US3507339A

US3507339A - Electromagnetically operated tapping device

Info

Publication number: US3507339A
Application number: US756057A
Authority: US
Inventors: John F De Mayo
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-12-23
Filing date: 1968-08-28
Publication date: 1970-04-21
Anticipated expiration: 1987-04-21

Description

April 21, 1970 J. F. DE MAYO 3,507,339

TROMAGNETICALLY OPERATED TAPPING DEVICE ELEC 3 Sheets-Sheet 1 Filed Aug. 28, 1968 ELECTRIC PULSE GENERATOR c R c E L E Fllm PULSE GENERATOR J. F. DE MAYO 3,507,339

ELECTROMAGNETICALLY OPERATED TAPPING DEVICE 3 Sheets-Sheet 2 ""lii FIG. 6

April 21, 1910 Filed Aug. 28, 1968 5 G l N w R I m a a A ril 21', 1910 J. F. DE MAYO 3,507,339

ELECTROMAGNET I CALLY OPERATED TAPP ING DEVICE Filed Aug. 28, 1968 3 Sheets-Sheet s United States Patent Ofiice 3,507,339 Patented Apr. 21, 1970 3,507,339 ELECTROMAGNETICALLY OPERATED TAPPING DEVICE John F. De Mayo, 21 MacArthur Ave., Plainview, N.Y. 11803 Continuation-impart of application Ser. No. 515,828, Dec. 23, 1965. This application Aug. 28, 1968, Ser. No. 756,057

Int. Cl. B25d 13/00; G01] 7/20; B64d 43/00 US. Cl. 173100 10 Claims ABSTRACT OF THE DISCLOSURE Means for cyclically tapping apparatus such as an instrument having a movable element to relieve static friction and thereby keep the movable element from sticking comprises a base which is secured to the apparatus, a pad on the base, a movable hammer arranged to strike the pad and an electromagnet which is periodically energized to cause the hammer to strike the pad and thereby impart periodic mechanical impulses to the base and to the apparatus to which it is secured.

This application is a continuation-in-part of my application Ser. No. 515,828 filed Dec. 23, 1965, and now abandonded.

This invention relates to an apparatus for tapping an instrument or other apparatus having a movable element, to prevent the movable element from sticking.

The apparatus having the movable element may be, for example, an indicator apparatus having a movable indieating element or a hydraulic or penumatic valve having movable means for closing, opening or adjusting to an intermediate position of the valve. The term tapping an apparatus as used herein does not refer only to direct tapping of the apparatus having the movable element but refers to any tapping effected by the apparatus of the invention provided that the mechanical impulses resulting from the tapping are transmitted to the apparatus having the movable element.

In the further discussion of the invention which follows, the sticking of the indicating element of an indicator apparatus will be referred to. However, it is to be understood that the invention is applicable to any apparatus having a movable element in which the movable element tends to stick.

The indicating element, such as a needle, of an indicator apparatus, such as an airplane altimeter, frequently tends to stick. The cause of the sticking is frequently static friction or static electricity; however, in describing the invention the cause of the sticking is not important. It is relevant to know only that the sticking of the indicating element can be avoided or remedied by subjecting the indicator apparatus to tapping. The tapping may be directly upon the indicator apparatus itself or it may be upon the instrument panel or other means mounting the indicator apparatus.

The sticking of an altimeter is referred to above because the consequences of the sticking of the indicator element in this indicator apparatus can be particularly serious. Thus, if the altimeter of an airplane incorrectly indicates the altitude because of sticking of the indicating element a crash may result. Especially in the case of jet powered airplanes this can be a serious problem, for in such airplanes there is relatively little engine vibration to free a stuck indicating element or to prevent the sticking of the indicating element. However, it will be appreciated that the invention is not limited in its applicability to airplane altimeters only.

