Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE IN~IENTION
1 - Field of the In~ention
This invention relates to a magnetic circuit
comprising two ferromagnetic half-shells and pro~ided ~ith
an air-gap and to arrangements and methods or adjusting one
parameter of the reluctance of the magnetic circuit.
Actually, adjusting for the known ma~netic
circuits is obtained by modifying the effective value of the
air-gap. Within the scope of this invention, the modification
is- obtained by adjustmen~ of the cross-section of a wall
and of distribution of the magnetic force lines in the air-
gap zone.
2 - Description of the prior art
It is current practice to use a great number of
magnetic circuits in the telecommunication technology area.
The telecommunicationindu5try in fact uses a very great number
of inductors which are formed o one or several suitable
coils. The coils are inserted in a cavity ormed by two
ferromagnetic half-shells of the casing of the magnetic
circuit.
In accordance with a known structur,e, each half-
shell comprises a base on top of which is fitted an external
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ring which is more or less complete, and a central core. -The
height of the external ring is slightly greater than that oP
the central core. The assembly of the two half-shells orms
a magnetic circuit of which the central core has an air-gap
limited by the two opposite surfaces of the central core.
In order to provide magnetic circuits having a
predetermined reluctance value, precautions must first be
taken in machining over
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the relative heig~-t of the e~-ternal ring and of the central core.
An arrangement suitable for such a machining is disclcsed in ~rench
Pa~en-t 2,2S3,047~ The reluctance value of the ma~etic circuit th~s
obtained is ne~r to tha-t of the predeterl~ined va3ue which must then~
ba precisely acljusted. Still referring to knol~n magnetic circuits
and in accordance with one of the most widely used methods, the
central core comprise~ a central bvre which allows rotational an~
transversal movement of a ~errite rod~ The ferrite rod is rigid~y
~ixed to a screw~ called adjustment screw, which mcves in a nut
secured to o~e of the two half-shells. The position of the ~errite
rocl near to the air-gap and/or more or less inside -the air-gap o~
the magnetic circuit provides a means of mak;ng adjustment to an
accuracy of about 10 and to a normal adjustment ran~e of 15 %.
However7 for reasons of miniaturization, magnetic circuits o~
very small dimensions are increasingly usedO The kno~n ma~netic
circ~i~s, as described above, have atleastb~th f~ng ~dvantaæes:
- reduction of the effecti~e cross-section of the central core
caused by the presence of the cylinclrical bore, and
- technioal di-fficulties of m~ing an adjustment screw with a
ferrite rod ~or a bore of which the diameter is less than,or abou-t9
t~o millimeters.
OBJECTS O~ THE INVENTION
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Accordingl~, an object of this invention is to pro~icle ~ew and
improved ferrite ma~ne-tic circuit~ A more particular obiect s to
provide magnetic circuit such that i~ makes use of a new arrangemen
for adjustin~ its reluc-t~lce to a predetermined YalueO
A further object of tkis invention to to provide ana~ngement
for adjusting the reluctance value or one paral~etero~ the reluctance
of a magnetic circuit, using a modern machining such as by means of
a laser beam for reducing at least one of the opposite sur~aces o~
the central core f~rmin~ the a r-~ap of the ma~netio circuit, b~
removing material.
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Another object ~f this in~ention is to provide an
arrangement which ena~es to ~odif~ at Least one of the
opposite surfaces of the central core of a magnetic circuit
by modifying of the distribution o~ magnetic force lines
which causes an increase of the reluctance of the magnetic
circuit.
It is an additional object of this inventio~ to
provide a method for adiusting the reluctance of a magnetic
circuit which does not make use of a ferromagnetic rod more
or less inserted into the air-cap of the core o the magnetic
circuit by ~eans of an adjustment screw, and which eliminates
all the disadvantages inherent in the adjustment scre~.
_UM~lARY OF THE INVENTION
The magnetic circui-t according to the in~ention,
comprises two ferromagnetic half-shells which are rigidly held
together and which are provided with central cores forming
an air-gap together. At least, one of the half-sheels includes
a thin wall which is near the air-gap and perforated with at
least one circular hole whose diameter is a function of a
predetermined value of the reluctance of the magnetic circuit.
The fact that there is no central bore along the
core improves the qualities of the magnetic circuit.
The gradual and partial piercing of the thin wall
is effected by means of a laser heam, the emission of which
is modulated by pulses having adjustable time and intensity.
In accordance with the invention, an automatic machine may
be used with advantage to perform the reluctance adjustment
of magnetic circults. This machine basically comprises a
machining laser source, a meter that mesures one significant
parameter of the reluctance of the magnetic circuit, and a
computer. The meter may be a self-inductance meter of a
frequency meter.
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The prese~ce o~ a hole cut in the thin w~
contact with the aiX-~ap increases the e~fecti~e ~alue o~
the air-gap and,
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¦consequently, incrcases the reluc-tance value c~nd de~reases specific
¦sel~-induct~lce coefficient Al. Let ~ ~1 be the self-induct~nce
¦variation produced by drilling a hole of diameter d~ .
