US2795672A - Frequency selective vibrating reed relay - Google Patents

Description

June 11, 1957 AQH. MAclszEwsKl EljAL FREQUENCY SELECTIVE VIBEATING REED RELAY Filed Aug. 1o. 195s 2 Shets-Sheet 1 af' farce June 11, 1957 A. H. MAclszEwsKl E-rAL 2,795,672

FREQUENCY sELEcTrvE VIERATING REED RELAY A:Uigritecl 'States Patent O FREQUENCY SELECTIVE VIBRATING REED RELAY Arthur H. Maciszewski and Richard Goldstein, River Forest, Ill., assignors to A. R. F. Products, Inc., River Forest, Ill., a corporation of Illinois Application August 10, 1953, Serial No. 373,346

' 12 claims. (cl. zoo- 91) This invention is concerned generally with a resonant or frequency selective vibrating reed relay, and more particularly with a damped relay of this character.

Resonant or frequency selective vibrating reed relays often are used in remote control apparatus, such as garage door openers, for controlling the operation of an apparatus or device in accordance with a signal generated at a remote location.

Resonant or frequency selective vibrating reed relays utilize a vibrating reed usually of metallic construction, having a predetermined fixed frequency of vibration. When such a reed is excited, generally magnetically, by a wave corresponding in frequency to the natural period of vibration of the reed, the reed vibrates. Suitable contacts are arranged for intermittent closing by the vibrating reed, and the intermittently closed contacts are utilized to control a further apparatus or device such as a conventional relay or a vacuum tube. Simple, undamped, resonant or frequency selective vibrating relays are subject to certain drawbacks.

In operating garage door openers and other types of apparatus, resonant relays are remotely controlled by radiovor magnetic waves. Random impulses due to at mospheric discharges or man-made electrical noise frequently cause false tripping of such relays. The transient response of such relays is generally poor. Furthermore, the actuating wave has to be held to very close limits in order properly to actuate a simple resonant relay. This calls for relatively complicated and expensive signaling devices.

lt is an object of this invention to provide a resonant relay or frequency selective vibrating reed relay which is relatively insensitive to random impulses.

Another object of this invention is to provide a resonant relay having superior transient response.

A further object of this invention is to provide a resonant relay of increased band width, i. e. a resonant relay that is responsive to signals varying from the selected frequency by a greater percentage than has been possible heretofore.

This invention contemplates achieving ythe above and other objects by providing an improved damped resonant relay.

Damping of various devices for diverse purposes has been accomplished heretofore. Viscous damping frequently is resorted to. In this type of damping the moving member is immersed in a fluid, usually oil. The retarding Vforce of the fluid isproportional to the velocity of the moving body and linear mechanical resistance is established. Linear resistance is necessary for proper control of the mechanical application factor or Q of a vibrating system. Energy is imparted to the lluid with each cycle of vibration, and appears as heat generated by the internal frictional forces of the uid. This change in temperature varies lthe viscosity of the iluid if the vibrations are continued for `any substantial length of time, and leads to wide variations in performance. This renders viscous 'damping highly vundesirable y for a rice resonant reed, and the necessary physical structure for viscous damping is obviously impractical for a resonant reed relay.

Vibration damping also is often achieved by means of a dash-pot consisting essentially of a cylinder and piston, one of which is flined and the other of which is attached to the moving body. One or the other of the cylinder and piston is usually provided with an opening, which may be adjustable, to allow air or some other gas to escape at a controlled rate. The damping due to air passage to and from the cylinder is proportional to `velocity and produces a linear mechanical resistance.

Dash-pots lack uniformity in operation unless they are held to extremely close and expensive manufacturing tolerances. Furthermore, there are rather great frictional forces associated with the piston and cylinder, and these frictional forces generally are larger than the damping force required with a resonant relay. Such frictional forces do not represent linear mechanical resistance and would cause extremely erratic performance of a resonant relay.

