Tapping Device For Generating Periodic Mechanical Pulses

Abstract

A tapping device for attachment to apparatus to impart periodic mechanical pulses thereto comprises a base adapted to be secured to the apparatus, an electromagnet mounted on the base and comprising a ferro-magnetic core and a winding, an anvil projecting up from the base at one side of the electromagnet and an armature support projecting up from the base at the opposite slide of the electromagnet. An armature extending across the top of the electromagnet has one end disposed above the anvil and the opposite end pivotally supported by the support. A spring acts on the armature to swing it away from the electromagnet while a screw extending through a hole in the armature and screwed into the core limits such movement. An electrical circuit periodically energizes the electromagnet to attract the armature and cause the armature to strike the anvil, thereby generating a mechanical pulse which is transmitted through the anvil and base to the apparatus on which the tapping device is mounted.

Description

FIELD OF INVENTION

The present invention relates to a tapping device for attachment to apparatus to impart periodic mechanical pulses to the apparatus on which the tapping device is mounted.

BACKGROUND OF INVENTION

It has been found that the sensitivity and accuracy of certain instruments can be materially improved by tapping the instruments and thereby reducing the effect of static friction on moving parts of the instrument. This is desirable, for example in instruments used on aircraft such as altimeters, electrical meters and gauges, as well as instruments used in the laboratory and factory. It is accordingly known to provide tapping devices which are secured to the base, casing or other part of the instrument so as to apply periodic mechanical pulses to the instrument. Tapping devices also have other applications, for example in equipment for conveying or dispensing particulate solid material where the transport or flow of the material is assisted by the periodic tapping.

Tapping devices are usually electrically operated and comprise an armature actuated by an electromagnet which is periodically energized from a power source, for example an oscillator circuit. While tapping devices have been available for several years, they have had the disadvantage that in general they have been too expensive, too large and have not had a sufficiently long useful life.

SUMMARY OF INVENTION

It is accordingly an object to the present invention to provide an electromagnetic tapping device which is of simple construction, inexpensive to manufacture, of small size and light weight and which has desirable operating characteristics and a long useful life.

In accordance with the present invention, the tapping device comprises a base adapted for attachment to apparatus on which the device is to be mounted, an electromagnet on the base and comprising a ferro-magnetic core perpendicular to the base and a winding around the core, an anvil projecting from the base at one side of the electromagnet and armature supporting means projecting from the base at the opposite side of the electromagnet. An armature extends across the free end of the electromagnet with one end disposed above the anvil and the other end pivotally supported by the support means for movement of the armature toward and away from the anvil. A spring acting between the armature and the support means tends to swing the armature away from the electromagnet and the anvil, such movement being limited by an adjustabale stop. A simple electrical circuit is provided for periodically energizing the electromagnet to attract the armature and cause it to strike the anvil, thereby generating a mechanical pulse which is transmitted through the anvil and the base to the apparatus on which the tapping device is mounted. The tapping device is preferably enclosed in a suitable housing which fits down onto the base. The means for limiting movement of the armature preferably comprises a screw which extends through a hole in the armature and is screwed into a tapped hole in the core of the electromagnet. The anvil and armature support and preferably also the core of the electromagnet are integral with the base, thereby providing a simple, compact and inexpensive construction.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be more fully understood from the following description in conjunction with the accompanying drawings which show by way of example a preferred embodiment of the inventionn and in which

FIG. 1 is a side view partially in section of tapping device in accordance with the present invention.

FIG. 2 is a plan view of the device with the housing shown in section so as to show the interior.

FIG. 3 is a side view partially in section showing a different construction of the base having integral therewith the anvil, armature support and core of the electromagnet.

FIG. 4 is a plan view of the base shown in FIG. 3. FIG. 5 is a diagram of a circuit for a periodically energizing the electromagnet, and

FIG. 6 is a time-voltage curve illustrating the output of the circuit shown in FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENT

The tapping device shown by way of example in FIGS. 1 and 2 has a frame 1 comprising a base portion 2, an anvil 3 projecting upwardly at one side of the base and two parallel posts 4a and 4b projecting upwardly at the opposite side of the base. The entire frame including the base, anvil and posts is of integral construction and is conveniently made as a metal stamping of ferro-magnetic sheet material, for example annealed iron or iron alloy. To facilitate the mounting and enclosure of the tapping device, the frame 1 is mounted on a subbase 5 which is generally rectangular with laterally projecting wing portions 5a having holes or notches 5b for the reception of screws or other means for mounting the tapping device on the apparatus on which it is to be used. While the frame 1 and the subbase 5 can, if desired, be suitably secured together, for example by spot welding or adhesive, this is generally not necessary as they are held together by the assembly of the magnet on the frame and subbase as described below.

