US2253602A - Vibrator - Google Patents

Description

ug- 26, 1941. E. L. BARIRETT v v2,253,602 y VI BRATOR Filed Feb. -20, 1939 r n n a n O l l n 'Psiemed Aug. 26, 1941 VIBRATOR Edward L. Barrett, La Grange, Ill., assignor to Utah Radio Products Company, Chicago, Ill., a corporation of Illinois l Application February 20, 1939, Serial No. 257,362

(Cl. 20o-90) 14 Claims.

The invention relates to improvements in vibrators or vibratory motors which may be, for example, of the general type exemplified in Edward L. Barrett Patent No. 1,924,082, issued lAugust 22, 1933. Such vibrators are utilized in so-called B-battery eliminators for radio receiving sets. The eliminator as a whole serves, in general, to convert low voltage direct current, such as that derived from a conventional six volt automobile storage battery, to high potential direct current of, for example, two hundred volts, suitable for use in supplying the plate circuits of the vacuum tubes in the radio receiver. The primary function of the Vibrator utilized in the eliminator is to break up direct current from the low voltage source into a series of short rapid impulses which are caused to iiow through the primary Winding of a step-up transformen These impulses of current in the primary Winding induce a, high alternating potential in the transformer secondary winding. This high alternating potential is then rectified by some suitable means comprising either a rectifier tube, as

illustrated in said Barrett patent, or 'rectifier contacts in the vibrator itself. Vibrators which serve only to interrupt the primary current are commonly known in the art as non-synchronous vibrators while those that additionally serve to rectify the secondary potential as well are commonly known as synchronous vibrators. 'Ihe present invention, like that of said Barrett patent, is applicable to either synchronous or non-synchronous vibrators.

Some of the improvements herein contemplated are particularly suited to meet the requirements of ,-a vibrator embodying a periodically energized electromagnet which is placed entirely outside the path of a reed which it vibrates, as in the case of the vibrator shown in said Barrett patent, although others of such improvements are also applicable to vibrators of the so-called hammer type in which a movable armature swings directly toward, rather than past, the cooperating electromagnet pole piece.

One object of the present invention is to provide a vibrator o f the type including a vibratory reed which is flexed in one direction by an actuating electromagnet A andl permitted to spring back in the opposite direction by deenergization of the electromagnet. which embodies means for insuring a full return swing r exure of the reed as it springs back. even though the electromagnet be reenergized in the course of such return swing of the reed with a consequent tendency to oppose the reed's return movement.

More specifically, it is an object of the invention to provide a vibrator of the type set forth in the preceding statement of object, and inV net on the spring-back of the reed with the nt result that the reed ilexes symmetrically on each side of its mid-position while in operation.

Another and more general object of the invention is to provide a novel form of vibrator characterized particularly by its smallover-all height and which preferably does not exceed the length of a reed included in it. By making the vibrator so short it is possible to mount it on a radio receiver chassis side by side with even the very short vacuum tubes developed for automobile radio sets, without having the vibrator proiected above the tops of the tubes or other parts on the chassis. A saving in over-al1 dimensions for the set is thus realized. -A number of factors in the novel vibrator construction herein disclosed contribute to the achievement of this result'. Among these factors are? (a) disposition of the actuating electromagnet at the side of the reed rather than at the end. but with the electromagnet arranged in a novel manner so mounting means, casing and vibrator assembly in such manner as to accommodate the mounting prongspr the like within a recess dened by the vibrator assembly within [the enclosing casing itself rather than exteriorly of it.

Still another object of the invention is to prof vide a novel form vof vibrator of such character as to minimize audible vibration of various parts with respect to each other, despite the tendency of the vibrating reed to set up sympathetic or secondary .vibrations in such parts in the assembly.

'111e' invention also resides in various structural improvements in the device by Virtue of which maximum efficiency together with quietness and precision of creration are combined with minimum cost and size.

Further objects and advantages of the invention will become apparent as the following -description proceeds, taken in connection with the accompanying drawing in which:

Figure 1 is a perspective View of a vibrator embodying the invention.l

Fig. 2 is an exploded perspective view of the vibrator of Fig. 1.

Fig. 3 is an enlarged side elevation of the vibrator of Fig. l with the enclosing casing of the unit shown in vertical section.

Fig. 4 is a top view of the unit shown in Fig. 3 with a portion of the reed guard broken away and the enclosing structure shown in transverse section.

