US3471844A - Position responsive signal generator - Google Patents

Description

Oct. 7, 1969' J. F. SCHUGT POSITION RESPONSIVE SIGNAL GENERATOR Filed July 8, 1966 OSCILLATOR FEEDBACK PATH SCHMITT TRIGGER DEMODULATOR H.F. OSCILLATOR ATTOE/VE'V United States Patent 3,471,844 POSITION RESPONSIVE SIGNAL GENERATOR Joseph F. Schugt, 1206 Vanderbilt Ave., Niagara Falls, N.Y. 14300 Filed July 8, 1966, Ser. No. 563,873 Int. Cl. G08c 21/00; H01f 21/10 US. Cl. 340-196 8 Claims The present invention is concerned with a position responsive signal generator and more particularly with one which is very sensitive to movements of a moveable member having narrowly spaced controlling portions.

It is quite old in the art to have two electromagnetic units Whose cores are separated by an air gap and which are inductively coupled with each other, there being interposed in the air gap, a member which has portions thereof which affect the transmission of flux through the air gap differently from other portions. With such an arrangement, the movement of the member affects the transmission of flux between the inductively coupled members. The output of the inductively coupled member may be employed in various manners.

The drawback of previous arrangements of this type is that it has been diflicult to confine the flux in the air gap to a relative narrow path so that the sensitivity of the apparatus to the position of the movable member has not been as great as might be desired. This is a drawback especially where it is desired to respond with great sensitivity to the position of closely spaced flux controlling portions or where such a movable member is rotated at very high speeds.

An object of the present invention is to provide an apparatus of the type referred to above which is extremely sensitive and which can detect very small incremental movements of such a movable member.

A further object of the present invention is to provide such apparatus in which the movable member is in the form of a rotatable disc which can be driven at relatively high speeds.

Broadly, these objects are accomplished by the provision of shielding means around each core which shielding means confines the flux passage through the air gap to a relatively narrow path bounded by small openings in the shielding means. The shielding means not only extends over the face of the coupled electromagnetic units but also surrounds these units peripherally and bridges over the air gap so that the path for the flux is confined to a relatively narrow band. The shielding means may also have longitudinal openings in the peripheral shielding to further confine the flux path.

I further employ in connection with my position responsive signal generator, an arrangement in which one coil is connected to a high frequency source of power and in which the other coil unit coupled therewith is coupled in a feedback relation to the source of power so that the output of the high frequency source of power is modulated in accordance with the position of the movable member.

Various other objects of the invention will become apparent from a consideration of accompanying claims, specification and drawing, of which FIGURE 1 is a schematic view of my position responsive signal generator including my improved inductive pickoif and the circuit associated therewith;

FIGURE 2 is a perspective view of the coils of my inductive pickotf and the mounting means therefor;

FIGURE 3 is a view showing the coil structure of FIG- URE 2 in association with a rotatable disc, the potting compound surrounding the coils being shown in section and the mounting and shielding means being shown partially in section;

FIGURE 4 is an exploded view of the coil structure and shielding means of my inductive pickolf;

FIGURE 5 is a plan view of the rotatable disc of my inductive pickoff, the shaft therefor being shown in section; and

FIGURE 6 is a view similar to FIGURE 5 of a modified form of the movable member of my inductive pickoff.

Referring first to FIGURE 1, the inductive pickoff broadly comprises a coil 11 which is energized from a high frequency source of energy and which is inductively associated with a pickup coil 12. Extending between the two coils 11 and 12 is a rotatable disc 13 which is either continuously rotated or moved in accordance with some condition which it is desired to sense.

As best shown in FIGURE 5, the disc 13, which is formed of a conductive metal such as aluminum, has a plurality of teeth 14 which are narrowly spaced about the periphery thereof. In the specific form shown, the teeth are uniformly spaced. The teeth 14 are designed to extend into the flux gap between coils 11 and 12 to retard the transmission of flux from coil 11 to coil 12.