According to the invention there is provided an apparatus for tapping an apparatus having a movable element to prevent the movable element from sticking, the essential elements of the apparatus for tapping being an electromagnet, an armature pivotally mounted with at least a portion within the magnetic field defined by the electromagnet when the electromagnet is energized, and a pad disposed in the path of movement defined by the armature when the electromagnet is energized and the armature is attracted by the magnetic field and moves toward the electromagnet. In its movement toward the electromagnet the armature taps the pad. The mechanical impulses of this tapping may be transmitted to the apparatus having the movable element; for example, in this instance of an indicator apparatus, this may be accomplished by having mounted the tapping apparatus on the back of the indicator apparatus or by having mounted the tapping apparatus on an instrument panel on which the indicator apparatus is mounted or by any equivalent arrangement providing for the transmission of the impulses to the indicator apparatus.

The coil of the electromagnet may be connected to electrical impulse generating means. The electrical impulses periodically energize the electromagnet, causing the electromagnet to attract the armature, and the armature in its movement toward the electromagnet strikes the above referred to pad thereby etfecting a single tap.

By providing for return of the armature to its initial or rest position when the energization of the electromagnet is discontinued or interrupted, i.e., when the electromagnet is deenergized, periodic tapping, corresponding in frequency to the frequency of the electrical energizing impulses, is attained. The duration and the frequency of the electrical energizing impulses may be selected to best overcome the sticking problem of the particular indicator apparatus for the particular conditions :of use of the indicator apparatus. For example, where the apparatus having a movable element is an airplane altimeter having movable indicator needle, effective preventing of sticking of the indicator needle may be obtained with apparatus according to the invention provided with electrical energizing impulses each of about 15 to 20 milliseconds in duration with deenergization intervals of about 30 milliseconds in duration. However, the duration and spacing of the energizing impulses may be varied with operating conditions.

Return of the armature to its rest position when the electromagnet is deenergized may be eifected by gravity if the tapping apparatus is mounted in its operating position so that the rest position of the armature is lower than the position of the armature when the armature taps the pad. However, more generally, return of the armature is effected by the provision of spring means biasing the armature away from the electromagnet. When the electromagnet is energized, it attracts the armature strongly enough to overcome the opposition of the spring means, however, thereby tensioning the spring means. When the electromagnet is deenergized the tensioned spring means moves the armature back to its rest position. The rate at which the force of the spring increases as the armature is moved by the electromagnet is selected so as to assure that the armature does not stick, for example by reason of residual magnetism, while minimum resistance is offered by the spring atthe beginning of the movement.

A member may be provided to limit the extent of movement of the armature away from the electromagnet when the electromagnet is deenergized. This member is disposed in the path of movement of the armature away from the electromagnet so that it blocks movement of the armature away from the electromagnet so that the armature may move only a certain predetermined distance from the armature. Thus, for example, in a tapping apparatus according to the invention for an airplane altimeter, the member which limits upward movement of the armature may be positioned so that the armature cannot move more than on the order of a tenth of an inch from the electromagnet; this numerical value is only exemplary. The rest position of the armature will not necessarily be against the member which limits upward movement of the armature provided the armature prevents excessive springing back of the armature. Means may be provided for adjusting the distance between the member and the electromagnet so that the maximum movement of the armature away from the electromagnet may be set to any desired magnitude.

Means may be provided for adjusting the distance between the part of the armature which strikes the pad and the pad. Thus, for example, it may be provided that the armature include a hammer member which taps the pad and the hammer member may be provided with means to extend it toward or withdraw it from the pad so that depending upon the setting of the hammer the distance through which the armature will move from its rest position to a position at which the hammer member taps the pad will be determined.

The invention will now be further described by reference to the drawings, in which:

FIG. 1 is a plan view of a first embodiment of an apparatus according to the invention;

FIG. 2 is a sectional view of the embodiment of FIG. 1 taken along section line 2-2;

FIG. 3 is a sectional view of the embodiment of FIG. 1 taken along section line 33;

FIG. 4 is an elevation view of a second embodiment of an apparatus according to the invention.

FIG. 5 is a plan of a further embodiment of the invention.

FIG. 6 is a sectional view taken along the section line 6-6 in FIG. 5.

FIGS. 7 and 8 are sectional views taken along the line 88 in FIG. 5 and illustrating steps in initially adjusting the apparatus.

FIG. 9 is a side view of another embodiment of the invention.

FIG. 10 is a plan view of the embodiment shown in FIG. 9, and

FIG. 11 is a circuit diagram of a circuit for supplying intermittent pulses for energizing the magnet.

