U.S. patent number 5,293,002 [Application Number 07/856,652] was granted by the patent office on 1994-03-08 for electrical device with embedded resin and visible resin inlet and discharge ducts.
This patent grant is currently assigned to Telemecanique. Invention is credited to Gilles Grenet, Gerard Pitault, Catherine Ullmann.
United States Patent |
5,293,002 |
Grenet , et al. |
March 8, 1994 |
Electrical device with embedded resin and visible resin inlet and
discharge ducts
Abstract
A proximity detector has a casing containing a probe (4) and a
printed circuit (3), the upper end of the casing being closed by a
plug (35) provided with a filling orifice (14) and with
connecting-pins (36). The nozzle of a plastic injector (13) is
fitted in position within the filling orifice, said nozzle being
provided with two adjacent ducts. A hardenable resin is caused by
centrifugation to flow into the casing via a first duct while
simultaneously driving-out the air which is present within the
casing via the second duct, thus ensuring rapid and efficient
filling. When the casing has been filled and the resin has
hardened, the injector (13) is cut-off in close proximity to the
plug (35). Complete filling can be checked by inspecting the
surface appearance of the two leading portions of solidified resin
flux which are thus visible at the level of the orifice (14).
Inventors: |
Grenet; Gilles (Mornac,
FR), Ullmann; Catherine (Lyons, FR),
Pitault; Gerard (Ruelle, FR) |
Assignee: |
Telemecanique (Rueil-Malmaison,
FR)
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Family
ID: |
9410935 |
Appl.
No.: |
07/856,652 |
Filed: |
March 20, 1992 |
Foreign Application Priority Data
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Mar 20, 1991 [FR] |
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91 03381 |
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Current U.S.
Class: |
174/541;
264/328.1 |
Current CPC
Class: |
B29C
31/041 (20130101); B29C 33/0077 (20130101); B29C
70/745 (20130101); B29C 39/24 (20130101); B29C
39/08 (20130101) |
Current International
Class: |
B29C
31/04 (20060101); B29C 33/00 (20060101); B29C
39/08 (20060101); B29C 39/04 (20060101); B29C
39/24 (20060101); B29C 70/00 (20060101); B29C
70/74 (20060101); H01L 023/28 () |
Field of
Search: |
;174/52.2,52.3,52.6,52.1
;264/297.2,328.1 ;164/410 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2041047 |
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Feb 1971 |
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DE |
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485095 |
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Dec 1917 |
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FR |
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2302179 |
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Sep 1976 |
|
FR |
|
2648745 |
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Dec 1990 |
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FR |
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WO82/01630 |
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May 1982 |
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WO |
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2033828 |
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May 1980 |
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GB |
|
Primary Examiner: Picard; Leo P.
Assistant Examiner: Horgan; Christopher
Attorney, Agent or Firm: Young & Thompson
Claims
What is claimed is:
1. An electrical device provided with a casing adapted to
accommodate electrical components (5, 6), in particular a proximity
detector in which a sensing probe (4) is placed at one end of the
casing while an opposite end of said casing is adapted to
accommodate insulated electrical connection means (18, 36) for
supplying the detector and transmitting signals delivered by said
detector, said components being embedded in a hardened insulating
resin within said casing, said electrical device comprising
furthermore an orifice (14) through which a resin surface is
visible and which comprises a visible flux inlet leading portion
and a visible flux discharge leading portion.
2. An electrical device according to claim 1 wherein said orifice
(14) comprises a portion wherein two duct portions are visible,
said inlet portion being located in one of said two duct portions
and said discharge leading portion being located in the other of
said two duct portions, said ducts portions being a cut-off end
portion of a resin injector having a first duct for introduction of
resin and a second duct for discharge of air.
3. An electrical device according to claim 1 wherein the casing
comprises a cylindrical shell (2, 33) and a plug (11, 35) through
which conductors (18, 36) are passed, said plug being tightly
fitted in an opening of the cylindrical shell at the end remote
from the probe (4), wherein the orifice (14) extends through the
plug (11, 35) in a direction parallel to a longitudinal axis of the
shell.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for embedding in resin
components which are located within the casing of an electrical
device such as a proximity detector.
The invention is also concerned with an electrical device provided
with a casing which is intended to house electric components, in
particular a proximity detector in which a sensing probe is placed
at one end of the casing while an opposite end of the casing is
intended to be fitted with insulated and conductive electrical
connecting means for supplying the detector and transmitting its
output signals. Within the casing, the electrical components are
embedded in a hardened insulating resin which fixes them in
position and forms a mechanical joint by adhesion to the internal
walls of the casing
The injection of hardenable material is intended to endow the
electrical device with very high reliability. This result is
achieved by virtue of insensitivity to impacts or vibrations,
electrical insulation of the components and total protection
against fluid or atmospheric agents of the environment.