Referring to FIGURE 1, coil 11 is connected to a high frequency oscillator 15 having output terminals 16 and 17 and feed- back terminals 18 and 19. The output terminals 16 and 17 are connected to coil 11 while the feedback terminals 18 and 19 are connected to coil 12. The feedback connection through terminals 18 and 19 is preferably of the regenerative type so that when the coils 11 and 12 are inductively coupled, the oscillation of the oscillator is sustained. When, however, one of the teeth 14 is located in the air gap between the coils 11 and 12 so as to suppress transmission of flux between the coils, the oscillator ceases to oscillate. The on-off high frequency output resulting from a continuous rotation of disc 13 is shown schematically at 23 where, it will be noted, the amplitude of the output rises rapidly and then abruptly disappears during the portion of the rotation of disc 13 in which one of the teeth 14 is interposed between the two coils 11 and 12. Each time when one of the teeth blocks the air gap, the magnitude of the high frequency voltage builds up again. The modulated output of the oscilator is connected through conductors 20 and 21 to a demodulator 22 to remove the high frequency components therefrom. The demodulated voltage is shown by the wave form 25. The output of demodulator 22 is then fed to a conventional Schmitt trigger circuit 27 to form a square wave output depicted at 28. The resulting output is a series of sharply triggered square wave pulses, the occurrence of which is dependent upon the position of teeth 14 of rotatable disc 13 with respect to the air gap between coils 11 and 12. While the disc 13 is continuously rotated, the frequency of the pulses depected in diagram 28 is in a fixed proportion to the angular velocity of disc 13.

Referring now to FIGURE 2, it will be noted that the coils 11 and 12 which are shown as being surrounded by potting compound are secured to a bracket 30 of conductive material having a down-turned mounting ear 31 through which extends an aperture 32 for mounting the coil structure of the inductive pickotf assembly. The relationship of coils 11 and 12 to the mounting member 30 is best shown in FIGURE 3. Here, the potting compound is shown in section. Referring to FIGURES 2 and 3, the mounting member 30 has a forwardly extending portion 33 of conductive material acting as part of the shielding means and to which the coils 11 and 12 and the rest of the shielding means, to be presently described, are secured. In FIGURES 1 and 3, the position of the inductive disc 13 with respect to coils 11 and 12 is shown. It will be noted that the inductive disc 13 is secured in a suitable manner to a shaft 35 which is either driven at a desired frequency or is positioned in accordance with some condition which it is desired to sense.

An important feature of my invention resides in the shielding surrounding the coils 11 and 12. It will be noted that coils 11 and 12 are surrounded by cylindrical shields 40 and 41. Shield 40 is shown as having a longitudinal. slot 42 extending the full length thereof and shield 41 is shown as having a similar slot 43 extending longitudinally the full length thereof. Secured to the inner end of the annular sleeve 40 is an end shield 45 having a slot 46 extending from the upper end of the shield downwardly to a point slightly below the lower edge of a core 44 extending longitudinally through the coil 11. The width of slot 46 in the end shield 45 is relatively narrow and corresponds in width to the slot 42 in the annular shield 40.

Associated with annular sleeve 41 surrounding coil 12 is an end shield 49 having a slot 50 therein which likewise extends from the upper edge of end shield 49 to a point slightly below the lower edge of a magnetic core 51 extending through the coil 12. Likewise, the slot 50 is relatively narrow and of the same width as the slot 43 in the annular sleeve 41.

It will be noted that the end shield 49 is somewhat greater in vertical extent than the end shield 45, the end shield 45 having associated therewith a further shielding member 53 of conductive material in the form of a longitudinal strip spaced by a narrow air gap from the upper end of shield 45. The vertical extent of the end shield 45 and the conductive strip 53 is substantially the same as that of end shield 49, the upper end of end shield 49 being secured to the conductive arm 33 of coil support 30. Similarly, the conductive strip 53 is likewise secured in conductive relation to the conductive member 33. Conductive member 33 thus acts to further confine the return flux from coils 11 and 12 to the narrow zone which is controlled by the teeth 14.

Secured to the outer end of the annular shield 41) associted with coil 11 is a plate 56 of insulating material having a plurality of conductive members 57 and 58 secured thereto. The ends of the conductive coil 11 are secured to these conductive members 57 and 58 to provide the terminals for coil 11. Similarly, an insulating plate 60 having conductive members 61 and 62 secured thereto is secured to the outer end of the annular shield 41 surrounding coil 12, the opposite ends of the conductor forming coil 12 being secured to the conductive members 61 and 62 which constitute end terminals for coil 12. When assembled, both coils 11 and 12 are completely shielded except for the outer ends, the narrow gap provided for flux by the slots 42 and 43, the slots 46 and 50 and the narrow gap existing between conductive member 53 and the end shield 45. The entire unit is held in position by potting compound to produce a unit similar to that of FIGURES 2 and 3. The potted coils and shield assembly is fastened to the conductor member 33 by a suitable adhesive such as an epoxy adhesive. The outer ends of the coils may also be shielded, but since this is less effective, the outer ends of the coil assembly may remain unshielded as shown in the drawing.

