Method of assembling a galvanomagnetic sensor in a cavity in a conducting plate

A Hall generator flexibly held in an aperture of a circuit plate by its contact strips is pressed between a perpendicular elongated flux concentrator with a tapered nose and the center strip of a somewhat resilient flat flux concentrator. A mounting sleeve provides for force-fitting the elongated flux concentrator and for mounting the two flux concentrators in fixed position on the circuit plate on opposite sides thereof. After the elongated flux concentrator is pressed into a position for flushly clamping the Hall generator under the spring effect of at least the flat flux concentrator, the elongated flux concentrator is permanently set with a little adhesive around its upper periphery to insure continuance of the clamping force. The two flux concentrators come quite close to appropriate portions of an external rotor of a brushless d.c. motor.

Reference to related patents and applications: U.S. Pat. No. 4,099,104, 
Muller; U.S. patent application Ser. No. 060,879, Muller, filed July 26, 
1979. 
This invention concerns the method of assembling a galvanomagnetic sensor 
and associated flux concentrating bodies on a printed circuit board, and 
more particularly a sensor of the Hall generator type on a circuit plate 
as part of an electric motor, especially a brushless d.c. electric motor 
having an external rotor carrying an annular magnet mounted on the 
bell-shaped or cup-shaped rotor structure. 
Swiss Pat. No. 504,132 discloses a motor of the kind last mentioned in 
which a sensor is mounted on a circuit plate and describes mounting of the 
assembly that includes the sensor. 
The structure there shown and the method disclosed for assembling it has 
the disadvantage that it is difficult to fit the sensor between its flux 
concentrators in a manner which is clearly free of unnecessary and 
disadvantageous air gaps. In many cases, the magnetic flux that is 
available for enabling the sensor to perform its function is not great. 
This is particularly the case when the sensor operates on stray flux, as 
is the case in the motor described in the above-mentioned Swiss patent. 
Furthermore, in many motors of the type just referred to there are nowadays 
used the so-called "rubber magnets" which are magnets made of an elastomer 
material in which ferrite particles are embedded. These rubber magnets are 
easy to shape, modify or treat, but they produce only low densities of 
usable magnetic flux, so that the stray flux density in the case of these 
magnets is particularly low. It then, for example, an undesired air gap of 
only 0.1 mm is produced at the location of the galvanomagnetic sensor, 
that can already mean that the available electric output signal is reduced 
by 50 percent, and an undesired air gap of 0.2 mm means a reject rather 
than a usable product. 
Since Hall generators are very expensive, such a result is highly 
undesirable for cost reasons alone. 
On account of the tight space requirements, it is necessary in many cases 
to use relatively large flux concentrating bodies as, for example, a 
complete ring in the case of the Swiss patent already mentioned. Normally, 
such a sensor can be assembled with its flux concentrators, which is to 
say in its own magnetic circuit, only when it is on the circuit plate to 
which it is connected electrically. This invention applies particularly in 
such arrangements which the magnetic circuit of the galvanomagnetic sensor 
is of relatively complicated construction. Hall generators with so-called 
catch plates ("Fangblechen") for flux concentration are known from the 
publication known as ETZ-A, Volume 81 (1960), pp. 323-327. 
The method of assembling and affixing the Hall generator to a plate there 
described is hardly satisfactory for the reason, among others, that 
wedge-shaped air gaps can easily arise adjacent to the Hall generator in 
this construction. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a suitable method and 
means for assembling a sensor with its flux concentrators on its 
supporting plate so as to produce a good output signal for the sensor and, 
at the same time, simplify the assembly. 
Briefly, a way has been found to mount the sensor so that it is clamped in 
a gapless fashion between its flux concentrating bodies so that the signal 
produced is not diminished by the presence of any unwanted air gaps. The 
galvanomagnetic sensor, which is typically a Hall generator mounted on a 
ferrite piece, is subject to a bias force that is at least approximately 
perpendicular to the plane of the circuit plate in which the sensor is 
seated (in a cavity in the plate). This feature is of great importance for 
avoiding uneven and particularly wedge-shaped air gaps resulting from 
uneven clamping of the sensor caused by clamping forces that are 
themselves unsymmetrical. In consequence with minimum assembly expense, 
the sensor arrangement providing a good output signal can be obtained and 
the number of rejects resulting from insufficiently careful assembly is 
drastically reduced. A flat flux concentrator of spectrocal shape is 
mounted below the conducting plate so that the sensor can be pressed 
against the bridge-strip portion thereof by the flat-nosed surface of a 
tapered portion of a substantially cylindrical upper flux concentrator 
that presses the sensor downward. A mounting piece having a cylindrical 
passage for the upper flux concentrator is riveted through the circuit 
plate and through the eyes of the lower flux concentrator, thus holding 
the assembly together. The passage for the upper flux concentrator is of 
slightly smaller diameter than the diameter of the flux concentrator body, 
so that a force fit can be obtained and a downward force maintained 
against the sensor and ultimately against the slightly yielding lower flux 
concentrator and the upper flux concentrator can be sealed in position. 
