US3003128A - Position measuring apparatus - Google Patents

Description

Oct. 3, 1961 a. SMITH POSITION MEASURING APPARATUS Original Filed larch 4, 19 59 R w M w 2 R MO m mm .m w M/ d m Hrv W a a a w/mi.

3,093,128 POSITION MEASURING APPARATUS Gray'don Smith, Concord, Mass, assignor to Clevite Corporation, Cleveland, Ohio Continuation of application Ser, No. 797,078, Mar. 4, 1959. This application Apr. 7, 1960,'Ser. No. 20,786 6 Claims. (Cl. 336-75) This invention relates to electrical position-measuring devices adapted to produce and transmit an electrical measurement signal directly corresponding to the posi-' tion-or location of a physically movable element; an example of a measuring device of this general character is described in detail in copending application Serial No.

690,363, filed October 15, 1957. More in particular, this invention relates to improvements adapted to provide electrical position-measuring devices that are highly compact and efficient in operation, and inherently less subject to the effects of variations in ambient temperature.

Prior devices of the general type described in the above copending application comprise a three-legged magnetic core structure having a primary winding wound on the center leg to produce flux around the two magnetic circuits formed by the outer legs. The relative distribution of the flux in the outer legs is controlled by a movableflux-barrier consisting of an electrically-conductive closed loop positioned to extendinto an air-gap formed in the center leg. Secondary windings are mounted on the outer legs and arranged to produce an electrical output signal inaccordance with the relative amounts of flux passing through these outer legs.

In devices of this "character, the presence of the air gap substantially increases the reluctance of the magnetic circuits throughwhich the flux passes, and this in turn reduces the -inductive impedance of the windings relative to theirefiective resistance. As a result, any change in the effective resistance of these windings, due for example to a change in ambient temperature, may alterthe output signal to an undesired extent. Moreover, therelatively high reluctance of the air-gap makes it possible for some of the flux to pass through closed paths which do not include the air-gap. This leakage" efiect reduces the amount of flux controlled by the fluxbarrier and thus reduces the eliiciency of operation.

In accordance with the present invention, however, these adverse effects are minimized by a construction which is compact and yet arranged to'provide a relatively low air-gap reluctance. Thus, the inductive impedance of thewindings is substantially increased over prior devices of the same overall physical size, and a larger percentage of the flux is controlled by the flux-barrier so as to assure good'sensitivity. Other objects, advantages and aspects of the present invention will be in part apparent from, and in part pointed out in, the following description consideredtogether with the accompanying drawings, in which;

FIGURE 1 is a plan view of a position-measuring device constructed in accordance with the present invention;

FIGURE 2 is 'a cross-section taken along line 2-2 of FIGURE 1; and

FIGURE 3 is a longitudinal section taken along line 3--3 of FIGURE 1.

Referring now to FIGURE 1, the device includes a threele'gged magnetic core structure having elongated top and bottom members 12, 14 with a pair of outer legs 16,18 and a center leg 20 extending therebetwcen. Betweenthe center leg and the top member is a V-shaped air-gap 22 formed by a wedge-like section 24 and *a deep mating trough 26. This air-gap has a'flength; wise dimension, defined herein as the lineal distance between the remote ends of the air-gap (ire. as measured 2 between the upper tips of the V in the disclosed embodiment), that is substantially greater thanthe corresponding lateral dimension? of the center leg 20, as measured from lefHo-right in FIGURE 1.

Referring also to FIGURE 2, an electrically-conductive flux-barrier generally indicated at 28 is positioned about the magnetic core structure 10 and includes an elongated control element 30 which extends lengthvrn'se through the air-gap. This control element-is V-shaped to conform to the air-gap configuration, and it in a plane that is parallel to the effective plane of thecore structure. The left-hand end of the control element is integral with an arm 32 which extends along one side of the top core member 12 and forms part ofabase member" 340i the flux-barrier. The right handend of the control elem'ent is integral withanother'arm '36 whichcxtends along the other side of top member 12 to the base member 34. Secured to the top of the base member is a support plate 38 which is movable (in the direction in dicated by the arrow in FIGURE 2) to vary the positioning of the control element 30 with respect to the airgap 22.

