Guard plate

The improved guard plate of this invention is used to protect the cylinder of a lock. It includes a relatively flat body, attached to the door in the vicinity of the cylinder, and a disc rotatably mounted between the door and the flat body. In an open position, an opening in the disc permits access to the cylinder; and, in the closed position, the solid portions of the disc do not permit access to the cylinder. In addition, rotatable fingers are provided so as to lock the rotatable discs in either the open or closed position.

BACKGROUND OF THE INVENTION 
The guard plates presently used for protecting lock cylinders are generally 
disposed over the cylinder on the outside surface of the door. Such plates 
prevent intruders from penetrating the cylinder and thus opening the door. 
One disadvantage of these guard plates is that the keyhole portion of the 
cylinder is still accessible to unwanted intruders. Thus, it is an object 
of this invention to provide a guard plate which will also cover the 
keyhole portion of the cylinder. In this way, the lock and its cylinder 
will be protected even more from tampering and from picking. Furthermore, 
the improved guard plate of this invention prevents glue or other foreign 
materials from getting into the keyhole or the cylinder itself.

DETAILED DESCRIPTION OF THE INVENTION 
As is best shown in FIGS. 1, 2 and 6, the improved guard plate includes a 
relatively flat body or plate 1, which is generally attached in a 
conventional manner to the outside surface of a door 3, such as by means 
of bolts 2. The body may be made from any strong material, but it is 
preferably made of metal. Further, a hole 7 is defined in the body 1 in 
order to provide access to the keyhole of the cylinder 8 of the lock. 
Positioned between the flat body 1 and the outer surface of the door 3 is a 
rotatably mounted disc 4. In the approximate center of the disc 4 a short 
stem or nub 5 is provided. This stem 5 of the disc 4 may then be 
positioned within a second hole or opening 6 within the body 1. Thus, the 
hole or opening 6 acts as a sort of bushing and permits rotation of the 
disc 4. Further any other conventionally known methods of rotatably 
mounting the disc 4 may be provided. In the preferred embodiment, a slot 
12 is provided on the front surface of the stem 5 (see FIG. 2). Then, a 
flat object, such as a special key-plate, can be inserted into the slot 12 
in order to rotate the disc 4. In some embodiments, the stem 5, and the 
slot 12, may be recessed partially within the hole 6 of the body 1, or, in 
other embodiments, the stem 5 may extend completely through the hole 6 and 
extend outward from the body 1. In still other embodiments, it is possible 
to eliminate the slot 12 and merely extend the stem 5 through the hole 6 
and to permit it to extend outward from the body 1. This way the stem can 
act as a sort of handle and may be easily rotated by the user's fingers. 
On the inner surface of the body 1 a circular groove or slot 11 is 
preferably positioned. A stop 10 is positioned on the outer surface of the 
disc 4 so that it may move within the circular slot 11 as the disc is 
rotated. In other embodiments, it is possible to provide the stop on the 
body 1 and the groove or slot 11 on the disc 4. In addition, a hole or 
opening 9, approximately equal in size to the hole or opening 7 in the 
body 1, is made in the disc 4. In the open position of the guard plate 
(see FIG. 6), the disc 4 is set so that its opening or hole 9 is aligned 
with the hole 7 in the body and access is provided to the keyhole of the 
cylinder 8 of the lock. As can be seen, the stop 10 is at one extreme end 
of the circular slot 11 and further clockwise rotation of the disc 4 is 
not possible. In order to prevent access to the keyhole of the cylinder, 
the disc 4 is rotated in a counterclockwise direction. This causes the 
hole or opening 9 of the disc to move away from the hole or opening 7 in 
the body 1. Thus, the solid portions of the disc effectively close the 
hole or opening 7 in the plate and prevent access to the keyhole of the 
cylinder. During this rotation of the disc, the stop 10 moves in the 
circular slot 11 until it reaches the other extreme end of the slot (see 
FIG. 1). At this point, further rotation of the disc 4 is not possible and 
the hole 7 is completely covered by the solid portions of the disc 4 (see 
FIG. 1). 
In order to prevent rotation of the disc 4 by intruders, a plurality of 
locking fingers 14, 15 and 16 are provided. The exact number of fingers 
provided is dependent on the degree of security desired. If more fingers 
are provided, then the guard plate will be more secure. Obviously, if less 
fingers are provided, the guard plate will be less secure. In the 
preferred embodiments, three fingers are provided, but it should be 
understood that any number of fingers may be used. 
Through holes 13 are provided in the body 1 near the periphery of the disc 
4. Then, the fingers 14, 15 and 16 are rotatably inserted into respective 
holes. Considering now the second finger 15 (see FIGS. 2 and 4), its 
construction will be considered, but it should be pointed out that the 
construction of all of the fingers is the same. The finger 15 is 
essentially round in shape with a circular flange 17 provided at its back 
