Patent GB-552449-A (GB)
Abstract: 552,449. R÷ntgen-ray apparatus. WATKINSON, E. J. W. Oct. 4, 1941, No. 12838. [Class 98 (i)] R÷ntgen-ray apparatus of the kind comprising a fluorescent screen, a cassette or film-holder carrying a number of films side-by-side and slidable between the screen and a Potter-Bucky diaphragm to present the films in sequence to the middle of the screen for exposure, and means to switch on the X-radiation and simultaneously to start the diaphragm in motion, comprises also a lead or lead-loaded mask with an aperture corresponding to the exposure area and arranged to slide automatically between the diaphragm and the screen immediately before the cassette reaches its operative position, and to be completely withdrawn from the screen at the same time as the cassette. The apparatus shown comprises a frame c carrying a lead or lead-loaded mask a with a central exposure aperture b, a frame g carrying a Potter- Bucky diaphragm, and a cassette-holder h, which are all provided with rollers engaging respective guide rails so that they may be slid to and from a position in front of a fluorescent screen k. The cassette-holder h is moved by an operating handle 24. A rod S rotatably mounted on it carries four pins equally-spaced along it and extending radially from it in mutually-perpendicular directions. On movement of the holder to the left one of these pins engages a fixed stop, so positioning the frame with one of the films in the exposure position. By means of fixed inclined cam surfaces which engage the pins during the sliding movements the rod is turned through angles of 90 degrees to bring each pin on it successively into engagement with the fixed stop, so that each movement to the left brings the next film to the exposure position. As a pin reaches the stop, it operates a plunger to close a switch which completes the circuit of a solenoid 10, Fig. 2, the plunger 11 of which then trips a latch 12 which latches a lever to a lever 13, The lever then moves under the action of a spring 21 and carries with it the mask frame c, to which it is connected by a link n, Fig. 1. As the mask comes into operative position a projection 3 on the lever j engages a lever 4, which through a push-rod 6 closes contacts 5 to energize a solenoid 7. This releases a latch 8 retaining a rod 18 secured to the frame g of the Bucky diaphragm, which then begins to move to the left under the action of a spring 22 and the control of a dash-pot 17. At the beginning of this movement a head 38 carried by the frame g releases a slidable bar 27, which then moves to the left and closes contacts to bring the X-ray tube into operation. At the end of the movement, the head engages a block 35 on a second bar 28 carrying one of the contacts, so raising this bar and disengaging it from a latching pin. The bar then moves to the left, opening the contacts to end the exposure. The lever 13, which is connected to the head 38 by a link 20, moves with it to the left, and finally is locked to the lever j by the latch 12. When the cassette holder h is moved to the right, after the exposure, its leading edge engages a pin 43 on the lever i and returns it, together with the lever 13, to the position shown, so restoring the mask and Bucky diaphragm to their initial positions. The head 38 re-sets the switch bars 27, 28 at the end of this movement.