¦ Approximately bas.ic variation ~ Al is propor tional to the , .
¦square of the di~neter of the hole. Also approximately~ total
¦variatio~ ~ ~ Al caused by piercing several holes of d;ia~eters d~,
¦ d2 d3, O . O dn is propor tional to the sum of the squares of these
¦diameters :
~ Al = ~ (~ d3 ~ .0O d2)
k is a coe~ficient of proportionality o~ which the value depends on
¦the pa~ameters of the ferrite ma;netic circuitO
¦ 1~ necessary, the relative value of adjus-tment ~ ~ Al ma~ be
very great, 2~ ~p and more; for khis purpose, it is sufficient t~
give the adjustm~nt thin wall a consequent dimension and -to cu~ one
¦or more holes of varying d~ameter in the thin wall~
¦ However, the inven-tion concerns ferri*e ma.netic circui~s9 th~
¦relati;e adjustment ~-alue of which i5 about 10 ~ of their sel*-
¦inductance coefficients Alo '~he adjustment method ena~les to obtain
la ver~ high ad3ustm~nt accuracy of abou~ 10 , and even be-tter if
¦required, for it is possible to very finely set the ~aterial amount
¦which is removed by the machining of a laser beam.
Given that magnetic circuits used in telecommun~ati~ uipment
¦ axe used with very low magnetic inductance of about one tentn of .
millitesla, the fact o~ locally reducing the cross-sectioll o~
ferrite even to a -fairly great de~ree does not reacn Yalues near to
saturation ~nduction whicll is of the order o-f a few hundreds of
m~liteslas.
¦ The adjustmellt method accordin~ to -the invention is fairly
¦ rapid and uses no moving mechanism in the magne-tic circuitO The
rhythm o~ adjusting the ma~netic clrcuits m~y be very great~ of
¦ about one adjusted magnetic circuit per secondO
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Another ad~an~ta~e o~ the magnetic circuit and o~
its adjustment method lies in its great reliabilit~, The
magnetic circuit comprises no added partl the relati~e
accuracy of which may be ~odified after the adjustment under
the influence of temperature of ~ibrations, a~d it is hi~hlY
reliable.
BRIEF DESCRIPTION OF THE DRA~INGS
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Other objects and advantages of this in~ention will
become apparent as the following description o~ preferred
embodiments, which description should be considered together
with the accompanying drawings, in which:
- Fig. 1 is a cross-sectional, elevational view taken along
line I-I of Fig. 2 of a magnetic circuit emb~dying the
invention;
- Fig. 2 is a top plan view of the magnetic circuit r
- Fig. 3 is a schematic block diagram of the arrangement for
utilization of the method of automatical adjustmenti and
- Figs. 4a, 4b and 4c illustrate three preferred con,figuratio~s
of the adjustment thin wall of a magnetic circuit embodying
the invention.
DESCRIPTI~N OF THE PREFERRED EMBODIMENTS
As shown in Fig. 1, a magnetic circuit embodying
the invention has the general shape of a casing which is
constituted by a bottom half-shell 1 and a top half-shell 2.
The two half-shells 1 and 2 are in ferrite and are rigidly
held in place by means of gluing or hooking material on the
external rings 1', 2' of the half-shells 1, 2, after the
coils 6 of the magnetic circuit are inserted. As illustrated
in Fig. 1, the two half-shells are not identical. l`he bottom
half-shell 1 has an entire central core 1" , and the central
core 2" of -the top half-shell 2 has a bore 3, hereinafter
called "adjustment bore". The central cores 1" and 2" are
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separed therebet~een b~.an air-~ap 4. The ~ore 3 has the
or~ o~ a blind h~le ~hich is separated ~. the air~ap
4 by a thin ~all 5r hereina~te~
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: .led "adjustment wa~", and mar be a cylindr.ical bore ~oc~ial to
the central cores ~" ~nd 2~o The coil or coils 6 are placed in -the
cavlty of the ma~netic circuit which extends between the c~*ernal
rings 1', 2' and the cores 1", 2". One or mor~ holes 7 ~re dr.illed
in the adjustment w~ll 5 in accordc~nce with -the adjustment methodO
It should be no*ed that before hole 7 is drilled, the ma~rnetic
circuit h~s substantially the same features as a marnetîc circuit of
the same dimensions o~ which the central core is not provided with
adjustment bore ~. ~ig. 2 illustrates a ~iew o-f the top face O-r
magnetic circuit which is ada~ted for use in accordance with the
invention~ In the ~ig. 2, it is again illustrated thetoph~-shel~
2, the adjustement bore 3 and the adjustment hole 7~ A body 8
carries the coil or coils 6 and emerges from the magnetic circui~
at two places~
Figo 3 shows schematically c~n arr~ngement for automatically
adjust-~ng the reluctance of the ma~net.ic circuit by means of a
laser sourceO . .