The most commonly used means or method employed in vibration damping devices lies in the use of rubber. As rubber is compressed and allowed to expand, it goes through a mechanical hysteresis curve, the area of which represents the energy per cycle required to travel the curve. The degree of damping cannot be controlled very closely with rubber, and such vibration dampers are used whenever the actual degree of damping is not Very important as long as suflicient damping is achieved. The degree of damping cannot be controlled anywhere near closely enough for use in a resonant relay. Additionally, the characteristics of rubber change with temperature (and the energy required to travel the hysteresis curve is converted into heat in the rubber) and rubber deteriorates with time to such an extent as to make the use of rubber inacceptable in a precision device.

It is an object of this invention to provide a new or improved damped resonant relay. More specifically, it is an object of this invention to provide an electromagnetically damped resonant relay.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

Fig. l is a side view of a resonant or frequency selective vibrating reed relay constructed in accordance with the principles of the invention;

Fig. 2 is a bottom plan View of the relay;

Fig. 3 is a schematic diagram illustrating an application of the relay;

Fig. 4 is a bottom View illustrating the magnetic damping action;

Fig. 5 is a side View illustrating the same;

Fig. 6 illustrates the D. C. transient characteristics of an undamped relay;

Fig. 7 illustrates the D. C. transient characteristics of the damped relay disclosed herein;

Fig. 8 illustrates the A. C. transient characteristics of an undamped relay;

Fig. 9 illustrates the A. C. transient characteristics of the damped relay disclosed herein;

Fig. 10 illustrates the Q or mechanical amplification factor of an undamped resonant relay and of the damped relay disclosed herein; and

Fig. 11 is a sectional view through the magnet core and winding showing the means for preventing operation at harmonic frequencies or higher mode resonances.

Referring now in greater particularity to the drawings, wherein like numerals are used to identify similar parts throughout, there may be seen in Figs. 1 and 2 a relay 20 Aconstructed in accordance with the principles ,of the invention. The specific illustrative relay constructed in accordance with the principles of this invention is capable of responding to a predetermined sub-audio frequency signal in the rangerof l to 32 C. P. S., although the principlcs are applicable to frequency selective relays operable at' other frequencies. Ten separate channels or frequency bands are available in the to 32 C. P. S. range, and a relay adjusted to one of the channels will not respond to signals in any other channels nor to signals of any other frequency whatsoever.

Therelay includes a frame 22 supporting a pole piece 24 on which `is placed the actuating coil 26. The frame 22 is provided with a right angularly disposed end or flange 28 to which is secured a spring hinge 30 by means .such as ,rivets 32 and back up plate 34. An armature36 is provided with a right angularly disposed end or ange 38 which is secured to the spring 3b by means such as rivets 40 and a back up plate 42. The free end 44 of the armature is aligned with and spaced from the pole piece 24 for magnetic attraction and repulsion thereby, it being understood that the pole piece, armature, frame, and spring hinge all are constructed of magnetic material.

A flat primary spring reed 46 is carried by the armature 36 and is electrically insulated therefrom by insulating spacers 48. A ring 50 is atiixed to the outer end of the spring 46, and the mass of the ring is determined in accordance with the compliance of the primary spring reed 46 to obtain the desired frequency of mechanical resonance.

A secondary flat spring reed 52 having an olfset at 54 is secured to the primary reed intermediate the ends thereof as at 56 and carries a Contact 58 of suitable electrically conducting material which is not readily damaged by frequent opening and closing of contacts. A second contact 60 is carried by a flat spring 62 in opposition to the first Contact for contacting engagement therewith. The spring 62 is substantially T-shaped and the cross bar or arm of the T is supported by means such as an insulating block 64 mounted on the frame 22. The spring 62 is adjustable for proper positioning of the Contact 60, and such adjustment may be effected by mounting the spring by means such as screws 66 threaded into the block 64 and passing through slots or over-sized holes in the spring 62. It will be understood that a pair of opposed lixed contacts could be provided for alternate engagement by the movable contact, although this is not illustrated.