Further advantages of the invention will be made clear in the detailed 
description that follows:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The circuit plate 10 shown in FIG. 1 is made of a suitable insulating 
material, for example, a glass fiber laminate. It has a rectangular 
aperture 11 for receiving the galvanomagnetic sensor 12 (see FIG. 2), 
which, in this case, is in the form of a Hall generator. Other forms of 
sensors which could be used are a magnetic diode, a field plate, etc. The 
conducting plate 10 has four conducting paths 13 of copper or gold. Near 
each of the two long sides of the rectangular aperture 11 are respectively 
located the round holes 14 and 15. 
The Hall generator 12, as shown in FIG. 2, has four connection tabs 16 (two 
for supplying the Hall current and two for picking up the output voltages 
that depend upon the magnetic field). As shown in FIGS. 2 and 3, the 
connection tabs 16 are soldered to the circuit path 13 so that the Hall 
generator itself does not receive any of the solder and, preferably, so 
that the Hall generator projects slightly above the surface of the 
conducting plate on the side from which the views of FIGS. 1, 2 and 3 are 
seen. This slight sticking out of the Hall generator results in practice 
by the spring-flexing of the connection tabs of the Hall generator. 
As shown, the four connecting paths 16 of the Hall generator extend past 
only two opposite sides or edges of the Hall generator which has the shape 
of a square wafer, so that the other two side edges of the wafer are clear 
of electrical connections. Extending across the last-mentioned side edges, 
a first flux concentrator 20 is placed as shown in FIG. 3 which has an 
aspect similar to the front part of an eyeglasses (spectacle) frame. It 
has a narrow central portion (or bridge) 21, connecting to open circles 
forming the eyes 22 and 23, the apertures of which are flush with the 
round holes 14 and 15 in the circuit plate 10, as is clear from FIG. 3. 
The middle strip or bridge 21 lies against the Hall generator 12 and 
presses it somewhat into the aperture 11, so that the Hall generator 12 
lies flat against the strip 21 under spring pressure. 
Of course, the Hall generator could lie more deeply in the aperture 11, in 
which case the flux concentrator 12 would have a step toward the interior 
of the aperture 11 so that, again, it could lie close and flush against 
the Hall generator 12 (under pressure from the other side of the Hall 
generator as will presently be explained). 
The first flux concentrator 12 can, for example, have a thickness of 0.75 
mm, the thickness of a typical thin sheet metal, and an overall length of 
13 mm. The middle strip or "bridge" may typically have a width of 1.5 mm. 
The Hall generator 12 is preferably one mounted on a ferrite base 24 (FIG. 
4) having, also, a small built-in ferrite flux concentrator on its upper 
side. The ferrite base and the flux concentrator 25 should preferably have 
a metallic surface in order to make possible direct contact without any 
interfering air gap. FIG. 4 shows how the ferrite base of the Hall 
generator 12 lies directly on the middle strip 21 of the first flux 
concentrator 20. 
As shown in FIG. 4, a mounting element 27, the exact form of which is 
apparent from FIGS. 7-9 and may generally be described as a sleeve with 
appendages, is now mounted on the conducting plate. The sleeve 27 consists 
of a non-magnetic material, which could be brass, but is preferably a 
thermoplastic resin, for example, the material commercially sold with the 
trademark "MACROLON." The sleeve has two cylindrical extensions 28 and 29 
for insertion through the holes 14 and 15 of the circuit plate 10 and 
through the eyes 22 and 23 of the first flux concentrator 20. 
These extensions 28 and 29 are fixed extensions of a main body portion 32 
that has a passage 33 down its middle which is typically circularly 
cylindrical in shape and in mounted position is coaxial with the 
galvanomagnetic sensor 12, as clearly appears in FIG. 4. 