2. Description of the Prior Art
A known method of filling with resin as disclosed in patent No.
FR-A-2 648 745 makes use of the centrifugation effect. While
centrifugation of resin does produce satisfactory results, it is
nevertheless found desirable to simplify and rationalize the
implementation of this method.
The object of the invention is therefore both to satisfy the
requirements of quality and reliability of the products obtained
and to achieve the aims of simplicity of manufacture and short
duration of the filling operation.
A further object of the invention is to obtain a particular
configuration of the product in correlation with the application of
the method.
SUMMARY OF THE INVENTION
In accordance with the invention, in order to embed in resin the
components contained in the casing of an electrical device:
a) the device is fixed in an eccentric position on a centrifugation
rotor by connecting an injection and discharge element to the
casing of the electrical device, said element being provided with a
filling duct for connecting the casing to a central zone of the
rotor and with a discharge duct for connecting the interior of the
casing to a discharge chamber;
b) the rotor is set in rotation in order to transfer by
centrifugation a predetermined quantity of fluid resin from the
central zone to the interior of the casing via the filling duct
while air escapes from the casing via the discharge duct and
rotation is maintained substantially until hardness of the resin
has been restored.
While centrifugation is in progress, the resin passes into the
casing and flows to that portion of the casing which is farthest
away from the axis of the centrifugation rotor. The air is thus
driven-out towards the axis and therefore towards the discharge
duct of the injector, thus escaping without encountering any
appreciable resistance.
The invention thus makes it possible to perform the filling
operation at a very high speed while ensuring concomitant degassing
in a short time with a high degree of efficiency.
Preferably, the injection and discharge element is a single
injector provided with the filling duct and with the discharge duct
and inserted in a single orifice of the casing. This single
injector is advantageously a pipette that can be cut-off. The
operating conditions are preferably such that the resin completely
fills the interior of the casing up to the discharge duct.
According to a second aspect of the invention, the electrical
device of the type indicated at the outset is distinguished by the
fact that an orifice provided in the casing of the device for
introduction of resin and discharge of air during manufacture
exhibits on completion of the filling operation a visible resin
surface having two leading portions of resin flux, namely an inlet
flux leader and a discharge flux leader.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 3 are sectional views of a proximity detector in
accordance with the invention during different stages of the
method.
FIG. 4 is a sectional view to a large scale showing the injector of
FIG. 2 before it is placed in position.
FIGS. 5 and 6 are views which are similar to FIG. 4, with portions
broken away, respectively after positioning of the injector on the
electrical device, then after filling of the device with resin.
FIG. 7 is a top view of a detail of the electrical device which has
been filled with resin.
FIGS. 8 and 9 are sectional views which are similar to FIG. 1 and
show two alternative forms of construction of detectors in
accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
The electrical devices concerned in the present invention consist
of inductive proximity detectors as illustrated in FIGS. 1, 8 and
9. However, these detectors are considered solely by way of example
and not in any limiting sense.
A first type of detector 1 shown in FIG. 1 in the state which
precedes the introduction of resin includes a cylindrical shell 2
having an axis X--X', an electronic device 3 which is constituted
by a preliminary assembly of a wire-wound sensing probe 4 with a
printed circuit card 5 which carries components 6. In this
instance, the assembly is formed by means of a mass 7 of suitable
resin which also establishes a mechanical connection between the
above-mentioned elements 4, 5 and a cup 8 having a skirt 9. The cup
8 houses the probe 4 while the front end-wall of said cup
constitutes a closure disk for one end 10 of the cylindrical
shell.
A plug 11 placed at an opposite end 2a of the cylindrical shell has
an internal skirt 12 tightly engaged in the end portion 2a of the
shell and a suitably cylindrical orifice 14 which extends right
through the end-wall of the plug. Said plug 11 also has a central
opening 16 through which the sheath 17 of an electric cable 18 is
passed in a tight fit.
The skirt of the plug and the skirt of the cup are applied in a
close and compliant fit against the internal cylindrical surface of
the shell.
The electric cable 18 contains insulated conductors 19, 20, 21, the
bared ends of which are electrically connected to suitable points
of the device 3 within the casing formed by the cylindrical shell
2, the cup 8 and the plug 11, a vacant internal space 22 being
defined by said casing.