A bar magnet 66 is supported concentrically with the ring 50 and is axially adjustable so that it may project into the ring a predetermined distance. By way of example, the bar magnet preferably is cylindrical in configuration and may be threaded into a suitable tapped bore 68 in an insulating block 70 carried by the frame 22. The block 70 may be, and preferably is, integral with the aforementioned block 64. Y

An illustrative means for operating the relay is shown in Fig. 3. The relay coil 26 is connected at` oneend to a source of B-lvoltage, and is connected at the other end to the plate 72 of an electron tube 74 which is illustrated simply as a vacuum triode, although it will be understood that other types of tubes or electronic valves could be used. The cathode 76 is shown as grounded through a resistor 78 and parallel capacitor 80. The grid 82 is shown as being grounded through a conventional grid resistor 84. The normal conduction of the tube 74 and hence the biasing current applied to the relay coil 26 is adjusted by any suitable means, for instance by providing an adjustable resistor in the cathode circuit of the tube. The biasing current is adjusted so as to pull the reed 46 and the contact 58 carried thereby toward the pole 24 and away from the contact 60, deflecting the spring hinge 30 in so doing. The reed 46 and the contacts and connections have been shown somewhat simplified in -Fig. 3 for illustrative purposes. It will be seen that a suitable control voltage is applied at 86 to the movable contact 58v and that the fixed contact 60 is connected to a con- 4 e trolled device 88 as at 90, said device being grounded or otherwise connected to 'a return line as at 92,

The actuating signal for. the resonant relay is suitably applied to the grid d2 of the tube '74 as indicated at input and this signal causes the potential applied to the coil 26 to vary in magnitude above and below the average value as established by the biasing current. This causes the reed to move toward and from the pole piece 24, and hence causes the lcontacts 58 and 60 to close intermittently. Of course, if the input signal is not of substantially the frequency of resonance of the reed 46 and weight 59, the reed will remain quiescent and the contacts lwill remain open.

Intermittent closing of the contacts causes the control voltage to be applicdto the control device 88 land thereby to effect the desired operation. important advantages are obtained by the mounting of the movable contact S8 on the second flexible reed 54. The contacts can close before the primary reed 46 reaches its maximum swing, and the secondary reed 54 'thereafter ilexes to maintain the contacts in engagement. This increases the duty cycle ortotal time during a. complete cycle that the contacts are closed. Furthermore, it reduces the physical reaction of the suddenly closed contacts back on the resonant system, thus avoiding an appreciable change in resonant frequency during the portion of the cycle that the contacts are closed. This tends to minimize hunting action and other erratic behavior of the relay.

As .earlier noted, simple vibrating reed relays have a high Q or ampliiication factor, and consequently have relatively narrow band widths in which they will respond. Simple resonant reeds are easily constructed having Qs of several hundred, but cannot be constructed to have low Qs when of suitable size for resonant relays. A low Q is attained according to the principles of this invention by means of the magnet 66 and ring 50.

The reed 46 is constructed of non-magnetic material such as beryllium copper. in a specific example constructed in accordance with the principles of this invention, the reed is f/lg, wide, 1% long and .098 inch thick. The ring 50 is constructed of pure copper and in the specific vembodiment has an outside diameter of 5/s and a hole diameter of 7/16". The ring is replaceable and has a thickness which varies in discrete steps from one ring to another to determine the operating or resonant frequency of the ring and reed. This frequency may be l0, ll, 13, l5, 17, 19, etc. cycles per second. The magnet 66 is a permanent magnet,` and in the specific example is constructed of Alnico V and is 1A in diameter and l" long. The magnet 66 normally is positioned as shown in Fig. 5 so that the end of the magnet projects approximately half way through the ring. The flux lines associated with the b ar magnet thus cross the body of the ring in `a direction outward from the center of the ring as shown in Figs. 4 and 5. As the ring is displaced by vibration of the reed 46, the ring cuts the lines of flux at all points on the periphery of the ring. A voltagethus is induced in the ring, and this voltage (E) is proportional to the velocity (v) of the ring, the llux density (B) of the field, and the mean circumference of the ring (l). Expressed mathematically, E=Bvl. Since the ring is made of copper, it comprises a closed electrical circuit of very low resistance. The small voltage induced thus causes appreciable current to ow around the ring. The Vdirection of the current, by Lenzs law, is such that the magneticeld it produces is of opposite polarity to the lield which causes it. The action of these opposing fields exerts a restraining force upon the moving ring. Since the liux density produced by the magnet, and the circumference of the ring are constant, the velocity of the ring is the only variable. The restraining force is there- `fore proportional to the velocity and is thus a linear mechanical resistance. The energy loss is converted to heat dissipated in the resistance of the ring, and the power so dissipated is so minute, being on the order of several A hundred millionths of a watt, that no significant temperature rise of the ring can be detected. This' extremely low order of magnitude illustrates the impracticability Vof damping a resonant reed relay by conventional damping means. The degree of damping required can be set by adjusting the amount of projection of the magnet rod 66 through the ring 50. Withdrawing the magnet (i. e. threading it further'into the bore 68) reduces the damping. When the magnet is withdrawn to the point where the ring no longer intersects any of the magnetic lines of force, the vibrating system is undamped.

