Apparatus and method employing foam sleeves for supporting magnetic sensors in a tubular housing

A magnetic sensor assembly including an elongated support is supported in a tubular housing by a pair of tapered foam sleeves that space the support from the inner surface of the housing and that resist movement of the assembly in the housing in a direction opposite to the direction of insertion of the assembly into the housing. The sleeves, which are either continuous hollow cylinders or are formed of wound strips, are attached to the support by adhesive tape at the leading end of each sleeve.

BACKGROUND OF THE INVENTION 
This invention relates to magnetic detector apparatus such as magnetic 
locators of the type described in the aforesaid patent, and is more 
particularly concerned with improvements in the support of magnetic 
sensors in tubular housings. 
In the magnetic detection apparatus described in Pat. No. 2,642,479 to 
Jones, a tube which serves as a mounting for magnetic sensors or detectors 
is supported in a tubular housing by sponge rubber bushings or rings. Such 
bushings can provide desired centering and shock mounting of the magnetic 
detectors in the housing. However, if they are small enough to permit the 
detector assembly to enter the housing axially, they do not perform their 
intended function well, and if they are large enough to perform their 
intended function, they tend to impede the insertion of the detector 
assembly into the housing axially. The present invention is directed to an 
improved apparatus and an improved method for supporting magnetic sensors 
in a tubular housing. 
BRIEF DESCRIPTION OF THE INVENTION 
An object of the invention is to permit insertion of a magnetic sensor 
assembly into a tubular housing axially, to shock mount and center the 
assembly in the housing, and to resist movement of the assembly in the 
housing in a direction opposite to the direction of insertion. 
In accordance with one of the broader aspects of the invention, apparatus 
for supporting magnetic sensors in a tubular housing comprises an 
elongated support adapted to have magnetic sensors mounted thereon, and a 
resiliently compressible sleeve through which the support extends, the 
sleeve being attached to the support and being tapered so that it is 
narrower at a leading end portion than at a trailing portion, whereby the 
elongated support may be inserted in the tubular housing axially, with the 
leading end portion of the sleeve entering the housing before the trailing 
portion, and the sleeve may engage the inner surface of the housing to 
shock mount the support in the housing and to resist movement of the 
support in the housing in a direction opposite to the insertion direction. 
In accordance with another broad aspect of the invention, a method of 
supporting a magnetic sensors in a tubular housing comprises providing a 
pair of spaced foam sleeves surrounding an elongated support on which 
magnetic sensors are mounted, attaching only the leading end portion of 
each sleeve to the support by wrapping adhesive tape about the leading end 
portion and the support, and inserting the assembly including the sensors, 
the support, and the sleeves axially into the housing so that the leading 
end portion of each sleeve enters the housing before the trailing portion 
of each sleeve and so that the sleeves engage the inner surface of the 
housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, FIG. 1 illustrates the external appearance of a 
magnetic locator A of the type disclosed in the aforesaid patent, which is 
incorporated herein by reference. The present invention may be 
advantageously employed in magnetic detection apparatus of that type or in 
other magnetic detection apparatus having a tubular housing in which a 
magnetic sensor assembly is to be mounted. Housing 10 of locator A is a 
hollow nonmagnetic cylinder connected at one end to a can 12 of larger 
diameter that contains electronics employed in the locator. Earphones 14 
are shown connected to can 12 by cable 16, although a loudspeaker may be 
employed in place of the earphones. In use, housing 10 may be grasped just 
below can 12 and swept back and forth along the ground to detect buried 
magnetic objects, producing an audible signal as set forth in the 
aforesaid patent. 
As shown in FIG. 2, within the housing 10 is a magnetic sensor assembly 18 
comprising a nonmagnetic support tube 20 with a longitudinal notch or 
groove 22 or 24 at each end in which a corresponding magnetic sensor 26 or 
28 is snap-fitted, all as described in the aforesaid patent. Retention of 
the magnetic sensors in the grooves may be assisted by adhesive tape 30 
wrapped about the sensors and the ends of the tube 20. A stiff excitation 
wire 32 extends through the sensors and the tube 20. Wire 32 is preferably 
of hairpin configuration with its ends soldered to a circuit board in the 
can 12. As described in the patent, each magnetic sensor may comprise a 
nonmagnetic housing containing a tubular magnetic core through which the 
excitation wire extends, and each sensor may comprise a signal coil would 
in a circumferential groove of the sensor housing. The signal coils are 
connected by wires 34 to a balanced signal circuit in can 12. As described 
in the patent, an AC excitation current is applied to the excitation wire 
32, but there will be no signal output from the balanced signal circuit 
until the locator is brought into proximity with a magnetic object. 
