Printed circuit board lock

A lock for retaining a printed circuit board within a frame, which can be used adjacent opposite front covers of the front edge of the printed circuit board to increase the structural rigidity of the frame when locked. This allows the printed circuit boards to be shipped within the frame direct from the factory within an entire fully tested system, with reliability, avoiding damage which often previously occurred due to vibrations and bouncing during transportation. Each lock is comprised of a lever, a protrusion for rotatably attaching the lever to the printed circuit board at a fulcrum point spaced from the axis of the lever, and a latch fixed to the lever at a position closer to the lever and closer to one end of the lever than the fulcrum point, whereby the latch can be rotated over-center relative to the fulcrum point into a cooperating hook and locked therein as the lever is rotated about the fulcrum point.

This invention relates to the field of printed circuit boards and 
particularly to a printed circuit board lock. 
Printed circuit boards are commonly retained parallel to each other in a 
housing, usually in a vertical orientation. During installation, the 
boards are pushed into the housing between upper and lower guides, which 
fix the planes in which the printed circuit boards are held. As each 
printed circuit board is pushed into final position, its edge, or a 
connector attached to its edge is forced into contact with a mating 
connector. 
While the force of entry into the mating connector is usually sufficient to 
retain a printed circuit board in position, transportion of the equipment 
sometimes causes sufficient vibration that the printed circuit board can 
become released from the connector. While the printed circuit board can be 
pushed back into mating position once the equipment is installed, thus 
re-establishing operability, vibration of the printed circuit board during 
transportion and flexure of the housing during bumping sometimes causes 
damage to the board, its contacts or the connector. 
A lever is often used at the front of the printed circuit board to aid 
insertion and extraction of the board. The lever is typically rotatably 
fixed to the bottom front edge of the printed circuit board, one end of 
the lever fitting into a slot in front of and below the printed circuit 
board. Pushing the handle of the lever forces the printed circuit board 
into place and into engagement with a connector. 
However, it has been found that the lever is unsatisfactory in many 
instances. Where a substantial number of printed circuit boards exhibit 
considerable weight in the housing, or where the printed circuit board 
housing structural members themselves resiliently bend under this 
influence or their own weight during bouncing in transportion, the printed 
circuit boards undergo substantial stress and sometimes are vibrated loose 
and are damaged. As a result the equipment sometimes does not work upon 
installation, requiring attendance of a serviceman and subsequent loss of 
time, money and goodwill. 
It is therefore important to ensure that the printed circuit boards are 
retained solidly in position within their housing, and particularly during 
the high vibration and bouncing often incurred during transportation. The 
present invention is a printed circuit board lock which securely retains 
printed circuit boards in position during such episodes, with a high 
degree of security, and in one embodiment causes the printed circuit 
boards to become structural members of the housing, increasing its 
rigidity and resistance to flexure. 
The subject printed circuit board lock utilizes a lever which is rotatably 
fixed to the front of a printed circuit board adjacent one edge, and has a 
latch which is positioned such that when the lever is pushed toward the 
front edge of the printed circuit board, the latch rotates into an 
over-center position and becomes hooked. With the lever retained in this 
position, the printed circuit board is locked into its position. 
In general, the invention is a printed circuit board lock comprising a 
lever, a protrusion for rotatably attaching the lever to the printed 
circuit board at a fulcrum point spaced from the axis of the lever, and a 
latch fixed to the lever at a position closer to the lever and closer to 
one end of the lever than the fulcrum point, whereby the latch can be 
rotated over-center relative to the fulcrum point into a cooperating hook 
and locked therein as the lever is rotated about the fulcrum point. 
Preferably the printed circuit board includes a guide for fixing the 
shortest distance between the fulcrum point and the bottom of the mouth of 
the hook, as the printed circuit board is slid edge-wise past the hook via 
the guide, the distance being no shorter than the distance between the 
fulcrum point and the edge of the latch opposite the fulcrum point. 
More particularly, the latch is comprised of a protrusion having an 
orthogonal axis parallel to the axis of the fulcrum. It should have a 
periphery opposite to the lever which describes at least a 180.degree. 
segment of a circle extending from a line parallel to the lever and 
preferably passing through the axis of the fulcrum. And has an indentation 
on the side of the lever which is cooperatively shaped to accept a lip of 
the hook. 
When the latch is positioned within the hook, and the board is positioned 
between guides, and mated to its connector, the board is retained from 
movement in all directions. With another latch noted within a hook across 
the other side of the board, the board being locked between the two; the 
board forms a structural member between the top and bottom of the housing, 
increasing its rigidity and resistance to flexure.

