Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: FRICTION FIT CONTACT PLATE
FIELD OF THE INVENTION:
The present invention relates to contact plates, and more particularly to
friction fit contact plates which have a means for releasably holding the
cover to the base by
a friction fitting.
BACKGROUND OF THE INVENTION:
Contact plates, also known as culture dishes or Petri dishes, are widely
known and used in laboratories for growing cell cultures, bacteria cultures,
and the like.
Conventional contact plates are comprised of two parts: 1 a base, which is
typically a
shallow open-ended cylindrical container; and 2 a cover, which is wider in
diameter than the
base, and fits over and covers the base.
Conventional contact plates are difficult for the user to lift and move
because
the cover is wider in diameter than the base and is loosely positioned over
the base. In
particular, the user must ensure that he or she has a firm grasp on both the
base and the
cover when lifting and moving the contact plate. Accordingly, either both
hands are
required to grasp and lift the contact plate, or the user must slide the
entire contact plate off
the edge of the working surface to grasp the contact plate. Alternatively, in
order to lift and
support the base, the user must tilt the contact plate to facilitate the
positioning of his or her
fingers underneath the base. This is undesirable because the tilting can shift
and disturb the
contents of the contact plate. Tilting of the contact plate may also cause the
cover to slide;
thus, making it awkward for the user to get a firm grasp on the contact plate.
Conventional contact plates are prone to accidental or inadvertent opening
which may contaminate the culture. Conventional contact plates are often
stacked together
on the working surface, in the incubator, or in the storage area for space
efficiency. As the
cover of a conventional contact plate is loosely positioned over the base, the
cover can be
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accidentally opened when the stacked contact plates are handled. In addition,
the cover of a
contact plate may open if the contact plate is jostled during handling. Thus,
it is highly
desirable to have contact plates which prevent accidental openings.
Various contact plates have been provided in which the cover is placed over
the base in a snug or tight fit. For example, U.S. Patent No. 5,725,123
discloses a cover
with individual elevations on the inner surface of the cover apron, which
press against the
outer surface of the base wall to secure the cover to the container.
Similarly, U.S Patent
No. 6,602,704 discloses a contact plate with a cover having a plurality of
ribs on the inner
surface which press against the outer surface of the base wall to secure the
cover to the
container. However, it has been found that these prior art arrangements have
elevations or
ribs which ride on an upwardly sloping surface. Once media lubricates the
surface, the
media acts as a lubricant and friction fit engagement is reduced and almost
eliminated,
leading to possible accidental opening of the contact plate.
There thus remains a need for a friction fit contact plate which overcomes the
disadvantages of the prior art.
SUMMARY OF THE INVENTION:
It is an object of the present invention to provide an improved contact plate,
wherein the cover can be reliably and securely held to the base to avoid the
accidental
opening of the cover. It is a further object of the present invention to
provide a contact
plate which can be lifted and manipulated by gripping the base or the cover.
It is an object of the present invention to provide a contact plate, which can
be efficiently and reliably stacked together, and can prevent the cover from
being
accidentally separated from the base.
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The present invention is directed to a contact plate comprising a base and a
cover. The base has a bottom wall for holding the culture medium and the like,
and a
circumferential sidewall extending upwardly from the bottom wall and attached
thereto.
The base further incorporates a flange extending outwardly from the lower edge
of the outer
periphery of the sidewall. The outer periphery of the base sidewall is
provided with a
generally perpendicular surface along the lower edge thereof. The cover has a
top wall,
which has a larger diameter than the base sidewall, and a circumferential
sidewall extending
downwardly from the top wall and attached thereto. The cover is provided with
a plurality
of projections on the inner surface to engage the generally perpendicular
surface of the
lower edge of the outer periphery of the base sidewall. The projections have a
diameter less
than the diameter of the generally perpendicular surface of the lower edge of
the outer
periphery of the base sidewall to provide a biasing force to retain the cover
on the base when
the projections engage the generally perpendicular surface of the lower edge
of the outer
periphery of the base sidewall.