Spaced sleeves 36 of resiliently compressible material are employed to 
support the sensor assembly 18 in the housing 10. As shown in FIG. 4, each 
sleeve comprises a foam cylinder with a central longitudinal bore 38. The 
wall thickness of the cylinder is preferably greater than the bore 
diameter. The sleeves may be formed of polyurethane foam, for example. 
Prior to insertion of sensor assembly 18 in housing 10, support tube 20 is 
inserted through the bores 38 of the sleeves in succession. Then the 
leading end of each sleeve (the end that enters housing 10 first) is 
attached to the support tube. As shown in FIG. 2, this is preferably 
accomplished by winding adhesive tape 39 about the leading end portion 40 
of each sleeve and about the adjacent region of support tube 20. The 
adhesive tape compresses the leading end portion of each sleeve and 
imparts a slight taper to each sleeve, so that the leading end portion 40 
of each sleeve is narrower than the trailing portion 42. 
The sleeves are preferably mounted on and attached to the support tube 20 
after the support tube has been assembled with the magnetic sensors 26 and 
28, the excitation wire 32, etc. Then the entire magnetic sensor assembly, 
including the sleeves, is inserted axially through the open end 44 of 
housing 10. When the magnetic sensor assembly 18 has been inserted in the 
housing, the excitation wire 32 and lead wires 34 are connected to a 
circuit board at the left end of housing 10 in FIG. 2, after which can 12 
is placed over the circuit board and attached to the housing 10. A cap 46 
is inserted in the open end 44 of housing 10 to close the housing. 
The sleeves 36 are of large enough diameter to engage the inner surface of 
housing 10 and to compress the sleeves somewhat as the assembly is 
inserted in the housing (from right to left in FIG. 2). Some force is 
required to insert the assembly 18 in the housing 10, but the taper of the 
sleeves facilitates insertion. Also, since the sleeves are attached to 
tube 20 only at their leading end portion, they are pulled into the 
housing by tube 20, and when the sleeves drag against the inner surface of 
the housing, they tend to contract transversely as they are pulled and 
expanded longitudinally. When the sleeves are at rest in the housing, they 
fit the housing snugly, providing excellent shock mounting of the magnetic 
sensor assembly 18 in housing 10. 
Although the sensor assembly is readily inserted in the housing, any 
tendency of the sensor assembly to move in a direction opposite to the 
insertion direction is strongly resisted by virtue of the taper of the 
sleeves and by virtue of the attachment of the sleeves to the support tube 
20 at their leading end portion only. Any force imparted to the sleeves by 
movement of the tube 20 in the direction to the right in FIG. 2 (as would 
occur during sweeping movement of locator A in FIG. 1) tends to compress 
the sleeves longitudinally and to expand them laterally. Thus the force 
required to move the sensor assembly in a direction opposite to the 
insertion direction is far greater than that required to insert the 
assembly in the housing. 
The arrangement shown in FIG. 2 for mounting the magnetic sensor assembly 
18 in tubular housing 10 provides excellent centering of the magnetic 
sensor assembly in the housing, which is desirable to avoid errors due to 
positioning of one of the magnetic sensors closer to the housing wall than 
the other. The embodiment of FIG. 3, which is disclosed in the aforesaid 
patent, has many of the advantages of the embodiment of FIG. 2 but does 
not provide as perfect centering. Since the embodiment of FIG. 3 differs 
from the embodiment of FIG. 2 only in the construction of the sleeves, the 
other parts will not be described. 
As shown in FIG. 3, sleeves 36' are formed by wrapping a foam strip about 
the support tube 20, Initially, each strip is a flat rectangular piece of 
foam, designated by reference character S in FIG. 5. The strip is then 
wrapped helically about the support tube 20 and held in that configuration 
by the adhesive tape 39, which is similarly (and, if desired, 
concurrently) wrapped so as to overlap both the foam strip and the support 
tube. This technique provides sleeves that are tapered, i.e., wider at the 
trailing end than at the leading end, and that are firmly secured to the 
support tube 20 at the leading end only. The magnetic sensor assembly 18 
with the sleeves 36' attached thereto is readily inserted in the housing 
10 in the manner described with respect to FIG. 2, and provides shock 
mounting and resistance to movement of the sensor assembly in a direction 
opposite to the insertion direction. However, the centering of the 
magnetic sensor assembly is not as good as in the embodiment of FIG. 2, 
and the thickness of the foam tends to be more critical as to production 
tolerances. The foam sleeves 36 can be stamped out from tubing with a 
punch and die set, and the thickness of the foam is not critical. 
While several embodiments of the invention have been shown and described, 
it will be apparent to those skilled in the art that changes can be made 
in these embodiments without departing from the principles and spirit of 
the invention, the scope of which is defined in the appended claims.