X-ray cassette with a window for illuminating patient data

An x-ray film cassette has a window for illuminating patient data and a slide movable over the window to shut out light. A counterpoise of ferromagnetic material is provided for locking the slide in a closed position and which can be released magnetically. The counterpoise is pivotably mounted about a tilt axis passing through its center of gravity. A spring member is provided for biasing the counterpoise such that an end face is positioned within the window to prevent movement of the slide.

BACKGROUND OF THE INVENTION 
The invention relates to an x-ray film cassette with a window for 
illuminating patient data and with a slide closing the window tightly 
against light, which can be locked in the closed position by a spring and 
unlocked magnetically. 
Our U.S. Pat. No. 3,962,585 issued June 8, 1976 shows an x-ray film 
cassette with a window for illuminating patient data. The window can be 
sealed tightly against light with a slide. The slide is secured against 
inadvertent opening of the window and consequent exposure of the section 
of film behind it. On a side facing the window, it is provided with a 
ferromagnetic tongue which springs into the window opening and which locks 
the slide in the closed position. To open the window it is necessary to 
slide a magnet along the exterior of the window so that the spring tongue 
is drawn out from the window opening by the magnet and is moved into an 
open position on the slide. In this position, the slide can be opened and 
closed again together with the tongue attached to it. In those x-ray film 
cassettes which ensure per se efficient protection against inadvertent 
opening of the slide, there is nevertheless a disadvantage that the spring 
tongue can be opened by a short hard blow, such as may occur, for example, 
if the cassette is dropped on the floor. If, in such a case, the shock 
direction has a sufficiently large component both in the direction of 
vibration of the spring and also in the direction in which the slide is 
opened, the window may burst open. Because the possibility of coordinating 
the film sheet to a specific patient is thus lost, this is extremely 
awkward, particularly if the x-ray exposures have already been effected. 
SUMMARY OF THE INVENTION 
An object of this invention is to develop a window closure for an x-ray 
film cassette wherein any unintentional opening of the window is 
precluded. This window closure should moreover be adapted to fit the thin 
cassette wall as well as possible and at the same time should be 
producible at a reasonable price. 
In an x-ray film cassette of this invention for locking a slide in the 
closed position there is coordinated a counterpoise of ferromagnetic 
material mounted pivotally about the axis of tilt passing through the 
center of gravity of the counterpoise and a spring pushing the 
counterpoise into the locking position. This method of construction has 
the particular advantage that the counterpoise which is supported at its 
center of gravity by the tilt axis, is completely weight balanced in every 
position of the cassette. This means that on dropping the cassette, the 
force of impact, no matter from what direction it comes, catches the 
counterpoise at the center of gravity without producing on it a torsional 
or pitching moment about the tilt axis. Thus, the slide is no longer 
released by a single impact. 
A particularly simple construction results if, in accordance with the 
invention, the axis of tilt of the counterpoise is aligned parallel to the 
plane of the window and perpendicular to the direction of displacement of 
the slide. In this way it is possible to use the entire front edge of the 
counterpoise aligned parallel to the axis of tilt as a stop. 
In a preferable development of the invention, the counterpoise may be 
attached to the side of the slide facing the window and may be pushed into 
the window opening in the locking position with the end face which is in 
front in the opening direction. This has the particular advantage that the 
ferromagnetic material of the counterpoise is attached to the slide and 
can be positioned for opening of the window by external magnetic forces. 
Moreover, this results in a sufficiently stable stop face of the 
counterpoise in the window opening.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates that part of a cassette cover 1 of an x-ray film 
cassette 2 in which there is inserted a window 3. The patient data on the 
x-ray film 4 lying in the cassette can be illuminated through this window. 
The window can be closed tightly against light by way of a slide 5 which 
can be moved in front of the window opening. The area of the cassette 
cover 1 in which the window 3 is located is covered on the cassette outer 
side with a frame-like panel 6 sunk flush in the cassette cover 1. This 
panel has a rectangular opening 7 which is a few millimeters larger than 
the window 3 in the cassette cover. The panel is attached to the cassette 
cover such that the opening 7 and the window 3 are located above one 
another. Set in between the frame-like panel 6 and the cassette cover 1 
there is a rectangular cavity 8 matched in height and width to the slide, 
but in length projecting beyond the length of the slide by slightly more 
than the length of the window. The slide 5 is mounted in this cavity so as 
to be displaceable in a longitudinal direction. The slide has a recess 9 
of trough-like shape on the inner side of the cassette. The width of the 
recess 9 is somewhat less than the width of the window opening. 
Approximately in the middle of the slide, the edge of the trough-shaped 
recess is provided on both sides with a groove 10 or 11, respectively, not 
quite extending to the base of the recess. In these grooves is inserted a 
see-saw like counterpoise or counter balance arm 14 of ferromagnetic 
material which is matched to the width of the recess and provided with two 
projections 12, 13 engaging in the grooves. The projections 12, 13 of the 
counterpoise 14 are disposed such that their connecting line cuts the 
center of gravity of the counterpoise. The width of the counterpoise 
without its projections is somewhat less than the width of the window 3 in 
the cassette cover 1. 