Fig. 5 is an exploded perspective View c the outer casing parts.

Fig. 5B is a fragmentary transverse secry mal view along the line SH-E in Fig. 5.

Fig. 6 is a wiring diagram of the circuit connections for the vibrator.

For purposes of illustration, the invention has been shown herein as embodied in a vibrator particularly adapted for use in an automobile radio receiving set. It will be understood, however, that this vibrator may also be used in other types o! installations. Furthermore, the particular vibrator shown is of the non-synchronous type, although it will be apparent that additional contacts may be added to complete a synchronous vibrator construction if desired. Among its principal elements the vibrator illustrated includes two pairs of main circuit controlling make and break contacts I0-II and I2--I3 (Fig. 3) that are alternatively opened and closed by a substantially freely vibratory reed I4, which is driven by an actuating electromagnet I5. In brief, the reed I4 is pulled to the left (as viewed in Fig. 3) closing contacts Ill- I I, and upon deenergization of the electromagnet springs back in the opposite direction to reopen contacts III- II and close the other set I2I3. This alternate opening and closing of the contacts proceeds at a rapid rate as the reed vibrates back and forth. e 'Ihe reed I4 is of the cantilever type and is adapted to flex substantially throughout its length, being preferably made from a nat strip of spring steel or bronze. The reed illustrated (Fig. 2) is of the same general form as that included in the vibrator which is disclosed in Edward L. Barrett et al. Patent No. 2,072,578, issued March 2, 1937. In particular, an elongated openingI is formed in the center of the reed in order to give it certain preferred flexing characteristics and also to insure unimpeded iiexure of the reed despite the multiplicity of the associated contacts. The opening I 6 increases in width adjacent the outer end of the re'ed, thereby providing substantially uniform exure to the outer end with a consequently greater time etilciency" for the vibrator. Such so-called time emclency is measured in terms of the ratio of the interval during each cycle of reed movement in which the contacts are closed to the interval in which they are open. It is desirable that the contacts should remain closed during as large a part of the time occupied by each cycle or reed movement as possible and for that reason the reed is arranged so that its free end portion beyond the contacts can swing through a substantial distance While the contacts remain closed.

Also included in the reed assembly is a rectangular armature I'I made of steel or other magnetizable material, which is spot welded or otherwise rigidly secured to the free end of the reed. This armature is disposed in driven relation with respect to the pole pieces of the electromagnet I5 as is hereinafter described in greater detail.

To minimize the height of the vibrator assembly the parts are arranged so that the length of the reed I4 constitutes the maximum longitudinal dimension of the assembly. For this pur pose the electroniagnet I5 is arranged at the side, rather than at the end of the reed as in many prior vibrators. The particular electrcmagnet shown (Figs. 2 and 3) includes a pair of op posed plate-like pole pieces I8 which may be economically fashioned as stampings from sheet metal. These pole pieces have projecting nose portions 18a arranged in closely spaced relation to the ends ot the armature II and edges of the free end of the reed I4, so that when the reed flexes to the left (as viewed in Fig. 3) it passes freely between the opposed pole pieces. A transverse core I9 joins the pole pieces I8 and has shouldered ends, the projecting portions of which pass through registering apertures in the pole pieces. These end portions of the core I9 may be peened at their edges to hold the pole pieces IB in place. The core I9 and pole pieces I8 are. of course, made of magnetizable material such.

. for example, as cold rolled steel. An energizing winding 20 is spooled on the core I9 and serves when energized to set up a field of magnetic flux, following in general the orbital path indicated by the line of arrows 2l in Fig. 4.

Provision has been made for a large amplitude of unimpeded reed swing. In particular, the surface of the Winding 20 presented to the adjacent side of the reed is contoured and located so as to match the curvature of the reed I4 when the latter swings toward the winding (see dotdash line position of reed I4 in Fig. 3). The particular winding 20 shown is generally elliptical in cross-section and, furthermore, its center1 at the core I9, is displaced longitudinally inward along the reed from the outer end of the latter. With this arrangement the magnetic ilux induced in the core I9 by the winding 20 completes its orbital path (see line of arrows 2l in Fig. 4) through the armature I1 by passing through the pole pieces I8 to their noses I8:l substantially along the line of arrows 2l in Fig. 3. In other words, the magnetic field set up by the electromagnet I5 is effectively presented to the armature I1 on the outer end of the reed I4, although thewinding and core for the electromagnet are displaced from the outer end of the reed sufficiently to prevent any obstruction to its movement.

