US2569105A - Magnetic position responsive device - Google Patents

Description

Sept. 25, 1951 w. J. JAMES 2,569,105

MAGNETIC POSITION RESPONSIVE DEVICE Filed Feb. 26, 1948 Patented Sept. 25, 1951 UNITED STATES PATENT OFFICE MAGNETIC POSITION RESPONSIVE navrca William J. James, Richmond, Calif.

Application February 2c, 1948, Serial N6. 11,14:

1 Claim. 1

The invention relates to magnetic devices designed for detecting position or movement of connected or related parts for either measuring or indicating such position or movement or for controlling the operation of devices in relation to such position or movement.

An object of the present invention is to provide a highly sensitive device of the character described which will afford a relatively great electrical output in response to minute changes in position, whereby the device may be compactly constructed with a minimum required movement of its moving part.

Another object of the present invention is to provide a device of the above character utilizing magnetic windings which may be completely sealed from the exterior of the device, thereby enabling the use of the device in liquids or atmospheres which would ordinarily be corrosive or injurious to the windings and related parts.

A further object of the present invention is to provide a device of the character described which is relatively insensible to temperature changes so as to permit its use under conditions involving wide temperature variations, and in which the magnetic forces are so balanced and opposed that only a small exterior force is required for operation.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will'be set forth in the following description of the preferred form of the invention which is illustrated in the drawing accompanying and forming part of the specification. It is to be understood, however, that variations in the showing made by the said drawing and description may be adopted within the scope of the invention as set forth in the claims.

Referring to said drawing:

Figure 1 is a cross sectional view of a magnetic position responsive device constructed in accordance with the present invention.

Figure 2 is a fragmentary perspective view of one of the field pieces of the device.

Figure 3 is a wiring diagram showing the electrical circuit of the device.

The magnetic position responsive device illustrated in the accompanying drawing includes a pair of field pieces 6 and I here of generally cylindrical form and mounted in concentric spaced relation in a shell or casing 8 so that end faces 3 and II of the field pieces are in spaced apart substantially parallel opposed relation. The casing 6 is here shown closed at its lower end by base plate l2 and at its opposite end by a cap l3, the space between the upper field piece 6 and the cap being sealed off by means of wax H or the like. As will be understood and more fully hereinafter discussed, the device may be used for a variety of applications which may dictate the shape and construction of the outer shell and its mountings.

Field pieces 6 and I are preferably constructed of iron or other suitable magnetic permeable material, and are provided in their end faces 9 and II with annular, preferably concentric recesses l6 and I! which open to the end faces 9 and l I and to the space l8 therebetween. A pair of toroidal coils or windings l9 and 2| are mounted in the recess 16 and in similar fashion toroidal coils 22 and 23 are mounted in the opposed recess l'l. These are complete and independent windings and the leads 24 and 26 therefor are brought out through radial slots 21 and 26 in the field pieces 6 and I and through apertures 29 and 3| in the outer casing 8 for connection exteriorly in the electric bridge circuit illustrated in Figure 3. The slots 21 and 28 also function to minimize circulating currents in the field pieces. With reference to this circuit, it will be noted that the coils l9 and 2! of the field piece 6 constitute a pair of opposite legs of the bridge, while the two coils 22 and 23 of field piece I constitute the other opposite legs of the bridge. An alternating electric potential designated by the letter 6 is connected to the bridge by conductors 32 and 33 at the common terminal 34 of coils l9 and 23, and the common terminal 36 of coils 2i and 23 respectively. The other ends of coils i9 and 22 are connected to form a center terminal 31 for the bridge, while the opposite ends of coils 2| and 23 are connected to the ends of a potentiometer 38, desirably of a variable inductance type which defines the opposite midpoint of the bridge. Thus a current passing to the bridge by conductor 32 divides, with part of the current moving through the upper side of the bridge as illustrated in Figure 3, traversing the coils l9 and 22 past the midterminal 31, and with part of the current moving through the lower side of the bridge traversing coils 23 and 2|, and across the potentiometer 36. The two parallel branches of the bridge are again joined at terminal 36 for completion of the circuit through conductor 33. An electrical responsive device here shown in the form of a meter 39 is connected between the two midpoints 31 and 38 of the bridge so as to respond to the voltage imbalance between these two bridge points. In the present drawing the device 99 is depicted as a meter which may be used for measuring the imbalance. As will be hereinafter more fully explained, the device 29 may consist of a relay or other electrically actuated device for controlling the operations of mechanisms to be operated in conjunction with the present position responsive device. As illustrated in Figure 3 the meter 39 is connected to mid-terminal 31 by conductor 4| and to the potentiometer 38 through a rheostat 42 and the moving contact arm 43 of the potentiometer. The function of the potentiometer is to control the imbalance voltage applied to the meter so that the meter can be set to zero position for a starting condition when a desired imbalance is present. The rheostat 42 functions to control the full scale deflection of the meter related to the amount of imbalance which will be present during a given operation.

