U.S. patent number 3,585,547 [Application Number 04/841,862] was granted by the patent office on 1971-06-15 for electromagnetic force motors having extended linearity.
This patent grant is currently assigned to Bell Aerospace Corporation. Invention is credited to Abdul R. Kassir, Salvatore A. Sciortino, Oded E. Sturman.
United States Patent |
3,585,547 |
Sturman , et al. |
June 15, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
ELECTROMAGNETIC FORCE MOTORS HAVING EXTENDED LINEARITY
Abstract
An improvement in electromagnetic force motors in which
linearity of the force versus input signal characteristic is
extended. Discrete sections of magnetically saturable material are
inserted in the flux path between the frames and permanent magnets
and have induction/magnetic force characteristics different from
the characteristic of the frame material to obtain magnetic
saturation paths thereat.
Inventors: |
Sturman; Oded E. (Arleta,
CA), Kassir; Abdul R. (San Gabriel, CA), Sciortino;
Salvatore A. (North Hollywood, CA) |
Assignee: |
Bell Aerospace Corporation
(N/A)
|
Family
ID: |
25285878 |
Appl.
No.: |
04/841,862 |
Filed: |
July 15, 1969 |
Current U.S.
Class: |
335/227; 335/236;
335/230 |
Current CPC
Class: |
H01F
7/14 (20130101) |
Current International
Class: |
H01F
7/08 (20060101); H01F 7/14 (20060101); H01f
007/13 () |
Field of
Search: |
;335/227,229,230,236,237 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Harris; G.
Claims
What we claim is:
1. In an electromagnetic force motor having a pair of pole pieces
spaced apart to provide an airgap therebetween;
an armature positioned with a portion thereof in said airgap, said
armature being adapted to move in said airgap from a null position
thereof thereby more closely approaching one of said pole
pieces;
a magnetic circuit in said motor including said pole pieces and
said armature and including permanent magnetic means for providing
polarizing flux and a frame member securing said pole pieces to
said permanent magnet means;
electrical signal receiving means disposed on said magnetic circuit
to establish magnetic flux therein of a strength proportional to a
received electrical signal;
the improvement of apparatus for extending the linearity of the
force versus input signal characteristic of said force motor,
comprising:
at least one discrete member of magnetically saturable material
disposed between said frame member and said permanent magnetic
means and having an induction/magnetic force characteristic
different from the induction/magnetic force characteristic of said
frame member so as to define a magnetic saturation path
thereat;
said permanent magnet polarizing flux being sufficient to
magnetically saturate said discrete member at a preselected
armature position other than its null position within said airgap
but being insufficient, at said preselected armature position to
magnetically saturate frame member material of the same
configuration as said discrete member.
2. The invention as defined in claim 1 in which said frame member
is formed integral with said pole pieces.
3. The invention as defined in claim 1 wherein a plurality of said
discrete members are disposed between said frame member and said
permanent magnetic means.
4. The invention as defined in claim 3 wherein each of said
discrete members has the same induction/magnetic force
characteristic.
5. The invention as defined in claim 3 wherein said discrete
members completely separate said frame member from said permanent
magnetic means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of art to which the invention pertains includes the field
of torque motors.
2. Description of the Prior Art
The use of force motors in the prior art has long been known. One
example of the utility of force motors is in the positioning of the
pilot valve such as a flapper or spool of an hydraulic servo valve.
The force motor in such applications is used as an element of a
control system and is adapted by its operating characteristics to
convert an electrical input signal into a desired mechanical
position of the spool valve. Force motors also have a wide variety
of other uses, for example, in automatic control systems for
industrial machinery.
Such force motors which utilize a large percentage of the airgap
for armature motion are typically faced with nonlinearity over all
but a small part of the airgap. In various of the prior art
applications it has long been desirable to provide force motors
which bear a linear relationship to the applied input signal and
wherein the force exerted upon the armature remains substantially
linear as it approaches the pole faces. This would permit
displacement of the armature over the entire gap.
A variety of schemes have been proposed to accomplish such
linearization, for example, reducing the effective length of the
cross-sectional area of a part of the armature and keeping that
portion always saturated magnetically, as illustrated in the U.S.
Pat. No. 3,071,174.Another linearization scheme provides recesses
on the face of the armature and a plurality of mating teeth on the
face of the pole pieces, for example, as shown in U.S. Pat. No.
2,930,945.
