Patent GB-412239-A (GB)
Title: Improvements in or relating to devices for controlling photographic exposures
IPC: G04F3/02
Filed: 1932-12-22
Abstract: 412,239. Time switches. HARVEY, E. A., Selo Works, Woodman Road, Warley, Brentwood, Essex. Dec. 22, 1932, No. 36372. [Class 38 (v).] A device for controlling photographic and particularly R÷ntgen ray exposures of the kind comprising in combination a manually-operable setting member movable in a fixed path from a zero position to different selected distances along the path, spring means normally operable automatically on release of the setting member or a part associated therewith to return it to zero, a governor to regulate the speed of return, and a switch or equivalent mechanism operated by the spring means or a part actuated thereby during the return movement to cause the exposure for a time determined by the time taken for the return movement is characterized by means for delaying the operation of the switch or equivalent mechanism on release of the setting member or a part associated therewith until the spring means have acquired under the control of the governor a substantially constant speed of operation. As shown in Fig. 1, a cam disc 5 is mounted on a shaft 6 to which is attached a disc 7 having a circular series of apertures below which are numbers on a fixed dial, the device being operated by insertion of the finger in one of the apertures, rotation of the disc 7 to a fixed finger catch and return through spring means to its initial position. The shaft 6 is coupled through a gear train and a one-way clutch to a governor 12. In the circuit of a relay 13 actuating a switch controlling the current in the hightension transformer of a R÷ntgen-ray apparatus is a switch 15. A slip plate 16 is maintained in frictional engagement with the disc 5 by a spring plate 17, the disc 5 being capable of overrunning the plate 16 in each direction of rotation. In the zero position the plate 16 is engaged by a stop 18 and the switch 15 is held open by a pivoted arm 19 having an abutment 20 resting on the protuberance 21 of the disc 5. When the dial is rotated the disc 5 and plate 16 are moved as a unit away from the stop 18, the plate 16 having a ramp 23 raising the abutment 20 clear of the disc 5. When the projection 24 engages the abutment 20 the slip plate is arrested, and the extent of over-run of the disc 5 on further rotation of the dial determines the length of the exposure. On release of the disc 7, the disc 5 and the plate 16 rotate together in the reverse direction until the plate 16 is arrested by the stop 18, when the abutment 20 drops on to the hollow 22 on the disc 5 to close the switch 15 until the disc 5 approaches its original position and the protuberance 21 lifts the abutment 20 to open the switch 15. In the modification shown in Fig. 3 a fast timing mechanism 30 and a slow timing mechanism 60 are provided. The switches 15 of the fast and slow mechanisms are connected in parallel with the relay 13. The contacts of the switch 15 of the mechanism 30 are connected to terminals 39, 40 and the contacts of the switch 15 of the mechanisms 60 to terminals 69, 70. Electromagnetic brakes 31, 61 are associated with the governors 12 of the mechanisms 30, 60 respectively. In the fast mechanism is arranged a switch 32 the contacts of which are connected to terminals 37, 38 and which is operated by a cam 33 on an arm 34 carried by the shaft 6. In the slow mechanism are arranged switches 62, 63 the contacts of which are connected to terminals 73, 74 and 75, 69 respectively and which are simultaneously operated by a cam 64 on an arm 65 rigid with the shaft 6. The brakes 31, 61 are in circuits including switches 36, 66 arranged for simultaneous operation by a push-button 93. The contacts of the switch 36 are connected to terminals 41, 42 and the contacts of the switch 66 to terminals 71, 72. The brakes 31, 61 are energized from mains or battery connected to terminals 90, 91 and the relay 13 is connected between terminals 91, 92. For exposures with either mechanism separately, the dial is operated and the brake released by the button 93, and for exposures in conjunction, the dials are set and on depression of the button 93 only the slow dial rotates, as the switch 36 for the brake of the fast mechanism is shunted by the switch 63. When the slow dial reaches zero, the switch 63 opens, breaking the energizing circuit of the brake 31 and allowing the fast dial to return to zero.