As can be seen from FIGS. 1 and 2, a spring tongue 15 is riveted onto one 
end face of the trough-shaped recess of the slide. The length of the 
spring tongue 15 is such that it somewhat overlaps the edge of the 
counterpoise 14 facing it. Due to its initial stress, the spring tongue 
thereby presses this edge of the counterpoise against the base of the 
recess 9. The other end of the counterpoise is thus forced a few 
millimeters out of the recess of the slide 5 and into the opening of the 
window 3 in the cassette cover 1. The counterpoise 14 is so orientated 
relative to the recess of the slide 5 that, with complete closure of the 
window 3, its forced-out end can still just spring into the opening of the 
window. This end of the counterpoise 14, forced into the opening of the 
window, is provided with a projecting stop lug 16 for reinforcement. In 
the opened position of the slide, this stop lug 16 abuts the inner wall of 
the cavity 8 between the cassette cover and the frame-like panel 6 on the 
cover. 
FIG. 3 shows a view of the cassette in a data illumination device 17 shown 
in part. This data illumination device is provided with guides 18, 19 for 
the insertion of the x-ray film cassette 2. In front of the point at which 
the window of the x-ray film cassette 2 is located when the latter is 
fully inserted into the guides 18, 19 of the data illumination device 17, 
a permanent magnet 20 is incorporated in the side wall of the data 
illuminating device facing the window. In the example embodiment of FIG. 
3, there is attached to the permanent magnet 20 a spring cam 21. This 
spring cam 21 is illustrated in FIG. 1 from the side, together with the 
permanent magnet 20. At its curved end it is provided with a groove 22 
which is matched to the width of a step 23 mounted on the outer side of 
the slide 5, extending vertically to the direction of displacement. The 
permanent magnet, together with the spring cam 21, can be displaced in the 
data illuminating device 17 by way of a drive 24, here illustrated 
schematically, along a guide path 25. On the two guides 18, 19 for the 
x-ray film cassette 2 there is provided a sensing element 28 or 29, 
respectively, coupled with a switch 26 or 27 for the complete insertion of 
the x-ray film cassette 2. The switches 26, 27 are mutually connected in 
series to the drive 24 for the permanent magnet 20 and the spring cam 21. 
An optical system for the data illumination, not illustrated here, is 
adjusted to the position of the window 3 of the x-ray film cassette 2 when 
the cassette is fully inserted into the data illuminating device 17. 
On complete insertion of the x-ray film cassette 2 into the illumination 
device 17, the window 3 is adjusted to the optical system of the data 
illumination device and the slide 5 closing the window is disposed below 
the permanent magnet 20 of the data illuminating device 17 such that the 
permanent magnet 20 is located exactly above the side of the counterpoise 
14 dipping into the window opening of the cassette over 1. The side of the 
counterpoise 14 spring biased into the window 3 is thereby pushed by the 
magnetic field of the permanent magnet 20 out of the window 3 and pushed 
against the force of the spring tongue 15 into the recess 9 of the slide 
5. The slide 5 is released in this position. Simultaneously the groove 22 
of the spring cam 21 comes into engagement with the step 23 of the slide 
5. As soon as the x-ray film cassette 2 is completely inserted into the 
guides 18, 19 of the data illuminating device 17, the two sensing elements 
28, 29 actuate the two switches 26, 27. These switch on the drive 24 for 
the permanent magnet 20. The permanent magnet 20 with its magnetic field 
moves the counterpoise 14 on the slide 5. The window 3 is opened. In the 
example embodiment of FIG. 3, the spring cam 22 in engagement with the 
slide is connected to the permanent magnet 20. The magnet 20 supports the 
magnetic field on opening and subsequent closing of the slide 5. After 
illumination of the patient data, the magnet is moved back into its 
original position again by the drive 24. The slide is thereby locked again 
and the window closed. With the slide 5 completely closed, as the x-ray 
film cassette 2 is drawn out of the data illuminating device 17, the 
spring cam 21 with its groove 22 initially slides out of the step 23 of 
the slide 25 and, in the further course of movement, the magnetic field 
releases the counterpoise 14. The counterpoise can now be tilted into its 
locking position by the spring tongue 15. The side of the counterpoise 14 
provided with the stop lug 16 is thereby pushed into the opening of the 
window 3. The window 3 is locked in this position. Since the counterpoise 
14 is supported in the slide 5 at its center of gravity by the two 
projections 12, 13, sudden impacts effecting the cassette 2 are also 
unable to exert moment on the counterpoise 14. The slide remains locked. 
The slide also cannot be pushed open by pushing on the step 23 attached to 
the exterior of the slide. 
It would also be possible for the permanent magnet 20 to be stationary in 
the data illumination device and for only the spring cam 21 to be moved by 
the drive 24. The magnetic displacement forces can be considerably 
increased if a further permanent magnet 30 is disposed on the opposite 
side of the cassette 2 inserted in the data illumination device 17, in 
coordination with the other side of the counterpoise. The position of such 
a second permanent magnet 30 relative to the window 3 is indicated in 
dashed lines in FIG. 2. 
Although various minor modifications may be suggested by those skilled in 
the art, it should be understood that we wish to embody within the scope 
of the patent warranted hereon, all such embodiments as reasonably and 
properly come within the scope of our contribution to the art.