In the embodiment illustrated in FIGS. 1 to 3, an armature 10 is pivotally mounted on a support for movement relative to an electromagnet 11. The support 15 is mounted on a base plate 21. The electromagnet 11 is mounted on the same base plate 21 by means of a stud 22. The base plate 21 is provided with slots to receive suitable screws or bolts 21a for securing it to the instrument or other apparatus on which the tapping device of the present invention is mounted. A portion of the casing of such apparatus is illustrated in FIG. 2 and designated A.

The pivotal mounting of the armature 10 on the support 15 is effected by means of a pivot 14. A spring 13 is attached at one end to a pin 23 mounted in the support 15 and at its other end to an extending end portion of the armature 10.

The magnetic core 18 is mounted in the hollow center of a bobbin 20. Around the bobbin 20 is wound a coil 19 of electrically conductive wire. The coil is connected to electric impulse generating means G (FIG. 1).

A limit member 16 for limiting the upward movement of the armature is mounted with a tongue 26 on an adjustment screw 27 by means of a pin 24 passing through a hole in each of the limit member 16 and the tongue 26, the pin 24 being joined at one end to the adjustment screw 27 and at its other end mounting a collar 25. The adjustment screw 27 is mounted in a tapped hole in a support 28 and the support 28 is mounted in the base plate 21. The support 28 is provided with a slot or channel 29 in which the tongue 26 fits. The tongue 26 is held in place in the slot 29 by means of a retaining ring 30 which is set in a groove about the circumference of the support 28.

As shown in FIGS. 1 to 3, the armature 10 includes a support 34 mounting a hammer member 17. The hammer member has a head 31 and a threaded shaft 32. The threaded shaft 32 fits into a tapped hole in the support 34. The end of the shaft 32 opposite the head 31 is provided with a slot 33 to accommodate a screwdriver. The pad 12 is disposed below the hammer member head 31 in a recess in the base plate 21.

When the electromagnet 11 is energized by means of an electrical impulse frorrf the electrical impulse generating means G, the armature 10, which initially is in its rest position as illustrated in the drawings, is attracted by the electromagnet, since at least a portion of the armature when in its rest position is disposed within the magnetic field of the energized electromagnet. The armature 10 therefore moves about the pivot 14 toward the electromagnet, its movement tensioning the spring 13, until the hammer member carried by the armature taps against the pad 12 on the base plate 21.

The electromagnet 11 is then deenergized by discontinuing or interrupting the energizing impulse from the electrical impulse generating means. The output of the electrical impulse generating means may be, on a plot of current versus time, an approximately square wave having periodic minima, which may be zero or essentially zero, the occurrence of these minima being referred to as discontinuing or interrupting the energizing impulse; in other words, at the least the current decreases to a level at which it does not cause the electromagnet 11 to produce a magnetic field strong enough to hold the armature 10. When the electromagnet 11 is deenergized, the tension in the spring 13 draws the armature 10 away from the electromagnet 11. The armature 10 may, due to momentum, continue past its rest position. However, the limit member 16 will block movement of the armature 10 excessively past its rest position.

The distance between the limit member 16 and the electromagnet 11 may be adjusted by means of the adjustment screw 27, thereby to adjust the extent, if any, the armature is allowed to move past its rest position.

The distance between the rest position of the. hammer member 31 (FIGS. 1 to 3) and the pad 12 may be adjusted by using a screwdriver in the slot 33 of the shaft 32, the threaded shaft 32 of the hammer member 31 thereby functioning in cooperation with the tapped hole in the support 34 as, in effect, an adjustment screw which is part of the hammer member 31 itself.

The purpose of the pad is to absorb any excessive mechanical impulses or shock which might be produced if the armature were to tap a hard metallic or plastic surface. Accordingly, the material for the pad should be less hard than materials such as iron or steel or hard plastics such as nylon. However, it is not intended that the pad function as a cushion in the sense of being highly resilient; accordingly, the material of which the pad is made need not be particularly resilient. Typical of the materials of which the pad may be made are hard cured rubbers including synthetic rubbers. An example of a suitable material for the pad is a silicone rubber cured with dibutyl tin dilaurate and having a durometer hardness on the Shore A scale of about 40 to 70; such silicone rubbers are well known and are described for example in Technical Data Book S3C of the General Electric Company. Another suitable material is Buna N having a hardness in the same range. The pad may be quite thin, and thus may be in the form of a film or thin sheet or disc material. In the embodiments shown in the drawings the pad has a thickness which is about .010" to .020" and preferably about .015". The pad is secured, for example by adhesive, in a recess in the base with its upper face approximately flush with the adjacent surface of the base. However, the upper face of the pad may project slightly, for example about 0.00 above the base surface.