The electromagnetically damped resonant relay disclosed herein is substantially insensitive to random impulses. The response of a simple undamped relay to a random impulse is shown in Fig. 6. A sudden D. C. pulse applied to the relay, which is to be expected in radio remote control systems from atmospheric discharges or man-made noise, causes the reed to be displaced a substantial distance. 'Ihe reed then vibrates due to its own inertia, and this vibration takes a substantial time to decay as illustrated by the curve 94 in Fig. 6. During part of this vibrating period, the amount of displacement is equal to or greater than the amount needed for the contacts to close, as indicated by the dashed line 96. Accordingly, spurious operation will be effected.

As shown in Fig. 7, the maximum amplitude of vibration `as indicated at 98 is less than the level at which the contacts close, the latter being indicated by the dashed iline 100, and the vibrations die out Very quickly as illustrated by the curve 102. Thus, the contacts of the damped relay disclosed herein do not close in response to random impulses, and there is no spurious operation.

When a transient voltage of the proper frequency is applied to an undamped resonant relay, the undamped reed suddenly swings to a maximum displacement as indicated at 104 (Fig. 8) of the envelope of the curve 106, representing the vibration of the reed. This large swing is followed by a minimum displacement swing as indicated at 108, and it is not until some time is passed as indicated at 110 before the reed lsettles down to a steady state of resonant vibration. The dashed line 112 indicates the vibration amplitude necessary for the closing of the contacts, and it will be apparent that the contacts will close only intermittently until the steady state of operation is'reached at 110. This is a most objectionable feature as it is likely to bring about improper operation of the controlled device. Furthermore, if the applied signal is of sufficiently short duration, the desired control action may not be effected. Correction cannot be made by increasing the driving voltage or reducing the spacing of the -contacts as this would render the relay more likely to be tripped by noise pulses.

On the other hand, the vibrating reed of the damped relay herein disclosed increases in amplitude of vibration relatively slowly as illustrated by the envelope 114 (Fig. 9) of the vibration curve 116. Following the first maximum Vamplitude of vibration as indicated at 118, the minimum amplitude as shown at 120 still lies above the line 122 illustrating the level of amplitude at which the contacts close. Steady state operation is quickly reached as illustrated at 124.

As heretofore noted, simple resonant reed relays have a high Q and relatively narrow band width. In Fig. l0 the curve 126 illustrates the Q of a simple resonant reed relay, the Q illustrated having a typical value of 200. With the electromagnetically damped relay herein disclosed a Q of 30 or less readily can be obtained as illustrated at 128 in Fig. 10. If the receiving device has a Q of 200, it will respond to frequencies to within about i.5% with a signal level of twice that required to operate at the center frequency, as can be ascertained from the curve of 126. The signal level must be increased to l0 times that required to operate at center frequency in order to operate the relay at frequenciesl of 13% from the center frequency. If the signal level were amplified to this extent, noise signals likewise would be amplified to this extent and the response of the undamped relay to the noise signals would be almost certain to cause spurious operation.