The coil ends are so connected in the circuit as to produce a common polarity of themagnetic fields so that the magnetic flux generated by coil I9 will be additive to the magnetic flux generated by coil 2|, and similarly the magnetic flux generated by coil 22 will be additive to the magnetic flux generated by coil 23. Desirably, also, the polarity of the field pieces thus established is such that the opposed end faces 9 and H will have similar polarity. As will be understood, the field pieces and their windings constitute cylindrical magnets having center cores 44 and 46 and peripheral fiux paths 4! and 49. Flux arrows 49 are here used to indicate the type of common polarity desired, it being noted at the instant of operation depicted in Figure l, the flux lines move axially outward in the center cores 44 and 46 toward the outer ends of the device and in an opposite direction in the peripheral flux paths 4'! and 48, it being noted that in the instance of each of the pole pieces the fiux paths are completed in the air space l8 between the faces 9 and H. In accordance with the present invention, and as an important feature thereof, there is mounted within the space l8 for reciprocation to and from the ends 9 and i I, an armature SI of magnetic permeable material which is in the fiux path above defined and which serves to carry the magnetic flux through that portion of the field in whichthe armature is located. As will be understood, the reluctance of the magnetic paths, and therefore the inductance of coils I9, 2|, 22 and 23, is directly controlled by the position of the armature. As the armature is moved from its position illustrated in field one toward the upper face 9 of the top field piece, the air gap between the armature and the field piece is reduced and the reluctance of the magnetic flow correspondingly decreased. In this movement, therefore, the inductance and impedance of coils i9 and 2! are increased, while the inductance and impedance of coils 22 and 23 are decreased. With reference to Figure 3, it will be seen that these simultaneous changes in impedance of all four coils cooperate in an additive fashion to change the imbalance of the bridge, and thereby send electrical current through the device 99. In a like manner, the movement of the armature I in the direction of the end face ll increases the impedance of the coils 22 and 23, while simultaneously decreasing the impedance of coils I9 and 2|, thus producing a maximum imbalance in an opposite direction.

Preferably the coils I9, 2| 22 and 29 are of substantially similar construction, thereby hav ing approximately equal inductance and impedance. In such case the bridge circuit would be approximately in balance with the armature located approximately midway between the pole faces I and il. Thereafter movement of the armature, say toward pole face 9, would cause a deflection of the meter 19 in one direction while a movement of the armature toward the pole face H would produce a reverse movement of the meter. For certain types of controls such a zero center meter reading is desirable. For example, where the device is applied to a steering apparatus or the like which is to be maintained on a steady course, deflections from such course may be thus immediately detected and corrective devices operated. In other installations and uses of the device such as for measuring position, or the like, it is desirable to have the meter read zero when the armature is adjacent one of the pole faces and to read maximum when the armature is adjacent the opposite pole face. This may be accomplished by biasing the meter by means of the variable reactance potentiometer 38, that is by moving the potentiometer arm 43 away from its electrical center sufficient to bias the meter to a zero position when the armature is at one of the pole faces. Desirably direct contact between the armature SI and the faces 9 and H of the pole pieces is avoided since a non-lineal response as well as sticking of the armature to the pole piece may be encountered at the point of engagement. To insure desired separation at all times, I prefer to cover the pole faces 9 and II with thin plates 45 and I of non-magnetic material such as aluminum or the like. These plates also function to seal of! the coils within the recesses I6 and I! to thereby prevent access thereto of any deleterious liquids or gases finding their way into the interior of the device.

Movement of the armature by the part or apparatus whose movement is to be measured or detected is here effected by an axial shaft 52 which is slideably carried in aligned axial bores 52 and 54 in the field pieces' 6 and I, and is connected between the field pieces to the armature ll. One end 56 of the shaft 52 is extended exteriorly of the device through the end plate 12 for connection to the part or apparatus with which the device is to be associated. Thus, the axial movement of shaft 52 is directly related to the deflection of meter 99 and the relative position of the shaft may be read directly on the meter. The shaft and exterior housing parts are preferably made of non-magnetic material such as brass or stainless steel so as to confine the magnetic path to the pole pieces, air space and armature, as above described. Preferably, and as here shown, anti-friction bearings 51 and II are used to facilitate the reciprocal axial movement of the shaft.

Due to the use of efficient cylindrical magnet construction and to the additive bridge imbalance characteristics above described, the device is highly sensitive to the position of the armature and to its change of position, and is capable of a high voltage output per unit of armature movement. For example, with an input of sixty volts, that is applied at e of the circuit illustrated in Figure 3, a net output of about fifteen volts may be obtained. This output is suflicient, of course, to operate various types of relays, motors, or other electrical controls, and may be rectified into D. C. for various types of controls when desired. Also,

I have found that the voltage output response is practically linear to movement over the full range of movement of the armature. Since the four coils of the device are all concentrated in a compact space, and approximately equally exposed to any temperature change, the device is practically insensitive to temperature changes, as all coils are affected alike by such change. Also, because of the general symmetrical construction of the unit on opposite sides of the armature and the general opposing of magnetic forces, very little external force-is required to move the armature. Accordingly, the device requires very little mechanical energy to operate and may, therefore, be used on other sensitive devices without impairing their operation. If desired, the armature may be biased to one of the pole positions by means of a spring or the like, so as to substan- Y tially uniformly resist movement to the other pole. Such a resilient construction may be used where the device is adapted for measuring pressure, that is, where a source of pressure to be measured is applied to overcome the resistance of a spring so biasing the armature position.

I claim:

A magnetic position responsive device comprising, a pair of cylindrical members of magnetic permeable material mounted in substantial axial alignment with end faces of said member in spaced opposed relation defining an air gap therebetween, each of said members being formed with an annular recess substantially concentric to the axis of said member and opening to said end face of said member, said recess being defined between a central core and a spaced concentric outer annular wall, an inductance winding mounted in each of said recesses and providing when electrically energized magnetic flux traversing said core and wall and emanating from said end face into said air gap, said cores being formed with axially aligned bores, a shaft of non-magnetic material slidably mounted for longitudinal reciprocation in said bores coaxially of said members, and an armature of magnetic permeable material mounted substantially concentrically on said shaft for movement therewith, said armature extending radially from said shaft into opposed relation with said outer annular walls and having its axially spaced sides substantially parallel to said end faces and for movement with said shaft while maintaining parallelism between said sides and end faces.

WILLIAM J. JAMES.

REFERENCES crrED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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