Patent GB-638146-A (GB)
Title: Improvements in and relating to electron optical instruments and cameras therefor
IPC: H01J37/22
Filed: 1946-11-08
Abstract: 638,146. Photographic plate-changing mechanisms. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 8, 1946, No. 33301. Convention date, Nov. 10, 1945. [Class 98 (i)] In an electron optical instrument comprising an evacuated envelope having a substantially horizontal axis along which a beam of electrons is ejected, a changing mechanism for photographic plates has a plate supply chamber supported above the electron beam, and a plate storage chamber positioned below the electron beam, each chamber having closure means therein and able to hold a number of plates, external means for operating the closure means of the supply chamber to release a plate so that it falls by gravity to a position wherein it intercepts the electron beam, means connected with the closure means of the storage chamber for supporting the plate in this position, and means including the closure means of the storage chamber for releasing the plate from this position to fall by gravity into the storage chamber, the plates being substantially vertical throughout the sequence of operation. The instrument may be an electron microscope or an electron diffraction instrument having an operating panel 1, Fig. 1, with an electron gun behind it, a focusing yoke 2, a chamber 4 with a manipulator 5 for a specimen 3, a container 7 through which electrons pass to a platechanging mechanism 8 and a fluorescent screen 6 on which the diffraction pattern is formed. The entire apparatus is evacuated. A shutter 9 is closed to out off the electron beam while a plate is dropped from the top of mechanism 8 to a position in front of the screen, the shutter is opened to make an exposure and then closed while the plate drops into the bottom of mechanism 8. This mechanism consists of a box 12, Fig. 2, with the container 7 and screen 6 fixed to the centre portion thereof, closed at its top end by a plate 20 from which depends a frame member 17 on which a magazine 14 and a receiver 15 are removably supported above and below the electron beam respectively. The magazine 14 is a rectangular box 42, Fig. 4, with a sloping bottom 43, and aperture in the wall 44 closed by a plate 47 spaced therefrom. Walls 44, 47 carry channel-members 45, 46 arranged to allow passage of air while excluding light. The photographic plates 32, in rectangular frames, rest vertically in the magazine and are pressed against the wall 49 by a spring 48. A press-button acting through " Sylphon " (Registered Trade Mark) bellows actuates a rod connected to a channel-member 50 movable longitudinally on the bottom wall 43. Movement of member 50 operates a closure plate in the magazine to uncover a slot at the lowest point in the wall 43, and also operates a plate having lugs with inclined edges which engage pins 36 on the bottom of the frame of the plate next but one to the wall 49, moving all the plates but one away from wall 49. The plate thus freed drops out of the magazine, and on release of the button the magazine is closed and the plates are again pressed by spring 48 against wall 49, so that the next plate may be dropped out when the button is again pressed. The released plate falls into guides 35, Fig. 2, on to a support 37 on the receiver 15, by which it is retained in the exposure position until the exposure has been made. Support 37 is attached to a closure plate covering an entry slot in the top of receiver 15, operated by a mechanism similar to that operating the closure plate of magazine 14. The closure plate of the receiver opens, carrying support 37 away from the plate 32, which drops into the receiver. If other plates are already in the receiver, they are pressed to the right in Fig. 2, but are drawn in the opposite direction by hooks (not shown) engaging notches in the frame of the last plate, the hooks being operated by a lever mechanism operated by the opening movement of the closure plate. The receiver and magazine can be removed from the box 12 and carried to a dark-room for loading and unloading. Specification 618,657, [Group XL (a)], is referred to.