In an aspect of the invention, the projections are angled slightly inwardly at
the lower edge to provide a contact surface for engagement with the generally
perpendicular
surface of the lower edge of the outer periphery of the base sidewall.
BRIEF DESCRIPTION OF THE DRAWINGS:
Preferred embodiments of the invention are shown in the drawings, wherein:
Figure 1 is an exploded perspective view of the contact plate of the present
invention
showing the cover and bas;.
Figure 2 is a cross-sectional side view of the contact plate of Figure 1 with
the cover
separated from the base;
Figure 3 is a cross-sectional side view of the contact plate of Figure 1 with
the cover
in the process of being placed on the base;
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Figure 4 is a cross-sectional side view of the contact plate of Figure 1 with
the cover
and base secured together; and
Figure 5 shows a detail view of the engagement means of the contact plate of
Figure
1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to Figures 1 to 5, a contact plate is generally indicated with
the numeral 10. The contact plate 10 of the present invention includes a base
14 and a
cover 18. The contact plate 10 is preferably fabricated from a plastic
material. However, it
can be appreciated that other suitable materials can be used. At least the
cover 18, but
preferably both the cover 18 and the base 14, is fabricated of a transparent
material to enable
the user to view the contents of the contact plate. It can also be appreciated
that the size of
the contact plate is not limited to any specific dimensions.
The base 14 includes a bottom wall 22 and a side wall 26, which extends
upward from the bottom wall 22 and extends continuously along its entire
periphery, to form
an upward facing receptacle 30 for holding the culture medium and the like.
Preferably, the
base 14 is formed from an unitary integrally molded piece of plastic wherein
the bottom wall
22 is integrally formed with the side wall 26. The side wall 26 is comprised
of a outer
surface area 34 and an inner surface area 38. The bottom wall 22 may be
provided with
suitable lines or a grid, as shown in the figures, so as to facilitate the
counting of the culture
in the conventional manner.
The base 14 provides at least one flange 42 extending outwardly from the
outer surface area 34 of the side wall 26 and attached thereto. The flange 42
is preferably
integrally formed with the side wall 26 and has a flange surface 43. In a
preferred
embodiment of the invention, as shown in the figures, the flange 42 extends
outwardly from
the outer surface area 34 of the side wall 26 and extends continuously along
the entire
periphery. Surrounding the contact plate 10 and extending downwardly from the
perimeter
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of the flange 42 is a short skirt 44, which may serve as a surface for
gripping and
manipulating the contact plate.
The cover 18 has a top wa1146 and a side wall 50, which extends
downwardly from the top wall 46 and extends continuously along its entire
periphery.
Preferably, the cover 18 is formed from a unitary integrally molded piece of
plastic wherein
the top wall 46 is integrally formed with the side wal150. The side wall 50
has an outer
surface area 56 and an inner surface area 60.
As best shown in the Figures, the cover 18 is positioned over the base
receptacle 30 in the closed position. The top wal146 has a larger diameter
than the base
side wall 26. The cover side wa1150 is of a size and configuration that it
surrounds and
overlaps the base side wa1126, wherein the edge 62 of the cover side wa1150
rests on and is
supported by the flange surface 43. The cover side wa1150 preferably has a
height greater
than the height of the base side wa1126.
As shown in the Figures, the cover 18 and base 14 have a means for
releasably holding the cover 18 to the base 14 of the contact plate 10 when
the cover 18 is in
the closed position, wherein the cover 18 is held to the base 14 by a positive
displacement
friction fit.
In the embodiment shown in the figures, the cover 18 includes a plurality of
inwardly extending projections 64, which extend inwardly from the inner
surface area 60.
The projections 64 are preferably disposed equaly speced around the inner
surface area 60.