An electromagnet 6 is positioned on the base portion 2 of the frame between the anvil 3 and the posts 4a, 4b. The electromagnet comprises a generally cylindrical core 7 of ferromagnetic material, for example soft iron or iron alloy, and a coil which surrounds the core and comprises an annular plastic coil form 8 and a winding 9. The core 7 has a tubular end portion 7a which extends through a chamfered hole in the base 2 and is peened over as seen in FIG. 1 so as to secure the core to the base. A screw 10 extending through a counter sunk hole in the subbase 5 and screwed into a tapered hole in the core secures the frame with the electromagnetic assembly to the subbase 5.

An armature 11 of ferro-magnetic material extends diametrically over the end of the electromagnet and has one end portion 11a disposed above the anvil while the opposite end 11b is of reduced width and is received between upper end portions of the posts 4a and 4b. A pivot pin 12 extends through aligned holes or slots 4c in the posts and a hole the reduced end portion 11b of the armature to provide a pivotal mounting of the armature for movement toward and away from the electromagnet and the anvil. As seen in FIG. 2, the armature 11 is of generally rectangular shape except for the reduced end portion 11b and chamfered corners 11c. As illustrated in FIG. 1, the armature 11 is movable about its pivot between a lower position approximately parallel to the base as shown in solid lines and an upper portion as shown in broken lines. Means is provided for biasing the armature to its upper position. As illustrated in the drawings the biasing means comprises a tension spring 13 the upper end of which extends through a slot 11d provided in the reduced end portion of the armature outwardly of the pivot pin 12 and hooked over an end edge portion of the armature. The lower end of the spring 13 is anchored on a pin 14 which extends between aligned holes in the posts 4a, 4b below the pivot pin 12. The spring 13 thus acts on the armature outward of the pivot pin 12 so as to tend to swing the armature upwardly away from the electromagnet and the anvil.

Means is provided for adjustably limiting the upward movement of the armature. As illustrated in the drawings, movement of the armature is limited by a cylindrically headed screw 15 which extends through a central hole 11d in the armature and is screwed into a tapped hole in the core 7 of the electromagnet. The hole 11d is sufficiently large to permit free movement of the armature. Metallic impact of the armature with the head of the screw is avoided by a bumper 16 in the form of an O-ring of elastomeric material which fits on the shank of the screw below the head. The O-ring preferably has a durometer of about 35 to 45. The stop can be adjusted by screwing the screw 15 inwardly or outwardly.

When the electromagnet is energized, the armature 11 is pulled down against the action of the spring 13 so as to strike the armature 3. However, in order to avoid metal-to-metal impact between the armature and the anvil, a non-metallic bumper 17 is provided between them. The bumper is sufficiently hard to generate a strong mechanical pulse when the armature strikes the anvil while at the same time avoiding excessive noise. It is preferably formed of durable impact resistant elastomeric material having a durometer of the order of 50 to 70. In FIG. 1 the bumper 17 is shown as being in the form of a cap which fits over the upper end of the anvil. Alternatively it may be in the form of a round or rectangular pad which is adhesively secured on the lower face of the end portion 11a of the armature and has an area greater than that of the upper end of the anvil. In either event, the thickness of the bumper material between the armature and the metallic portion of the anvil is sufficient to provide suitable bumper effect and avoid rapid cutting or wear of the bumper material. By way of example it may be of a thickness of the order of .05 inch.

The tapping unit is enclosed by a cup-shaped cover 20, which is shown as being of rectangular configuration. The cover fits over the unit and is retained by a snap fit with the subbase 5. Other retaining means may if desired be provided. The cover is formed of any suitable material, for example aluminum or plastic.

An alternative form of frame is illustrated in FIGS. 3 and 4 in which corresponding parts are designated by the same reference numerals as in FIGS. 1 and 2 with the addition of 20. Instead of being formed as a sheet metal stamping as illustrated in FIGS. 1 and 2, the frame 21 shown in FIGS. 3 and 4 is conveniently made by powdered metallurgy techniques of molding and sintering. In this manner not only the anvil 23 and armature supporting posts 24a and 24b, but also the magnetic core 27 are made integral with the base 22. The base 22 is generally rectangular with laterally projecting side wings 22a provided with openings 22b to receive fastening means for securing the tapping unit to the apparatus on which it is to be used. Since the base is of shape conveniently to receive the cover, no subbase corresponding to the subbase 5 of FIGS. 1 and 2 is required. The cover fits down over the edges of the base 22 and is held by a snap or friction fit. As in the embodiment of FIGS. 1 and 2, the cover is provided at opposite sides with notched or recessed edge portions to accommodate the laterally projecting wings of the base. As other parts of the tapping unit may be the same as illustrated in FIGS. 1 and 2 and described above, they are not shown in FIGS. 3 and 4. The core 27 is provided with an axially extending tapped hole to receive the screw 15 illustrated in FIG. 1.