As FIG. 4 also shows, the extensions 28 and 29 are riveted in place by heat 
deformation of their ends. FIG. 4 shows the rivet head 34 of the extension 
28, but shows the extension 29 as it appears before riveting. In FIG. 5, 
the extension 29 is also provided with a rivet head 35. In this manner the 
first flux concentrator 20 is immovably fixed on the circuit plate 10 in 
its position lying against the Hall generator 12 and, at the same time, 
the sleeve 32 is fastened in the desired position on the circuit plate 10. 
The next step of assembly is to mount a second flux concentrator 37 as 
shown in FIG. 5. This member has a cylindrical shape over the larger 
portion of its length, with a diameter, for example, of 3.1 mm, the total 
length of the flux concentrator 37 being, for example, 6 mm, including the 
taper of its end facing the Hall generator 12 which has frustoconical 
shape tapering down to about 1/3 of the diameter of the cylindrical 
portion, thus to 1 mm so that its cross-sectional area at this end is 
reduced to about 1/9 of the cross-sectional area of the cylindrical 
portion, correspondingly increasing the magnetic flux there, approximately 
nine-fold. 
The inner diameter of the passage 33 is somewhat smaller than that of the 
cylindrical portion of the flux concentrator 37, for example, only 3.05 
mm, so that the flux concentrator 37 is insertable only by a force 39 
(FIG. 5) and can be pushed down to flush contact against the Hall 
generator 12, pressing the latter against the first flux concentrator 20, 
so that the Hall generator 12 is clamped in between the two flux 
concentrators 20 and 37 without interfering air gaps as shown in FIG. 6. 
The relatively thin flux concentrator 20 is thus normally somewhat deformed 
elastically, so that it operates as a spring which presses the Hall 
generator 12 against the second flux concentrator 37. The flux 
concentrator 37 is permanently fixed in this position by a drop 42 of a 
single-component adhesive, as shown in FIG. 6. The mounting of the 
assembly is thereby completed. 
FIG. 6 also shows a preferred relative position of the assembly just 
described on the circuit plate 10 and the external rotor 43 of a brushless 
d.c. motor. (The axis of rotation would lodge somewhere to the right in 
the FIG. 6 drawing. 
The rotor 43 comprises a rotor bell 44 and a radially polarized permanent 
magnet 45 that extends from the cup or bell 44 to a position quite close 
to the second flux concentrator 37. In the illustrated preferred 
configuration, the stray or spreading field from the north pole N of the 
magnet 45 proceeds to the flux concentrator 37 and the stray or spreading 
field from the south pole S proceeds through the ferromagnetic rotor bell 
44 and then through the first flux concentrator 20, so that all together 
there is produced a sufficiently great magnetic flux density at the Hall 
generator 12, resulting in the generation of a sufficiently large signal. 
If needed, the first and/or second flux concentrator can, of course, be 
made larger in order to obtain still stronger signals. This depends upon 
the particular application and particularly from the amount of 
amplification available in the control circuit. 
It is also evident that instead of by thermal riveting of the flux 
concentrator 20 and the sleeve 32 onto the plane 10, other kinds of 
fastening can be used. The illustrated type of fastening is preferred, 
however. 
FIG. 10 shows a first modification of the configuration of FIG. 6 that is 
particularly well suited for an external rotor type of brushless d.c. 
motor and provides a relatively high output signal for the sensor 
arrangement according to the present invention. Parts which are the same 
or operate in the same way, as in the previous figures, are designated in 
FIG. 10 with the same reference numerals and are accordingly not again 
described here. The same applies for the variants shown in FIGS. 11 and 
12. 
The first flux concentrator 50 in FIG. 10 is provided at its left or 
radially outward end with a section 51 bent up at right angles, which 
passes through a perforation 52 in the circuit plate 10 and projects 
upward out of it. The end section 51 has a rectangular cross-section which 
is not shown in the drawing, which may for example have the dimensions of 
0.75.times.4 mm and, for example, may have the length of 5 mm or whatever 
is appropriate to enable it to overlap the inner surface of the rotor bell 
44 with the formation of a radial air gap 53 for a part of its length, as 
shown in FIG. 10. The second flux concentrator 37 lies, as shown, rather 
close to the rotor magnet 45. FIG. 10 schematically shows at 54 the 
magnetic lines of force in the air gap 53 and at 55, the magnetic lines of 
force that extend from the rotor magnet 45 to the second flux concentrator 
37. In all other respects, the manner of operation is the same as in the 
case of FIG. 6. Here also, the Hall generator 12 is symmetrically clamped 
so that it is held aflush against the two flux concentrators 37 and 50, 
and no wedge shaped air gaps can arise. 