I The outer legs 16, 18 are provided with respective identical primary windings 40, 42 which are energized in series by a source of alternating current indicated by terminals 44., Respective identical secondary windings 46, 48 also are wound on these legs and are connected in series-opposition to an electrical-sensing unit diagrammatically indicated at 50 as a volt meter adapted to indicatethe magnitudeof the output signal. The particular winding arrangement shown herein also is described and discussed in detail in copending application Serial No; 768,730, filed October 21, 1958 by. the present applicant;

. As indicated by the dashed lines 52, 54 in FIGURE 1, the magnetic core 10 formstwo magnetic circuits both pmsing' throughwa common core portion includingthc center leg 20 and wedge-like section 24. The left-hand one of these magnetic circuits 52 passes beneath the flux-barrier arm 32 and crosses the air-gap (see alsov FIGURE 3) beneath the controlelement 30, The righthand magnetic circuit 54 passes above the other fluxbarrier arm 36 and crosses the air-gap above-the control element 30. Since no net flux can pass through the closed electrically-conductive loop represented by theflux-barrier' 28, these two magnetic circuits are effectively isolated from each other. That is, all'the flux (except leakage flux) produced by the left-hand primary winding 40 crosses the air-gap 22 below the control element 30, and similarly all the flux produced by the right-hand primary winding 42 passes across the air-gap above this control element.

Referring now to FIGURE 2, when the flux-barrier 28 is positioned with its control element 30 in the center of the air-gap 22 (as shown), the area of the air-gapto the left of the control element willbe equal to the area to the right of this element. Hence, the magnetic reluctances of the two circuits 52, 54 will be equal and the two primary windings 40, 42 will present equal impedances to the source of current 44. In that case, the voltages across. the primary windings will'be equal and consequently the flux produced around the respective magnetic circuits 52, 54 by these windings will be equal.

Thus, equal voltages will be induced in the series-opposed seoondarywindings 46, 48 with the result that no net voltage will betransmitted to meter 50. I

If the flux-barrier 28 is moved by the support plate 38 to theleft (FIGURE 2), the air-gap area to the left of control element 30 will decrease while the area to the right will increase. Therefore, the reluctance of magnetic circuit 52 will decrease while the reluctance of magnetic circuit 54 will increase, so that the of primary winding 40 isincreasedand the impedance of 3,003,128 7 Patented Oct. 3, 1961 l c v 3 I primary winding 42 is decreased. Consequently, the voltage applied across winding 49 will go up, while the volttage applied across winding 42 will go down, and the fiux through the left-hand outer leg16 thus will increase while" the flux throughthe right-hand outer leg 18 will decrease.

With these changes of flux in the outer legs 16 and 18, the voltages induced in the secondary windings 40, 42 will be correspondingly unbalanced so that a net output voltage will be transmitted to meter 50. The magnitude of this voltage is proportional to the extent of movement of the flux-barrier 28, and the phase of this voltage is determined by the direction of flux-barrier movement away from its center position, i.e. either left or right as-viewed in FIGURE 2.

Because the air-gap 22 extends down the center leg 20 for a substantial distance, rather than directly across this leg, the lengthwise dimension of the air-gap is substantially increased over prior devices of this general class of the same overall size. Accordingly, the effective area of the air-gap is increased thereby reducing the reluctance of the magnetic circuits traversing the gap. With a lowered magnetic reluctance, the inductive impedances of the windings are increased relative to the winding resistances, thereby reducing any variations in the output signal resulting from changes in winding resistance such as might be caused by changes in ambient temperature. In addition, the lowered reluctance of the air-gap tends to reduce the relative amount of stray flux, i.e. flux which does not cross the gap, and thus increases the efiiciency of operation.

Although in the specific preferred embodiment described herein the air-gap is in the shape of a V, other gap shapes can be utilized to achieve at least some of the advantages of the present invention. In any event, the core should be arranged in such a manner that at least a part of the gap, as viewed in a sectional plane through the gap, extends in a direction that is non-perpendicular to the flux-axis (that is, the principal direction of the flux) of the magnetic material adjacent the air-gap. For example, in the described embodiment as viewed in the plane of FIGURE 1, both sides of the V extend in directions that are non-perpendicular to the average direction of the flux passing longitudinally (i.e. axially) through section 24 and center leg 20.

When the air-gap is elongated in this manner, the flux crossing the gap should be controlled by a flux-barrier having a control element which extends parallel to the air-gap direction that is non-perpendicular to the fluxaxis of the adjacent magnetic material. In addition, this element should be movable in a direction having at least a component that is perpendicular to the longitudinal axis of the control element; e.g. in the preferred embodiment, element 30 moves at right angles to a plane passing through the two arms of the V defined by this element. The air-gap, as viewed in any vertical cross-sectional plane through FIGURE 1, extends parallel to this direction of movement. Thus, regardless of the particular contour or shaping selected for the gap, a mating flux-barrier element can be provided which is freely movable through the gap to control the relative amounts of flux passing through the two separate magnetic circuits 52, 54.

Accordingly, there has been provided a position-measuring device having important advantages as compared to prior constructions. Although a specific preferred embodiment of the invention has been set forth in detail, it is desired to emphasize that this is not intended to be exhaustive or necessarily limitative; on the contrary, the showing herein is for the purpose of illustrating the invention and thus to enable others skilled in the art to adapt the invention in such ways as meet the requirements of particular applications, it being understood that various modifications may be made without departing from the scope of the invention as limited by the prior art.