Another embodiment of the invention is illustrated in FIG. 4 in which like parts are designated by the same reference numerals as in FIGS. 1 to 3 and corresponding but somewhat different parts are designated by the reference numerals with a prime added. The electromagnet 11 is mounted on the base plate 21 by means of a mounting screw 22' which extends through a washer 22a and is screwed into a tapped hole in the pole piece 18' of the electromagnet. An armature 10' is pivotally mounted at one end on an upstanding support 15 by a hinge connection 14. At the other end of the armature 10, there is provided a hammer portion 17' adapted to strike a pad 12' which is received in a recess in the upper end of a cylindrical upstanding portion 21b on the base 21. The parts are so proportioned that the armature 10' will not strike the pole piece 18' of the electromagnet before the hammer portion 17' strikes the pad 12. However, to avoid any possibility of metal-to-metal contact between the armature and the electromagnet, there may be provided on the top of the latter a layer 18a of non-metallic material, for example, a plastic or rubber composition.

The embodiment illustrated in FIG. 4 operates in the same manner as that of FIGS. 1 to 3. When the electromagnet 11 is periodically energized by a pulse generator G, the armature 10 is attracted toward the electromagnet, causing the hammer portion 17' to strike the pad 12 provided on the upwardly projecting portion 21b of the base plate 21. The impulse resulting from the impact of the hammer portion 17' with the pad 12' is transmitted through the base plate to the instrument or other apparatus on which the base plate is secured. In the intervals between energization of the electromagnet, the armature 10' is moved away from the electromagnet by the spring 13. As in the first embodiment, outward movement of the armature 10' is limited by the limit member 16.

In a further embodiment illustrated in FIGS. to 8, an electromagnet 40 comprising an annular coil 41 wound on plastic bobbin 41a and surrounding a pole piece 42 which is secured to a base plate 43 by a stud 42a on the pole piece extending through an opening provided in the base plate. A flange 4212 on the pole piece secures the coil in lace. An armature 44 is pivotally mounted on a support member 45 projecting upwardly from the base plate by means of a pin 46 which projects laterally from opposite sides of the armature and is received in notches provided in the upper end of the support 45. The width of the armature is approximately equal to the diameter of the pole piece 42. A hammer portion 47 provided on the opposite end of the armature '44 is adapted to strike a pad secured in a recess in the upper face of the base plate 43. A spring 50 acting between a projecting end portion of the armature 44 and a pin 51 on the support 45 acts to move the armature away from the electromagnet when the latter is not energized. Upward movement of the armature is limited by engagement with the end of a screw 52 which is screwed through a tapped hole in a U-shaped bracket 53 which extends over the electromagnet and armature as seen in FIG. 6 and has opposite end portions secured to the base plate 43, for example, by screws 54.

When the tapping device is initially assembled, the screw 52 has a head portion 52a by which the screw can be rotated to adjust it upwardly or downwardly relative to the supporting bracket 53. Adjustment of the screw 52 controls the length of the stroke of the hammer 42 and thereby the force of the impact with which it strikes the pad 48 on the base plate 43. When the screw 52 has been adjusted to provide the desired impact force, it is cut off as seen in FIGS. 6 and 8 and soldered in place. A nonmetallic layer 55 formed for example of rubber or plastic composition is provided on the upper face of the armature 44 to avoid metal-to-metal contact between the armature and the screw 52.