The orifice 14 serves on the one hand to fill the casing with a
hardenable resin 22' (FIG. 3) which is supplied under pressure
under the action of centrifugation forces and on the other hand to
carry out simultaneous removal of air which is initially present
within the internal space 22. In order to perform this double
operation, the nozzle 25 of a double-duct injector 13 in the form
of a pipette which is advantageously made of plastic is inserted in
the orifice 14 and the other end 28 of the injector is connected to
a resin supply device (see FIG. 4). At the time of insertion, the
nozzle 25 having a chamfered tip 27 penetrates into the orifice 14
until a slightly convergent conical outer surface 26 of said tip is
applied in leak-tight manner against a surface 15 which delimits
the orifice 14 (as shown in FIG. 2).
In order to perform its double function of introduction of resin
and of degassing, the injector has two adjacent ducts 41 and 42
separated by a thin partition-wall 43. The feed duct 41 serves to
supply the resin while the discharge duct 42 serves to remove the
air, then to discharge a slight excess quantity of resin. In the
operating position, the duct 42 is located above the duct 41.
When the detector has been placed for example horizontally in an
eccentric position on a centrifugation rotor 60 having an axis
Y--Y' (FIGS. 1 and 5) perpendicular to X--X', the rotor is set in
rotation while admitting a predetermined quantity of resin into a
central zone 66 of the rotor under controlled conditions. The resin
thus passes from the central zone 66 of the rotor to the interior
of the casing 22 via the duct 41 and the orifice 14. The air
escapes through the orifice 14 and the duct 42.
To this end, the duct 42 which is of greater length than the feed
duct 41 projects into the central zone 66 of the rotor towards the
axis Y--Y' of said rotor. During centrifugation, the resin 217
which is introduced into the central zone of the rotor forms a ring
218 at the periphery of the central zone 66 by passing beneath the
duct 41. The duct 42 forms within the chamber 66 a projection which
is greater than the radial dimension of the ring 218, with the
result that it remains free of resin while air escapes into the
upper region of the zone 66 which thus forms an air escape volume
(as shown in FIG. 5). When all of the air has escaped, the resin
flows back through the duct 42 until achievement of the final
situation shown in FIG. 6 in which the necessary quantity of resin
has been entirely introduced and the air has been completely
discharged.
When the resin has hardened, the tip of the injector 13 is cut-off
in close proximity to the orifice 14 along the plane P. FIG. 7
shows the appearance of the detector 1 in the vicinity of the
orifice 14 with two flux leaders of resin which has hardened in the
cut-off portions of the ducts 41 and 42 of the injector 13.
It will be noted that a detector which has been filled with resin
in accordance with the invention has a characteristic appearance
with its two resin flux leaders. The simultaneous presence of these
leaders makes it possible to ensure by checking that the air within
the casing has been completely removed and that no accessible
hollow spaces remain therein.
A second type of detector 31 which is visible in FIG. 8 is similar
in design to the detector mentioned above except in regard to the
end portion 32 of the cylindrical shell 33 which is remote from the
probe 4. This end portion 32 has a neck 34 in which is engaged a
plug 35. The outer face of said plug is adapted to carry conductive
through-pins such as the pin 36 which are insulated with respect to
each other so as to form a base 37 designed to receive a removable
connector (not shown in the drawings).
In a third type of detector 51 which is shown in FIG. 9, the
cylindrical shell 52 has an internal diameter substantially equal
to the external diameter of the sheath of the cable 18 so that,
after insertion of the cable 18 within the cylindrical shell 52,
the corresponding end of the shell is made air-tight. A lateral
hole 56 is formed in the shell 52 near the cable-insertion end
thereof and corresponds in diameter to the nozzle of the injector
13 in order to permit air-tight fitting of the injector nozzle
within said hole. At the time of centrifugation, the axis X--X' of
the detector can be placed in parallel relation to the rotor
axis.
The use of a field of centrifugation forces several hundred times
higher than that of gravity proves extremely advantageous in order
to carry out air blow-out and rapid filling of the internal space
but also in order to facilitate the discharge of residual air
bubbles which would otherwise be liable to nestle around certain
components. In addition, perfect adhesion is acquired between on
the one hand the mass of resin 22' which occupies the internal
space 22 and on the other hand the internal wall of the cylindrical
shell, the pre-mounted subassembly 3, the cable sheath and the plug
(when present).
In accordance with the invention, preference is given to a
hardenable resin which may be composite, which is endowed at the
same time with good electrical insulating properties, low
viscosity, high fluidity, a short hardening time at room
temperature, is low in capital cost and exhibits low volume
shrinkage during the hardening stage, as well as good performances
of adhesion to the plastic or metallic material of the casing.
* * * * *