The coil 6 o~ the ma.gnetic circuit to be adjus*ed is comlected
to the input o~ meter10 which measures a parameter of the relu.c-t~nc~
of the magnetic circuit, such as the self inductanceO A ~omputer 11
has one input w~ich is connected to -the data output of.the meter 1
and another input ~hich i~ connected to the data output o~ a storag~
circuit 12. The storage circuit 12 comprises aprocessorwh1ch stcres
programs and the predetermined reluctance va~ue ~hmust be obtained
for setting the magnetic circuitO The computer 11 is self-aclapting
or machine 1 earning. According to the pre-s tored program in the
circuit 12, the compu-ter 11 determines the paran~eters -~or adjusting
the laser source 140 These parameters are orieIl~a~ion9 intensity~,
operation time and comrergence of` the laser beam 15 which is emi-tted
from the laser scurce 14, and are determined in the computer 11
*rom the comparison of the sel-f'-induc-tance value ~hioh is measured
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and transmitted frorrl the meter 1() and the predetermined sel~-
induc~ance ~alue wll:ich is stores and transmitted :Erom the storc~e
circuit 12., ~ w.ire bus ~3 connects the output of the computer 11
and the data inpu-t of the laser source 14 and conveys -tha data
required :for settin~; the parame ters o-f the er.lission of the laser
beam 150
~ he use of a laser source 14 pro~rides a simple means f`or
adjusting the reluctance of` the maglletiC circuitD The removal of
ferromagllLetic material required for the relu~tance adjustment is
effec1:ed on a l~agrlet:ic circuit fitted with its coil in ope~ating
condition. This means that the adjustment is performecl during its,
real operation state and may be applied to an inductor or a
tranLsformer which :~orms part of an operating electronic: assemblyO
F~r this reason, the magnetio circults composing the inductor or
the transformer are adjusted under their normal conditlot~s oi~
opera~,i on~.
_.~perience has shown that thc method o:~ matter rem~ing by
means o:E~ a laser beam causes no appreciable disturbance to the
ferrite magnetic circuit. In fact9 the adjustment thin wall 5 o~
the magnetic circuit enables a machinin,~ by means o~ the lase:r beam
l S whi~h ~ s very localized in space and in time.,
. In order to obtain other con~igurati on of the ad jus tin~ thin
wall9 the computer 11 may transmit : ; ~arious data for controlling
the laser emission in the souroe 147 under -the control of di~erent
programs which are stored in the stora~e circuit 120 Fig~. 4a, 4b
and 4c illustrate three e~amples of con:fi,gurations ~ich may be
t~sen by the ~djustment thin wall of the magnetic circuit, once the
magnetic circui.t has been adjusted~ The adjustment wall 5a shown
in P`ig. 4a has been drilled with a single hole 7a of which the
diameter is calculated to provide the predetermined value of self-
inductance as near as possibleO As show~ in I~igo l~b~ the adjustment
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wall 5b s drilled wiih n plur~lity of ind~ntio~i hol~s 7b whioh
are distributed on a spiral. The self-induc-t~lce is measured a~ter
each hole is drilled to determine whether another hole should ba
drqlled or not~ The adjus-tr~en~ wall 5c i:Llustrated in ~ig. 4~
corresponds to the use by the computer t1 of a program that set3
the diameter of e~ch of the plurality o~ holes 7~ to be drilled
aLter each measurement o~ sel~-inductance,, in order to approach the
predetermined self-inductance value by trial and error. The h~les
7c are drilled and also centred along a spiral on the adjustment
wall 5c and have practically decreasing diameters. This working
method in accordance with the Figo l~c gives both great rapidity o~
operation and Yer~ accurate adjus-tment.
As an example of the use of this last method, automatic
adjustment of self-inductance is carried out wi-th an accuracy o~
1~ at the rate of one magnetic circuit per secOnd. ~or example,
a magnetic circuit has a cross-section o~ the central core 11l 3 2~1
o~ 26 mm , a cro~s-section of the adjustment bore 3 o~ 7 mm and a
thickness of ~djust~ent wall 5c of 0.3 ~m~ Machining is e~ected
by laser beam the emission o~ which is modulated by puIs~s ha~ing a
time of 0~5 ~0 Each pulse remo~es material to a depth o~ 50 ~m.
Acccrding to the embodiment described above in refere~e to
Fig~ 1~ the two half-shells 1 and 2 are different. Howevert i-t is
contemplated ~or a multitude of reasons~ economy among others~ that
two ide~tical hal~-shells may be combined to form a magne~c circuit
embodying the invention ~ithout departing ~rom the principles
illustrated herein. In this case; the ma~,net:ic circuit thus ~ormed¦
is adjusted either sil~ultaneously or alternatively by laser
machining on one and/or -the other o~ the adjustment walls of the
half-shells~ It is,therefo~e~ intended that this in~r~ltion be
limited only by the scope of the amended cl~imsO