However, withl the damped relay herein disclosed having a Q of 30 it may be seen that a band width of m30/2; is present with signal levels only about twice that required for operation at the center of the band. Accordingly, limiting circuits can be used ahead of the relay to limit random noise pulses to a magnitude on the same order as that required for steady state operation of the relay at the center of the band. Consequently, the damped relay is the only means of achieving wide band width which also permits useful limiting of random noise pulses .ahead of the relay. It will be understood that the wide rband width allows an inexpensive signaling device to be used. A signaling device having a frequency tolerance of -2% can be fabricated simply and economically, but a relatively complicated and expensive signaling device would be needed to hold the frequency tolerance to`i.5%.

Spnrious operation of resonant relays can be caused by signals which are multiples or harmonics of the natural resonant frequency ofy the reed vibrating system. Such spurious operation is avoided in the relay disclosed herein as shown in Fig. l1. The soft iron pole piece 24 is surrounded by a` cylindrical copper sleeve V130 on which the coil 26 is wound. The coil is held in place according to conventional practice by insulating spool ends 132, and the pole piece 24 is secured to the frame 22 by peenirig the end of the pole piece as at 134.

Response of the mechanically resonant system vto multiple or harmonic frequencies is reduced by holding the mass of the reed and parts carried thereby to a minimum and by proper proportioning of the compliance between the primary reed and the spring hinge. The further provision of the Copperv sleeve 130 substantially eliminates all such response to the higher frequencies. The copper Isleeve has a voltage induced in it as a result of a flux variation through the soft iron pole piece. The induced voltage causes a current to ow through the sleeve, and this current sets up an opposing magnetic flux reducing the total flux. The magnitude of the induced voltage and consequently of the opposing flux is a function of frequency, increasing with frequency as an exponential function. Thus, the forces acting on the vibrating reed system are substantially less at frequencies corresponding to the spurious modes of mechanical resonance than at the desired operational frequency. This results in a relay which is substantially free from response at higher frequencies than its intended operating band.

It now `should be apparent that the electromagnetically damped resonant or frequency selective vibrating reed relay herein disclosed is substantially insensitive to random impulses, has a superior transient response, and `has a relatively large band width. Additionally, response at multiple or harmonic frequencies is substantially eliminated. The contact duty cycle is increased and the reaction upon contact closure is minimized by the secondary reed carrying the moving contact.

The specific example herein shown and described will be understood as illustrative only. Various changes in structure may be made without departing from the spirit and scope of this invention as set forth in the ensuing claims. 4

The invention is hereby claimed as follows:

l. A resonant relay comprising a frame, a vibratile reed having a predetermined natural frequency of vibration and carried from said frame, said reed having a portion of magnetic material, electrical contacts respectively carried from said frame and from said reed, said contacts being alternately open and closed upon vibration of said reed, magnet means supported from said frame and including a coil adapted to establish an alternating magnetic field at the same frequency as the predetermined natural frequency of vibration of said reed, magnetic damping means, and conductive damping means, said damping means beingV carried in proximity to and movable relative to one another, one from said frame and the other from said reed, electromagnetically to damp the vibrations of said reed.

2. A resonant relay as set forth in claim 1 wherein the conductive damping means comprises a continuous ring.

f 3. A resonant relay as set forth in claim 1 and further including means for relatively adjusting the positions of said magnetic damping means and of said conductive damping means to adjust the damping.

4. A resonant relay comprising a frame, a vibratile reed having a predetermined natural frequency of vibration and carried from said frame, said reed having a portion of -magnetic material, electrical contacts respectively carried from said frame and from said reed, said contacts being alternately open and closed upon vibration of said reed,'magnet means supported from said frame and including a coil adapted to establish an alternating magnetic field at the same frequency as the predetermined natural frequency of vibration of said reed, continuous ring damping means, magnetic damping means, means for supporting said damping means adjacent to and movable relative to one another in inductive relation, one from said reed and one from said frame, and means for adjusting the magnetic field of said magnetic means acting on said ring damping means to adjust the damping.