Preferably, there are at least two projections 64 provided on the inner
surface, more
prefarably at least three projections 64 and most preferably up to six
projections 64. Each
projection 64 has a generally perpendicular lower surface 68 with an inwardly
angled
contact surface 72 adjacent the lower end thereof.
The outer surface 34 of the sidewall 26 of the base 14 is provided with a
generally perpendicular surface 76 along the lower edge of the outer surface
of the sidewall
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34 to provide an engagement surface for the perpendicular lower surface 68 and
inwardly
angled contact surface 72 of the cover 18.
The operation of the friction fit engagement of the contact plate 10 of the
present invention will now be explained with reference to Figures 2 to 5. As
shown in
Figure 5, the projections 64 have a diameter less than the diameter of the
generally
perpendicular surface 76 of the lower edge of the outer periphery 34 of the
base sidewall 26
to provide a biasing force to retain the cover 18 on the base 14 when the
projections 64
engage the generally perpendicular surface 76 of the lower edge of the outer
periphery 34 of
the base sidewall 26. The difference in diameters is represented in Figure 5
by the letter D.
As the cover 18 is placed downwardly over the base 14, the generally
perpendicular lower
surface 68 and preferably the inwardly angled contact surface 72 of the
projections 64
encounter the generally perpendicular lower surface 76 of the outer periphery
of the sidewall
26 of the base 14. Since the diameter of the generally perpendicular lower
surface 68 and
preferably the inwardly angled contact surface 72 of the projections 64 is
less than the
diameter of the generally perpendicular lower surface 76 of the periphery of
the sidewal126
, the projections 64 and hence the sidewall 50 of the cover 18 is biased
outwardly as the
lower surface of the projection 68 and preferably the inwardly angled contact
surface 72
encounters and rides over the generally perpendicular surface 76 of the lower
periphery of
the sidewall 26 of the basel4. The biasing outwardly of the projections 64 and
the cover 18
provides a positive biasing force against the base 14 to releasably hold the
cover 18 on the
base 14. In order to remove the cover 18, a force greater than this positive
biasing force
must be exerted to lift the cover 18 off the base 14.
As shown in figures 2 to 5, the provision of the inwardly angled contact
surface 72 at the lower edge of the generally perpendicular lower surface 68
of the
projections 64, provides an increased biasing force as well as a point contact
between the
cover 18 and the base 14. This increased biasing and point contact increases
the positive
biasing force releasably holding the cover 18 to the base 14 and reduces the
likelihood of
accidental opening of the contact plate 10.
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The contact plate of the present invention provides an easy to use friction
fit
contact plate which can be easily handled in all of the operation steps
commonly employed.
The extent of the positive biasing force provide by the structures of the
contact plate of the
present invention allows the plate to be handled with reduced risk of
accidental opening as
compared to prior art friction fit contact plates. The contact plate of the
present invention
can be opened for specimen handling by exerting a force to overcome the
positive biasing
force. This can easily be accomplished by the technician or automated handling
apparatus.
While the contact plate of the present invention provides a positive biasing
force greater than the prior art friction fit contact plates, the contact
plate can still be used in
automatic filling and handling equipment commonly utilized as such equipment
can exert
sufficient opening force to overcome the positive biasing.
In some applications, it may be desirable to stack a series of contact plates
10
on top of each other. The skirt 44, which surrounds the contact plate 10 and
extending
downwardly from the perimeter of the flange 42, has a larger diameter than the
top wall 46
of the cover 18, thereby providing a means for preventing the shifting of the
lower-
positioned contact plate. The base 14 may also include a groove which has the
same
diameter as the top wall 46 of the cover 18, thereby providing a means for
restricting the
shifting of the lower-positioned contact plate.
Although various preferred embodiments of the present invention have been
described herein in detail, it will be appreciated by those skilled in the
art, that variations
and modifications may be made thereto without departing from the scope of the
appended
claims.
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