Integral latching mechanism for module front plate

A latching mechanism for latching the front plate of a circuit board module to the circuit board module rack effected by merely inserting the module in the rack. The mechanism includes a resilient tab having a prong with a tapered head. The prong mates with an aperture of a mount on the rack such that at full insertion of the module the head engages the mount through the aperture thus precluding withdrawal of the module from the rack. Depressing the resilient tab allows withdrawal of the prong from the mount through the aperture to unlatch the mechanism and permit withdrawal of the module from the rack.

BACKGROUND 
The present invention relates to latching devices and in particular to a 
device for latching a circuit board module to its mounting rack. 
Complex and large electric circuit networks such as systems control 
networks for ships or nuclear reactors are typically broken down into a 
plurality of small circuits each mounted on a modular circuit board. The 
circuit boards, which are electrically interconnected to make up the 
network, enable fast and easy replacement of failed circuit parts as well 
as greater flexibility of design. 
Circuit boards are typically rectangular and mounted vertically in racks. 
Generally, the top and bottom edges of the boards slide in tracks and the 
back edge is equipped with some electrical connector means. 
The front of the circuit board module is equipped with a plate for 
handling, identification and asthetic purposes. Also some mechanism is 
typically provided to lock the circuit board module to the circuit board 
rack. This is desired to prevent withdrawal of the module and thereby 
breaking of the circuit network in the event of some withdrawal force 
being applied to the circuit board by accident, e.g., earthquakes, 
vibrations, sudden ship reeling movements or jarring by the end of a 
janitor's mop handle. The present invention is such a latching mechanism. 
One known prior art latching mechanism is the screw type. A machined screw 
extends through the front plate of the module and threadingly engages a 
threaded hole on the rack. The shortcomings of the screw type include the 
necessity of manufacturing, stocking and assembling costly machined parts 
and the need to employ a separate tool to assure a positive and lasting 
engagement. 
Another known prior art latching mechanism is the plunger type wherein a 
plunger is slidably disposed in an expandable sleeve attached to the front 
plate. Upon insertion of the modular circuit board into the rack, the 
sleeve penetrates a hole provided therefor. Once so positioned, forcing 
the plunger through the sleeve expands the sleeve to a dimension greater 
than that of the hole and thereby effecting a latch, to preclude 
withdrawal of the sleeve through the hole. The shortcomings of the plunger 
type include stocking and assembly costs, the fact that currently there is 
but a single source of supply for this particular device and the ability 
to completely insert the circuit board module into working position in the 
rack without actually effecting the latch. 
SUMMARY OF THE INVENTION 
The present invention overcomes the disadvantages of the prior art latching 
mechanisms by providing a mechanism integral to the front plate, 
eliminating separate parts and insuring positive lasting engagement 
automatically by merely fully inserting the module. No tools or further 
actions beyond mere insertion are required. Moreover, the integral 
mechanism dimensions are such that it can directly replace the plunger 
type mechanism. 
The integral mechanism includes a prong having a shaft ending in a head 
tapered to a point. The prong is resiliently mounted to the circuit card 
module front plate and is aligned with a hole on the circuit card module 
rack. As the card is inserted into the rack the tapered surface of the 
prong near the point thereof engages the edge of the hole. Further 
insertion of the card forces the resilient mounting means to deflect as 
the tapered surface bears against the hole edge. 
Upon the head being completely inserted through the hole, the resilient 
means urges the prong back toward its original position thus latching the 
head behind the mount plate. The module may be unlatched by positioning 
the prong head in alignment with the hole and withdrawing the circuit 
board module and thus the integrated latching prong head from the mount 
plate hole. 
It is an object of the present invention to provide a latching mechanism 
for a modular circuit board. 
It is a further object of the invention to provide a latching mechanism for 
a modular circuit board which is integral with the circuit board module 
front plate. 
It is another object of the invention to provide a latching mechanism with 
the foregoing advantages and which eliminates the use of a plurality of 
parts. 
It is yet another object of the invention to provide a latching mechanism 
with the foregoing advantages and which eliminates the requirement of 
tools to effect the latch. 
It is a further object of the invention to provide a latching mechanism 
with the foregoing advantages and which insures positive latching 
engagement automatically by merely inserting the module into its rack. 
Other objects and advantages of the present invention will become readily 
apparent from the following description and drawings which illustrate a 
preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Refer now to FIG. 1 there being shown a plurality of circuit board modules, 
generally referred to by reference numeral 10, incorporating the preferred 
embodiment of the latching mechanism according to the present invention. 
Circuit board modules 10 are shown in position in circuit board module 
rack 14. Rack 14 may be of any suitable construction which provides the 
following essential features: (1) Circuit board module alignment, this is 
illustrated by upper and lower tracks 16 and 17 respectively. (2) Circuit 
board module support, this is illustrated by support beam 15 extending 
between module mount 26 and rack back wall 13. (3) Electrical connection 
plugs 18 (only one in view) provide for electrical interconnection of the 
circuit board modules. 
Modular front plate 12 is molded from a polycarbonate base resin. Number 
940 clear LEXAN (a registered trademark of General Electric Company) is 
used in the preferred embodiment. This material provides sufficient 
strength for support and resiliency for operation of the latch as 
described in more detail below. Tint or coloring may be added to the resin 
as desired for aesthetic effect. 
Also shown in FIG. 1 are latch apertures 24 of mount 26. An aperture 24 is 
provided for each circuit board module 10. 
Refer now to FIG. 2 there being shown a side view of a circuit board module 
10 of FIG. 1. Circuit board 11 is secured to plate 12 by screws 33. 