The operation of the embodiment shown in FIGS. 5 to 8 is the same as that described with reference to FIGS. 1 to 3. When the electromagnet 40 is energized by the pulse generator G, the armature 44 is attracted toward the electro-magnet, causing the hammer 47 to strike the pad 48 on the base plate 43 and thereby transmit a pulse to the apparatus on which the device is mounted. The rate of the spring is selected so as to offer only small resistance as the armature begins its movement toward the electro-magnet but to exert sufficient force on the armature at the end of the stroke to avoid the possibility of the armature sticking by reason, for example, of residual magnetism in the core 42. For example, the spring may exert a force of 2 to 4 grams on the armature when in its upper position and 25 grams to the end of the downward stroke.

In order to provide an efiicient and effective magnetic circuit, the pole piece 42, base plate 43, upright 45 and armature 44 are of high permeability magnetic material. The bracket 53 and screw 52 are preferably of nonmagnet material, for example, brass. The hammer 47 may be formed of non-magnetic material such as brass or alternatively may be of magnetic material such as iron so as to form a part of the magnetic circuit.

In FIGS. 9 and 10, there is shown a further embodiment of the invention in which an electro-magnet having a core piece surrounded by an annular coil is mounted on a base plate 63 having

holes

63a and 63b to receive screws or bolts for securing it to an instrument or other apparatus on which the device is mounted. An armature 64 is pivotally mounted near one end on a support 65 projecting from the base. The pivot comprises a pin 66 extending through and projecting laterally from the armature and having portions received in notches at the upper end of the support 65. A hammer 67 carried by the opposite end of the armature 64 is adapted to strike a pad 68 secured in a recess in the upper surface of the base plate 63. Return movement of the armature is provided by a spring 70 extending between a stud 71 on the support 65 and a projecting end portion of the armature 64. Upward movement of the armature is limited by a stud 72 screwed through a threaded opening in a U- shaped bracket 73 which extends up over the electromagnet and the armature and has its lower ends secured to opposite sides of the base plate. A layer of rubber or plastic material 75 on the upper face of the armature 64 prevents metal-to-metal contact between the armature and the lower end of the stud 72. The operation of the embodiment shown in FIGS. 9 and 10 is the same as has already been described.

The apparatus in accordance with the present invention differs from a vibrator in that the armature 10 carrying the hammer 17 (with reference to FIGS. 1 to 3) is not continuously in motion but is actuated at selected intervals spaced by rest periods in which the armature is in its upper or relaxed position. Accordingly, the pulse generator G supplies current pulses to the coil 19 of the electromagnet 11 at correspondingly spaced intervals,

the electromagnet being deenergized during the rest period. The period during which the electromagnet is energized should not exceed the period during which it is deenergized and should preferably be less. Preferably the electro-magnet is energized for a period sufficient to cause the hammer to strike the pad and is deenergized the rest of the time. For example, if the electromagnet is to be energized 20 times a second, the period during which the electromagnet is energized is preferably 15 to 20 milliseconds and the period during which the electromagnet is deenergized is 35 to 30 milliseconds. The electromagnet is preferably energized by pulsating direct current with an approximately square wave form and a voltage which is preferably of the order of 24 to 32 volts.

An example of a suitable electric pulse generator is illustrated in FIG. 11. The circuit shown is a DC multivibrator comprising two transistors and 81. The bases of the transistors are connected to a positive voltage line 82 through

resistors

83 and 84 respectively. The emitters of the transistors are connected to a negative coltage line 85 through

diodes

86 and 87 respectively. The collector of transistor 80 is connected to the positive line 82 through a resistance 88 and is also connected through a capacitor 89 to the base of the transistor 81. The collector of transistor 81 is connected through a capacitor 90 to the base of the transistor 80 and is also connected through the coil of the electromagnet (here designated coil 19) to the poistive line 82. A diode 91 protects the circuit against any back EMF of the coil. The circuit is connected to a power supply through a voltage dropping resistance 92 and a diode 93. The diode 93 acts as a rectifier so that the circuit can be operated from an alternating current power supply as well as a direct current. When the circuit is operated from a DC power supply, the diode 93 protects it against accidental reversal of polarity.

Capacitors

94 and 95 are connected across the line as decoupling filters.

With the circuit shown, the

transistors

80 and 81 are alternately conductive. When the transistor 81 is conductive, current is supplied to the electromagnet coil 19 to energize the coil. When transistor 80 is conductive, the coil is deenergized. The periods during which the respective transistors are conductive is determined by suitable selection of the RC characteristics of the circuit. Although the electromagnet coil has been designated by the reference numeral 19 in FIG. 11, it will be understood that the circuit shown can be used with any of the devices illustrated.

