Patent GB-650049-A (GB)
Title: Improvements in or relating to x-ray apparatus
Inventor: CALDWELL JOHN THOMAS
IPC: G03B42/02
Filed: 1947-12-10
Abstract: 650,049. X-ray cassette holders. GENERAL ELECTRIC CO., Ltd. Dec. 10, 1947, No. 32597. [Class 98 (i)] A cassette holder movably mounted relative to an X-ray source comprises a framework supporting a cassette, a screen of X-ray opaque material consisting of two or more parts each mounted for independent movement on the framework so that by varying the positions of the parts on the framework different portions of the cassette can be successively unscreened, and projecting members equal in number to the portions of the cassette to be unscreened which co-operate successively with a stop fixed with respect to the X-ray source to enable the cassette holder to be brought to successive positions in which the successively unscreened portions of the cassette are in the same position with respect to the X-ray source. The cassette holder and a fluorescent screen are independently slidable on parallel rails. The cassette holder consists, as shown, of a frame 1 supporting the cassette 2, and having rollers 3 sliding in the parallel members. The screen consists of two lead sheets 5, 6 on frameworks 7, 8 respectively, slidable on rods adjacent the cassette on the same side thereof as the X-ray source. Each lead sheet covers one-third of the cassette. Frameworks 7, 8 have spring-loaded catches 9, 10 engaging grooves 11, 12 in a rod 13 rotatably mounted in the frame 1 when the screens are as far to the right as possible, leaving a portion of the cassette on the left unscreened. The holder 1 is first withdrawn from the X-ray field and the tube switched on for screening. The tube is then switched off and prepared for radiography. This may be effected by the movement of the holder into a position where the unscreened portion of the cassette is central in the ray path by sliding the holder on the parallel supports until a cam 14 on the rod 13 abuts a projection attached to the supports, and the radiograph is made. When the holder is withdrawn from the exposure position, a lever 17 pivoted to the frame is rocked, and, by means of a ratchet connection 18, rotates the shaft 13 through 60 degrees. This rotation disengages catch 9 from the groove 11, allowing screen 5 to move under action of a tension-spring 20 to the left, leaving the central part of cassette uncovered. The cam 14 is rotated out of position and a cam 15 rotated into position to abut the projection on the supports, so that the unscreened portion is again brought into position for a second exposure. The holder is again withdrawn, and the rod 13 rotated 60 degrees, releasing screen 6 which moves under spring-action, leaving the righthand portion of the cassette unscreened. Cam 15 moves out of position and a third cam 16 moves into position to locate the cassette for a third exposure. The holder is then withdrawn, rod 13 is returned to its original position by a handle 19, the screens are returned by a rod 21 fixed to the frame 7, and cassette 2 is replaced by a new cassette for further exposures. According to the Provisional Specification, cam 16 is replaced by a stop fixed to the frame 1, and a diaphragm may slide independently parallel to the fluorescent screen and cassette holder. Specification 601,262 is referred to.