This application is a continuation of my application Serial No. 797,078, filed March 4, 1959.

I claim:

1. In a position-measuring device adaptedto produce an electrical measurement signal for transmission to a remote electrical sensing or indicating means; apparatus comprising a core structure including magnetic material arranged to form two magnetic circuits having a common portion, primary winding means wound on said core structure to produce flux around said two magnetic circuits, said core structure being provided with air-gap means in series with both of said magnetic circuits; the magnetic material of said core structure being shaped to define a configuration for said air-gap means wherein at least a part of said air-gap means extends in a direction that is non-perpendicular to the flux-axis of the magnetic material adjacent said air-gap means on at least one side thereof; electrically-conductive flux-barrier means mounted about said core structure and forming a closed conductive loop adapted to control the relative division of said flux between said two magnetic circuits, said flux-barrier means including a control element positioned in said part of said air-gap means and extending essentially parallel to said direction thereof; support means mounting said flux-barrier means for movement effectively at right angles to said direction of said part of said air-gap means; and secondary winding means coupled to said core structure for producing a signal in accordance with the relative distribution of said flux between said two magnetic circuits.

2. In a position-measuring device adapted to produce an electrical signal for transmission to a remote electricalsensing means; apparatus comprising, in combination, a three-legged core structure including magnetic material arranged to form two magnetic circuits wherein the center leg is common to both of the circuits, primary winding means wound on said core structure to produce flux around said two magnetic circuits, said core structure be ing formed with an airgap in series with said center leg, at least a substantial part of said air-gap extending in a lengthwise direction that is non-perpendicular to the axis of said center leg; an electrically-conductive flux-barrier mounted about said core structure to control the relative division of said flux between said two magnetic circuits, said flux-barrier including an elongated control element positioned in said air-gap and extending longitudinally along the lengthwise direction thereof, said control element being shaped to conform to the contour of said airgap in said lengthwise direction; support means mounting said flux-barrier for movement in a direction that is perpendicular to said lengthwise direction of said air-gap; and secondary winding means coupled to said core structure for producing a signal in accordance with the relative distribution of said flux between said two magnetic circuits.

3. In a position-measuring device adapted to produce an electrical signal for transmission to a remote electrical sensing means; apparatus comprising, in combination, core structure including magnetic material arranged to form two magnetic circuits having a common portion, first and second primary windings wound on said core structure remote from said common portion to produce flux around said two magnetic circuits, said primary windings being connected in series, said core structure being formed with an air-gap in series with both of said magnetic circuits, at least a substantial part of the lengthwise dimension of said air-gap extending in a direction that is nonperpendicular to the flux-axis of the magnetic material adjacent said air-gap; electrically-conductive flux-barrier means positioned adjacent said air-gap to control the relative division of said flux between said two magnetic circuits, said fiux-barrier means including an elongated control element positioned in said air-gap and extending along the lengthwise dimension thereof, said control element being shaped to conform to the shape of the lengthwise dimension of said air-gap; support means for mount: ing said flux-barrier means for movement in a direction having at least a component that is perpendicular to said lengthwise dimension of said air-gap; and first and second secondary windings coupled to said core structure remote from said common portion for producing a signal in accordance with the relative distribution of said flux between said two magnetic circuits.

4. In a position-measuring device adapted to produce an electrical signal for transmission to a remote electricalsensing means; apparatus comprising, in combination, a three-legged core structure including magnetic material arranged to form two magnetic circuits and wherein the center leg is common to both circuits, primary winding means wound on said core structure to produce flux around saidtwo magnetic circuits, said core structure be ing formed with a V-shaped air-gap in series with said center leg, at least a substantial part ofthe long arms of, said V-shaped air-gap extending in directions that are nonperpendicular to the longitudinal axis of saidcenter leg;

electrically-conductive flux-barrier means positioned in structure for producing a signal in accordance 'with the relative distribution of saidflux between said two magnetic circuits.

5. In a position-measuring device adapted to produce an electrical signal for transmission to electrical-sensing means; apparatus comprising, in combination, a threesaid structure being arranged to form two magnetic circuits with the center leg common to both circuitsprimary winding means wound on said core structure to produce flux around said two magnetic circuits, said core structure being formed with an air-gap in series with said center leg; electrically-conductive flux-barriermeans positioned adjacent said core structure to control the relative division of said flux between said two magnetic circuits, said fluxbarrier means including an elongated control element positioned in said ,air-gapand extending parallel to the efiective plane of said core structure; said flux-barrier means further including a base member positioned adjacent said core structure top member and having a pair of arms extendingdown along opposite sides of said top member to the respective ends of said control element, thereby to establish an electrically-conductive closed loop surrounding said top member; support means for mounting said flux-barrier means for movement in a direction that is perpendicular to the longitudinal dimension of said control element; and secondary winding means coupled to v i No references cited.

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