While I have referred to the end shielding members 45, 49 and 53 as being made of conductive material, I have found it desirable in some cases to form the end shields 49 and the assembly of shielding members 45 and 53 of copper clad insulating material such as fiber glass with the copper etched away to form the slots 46 and 50 and the transverse slot shown between conductive strip 53 and end shield 45.

Also, while I have shown the annular shields 4t and 41 as being provided with longitudinal slots 42 and 43, it is not necessary to have the longitudinal slots extend to the outer ends of the annular shields 40 and 41. In fact, these slots may be entirely omitted when the diameter of the annular shields is sufficiently great that the transverse slot beneath the strip 53 is below the upper wall of the annular shield to permit the flux to re-enter the area around coil 11 within the annular shield 40.

Referring to the flux paths present, it will be noted that the major portion of the alternating flux produced by coil 11 can pass out from the inward end of core 44 through the slot 46 back through the transverse slot between strip 53 and the main portion of end shield.45, through the slot 42, and back to the outer end of core 44. Also, a small portion of the flux will pass through the slot 50, the inner portion of the ferro-magnetic core 51, and back through the longitudinal slot 43, the slot 50, the transverse slot below strip 53, the longitudinal slot 42, and back to the outer end of the core 44. This is the condition which exists when no tooth 14- is in alignment with the slots 46 and 50. I have found it highly desirable to provide the transverse slot between strip 53 and end shield rather than using merely an end shield like member 49. The reason for this is apparently that the flux returning through the slot in end shield member 49 is forced downwardly and confined in a vertical direction as it passes between the end shield 45 and the shielding strip 53. It is then drawn together as it enters slot 42. Thus a focusing action for the return flux is provided. If the end shield 45 is formed like shield 49, the flux would not be forced down to facilitate its passage back into slot 42, and the flux path would not be as precisely controlled by the position of tooth 14.

It will be noted that ferro-magnetic core 44 is relatively short as compared with ferro-magnetic core 51. The core 51 should be relatively large to provide as much induction coupling as possible. Core 44, on the oher hand, should be relatively small to reduce the high frequency losses.

By confining the flux to the relatively narrow paths defined by slots 42, 46, 43 and 50, the result is that the pickoif is extremely sensitive to the position of the teeth 14 of the movable member 13. It thus becomes possible to have an apparatus which is highly sensitive and yet does not require extremely small tolerances such as has been required by other inductive pickolfs. I am able to use an air gap of 0.1 to 0.12 inch while obtaining the sensitivity that would otherwise necessitate an air gap of only .025 inch in the absence of the shielding with its narrow slots. Furthermore, with this structure, I am able to use a conductive disc 13 of approximately four inches in diameter and yet still obtain pulses per revolution with high pulse rates as high as several thousand per second.

By employing the shielding construction just discussed, and by employing a Schmitt trigger or similar pulse shaping circuit it is possible to obtain with a very compact apparatus a large number of very sharp pulses. As mentioned above, it is readily possible with this apparatus to obtain 6 sharp pulses per revolution of disc 13 at disc speeds which will result in pulse rates as high as ten thousand pulses per second.

While I have shown a disc having conductive teeth which are successively brought into the air gap, it is possible to employ a disc having magnetic teeth in which the flux transmission between the coils 11 and 12 is increased rather than decreased when a tooth appears. I have found, however, that far superior results are obtained by the use of non-ferrous conductive teeth to magnetic teeth. This is due to the fact that the insertion of a conductive shield, such as formed by a tooth 14 has a much more marked effect upon the transmission of flux between the energized and pickup coils than does the insertion of a magnetic tooth. In some cases, a small magnetic inlay of ferrous material in the center area of each of the non-ferrous metal teeth has been found to further improve the control action of small control teeth.

While I have shown an oscillator 15 which only depends upon the inductive coupling between coils 11 and to initiate high frequency oscillation by filtered-out, narrow pulses occurring at a relatively low frequency, e.g. at /s of the original oscillation frequency. This high frequency oscillation will be sustained, however, only when a tooth 14 is not in the air gap. Thus one will obtain a continuous high frequency oscillation only during those portions of the rotation of disc 13 where a tooth 14 is not present in the air gap.

MODIFICATION OF FIGURE 6 In FIGURE 6, I have shown a disc 70 formed of insulating material on which there are a plurality of conductive segments 72. These can be applied by any of the techniques used in making printed circuits. The arrangement of FIGURE 6 is highly satisfactory where excessive speeds of the disc and excessive temperature variations are not encountered. If there are excessive temperature variations or excessive speed the disc of FIGURE 6 may not provide suflicient control action throughout the desired operation range.