Turning to FIG. 1, a housing 1 is shown within which a plurality of printed 
circuit boards 2 are held. The housing may of course simply be a rack 
shelf in which printed circuit boards are held. Upper and lower guides 3 
and 4 retain the printed circuit boards in parallel relationship from 
front to rear of the housing, and serve to guide the printed circuit 
boards directly to mating connectors at the rear of the housing. 
As described earlier, during transportion the housing often flexes and 
vibrates and the printed circuit boards are sometimes released from their 
connectors and can slip out of one or both guides, which sometimes damages 
the printed circuit boards. 
Turning now to FIG. 2, a side view of the front bottom corner of the 
printed circuit board is shown. Printed circuit board 5 is passed into a 
printed circuit board housing or the like, sideways restrained by guides 
(not shown) in a well known manner. The bottom of a guide is depicted for 
illustration purposes as the surface 6. The printed circuit board is slid 
between the guides in the usual manner, between similar surfaces 6 at the 
top and bottom of the board, which generally fixes the position of the 
printed circuit board in a particular plane. Of course there will be some 
tolerance and play, since it is desired to slide the printed circuit board 
in smoothly, without binding. As the printed circuit board reaches close 
to the end of its travel it encounters a connector, for which considerable 
force is required to ensure mating. 
The printed circuit board lock which is the subject of this invention can 
be used at the bottom front corner, top front corner, or preferably, both 
front corners of the printed circuit board. 
According to the present invention, a lever 7 is rotatably attached to the 
printed circuit board at a fulcrum point 8. The manner of attachment is 
not critical, and can be, for example, a rivet having a head at one side 
of the printed circuit board, passing through a hole in the board and a 
hole in an extension 9 to the lever 7, and a washer and a C spring clamp 
which retains the entire assembly together. As lever 7 is moved, it is 
rotated about fulcrum point 8 on printed circuit board 5. 
A latch 10 is also fixed to the lever. The latch is located at a position 
closer to the lever and closer to the outside end of the lever than the 
fulcrum point. Thus as the lever 7 is rotated into a position parallel to 
the front edge 11 of the printed circuit board 5, the latch 10 is rotated 
over-center relative to fulcrum point 8. 
The latch 10 fits into a hook 12 which is shaped cooperatively with the 
latch 10. 
Preferably the hook is comprised of a bottom ledge 13 having an upwardly 
shaped lip which itself has a top edge 14 which extends back over part of 
the ledge. The hook is fixed to the guide with the lip extending forwardly 
thereof. While the lip need not be fixed directly to the guide, it should 
be linked thereto at least through an intermediary structure since the 
position of the bottom of the printed circuit board relative to the hook 
should be predetermined and related to the interface between the board and 
the guide. 
The latch preferably is comprised of a protrusion extending between the 
extension and the lever, past the printed circuit board. It has a 
periphery opposite to the lever which describes at least a 180.degree. 
segment of a circle extending from a line parallel to the lever and 
preferably passing through the axis of the fulcrum. More generally, the 
portion of the latch which slides within the hook as the lever is moved 
should have a rounded periphery. 
The periphery of the latch is indented close to the lever, cooperatively 
shaped to accept the lip when the latch is coupled into the hook. 
It is preferred that the lip of the hook forward of the bottom ledge should 
be rounded with a similar radius as the latch. In addition, the distance 
from the inside of the ledge just under the lip, through the center of 
rotation of the latch when coupled into the hook should be the diameter of 
the latch. 
It is preferred that the latch should extend below the bottom of the 
printed circuit board, although it is clear that with suitable design of 
the guide and hook, it can be restricted to a position alongside the 
printed circuit board. 
Reference is now made to FIGS. 3, 4 and 5 in conjunction with FIG. 2. 
Since the printed circuit board is held between surfaces 6, as it is slid 
into the housing the fulcrum point 8 can only take the position along line 
15. When the printed circuit board is in its final position, fulcrum point 
8 is at position 16. It should be noted that this is over-center relative 
to the center of rotation of latch 10, within hook 12. 
With the printed circuit board initially slid into position, the lever 7 is 
at a wide angle relative to the front edge of printed circuit board 5, 
with latch 10 just being introduced into hook 12. 
