/71 Heading G1A [Also in Division G3] A photo-electric scanner for scanning an information carrier to generate control signals for e.g. a circular knitting machine is provided with lamp voltage and current control apparatus to protect the lamp from damage due to extended overloading. The scanning operation can involve continuous movement or stepping of the information carrier along between lamps and photocells, the control signals being generated during each step of movement. To avoid heating up and damage of the carrier during periods when it is stationary the lamps may be switched off between each period of movement, but a time lag in attaining full intensity is experienced each time the motion is restarted. The invention provides circuitry whereby a lamp may be overloaded to obtain a quick build up of intensity without damage thereto. The circuit includes a photo-sensor 37 which monitors the lamp 13 intensity, which is compared with a desired intensity signal at 41 to develop a difference signal which causes control 45 to change element 33 e.g. a potentiometer and thus the lamp light output. Circuit 47 limits the current so that it cannot go above a value Imax set at 49. The voltage control for the lamp is via a limiter circuit 50. Before switch 53 is closed to start a scanning cycle (which includes motion of the carrier through motor 65), the voltage supplied is at a level U R  determined by terminal 69 and the lamp is a low intensity output condition. On closing switch 53, the switch 55 is closed so that an overvoltage U H  is applied from terminal 59 I max  is rapidly obtained, and limiter 47 starts to operate. Once I max  has been obtained, the voltage rises more slowly (with the current on I max ) until the desired high intensity # is reached At tone t, when this has occurred, lower constant values of U and I are needed to maintain the desired high intensity, the value of U in fact now reaching a value lower than the rated voltage for the lamp. In the event of dirt on the lamp or pivoting of the photocell, which would cause a lower intensity to be sensed than was actually being emitted, the lamp is prevented from continued overloading by, at time t 2 , the delay or time-lag element 54 becoming effective and causing 55 to reopen. However, switch 57 is still closed, through the action of time-lag element 67 and so U max  is set by terminal 61 which is at the rated value U N  for the lamp. If the time t 3  when motion of the information carrier actually commences is determined by the inertia of the system, then switch 63 may be switched on in synchronism with switch 53. If the inertia is less and a time shorter than t o  to t 1  is needed for motion to start, 63 is provided with some delay or a link 64 is provided which arrange for switch 63 to operate only when the desired intensity has been reached (null difference value). Time lag 67 determines end point of scan at time t 6 . A detail circuit of the control and limiter circuits is provided Fig. 4 (not shown) in which 37 is a photo-resistor.