Patent GB-735018-A (GB)
Title: Improvements in x-ray apparatus
IPC: G03B42/02
Filed: 1953-12-14
Abstract: 735,018. X-ray apparatus. PICKER X-RAY CORPORATION WAITE MANUFACTURING DIVISION, Inc. Dec. 14, 1953, No. 34766/53. Class 98 (1). In X-ray apparatus having a fluoroscopic screen arm embodying a frame, a trackway thereon and a cassette carrier mounted for movement along the trackway between storage and exposure positions, an electric motor is connected to the carrier so as to move it along the trackway and a settable device is carried by the frame and co-operates with the carrier for engaging and selectively stopping it at a predetermined point on the trackway. As shown in Fig. 3, a column 12 is movable longitudinally and transversely of a tiltable table 11, and carries an X-ray tube (not shown) below the table. An arm 20 supporting the fluorescent screen 22 and the cassette 26 is hinged at 21 to a bracket 15 slidable on column 12 so that the arm, when locked in position, holds the screen and cassette over the table, but can be swung aside for positioning the patient. Screen and cassette support.-The arm 20 comprises longitudinal channel-shaped members 30, 31, Fig. 10, formed with ribs 32, 33, 34, 35, 36, 37, 38 and joined by end bars 39, 40, Fig. 9. The bottom of the frame is closed by a plate 41, and the top is partially closed by the fluorescent screen 22, leaving a well for loading a cassette tray 25, which has wheels 45, 46, 47, 48 engaging ribs 32, 36 so that it may slide the full length of support 20. The tray has a recess shaped as shown so that a cassette may be placed therein with its longer dimension either along or across the screen support. The tray 25 is movable by an electric motor 50 which drives through a slipping clutch a pinion 52 engaging rack teeth 53 on a bar 54 slidable between rib 35 and the side of member 31. A further set of teeth 55 formed on the side of bar 54 engage gear teeth 58 formed on a link 56 pivoted to the frame and carrying a roller 59 engaging a channel-sectioned guide 60 on tray 25. A shaft 65 journalled in the side of the frame carries a handle 51 and a boomerang-shaped arm 68 with a long pin 69 and a short pin 70. When the cassette is to be exposed in halves separated transversely of the arm, it is placed transversely in tray 25, handle 51 is turned to bring long pin 69 into the path of a projection 71 on tray 25, and a radiographic mask 79 with an aperture of the size of the area to be exposed is inserted between ribs 33, 34 and 37, 38. The motor 50 is energized by depressing a button switch 75 on the screen handle 76, moving tray 25 through bar 54 and link 56 until projection 71 engages pin 69. The motor 50 continues to rotate with the clutch slipping, so that tray 25 is held in position with the leading half of the cassette exposed. After exposure switch 75 is released, the circuit to the motor being such that the motor is then reversed so that the tray 25 is retracted to its starting position, where a limit switch 78 is opened to stop the motor. A spring-urged pawl 81 on the tray rides over pin 69 during the forward movement, but during the return movement it moves the pin so that handle 51 is in a neutral position with both pins 69 and 70 are out of the path of projection 71. When switch 75 is pressed again, therefore, the tray moves to the end of arm 20 and the second half of the cassette is exposed. Release of the switch returns the tray as before. In a modification, shaft 65 is depressible against spring means. In this case, after the first exposure, instead of returning the tray by releasing switch 75, the handle 51 is depressed so that pin 69 clears projection 81, and the tray moves on to the second exposure position. To expose the whole cassette, handle 51 is turned to bring the short pin 70 into the path, not of projection 71 itself, but of a depending lip thereof, so that the tray is arrested later in its travel. Pin 70 is short enough to clear pawl 81. A mask with an aperture the full size of the cassette replaces mask 79. The cassette may be exposed in halves separated longitudinally with pin 70 in the path of the lip on projection, and using a mask with an aperture of the required size. After the first exposure, the cassette is turned through 180 degrees in its own plane and the second half is exposed. The cassette may also be exposed in four quarters. A plate 43 (Fig. 3) on the arm 20 may bear marks which indicate the positions to which handle 51 is to be turned for each mode of exposure. Shutter control.-The shutter control levers 200, 201 are mounted next to the screen 22, and are linked by rods and bell-crank levers to arms 210, 211, Fig. 9. These arms engage rods 212, 213 of non-circular cross-section on which they can slide without turning. The rods extend longitudinally along column 12 and have arms 214, 215 thereon connected to shutter-control rods 216, 217. Screen frame latch.-A latch, not shown, holds arm 20 in position, but can be released so that the arm can swing about hinge 21. This latch also effects locking of bracket 15 to column 12. As shown in Fig. 21, a rack 100 is fixed to column 12 and a pawl 101 is pivoted in a housing 103 mounted on bracket 15. The pawl has spring fingers 109 which grip rack 100 on opposite sides thereof. A lever pivoted in the housing 103 at 110 has arms 111, 112. A cam 107 on the operating shaft of the latch normally occupies the full-line position, wherein arm 111 of the lever is pressed by a spring 113 to its full-line position so as to press the lower part of pawl 101 to hold it clear of rack 100, so that the bracket 15 may move freely along the column 12. The arm 20 is meanwhile latched. On rotation of the latch arm through 45 degrees, cam 107 and arms 111, 112 are moved to their dotted-line positions wherein pawl 101 is free to pivot. If the bracket is moved downwards, the action of arms 109 moves the pawl out of engagement with rack 100. Counterweights normally cause a tendency for the bracket to move upwards, and in any such upward movement the action of arms 109 moves pawl 101 into engagement with rack 100, thereby preventing further movement. Further rotation of the latch arm releases arm 20 from the bracket, and also frees the bracket for movement along the column. Protective apron.-A lead-rubber apron 140, Figs. 3 and 5, is fixed to a tube 141 supported by telescopic members 142, 143. Member 142 is hinged at 145 to the screen frame; the other end can be engaged by a bracket 146 when the table is horizontal, or by a bracket 147 when the table is vertical. The inner member 143 is slid out further to engage bracket 147, which is further from the hinge than bracket 145. Exposure timing.-If desired, a timer may be mounted on the screen frame to be brought into position only when the cassette is in exposure position. As shown in Fig. 47, the timer tube 162 is mounted on an arm 161 pivoted to the frame near a corner of the screen 22. Normally the arm is clear of the screen, but a pinion meshing with bar 54 drives the arm through a slipping clutch to swing it to position 161A where it is in the centre of the exposure area. A pin-and-slot device limits the movement so that the timer is in position before completion of the shortest movement of tray 25. On retraction of the cassette, the arm 161 is swung back. The X-ray tube voltage is increased when a radiograph is to be made, by known automatic means. Bucky grid.-When a Bucky grid is to be used, the grid 190, Fig. 50, is mounted in a frame 191 by springs 192. The frame 191 is inserted into guides provided between bottom plate 41 and mask 79 (Fig. 10). The shock of the stoppage of the cassette sets the grid into vibration. Vibrations in the supporting structure are quickly damped out, but the grid vibrates throughout the exposure. The vibration is made asynchronous and so prevents the formation of grid lines. U.S.A. Specifications 2,097,095, 2,184,962 and 2,259,036 are referred to.