Several factors make necessary such a free motion of the reed I4. In the first place, the interrupted current from the vibrator is fed into an electrical network having certain electrical constants calculated on the basis of a` predetermined and generally xed frequency of reed vibration. Obviously, if the reed strikes any obstruction the rhythm of its motion will be destroyed. The contacts controlled by it will bounce and chatter and severe arcing will take place between them, all leading to the early destruction of the contacts. This was a prime deficiency of the old hammer type of device in which the reed or the like moved toward, rather than past, the associated magnet pole piece. Furthermore, as was previously noted, wide amplitude of reed motion during normal operation is requisite for good time efliciency. On the other hand, the amplitude of reed motion is likely to increase during operation because of overvoltage applied to the electromagnet.

battery is usually ratedat, say, six volts, the actual voltage supplied from the battery-generator system in the automobile frequently reaches nine volts. Such a fifty per cent increase in voltage naturally greatly strengthens the pull exerted by the electromagnet on the reed 'and the reed must consequently be arranged so that it will not strike any obstruction even under such abnormal conditions. In general, the present vibrator is so constructedv as to give efficient electromagnet operation and good time efficiency while at the same time permitting of very wide variations in electromagnet voltage, all without danger of impediment tog the rhythmic motion of the reed I4..

Support of the reed I4 and electromagnet I5 in proper operative relation is accomplished by a frame 22 (Figs. 2 and 3).

In this connection it should be noted that even though an automobile storage use of a fused metal joint effectively prevents such action, however.

In its idle position the reed I4 occupies a substantially straight line position (shown in full lines in Fig. 3) and in which both of the pairs of the main make and break contacts III-II and I2-I3 are open. Of these contacts, the contacts' II and I2 are carried by resilient contact supporting fingers 26 and 21 (Fig. 2) of an inverted T-shape with the ends of the T riveted to the side portions of the reed I4. The upwardly extending legs of the fingers 26-21 are bent laterallyA out of the plane of the reed (Fig. 3). 'I'he cooperating fixed or stationary contacts III and I3 are, in turn, carried by similar contact fingers 28 and 29 preferably fashioned as stampings from resilient sheet metal, the two contact fingers 28 and 29 being substantially identical in form. All of the contact points I0. to I3 may be made of tungsten or other suitable Contact material. v

The reed I4 and the opposed side contact fingers 28 and 29 are held in assembled relation on At its lower end the frame 22 is fixed to the butt of the reed I4 while the other or upper leg of the frame is notched. as indicated at 23 (Fig. 2) to receive complemental locating lugs 24 on the pole pieces I8.

Precise determination of the clearance between the pole pieces I3 and the ends oi the armature I1 or edges of the reed I4 is of primary importance. This clearance is preferably of the order of only about 0.003 of a-n inch. \If it is too large a correspondingly large air. gap is introduced in the magnetic circuit (see line of arrowsv 2l in-Fig. 4) so that the effective pull of the electromagnet on the armature is reduced, especially at starting. On the other hand, if the clearance is s o small that either the armature Il or reed I4 touch the pole pieces at all the rhythm of reed motion is destroyed and the device rendered inoperative. To accomplish this precision of pole piece location in the present vibrator, the reed I4 is fixed in position on the frame 22 and the pole pieces I8 are located approximately in position by the lugs 24'and intertting ends of the core |9. Then thin sheet metal gauges (not shown) of proper thickness are inserted between the ends of the armature I1 and the opposed pole piece faces. Thereafter, the pole pieces I8 are` pushed in toward each other against the gauges lso that they are located in exactly the proper v position. With the pole pieces so located by the ,gauges they are then fixed in position on the frame 22 by fused metal joints, shown as lines of solder at 25 (Figs. 1 and 3).