FIG. 11 shows a second modification that is likewise very well suited for a 
motor with an external rotor, only a small part of the rotor and the 
complete sensor assembly again being shown. 
The sleeve 27' is in this case provided with a somewhat wider base than in 
the other examples, so as to make room for two bores 58 and 59 for 
respectively seating the rivets 60 and 61, of which the lefthand rivet 61 
is made of magnetically soft wheel, while the righthand rivet 60 may for 
example be of brass. Alternatively, the righthand rivet 60 and its 
mounting hole in the member 27' could be replaced by a cylindrical 
downward extension, such as is shown in the first embodiment. 
The lefthand rivet 61 of FIG. 11 serves here as a flux guiding piece, and 
the magnetic lines of force 62 are accordingly shown going from it to the 
rotor bell 44, while the magnetic lines of force from the rotor magnet 43 
to the second flux concentrator 37 are indicated at 63. The rotor bell 44 
is here shown extending down to the vicinity of the upper head of the 
rivet 61, while the rotor magnet 45 is so arranged that its lower inward 
edge overlaps slightly the flux concentrator 37 and its holding sleeve, 
leaving a small air gap. 
FIG. 12 shows (on an enlarged scale of about 2:1) a variant mounting for a 
sensor assembly 65 which corresponds in its construction basically to the 
first illustrated embodiment (FIG. 6). In FIG. 12, a part of the stator 66 
of a brushless d.c. motor is shown, as well as a portion of external rotor 
43, and the axis of rotation of the latter is indicated at 67. A small 
radial operating air gap 68 appears between the stator 66 and the magnet 
45 of the rotor 43. 
The conductor plate 10 is in this case in the shape of a flat annulus and 
has a diameter that is smaller than the inner diameter of the rotor bell 
44, so that it can lie inside the lower extremity of the rotor bell 44, 
leaving only a relatively small air gap 68a between the latter and the 
first flux concentrator 20. The lower inner edge of the rotor magnet 45, 
which here also is preferably a so-called rubber magnet (mixture of hard 
ferrite powder and rubber), lies close to the second flux concentrator 37, 
so that there also only a small air gap 69 is present. The magnetic flux 
then goes from the inner side of the rotor magnet 45, across the air gap 
69 to the second flux concentrator 37, thence through the Hall generator 
12 to the first flux concentrator 20 and from there across the air gap 68a 
and through the rotor bell 44 back to the magnet 45. In consequence, there 
results a relatively powerful signal at the output of the Hall generator 
12, because the magnetic flux concentration in the Hall generator 12 is 
very large. 
It is important in all the illustrative examples that the Hall generator 12 
is symmetrically clamped, i.e. that the same clamping forces are exerted 
on both sides, in contrast to arrangements in which a flux concentrator 
lies against a Hall generator only on one side and thereby feeds the 
possibility that a wedge-shaped air gap can form. If, for example, in FIG. 
11 one of the two rivets 60 or 61 were left out, this risk would arise. 
The clamping provided symmetrically on two sides, or on more than two 
sides, thus provides a distinctive feature of the invention in its 
preferred form in order to obtain a clamping force that operates as 
perpendicularly as possible on the Hall generator 12. 
A sensor assembly and mounting according to the present invention is 
suitable for all control purposes, for example also for control of shelf 
storage lifts, applications in motor vehicle equipment, burglar alarms, 
etc. It is also evidently possible to equip the second and/or the first 
flux concentrator with an extension for preferentially catching or 
diverting spreading fields from one of the stator poles according to the 
teaching of German Pat. No. 2,612,464, to which reference is made for 
further details of such an arrangement. 
It should be further mentioned that the part 37 can also be made as a 
stamping and does not need to have a cylindrical cross-section, although 
the cylindrical form is currently the preferred form. 
It should also be mentioned that the invention is also suitable for use in 
a motor of the kind illustrated in the copending application of the 
present applicant owned by the assignee of the present application, Ser. 
No. 060,879, filed July 26, 1979. 
It will accordingly be understood that although the invention has been 
described with reference to particular illustrative embodiments, with 
mention of certain other possible variations, many modifications and 
variations are possible within the inventive concept.