Patent Number: 047605898
Section: summary

FIELD OF THE INVENTION This invention relates to diagnostic X-ray apparatus and more particularly to: (a) an improved grid cabinet and (b) a film cassette tray. The grid cabinet can either include a stationary grid or a movable grid. The grid cabinet with a movable grid is also known as Bucky. BACKGROUND OF THE INVENTION In X-ray medical examinations the X-ray films of varying sizes conventionally packaged in cassettes are used. Generally, a film cassette is placed on the cassette tray which in turn is inserted into the grid cabinet. To screen secondary radiation from the film, stationary or moving lead line grids are used. Reciprocatory movement of the grids over the film prevents the grid lines from being photographed. It is desirable to have the film cassette automatically centered in the grid cabinet in such a way that the film is aligned with the X-ray beam. It is also desirable to sense the size of the film cassette and automatically communicate this information to a beam collimator for an automatic adjustment of the collimator's shutters in order to match the area of the X-ray beam with the film size. Linear or rotary potentiometers are used for communicating the information. There are several cassette trays on the market which feature automatic centering of the film cassette and cassette size sensing for automatic collimation. All of the existing arts use a very similar centering system utilizing four jaws sliding from the center of the tray. Generally, means for cassette centering and means for cassette size sensing with sensing potentiometers are disposed in the tray, said tray being completely removable from the grid cabinet. Means for actuating grid to move over the film is traditionally disposed in the side of the cabinet and the grid motion is usually reciprocatory linear or damping sinusoidal. SUMMARY OF INVENTION A device, according to this invention, comprising a grid cabinet and a cassette tray offers the following significant improvements: (1) means for sensing both the width and the length of a cassette, is disposed in the cabinet and not in the tray eliminating a need for an electrical connector between the cabinet and the tray. This system allows for an alternative automatic collimation of an X-ray beam with the cassette size by a direct mechanical linkage of sensing components with the controls of the collimator's shutters and, therefore, eliminating a need for conventionally used potentiometers and servomechanisms and substantially reducing cost. (2) means for centering a cassette in the tray comprising of pivotal arms adapted to open respective pairs of cassette centering jaws and pivoting about respective pivot points located in two different places on the tray; this system allows for a substantial reduction in the thickness of the tray. (3) specially designed ball rolling slides as guide means for all linear movements of the tray, the centering jaws and a grid frame which utilize structure of the moving components as an integral structure of the slides. This design offers smooth motion, friction reduced only to rolling and greater durability. (4) two ways for inserting a grid into the frame; (a) from the top, (b) from the front of the frame. (5) means for actuating a grid in the grid frame to move over the cassette compact enough to be disposed in the back of the cabinet and not on the side as in the previous art; this allows for reduced width of the cabinet and, therefore, for a longer travel of said cabinet in the X-ray table and, as a result, for larger coverage of a patient. (6) the means for actuating the grid with a specially designed cam aided by a progressive spring to: firstly, accelerate the grid substantially instantaneously to a high speed to allow for very short exposures; secondly, to slow the grid down to accommodate longer exposures; and further, including an off-set bushing affixed to a cam follower to reverse the grid travel direction at random points.