-Minimization of noise during operation is also laccomplished by using the fused metal joints 25 between the pole pieces I8 and frame 22. Since the reed I4 vibrates at a frequency ofthe order.

ting lugs or some such arrangement is used for holding the framey and electromagnet parts together. there will be a tendency for them to vithe lower leg of the frame 22 in a so-called stack. In this stack electrical insulators or laminations l30. are interposed between the reed and the contact supporting fingers on its opposite sides (Fig. 2). Additionally, the stack includes metal spacers or laminations 3l and 32, as well as a metal end plate or spacer 33. A laterally extending lug 32aL is fashioned on the side of the spacer 32 in order to` complete an electric circuit to the reed I4 and through the latter to the contacts II and I2. Similarly, lugs'28 and 25)a are used for connecting suitable conductors to the corresponding contacts fingers 28 and 29. Registering holes 34 are formed in al1 of the stack parts, as well as in the frame 22 so that the stack may be held in position by a screw 35 inserted through them and threaded in a nut 36 provided with a lock-washer 31. 'I'he holes 34 in the intermediate parts in the stack, i. e., the reed I4, fingers 28 and 29, and spacers 3| and 32, are

ing electromagnet is periodically energized by electric current supplied under the control of the vibrating reed itself so that the latter will be maintained in vibration at a predetermined frequency, which dependslargely upon the inherent 'flexing characteristics or natural frequency of the reed. Several circuit arrangements are available for controlling the energizationV of the electromagnet in this general manner, one of these l being illustrated in Barrett Patent No. 1,924,082

referred to above and in which the electromagnet l circuit is controlled through the medium of the main interrupting contacts of the vibrator. Another arrangement is described in Edward L. Barrett Patent No. 2,120,273, issued June 14, 1938, and Vin which a separate set of magnet controlling contacts are utilized for periodically interrupting the now of current to the electromagnet. The first of these arrangements, namely, that shown in said Barrett Patent No. 1,924,082 has been utilized in the present vibrator. although it trate or chatterwith respect' to each other. The

will be apparent to those skilled in the art that if desired the vibrator herein shown may be provided with separate magnet controlling contacts like those described in said Patent No. 2,120,273.

Common to all of the electromagnet energizing arrangementsnoted above is the fact that after the reed has been pulled in one direction and the magnet deenergized, the electromagnet energizing circuit is reestablished at about the time the reed reaches its central or mid-position and remains established during all of the time that the reed is flexing on the opposite side of its midposition. For example, in the vibrator of Fig. 3, the reed I4 starts from the initial position shown in full lines. Upon energization of the electromagnet I the armature Il is pulled to the left so that the reed I4 flexes to the dot-dash line position shown. In a manner which will hereinafter appear, the electromagnet is, however, deenergized as the reed exes in this initial direction so that the reed is permitted to spring back in the opposite direction, that is, to the right. At about the time or shortly before the reed returns to its central position, however, the electromagnet energizing circuit is reestablished so that as the reed iiexes in the opposite direction (to the right of its mid-position as viewed in Fig. 3) the reenergized electromagnet I5 tends to oppose such movement. It is very desirable, however, that the flexure of the reed I4 on each side of its central position should be symmetrical so that the contact opening and closing operations of the two pairs of contacts IU--II and I2--I3 will be substantially identical. Otherwise, the wave form of the interrupted current may be impaired and the contact points themselves damaged.

In accordance with one aspect of the present invention, a novel arrangement has been provided Ior insuring symmetricalmovement of the reed I4 on each side of its central position even though a single actuating electromagnety I5 is used for driving itin the manner described above. In the illustrative construction this is accomplished by making the plate-like base of the contact supporting finger 26 substantially longer than that of the finger 21 (Fig. 3). In other words, two plate-like reenforcing members are fixed in opposed relation to opposite faces of the reed with that on the face toward which motion f takes place under the influence of electromagnet pull longer than that on the other reed face. As a result, the reed I4 flexes more readily to the right (as viewed in Fig. 3) than to the left and this diierence in flexibility compensates for the opposing effect of the reenergized electromagnet I5 upon the spring-back of the reed. As the reed I4 is flexed in one direction by the pull of the electromagnet I5 (to the left as viewed in Fig. 3), the resilient reed assembly stores up energy in excess of that stored up upon its iiexure in the opposite direction and this excess energy is expended as the reed fiexes away from the direction of pull of the electromagnet so as to effectively overcome the decelerating eiect of the electromagnet. The net result is a uniform and symmetrical motion of the reed I4 on both sides of its central position.

Minimization of the over-all height of the vibrator unit is further aided by the novel enclosing and mounting structure herein disclosed. Briefly stated, the vibrator unit is of inverted L- shape in outline (Fig. 3) and the recess or space A defined by the L is used to receive mounting receptacles 38. Mounting prongs fixed on the radio receiving set chassis (not shown) are thrust into these receptacles 3B, which are oi conventional form, to hold the unit in place on the chassis and to complete circuit connections to the sets of contacts in the vibrator. Such an arrangement is to be contrasted with that shown, for example, in Barrett et al. Patent No. 2,072,578 issued March 2, 1937, in which the vibrator unit is mounted on prongs which extend from the bottom of the unit and thereby increase its overall height. By the use of the L-shaped assembly herein shown, the outer casing may be made of substantially uniform cross-section throughout its length and of a cross-sectional area only sufficient to accommodate the vibrator itself while still leaving ample room for the prong receptacles within the coniines of the easing. In this way a substantial saving in over-all height is realized.