Each of the foregoing devices attempts to utilize magnetic
saturation to obtain linearization by carefully formulating the
configuration of the magnetically permeable material that defines
the flux path. Although each of these devices operate for the
purpose intended, problems sometimes arise in manufacturing to the
close tolerances required to obtain acceptable devices. There is a
need, therefore, for a simple means for attaining magnetic
saturation appropriate to the linearization of the force versus
input signal characteristic of the force motor.
SUMMARY OF THE INVENTION
The present invention provides an improvement in electromagnetic
force motors in which linearity of the force versus input signal
characteristic is extended. A motor is provided of the
electromagnetic force type, that is, having a pair of pole pieces
spaced apart by frame members to provide an airgap therebetween, an
armature within the airgap and permanent magnet means defining a
magnetic circuit. The improvement of this invention comprises
providing at least one discrete member of magnetically saturable
material between the frame member and permanent magnet means and
having an induction/magnetic force characteristic different from
the induction/magnetic force characteristic of the frame member.
Polarizing flux from the permanent magnet, is sufficient to
magnetically saturate the discrete member, but would be
insufficient to magnetically saturate that member if constituted of
the frame material. In particular embodiments, a plurality of
magnetically saturable discrete members is provided to completely
separate the frame members from the permanent magnets. The present
invention is an improvement over the invention disclosed in U.S.
Pat. No. 3,517,360.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic, cross-sectional view of an electromagnetic
force motor utilizing the present invention; and
FIG. 2 is a cross-sectional view of the apparatus illustrated in
FIG. 1, taken on line 2-2 of FIG. 1, in the direction of the
arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the FIGS. there is illustrated in schematic manner an
electromagnetic force motor constructed in accordance with the
present invention. The force motor includes frame members 10 and 12
which are formed to define oppositely disposed pairs of pole pieces
14, 16 and 18, 20. An armature 22 is supported about a pivot point
24 between the pole pieces. Although not shown in the schematic
drawing herein, the armature can support a flapper so as to serve
as the first stage of a control valve, all as well known to the
art. Further, a coil 25 is positioned about the armature 22 and is
adapted to receive an electrical input signal which thereby causes
the armature to take a physical position, displaced from the Null
position (illustrated), depending upon the strength of the applied
input signal and the polarity thereof.
In prior art torque motors, a pair of permanent magnets would be
secured between the frame members, directly contacting the frame
members. In the present invention, permanent magnets 26 and 28 are
also affixed to the frame members 10 and 12, so as to bridge the
frame members and provide magnetic flux for the torque motor.
However, in the present invention the permanent magnets 26 and 28
are separated from the frame members 10 and 12 by means of inserts
30, 32, 34 and 36, as hereinafter described. The inserts and
permanent magnets are secured between the edges of the frame
members 10 and 12 by means of machine screws 38 and nuts 40
therefor extending through the edges of the frame members, as shown
in the drawings.
The inserts 30, 32, 34 and 36 are of magnetically permeable
material having a predetermined induction/magnetic force
characteristic which is different from the induction/magnetic force
characteristic of the material of which the frame members 10 and 12
are constituted. The induction/magnetic force characteristic of
each of the inserts 30, 32, 34 and 36 is such that the magnetic
flux from the permanent magnet 10 and 12 is sufficient to
magnetically saturate the inserts at a preselected armature 22
position within the airgap between the poles 14, 16 and 18, 20, but
is insufficient at that armature position for magnetic saturation
if the inserts were constructed of the same material as the frame
members 10 and 12. In other words, the inserts 30, 32, 34 and 36
are constructed of material which passes its maximum magnetic
induction at a particular position of the armature 22 in the airgap
displaced from its Null position.
With prior art torque motors, as the armature approaches one of the
pole faces, the reluctance due to the gap decreases, resulting in
an increase in flux from the permanent magnet, which increase is
proportional to the square of the armature displacement. At the
same time, a linearly increased amount of such nonlinear flux
passes through the gap. The total result is a flux increase that is
nonlinear with respect to armature displacement. However, when the
present invention is utilized, as a result of saturation of the
inserts 30, 32, 34 and 36, a decrease in reluctance does not effect
an increase in flux. Since the gap is decreasing in length the
number of flux lines passing therethrough does increase; however,
this increase is in linear proportion to such decreasing gap
length, i.e., in linear proportion to armature displacement.
* * * * *