In FIG. 5, there is shown schematically a circuit for periodically energizing the electromagnet 6 of the tapping device. One terminal B of winding 9 of the electromagnet is connected to one side of a 115 volt, 60 cycle supply line while the other terminal A is connected to one terminal of a half wave rectifier 31 the other terminal of which is connected to the other side of the supply line 30. The rectifier 31 is preferably a suitable solid state rectifier having a low resistance in one direction and a very high resistance in the opposite direction. By reason of the half wave rectification of the alternating power supply, the voltage across the points A-B appears essentially as illustrated in FIG. 6 by the curve 32. It will be seen that the circuit supplies spaced uni-directional pulses 32a for energizing the electromagnet 6 so as to attract the armature 11 and cause it to strike the anvil 3. It will be seen that the voltage is applied to the electromagnet 6 for approximately half of each cycle of alternation of the current supplied by the source 30. However, the period of time during which the voltage energizes the electromagnet sufficiently to attract the armature against the force of the spring 13 is somewhat less. Small reverse voltage peaks 32b result from the inductance of the magnet winding. While the power supply is shown by way of example as being 115 volts, 60 cycles, single phase current, it will be understood that other frequencies and voltages may be used as desired.

The operation of the tapping unit in accordance with the invention will be readily understood from the foregoing description. The unit is secured to the apparatus on which it is to be used by screws or other fastening means received in the notches 2b or 22b of the base so that the unit is held firmly on the apparatus in such manner as to transmit mechanical pulses to it. The terminals B and C of the circuit as illustrated in FIG. 5 are then connected to a suitable source of single phase alternating current. By reason of the half wave rectifier 31, the alternating current is converted into essentially unidirectional pulsating current with spaced pulses which intermittently energize the electromagnet 6 to attract the armature 11 against the force of the spring 13, thereby causing it to strike the anvil 3 and generate a mechanical pulse which is transmitted through the anvil and the base to the apparatus on which the unit is mounted. Betwen successive energizing pulses, the magnet 6 is deenergized so as to release the armature 11, whereupon it is returned to its rest position by the spring 13. By thus energizing the electromagnet periodically to cause the armature to strike the anvil there is generated a series of uniformly spaced mechanical pulses which are transmitted to the apparatus on which the tapping device is mounted.

In accordance with the present invention there is thus provided a tapping unit which is highly efficient and yet small, compacted and inexpensive. By way of example, the overall demensions of the device with the cover in place (except for the attaching wings) may be approximately 1 inch long, 0.6 inch wide, and 0.6 inch high. However, it will be understood that the size of the device can be varied according to the apparatus on which it is to be used and that the invention is in no way limited to details of the embodiment illustrated in the drawings and herein particularly described.

Claims

1. A tapping device to be mounted on apparatus for imparting periodic mechanical pulses thereto, comprising a base for attachment to said apparatus, and electromagnet on said base and comprising a ferromagnetic core perpendicular to the base and a winding around said core, an anvil projecting from said base at one side of said electromagnet and parallel to said core, armature supporting means projecting from said base at the opposite side of said electromagnet from said anvil, an armature extending across said electromagnet from said supporting means to said anvil, said anvil having a first end disposed above said anvil and a second end pivotally supported by said supporting means for movement of said armature between a first position in which said first end of the armature engages said anvil and a second position in which said first end of said armature is spaced from said anvil, means biasing said armature in a direction from said first position to said second position, means limiting movement of said armature in said direction, and circuit means for periodically energizing said electromagnet at regular fractional-second intervals to attract said armature and thereby cause said first end of said armature to strike said anvil to generate a mechanical pulse which is transmitted through said base to apparatus on which said tapping device is mounted.

2. A tapping device according to claim 1, in which said means limiting movement of the armature comprises a screw extending through a hole in the armature and screwed adjustably in a central tapped hole in said core,

3. A tapping device according to claim 2, further comprises a ring of elastomeric material surrounding said screw below the head and engageable by said armature to prevent metal-to-metal contact between said armature

4. A tapping device according to claim 1, in which said anvil and said

5. A tapping device according to claim 4, in which said base, anvil and

6. A tapping device according to claim 1, in which said base, anvil armature supporting means and core comprise a single sintered powdered

7. A tapping device according to claim 1, in which said armature supporting means comprises two posts projecting up from said base, said armature having said second end portion disposed between said posts and pivotally supported by a pin extending through aligned openings in said posts and

8. A tapping device according to claim 7, in which said biasing means comprises a tension spring acting between said second end portion of said

9. A tapping device according to claim 1, in which a pad of elastomeric material between said armature and said anvil prevents metal-to-metal

10. A tapping device according to claim 9, in which said pad comprises a cap of elastomeric material fitting on the upper end of said anvil.