In the illustrative construction the outer casing, designated generally by the numeral 39 (Fig. 3), is made up ol' two sheet metal sections 4t2-4I (Fig. 5). Each of these casing sections is of U- shape. They are arranged in opposed relation as shown in Fig. 5 so that the section 4U constitutes the top and side walls of the casing while the section 4I constitutes the bottom as well as the front and back walls of the casing. To hold the casing sections 4U--4I in assembled relation, a iiange 42 is fashioned about the entire periphery of the section 40. This flange is U- shaped in cross-section (Fig. 5H) and receives the adjacent edges of the section 4I. The flanged section 40 is made of resilient sheet metal so that it can be sprung or snapped into place on the lower section 4I with the recessed ange 42 tting snugly about the edges of the inner or lower section 4I The prong receptacles 38 project through registering apertures 43 (Fig. 3) and their edges are spun over so as to hold the receptacles fixed to the bottom wall of the casing.

In order to prevent the transmission of sound from the vibrator unit, it is enclosed in suitable sound insulating material. This has been shown herein (Figs. 3 and 4) as a cup-shaped sock 44 of sponge rubber having a generally L-shaped recess therein conforming to the contour of the vibrator. The open side of the sock 44 is closed by a rectangular cover 45 also made of sponge rubber and having an inner lining or reenforcing facing y46 made of cardboard or the like. This facing 46 holds the sponge rubber cover 45 out of contact with the vibrator parts. To hold the vibrator in place within the sound insulating enclosing casing 44--45, a series of projections on the vibrator are utilized. These have 4been shown herein as a tail 41 on the frame 22 at the lower end of the vibrator and ears 48 on the pole pieces I8 at the upper end of the vibrator (Fig. 3) as Well as the projecting ends on the electromagnet core I9 at the sides of the vibrator (Fig. 4). Each of these several projections is received in a corresponding` registering recess in the sock 44 so that the vibrator is effectually held against displacement in any direction and despite any tilting or shaking of the device.

To prevent the upper end wall of the sock 44 from inadvertently contacting the reed I4 and thus destroying the rhythm of its motion the guard plate 49 is utilized (Figs. 2 and 3). This guard plate is fashioned of some nonmagnetic material, such, for example, as brass, since it bridges the pole pieces I8. It is generally rectangular in shape and is notched at 50 to engage the ears 48 on the pole pieces I8, being pressfitted between the same to hold it in place.

In the operation of the vibrator it is connected in a circuit substantially like that of Fig. 6. Current is supplied from a low voltage direct current source such as a storage battery I, and the vibrator serves to interrupt the current so that it flows in impulses through the -primary winding 52 of a suitable step-*up transformer 53, thereby inducing a high alternating potential in the transformer secondary winding 54. Upon closure of a starting switch 55, current is supplied to the electromagnet energizing winding 20 (through a circuit 55-56--20-51-58-52-5 I) thereby causing the armature I1 to be attracted and swung upward (as viewed in Fig. 6) to close the contacts IO-I I. Closure of these latter contacts completes a circuit from the battery 5I through the upper half of the transformer primary wind) ing 5 2. This circuit established through the contacts IU-II is in shunt with the circuit through the electromagnet winding 20, however, and since the electromagnet winding is of substantially higher resistance than the transformer primary winding the elec'tromagnet is effectually deenergized. As a result, the reed I4 is permitted to spring back in the opposite direction. This return motion of the reed I4 reopens the contacts Ill- II and closes the other srt of main contacts I2-I3. Closure of these latter contacts completes a circuit from the battery 5I through the other half of the transformer primary winding 52. During this return motion of the reed I4, the circuit for the electromagnet winding 20 is effectually reestablished as soon as the contacts III-I I open since the shunt is thereby removed from the electromagnet winding. Accordingly, the spring-back of the reed I4 must be sufficiently forceful to overcome the effect of the reenergized magnet and it is for this reason that the unsymmetrical reenforcing structure for the reed I4, previously described, is preferably utilized to insure a symmetrical reed motion. After complethe electromagnet Winding 20 which is substantially double that of the battery 5I. Thus, when the contacts I2-I3 close, the battery 5I is connected across the lower half of the transformer primary winding 52. This lower half of the windingis coupled in inductive relation with the upper half of the same winding so that the primary winding. constitutes in effect an autotransformer, Accordingly, a potential appears at the upper terminal of the transformer primary winding 52 which is substantially double that of the battery 5I since the ratio of turns of the whole of the winding 52 to one-half thereof is two to one. In View of this so-called double voltage effect, there is a particularly strong opposition to completion of the reed spring-back motion, and consequently the improved reed assembly shown is especially desirablea I claim as my invention:

1. A vibrator comprising, in combination, a cantilever reed supported for vibration at a periodicity generally determined by the natural frequency of the reed, said reed occupying a gen- 75 erally straight-line mid-position when idle, means including an electromagnet for exing the reed in one direction, the spring-back of the reed upon deenergization of said electromagnet serving to flexv the same in the opposite direction, and means cooperating with said reed for causing the same to flex in said opposite direction through an amplitude substantially equal to that in said one direction under the pull of said electromagnet and despite reenergization of said electromagnet during the spring-back of said reed.

2. A vibrator comprising, in combination, a cantilever reed supported for vibration at a. periodicity generally determined by the natural frequency of the reed, said reed occupying a. generally straight-line mid-position when idle, means including an electromagnet for flexing the reed in one direction, the spring-back of the reed upon deenergization of said electromagnet serving to flex the same in the opposite direction, and means affording a greater resistance to flexure of said reed in said one direction than in said opposite direction to compensate forthe effect of a reenergization of said electromagnet during the spring-back of said reed in said opposite direction. f

3. A vibrator comprising, in combination, a cantilever reed supported for vibration at a periodicity generally determined by the natural frequency of the reed, said reed occupying a generally straight-line mid-position when idle, means including an electromagnet for flexing the reed in one direction, the spring-back of the reed upon deenergization of said electromagnet serving to flex the same in the opposite direction, and means including reenforcing plates fixed in opposed relation to opposite sides of said reed adjacent the mid-portion thereof for resisting to a greater extent flexure of said reed in said one direction than in said opposite direction to compensate for the effect of a reenergization of said electromagnet during the spring-back of said reed in said opposite direction, the plate on the face of said reed toward which it flexes during movement in said one direction being substantially longer than the other of said reenforcing plates.

4. A vibrator comprising, in combination, a cantilever reed supported for vibration at a periodicity generally determined by the natural frequency of the reed, said reed occupying a generally straight-line mid-position when idle, contact means on each side of said reed adapted to be actuated thereby upon flexure of the reed in option, the plate on the face of said reed toward which it ilexes during movement in said one direction being substantially longer than other of said reenforcing plates, contact supporting fingers integral with said pla-tes and projecting laterally therefrom out of the plane of said reed. and cooperating stationary contact fingers in opposed relation to said first named contact fingers. 5. A vibrator embodying an electromagnet, and

a periodic circuit interrupting means including a vibratory cantilever reed arranged to be flexed in one direction by the field of said electromagnet to cause the reed to vibrate for not only controlling an external circuit but for also deenergizing said magnet when said reel fiexes toward said field during its vibration and for reenergizing said magnet upon fiexure of the reed in reverse direction, said vibrator being characterized by the provision of means for mechanically storing up energy during each flexure of the reed toward said field in excess of that stored up upon flexure in the opposite direction and expending the same to augment the next succeeding reed fiexure in the opposite direction, thereby insuring a full symmetrical reverse flexure of the reed in such opposite direction even against the pull of the reenergized electromagnet.

6. A vibrator comprising, in combination, a vibratory reed, two sets of make and break contacts located respectively on opposite sides of said reed, both of said sets of contacts being open when said reed is in a central idle position and being arranged for closure by said reed upon its fiexure in corresponding opposite directions, means including an electromagnet for flexing said reed laterally in one direction to close one of said sets of contacts, the spring-back of said reed upon deenergization of said electromagnet serving to flex it in the opposite direction to open said one set of contacts and to close the second set, means for utilizing closure of said first set of contacts to shunt said electromagnet and thereby deenergize the same, and means for conipensating for the retarding effect on said reed of the reenergization of said electromagnet during the spring-back thereof to insure symmetrical vibration of the reed on each side of its mid-position.