As lever 7 is rotated toward the front edge 11 of printed circuit board 5, 
the latch 10 drops to the bottom ledge 13 of the hook. Lever 7 is then 
pushed further to a position parallel to the front edge 11 of printed 
circuit board 5, causing further rotation of latch 10 in hook 12. The 
latch 10 becomes a fulcrum point, against which insertion stress of the 
printed circuit board can be exerted, and the printed circuit board is 
forced backward into the housing, into engagement with a connector. The 
fulcrum point 8 goes over-center relative to the rotation point of latch 
10. Past the center point (i.e. over-center) latch 10 rises slightly 
within hook 12, with indentation 20 going into engagement with the top 
edge 14 of the lip of the hook. 
Accordingly, with lever 7 held in position, even with considerable 
vibrational stress which widens the distance between top and bottom 
surfaces 6, the printed circuit board is locked into position against the 
adjacent surface 6, since it cannot move in any direction within the plane 
of the printed circuit board. 
With the printed circuit board having a lock adjacent both its top and 
bottom edges, once locked the printed circuit board itself becomes a 
structural member of the housing and serves to strengthen resistance 
against widening the distance between top and bottom surfaces 6 during 
bouncing, vibration, etc. which is often encountered during 
transportation. A side view of a structure of this form is shown in FIG. 
6. 
Printed circuit board 5 has a bottom lever 7 and corresponding top lever 
7A, extensions 9 and 9A of the levers being rotatably fixed to the printed 
circuit board at fulcrum points 8 and 8A respectively. A pair of latches 
10 and 10A are fixed to levers 7 and 7A respectively which are similar to 
the structure described with reference to FIG. 2. The latches 10 and 10a 
are shown in FIG. 6 locked into position within hooks 12 and 12a. 
It may be seen that with levers 7 and 7A positioned parallel to the front 
edge 11 of printed circuit board 5, the indentations 20 and 20A bear 
against top edges 14 and 14A of the hooks, leaving a space between the 
bottom edges 13 and 13A and the nearest edges of latches 10 and 10A. 
Since the positions of the latches are over-center relative to the fulcrum 
points 8 and 8a, the latches tend both to retain their locked positions, 
and to force printed circuit board 5 into its mating connector (to the 
right of the printed circuit board in FIG. 6, not shown). 
The double lock is highly effective and also forms a rigid structural 
member between the hooks 12 and 12A, which themselves are fixed to the 
printed circuit board housing. The resulting structure thus not only 
retains the printed circuit boards more securely than in the past, but 
helps increase the structural rigidly of the housing which further reduces 
the incidence of the printed circuit boards vibrating loose. 
The lever 7 (or levers 7 and 7A) is preferably held in position using a 
structure to be described below, although other forms of lever latches can 
be used. A metal or plastic sphere 25 is disposed at one end of a narrow 
post 26, which has its other end fixed perpendicular to the inner edge of 
lever 7. A frame member 27 is attached to the printed circuit board 5 
using any convenient means (such as rivets passing through retention 
flanges 28 and 28a) and extends forwardly of and parallel to the front 
edge 11 of the printed circuit board 5. The frame member 27 contains holes 
29 and 29A having resilient edges, a diameter smaller than sphere 25, and 
approximately the diameter of post 26. The axis of hole 29 should be 
co-extensive with the axis of post 26 when lever 7 is rotated into 
parallel alignment with the front edge of the printed circuit board. 
As lever 7 is rotated parallel to the front edge 11 of printed circuit 
board 5, locking the latch into the hook 12, sphere 25 is forced through 
hole 29 which, having resilient edges, opens to allow it to pass through. 
As soon as the sphere 25 is passed through, the resilient edges of hole 29 
close, retaining the post in position. The lever 7 is thus held in 
position parallel to front edge 11 of printed circuit board 5, holding the 
lock closed. 
Operation of lever 7A is similar to that described above, similar elements 
being given similar reference numerals with suffix A. 
Use of the printed circuit board lock described above is expected to 
substantially reduce the installation time of complex equipment having a 
large number of printed circuit boards. Where in the past equipment was 
shipped with printed circuit boards already installed, having a high risk 
of damage, or being shipped with printed circuit boards separately 
packaged, which require installation on site, now complete racks of 
equipment involving large numbers of printed circuit boards can be shipped 
with printed circuit boards already installed, with security and safety. 
This is expected to considerably reduce cost since the printed circuit 
boards can be inserted using factory labour, the fully assembled equipment 
tested, and shipped as tested with confidence. The extra labour of removal 
of printed circuit boards at the factory and reinstallation on site is 
avoided. 
A person understanding this invention may now conceive of changes or other 
embodiments using the principles described herein. All are considered to 
be within the sphere and scope of this invention as defined in the claims 
appended hereto.