Electrical connectors 19 provide electrical interface with plug 18. Front 
plate 12 includes latch block 20, arm tab 21 and prong 22 as well as other 
parts, all molded in one piece from LEXAN. Front plate 12 is described in 
more detail below. 
Refer now to FIG. 3 there being shown a screw type latching mechanism of 
the prior art. Machined screw 32 is held in circuit board module front 
plate 30 by c-clip 34 and threadingly engages threaded-bore 31 of module 
mount 27. Bearing washer 36 is provided to prevent marring of plate 30. As 
discussed above, the disadvantages of this arrangement include the 
necessity of manufacturing, stocking and assembling costly machined parts 
and the need to employ a separate tool, e.g., screw driver, allen wrench, 
to assure a positive and lasting engagement. 
FIGS. 4, 5 and 6 illustrate a plunger type latching mechanism of the prior 
art. FIG. 4 shows the position of module front plate 40 before the circuit 
board module is fully inserted into the circuit board module rack. 
Expander 46 extends through circuit board module front plate 40 and is in 
alignment with aperture 24 of module mount 26. In FIG. 5 the circuit board 
module is fully inserted, expander 46 is in position in aperture 24, 
however, no latch is effected. In FIG. 6, plunger 41 is inserted thereby 
expanding expander 46 to a dimension greater than aperture 24 to effect 
the latch. As noted above the disadvantages of the plunger type latching 
mechanisms include stocking and assembling costs, the fact that there is 
but a single source of supply for this particular device and the ability 
to completely insert the circuit board module into working position in the 
rack without actually effecting the latch, thus enabling accidental 
withdrawal. 
Refer now to FIG. 7, there being shown the preferred embodiment of the 
integral latching mechanism according to the invention. Circuit board 11 
mounted on module front plate 12 of circuit board module 10 is shown in a 
not fully inserted position in rack 14. Latch block 20 is integral with 
and protrudes from the lower portion of front plate 12 and serves to 
provide a finger hold for withdrawing module 10 from rack 14. Latch tab 21 
extends from latch block 20 toward the rear and toward module mount 26 of 
rack 14. Prong 22 extends from latch tab 21 also in the rear direction. 
Prong 22 includes a shaft portion 25 extending between tab 21 and prong 
shoulder 34 and a tapered head 28 between shoulder 34 and tip 23. 
Referring now to FIG. 8, with module 10 in tracks 16 and 17 prong 22 is 
aligned such that upon inserting module 10 tapered head 28 of prong 22 
bears upon the lower edge of aperture 24 of module mount 26. Shoulder 34 
is diametrically smaller than aperture 24 to enable passage of prong 22 
therethrough. 
Refer now to FIG. 9 upon full insertion of module 10 into rack 14, 
whereupon connectors 19 mate with plug 18, shoulder 34 has completely 
traversed aperture 24 and shaft 25 lies through aperture 24. As discussed 
above, in the preferred embodiment the front plate material is chosen such 
that tab 21 provides the requisite resiliency to elastically bend as the 
edge of aperture 24 bears upon tapered head 28 and to rebound to its 
original position as shoulder 34 clears aperture 24. Once tab 21 has 
rebounded, the latch is effected as shoulder 34 interfacing with module 
mount 26 will preclude withdrawal of module 10 from rack 14. 
Refer now to FIG. 10, there being shown a perspective view of front plate 
12 of module 10 absent circuit board 11. Front plate 12 is form molded in 
one piece and includes all the parts shown in FIG. 10. Front wall 49 of 
front plate 12 is oriented perpendicular to side wall 48. Circuit board 11 
(See FIG. 2) is attached flush to side wall 48 by screws 33 and screw 
holes 35. Upper gusset 52 and lower gusset 53 provide support to maintain 
the perpendicular relationship of front wall 49 and side wall 48. Latch 
block 20 extends from front wall lower portion 51 of front wall 49 towards 
the front thereof at and below lower gusset 53. Latch tab 21 extends below 
block 20 from the front lower edge thereof towards the rear ending in tab 
lip 39. Prong 22 extends below gusset 53 from tab lip 39 towards the rear. 
Refer now to FIG. 11, a rear view of prong 22 being shown therein. In this 
view the latching mechanism is in the latched position with prong 22 
extending through hole 24 and engaging mount 26. Tab lip 39 and lower lip 
38 of latch tab 21 are shown in phantom. 
FIG. 12 illustrates in more detail further salient features of the latching 
mechanism of the preferred embodiment. Latch block 20 is hollow and 
provided with latch block support gusset 29 for strength. Upper lip 37 and 
lower lip 38 along with grip treads 36 provide finger and thumb holds for 
squeezing latch tab 21 toward latch block 20 and for withdrawing module 10 
from rack 14. 
The preferred embodiment of the invention as described above was formed in 
one piece from Number 940 clear LEXAN. However, the invention is not 
limited thereto, and may be formed in any suitable number of pieces or 
from any material or combination or materials as required or desired in a 
particularcircumstance. 
For simplicity in the preferred embodiment the resiliency of tab 21 is 
provided by the resiliency of the specific material from which tab 21 is 
formed. However, the invention is not limited thereto and other means, 
e.g., springs, may be employed to provide such resiliency. 
The above description and drawings are only illustrative of one embodiment 
which achieves the objects, features and advantages of the present 
invention and it is not intended that the present invention be limited 
thereto. Any modifications of the present invention which come within the 
spirit and scope of the following claims are considered part of the 
present invention.