7. A vibratorl embodying a vibratory reed, and an electromagnet for flexing the reed laterally in one direction, `the spring-back of said reed upon deenergization of said electromagnet serv- ,ing to flex it in the opposite direction, and characterized by the inclusion of means for compensating for the retarding effect on said reed of a reenergization of said electromagnet during the spring-back thereof to insure symmetrical vibration of the reed on each side of its mid-position.

8. A vibrator comprising, in combination, a vibratory cantilever reed of generally rectangular outline, an armature on the free end of said reed, an actuating electromagnet cooperating with said armature and located substantially at one side of the free end thereof, said electromagnet being provided with a pole piece projecting into close' proximity to said armature but located entirely out of the path thereof, a supporting frame for said reed and said electromagnet, said frame and said electromagnet being located laterally of said reed and between the ends thereof so that the length of the reed determines the over-al1 length of the assembly, and said electromagnet including an actuating winding having its axis transverse to said reed and paralleling a side face of the reed, said electromagnet being located at one side of the reed with the surface of the winding adjacent the reed curved outwardly away from the same to match generally the curvature of the reed when the latter is flexed toward the winding, said winding being displaced a sufficient distance longitudinally inward from the free end of said reed so as to permit maximum reed flexure under even excess voltage on said winding .without obstruction of the reed by said laterally located winding.

9. A vibrator comprising, in combination, a vibratory cantilever reed, and an actuating electromagnet for said reed embodying a pair of opposed pole pieces located at opposite side edges of the free end of the reed and past the opposed faces of which the reed swings in its vibratory movement, and characterized by the provision of a transverse core joining said pole pieces and encircled by an actuating winding having its outer surface adjacent the side face of said reed curved outwardly away from the same to match generally the curvature of the reed when the latter is flexed toward the winding so as to permit maximum reed flexure under even excess voltage on said winding Without obstruction of the reed by said laterally located winding.

10. A vibrator comprising, in combination, a vibratory cantilever reed, means including a frame for supporting said reed and having a portion projecting from the fixed end thereof along one side of the reed toward the free end thereof, an actuating electromagnet for said reed located at one side thereof and embodying a pair of platelike opposed pole pieces at opposite side edges of the reed between which the free reed end swings and joined by a structurally separate transverse core, means for securing said pole pieces on the ends of said core to locate the same in approximate position with respect to said reed, and additional means for securing said pole p1eces fixedly in position on said frame tol hold the same in accurately dimensioned and closely spaced relation to said reed.

11. A vibrator comprising, in combination, a vibratory cantilever reed, means including a frame made of non-magnetic metal for supporting said reed and having an integral portion projecting from the fixed end thereof along one side of the reed toward the free end thereof, an actuating electromagnet for said reed located at one side thereof and embodying a pair of plate-like opposed pole pieces made of magnetizable metal at opposite sideI edges of the reed between which the free reed end swings and joined by a structurally separate transverse core, means for securing said pole pieces on the ends of said core to locate the same in approximate position with respect to said reed, and additional means including a fused metal joint between said metal frame and pole pieces for securing said pole pieces fixedly in position on said frame to hold the same in accurately dimensioned and closely spaced relation to said reed.

l2. In a device of the type described, the combination of a periodic circuit interrupter assembly of generally L-slhaped outline; a hollow casing enclosing said assembly, said casing being of substantially uniform cross-sectional area throughout its length; and a prong-receptacle, for mounting the'device and for completing a circuit connection to said assembly, located Within the recess in said casing defined by said L-shaped as- Sembly,

13. In a device of the type described, the combination of a frame, a vibratory reed carried by said frame, an actuating electromagnet for said reed also carried by said frame and projecting laterally from one side of said reed, and a mounting device for the unit located substantially in the space defined between the angularly disposed electromagnet and reed, whereby the maximum longitudinal dimension of the device is determined only by the length of the reed.

14. In a device of the typ'e described, the combnation of a periodic, circuit` interrupter assembly of generally inverted L-shaped outline; a hollow casing enclosing said assembly and having a rigid bottom wall, said casing being of substantially uniform cross-sectional Varea. throughout its length; anda prong-receptacle, for mounting the device and for establishing a. circuit connection to said assembly, located Within the recess in said casing defined by said inverted L-shaped assembly and fixed to said bottom wall of said Casing.

EDWARD L. BARRETT.

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