Patent GB-601262-A (GB)
Title: Improvements in or relating to x-ray apparatus
IPC: G03B42/02
Filed: 1945-07-04
Abstract: 601,262. R÷ntgen-ray apparatus. CARTER, J. E. July 4, 1945, No. 17053. [Class 98 (i)] Apparatus for taking X-ray photographs comprises a holder for the sensitive film or plate, said holder being adapted to be moved to a non-exposure position, which allows a visual X-ray observation to be made, and to an exposure position, and means, operating in response to the movement of said holder, to ensure that the intensity of X-ray emission when the holder is in the exposure position is greater than that when it is in the non-exposure (observation) position. The apparatus includes a rotatable shaft 8 extending parallel to the direction of movement of the cassette holder 1 and having three radially projecting exposure stops 10, 11, 12 disposed at equal longitudinal and angular intervals along the shaft; and means for automatically rotating the shaft as the holder is reciprocated comprising a cam unit 13 carried by the holder which engages one of the three exposure stops in alternation with one. of three equally-spaced radially projecting stops 9a, 9b, 9c at the observation position so as to bring an unexposed portion of the plate or film into the exposure position. As shown, the apparatus is ready to start a cycle of operations, one, 9a, of the three observation stops being vertical and the first, 10, of the three exposure stops lagging 30 degrees behind it. A master switch is first closed, supplying a low current to the filaments of the valve rectifying system for the X-ray tube, and when the operator desires to make an observation he closes a foot switch supplying the full H.T. to the rectifier system, thus producing a low intensity X-ray beam. Having made his observation, he releases the foot switch and presses a button 7 (Fig. 5) to release the mutilated disc 41 on the shaft 8 from the projection 44. The loaded cassette holder is then moved towards the first exposure position (indicated by dotted lines in Fig. 3). As the holder moves to the right the element 39 (Fig. 20) of the cam unit 13 engages the observation stop 9a and rotates the shaft 8 through 30 degrees, after which the cam unit is clear of the stop 9a. The right side of the cam element 38 as seen in Fig. 20 then engages the first exposure stop 10 and thus rotates the shaft 8 a second 30 degrees, after which the stop 10 comes to rest in the well of the element 38, positioning the holder 1 in the first exposure position with the first third of the sensitive surface behind the aperture 3 in the lead screen 2. During the first shaft rotation of 30 degrees, one 60 degrees segment of a three segment cam 16 closes a switch 14 increasing the filament current of the rectifier system, and during the second 30 degrees rotation this switch remains closed, while at the end of it one of three equallyspaced pips on a wheel 17 momentarily closes switch 15 which trips a relay switching on the H.T. supply for the exposure period. The exposure made, the cassette is pushed back to the observation position during which movement the shaft 8 makes two further rotations of 30 degrees, the third and fourth steps of rotation of the shaft, as first the cam element 40 engages the exposure stop 10 and then the left side of the cam element 38 engages the observation stop 9b, the switch 14 opening and thus reducing the rectifier filament current at the start of the third rotation. This sequence is repeated for the second and third exposures with the difference that the stops causing rotation of the shaft are 9b, 11, 9c and 9c, 12, 9a respectively, and the second and third portions of the sensitive surface are exposed. If at any instant prior to exposure the operator desired to make a further observation, he depresses a button 48 which causes a pawl 49 (Fig. 7) to engage one of the teeth on the wheel 51 and rotate the shaft backwards 60 degrees, returning the holder to the previous observation position. To return the apparatus to the starting position without completing the cycle, the master switch is opened, the cassette holder moved to a position in which the cam unit cannot engage any of the stops and the handle 52 is moved in an anticlockwise direction as viewed from the left-hand end of the apparatus until it is parallel to the fixed vertically depending arm 53, which position the handle 52 occupies at the end of the eleventh step of rotation of rotation. Thus, on returning the holder to the observation position, the shaft completes the final step of rotation back to the starting position.