5. A resonant relay as set forth in claim 4 wherein the magnetic damping means comprises a permanent bar magnet carried from said frame, said ring damping means is carried from .said reed in axial alignment with said bar magnet, and the means for adjusting the magnetic field acting on said ring damping means comprises means for adjusting said bar magnet relatively axially of said ring damping means.

6. A resonant reed relay comprising a frame having a base and an arm disposed at an angle thereto, a magnet pole mounted on said base, an actuating coil wound on said pole, a vibrating system including an armature of magnetic material, a flexible reed mounted on said armature, and a highly conductive closed ring carried at the end of said ring, said vibrating system having a predetermined natural frequency of Vibration, a spring hinge mounting said vibrating system on the arm of said frame with said armature aligned with said magnet pole for vibration of said system when said coil is energized at said predetermined frequency, a bar magnet carried from said frame in axial alignment with said ring and proximate said ring for damping the vibrations of said system, and electrical contacts carried from said frame and from said vibrating system and alternately open and closed upon vibration of said system.

7. A resonant reed relay comprising a frame having a base and an arm disposed at an angle thereto, a magnet pole mounted on said base, an actuating coil wound on said pole, a Vibrating system including an armature of magnetic material, a flexible reed mounted on said armature, and a highly conductive closed ring carried at the end of said reed, said vibrating system having a predetermined natural frequency of vibration, a spring hinge mounting said vibrating system on the arm of said frame with said armature aligned with said magnet pole for vi' bration of said system when said coil is energized at said predetermined frequency, a bar magnet carried from said frame in axial alignment with said ring and proximate said ring for damping the vibrations of said system, a flexible reed carried by said vibrating reed, a movable electrical contact carried by said flexible reed, a fixed electrical contact carried from said frame and engageable with said movable contact upon vibration of said vibrating system, and a highly conductive sleeve interposed between said magnet pole and said coil to induce a bucking magnetic field increasing with frequency to reduce the total magnetic eld progressively with frequency and thereby substantially to eliminate response at higher modes of operation.

8. A resonant relay as set forth in claim 1, and further including a resilient member on the reed, the electrica'l contact carried from the reed being mounted on said resilient member.

9. A resonant relay as set forth in claim 1, wherein the magnet means further includes a magnet pole and a highly conductive sleeve encircling said pole, the coil being mounted about said sleeve and pole whereby the sleeve induces a bucking magnetic field increasing with frequency to reduce the total magnetic field with increasing frequency.

10. A resonant relay comprising a frame, a vibratile reed having a predetermined natural frequency of vibration and carried from said frame, said reed having a portion of magnetic material, electrical contacts respectively carried from said frame and from said reed, said contacts being alternately open and closed upon vibration of said reed, magnet means supported from said frame and including a coil adapted to establish an alternating magnetic iield at the same frequency as the predetermined natural frequency of vibration of said reed, continuous ring damping means, magnetic damping means, and means for supporting said damping means adjacent to and movable relative to one another in inductive relation, one from said reed and one from said frame.

11. A resonant relay as set forth in claim 10 and further including a resilient member mounted on said reed, the electrical contact carried from said reed being mounted on said resilient member.

12. A resonant relay as set forth in claim 10 wherein the magnet means further includes a magnetic pole and a highly conductive sleeve thereon, said coil encircling said sleeve, said sleeve inducing a bucking magnetic field increasing with frequency to reduce the total magnetic field increasing with frequency.

References Cited in the file of this patent UNITED STATES PATENTS 149,797 Siemens Apr. 14, 1874 729,811 Thomson June 2, 1903 1,006,090 Hoge Oct. 17, 1911 1,378,869 Kaisling May 24, 1921 1,471,890 French Oct. 23, 1923 1,652,550 Yaeger Dec. 13, 1927 1,676,979 Cheeseman July 10, 1928 1,946,299 Traver Feb. 6, 1934 2,392,981 Fischler Jan. 15, 1946

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