While for convenience of description, reference has been made to upward and downward movement and direction, it will be understood that the apparatus in accordance with the invention can be mounted and operated in any desired position. The modification shown in FIG. 4 is particularly suitable for mounting in an inverted position from that shown in the drawings since the hammer 17' is of less mass and hence less affected by the force of gravity. Insofar as they are compatible, the various characteristics and features of the several embodiments illustrated in the drawings are mutually interchangeable. Moreover, other variations can be made in details of construction, the illustrated embodiments being shown merely by way of example.

I What I claim is:

1. Means for cyclically tapping an apparatus having a movable element to relieve static friction and thereby prevent the movable element from sticking, comprising a base having means for securing said base to said apparatus', non-metallic impact pad means on said base; hammer means for striking said pad means; means on said base for pivotally mounting said hammer means for free movement into and out of engagement with said pad means; means for actuating said hammer means comprising an electromagnet mounted on said base and having a coil and a pole piece, an armature comprises in said hammer means and attracted to said pole piece when said electromagnet is energized and means biasing said armature to move away from said pole piece when the electromagnet is deenergized; means limiting movement of said armature away from said pole piece, and pulse generator means for periodically energizing said electromagnet at regular intervals to actuate said hammer means to strike said pad means periodically and thereby transmit periodical mechanical impulses tosaid base and from said base to said apparatus to relieve static friction and thereby free said movable element.

2. Tapping means according to claim 1, in which said limiting means comprises means for varying the stroke of said hammer means and thereby varying the force of impact of said hammer means on said paid means.

3. Tapping means according to claim 1, in which nonmetallic resilient impact damping means is disposed between said armature and said limiting means to avoid a 8 metal-to-metal impact between said armature and said limiting means.

4. Tapping means according to claim 1, in which base, mounting means, armature and pole piece are of magnetic material having high permeability and said limiting means comprises non-magnetic material.

5. Tapping means according to claim 1, in which said armature is pivotally mounted intermediate its ends, and in which said hammer means comprises a hammer carried by one end portion of the armature and said biasing means comprises a tension spring attached to an opposite end portion of the armature.

6. Tapping means according to claim 1, in which the duration of said pulses is less than that of the intervals between successive pulses.

7. Tapping means according to claim 1, in which said armature comprises a bar of magnetic material disposed approximately parallel to said base, pivotally supported at one end by said mounting means, extending across said pole piece and having a free end extending beyond said electromagnet, and in which said hammer means comprises said armature and a hammer portion carried by the free end of said armature and extending toward said base.

8. Tapping means according to claim 7, in which said pad means comprises a layer of synthetic material secured on a portion of the base in position to be struck by said hammer portion.

9. Tapping means according to claim 8, in which said portion of the base is recessed and a free surface of said synthetic material is approximately flush with the adjacent surface of said base.

10. Means for cyclically tapping an apparatus having .a movable element to relieve static friction and thereby prevent the movable element from sticking, comprising a base having means for securing the base to said apparatus; non-metallic pad means on said base; hammer means for striking said pad means comprising an armature pivotally mounted on said base and a hammer carried by said armature in position to strike said pad means; an electromagnet mounted on said base in position to attract said'armature when said elcctromagnet is energized to actuate said hammer to strike said pad means, means biasing said armature to move said hammer away from said pad means; means limiting movement of said hammer away from said pad means including non-metallic impact damping means engageable by said hammer means; and pulse generator means for periodically energizing said electromagnetic means at regular intervals to actuate said hammer means periodically to strike said pad means and thereby transmit periodical mechanical impulses to said base and to said apparatus on which said base is secured to relieve static friction and thereby free said movable element.

References Cited 7 UNITED STATES PATENTS 2,396,383

ERNEST R. PURSER, Primary Examiner U.S. C1. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 507 339 Dated April 21 1970 Inventor) John F. De Mayo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 53, delete "comprises" and insert -comprised-.

Signed and sealed this 10th day of December 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents I i g FORM po'wso (1069) USCOMM-DC eons-Pen