end. Preferably the diameter of the flange 17 is greater than the 
respective through hole 13. This prevents the finger from being easily 
removed from the improved guard plate. The rounded portions of the flanges 
interact with respective circular grooves 18 located on the periphery of 
the disc 4. This effectively prevents rotation of the disc 4. The flange 
portion 17 of each of the fingers is further provided with cutoff portions 
23. When the fingers are rotated so that the cutoff portions 23 are 
aligned with the respective grooves 18, the fingers no longer serve to 
prevent rotation of the disc 4. 
As best shown in FIGS. 3, 4 and 5, each of the fingers 14, 15 and 16 is 
provided with a slot 20 on its front face. A flat object, such as the 
special key-plate used to rotate the disc 4, may then be fitted into the 
slots 20 of the fingers and used to rotate the fingers. If desired, the 
front face of the fingers may be recessed within the respective through 
holes 13. In other embodiments, it is possible for the fingers to extend 
through the holes 13 and extend outward from the body 1. In such a case, 
it may be desirable to provide an enlarged head 29 on the front face of 
the finger, in order to facilitate rotation of the fingers (see FIG. 7). 
Alternatively, in another embodiment of the fingers, small holes 33 may be 
provided on the front face of the fingers (FIG. 10). Then, the special key 
may be inserted into the holes to rotate the fingers. Furthermore, any 
other known method of rotating the fingers may be used. 
It is preferable that alignment marks 19 be provided on the front faces of 
the fingers. In addition, additional alignment marks 21 should be placed 
on the surface of the body 1 near the fingers. Thus, when the fingers are 
rotated, the user knows that the cutoff portions 23 of the flange 17 will 
be aligned with the grooves 18 when the alignment mark 19 is aligned with 
a certain alignment mark 21. To facilitate this process of identifying the 
correct alignment mark 21, numbers 22 may be provided near the alignment 
marks 21. Then, the user of the improved guard plate may need only 
remember a simple combination for the fingers. In the embodiments shown in 
this application (see FIG. 6), the combination is 4 6 5. As can be seen 
from FIGS. 3-5, the cutoff portions 23 of the flanges 17 of the fingers 
may be made at different angles to the alignment mark 19 of that finger. 
For example, the cutoff portion 23 of the finger 14 is at an angle A1 to 
the alignment mark 19, the cutoff portion 23 of the finger 15 is at an 
angle B1 to the alignment mark 19, and the cutoff portion 23 of the finger 
16 is at angle C1 to the alignment mark 19. To change the combination of 
the guard plate, one merely has to reposition the fingers or to insert 
different fingers. 
In some embodiments of the device, it may be desirable to eliminate the 
flange portion of the fingers. In such a case, one portion of the rounded 
fingers would be essentially flat. When this flat portion was aligned with 
the grooves 18, rotation of the disc 4 would be possible. 
Because of the nature of this device, a high degree of accuracy in 
positioning the fingers is not necessary in order to permit rotation of 
the disc 4. Thus, if only a portion of the cutoff portion 23 is within the 
circular groove, rotation of the disc 4 will cause the corner 24 of the 
groove 18 to rotate the finger until the entire cutoff portion 23 is 
aligned with the groove 18. Thus, a high degree of accuracy in placing the 
alignment marks 19 and 21 is not required. 
In the preferred embodiments, a backing plate 25 may be inserted between 
the rotatable disc 4 and the door 3. This plate would be used to keep the 
disc 4 securely against the inner surface of the body 1. In addition, an 
elastic spacer 26 may then be provided between the plate 25 and the outer 
surface of the door 3. The plate 25 has an opening 28 within which the 
cylinder 8 is aligned. Obviously, the elastic spacer 26 must also have an 
opening within which the cylinder 8 may be positioned. 
In order to provide for more accurate positioning of the fingers, teeth 27 
may be provided on the back end of the flange 17 (see FIG. 8). A matching 
set of teeth would then be provided on the plate 25. In the normal 
position, these teeth would prevent easy rotation of the fingers. During 
intended rotation of the fingers, inward pressure of the fingers would 
cause the plate 25 to be moved toward the door, because of the action of 
the elastic spacer 26, and the fingers would be permitted to rotate to a 
certain extent. Thus, more accurate alignment of the alignment marks 19 
and 21 may be provided. 
In still another embodiment (see FIG. 9), the body 1 may be made of three 
plates 30, 31 and 32. The outer plate 30 is essentially flat and is 
provided with a hole 7 to provide access to the cylinder 8. Further, this 
outer plate 30 has the opening 6 into which the stem 5 of the disc 4 is 
positioned. The middle plate 31 has a circular recess 34 into which the 
disc 4 may be positioned. In addition, the middle plate 31 has circular 
recesses 35 into which the flange portion 17 of the fingers may be 
positioned. The inner plate 32 is provided with a substantially 
rectangular recess 36 into which the backing plate 25 may be positioned.