I claim as my invention:

1. A position responsive signal generator comprising: a plurality of electromagnetic units each having a core of magnetic material and a winding thereon, said cores having aligned portions with adjacent pole faces spaced apart to provide a narrow air gap therebetween, shielding means surrounding each of said electromagnetic units, said shielding means extending peripherally around each of said magnetic units except for a single longitudinal slot in the shielding means for each electromagnetic unit extending for substantially the full length of said electromagnetic unit, said shielding means extending over the adjacent faces of said electromagnetic units except for aligned relatively small slots continuous with said longitudinal slots, and a movable member having a part thereof movable through said air gap and having thereon a plurality of relatively small portions having a different effect on flux transmission through said air gap than the rest of said member so that as said movable member assumes a position in which one of said relatively small portions extends between said aligned slots in said shielding means, the inductive coupling between said electromagnetic units is abruptly changed.

2. The position responsive apparatus of claim 1 in which said relatively small portions on said movable member are portions of conductive material to reduce the transmission of flux through said air gap.

3. The position responsive apparatus of claim 1 in which the movable member is in the form of a rotatable disc and in which said relatively small portions on said member are portions of conductive material on said member uniformly disposed radially from the center of said disc.

4. The position responsive apparatus of claim 1 in which the Winding of one of said electromagnetic units is energized from an alternating current source of power and the other electromagnetic unit is inductively coupled therewith to an extent dependent upon the position of said movable disc.

5. The position responsive apparatus of claim 4 in which the shielding means for the electromagnetic unit coupled to said source has a further slot communicating with and transverse to said longitudinal and said relatively small slot in the shielding means for that electromagnetic unit to provide a more precisely controlled flux path.

6. The position responsive apparatus of claim 1 in which the winding of one of said electromagnetic units is energized from a high frequency source of energy and in which the winding of the other electromagnetic unit is coupled in feedback relation to said source to modulate the output thereof in accordance with the position of said movable member.

7. The position responsive apparatus of claim 6 in which the modulated output of said source of energy is demodulated and employed to control a trigger circuit to generate pulses.

8. The position responsive apparatus of claim 1 in which there is a further conductive shielding member bridging the air gap to further confine the flux path between said coils.

References Cited UNITED STATES PATENTS 2,234,184 3/1941 MacLoren 340-186 2,976,495 3/1961 Unger 336-84 3,064,191 11/1962 Dever 340196 THOMAS B. HABECKER, Primary Examiner US. Cl. X.R. 336-87

Claims (1)

1. A POSITION RESPONSIVE SIGNAL GENERATOR COMPRISING: A PLURALITY OF ELECTROMAGNETIC UNITS EACH HAVING A CORE OF MAGNETIC MATERIAL AND A WINDING THEREON, SAID CORES HAVING ALIGNED PORTIONS WITH ADJACENT POLE FACES SPACED APART TO PROVIDE A NARROW AIR GAP THEREBETWEEN, SHIELDING MEANS SURROUNDING EACH OF SAID ELECTROMAGNETIC UNITS, SAID SHIELDING MEANS EXTENDING PERIPHERALLY AROUND EACH OF SAID MAGNETIC UNITS EXCEPT FOR A SINGLE LONGITUDINAL SLOT IN THE SHIELDING MEANS FOR EACH ELECTROMAGNETIC UNIT EXTENDING FOR SUBSTANTIALLY THE FULL LENGTH OF SAID ELECTROMAGNETIC UNIT, SAID SHIELDING MEANS EXTENDING OVER THE ADJACENT FACES OF SAID ELECTROMAGNETIC UNITS EXCEPT FOR ALIGNED RELATIVELY SMALL SLOTS CONDINUOUS WITH SAID LONGITUDINAL SLOTS, AND A MOVABLE MEMBER HAVING A PART THEREOF MOVABLE THROUGH SAID AIR GAP AND HAVING THEREON A PLUALITY OF RELATIVELY SMALL PORTIONS HAVING A DIFFERENT EFFECT ON FLUX TRANSMISSION THROUGH SAID GAP THAN THE REST OF SAID MEMBER SO THAT AS SAID MOVABLE MEMBER ASSUMES A POSITION IN WHICH ONE OF SAID RELATIVELY SMALL PORTIONS EXTENDS BETWEEN SAID ALIGNED SLOTS IN SAID SHIELDING MEANS, THE INDUCTIVE COUPLING BETWEEN SAID ELECTROMAGNETIC UNITS IS ABRUPTLY CHANGED.

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